phd_thesis/tex/thesis.tex

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% acronyms for the lazy

\renewcommand{\glossarysection}[2][]{} % remove glossary title
\makeglossaries{}
\newacronym{act}{ACT}{adoptive cell therapies}
\newacronym{car}{CAR}{chimeric antigen receptor}
\newacronym[longplural={monoclonal antibodies}]{mab}{mAb}{monoclonal antibody}
\newacronym{ecm}{ECM}{extracellular matrix}
\newacronym{cqa}{CQA}{critical quality attribute}
\newacronym{cpp}{CPP}{critical process parameter}
\newacronym{dms}{DMS}{degradable microscaffold}
\newacronym{doe}{DOE}{design of experiments}
\newacronym{gmp}{GMP}{Good Manufacturing Practices}
\newacronym{cho}{CHO}{Chinese hamster ovary}
\newacronym{all}{ALL}{acute lymphoblastic leukemia}
\newacronym{pdms}{PDMS}{polydimethylsiloxane}
\newacronym{dc}{DC}{dendritic cell}
\newacronym{il2}{IL2}{interleukin 2}
\newacronym{rhil2}{rhIL2}{recombinant human interleukin 2}
\newacronym{apc}{APC}{antigen presenting cell}
\newacronym{mhc}{MHC}{major histocompatibility complex}
\newacronym{elisa}{ELISA}{enzyme-linked immunosorbent assay}
\newacronym{nmr}{NMR}{nuclear magnetic resonance}
\newacronym{haba}{HABA}{4-hydroxyazobenene-2-carboxylic-acid}
\newacronym{pbs}{PBS}{phosphate buffered saline}
\newacronym{bca}{BCA}{bicinchoninic acid assay}
\newacronym{bsa}{BSA}{bovine serum albumin}
\newacronym{stp}{STP}{streptavidin}
\newacronym{stppe}{STP-PE}{streptavidin-phycoerythrin}
\newacronym{snb}{SNB}{sulfo-nhs-biotin}
\newacronym{cug}{CuG}{Cultispher G}
\newacronym{cus}{CuS}{Cultispher S}
\newacronym{pbmc}{PBMC}{peripheral blood mononuclear cells}
\newacronym{macs}{MACS}{magnetic activated cell sorting}
\newacronym{aopi}{AO/PI}{acridine orange/propidium iodide}
\newacronym{igg}{IgG}{immunoglobulin G}
\newacronym{pe}{PE}{phycoerythrin}
\newacronym{fitc}{FITC}{Fluorescein}
\newacronym{fitcbt}{FITC-BT}{Fluorescein-biotin}
\newacronym{ptnl}{PTN-L}{Protein L}
\newacronym{af647}{AF647}{Alexa Fluor 647}
\newacronym{anova}{ANOVA}{analysis of variance}
\newacronym{crispr}{CRISPR}{clustered regularly interspaced short
  palindromic repeats}
\newacronym{mtt}{MTT}{3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide}
\newacronym{bmi}{BMI}{body mass index}
\newacronym{a2b1}{A2B1}{integrin $\upalpha$1$\upbeta$1}
\newacronym{a2b2}{A2B2}{integrin $\upalpha$1$\upbeta$2}
\newacronym{til}{TIL}{tumor infiltrating lymphocytes}
\newacronym{nsg}{NSG}{NOD scid gamma}

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% with the latest package yet (texlive-science)

\sisetup{per-mode=symbol,list-units=single}
\DeclareSIUnit\IU{IU}
\DeclareSIUnit\rpm{RPM}
\DeclareSIUnit\dms{DMS}
\DeclareSIUnit\cell{cells}
\DeclareSIUnit\ab{mAb}
\DeclareSIUnit\molar{M}
\DeclareSIUnit\gforce{\times{} g}

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\newcommand{\mytitle}{
  \Large{
    \textbf{
      Optimizing T Cell Manufacturing and Quality Using Functionalized
      Degradable Microscaffolds
    }
  }
}

\newcommand{\mycommitteemember}[3]{
  \begin{flushleft}
    \noindent
    #1 \\
    #2 \\
    \textit{#3}
  \end{flushleft}
}

\newcommand{\invivo}{\textit{in vivo}}
\newcommand{\invitro}{\textit{in vitro}}
\newcommand{\exvivo}{\textit{ex vivo}}

\newcommand{\cd}[1]{CD{#1}}
\newcommand{\anti}[1]{anti-{#1}}
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\newcommand{\acd}[1]{\anti{\cd{#1}}}
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\newcommand{\ptmem}{\cdp{62L}\pos{CCR7}}
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\newcommand{\miltenyi}{Miltenyi Biotech}
\newcommand{\bl}{Biolegend}

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\begin{document}

\begin{titlepage}
  \begin{mytitlepage}
    \mytitle{}

    \vfill

    \Large{
      A Dissertation \\
      Presented to \\
      The Academic Faculty \\

      \vspace{1.5em}

      by

      \vspace{1.5em}

      Nathan John Dwarshuis, B.S. \\

      \vfill

      In Partial Fulfillment \\
      of the Requirements for the Degree \\
      Doctor of Philosophy in Biomedical Engineering in the \\
      Wallace H. Coulter Department of Biomedical Engineering

      \vfill

      Georgia Institute of Technology and Emory University \\
      August 2021

      \vfill

      COPYRIGHT \copyright{} BY NATHAN J. DWARSHUIS
    }
  \end{mytitlepage}
\end{titlepage}

\onecolumn \pagenumbering{roman}
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  \mytitle{}
\end{mytitlepage}

\vfill

\large{
  \noindent
  Committee Members

  \begin{multicols}{2}
    \begin{singlespace}

      \mycommitteemember{Dr.\ Krishnendu\ Roy\ (Advisor)}
      {Department of Biomedical Engineering}
      {Georgia Institute of Technology and Emory University}

      \vspace{1.5em}

      \mycommitteemember{Dr.\ Madhav\ Dhodapkar}
      {Department of Hematology and Medical Oncology}
      {Emory University}

      \vspace{1.5em}

      \mycommitteemember{Dr.\ Melissa\ Kemp}
      {Department of Biomedical Engineering}
      {Georgia Institute of Technology and Emory University}

      \columnbreak{}
      \null{}
      \vfill

      \mycommitteemember{Dr.\ Wilbur\ Lam}
      {Department of Biomedical Engineering}
      {Georgia Institute of Technology and Emory University}

      \vspace{1.5em}

      \mycommitteemember{Dr.\ Sakis\ Mantalaris}
      {Department of Biomedical Engineering}
      {Georgia Institute of Technology and Emory University}

    \end{singlespace}
  \end{multicols}

  \vspace{1.5em}

  \hfill Date Approved:
}

\clearpage

\chapter*{acknowledgements}
\addcontentsline{toc}{chapter}{acknowledgements} 

Thank you to Lex Fridman and Devin Townsend for being awesome and inspirational.

\clearpage

\chapter*{summary}
\addcontentsline{toc}{chapter}{summary} 

\Gls{act} using \gls{car} T cells have shown promise in treating cancer, but
manufacturing large numbers of high quality cells remains challenging. Currently
approved T cell expansion technologies involve \anti-cd{3} and \anti-cd{28}
\glspl{mab}, usually mounted on magnetic beads. This method fails to
recapitulate many key signals found \invivo{} and is also heavily licensed by a
few companies, limiting its long-term usefulness to manufactures and clinicians.
Furthermore, we understand that highly potent T cells are generally
less-differentiated subtypes such as central memory and stem memory T cells.
Despite this understanding, little has been done to optimize T cell expansion
for generating these subtypes, including measurement and feedback control
strategies that are necessary for any modern manufacturing process.

The goal of this thesis was to develop a microcarrier-based \gls{dms} T cell
expansion system as well as determine biologically-meaningful \glspl{cqa} and
\glspl{cpp} that could be used to optimize for highly-potent T cells. In Aim 1,
we develop and characterized the \gls{dms} system, including quality control
steps. We also demonstrate the feasiblity of expanding highly-potent memory and
CD4+ T cells, and showing compatibility with existing \gls{car} transduction
methods. In aim 2, we use \gls{doe} methodology to optimize the \gls{dms}
platform, and develop a computational pipeline to identify and model the effect
of measurable \glspl{cqa} and \glspl{cpp} on the final product. In aim 3, we
demonstrate the effectiveness of the \gls{dms} platform \invivo{}. This
thesis lays the groundwork for a novel T cell expansion method which can be used
in a clinical setting, and also provides a path toward optimizing for product
quality in an industrial setting.

\clearpage

\tableofcontents

\clearpage

\listoffigures

\clearpage

\listoftables

\clearpage

% \twocolumn
\chapter*{acronyms}
\addcontentsline{toc}{chapter}{acronyms}

\printglossary[type=\acronymtype]

\clearpage
\pagenumbering{arabic}

\clearpage

\chapter{introduction}

\section*{overview}

% TODO this is basically the same as the first part of the backgound, I guess I
% can just trim it down

T cell-based immunotherapies have received great interest from clinicians and
industry due to their potential to treat, and often cure, cancer and other
diseases\cite{Fesnak2016,Rosenberg2015}. In 2017, Novartis and Kite Pharma
received FDA approval for \textit{Kymriah} and \textit{Yescarta} respectively,
two genetically-modified \gls{car} T cell therapies against B cell malignancies.
Despite these successes, \gls{car} T cell therapies are constrained by an
expensive and difficult-to-scale manufacturing process with little control on
cell quality and phenotype3,4. State-of-the-art T cell manufacturing techniques
focus on \acd{3} and \acd{28} activation and expansion, typically
presented on superparamagnetic, iron-based microbeads (Invitrogen Dynabead,
Miltenyi MACS beads), on nanobeads (Miltenyi TransACT), or in soluble tetramers
(Expamer)\cite{Roddie2019,Dwarshuis2017,Wang2016, Piscopo2017, Bashour2015}.
These strategies overlook many of the signaling components present in the
secondary lymphoid organs where T cells expand \invivo{}. Typically, T cells are
activated under close cell-cell contact, which allows for efficient
autocrine/paracrine signaling via growth-stimulating cytokines such as
\gls{il2}. Additionally, the lymphoid tissues are comprised of \gls{ecm}
components such as collagen, which provide signals to upregulate proliferation,
cytokine production, and pro-survival pathways\cite{Gendron2003, Ohtani2008,
  Boisvert2007, Ben-Horin2004}. We hypothesized that culture conditions that
better mimic these \invivo{} expansion conditions of T cells, can significantly
improve the quality and quantity of manufactured T cells and provide better
control on the resulting T cell phenotype.

% TODO mention the Cloudz stuff that's in my presentation

A variety of solutions have been proposed to make the T cell expansion process
more physiological. One strategy is to use modified feeder cell cultures to
provide activation signals similar to those of \glspl{dc}\cite{Forget2014}.
While this has the theoretical capacity to mimic many components of the lymph
node, it is hard to reproduce on a large scale due to the complexity and
inherent variability of using cell lines in a fully \gls{gmp}-compliant manner.
Others have proposed biomaterials-based solutions to circumvent this problem,
including lipid-coated microrods\cite{Cheung2018}, 3D-scaffolds via either
Matrigel\cite{Rio2018} or 3d-printed lattices\cite{Delalat2017}, ellipsoid
beads\cite{meyer15_immun}, and \gls{mab}-conjugated \gls{pdms}
beads\cite{Lambert2017} that respectively recapitulate the cellular membrane,
large interfacial contact area, 3D-structure, or soft surfaces T cells normally
experience \invivo{}. While these have been shown to provide superior expansion
compared to traditional microbeads, none of these methods has been able to show
preferential expansion of functional naïve/memory and CD4 T cell populations.
Generally, T cells with a lower differentiation state such as naïve and memory
cells have been shown to provide superior anti-tumor potency, presumably due to
their higher potential to replicate, migrate, and engraft, leading to a
long-term, durable response\cite{Xu2014, Fraietta2018, Gattinoni2011,
  Gattinoni2012}. Likewise, CD4 T cells are similarly important to anti-tumor
potency due to their cytokine release properties and ability to resist
exhaustion\cite{Wang2018, Yang2017}. Therefore, methods to increase naïve/memory
and CD4 T cells in the final product are needed, a critical consideration being
ease of translation to industry and ability to interface with scalable systems
such as bioreactors.

% TODO probably need to address some of the modeling stuff here as well

This thesis describes a novel degradable microscaffold-based method derived from
porous microcarriers functionalized with \acd{3} and \acd{28} \glspl{mab}
for use in T cell expansion cultures. Microcarriers have historically been used
throughout the bioprocess industry for adherent cultures such as stem cells and
\gls{cho} cells, but not with suspension cells such as T
cells\cite{Heathman2015, Sart2011}. The microcarriers chosen to make the DMSs in
this study have a microporous structure that allows T cells to grow inside and
along the surface, providing ample cell-cell contact for enhanced autocrine and
paracrine signaling. Furthermore, the carriers are composed of gelatin, which is
a collagen derivative and therefore has adhesion domains that are also present
within the lymph nodes. Finally, the 3D surface of the carriers provides a
larger contact area for T cells to interact with the \glspl{mab} relative to
beads; this may better emulate the large contact surface area that occurs
between T cells and \glspl{dc}. These microcarriers are readily available in
over 30 countries and are used in an FDA fast-track-approved combination retinal
pigment epithelial cell product (Spheramine, Titan Pharmaceuticals) {\#}[Purcell
documentation]. This regulatory history will aid in clinical translation. We
show that compared to traditional microbeads, \gls{dms}-expanded T cells not
only provide superior expansion, but consistently provide a higher frequency of
naïve/memory and CD4 T cells (CCR7+CD62L+) across multiple donors. We also
demonstrate functional cytotoxicity using a CD19 \gls{car} and a superior
performance, even at a lower \gls{car} T cell dose, of \gls{dms}-expanded
\gls{car}-T cells \invivo{} in a mouse xenograft model of human B cell
\gls{all}. Our results indicate that \glspl{dms} provide a robust and scalable
platform for manufacturing therapeutic T cells with higher naïve/memory
phenotype and more balanced CD4+ T cell content.

\section*{hypothesis}

The hypothesis of this dissertation was that using \glspl{dms} created from
off-the-shelf microcarriers and coated with activating \glspl{mab} would lead to
higher quantity and quality T cells as compared to state-of-the-art bead-based
expansion. The objective of this dissertation was to develop this platform, test
its effectiveness both \invivo{} and \invivo{}, and develop computational
pipelines that could be used in a manufacturing environment.

\section*{specific aims}

The specific aims of this dissertation are outlined in
\cref{fig:graphical_overview}.

\begin{figure*}[ht!]
  \begingroup

  \includegraphics[width=\textwidth]{example-image-a}

  \endgroup
  \caption[Project Overview]{High-level workflow.}
  \label{fig:graphical_overview}
\end{figure*}

\subsection*{aim 1: develop and optimize a novel T cell expansion process that
  mimics key components of the lymph nodes}

% TODO this might be easier to break apart in separate aims

In this first aim, we demonstrated the process for manufacturing \glspl{dms},
including quality control steps that are necessary for translation of this
platform into a scalable manufacturing setting. We also demonstrate that the
\gls{dms} platform leads to higher overall expansion of T cells and higher
overall fractions of potent memory and CD4+ subtypes desired for T cell
therapies. Finally, we demonstrate \invitro{} that the \gls{dms} platform can be
used to generate functional \gls{car} T cells targeted toward CD19.

\subsection*{aim 2: develop methods to control and predict T cell quality}

For this second aim, we investigated methods to identify and control \glspl{cqa}
and glspl{cpp} for manufacturing T cells using the \gls{dms} platform. This was
accomplished through two sub-aims:

\begin{itemize}
  \item[A --] Develop computational methods to control and predict T cell
    expansion and quality
  \item[B --] Perturb \gls{dms} expansion to identify additional mechanistic
    controls for expansion and quality
\end{itemize}

\subsection*{aim 3: confirm potency of T cells from novel T cell expansion
  process using \invivo{} xenograft mouse model}

In this final aim, we demonstrate the effectiveness of \gls{dms}-expanded T
cells compared to state-of-the-art beads using \invivo{} mouse models for
\gls{all}.

\section*{outline}

In Chapter~\ref{background}, we provide additional background on the current
state of T cell manufacturing and how the work in this dissertation moves the
field forward. In Chapters~\ref{aim1},~\ref{aim2a},~\ref{aim2b}, and~\ref{aim3}
we present the work pertaining to Aims 1, 2, and 3 respectively. Finally, we
present our final conclusions in Chapter~\ref{conclusions}.

\chapter{background and significance}\label{background}
\section*{background}

% TODO break this apart into mfg tech and T cell phenotypes/quality
% TODO consider adding a separate section on microcarriers and their use in
% bioprocess
% TODO add stuff about T cell licensing
\subsection*{current T cell manufacturing technologies}

\Gls{car} T cell therapy has received great interest from both academia and
industry due to its potential to treat cancer and other
diseases\cite{Fesnak2016, Rosenberg2015}. In 2017, Novartis and Kite Pharma
acquired FDA approval for \textit{Kymriah} and \textit{Yescarta} respectively,
two \gls{car} T cell therapies against B cell malignancies. Despite these
successes, \gls{car} T cell therapies are constrained by an expensive and
difficult-to-scale manufacturing process\cite{Roddie2019, Dwarshuis2017}.

Of critical concern, state-of-the-art manufacturing techniques focus only on
Signal 1 and Signal 2-based activation via \acd{3} and \acd{28} \glspl{mab},
typically presented on a microbead (Invitrogen Dynabead, Miltenyi MACS beads) or
nanobead (Miltenyi TransACT), but also in soluble forms in the case of antibody
tetramers (Expamer)\cite{Wang2016, Piscopo2017, Roddie2019, Bashour2015}. These
strategies overlook many of the signaling components present in the secondary
lymphoid organs where T cells normally expand. Typically, T cells are activated
under close cell-cell contact via \glspl{apc} such as \glspl{dc}, which present
peptide-\glspl{mhc} to T cells as well as a variety of other costimulatory
signals. These close quarters allow for efficient autocrine/paracrine signaling
among the expanding T cells, which secrete gls{il2} and other cytokines to
assist their own growth. Additionally, the lymphoid tissues are comprised of
\gls{ecm} components such as collagen, which provide signals to upregulate
proliferation, cytokine production, and pro-survival pathways\cite{Gendron2003,
  Ohtani2008, Boisvert2007, Ben-Horin2004}.

A variety of solutions have been proposed to make the T cell expansion process
more physiological. One strategy is to use modified feeder cell cultures to
provide activation signals similar to those of \glspl{dc}\cite{Forget2014}.
While this has the theoretical capacity to mimic several key components of the
lymph node, it is hard to reproduce on a large scale due to the complexity and
inherent variability of using cell lines in a fully \gls{gmp}-compliant manner.
Others have proposed biomaterials-based solutions to circumvent this problem,
including lipid-coated microrods\cite{Cheung2018}, 3D-scaffolds via either
Matrigel\cite{Rio2018} or 3d-printed lattices\cite{Delalat2017}, ellipsoid
beads\cite{meyer15_immun}, and \gls{mab}-conjugated \gls{pdms}
beads\cite{Lambert2017} that respectively recapitulate the cellular membrane,
large interfacial contact area, 3D-structure, or soft surfaces T cells normally
experience \textit{in vivo}. While these have been shown to provide superior
expansion compared to traditional microbeads, no method has been able to show
preferential expansion of functional memory and CD4 T cell populations.
Generally, T cells with a lower differentiation state such as memory cells have
been shown to provide superior anti-tumor potency, presumably due to their
higher potential to replicate, migrate, and engraft, leading to a long-term,
durable response\cite{Xu2014, Gattinoni2012, Fraietta2018, Gattinoni2011}.
Likewise, CD4 T cells are similarly important to anti-tumor potency due to their
cytokine release properties and ability to resist exhaustion\cite{Wang2018,
  Yang2017}, and no method exists to preferentially expand the CD4 population
compared to state-of-the-art systems.

Here we propose a method using microcarriers functionalized with \acd{3} and
\acd{28} \glspl{mab} for use in T cell expansion cultures. Microcarriers have
historically been used throughout the bioprocess industry for adherent cultures
such as stem cells and \gls{cho} cells, but not with suspension cells such as T
cells\cite{Heathman2015, Sart2011}. The carriers have a macroporous structure
that allows T cells to grow inside and along the surface, providing ample
cell-cell contact for enhanced autocrine and paracrine signaling. Furthermore,
the carriers are composed of gelatin, which is a collagen derivative and
therefore has adhesion domains that are also present within the lymph nodes.
Finally, the 3D surface of the carriers provides a larger contact area for T
cells to interact with the \glspl{mab} relative to beads; this may better
emulate the large contact surface area that occurs between T cells and
\glspl{dc}.

\subsection*{strategies to optimize cell manufacturing}

The \gls{dms} system has a number of parameters that can be optimized, and a
\gls{doe} is an ideal framework to test multiple parameters simultaneously. The
goal of \gls{doe} is to answer a data-driven question with the least number of
resources. It was developed in many non-biological industries throughout the
\nth{20} century such as the automotive and semiconductor industries where
engineers needed to minimize downtime and resource consumption on full-scale
production lines.

% TODO add a bit more about the math of a DOE here

\Glspl{doe} served three purposes in this dissertation. First, we used them as
screening tools, which allowed us to test many input parameters and filter out
the few that likely have the greatest effect on the response. Second, they were
used to make a robust response surface model to predict optimums using
relatively few resources, especially compared to full factorial or
one-factor-at-a-time approaches. Third, we used \glspl{doe} to discover novel
effects and interactions that generated hypotheses that could influence the
directions for future work.

\subsection*{strategies to characterize cell manufacturing}

A number of multiomics strategies exist which can generate rich datasets for T
cells. We will consider several multiomics strategies within this proposal:

\begin{description}
\item[Luminex:] A multiplexed bead-based \gls{elisa} that can measure
  many bulk (not single cell) cytokine concentrations simultaneously
  in a media sample. Since this only requires media (as opposed to
  destructively measuring cells) we will use this as a longitudinal
  measurement.
\item[Metabolomics:] It is well known that T cells of different
  lineages have different metabolic profiles; for instance memory T
  cells have larger aerobic capacity and fatty acid
  oxidation\cite{Buck2016, van_der_Windt_2012}. We will interrogate
  key metabolic species using \gls{nmr} in collaboration with the
  Edison Lab at the University of Georgia. This will be both a
  longitudinal assay using media samples (since some metabolites may
  be expelled from cells that are indicative of their phenotype) and
  at endpoint where we will lyse the cells and interogate their entire
  metabolome.
\item[Flow and Mass Cytometry:] Flow cytometry using fluorophores has been used
  extensively for immune cell analysis, but has a practical limit of
  approximately 18 colors\cite{Spitzer2016}. Mass cytometry is analogous to
  traditional flow cytometry except that it uses heavy-metal \gls{mab}
  conjugates, which has a practical limit of over 50 markers. This will be
  useful in determining precise subpopulations and phenotypes that may be
  influencing responses, especially when one considers that many cell types can
  be defined by more than one marker combination. We will perform this at
  endpoint. While mass cytometry is less practical than simple flow cytometers
  such as the BD Accuri, we may find that only a few markers are required to
  accurately predict performance, and thus this could easily translate to
  industry using relatively cost-effective equipment.
\end{description}

% TODO add a computational section

% TODO add a section explaining causal inference since this is a big part of
% the end of aim 1

\section{Innovation}

\subsection{Innovation}

Several aspects of this work are novel considering the state-of-the-art
technology for T cell manufacturing:

\begin{itemize}
\item \Glspl{dms} offers a compelling alternative to state-of-the-art magnetic
  bead technologies (e.g. DynaBeads, MACS-Beads), which is noteworthy because
  the licenses for these techniques is controlled by only a few companies
  (Invitrogen and Miltenyi respectively). Because of this, bead-based expansion
  is more expensive to implement and therefore hinders companies from entering
  the rapidly growing T cell manufacturing arena. Providing an alternative as we
  are doing will add more options, increase competition among both raw material
  and T cell manufacturers, and consequently drive down cell therapy market
  prices and increase innovation throughout the industry.
\item This is the first technology for T cell immunotherapies that selectively
  expands memory T cell populations with greater efficiency relative to
  bead-based expansion Others have demonstrated methods that can achieve greater
  expansion of T cells, but not necessarily specific populations that are known
  to be potent.
\item We propose to optimize our systems using \gls{doe} methodology, which is a
  strategy commonly used in other industries and disciplines but has yet to gain
  wide usage in the development of cell therapies. \Glspl{doe} are advantageous
  as they allow the inspection of multiple parameters simultaneously, allowing
  efficient and comprehensive analysis of the system vs a one-factor-at-a-time
  approach. We believe this method is highly relevant to the development of cell
  therapies, not only for process optimization but also hypotheses generation.
  Of further note, most \textit{in vivo} experiments are not done using a
  \gls{doe}-based approach; however, a \gls{doe} is perfectly natural for a
  large mouse study where one naturally desires to use as few animals as
  possible.
\item The \gls{dms} system is be compatible with static bioreactors such as the
  G-Rex which has been adopted throughout the cell therapy industry. Thus this
  technology can be easily incorporated into existing cell therapy process that
  are performed at scale.
\item We analyzed our system using a multiomics approach, which will enable the
  discovery of novel biomarkers to be used as \glspl{cqa}. While this approach
  has been applied to T cells previously, it has not been done in the context of
  a large \gls{doe}-based model. This approach is aware of the whole design
  space, and thus enables greater understanding of process parameters and their
  effect on cell phenotype.
\end{itemize}

\chapter{aim 1}\label{aim1}

\section{introduction}

The first aim was to develop a microcarrier system that mimics several key
aspects of the \invivo{} lymph node microenvironment. We compared compare this
system to state-of-the-art T cell activation technologies for both expansion
potential and memory cell formation. The governing hypothesis was that
microcarriers functionalized with \acd{3} and \acd{28} \glspl{mab} will
provide superior expansion and memory phenotype compared to state-of-the-art
bead-based T cell expansion technology.

% TODO this doesn't flow that well and is repetitive with what comes above

Microcarriers have been used throughout the bioprocess industry for adherent
cell cultures such as \gls{cho} cells and stem cells, as they are able to
achieve much greater surface area per unit volume than traditional 2D
cultures\cite{Heathman2015, Sart2011}. Adding adhesive \glspl{mab} to the
microcarriers will adapt them for suspension cell cultures such as T cells.
Consequently, the large macroporous structure will allow T cells to cluster more
closely, which in turn will enable better autocrine and paracrine signaling.
Specifically, two cytokines that are secreted by T cells, IL-2 and IL-15, are
known to drive expansion and memory phenotype respectively\cite{Buck2016}.
Therefore, the proposed microcarrier system should enable greater expansion and
better retention of memory phenotype compared to current bead-based methods.

\section{methods}
\subsection{dms functionalization}

\begin{figure*}[ht!]
  \begingroup

  \includegraphics{../figures/dms_flowchart.png}

  \endgroup
  \caption[\gls{dms} Flowchart]{Overview of \gls{dms} manufacturing process.}
  \label{fig:dms_flowchart}
\end{figure*}

Gelatin microcarriers (\gls{cus} or \gls{cug}, GE Healthcare, DG-2001-OO and
DG-0001-OO) were suspended at \SI{20}{\mg\per\ml} in 1X \gls{pbs} and
autoclaved. All subsequent steps were done aseptically, and all reactions were
carried out at \SI{20}{\mg\per\ml} carriers at room temperature and agitated
using an orbital shaker with a \SI{3}{\mm} orbit diameter. After autoclaving,
the microcarriers were washed using sterile \gls{pbs} three times in a 10:1
volume ratio. \product{\Gls{snb}}{\thermo}{21217} was dissolved at
approximately \SI{10}{\micro\molar} in sterile ultrapure water, and the true
concentration was then determined using the \gls{haba} assay (see below).
\SI{5}{\ul\of{\ab}\per\mL} \gls{pbs} was added to carrier suspension and allowed
to react for \SI{60}{\minute} at \SI{700}{\rpm} of agitation. After the
reaction, the amount of biotin remaining in solution was quantified using the
\gls{haba} assay (see below). The carriers were then washed three times, which
entailed adding sterile \gls{pbs} in a 10:1 volumetric ratio, agitating at
\SI{900}{\rpm} for \SI{10}{\minute}, adding up to a 15:1 volumetric ratio
(relative to reaction volume) of sterile \gls{pbs}, centrifuging at
\SI{1000}{\gforce} for \SI{1}{\minute}, and removing all liquid back down to the
reaction volume.

To coat with \gls{stp}, \SI{40}{\ug\per\mL} \product{\gls{stp}}{Jackson
  Immunoresearch}{ 016-000-114} was added and allowed to react for
\SI{60}{\minute} at \SI{700}{RPM} of agitation. After the reaction, supernatant
was taken for the \gls{bca} assay, and the carriers were washed analogously to
the previous wash step to remove the biotin, except two washes were done and the
agitation time was \SI{30}{\minute}. Biotinylated \glspl{mab} against human CD3
\catnum{\bl}{317320} and CD28 \catnum{\bl}{302904} were combined in a 1:1 mass
ratio and added to the carriers at \SI{0.2}{\ug\of{\ab}\per\mg\of{\dms}}. Along
with the \glspl{mab}, sterile \product{\gls{bsa}}{Sigma}{A9576} was added to a
final concentration of \SI{2}{\percent} in order to prevent non-specific binding
of the antibodies to the reaction tubes. \glspl{mab} were allowed to bind to the
carriers for \SI{60}{\minute} with \SI{700}{\rpm} agitation. After binding,
supernatants were sampled to quantify remaining \gls{mab} concentration using an
\product{\anti{\gls{igg}} \gls{elisa} kit}{Abcam}{157719}. Fully functionalized
\glspl{dms} were washed in sterile \gls{pbs} analogous to the previous washing
step to remove excess \gls{stp}. They were washed once again in the cell culture
media to be used for the T cell expansion.

The concentration of the final \gls{dms} suspension was found by taking a
\SI{50}{\uL} sample, plating in a well, and imaging the entire well. The image
was then manually counted to obtain a concentration. Surface area for
\si{\ab\per\um\squared} was calculated using the properties for \gls{cus} and
\gls{cug} as given by the manufacturer {Table X}.

%TODO this bit belongs in the next aim
% In the case of the \gls{doe} experiment where
% variable mAb surface density was utilized, the anti-CD3/anti-CD28 mAb mixture
% was further combined with a biotinylated isotype control to reduce the overall
% fraction of targeted mAbs (for example the 60\% mAb surface density corresponded
% to 3 mass parts anti-CD3, 3 mass parts anti-CD8, and 4 mass parts isotype
% control).

\subsection{dms quality control assays}

Biotin was quantified using the \product{\gls{haba} assay}{Sigma}{H2153-1VL}. In
the case of quantifying \gls{snb} prior to adding it to the microcarriers, the
sample volume was quenched in a 1:1 volumetric ratio with \SI{1}{\molar} NaOH
and allowed to react for \SI{1}{\minute} in order to prevent the reactive ester
linkages from binding to the avidin proteins in the \gls{haba}/avidin premix.
All quantifications of \gls{haba} were performed on an Eppendorf D30
Spectrophotometer using \product{\SI{70}{\ul} cuvettes}{BrandTech}{759200}. The
extinction coefficient at \SI{500}{\nm} for \gls{haba}/avidin was assumed to be
\SI{34000}{\per\cm\per\molar}.

\gls{stp} binding to the carriers was quantified indirectly using a
\product{\gls{bca} kit }{\thermo}{23227} according to the manufacturer’s
instructions, with the exception that the standard curve was made with known
concentrations of purified \gls{stp} instead of \gls{bsa}. Absorbance at
\SI{592}{\nm} was quantified using a Biotek plate reader.

\Gls{mab} binding to the microcarriers was quantified indirectly using an
\gls{elisa} assay per the manufacturer’s instructions, with the exception that
the same antibodies used to coat the carriers were used as the standard for the
\gls{elisa} standard curve.

Open biotin binding sites on the \glspl{dms} after \gls{stp} coating was
quantified indirectly using \product{\gls{fitcbt}}{\thermo}{B10570}.
Briefly, \SI{400}{\pmol\per\ml} \gls{fitcbt} were added to \gls{stp}-coated
carriers and allowed to react for \SI{20}{\minute} at room temperature under
constant agitation. The supernatant was quantified against a standard curve of
\gls{fitcbt} using a Biotek plate reader.

\Gls{stp} binding was verified after the \gls{stp}-binding step visually by
adding \gls{fitcbt} to the \gls{stp}-coated \glspl{dms}, resuspending in
\SI{1}{\percent} agarose gel, and imaging on a \product{lightsheet
 microscope}{Zeiss}{Z.1}. \Gls{mab} binding was verified visually by first
staining with \product{\anti{\gls{igg}}-\gls{fitc}}{\bl}{406001}, incubating for
\SI{30}{\minute}, washing with \gls{pbs}, and imaging on a confocal microscope.

\subsection{t cell culture}

% TODO verify countess product number
Cryopreserved primary human T cells were either obtained as sorted
\product{\cdp{3} T cells}{Astarte Biotech}{1017} or isolated from
\product{\glspl{pbmc}}{Zenbio}{SER-PBMC} using a negative selection
\product{\cdp{3} \gls{macs} kit}{\miltenyi}{130-096-535}. T cells were activated
using \glspl{dms} or \product{\SI{3.5}{\um} CD3/CD28 magnetic
  beads}{\miltenyi}{130-091-441}. In the case of beads, T cells were activated
at the manufacturer recommended cell:bead ratio of 2:1. In the case of
\glspl{dms}, cells were activated using \SI{2500}{\dms\per\cm\squared} unless
otherwise noted. Initial cell density was \SIrange{2e6}{2.5e6}{\cell\per\ml} to
in a 96 well plate with \SI{300}{\ul} volume. Serum-free media was either
\product{OpTmizer}{\thermo}{A1048501} or
\product{TexMACS}{\miltenyi}{170-076-307} supplemented with
\SIrange{100}{400}{\IU\per\ml} \product{\gls{rhil2}}{Peprotech}{200-02}. Cell
cultures were expanded for \SI{14}{\day} as counted from the time of initial
seeding and activation. Cell counts and viability were assessed using
\product{trypan blue}{\thermo}{T10282} or \product{\gls{aopi}}{Nexcelom
  Bioscience}{CS2-0106-5} and a \product{Countess Automated Cell Counter}{Thermo
  Fisher}{Countess 3 FL}. Media was added to cultures every \SIrange{2}{3}{\day}
depending on media color or a \SI{300}{\mg\per\deci\liter} minimum glucose
threshold. Media glucose was measured using a \product{GlucCell glucose
  meter}{Chemglass}{CLS-1322-02}.

% TODO this belongs in aim 2
% In order to remove \glspl{dms} from
% culture, collagenase D (Sigma Aldrich) was sterile filtered in culture media and
% added to a final concentration of \SI{50}{\ug\per\ml} during media addition.

Cells on the \glspl{dms} were visualized by adding \SI{0.5}{\ul}
\product{\gls{stppe}}{\bl}{405204} and \SI{2}{ul}
\product{\acd{45}-\gls{af647}}{\bl}{368538}, incubating for \SI{1}{\hour}, and
imaging on a spinning disk confocal microscope.

\subsection{chemotaxis assay}

% TODO not sure about the transwell product number
Migratory function was assayed using a transwell chemotaxis assay as previously
described\cite{Hromas1997}. Briefly, \SI{3e5}{\cell} were loaded into a
\product{transwell plate with \SI{5}{\um} pore size}{Corning}{3421} with the
basolateral chamber loaded with \SI{600}{\ul} media and 0, 250, or
\SI{1000}{\ng\per\mL} \product{CCL21}{Peprotech}{250-13}. The plate was
incubated for \SI{4}{\hour} after loading, and the basolateral chamber of each
transwell was quantified for total cells using \product{countbright
  beads}{\thermo}{C36950}. The final readout was normalized using the
\SI{0}{\ng\per\mL} concentration as background.

\subsection{degranulation assay}

Cytotoxicity of expanded \gls{car} T cells was assessed using a degranulation
assay as previously described\cite{Schmoldt1975}. Briefly, \num{3e5} T cells
were incubated with \num{1.5e5} target cells consisting of either \product{K562
wild type cells}{ATCC}{CCL-243} or CD19- expressing K562 cells transformed
with \gls{crispr} (kindly provided by Dr.\ Yvonne Chen, UCLA)\cite{Zah2016}.
Cells were seeded in a flat bottom 96 well plate with \SI{1}{\ug\per\ml}
\product{\acd{49d}}{eBioscience}{16-0499-81}, \SI{2}{\micro\molar} \product{monensin}{eBioscience}{
00-4505-51}, and \SI{1}{\ug\per\ml} \product{\acd{28}}{eBioscience}{302914} (all
functional grade \glspl{mab}) with \SI{250}{\ul} total volume. After
\SI{4}{\hour} incubation at \SI{37}{\degreeCelsius}, cells were stained for CD3,
CD4, and CD107a and analyzed on a BD LSR Fortessa. Readout was calculated as the
percent \cdp{107a} cells of the total \cdp{8} fraction.

\subsection{car expression}

\gls{car} expression was quantified as previously described\cite{Zheng2012}.
Briefly, cells were washed once and stained with \product{biotinylated
  \gls{ptnl}}{\thermo}{29997}. After a subsequent wash, cells were stained with
\product{\gls{pe}-\gls{stp}}{\bl}{405204}, washed again, and analyzed on a
BD Accuri. Readout was percent \gls{pe}+ cells as compared to secondary controls
(\gls{pe}-\gls{stp} with no \gls{ptnl}).

\subsection{car plasmid and lentiviral transduction}

The anti-CD19-CD8-CD137-CD3z \gls{car} with the EF1$\upalpha$
promotor\cite{Milone2009} was synthesized (Aldevron) and subcloned into a
\product{FUGW}{Addgene}{14883} kindly provided by the Emory Viral Vector Core.
Lentiviral vectors were synthesized by the Emory Viral Vector Core or the
Cincinnati Children's Hospital Medical Center Viral Vector Core. To transduce
primary human T cells, \product{retronectin}{Takara}{T100A} was coated onto
non-TC treated 96 well plates and used to immobilize lentiviral vector particles
according to the manufacturer's instructions. Briefly, retronectin solution was
adsorbed overnight at \SI{4}{\degreeCelsius} and blocked the next day using
\gls{bsa}. Prior to transduction, lentiviral supernatant was spinoculated at
\SI{2000}{\gforce} for \SI{2}{\hour} at \SI{4}{\degreeCelsius}. T cells were
activated in 96 well plates using beads or \glspl{dms} for \SI{24}{\hour}, and
then cells and beads/\glspl{dms} were transferred onto lentiviral vector coated
plates and incubated for another \SI{24}{\hour}. Cells and beads/\glspl{dms}
were removed from the retronectin plates using vigorous pipetting and
transferred to another 96 well plate wherein expansion continued.

\subsection{statistical analysis}

For 1-way \gls{anova} analysis with Tukey multiple comparisons test,
significance was assessed using the \inlinecode{stat\_compare\_means} function
with the \inlinecode{t.test} method from the \inlinecode{ggpubr} library in R.
For 2-way \gls{anova} analysis, the significance of main and interaction effects
was determined using the car library in R.

% TODO not all of this stuff applied to my regressions
For least-squares linear regression, statistical significance was evaluated the
\inlinecode{lm} function in R. Stepwise regression models were obtained using
the \inlinecode{stepAIC} function from the \inlinecode{MASS} package with
forward and reverse stepping. All results with categorical variables are
reported relative to baseline reference. Each linear regression was assessed for
validity using residual plots (to assess constant variance and independence
assumptions), QQplots and Shapiro-Wilk normality test (to assess normality
assumptions), Box-Cox plots (to assess need for power transformations), and
lack-of-fit tests where replicates were present (to assess model fit in the
context of pure error). Statistical significance was evaluated at $\upalpha$ =
0.05.

% TODO add meta-analysis section

\section{results}

\subsection{DMSs can be fabricated in a controlled manner}

Two types of gelatin-based microcariers, \gls{cus} and \gls{cug}, were
covalently conjugated with varying concentration of \gls{snb} and then coated
with \gls{stp} and \glspl{mab} to make \glspl{dms}. Aside from slight
differences in swelling ratio and crosslinking chemistry {\#}[Purcell
documentation], the properties of \gls{cus} and \gls{cug} were the same
(\cref{tab:carrier_props}). We chose to continue with the \gls{cus}-based
\glspl{dms}, which showed higher overall \gls{stp} binding compared to
\gls{cug}-based \glspl{dms} (\cref{fig:cug_vs_cus}). We showed that by varying
the concentration of \gls{snb}, we were able to precisely control the amount of
attached biotin (\cref{fig:biotin_coating}), mass of attached \gls{stp}
(\cref{fig:stp_coating}), and mass of attached \glspl{mab}
(\cref{fig:mab_coating}). Furthermore, we showed that the microcarriers were
evenly coated with \gls{stp} on the surface and throughout the interior as
evidenced by the presence of biotin-binding sites occupied with \gls{stp}-\gls{fitc}
on the microcarrier surfaces after the \gls{stp}-coating step
(\cref{fig:stp_carrier_fitc}). Finally, we confirmed that biotinylated
\glspl{mab} were bound to the \glspl{dms} by staining either \gls{stp} or
\gls{stp} and \gls{mab}-coated carriers with \antim{\gls{igg}-\gls{fitc}} and imaging
on a confocal microscope (\cref{fig:mab_carrier_fitc}). Taking this together, we
noted that the maximal \gls{mab} binding capacity occurred near \SI{50}{\nmol}
biotin input (which corresponded to \SI{2.5}{\nmol\per\mg\of{\dms}}) thus we
used this in subsequent processes.

% TODO add paragraph explaining the qc stuff

% TODO add paragraph explaining the reaction kinetics stuff

% TODO flip the rows of this figure (right now the text is backward)
\begin{figure*}[ht!]
  \begingroup

  \includegraphics{../figures/dms_coating.png}
  \phantomsubcaption\label{fig:stp_carrier_fitc}
  \phantomsubcaption\label{fig:mab_carrier_fitc}
  \phantomsubcaption\label{fig:cug_vs_cus}
  \phantomsubcaption\label{fig:biotin_coating}
  \phantomsubcaption\label{fig:stp_coating}
  \phantomsubcaption\label{fig:mab_coating}

  \endgroup
  \caption[\gls{dms} Coating]
  {\gls{dms} functionalization results.
    \subcap{fig:stp_carrier_fitc}{\gls{stp}-coated or uncoated \glspl{dms}
      treated with \gls{fitcbt} and imaged using a lightsheet microscope.}
    \subcap{fig:mab_carrier_fitc}{\gls{mab}-coated or \gls{stp}-coated
      \glspl{dms} treated with \anti{\gls{igg}} \glspl{mab} and imaged using a
      lightsheet microscope.} \subcap{fig:cug_vs_cus}{Bound \gls{stp} surface
      density on either \gls{cus} or \gls{cug} microcarriers. Surface density
      was estimated using the properties in~\cref{tab:carrier_props}} Total
    binding curve of \subcap{fig:biotin_coating}{biotin},
    \subcap{fig:stp_coating}{\gls{stp}}, and
    \subcap{fig:mab_coating}{\glspl{mab}} as a function of biotin added. }
  \label{fig:dms_flowchart}
\end{figure*}

% TODO these caption titles suck
% TODO combine this DOE figure into one interaction plot
\begin{table}[!h] \centering
  \caption{Properties of the microcarriers used}
  \label{tab:carrier_props}
  \input{../tables/carrier_properties.tex}
\end{table}

\begin{figure*}[ht!]
  \begingroup

  \includegraphics{../figures/dms_qc.png}
  \phantomsubcaption\label{fig:dms_qc_doe}
  \phantomsubcaption\label{fig:dms_qc_ph}
  \phantomsubcaption\label{fig:dms_qc_washes}
  \phantomsubcaption\label{fig:dms_snb_decay_curves}

  \endgroup
  \caption[\gls{dms} Quality Control]
  {\gls{dms} quality control investigation and development
    \subcap{fig:dms_qc_doe}{\gls{doe} investigating the effect of initial mass
      of microcarriers, reaction temperature, and biotin concentration on
      biotin attachment.}
    \subcap{fig:dms_qc_ph}{Effect of reaction ph on biotin attachment.}
    \subcap{fig:dms_qc_washes}{effect of post-autoclave washing of the
      microcarriers on biotin attachment.}
    \subcap{fig:dms_snb_decay_curves}{Hydrolysis curves of \gls{snb} in
      \gls{pbs} of differing pH.}
    All statistical tests where p-values are noted are given by two-tailed t
    tests.
  }
  \label{fig:dms_flowchart}
\end{figure*}

\begin{figure*}[ht!]
  \begingroup

  \includegraphics{../figures/dms_timing.png}
  \phantomsubcaption\label{fig:dms_biotin_rxn_mass}
  \phantomsubcaption\label{fig:dms_biotin_rxn_frac}
  \phantomsubcaption\label{fig:dms_stp_per_time}

  \endgroup
  \caption[\gls{dms} Reaction kinetics]
  {Reaction kinetics for microcarrier functionalization.
    \subcap{fig:dms_biotin_rxn_mass}{Biotin mass bound per time}
    \subcap{fig:dms_biotin_rxn_frac}{Fraction of input biotin bound per time}
    \subcap{fig:dms_stp_per_time}{\Gls{stp} bound per time.}
  }
  \label{fig:dms_kinetics}
\end{figure*}

\subsection{DMSs can efficiently expand T cells compared to beads}

% TODO add other subfigures here
We next sought to determine how our \glspl{dms} could expand T cells compared to
state-of-the-art methods used in industry. All bead expansions were performed as
per the manufacturer’s protocol, with the exception that the starting cell
densities were matched between the beads and carriers to
~\SI{2.5e6}{\cell\per\ml}. Throughout the culture we observed that T cells in
\gls{dms} culture grew in tight clumps on the surface of the \glspl{dms} as well
as inside the pores of the \glspl{dms}
(\cref{fig:dms_cells_phase,fig:dms_cells_fluor}). Furthermore, we observed that
the \glspl{dms} conferred greater expansion compared to traditional beads, and
significantly greater expansion after \SI{12}{\day} of culture {Figure X}. We
also observed no T cell expansion using \glspl{dms} coated with an isotype
control mAb compared to \glspl{dms} coated with \acd{3}/\acd{28} \glspl{mab}
{Figure X}, confirming specificity of the expansion method.

% TODO make sure the day on these is correct
\begin{figure*}[ht!]
  \begingroup

  \includegraphics{../figures/cells_on_dms.png}
  \phantomsubcaption\label{fig:dms_cells_phase}
  \phantomsubcaption\label{fig:dms_cells_fluor}

  \endgroup
  \caption[T cells growing on \glspl{dms}]
  {Cells grow in tight clusters in and around functionalized \gls{dms}.
    \subcap{fig:dms_cells_phase}{Phase-contrast image of T cells growing on
      \glspl{dms} on day 7}
    \subcap{fig:dms_cells_fluor}{Confocal images of T cells in varying z-planes
      growing on \glspl{dms} on day 9. \Glspl{dms} were stained using
      \gls{stppe} (red) and T cells were stained using \acd{45}-\gls{af647}.}
  }
  \label{fig:dms_cells}
\end{figure*}

% TODO add a regression table to quantify this better
% TODO state the CI of what are inside the carriers
We also asked how many cells were inside the \glspl{dms} vs. free-floating in
suspension and/or loosely attached to the surface. We qualitatively verified the
presence of cells inside the \glspl{dms} using a \gls{mtt} stain to opaquely
mark cells and enable visualization on a brightfield microscope
(\cref{fig:dms_inside_bf}). After seeding \glspl{dms} at different densities and
expanding for \SI{14}{\day}, we filtered the \glspl{dms} out of the cell
suspension and digested them using dispase to free any cells attached on the
inner surface. We observed that approximately \SI{15}{\percent} of the total
cells after \SI{14}{\day} were on the interior surface of the \glspl{dms}
(\cref{fig:dms_inside_regression}).

%, and this did not significantly change with initial seeding density (Supplemental Table 1).

% TODO add this to the methods section
% TODO double check the timing of this experiment (it might not be day 14)
% TODO provide the regression results and coefficients from this
\begin{figure*}[ht!]
  \begingroup

  \includegraphics{../figures/dms_inside.png}
  \phantomsubcaption\label{fig:dms_inside_bf}
  \phantomsubcaption\label{fig:dms_inside_regression}

  \endgroup
  \caption[A subset of T cells grow in interior of \glspl{dms}]
  {A percentage of T cells grow in the interior of \glspl{dms}.
    \subcap{fig:dms_inside_bf}{T cells stained dark with \gls{mtt} after
      growing on either coated or uncoated \glspl{dms} for 14 days visualized
      with brightfield microscope.}
    \subcap{fig:dms_inside_regression}{Linear regression performed on T cell
      percentages harvested on the interior of the \glspl{dms} vs the initial
      starting cell density.}
  }
  \label{fig:dms_inside}
\end{figure*}

\subsection{DMSs lead to greater expansion and memory and CD4+ phenotypes}

After observing differences in expansion, we further hypothesized that the
\gls{dms} cultures could lead to a different T cell phenotype. In particular, we
were interested in the formation of naïve and memory T cells, as these represent
a subset with higher replicative potential and therefore improved clinical
prognosis\cite{Gattinoni2011, Wang2018}. We measured naïve and memory T cell
frequency staining for CCR7 and CD62L (both of which are present on lower
differentiated T cells such as naïve, central memory, and stem memory
cells\cite{Gattinoni2012}). Using three donors, we noted again \glspl{dms}
produced more T cells over a \SI{14}{\day} expansion than beads, with
significant differences in number appearing as early after \SI{5}{\day}
(\cref{fig:dms_exp_fold_change}). Furthermore, we noted that \glspl{dms}
produced more memory/naïve cells after \SI{14}{\day} when compared to beads for
all donors (\cref{fig:dms_exp_mem,fig:dms_exp_cd4}) showing that the \gls{dms}
platform is able to selectively expand potent, early differentiation T cells.

Of additional interest was the preservation of the CD4+ compartment. In healthy
donor samples (such as those used here), the typical CD4:CD8 ratio is 2:1. We
noted that \glspl{dms} produced more CD4+ T cells than bead cultures as well as
naïve/memory, showing that the \gls{dms} platform can selectively expand CD4 T
cells to a greater degree than beads (Figure 2c). The trends held true when
observing the CD4+ and CD8+ fractions of the naïve/memory subset (CD62L+CCR7+)
(\cref{fig:dms_exp_mem4,fig:dms_exp_mem8}).

\begin{figure*}[ht!]
  \begingroup

  \includegraphics{../figures/dms_vs_bead_expansion.png}
  \phantomsubcaption\label{fig:dms_exp_fold_change}
  \phantomsubcaption\label{fig:dms_exp_mem}
  \phantomsubcaption\label{fig:dms_exp_cd4}
  \phantomsubcaption\label{fig:dms_exp_mem4}
  \phantomsubcaption\label{fig:dms_exp_mem8}

  \endgroup
  \caption[\gls{dms} vs bead expansion]
  {\gls{dms} lead to superior expansion of T cells compared to beads across
    multiple donors.
    \subcap{fig:dms_exp_fold_change}{Longitudinal fold change of T cells grown
      using either \glspl{dms} or beads. Significance was evaulated using t
      tests at each timepoint}
    Fold change of subpopulations expanded using either \gls{dms} or beads at
    day 14, including 
    \subcap{fig:dms_exp_mem}{\ptmem{} cells},
    \subcap{fig:dms_exp_cd4}{\pth{} cells},
    \subcap{fig:dms_exp_mem4}{\ptmemh{} cells}, and
    \subcap{fig:dms_exp_mem8}{\ptmemk{} cells}. \sigkey{}
  }
  \label{fig:dms_exp}
\end{figure*}

% TODO add a paragraph for this figure

% TODO this figure has weird proportions
\begin{figure*}[ht!]
  \begingroup

  \includegraphics{../figures/dms_phenotypes.png}
  \phantomsubcaption\label{fig:dms_phenotype_mem}
  \phantomsubcaption\label{fig:dms_phenotype_cd4}

  \endgroup
  \caption[Representative flow plots of \ptmem{} and \pth{} T cells]
  {Representative flow plots of \ptmem{} and \pth{} T cells at day 14 of
    expansion using either beads or \glspl{dms}. For three representative donor
    samples, phenotypes are shown for \subcap{fig:dms_phenotype_mem}{\ptmem{}}
    and \subcap{fig:dms_phenotype_cd4}{\pth}. Each population was also gated on
    \cdp{3} T cells.
  }
  \label{fig:dms_phenotype}
\end{figure*}

\subsection*{DMSs can be used to produce functional CAR T cells}

After optimizing for naïve/memory and CD4 yield, we sought to determine if the
\glspl{dms} were compatible with lentiviral transduction protocols used to
generate \gls{car} T cells27,28. We added a \SI{24}{\hour} transduction step on
day 1 of the \SI{14}{\day} expansion to insert an anti-CD19 \gls{car}29 and
subsequently measured the surface expression of the \gls{car} on day 14
\cref{fig:car_production_flow_pl,fig:car_production_endpoint_pl}. We noted that
there was robust \gls{car} expression in over \SI{25}{\percent} of expanded T
cells, and there was no observable difference in \gls{car} expression between
beads and \glspl{dms}.

We also verified the functionality of expanded \gls{car} T cells using a
degranulation assay\cite{Zheng2012}. Briefly, T cells were cocultured with
target cells (either wild-type K562 or CD19-expressing K562 cells) for
\SI{4}{\hour}, after which the culture was analyzed via flow cytometry for the
appearance of CD107a on CD8+ T cells. CD107a is found on the inner-surface of
cytotoxic granules and will emerge on the surface after cytotoxic T cells are
activated and degranulate. Indeed, we observed degranulation in T cells expanded
with both beads and \glspl{dms}, although not to an observably different degree
\cref{fig:car_production_flow_degran,fig:car_production_endpoint_degran}. Taken
together, these results indicated that the \glspl{dms} provide similar
transduction efficiency compared to beads.

We also verified that expanded T cells were migratory using a chemotaxis assay
for CCL21; since \glspl{dms} produced a larger percentage of naïve and memory T
cells (which have CCR7, the receptor for CCL21) we would expect higher migration
in \gls{dms}-expanded cells vs.\ their bead counterparts. Indeed, we noted a
significantly higher migration percentage for T cells grown using \glspl{dms}
versus beads (\cref{fig:car_production_migration}). Interestingly, there also
appeared to be a decrease in CCL21 migration between transduced and untransduced
T cells expanded using beads, but this interaction effect was only weakly
significant (p = 0.068). No such effect was seen for \gls{dms}-expanded T cells,
showing that migration was likely independent of \gls{car} transduction.

\begin{figure*}[ht!]
  \begingroup

  \includegraphics{../figures/car_production.png}
  \phantomsubcaption\label{fig:car_production_flow_pl}
  \phantomsubcaption\label{fig:car_production_endpoint_pl}
  \phantomsubcaption\label{fig:car_production_flow_degran}
  \phantomsubcaption\label{fig:car_production_endpoint_degran}
  \phantomsubcaption\label{fig:car_production_migration}

  \endgroup
  \caption[\glspl{dms} produce functional \gls{car} T cells]
  {\glspl{dms} produce functional \gls{car} T cells.
    \subcap{fig:car_production_flow_pl}{Representative flow cytometry plot for
      transduced or untransduced T cells stained with \gls{ptnl}.}
    \subcap{fig:car_production_endpoint_pl}{Endpoint plots with \gls{anova} for
      transduced or untransduced T cells stained with \gls{ptnl}.}
    \subcap{fig:car_production_flow_degran}{Representative flow plot for
      degenerating T cells.}
    \subcap{fig:car_production_endpoint_degran}{Endpoint plots for transduced or
    untransduced T cells stained with \cd{107a} for the degranulation assay.}
    \subcap{fig:car_production_migration}{Endpoint plot for transmigration assay
    with \gls{anova}.} All data is from T cells expanded for \SI{14}{\day}.
  }
  \label{fig:dms_phenotype}
\end{figure*}

\subsection{DMSs do not leave antibodies attached to cell product}

We asked if \glspl{mab} from the \glspl{dms} detached from the \gls{dms} surface
and could be detected on the final T cell product. This test is important for
clinical translation as any residual \glspl{mab} on T cells injected into the
patient could elicit an undesirable \antim{\gls{igg}} immune response. We did
not detect the presence of either \ahcd{3} or \ahcd{28} \glspl{mab} (both of
which were \gls{igg}) on the final T cell product after \SI{14}{\day} of
expansion (\cref{fig:nonstick}).

\begin{figure*}[ht!]
  \begingroup

  \includegraphics{../figures/nonstick.png}

  \endgroup
  \caption[\glspl{mab} do not detach from \glspl{dms}]
  {\glspl{mab} do not detach from microcarriers onto T cells in a detectable
    manner. Plots are representative manufacturing runs harvest after
    \SI{14}{\day} of expansion and stained with \anti{\gls{igg}}.
  }
  \label{fig:nonstick}
\end{figure*}

\subsection{DMSs consistently outperform bead-based expansion compared to
beads in a variety of conditions}

n order to establish the robustness of our method, we combined all experiments
performed in our lab using beads or \glspl{dms} and combined them into one
dataset. Since each experiment was performed using slightly different process
conditions, we hypothesized that performing causal inference on such a dataset
would not only indicate if the \glspl{dms} indeed led to better results under a
variety of conditions, but would also indicate other process parameters that
influence the outcome. The dataset was curated by compiling all experiments and
filtering those that ended at day 14 and including flow cytometry results for
the \ptmem{} and \pth{} populations. We further filtered our data to only
include those experiments where the surface density of the CD3 and CD28
\gls{mab} were held constant (since some of our experiments varied these on the
\glspl{dms}). This ultimately resulted in a dataset with 162 runs spanning 15
experiments between early 2017 and early 2021.

% TODO add some correlation analysis to this

Since the aim of the analysis was to perform causal inference, we determined 6
possible treatment variables which we controlled when designing the experiments
included in this dataset. Obviously the principle treatment parameter was
‘activation method’ which represented the effect of activating T cells with
either beads or our DMS method. We also included ‘bioreactor’ which was a
categorical for growing the T cells in a Grex bioreactor vs polystyrene plates,
‘feed criteria’ which represented the criteria used to feed the cells (using
media color or a glucose meter), ‘IL2 Feed Conc’ as a continuous parameter for
the concentration of IL2 added each feed cycle, and ‘CD19-CAR Transduced’
representing if the cells were lentivirally transduced or not. Unfortunately,
many of these parameters correlated with each other highly despite the large
size of our dataset, so the only two parameters for which causal relationships
could be evaluated were ‘activation method’ and ‘bioreactor’. We should also
note that these were not the only set of theoretical treatment parameters that
we could have used. For example, media feed rate is an important process
parameter, but this was dependent on the feeding criteria and the growth rate of
the cells, which in turn is determined by activation method. Therefore, ‘media
feed rate’ (or similar) is a ‘post-treatment parameter’ and would have violated
the backdoor criteria and severely biased our estimates of the treatment
parameters themselves.

In addition to these treatment parameters, we also included covariates to
improve the precision of our model. Among these were donor parameters including
age, \gls{bmi}, demographic, and gender, as well as the initial viability and
CD4/CD8 ratio of the cryopreserved cell lots used in the experiments. We also
included the age of key reagents such as IL2, media, and the anti-aggregate
media used to thaw the T cells prior to activation. Each experiment was
performed by one of three operators, so this was included as a three-level
categorical parameter. Lastly, some of our experiments were sampled
longitudinally, so we included a boolean categorical to represented this
modification as removing conditioned media as the cell are expanding could
disrupt signaling pathways.

% TODO the real reason we log-transformed was because box-cox and residual plots
We first asked what the effect of each of our treatment parameters was on the
responses of interest, which were fold change of the cells, the \ptmemp{}, and
\dpthp{} (the shift in \pthp{} at day 14 compared to the initial \pthp{}). We
performed a linear regression using activation method and bioreactor as
predictors (the only treatments that were shown to be balanced)
(\cref{tab:ci_treat}). Note that fold change was log transformed to reflect the
exponential nature of T cell growth. We observe that the treatments are
significant in all cases except for the \dpthp{}; however, we also observe that
relatively little of the variability is explained by these simple models ($R^2$
between 0.17 and 0.44).

% TODO add the regression diagnostics to this
We then included all covariates and unbalanced treatment parameters and
performed linear regression again
(\cref{tab:ci_controlled,fig:metaanalysis_fx}). We observe that after
controlling for additional noise, the models explained much more variability
($R^2$ between 0.76 and 0.87) and had relatively constant variance and small
deviations for normality as per the assumptions of regression analysis {Figure
  X}. Furthermore, the coefficient for activation method in the case of fold
change changed very little but still remained quite high (note the
log-transformation) with \SI{143}{\percent} increase in fold change compared to
beads. Furthermore, the coefficient for \ptmemp{} dropped to about
\SI{2.7}{\percent} different and almost became non-significant at $\upalpha$ =
0.05, and the \dpthp{} response increased to almost a \SI{9}{\percent} difference
and became highly significant. Looking at the bioreactor treatment, we see that
using the bioreactor in the case of fold change and \ptmemp{} is actually harmful
to the response, while at the same time it seems to increase the \dpthp{}
response. We should note that this parameter merely represents whether or not
the choice was made experimentally to use a bioreactor or not; it does not
indicate why the bioreactor helped or hurt a certain response. For example,
using a Grex entails changing the cell surface and feeding strategy for the T
cells, and any one of these ‘mediating variables’ might actually be the cause of
the responses.

% TODO these tables have extra crap in them that I don't need to show
\begin{table}[!h] \centering
  \caption{Causal Inference on treatment variables only}
  \label{tab:ci_treat}
  \input{../tables/causal_inference_treat.tex}
\end{table}

\begin{table}[!h] \centering
  \caption{Causal Inference on treatment variables and control variables}
  \label{tab:ci_controlled}
  \input{../tables/causal_inference_control.tex}
\end{table}

\begin{figure*}[ht!]
  \begingroup

  \includegraphics{../figures/metaanalysis_effects.png}
  \phantomsubcaption\label{fig:metaanalysis_fx_exp}
  \phantomsubcaption\label{fig:metaanalysis_fx_mem}
  \phantomsubcaption\label{fig:metaanalysis_fx_cd4}

  \endgroup
  \caption[Meta-analysis effect sizes]
  {\glspl{dms} exhibit superior performance compared to beads controlling for
    many experimental and process conditions. Effect sizes for
    \subcap{fig:metaanalysis_fx_exp}{fold change},
    \subcap{fig:metaanalysis_fx_mem}{\ptmemp{}}, and
    \subcap{fig:metaanalysis_fx_cd4}{\dpthp{}}. The dotted line represents
    the mean of the bead population. The red and blue dots represent the effect
    size of using \gls{dms} instead of beads only considering treatment
    variables (\cref{tab:ci_treat}) or treatment and control variables
    (\cref{tab:ci_controlled}) respectively.
  }
  \label{fig:metaanalysis_fx}
\end{figure*}

\section{discussion}

% TODO this is fluffy
We have developed a T cell expansion system that recapitulates key features of
the in vivo lymph node microenvironment using DMSs functionalized with
activating mAbs. This strategy provided superior expansion with higher number of
naïve/memory and CD4+ T cells compared to state-of-the-art microbead technology
(Figure 2). Other groups have used biomaterials approaches to mimic the in vivo
microenvironment13–15,17,34; however, to our knowledge this is the first system
that specifically drives naïve/memory and CD4+ T cell formation in a scalable,
potentially bioreactor-compatible manufacturing process.

Memory and naïve T cells have been shown to be important clinically. Compared to
effectors, they have a higher proliferative capacity and are able to engraft for
months; thus they are able to provide long-term immunity with smaller
doses19,35. Indeed, less differentiated T cells have led to greater survival
both in mouse tumor models and human patients20,36,37. Furthermore, clinical
response rates have been positively correlated with T cell expansion, implying
that highly-proliferative naïve and memory T cells are a significant
contributor18,38. Circulating memory T cells have also been found in complete
responders who received CAR T cell therapy39.

Similarly, CD4 T cells have been shown to play an important role in CAR T cell
immunotherapy. It has been shown that CAR T doses with only CD4 or a mix of CD4
and CD8 T cells confer greater tumor cytotoxicity than only CD8 T cells22,40.
There are several possible reasons for these observations. First, CD4 T cells
secrete proinflammatory cytokines upon stimulation which may have a synergistic
effect on CD8 T cells. Second, CD4 T cells may be less prone to exhaustion and
may more readily adopt a memory phenotype compared to CD8 T cells22. Third, CD8
T cells may be more susceptible than CD4 T cells to dual stimulation via the CAR
and endogenous T Cell Receptor (TCR), which could lead to overstimulation,
exhaustion, and apoptosis23. Despite evidence for the importance of CD4 T cells,
more work is required to determine the precise ratios of CD4 and CD8 T cell
subsets to be included in CAR T cell therapy given a disease state.

% TODO this might be more appropriate for aim 2b where I actually talk about
% the signaling and why this might matter
There are several plausible explanations for the observed phenotypic differences
between beads and DMSs. First, the DMSs are composed of a collagen derivative
(gelatin); collagen has been shown to costimulate activated T cells via
\gls{a2b1} and \gls{a2b2}, leading to enhanced proliferation, increased
IFN$\upgamma$ production, and upregulated CD25 (IL2R$\upalpha$) surface
expression8,10,11,41,42. Second, there is evidence that providing a larger
contact area for T cell activation provides greater stimulation16,43; the DMSs
have a rougher interface than the 5 µm magnetic beads, and thus could facilitate
these larger contact areas. Third, the DMSs may allow the T cells to cluster
more densely compared to beads, as evidenced by the large clusters on the
outside of the DMSs (Figure 1f) as well as the significant fraction of DMSs
found within their interiors (Supplemental Figure 2a and b). This may alter the
local cytokine environment and trigger different signaling pathways.
Particularly, IL15 and IL21 are secreted by T cells and known to drive memory
phenotype44–46. We noted that the IL15 and IL21 concentration was higher in a
majority of samples when comparing beads and DMSs across multiple timepoints
(Supplemental Figure 18) in addition to many other cytokines. IL15 and IL21 are
added exogenously to T cell cultures to enhance memory frequency,45,47 and our
data here suggest that the DMSs are better at naturally producing these
cytokines and limiting this need. Furthermore, IL15 unique signals in a trans
manner in which IL15 is presented on IL15R to neighboring cells48. The higher
cell density in the DMS cultures would lead to more of these trans interactions,
and therefore upregulate the IL15 pathway and lead to more memory T cells.

% TODO this mentions the DOE which is in the next aim
When analyzing all our experiments comprehensively using causal inference, we
found that all three of our responses were significantly increased when
controlling for covariates (Figure 3, Table 2). By extension, this implies that
not only will DMSs lead to higher fold change overall, but also much higher fold
change in absolute numbers of memory and CD4+ T cells. Furthermore, we found
that using a Grex bioreactor is detrimental to fold change and memory percent
while helping CD4+. Since there are multiple consequences to using a Grex
compared to tissue-treated plates, we can only speculate as to why this might be
the case. Firstly, when using a Grex we did not expand the surface area on which
the cells were growing in a comparable way to that of polystyrene plates. In
conjunction with our DOE data {Figure X} which shows that high DMS
concentrations favor CD4+ and don’t favor memory fraction, one possible
explanation is that the T cells spent longer times in highly activating
conditions (since the beads and DMSs would have been at higher per-area
concentrations in the Grex vs polystyrene plates). Furthermore, the simple fact
that the T cells spent more time at high surface densities could simply mean
that the T cells didn’t expands as much due to spacial constraints. This would
all be despite the fact that Grex bioreactors are designed to lead to better T
cell expansion due to their gas-permeable membranes and higher media-loading
capacities. If anything, our data suggests we were using the bioreactor
sub-optimally, and the hypothesized causes for why our T cells did not expand
could be verified with additional experiments varying the starting cell density
and/or using larger bioreactors.

A key question in the space of cell manufacturing is that of donor variability.
To state this precisely, this is a second order interaction effect that
represents the change in effect of treatment (eg bead vs DMS) given the donor.
While our meta-analysis was relatively large compared to many published
experiments usually seen for technologies at this developmental stage, we have a
limited ability in answering this question. We can control for donor as a
covariate, and indeed our models show that many of the donor characteristics are
strongly associated with each response on average, but these are first order
effects and represent the association of age, gender, demographic, etc given
everything else in the model is held constant. Second order interactions require
that our treatments be relatively balanced and random across each donor, which
is a dubious assumption for our dataset. However, this can easily be solved by
performing more experiments with these restrictions in mind, which will be a
subject of our future work.

Furthermore, this dataset offers an interesting insight toward novel hypothesis
that might be further investigated. One limitation of our dataset is that we
were unable to investigate the effects of time using a method such as
autoregression, and instead relied on aggregate measures such as the total
amount of a reagent added over the course of the expansion. Further studies
should be performed to investigate the temporal relationship between phenotype,
cytokine concentrations, feed rates, and other measurements which may perturb
cell cultures, as this will be the foundation of modern process control
necessary to have a fully-automated manufacturing system.

In addition to larger numbers of potent T cells, other advantages of our DMS
approach are that the DMSs are large enough to be filtered (approximately 300
µm) using standard 40 µm cell filters or similar. If the remaining cells inside
that DMSs are also desired, digestion with dispase or collagenase may be used.
Collagenase D may be selective enough to dissolve the DMSs yet preserve surface
markers which may be important to measure as critical quality attributes CQAs
{Figure X}. Furthermore, our system should be compatible with
large-scale static culture systems such as the G-Rex bioreactor or perfusion
culture systems, which have been previously shown to work well for T cell
expansion12,50,51. The microcarriers used to create the DMSs also have a
regulatory history in human cell therapies that will aid in clinical
translation.; they are already a component in an approved retinal pigment
epithelial cell product for Parkinson’s patients, and are widely available in 30
countries26.

It is important to note that all T cell cultures in this study were performed up
to 14 days. Others have demonstrated that potent memory T cells may be obtained
simply by culturing T cells as little as 5 days using traditional beads30. It is
unknown if the naïve/memory phenotype of our DMS system could be further
improved by reducing the culture time, but we can hypothesize that similar
results would be observed given the lower number of doublings in a 5 day
culture. We should also note that we investigated one subtype (\ptmem{}) in
this study. Future work will focus on other memory subtypes such as tissue
resident memory and stem memory T cells, as well as the impact of using the DMS
system on the generation of these subtypes.

% TODO this sounds sketchy
Another advantage is that the DMS system appears to induce a faster growth rate
of T cells given the same IL2 concentration compared to beads (Supplemental
Figure 8) along with retaining naïve and memory phenotype. This has benefits in
multiple contexts. Firstly, some patients have small starting T cell populations
(such as infants or those who are severely lymphodepleted), and thus require
more population doublings to reach a usable dose. Our data suggests the time to
reach this dose would be reduced, easing scheduling a reducing cost. Secondly,
the allogeneic T cell model would greatly benefit from a system that could
create large numbers of T cells with naïve and memory phenotype. In contrast to
the autologous model which is currently used for Kymriah and Yescarta,
allogeneic T cell therapy would reduce cost by spreading manufacturing expenses
across many doses for multiple patients52. Since it is economically advantageous
to grow as many T cells as possible in one batch in the allogeneic model
(reduced start up and harvesting costs, fewer required cell donations), the DMSs
offer an advantage over current technology.

% TODO this is already stated in the innovation section
It should be noted that while we demonstrate a method providing superior
performance compared to bead-based expansion, the cell manufacturing field would
tremendously benefit from simply having an alternative to state-of-the-art
methods. The patents for bead-based expansion are owned by few companies and
licensed accordingly; having an alternative would provide more competition in
the market, reducing costs and improving access for academic researchers and
manufacturing companies.

% TODO this isn't relevent to this aim but should be said somewhere
Finally, while we have demonstrated the DMS system in the context of CAR T
cells, this method can theoretically be applied to any T cell immunotherapy
which responds to anti-CD3/CD28 mAb and cytokine stimulation. These include
\glspl{til}, virus-specific T cells (VSTs), T cells engineered to express
$\upgamma\updelta$TCR (TEGs), $\upgamma\updelta$ T cells, T cells with
transduced-TCR, and CAR-TCR T cells53–58. Similar to CD19-CARs used in liquid
tumors, these T cell immunotherapies would similarly benefit from the increased
proliferative capacity, metabolic fitness, migration, and engraftment potential
characteristic of naïve and memory phenotypes59–61. Indeed, since these T cell
immunotherapies are activated and expanded with either soluble mAbs or
bead-immobilized mAbs, our system will likely serve as a drop-in substitution to
provide these benefits.

\chapter{aim 2a}\label{aim2a}

\section{introduction}
\section{methods}
\section{results}
\section{discussion}

\chapter{aim 2b}\label{aim2b}

\section{introduction}
\section{methods}
\section{results}
\section{discussion}

\chapter{aim 3}\label{aim3}

\section{introduction}
\section{methods}

\subsection{CD19-CAR T cell generation}

% TODO describe how T cells were grown for this aim

% TODO describe how the luciferase cells were generated (eg the kwong lab)

\subsection{\invivo{} therapeutic efficacy in NSG mice model}

% TODO use actual product numbers for mice
All mice in this study were male \gls{nsg} mice from Jackson Laboratories. At
day 0 (-7 day relative to T cell injection), 1e6 firefly luciferase-expressing
\product{Nalm-6 cells}{ATCC}{CRL-3273} suspended in ice-cold PBS were injected
via tail vein into each mouse. At day 7, saline or CAR T cells at the indicated
doses from either bead or DMS-expanded T cell cultures (for 14 days) were
injected into each mouse via tail vein. Tumor burden was quantified
longitudinally via IVIS Spectrum In Vivo Imaging System (Perkin Elmer). Briefly,
200ug/mice luciferin at 15 mg/ml in PBS was injected intraperitoneally under
isoflurane anesthesia into each mouse and waited for at least 10 minutes before
imaging. Mice were anesthetized again and imaged using the IVIS. Mice from each
treatment group/dose were anesthetized, injected, and imaged together, and
exposure time of the IVIS was limited to avoid saturation based on the signal
from the saline group. IVIS images were processed by normalizing them to common
minimum and maximum photon counts and total flux was estimated in terms of
photons/second. Endpoint for each mouse was determined by IACUC euthanasia
criteria (hunched back, paralysis, blindness, lethargy, and weight loss).
Mice were euthanized according to these endpoint criteria using carbon dioxide
asphyxiation.

\subsection{statistics}

For the \invivo{} model, the survival curves were created and statistically
analyzed using GraphPad Prism using the Mantel-Cox test to assess significance
between survival groups.

\section{results}

\subsection{DMS-expanded T cells show greater anti-tumor activity \invivo{}
  compared to beads}

% figure showing the experimental model and dosing strategy
% table for % CAR+ T cells injected into the mice
% figure for the mem and CAR+ percent injected into the mice
% figure showing IVIS images
% figure showing the surival curves

\subsection{Beads and DMSs perform similarly at earlier timepoints}

% figure showing the experimental model and dosing strategy
% figure for the mem and CAR+ percent injected into the mice
% figure showing IVIS images
% figure showing the photon plots per time

\section{discussion}

\chapter{conclusions and future work}\label{conclusions}
\section{conclusions}
\section{future work}

\onecolumn
\clearpage

% TODO some people put appendices here....not sure if I need to

\chapter{References}
\renewcommand{\section}[2]{} % noop the original bib section header

\bibliography{references}

\bibliographystyle{naturemag}

\end{document}