Stem Cell Memory Research Articles

Development of a Multiscale Mechanistic Modelling Framework Integrating Differential Cellular Kinetics of CAR-T Cell Subsets and Immunophenotypes in Cancer Patients.

Chimeric antigen receptor (CAR) T-cell subsets and immunophenotypic composition of the pre-infusion product, as well as their longitudinal changes following infusion, are expected to affect CAR-T cell expansion, persistence, and clinical outcomes. Herein, we sequentially evolved our previously described cellular kinetic-pharmacodynamic (CK-PD) model to incorporate CAR-T cell product-associated attributes by utilizing published preclinical and clinical datasets from two affinity variants (FMC63 and CAT19 scFv) anti-CD19 CAR-T cells. In step 1, a unified cell-level PD model was used to simultaneously characterize the in vitro killing datasets of two CAR-Ts against CD19+ cell lines at varying effector: target (E: T) ratios. In step 2, an augmented CK-PD model for anti-CD19 CAR-Ts was developed, by integrating CK dataset(s) from two bioanalytical measurements (qPCR and flow cytometry) in cancer patients. The model described the differential in vivo expansion properties of CAR-T cell subsets. The estimated expansion rate constant was ~1.12-fold higher for CAR+CD8+ cells in comparison to CAR+CD4+ T cells. In step 3, the model was extended to characterize the disposition of four Immunophenotypic populations of CAR-T cells, including stem-cell memory (TSCM ), central memory (TCM ), effector memory (TEM ) and effector (TEFF ) cells. The model adequately characterized the longitudinal changes in immunophenotypes post anti-CD19 CAR-T cell infusion in acute lymphocytic leukemia paediatric patients. Polyclonality in the pre-infusion product was identified as a categorical covariate influencing differentiation of immunophenotypes. In the future, this model could be leveraged a priori towards optimizing the composition of CAR-T cell infusion product, and further understand the CK-PD relationship in patients.

Cell Granularity Reflects Immune Cell Function and Enables Selection of Lymphocytes with Superior Attributes for Immunotherapy.

In keeping with the rule of "form follows function", morphological aspects of a cell can reflect its role. Here, it is shown that the cellular granularity of a lymphocyte, represented by its intrinsic side scatter (SSC), is a potent indicator of its cell state and function. The granularity of a lymphocyte increases from naïve to terminal effector state. High-throughput cell-sorting yields a SSChigh population that can mediate immediate effector functions, and a highly prolific SSClow population that can give rise to the replenishment of the memory pool. CAR-T cells derived from the younger SSClow population possess desirable attributes for immunotherapy, manifested by increased naïve-like cells and stem cell memory (TSCM )-like cells together with a balanced CD4/CD8 ratio, as well as enhanced target-killing in vitro and in vivo. Altogether, lymphocyte segregation based on biophysical properties is an effective approach for label-free selection of cells that share collective functions and can have important applications for cell-based immunotherapies.

Anti-CD117 CAR T cells incorporating a safety switch eradicate human acute myeloid leukemia and hematopoietic stem cells

Discrimination between hematopoietic stem cells and leukemic stem cells remains a major challenge for acute myeloid leukemia immunotherapy. CAR Tcells specific for the CD117 antigen can deplete malignant and healthy hematopoietic stem cells before consolidation with allogeneic hematopoietic stem cell transplantation in absence of cytotoxic conditioning. Here we exploit non-viral technology to achieve early termination of CAR Tcell activity to prevent incoming graft rejection. Transient expression of an anti-CD117 CAR by mRNA conferred Tcells the ability to eliminate CD117+ targets invitro and invivo. As an alternative approach, we used a Sleeping Beauty transposon vector for the generation of CAR Tcells incorporating an inducible Caspase 9 safety switch. Stable CAR expression was associated with high proportion of T memory stem cells, low levels of exhaustion markers, and potent cellular cytotoxicity. Anti-CD117 CAR Tcells mediated depletion of leukemic cells and healthy hematopoietic stem cells in NSG mice reconstituted with human leukemia or CD34+ cord blood cells, respectively, and could be terminated invivo. The use of a non-viral technology to control CAR Tcell pharmacokinetic properties is attractive for a first-in-human study in patients with acute myeloid leukemia prior to hematopoietic stem cell transplantation.

T memory stem cell characteristics in autoimmune diseases and their promising therapeutic values.

Memory T cells are conventionally subdivided into T central memory (TCM) and T effector memory (TEM) cells. However, a new subset of memory T cells named T memory stem cell (TSCM) cells has been recognized that possesses capabilities of both TCM and TEM cells including lymphoid homing and performing effector roles through secretion of cytokines such as interleukin-2 (IL-2) and interferon-gamma (IFN-γ). The TSCM subset has some biological properties including stemness, antigen independency, high proliferative potential, signaling pathway and lipid metabolism. On the other hand, memory T cells are considered one of the principal culprits in the pathogenesis of autoimmune diseases. TSCM cells are responsible for developing long-term defensive immunity against different foreign antigens, alongside tumor-associated antigens, which mainly derive from self-antigens. Hence, antigen-specific TSCM cells can produce antitumor responses that are potentially able to trigger autoimmune activities. Therefore, we reviewed recent evidence on TSCM cell functions in autoimmune disorders including type 1 diabetes, systemic lupus erythematosus, rheumatoid arthritis, acquired aplastic anemia, immune thrombocytopenia, and autoimmune uveitis. We also introduced TSCM cell lineage as an innovative prognostic biomarker and a promising therapeutic target in autoimmune settings.

Neoantigen-specific stem cell memory-like CD4+ T cells mediate CD8+ T cell-dependent immunotherapy of MHC class II-negative solid tumors.

CD4+ T cells play key roles in a range of immune responses, either as direct effectors or through accessory cells, including CD8+ T lymphocytes. In cancer, neoantigen (NeoAg)-specific CD8+ T cells capable of direct tumor recognition have been extensively studied, whereas the role of NeoAg-specific CD4+ T cells is less well understood. We have characterized the murine CD4+ T cell response against a validated NeoAg (CLTCH129>Q) expressed by the MHC-II-deficient squamous cell carcinoma tumor model (SCC VII) at the level of single T cell receptor (TCR) clonotypes and in the setting of adoptive immunotherapy. We find that the natural CLTCH129>Q-specific repertoire is diverse and contains TCRs with distinct avidities as measured by tetramer-binding assays and CD4 dependence. Despite these differences, CD4+ T cells expressing high or moderate avidity TCRs undergo comparable in vivo proliferation to cross-presented antigen from growing tumors and drive similar levels of therapeutic immunity that is dependent on CD8+ T cells and CD40L signaling. Adoptive cellular therapy (ACT) with NeoAg-specific CD4+ T cells is most effective when TCR-engineered cells are differentiated ex vivo with IL-7 and IL-15 rather than IL-2 and this was associated with both increased expansion as well as the acquisition and stable maintenance of a T stem cell memory (TSCM)-like phenotype in tumor-draining lymph nodes (tdLNs). ACT with TSCM-like CD4+ T cells results in lower PD-1 expression by CD8+ T cells in the tumor microenvironment and an increased frequency of PD-1+CD8+ T cells in tdLNs. These findings illuminate the role of NeoAg-specific CD4+ T cells in mediating antitumor immunity via providing help to CD8+ T cells and highlight their therapeutic potential in ACT.

Abundance of T Stem Cell Memory in F-CAR-T Cells CausingYounger Phenotypes

This study will introduce a novel anti-CD19 CAR-T technology – FasT CAR-T (F-CAR-T)- shortens production time,increases production quality, and produces healthier T cells with a younger phenotype. This study also investigates theeffect of the abundance of T stem cell memory in F-CAR-T cells’ correlation with younger phenotypes, leading to betterpersistence in T cells by manipulating the number of Car T cells injected into Raji xenografts. Using mouse cell lines,RAJI xenograft models, and F-CAR-T cells, this study will measure cell proliferation of Tscm, CD45RO-, CD62L+,and PD1/Lag3/Tim3 by flow cytometry and count Car expressing cells using SCFV antibodies. The experiment resultswill show if F-CAR T cells have significantly greater expansion and T stem cell memory than C-CAR-T cells. TheC-CAR-T cells with less exhaustion, indicating the effect of T stem cell memory distinguishing F-CAR-T therapy fromconventional CAR-T therapy. The result of this study will provide critical information for the future clinical trial ofF-CAR-T cell therapy. This work can inspire to utilize the T stem cell memory, which exhibits great antitumor activity,to explore the mechanism of modulation of CAR-T cell metabolism and T cell differentiation.

FRI-216 - Detection and functional analysis of HBV-specific stem cell memory T cells (Tscm)

FRI-216 - Detection and functional analysis of HBV-specific stem cell memory T cells (Tscm)

Total T Cell Density and Expression of T Memory Stem Cell Markers are Associated with Better Prognosis in Colon Cancer.

Immune checkpoint inhibitors have achieved limited clinical effectiveness in colon cancer. Stem memory T cells (TSCMs) and in-situ cytotoxic T cells are dominant contributors to host immunity. Currently, data on the correlation between TSCM and T cell abundance and clinicopathological characteristics in colon cancer are largely unavailable. In-situ cytotoxic T cells are identified based on the quantification of CD3+ and CD8+ markers using immunohistochemistry (IHC) in the core of the tumor and the invasive margin of the tumor. The expression of representative markers of TSCMs, CD27 and CD95, was assayed using IHC in colon cancer tissues. Correlations between the levels of each marker and the clinicopathological characteristics as well as prognosis were evaluated. High densities of CD3+ and CD8+ T cells correlated with stage I-II tumors, whereas a lower infiltration of cytotoxic T cells correlated with advanced-stage tumors. CD27 and CD95 were both expressed in the membrane of T cells present in the tumor stroma and their levels showed a negative correlation with the TNM stage. CD3, CD8, and CD27 were expressed at the same locations simultaneously, indicating their coordinated action against cancer. In addition, cytotoxic T cell densities and CD27 and CD95 expression remained independent prognostic factors for overall survival. In-situ cytotoxic T cells and TSCMs play important roles in colon cancer development. TSCMs marker CD27 and CD95 were both indicators of survival in patients with colon cancer. Thus, it is believed that TSCMs represent a desirable population for future use in combination immunotherapy.

A Novel Autologous CAR-T Therapy, YTB323, with Preserved T-cell Stemness Shows Enhanced CAR T-cell Efficacy in Preclinical and Early Clinical Development.

Traditional CAR T-cell manufacturing requires extended ex vivo cell culture, reducing naive and stem cell memory T-cell populations and diminishing antitumor activity. YTB323, which expresses the same validated CAR as tisagenlecleucel, can be manufactured in <2 days while retaining T-cell stemness and enhancing clinical activity at a 25-fold lower dose. See related commentary by Wang, p. 1961. This article is featured in Selected Articles from This Issue, p. 1949.

Naive phenotype antigen-specific CD4 +T cells persist in the memory repertoire after vaccination

Abstract Immunization leads to activation and differentiation of antigen-specific T cells, resulting in the development of immunological memory. However, how the human immune repertoire changes after vaccination remains incompletely understood. Here, we used the live attenuated yellow fever virus (YFV) vaccine or the SARS-CoV-2 mRNA vaccine as models to track post-vaccine kinetics in healthy donors. We quantified and characterized 36 distinct YFV-specific T cell populations and 25 SARS-CoV-2-specific populations by direct ex vivo peptide-MHC tetramer staining. Unexpectedly, we found naïve-phenotype vaccine-specific T cells reappearing after vaccination. On average, 20% of T cells retained a naive phenotype by CD45RO and CCR7 staining although each population had previously expanded after vaccination. A subset of naïve-like T cells expressed other differentiation markers consistent with T memory stem cells (TSCM), but some naïve-like T cells were negative for all memory markers tested. These naïve-phenotype T cells were able to respond to antigens and showed an increased expression of a recent thymic immigrant marker CD31. In conclusion, our results provided the surprising finding that the post-exposure T cell repertoire contains naïve antigen-specific T cells. We plan to test the possibility that the thymus continues to add new T cells into the adult immune repertoire in future experiments. NIH (R01 AI134879) NIH (R01 AO66358)

IL-12 alters T-cell metabolism to augment anti-tumor immunotherapy

Abstract To better limit tumor growth, adoptive T cell therapy (ACT), a cutting-edge new strategy for treating cancer, permits patients’ T cells to be modified. Long-lived central memory cells (Tcm), a specific subset of T cells, have been demonstrated through studies conducted in our group and others to be more effective at controlling tumor burden. Powerful inflammatory cytokine IL-12 has been extensively studied for its roles in the interaction of innate and adaptive immunity; however, therapeutic potential has not been optimized. We hypothesized that ex vivo administration of IL-12 may improve metabolic fitness and anti-tumor capabilities of T cells. Using a B16 murine melanoma model and T cells that are reactive to the melanoma epitope gp100, we found ex-vivo conditioning with IL-12 increased stem cell memory (Tscm) and central memory (Tcm) T cell populations. Additionally, we found unique metabolic signatures and proliferation patterns were dependent on IL-12 duration. We also observed enhanced engraftment and tumor control for up to 60 days after adoptively transferring these cells into animals with subcutaneous melanoma tumors. These metabolically conditioned T cells showed improved mitochondrial mass and function, elevated cytokine output, and perforin expression. Aside from switching from glycolysis to oxidative phosphorylation, these cells were also able to continue producing cytokines even when glucose or pyruvate levels dropped. Together, these findings imply that IL-12 modifies T cells’ reliance on glucose for energy while preserving their anti-tumor ability, potentially amplifying their ability to fight tumors in nutrient deprived microenvironments. IL-12 could therefore have a large impact on future ACT strategies. R01 CA250458, R01 CA236379

Abstract CT125: A Phase 1 study to evaluate the safety and tolerability of a combination autologous CD19 CAR T cell therapy (SYNCAR-001) and orthogonal IL-2 (STK-009) in subjects with relapsed or refractory CD19 expressing hematologic malignancies (NCT05665062)

Abstract Background: Chimeric antigen receptor T cell therapy (CAR T) has demonstrated remarkable clinical efficacy in hematological malignancies. However, compromised T cell effector function, proliferation, and persistence can limit CAR T from reaching their full curative potential. Interleukin-2 (IL-2) is a potent stimulator of T cells, however therapeutic use of IL-2 is limited by systemic toxicity due its pleiotropy. Therefore, to provide a selective IL-2 signal to engineered T cells, we have developed a human orthogonal ligand/receptor system consisting of a half-life extended pegylated IL-2 mutein (STK-009) and a mutated IL-2 Receptor Beta (hoRb) that responds to STK-009 but not wild type IL-2. SYNCAR-001 is an autologous CAR T co-expressing a CD19 CAR and hoRb on the T cell surface. In mouse models of refractory lymphoma, STK-009 treatment led to expansion and activation of SYNCAR-001 cells with a maintenance of stem cell memory and effector T cell phenotypes. When added to SYNCAR-001, STK-009 increased complete response rate and durable responses in a dose dependent manner. In non-human primate studies, STK-009 alone demonstrated no significant biological activity in IL-2 sensitive populations (T cells or NK cells) and was tolerable without toxicity. Methods: This is a first-in-human, open-label, dose escalation study of combination SYNCAR-001 + STK-009 in adults with relapsed or refractory (r/r) CD19+ hematologic malignancies. The objectives of this study are to evaluate the safety, preliminary efficacy, pharmacokinetics, immunogenicity, and pharmacodynamics of SYNCAR-001 + STK-009. Dose escalation follows a standard 3+3 design with STK-009 being escalated while SYNCAR-001 is held at a single fixed dose. A dose extension will enroll a cohort of patients treated at a selected dose level and indication based on dose escalation findings. SYNCAR-001 is dosed intravenously (IV) once at Day 0 and STK-009 is dosed subcutaneously (SC) over the course of the study. Participants receive a single safety lead-in dose of STK-009 prior to lymphodepletion and subsequent SYNCAR-001 infusion. After SYNCAR-001 initiation, STK-009 is dosed SC weekly for 12 weeks and then monthly for 3 months. Eligible participants include individuals with r/r chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) and selected r/r B-cell non-Hodgkin lymphoma (NHL subtypes of large B cell, mantle cell, and indolent lymphoma). Prior CD19 CAR use is excluded. The primary endpoint of safety includes outcomes such as adverse events and dose-limiting toxicities. Secondary endpoints include assessments of response, pharmacokinetics, and immunogenicity. Exploratory endpoints include assessment of immune cell populations, and relevant gene/protein expression, as well as persistence, phenotype, and functionality of SYNCAR-001 in the peripheral blood and/or bone marrow in response to STK-009. Citation Format: Maria Lia Palomba, Matthew G. Mei, Paolo F. Caimi, Matthew Cortese, Marco Davila, Greg Yadnik, Nestor Huang, David Mou, Martin Oft, Paul-Joseph Aspuria, Anita Mehta-Damani, Navneet Ratti, Naiyer Rizvi, Alex Azrilevich, Ran Reshef. A Phase 1 study to evaluate the safety and tolerability of a combination autologous CD19 CAR T cell therapy (SYNCAR-001) and orthogonal IL-2 (STK-009) in subjects with relapsed or refractory CD19 expressing hematologic malignancies (NCT05665062) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT125.

SIRT2 inhibition by AGK2 enhances mycobacteria-specific stem cell memory responses by modulating beta-catenin and glycolysis

Bacille Calmette-Guerin (BCG) generates limited long-lasting adaptive memory responses leading to short-lived protection against adult pulmonary tuberculosis (TB). Here, we show that host sirtuin 2 (SIRT2) inhibition by AGK2 significantly enhances the BCG vaccine efficacy during primary infection and TB recurrence through enhanced stem cell memory (TSCM) responses. SIRT2 inhibition modulated the proteome landscape of CD4+ Tcells affecting pathways involved in cellular metabolism and T-cell differentiation. Precisely, AGK2 treatment enriched the IFNγ-producing TSCM cells by activating β-catenin and glycolysis. Furthermore, SIRT2 specifically targeted histone H3 and NF-κB p65 to induce proinflammatory responses. Finally, inhibition of the Wnt/β-catenin pathway abolished the protective effects of AGK2 treatment during BCG vaccination. Taken together, this study provides a direct link between BCG vaccination, epigenetics, and memory immune responses. We identify SIRT2 as a key regulator of memory Tcells during BCG vaccination and project SIRT2 inhibitors as potential immunoprophylaxis against TB.

Abstract 4108: Transient epigenetic reprogramming enhances T-cell proliferation and tumor clearance

Abstract Manufacturing-induced differentiation and accelerated T-cell exhaustion prevent CAR-T therapies from reaching their full therapeutic potential and broader application in the treatment of cancer. To combat these inherent challenges, Turn Biotechnologies is developing its novel and proprietary mRNA-based technology, Epigenetic Reprogramming of Aging (ERATM), to i) preserve a less differentiated status; ii) diminish (or even eliminate) exhaustion; and iii) improve the cytotoxicity and efficacy of CAR-T cell cells. Prolonged CAR-T cell manufacturing process leads to a more differentiated and effector-like phenotype, which is susceptible to accelerated exhaustion in vivo. Unfortunately, clinical evidence suggests that less differentiated and stem-cell like CAR-T products have increased proliferative capacity, reduced exhaustion, and greater efficacy. Additionally, aging is known to compromise T-cell function, reducing chances of CAR-T therapy candidacy for older patients. These compounded effects of manufacturing and aging severely limit CAR-T cell functionality in terms of proliferation, perdurance, and cytotoxic capacity, as well as precluding wider patient access. Leveraging our previous work with other aged human cells, we hypothesized that the transient expression of ERATM factors could impact manufacturing of CAR-T cells by mitigating their differentiation, promoting T stem cell memory (Tscm) phenotype, reducing/eliminating exhaustion, and resetting the epigenetic clock in CAR-T cells. Here, we present preclinical data showing that ERATM treatment of T cells delivered using our proprietary eTurnaTM platform can restore youthful functionality, reducing exhaustion and effects of aging, improving their ability to fight cancer while safely maintaining cellular identity. ERATM -treated T cells have higher proliferation capacity and cytotoxicity upon tumor cell engagement in vitro compared to control cells. Treatment of ERATM -treated T-cells also increases the production of beneficial cytokines to support their survival and cytotoxic activity. Importantly, ERATM treatment preserves T-cell identity and T-cell repertoire, while avoiding unwanted hyperproliferation or clonal expansion. In murine models of hematological cancers, these effects of ERATM treatment on T-cells results in superior cancer cell killing and clearance. These benefits of ERATM technology to current CAR-T manufacturing processes have the potential to translate into the clinic as improved patient outcomes and survival with reduced side effects, thereby expanding patient access and enabling immunotherapies to serve as a first-in-line lifesaving solution. Citation Format: Alec McQuiston, Junbao Yang, Jason Romero, Naveen Bojjireddy, Travis McQuiston, Vittorio Sebastiano, Mustafa Turkoz. Transient epigenetic reprogramming enhances T-cell proliferation and tumor clearance. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4108.

Abstract 3472: A tumor draining lymph node CD8 T cell memory response is pivotal for a decrease in recurrence after neoadjuvant anti PD-1 therapy for NSCLC

Abstract Background: Non-small cell lung cancer (NSCLC) is the leading cause of cancer death worldwide. Even at early stages, death rates remain disproportionately high due to metastatic recurrence. Recently, blockade of the PD-1/PD-L1 axis has shown impressive increases in recurrence-free survival in a subset of patients. While efforts to decrease relapse have focused on decreasing residual micrometastatic disease at the time of definitive treatment, PD-1 directed therapy may allow for an adaptive immune response and the establishment of anti-tumor immunosurveillance. Building on results from a clinically relevant murine model of metastatic relapse after tumor resection and robust assays on systematically characterized tumor, lymph node and blood samples of early-stage lung cancer patients, we posit that immunologic CD8 T cell memory may be a primary mechanism of metastatic protection. Methods: We utilized a syngeneic murine model of metastatic lung adenocarcinoma (344SQ) after resection of tumor, tumor draining lymph node (tdLN) and non-draining lymph nodes (ndLN). Using bioluminescent imaging (BLI) and flow cytometric analysis we monitored T cell kinetics and anti-tumor activity after administration of anti-PD-1 antibody and/or KD033, a fusion antibody combining a high affinity anti-PD-L1 IgG1 antibody with an IL-15Rα sushi binding domain. Tumor/tdLN and ndLN T cells were characterized for PD-1/TCF-1/CD62L/CD44/CXCR5 memory phenotypes. In parallel, we analyzed resected tumor, tdLN and ndLN from early-stage NSCLC patients. Results: tdLN from murine models and early-stage patients maintain robust PD-1+ CXCR5+ CD8 T cell memory phenotypes not significantly found in the primary tumor, ndLN and peripheral blood. Neoadjuvant treatment with PD-1 blockade alone had a heterogenous response, with robust proliferation of T cell central and stem cell memory populations (CM &amp; SCM) at the tdLN in responders compared to non-responders (p&amp;lt;0.05). Combination therapy with IL-15Rα agonist (KD033) potentiated diverse PD-1+ CXCR5+ CD8 stem cell like memory subsets in the tdLN and subsequent response at the primary tumor (100%) as well as displayed superior protection against metastatic recurrence up to 200 days compared to PD-1 inhibition or KD033 alone (median survival undetermined vs. 120d, 161d respectively p&amp;lt;0.05). Removal of tdLN or blockade of lymph node migration with FTY720 prior to therapy decreased a population of SCM and CM CD8 T cells found in the primary tumor, decreased primary tumor response and altered systemic memory subpopulations in the ndLN (p&amp;lt;0.05). Conclusions: Our data strongly points to a T cell memory response within the tumor draining lymph node as a possible driver of protection from systemic cancer recurrence, laying the groundwork for a new therapeutic strategy aimed at establishing CD8 immunosurveillance for protection from cancer recurrence. Citation Format: Tatiana Delgado Cruz, Geoffrey J. Markowitz, Mitchell Martin, Arshdeep Singh, Shelley Yang Bai, Nasser Altorki, Timothy McGraw, Vivek Mittal, Jonathan Villena-Vargas. A tumor draining lymph node CD8 T cell memory response is pivotal for a decrease in recurrence after neoadjuvant anti PD-1 therapy for NSCLC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3472.

Abstract 3190: ALA-CART induces global transcriptional changes leading to enhanced potency and persistence of CAR T cells against both lymphoid and myeloid acute leukemias

Abstract Chimeric antigen receptor (CAR) T cell therapy has revolutionized cancer treatment, demonstrating clinical success in B-cell malignancies that are refractory to standard therapies. Relapses after CAR therapy has demonstrated the limitations of current CAR T cell therapies to target antigen-low tumors and induce consistent persistence. Furthermore, the success of CAR T cell therapy in B-lineage malignancies has not yet been translated to acute myeloid leukemia (AML). The targeting of myeloid-restricted antigens, such as CD33, with standard 2nd generation CAR T cells has not yielded similar clinical responses as ALL. Therefore, we hypothesize that novel CAR T cell strategies will be required to improve responses in non-B cell malignancies. We identified that CAR T cells inefficiently activate the scaffolding protein LAT in response to low levels of antigen, leading to diminished efficacy. We designed a bicistronic construct consisting of a clinically active 2nd generation CD22-BBz CAR along with a novel Adjunctive LAT Activating CAR incorporating the intracellular signaling domain of LAT (ALA-CART) to overcome this deficiency of signaling in CAR T cells. In xenograft models, 22ALA-CART cells completely eradicated CD22-low leukemia, which is not responsive to standard CD22-BBz CAR T cells. We have extended these findings to CD19-directed ALA-CART cells, which eradicate CD19-low leukemia that is otherwise resistant to standard CD19-BBz CAR T cells. To understand how ALA-CART improves responses to antigen-low leukemia, we evaluated the in vivo potency of ALA-CART relative to 2nd generation CARs and found ALA-CART cells could eradicate ALL in xenograft models at lower doses than standard CAR T cells. RNA-Seq analysis demonstrated global differences in ALA-CART cells in the resting state reflecting a less differentiated state, which corresponded to an enrichment of T stem cell memory cells and enhanced in vivo persistence. Stimulation through the ALA-CART receptor led to widespread changes in transcription factor activity in T cells which were distinct from standard CAR activation, particularly inducing significantly lower interferon response factor activity which has been associated with CAR T cell failure in patients. As strategies targeting myeloid lineage-restricted antigens with 2nd generation CAR T cells have not yet produced the clinical success seen with ALL-directed CAR therapy, we tested whether the ALA-CART platform could improve the activity of CD33-directed CAR T cells. CD33 ALA-CART cells demonstrated improved in vivo potency and exhibited enhanced memory potential like our results with ALL-directed ALA-CART. Thus, through the reversal of signaling deficits intrinsic to 2nd generation CARs, the ALA-CART platform improves the potency and persistence of CAR T cell therapy against both lymphoid and myeloid acute leukemias. Citation Format: Catherine Danis, Lillie Leach, Christopher Ebmeier, Amanda Novak, Etienne Danis, M. Eric Kohler. ALA-CART induces global transcriptional changes leading to enhanced potency and persistence of CAR T cells against both lymphoid and myeloid acute leukemias [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3190.

Naive T cells inhibit the outgrowth of intractable antigen-activated memory T cells: implications for T-cell immunotherapy

BackgroundThe wider application of T cells targeting viral tumor-antigens via their native receptors is hampered by the failure to expand potent tumor-specific T cells from patients. Here, we examine reasons...

Virus-Specific Stem Cell Memory CD8+ T Cells May Indicate a Long-Term Protection against Evolving SARS-CoV-2

Immune memory to SARS-CoV-2 is key for establishing herd immunity and limiting the spread of the virus. The duration and qualities of T-cell-mediated protection in the settings of constantly evolving pathogens remain an open question. We conducted a cross-sectional study of SARS-CoV-2-specific CD4+ and CD8+ T-cell responses at several time points over 18 months (30-750 days) post mild/moderate infection with the aim to identify suitable methods and biomarkers for evaluation of long-term T-cell memory in peripheral blood. Included were 107 samples from 95 donors infected during the periods 03/2020-07/2021 and 09/2021-03/2022, coinciding with the prevalence of B.1.1.7 (alpha) and B.1.617.2 (delta) variants in Bulgaria. SARS-CoV-2-specific IFNγ+ T cells were measured in ELISpot in parallel with flow cytometry detection of AIM+ total and stem cell-like memory (TSCM) CD4+ and CD8+ T cells after in vitro stimulation with peptide pools corresponding to the original and delta variants. We show that, unlike IFNγ+ T cells, AIM+ virus-specific CD4+ and CD8+ TSCM are more adequate markers of T cell memory, even beyond 18 months post-infection. In the settings of circulating and evolving viruses, CD8+ TSCM is remarkably stable, back-differentiated into effectors, and delivers immediate protection, regardless of the initial priming strain.

High frequency of memory stem cells with a distinct gene signature in HIV patients with treatment interruption.

Reservoirs of HIV remain a major obstacle to the complete eradication of virus despite regular anti-retroviral therapy (ART). Memory stem cells (Tscm), one of the major reservoirs, are relatively less studied owing to their presence in lower numbers and inaccessible anatomical locations. We have evaluated the molecular characteristics of Tscms in patients with ART interruption (n=15) versus patients on uninterrupted ART (n=12) using flow cytometry. RNA sequencing was done in the sorted Tscms to study the differential gene expression. Patients with ART interruption had significantly lower baseline CD4+T-cell counts and high viral loads as compared to patients on ART. The former group had significantly higher frequency of CD4+ and CD8+Tscms with a higher expression of PD-1 on CD8+Tscms. The transcriptome profile of Tscm was significantly different among the patient groups. The main pathways were cellular and metabolic pathways, cellular development pathways, cell differentiation and negative regulation of cellular migratory pathways. An increased yet dysfunctional CD8+ memory stem cells describe HIV-1-infected patients with break-in ART and a distinct transcriptional signature of CD4+ Tscm as compared to those of patients on ART. A more detailed understanding of the biology and dynamics of Tscm in future studies is warranted. Strategies to improve the functionality of the CD8+ Tscm will help these patients to tackle the outburst of viral replication that occurs after the cessation of therapy.

Abstract P3-08-07: Self-renewal signatures of peripheral blood T cells are associated with successful engraftment to establish a humanized mouse model of breast cancer

Abstract Background: Stable humanized immune mice transplanted with peripheral blood mononuclear cells (PBMCs) derived from breast cancer patients are important models for assessing the tumor immune responses and the tumor immune microenvironment in breast cancer, helping to advance both pre-clinical and clinical research. The PBMCs of breast cancer patients exhibit various differences from those of healthy individuals depending on the stage of cancer progression, subtype, and type of treatment. Recent studies indicate an association of the self-renewal signatures of T cells with successful generation of a humanized mouse model; however, the optimal T cell signature for the successful generation of a humanized mouse model derived from cancer patient cells is poorly understood. Therefore, we examined the relationship between the signature of T cell subsets, focusing on the self-renewal signatures, in PBMCs derived from patients with breast cancer and the successful generation of a humanized immune mouse model. Materials and Methods: We collected PBMCs from 12 patients with breast cancer. All samples were stimulated with interleukin-2 and beads coated with CD3 and CD28 agonist antibodies to expand T cells. After washing, 1 × 10^7 cells/mouse were intraperitoneally injected into NOD/Shi-scid IL2rgamma (null) (NOG) mice. Transplants were performed on three mice per case. Successful engraftment of immune cells into NOG mice was defined by the presence of human CD45+ cells in one or more mice. Self-renewal signatures of in vitro expanded T cells before injection into NOG mice, including the markers T cell factor-1 (TCF-1), CD45RA, CCR7, CD95, and CXCR3, were determined using flow cytometry, mass cytometry and quantitative RT-PCR. Comparisons between groups of data were evaluated by t-test. Results: The success rate of engraftment of immune cells derived from breast cancer patients into NOG mice was 66.7% (8 out of 12 patients). After expansion, the magnitude of the CD8+ stem cell memory subset and the TCF-1 expression level on the CD4+ and CD8+ T cells in the engrafted group were significantly higher than those in non-engrafted group. TCF-1 and CCR7 mRNA levels in the engrafted group were upregulated compared with those in non-engrafted group. The success of engraftment was not associated with clinical characteristics such as breast cancer progression, subtype, or prior chemotherapy treatment. Conclusion: The self-renewal signatures of T cells from breast cancer patients were associated with successful engraftment of a humanized mouse model. These results suggest that prior identification of the self-renewal signatures of the T-cell population is of direct relevance to the appropriate design of a pre-clinical model for testing immunotherapies and for elucidating the characteristics of the tumor immune microenvironment. Citation Format: Yukiko Fukui, Kosuke Kawaguchi, Ryuji Murakami, Wei Li, Yuki Nakamura, Yurina Maeshima, Sunao Tanaka, Shinpei Kawaoka, Eiji Suzuki, Masakazu Toi. Self-renewal signatures of peripheral blood T cells are associated with successful engraftment to establish a humanized mouse model of breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-08-07.