Abstract Background: There is growing evidence that responsiveness to immunotherapy is influenced by the composition of a patient’s gut microbiota. Recent analysis identified strong correlations between abundance of gut microbial species and positive response to immune based therapies in cancer patients. Further, enrichment of commensal microbes can promote immunostimulatory effects, immune based anti-tumor responses, and increased cytotoxic T cell abundance within the TME. Conversely, the presence of gut microbes known to cause inflammatory states in gut tissues may be correlated to negative immunotherapy outcomes or toxicities. To this end, we aimed to evaluate the impact of microbiome manipulation on gut microbe diversity, systemic immunity, local TME, and PSCA-targeted chimeric antigen receptor (CAR) T cell therapy in our established syngeneic prostate cancer mouse model. Methods: In an immune competent mouse model of PSCA+ prostate cancer developed in our lab, we sequentially modified the gut microbiome using antibiotic clearance followed by distinct human derived fecal matter transfers (CPI-FMT, HD-FMT, or No-FMT). Simultaneously, we treated microbiome modified tumor bearing mice with PSCA-targeting CAR T cells and measured differences in anti-tumor efficacy and survival. To provide mechanistic insight, we performed longitudinal whole genome sequencing (WGS) of fecal matter microbes and RNA sequencing on spleen and tissues following FMT administration. Results: In our model, a unique checkpoint inhibitor (CPI) treated patient derived human FMT (CPI-FMT) improved PSCA-CAR anti-tumor responses relative to healthy donor (HD-FMT) or No-FMT treatment controls. CPI-FMT administration also significantly improved overall survival in CAR T cell and non-targeting T cell control treated mice. Temporal analysis of microbes present in the gut following CPI-FMT and HD-FMT treatment show CPI-FMT treated mice exhibit favorable maintenance of gut microbe species richness and significant increase in microbiota diversity. We identify CPI-FMT provides an enrichment of specific microbes associated with preservation of gut homeostasis and improved immune response. RNA sequencing analysis on tumor tissues show differential transcription of immune related pathways following FMT which may influence immune and CAR T cell function. Conclusions: We show that our mouse prostate cancer model is sensitive microbiome modulation and can significantly impact PSCA-CAR T cell directed anti-tumor responses. Temporal WGS analysis of gut fecal matter reveal enrichment suggest specific species abundances which may promote gut homeostasis over dysbiosis or inflammatory states and may account for improved CAR T cell response. We aim to further develop this model to interrogate candidate targeted microbiome modifiers which may impact mechanisms which promote CAR T cell and immune function. Citation Format: John Paul Murad, Lea Christian, Yukiko Yamaguchi, Lupita Lopez, Ching Ouyang, Hirokazu Sato, Bryce Jarman, Sean Stromberg, Stephen J. Forman, Stephen Van Dien, Stephanie Culler, Saul J. Priceman. Microbiome modification impacts PSCA directed chimeric antigen receptor (CAR) T cell therapy for prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6676.

Advancing chimeric antigen receptor (CAR)-engineered T cells for the treatment of solid tumors is a major focus in the field of cellular immunotherapy. Several hurdles have hindered similar CAR T cell clinical responses in solid tumors as seen in hematological malignancies. These challenges include on-target off-tumor toxicities, which have inspired efforts to optimize CARs for improved tumor antigen selectivity and overall safety. We recently developed a CAR T cell therapy targeting prostate stem cell antigen (PSCA) for prostate and pancreatic cancers, showing improved pre-clinical antitumor activity and T cell persistence by optimizing the intracellular co-stimulatory domain. Similar studies were undertaken to optimize HER2-directed CAR T cells with modifications to the intracellular co-stimulatory domain for selective targeting of breast cancer brain metastasis. In the current study, we evaluate various nonsignaling extracellular spacers in these CARs to further improve tumor antigen selectivity. Our findings suggest that length and structure of the extracellular spacer can dictate the ability of CARs to selectively target tumor cells with high antigen density, while sparing cells with low antigen density. This study contributes to CAR construct design considerations and expands our knowledge of tuning solid tumor CAR T cell therapies for improved safety and efficacy.

BACKGROUND:The immune suppressive tumor microenvironment (TME) that inhibits T cell infiltration, survival, and antitumor activity has posed a major challenge for developing effective immunotherapies for solid tumors. Chimeric antigen receptor (CAR)-engineered T cell therapy has shown unprecedented clinical response in treating patients with hematological malignancies, and intense investigation is underway to achieve similar responses with solid tumors. Immunologically cold tumors, including prostate cancers, are often infiltrated with abundant tumor-associated macrophages (TAMs), and infiltration of CD163+ M2 macrophages correlates with tumor progression and poor responses to immunotherapy. However, the impact of TAMs on CAR T cell activity alone and in combination with TME immunomodulators is unclear.METHODS:To model this in vitro, we utilized a novel co-culture system with tumor cells, CAR T cells, and polarized M1 or M2 macrophages from CD14+ peripheral blood mononuclear cells collected from healthy human donors. Tumor cell killing, T cell activation and proliferation, and macrophage phenotypes were evaluated by flow cytometry, cytokine production, RNA sequencing, and functional blockade of signaling pathways using antibodies and small molecule inhibitors. We also evaluated the TME in humanized mice following CAR T cell therapy for validation of our in vitro findings.RESULTS:We observed inhibition of CAR T cell activity with the presence of M2 macrophages, but not M1 macrophages, coinciding with a robust induction of programmed death ligand-1 (PD-L1) in M2 macrophages. We observed similar PD-L1 expression in TAMs following CAR T cell therapy in the TME of humanized mice. PD-L1, but not programmed cell death protein-1, blockade in combination with CAR T cell therapy altered phenotypes to more M1-like subsets and led to loss of CD163+ M2 macrophages via interferon-γ signaling, resulting in improved antitumor activity of CAR T cells.CONCLUSION:This study reveals an alternative mechanism by which the combination of CAR T cells and immune checkpoint blockade modulates the immune landscape of solid tumors to enhance therapeutic efficacy of CAR T cells.

Background The immune suppressive tumor microenvironment (TME) that inhibits T cell infiltration, survival, and anti-tumor activity has posed a major challenge for developing effective immunotherapies for solid tumors. Chimeric antigen receptor (CAR)-engineered T cell therapy has shown unprecedented clinical response in treating patients with hematological malignancies, and intense investigation is underway to achieve similar responses with solid tumors. Immunologically cold tumors, including prostate cancers, are often infiltrated with abundant tumor-associated macrophages (TAMs), and infiltration of CD163 + M2 macrophages correlates with tumor progression and poor responses to immunotherapy. However, the impact of TAMs on CAR T cell activity alone and in combination with TME immunomodulators is unclear. Methods To model this in vitro , we utilized a novel co-culture system with tumor cells, CAR T cells, and polarized M1 or M2 macrophages from CD14 + PBMCs collected from healthy human donors. Tumor cell killing, T cell activation and proliferation, and macrophage phenotypes were evaluated by flow cytometry, cytokine production, RNA sequencing, and functional blockade of signaling pathways using antibodies and small molecule inhibitors. We also evaluated the TME in humanized mice following CAR T cell therapy for validation of our in vitro findings. Results We observed inhibition of CAR T cell activity with the presence of M2 macrophages, but not M1 macrophages, coinciding with a robust induction of PD-L1 in M2 macrophages. We observed similar PD-L1 expression in TAMs following CAR T cell therapy in the TME of humanized mice. PD-L1, but not PD-1, blockade in combination with CAR T cell therapy altered phenotypes to more M1-like subsets and led to loss of CD163 + M2 macrophages via IFNγ signaling, resulting in improved anti-tumor activity of CAR T cells. Conclusion This study reveals an alternative mechanism by which the combination of CAR T cells and immune checkpoint blockade modulates the immune landscape of solid tumors to enhance therapeutic efficacy of CAR T cells.

Chimeric antigen receptor (CAR) T cell therapy has led to impressive clinical responses in patients with hematological malignancies; however, its utility in patients with solid tumors has been limited. While CAR T cells for the treatment of advanced prostate cancer are being clinically evaluated and are anticipated to show bioactivity, their safety and the impact of the immunosuppressive tumor microenvironment (TME) have not been faithfully explored preclinically. Using a novel human prostate stem cell antigen knock-in (hPSCA-KI) immunocompetent mouse model and syngeneic murine PSCA CAR T cells, we performed analyses of normal and tumor tissues by flow cytometry, immunohistochemistry, and/or RNA sequencing. We further assessed the beneficial impact of cyclophosphamide (Cy) pre-conditioning on modifications to the immunosuppressive TME and impact on PSCA-CAR T cell safety and efficacy. We observed an in vivo requirement of Cy pre-conditioning in uncovering the efficacy of PSCA-CAR T cells in prostate and pancreas cancer models, with no observed toxicities in normal tissues with endogenous PSCA expression. This combination also dampened the immunosuppressive TME, generated pro-inflammatory myeloid and T cell signatures in tumors, and enhanced the recruitment of antigen-presenting cells, and endogenous as well as adoptively-transferred CAR T cells, resulting in long-term anti-tumor immunity.

BackgroundThe immune suppressive tumor microenvironment (TME) that inhibits T cell infiltration, survival, and anti-tumor activity has posed a major challenge for developing effective immunotherapies for solid tumors. Chimeric antigen receptor T cell therapy has shown unprecedented clinical response in treating patients with hematological malignancies, and intense investigation is underway to achieve similar responses with solid tumors. Immunologically cold tumors, including prostate cancers, are often infiltrated with abundant macrophages, and infiltration of M2 macrophages correlates with metastasis and poor prognosis.MethodsTo model this in vitro, we utilized a novel co-culture system with tumor cells, prostate stem cell antigen (PSCA)-directed CAR T cells, and polarized macrophages. To investigate the TME in vivo, we took advantage of ”humanized” MISTRG mice, which are immunocompromised mice with knocked-in human genes that support human hematopoiesis and efficient tumor-infiltration of myeloid cell populations. Humanized MISTRG mice were intratibially engrafted with LAPC9 tumor cells to model bone metastatic disease.ResultsWe observed significant hampering of PSCA-CAR T cell activity in vitro with the presence of M2 macrophages, but not M1 macrophages, coinciding with a robust induction of PD-L1 in both tumor cells and macrophages. We also observed PD-L1 expression in tumor-associated macrophages infiltrating tumors following PSCA-CAR T cell therapy in the humanized mice. Anti-PD-L1 monoclonal antibodies in combination with CAR-T cell therapy altered phenotype and survival of M2 macrophages, resulting in improved anti-tumor activity of PSCA-CAR T cells in the presence of M2 macrophages.ConclusionsRecently, immune checkpoint (IC) blockade (ICB) has been utilized in combination with chimeric antigen receptor (CAR) T cell therapy, with the notion that induction of immune responses with CAR T cells may instigate checkpoint pathways in immunologically cold tumors that would otherwise not respond to ICB. This study gives insights to a mechanism by which CAR T cells and ICB work in synergy to modulate immune landscape of immunologically cold tumors, and our ongoing studies will continue to elucidate the TME-mediated immunosuppression of CAR T cell therapy.

Background: Tumor-associated macrophages (TAMs) play a key role in cutaneous T cell lymphoma (CTCL) growth and neoplastic T cells escape immune surveillance via PD1-PD-L1 axis (Querfeld, C., et al., Blood 2019; Khodadoust, M.S., et al., J Clin Oncol, 2020). There remains a lack of knowledge about how cytokines regulate the mechanisms controlling tumor-growth and polarize the tumor microenvironment (TME). Methods and Results: To investigate PD-L1 and PD1 expression on TAMs and T cells in mycosis fungoides (MF) and the leukemic variant Sézary syndrome (SS) patients, we performed multiplex immunofluorescence (IF) staining of lesional skin samples of MF patients that demonstrated co-localization of PD-L1 on CD163+ M2 macrophages and PD1 expression on CD4+ and CD8+ T cells. In addition, significant enrichment of CD14+ and CD16+/CD14dim CD163+ M2-like monocytes/macrophages with upregulated PD-L1 expression in SS patients compared to healthy donors (HDs) was found via FACS analysis. We also performed 30-plex Luminex cytokine assay on plasma samples, which showed significantly increased IL-6, IL-10, IFNγ and TNFα levels in plasma of MF/SS compared to HDs. To investigate whether polarization towards an M2-like macrophage phenotype with increased PD-L1 expression correlated with the cytokine expression from CTCL-TME, we cultured total PBMCs from HDs with conditioned media (CM) from well established CTCL cell lines MyLa and HuT78 and analyzed PD-L1 mRNA, total PD-L1 protein and PD-L1 surface expression on M2-like macrophages. Significantly increased expression of PD-L1 protein in total PBMCs, especially on CD14+ and CD16+/CD14dim M2-like macrophages was seen. To understand whether distinct cytokines are associated with PD-L1 upregulation on CD163+ M2-like populations, total PBMCs from HDs were stimulated with human recombinant IL-6, IL-10, IFNγ or TNFα. Antibody blocking studies were conducted by adding anti human IL-6, IL-10, IFNγ or TNFα to the cultures with CM. TNFα stimulation significantly increased the CD14+ M2-like subset, but did not affect CD16+/CD14dim M2-like subset. We observed increased PD-L1 expression on both M2-like populations with TNFα compared to other cytokines. In contrast, blockade of TNFα significantly decreased the CD14+ M2-like subset with reduced PD-L1 expression and increased CD16+/CD14dim M2-like cells with upregulated PD-L1 expression. To explore whether the STAT pathway regulates PD-L1 expression through cytokines from CTCL TME, we incubated total PBMCs from HDs in CM of MyLa and HuT78 cells with/without a pan-STAT inhibitor, and in media alone. Inhibition of STAT signaling decreased CD14+ M2-like macrophage population, but did not alter the CD16+/CD14dim M2-like population. In addition, pan-STAT inhibition significantly reduced surface expression of PD-L1 on both CD14+ and CD16+/CD14dim M2-like macrophages. The effects of cytokines on STAT signaling components in regulating PD-L1 expression were also investigated by FACS and immunoblots. TNFα blockade significantly downregulated PD-L1, but also pSTAT1, pSTAT3 and pNF-κB levels, illustrating the role of TNFα on STAT1, STAT3 and NF-κB pathways in conjunction with PD-L1 expression. Stimulation with TNFα increased pSTAT3 level in CD14+ M2-like macrophages, while it did not significantly change pSTAT3 in CD16+/CD14dim M2-like macrophages. Anti-TNFα reduced pSTAT3 levels in CD14+ M2-like macrophages, but profoundly increased PD-L1 in CD16+/CD14dim M2-like macrophages, which aligns with our data of increased PD-L1 expression on CD16+/CD14dim M2-like macrophages following TNFα blockade. Conclusion: We profiled immune alterations of monocyte/macrophages populations and PD-L1 expression in CTCL regulated by selected cytokines. Our results support the dominant role of TNFα in the CTCL microenvironment. Here we show that TNFα potentiates the immunosuppressive TME through macrophage polarization and STAT-mediated PD-L1 regulation. Our results identify potential targets for combination immunotherapy. Disclosures Zain: Seattle Genetics: Research Funding; Mundai Pharma: Research Funding; Kyowa Kirlin: Research Funding. Abdulla:Johnson Johnson: Research Funding; Mallinckrodt: Consultancy, Speakers Bureau. Rosen:Seattle Genetics: Consultancy; NeoGenomics: Consultancy; Aileron Therapeutics: Consultancy; Novartis: Consultancy; Pebromene: Consultancy; Celgene: Speakers Bureau; Abbvie: Speakers Bureau; paradigm Medical Communications: Speakers Bureau. Querfeld:Trillium: Consultancy; Stemline: Consultancy; Bioniz: Consultancy; Helsinn: Consultancy; Celgene: Research Funding; Kyowa Kirin: Consultancy; MiRagen: Consultancy.

Advancing chimeric antigen receptor (CAR)-engineered adoptive T cells for the treatment of solid cancers is a major focus in the field of immunotherapy, given impressive recent clinical responses in hematological malignancies. Prostate cancer may be amenable to T cell-based immunotherapy since several tumor antigens, including prostate stem-cell antigen (PSCA), are widely over-expressed in metastatic disease. While antigen selectivity of CARs for solid cancers is crucial, it is problematic due to the absence of truly restricted tumor antigen expression and potential safety concerns with "on-target off-tumor" activity. Here, we show that the intracellular co-stimulatory signaling domain can determine a CAR's sensitivity for tumor antigen expression. A 4-1BB intracellular co-stimulatory signaling domain in PSCA-CARs confers improved selectivity for higher tumor antigen density, reduced T cell exhaustion phenotype, and equivalent tumor killing ability compared to PSCA-CARs containing the CD28 co-stimulatory signaling domain. PSCA-CARs exhibit robust in vivo anti-tumor activity in patient-derived bone-metastatic prostate cancer xenograft models, and 4-1BB-containing CARs show superior T cell persistence and control of disease compared with CD28-containing CARs. Our study demonstrates the importance of co-stimulation in defining an optimal CAR T cell, and also highlights the significance of clinically relevant models in developing solid cancer CAR T cell therapies.

Abstract Advancing chimeric antigen receptor (CAR)-engineered adoptive T cells for the treatment of solid cancers is a major focus in the field of immunotherapy, given impressive recent clinical responses in hematological malignancies. Prostate cancer should be amenable to CAR-based immunotherapy given that several tumor antigens, including prostate stem-cell antigen (PSCA), are widely over-expressed in metastatic disease. The selectivity of CARs for solid cancers is crucial, however, due to the absence of truly restricted tumor antigen expression and potential safety concerns with “on-target off-tumor” activity. Here, we show that optimized co-stimulatory signaling and extracellular spacer domains are essential in defining a CAR’s selectivity towards tumor cells that over-express the target antigen. The 4-1BB co-stimulatory domain in PSCA-CARs confers enhanced tumor selectivity with dampened yet dose-responsive cytokine production, reduced T cell exhaustion phenotype, and equivalent tumor killing ability compared to PSCA-CARs containing the CD28 co-stimulatory domain. CARs containing a short extracellular spacer demonstrate the most selective killing of high PSCA-expressing tumors but are unable to produce the inflammatory cytokines important for a complete anti-tumor response. We show that longer extracellular spacers in PSCA-CARs are necessary for both tumor killing and cytokine production. PSCA-CARs exhibit robust in vivo anti-tumor activity in subcutaneous and orthotopic bone-metastatic patient-derived prostate cancer xenograft models, and 4-1BB-containing CARs show superior persistence in controlling metastatic disease compared with CD28-containing CARs. Our study demonstrates the critical impact of CAR components in defining an optimized tumor-selective CAR T cell, and also highlights the importance of clinically relevant animal models in developing effective solid cancer CAR T cell therapies. Citation Format: Kelly Kennewick, Dileshni Tilakawardane, Ethan Gerdts, John Murad, Anthony Park, Brook Jeang, Yukiko Yamaguchi, Stephen J. Forman, Saul Priceman. Extracellular spacer and co-stimulatory domains define target sensitivity and persistence of CAR T cells for the treatment of PSCA+ bone metastatic prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4981. doi:10.1158/1538-7445.AM2017-4981

Significance A layer of fat surrounds the heart in most mammals, including humans. The biology of this tissue has been speculated for centuries, but never subjected to experimental analysis because common experimental model species are thought to not have this tissue. In this study, we show that rodents have cardiac fat, albeit in a very specific location in the heart. We implicate the origin of this tissue from the epicardium (the outer epithelium of the heart) and the underlying mechanisms that account for its derivation. By comparing human and mouse epicardial cells, we provide an explanation for the prominent species differences in the presence and amount of cardiac adipose tissue.

Loss-of-function mutations in ABCC6 can cause chronic or acute forms of dystrophic mineralization described in disease models such as pseudoxanthoma elasticum (OMIM 26480) in human and dystrophic cardiac calcification in mice. The ABCC6 protein is a large membrane-embedded organic anion transporter primarily found in the plasma membrane of hepatocytes. We have established a complex experimental strategy to determine the structural and functional consequences of disease-causing mutations in the human ABCC6. The major aim of our study was to identify mutants with preserved transport activity but failure in intracellular targeting. Five missense mutations were investigated: R1138Q, V1298F, R1314W, G1321S and R1339C. Using in vitro assays, we have identified two variants; R1138Q and R1314W that retained significant transport activity. All mutants were transiently expressed in vivo, in mouse liver via hydrodynamic tail vein injections. The inactive V1298F was the only mutant that showed normal cellular localization in liver hepatocytes while the other mutants showed mostly intracellular accumulation indicating abnormal trafficking. As both R1138Q and R1314W displayed endoplasmic reticulum localization, we tested whether 4-phenylbutyrate (4-PBA), a drug approved for clinical use, could restore their intracellular trafficking to the plasma membrane in MDCKII and mouse liver. The cellular localization of R1314W was significantly improved by 4-PBA treatment, thus potentially rescuing its physiological function. Our work demonstrates the feasibility of the in vivo rescue of cellular maturation of some ABCC6 mutants in physiological conditions very similar to the biology of the fully differentiated human liver and could have future human therapeutic application.

Pseudoxanthoma elasticum (PXE) is a heritable disease characterized by calcified elastic fibers in cutaneous, ocular, and vascular tissues. PXE is caused by mutations in ABCC6, which encodes a protein of the ATP-driven organic anion transporter family. The inability of this transporter to secrete its substrate into the circulation is the likely cause of PXE. Vitamin K plays a role in the regulation of mineralization processes as a co-factor in the carboxylation of calcification inhibitors such as Matrix Gla Protein (MGP). Vitamin K precursor or a conjugated form has been proposed as potential substrate(s) for ABCC6. We investigated whether an enriched diet of vitamin K1 or vitamin K2 (MK4) could stop or slow the disease progression in Abcc6-/- mice. Abcc6-/- mice were placed on a diet of either vitamin K1 or MK4 at 5 or 100 mg/kg at prenatal, 3 weeks or 3 months of age. Disease progression was quantified by measuring the calcium content of one side of the mouse muzzle skin and histological staining for calcium of the opposing side. Raising the vitamin K1 or MK4 content of the diet increased the concentration of circulating MK4 in the serum. However, this increase did not significantly affect the MGP carboxylation status or reduce its abnormal abundance, the total calcium content or the pathologic calcification in the whiskers of the 3 treatment groups compared to controls. Our findings showed that raising the dietary intake of vitamin K1 or MK4 was not beneficial in the treatment of PXE and suggested that the availability of vitamin K may not be a limiting factor in this pathology.