Pooled screening for CAR function identifies novel IL13Rα2-targeted CARs for treatment of glioblastoma.

Chimeric antigen receptor therapies have demonstrated potent efficacy in treating B cell malignancies, but have yet to meaningfully translate to solid tumors. Here, we utilize our pooled screening platform, CARPOOL, to expedite the discovery of CARs with anti-tumor functions necessary for solid tumor efficacy. We performed selections in primary human T cells expressing a library of 1.3×10 6 3 rd generation CARs targeting IL13Rα2, a cancer testis antigen commonly expressed in glioblastoma. Selections were performed for cytotoxicity, proliferation, memory formation, and persistence upon repeated antigen challenge. Each enriched CAR robustly produced the phenotype for which it was selected, and one enriched CAR triggered potent cytotoxicity and long-term proliferation upon in vitro tumor rechallenge. It also showed significantly improved persistence and comparable antigen-specific tumor control in a microphysiological human in vitro model and a xenograft model of human glioblastoma. Taken together, this work demonstrates the utility of extending CARPOOL to diseases beyond hematological malignancies and represents the largest exploration of signaling combinations in human primary cells to date.

Unveiling the Influence of Tumor Microenvironment and Spatial Heterogeneity on Temozolomide Resistance in Glioblastoma Using an Advanced Human In Vitro Model of the Blood-Brain Barrier and Glioblastoma.

Glioblastoma (GBM) is the most common primary malignant brain cancer in adults with a dismal prognosis. Temozolomide (TMZ) is the first-in-line chemotherapeutic; however, resistance is frequent and multifactorial. While many molecular and genetic factors have been linked to TMZ resistance, the role of the solid tumor morphology and the tumor microenvironment, particularly the blood-brain barrier (BBB), is unknown. Here, the authors investigate these using a complex in vitro model for GBM and its surrounding BBB. The model recapitulates important clinical features such as a dense tumor core with tumor cells that invade along the perivascular space; and a perfusable BBB with a physiological permeability and morphology that is altered in the presence of a tumor spheroid. It is demonstrated that TMZ sensitivity decreases with increasing cancer cell spatial organization, and that the BBB can contribute to TMZ resistance. Proteomic analysis with next-generation low volume sample workflows of these cultured microtissues revealed potential clinically relevant proteins involved in tumor aggressiveness and TMZ resistance, demonstrating the utility of complex in vitro models for interrogating the tumor microenvironment and therapy validation.

G9a/GLP inhibition during ex vivo lymphocyte expansion increases in vivo cytotoxicity of engineered T cells against hepatocellular carcinoma.

Engineered T cells transiently expressing tumor-targeting receptors are an attractive form of engineered T cell therapy as they carry no risk of insertional mutagenesis or long-term adverse side-effects. However, multiple rounds of treatment are often required, increasing patient discomfort and cost. To mitigate this, we sought to improve the antitumor activity of transient engineered T cells by screening a panel of small molecules targeting epigenetic regulators for their effect on T cell cytotoxicity. Using a model for engineered T cells targetting hepatocellular carcinoma, we find that short-term inhibition of G9a/GLP increases T cell antitumor activity in in vitro models and an orthotopic mouse model. G9a/GLP inhibition increases granzyme expression without terminal T cell differentiation or exhaustion and results in specific changes in expression of genes and proteins involved in pro-inflammatory pathways, T cell activation and cytotoxicity.

Immunosuppressive Drug-Resistant Armored T-Cell Receptor T Cells for Immune Therapy of HCC in Liver Transplant Patients.

BACKGROUND AND AIMS: HBV-specific T-cell receptor (HBV-TCR) engineered T cells have the potential for treating HCC relapses after liver transplantation, but their efficacy can be hampered by the concomitant immunosuppressive treatment required to prevent graft rejection. Our aim is to molecularly engineer TCR-T cells that could retain their polyfunctionality in such patients while minimizing the associated risk of organ rejection. APPROACH AND RESULTS: We first analyzed how immunosuppressive drugs can interfere with the in vivo function of TCR-T cells in liver transplanted patients with HBV-HCC recurrence receiving HBV-TCR T cells and in vitro in the presence of clinically relevant concentrations of immunosuppressive tacrolimus (TAC) and mycophenolate mofetil (MMF). Immunosuppressive Drug Resistant Armored TCR-T cells of desired specificity (HBV or Epstein-Barr virus) were then engineered by concomitantly electroporating mRNA encoding specific TCRs and mutated variants of calcineurin B (CnB) and inosine-5'-monophosphate dehydrogenase (IMPDH), and their function was assessed through intracellular cytokine staining and cytotoxicity assays in the presence of TAC and MMF. Liver transplanted HBV-HCC patients receiving different immunosuppressant drugs exhibited varying levels of activated (CD39+ Ki67+ ) peripheral blood mononuclear cells after HBV-TCR T-cell infusions that positively correlate with clinical efficacy. In vitro experiments with TAC and MMF showed a potent inhibition of TCR-T cell polyfunctionality. This inhibition can be effectively negated by the transient overexpression of mutated variants of CnB and IMPDH. Importantly, the resistance only lasted for 3-5 days, after which sensitivity was restored. CONCLUSIONS: We engineered TCR-T cells of desired specificities that transiently escape the immunosuppressive effects of TAC and MMF. This finding has important clinical applications for the treatment of HBV-HCC relapses and other pathologies occurring in organ transplanted patients.

MBNL1 alternative splicing isoforms play opposing roles in cancer.

The extent of and the oncogenic role played by alternative splicing (AS) in cancer are well documented. Nonetheless, only few studies have attempted to dissect individual gene function at an isoform level. Here, we focus on the AS of splicing factors during prostate cancer progression, as these factors are known to undergo extensive AS and have the potential to affect hundreds of downstream genes. We identified exon 7 (ex7) in the MBNL1 (Muscleblind-like 1) transcript as being the most differentially included exon in cancer, both in cell lines and in patients' samples. In contrast, MBNL1 overall expression was down-regulated, consistently with its described role as a tumor suppressor. This observation holds true in the majority of cancer types analyzed. We first identified components associated to the U2 splicing complex (SF3B1, SF3A1, and PHF5A) as required for efficient ex7 inclusion and we confirmed that this exon is fundamental for MBNL1 protein homodimerization. We next used splice-switching antisense oligonucleotides (AONs) or siRNAs to compare the effect of MBNL1 splicing isoform switching with knockdown. We report that whereas the absence of MBNL1 is tolerated in cancer cells, the expression of isoforms lacking ex7 (MBNL1 Δex7) induces DNA damage and inhibits cell viability and migration, acting as dominant negative proteins. Our data demonstrate the importance of studying gene function at the level of alternative spliced isoforms and support our conclusion that MBNL1 Δex7 proteins are antisurvival factors with a defined tumor suppressive role that cancer cells tend to down-regulate in favor of MBNL +ex7 isoforms.