SUMMARY The high expression across multiple tumor types and restricted expression in normal tissues make B7-H3 an attractive target for immunotherapy. We generated chimeric antigen receptor (CAR) T cells targeting B7-H3 (B7-H3.CAR-Ts) and found that B7-H3.CAR-Ts controlled the growth of pancreatic ductal adenocarcinoma, ovarian cancer and neuroblastoma in vitro and in orthotopic and metastatic xenograft mouse models, which included patient-derived xenograft. We also found that 4–1BB co-stimulation promotes lower PD-1 expression in B7-H3.CAR-Ts, and superior antitumor activity when targeting tumor cells that constitutively expressed PD-L1. We took advantage of the cross-reactivity of the B7-H3.CAR with murine B7-H3, and found that B7-H3.CAR-Ts significantly controlled tumor growth in a syngeneic tumor model without evident toxicity. These findings support the clinical development of B7-H3.CAR-Ts.

Purpose: A delay in encountering the cognate antigen while in the circulation, and the suboptimal costimulation received at the tumor site are key reasons for the limited activity of chimeric antigen receptor-redirected T cells (CAR-T) in solid tumors. We have explored the benefits of incorporating the IL15 cytokine within the CAR cassette to provide both a survival signal before antigen encounter, and an additional cytokine signaling at the tumor site using a neuroblastoma tumor model. Experimental Design: We optimized the construct for the CAR specific for the NB-antigen GD2 without (GD2.CAR) or with IL15 (GD2.CAR.15). We then compared the expansion, phenotype, and antitumor activity of T cells transduced with these constructs against an array of neuroblastoma cell lines in vitro and in vivo using a xenogeneic metastatic model of neuroblastoma. Results: We observed that optimized GD2.CAR.15-Ts have reduced expression of the PD-1 receptor, are enriched in stem cell-like cells, and have superior antitumor activity upon repetitive tumor exposures in vitro and in vivo as compared with GD2.CAR-Ts. Tumor rechallenge experiments in vivo further highlighted the role of IL15 in promoting enhanced CART antitumor activity and survival, both in the peripheral blood and tissues. Finally, the inclusion of the inducible caspase-9 gene (iC9) safety switch warranted effective on demand elimination of the engineered GD2. CAR.15-Ts. Conclusions: Our results guide new therapeutic options for GD2.CAR-Ts in patients with neuroblastoma, and CART development for a broad range of solid tumors.

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The heterogeneous expression of tumor-associated antigens limits the efficacy of chimeric antigen receptor (CAR)redirected T cells (CAR-Ts) for the treatment of glioblastoma (GBM). We have found that chondroitin sulfate proteoglycan 4 (CSPG4) is highly expressed in 67% of the GBM specimens with limited heterogeneity. CSPG4 is also expressed on primary GBM-derived cells, grown in vitro as neurospheres (GBM-NS), which recapitulate the histopathology and molecular characteristics of primary GBM. CSPG4.CAR-Ts efficiently controlled the growth of GBM-NS in vitro and in vivo upon intracranial tumor inoculation. Moreover, CSPG4.CAR-Ts were also effective against GBM-NS with moderate to low expression of CSPG4. This effect was mediated by the in vivo up-regulation of CSPG4 on tumor cells, induced by tumor necrosis factor- (TNF) released by the microglia surrounding the tumor. Overall, the constitutive and TNF-inducible expression of CSPG4 in GBM may greatly reduce the risk of tumor cell escape observed when targeted antigens are heterogeneously expressed on tumor cells.

Highlights d LCK promotes basal CAR-CD3z phosphorylation in the synapse of CAR.CD28z d THEMIS-SHP1 counteracts the effect of LCK in the synapse of CAR.4-1BBz d Engineering LCK kinase tunes up the antitumor activity of CAR.4-1BBz-T cells d Engineering druggable SHP1 phosphatase tunes down the function of CAR.