Delivery of B7H3-targeted CAR-T cells in injectable silk hydrogels and effects on the efficacy in treating solid tumors.

e15182 Background: Chimeric antigen receptor (CAR)-T cell immunotherapy has been shown to be highly efficacious in the treatment of blood cancers, but remains far from satisfactory in treating solid tumor due to inadequate intra-tumor CAR-T cell infiltration. CAR-T cells delivered in the traditional way exhibit poor activity against solid tumors, as it is challenging for the cells to find, infiltrate, and expand within the typically immunosuppressive tumor microenvironment following systemic administration. Methods: Here, in this report, we engineered a self-assembled and injectable biomaterial platform for CAR-T cell delivery based on silk hydrogels. The antitumor activities of B7H3-targeted CAR-T cells encapsulated by silk hydrogels were evaluated in vitro and in vivo . Results: CAR-T cell proliferation and survival were not affected by silk hydrogel encapsulation. Moreover, B7H3-targeted CAR-T cells released from the silk hydrogels had the ability to migrate towards the tumor cells expressing target antigen B7H3, eventually resulting in tumor cell clearance in vitro . To evaluate the effect of silk hydrogels on CAR-T cell treatment of solid tumors in vivo , B7H3-targeted CAR-T cells and IL-2 were co-encapsulated in silk hydrogels, and the hydrogel mixtures were administered subcutaneously at the proximal or distal sites in NSG mice bearing subcutaneous human melanomas (A375-luc). Notably, subcutaneous administration of hydrogel mixtures at proximal or distal sites to tumors both resulted in complete tumor clearance, and CAR-T cells were still detectable in peripheral blood three weeks post treatment, indicating that the unique architecture of silk hydrogel enabled long-term retention, viability, and activation of CAR-T cells. Next, NSG mice with orthotopic xenografts of human bladder tumors (5637-luc) were treated with B7H3-targeted CAR-T cells. Subcutaneous co-delivery of CAR-T cells and IL-2 in silk hydrogels substantially eradicated the bladder tumors in NSG mice, suggesting that CAR-T cells encapsulated in silk hydrogels had the ability to migrate from the subcutaneous tissue into the bladder tumor site to kill the target cells and to provide a long-term protection. Conclusions: Co-delivery of CAR-T cells and stimulatory cytokine with injectable silk hydrogels ensured sufficient long-term retention, activation and expansion of CAR-T cells, profoundly improved the efficacy in treating solid tumors in mice. Our study also demonstrated that CAR-T cells delivered in silk hydrogels at proximal or distal sites to tumors elicited similar efficacy, suggesting that this CAR-T cell delivery approach may be more beneficial for the treatment of metastases or tumors that are not easily accessible via direct injection. Acknowledgements: This work was supported by the National Natural Science Foundation of China (82202034 and 82472162), the Chongqing Natural Science Foundation General Project (CSTB2024NSCQ-MSX1294), and the Xinjiang National science foundation science and technology aid project (No.2022E02128).