ID #535 IMiD-regulated Itag2 CAR-T Cells Improve B7-H3–targeted Anti-Tumour Activity and Persistence with Translational Potential in Paediatric B7-H3–expressing CNS Tumours

Abstract CAR-T cell therapies are effective in haematological malignancies, yet responses in solid tumours remain limited by tonic signalling, exhaustion, and poor persistence. B7-H3 is expressed most high-risk paediatric brain tumours, making it an attractive target for CAR-T cell immunotherapy in CNS malignancies. Switchable CAR-T cell technologies enable pharmacologic control of CAR expression using drug-inducible degron tags. The iTAG2 degron permits reversible downregulation of CAR expression both during manufacture—limiting tonic signalling and T-cell exhaustion prior to infusion—and following administration, offering a potential strategy for reversing tumour-induced T cell exhaustion. Immunomodulatory drugs (IMiDs) act as molecular glues that induce cereblon-mediated proteasomal degradation of degron-tagged proteins. We evaluated the effects of IMiDs, including Iberdomide and Pomalidomide, on anti–B7-H3 TE9-28z-iTAG2 CAR-T cells to achieve reversible control of CAR expression either during manufacture or post-manufacture. Functional activity of CAR-T cells, generated in GMP-compatible conditions, was assessed in vitro using solid tumour cell lines, including the Med8A medulloblastoma brain tumour model, and in vivo using NSG mouse models of medulloblastoma and neuroblastoma. Compared with CAR-T cells manufactured in the absence of IMiDs, iTAG2 CAR-T cells exposed to IMiDs during manufacture demonstrated enhanced proliferation, increased cytotoxicity, and elevated cytokine production in vitro upon tumour challenge. In vivo, IMiD-manufactured iTAG2 CAR-T cells showed superior tumour control and increased proliferative capacity. Post-manufacture regulation of CAR expression using IMiD scheduling was also evaluated. In long-term tumour challenge assays, IMiD-induced CAR downregulation prolonged CAR-T cell functional persistence and was associated with reduced markers of T-cell exhaustion. Incorporation of IMiDs either during manufacture or following infusion enhances the functional activity and therapeutic potential of iTAG2-regulated anti–B7-H3 CAR T cells. TE9-28z-iTAG2 CAR T cells are being evaluated in a Phase I study of repeated intracerebroventricular administration in children and young adults with recurrent or refractory high-grade CNS tumours.