Expression of the switch receptor PD1/IL15Rβ in MSLN-CAR-T cells overcomes PD1/PDL1 signaling in solid tumors

The immunosuppressive tumor microenvironment (TME) limits the efficacy of chimeric antigen receptor (CAR) T cells in solid tumors by inducing T cell exhaustion through inhibitory receptors, such as PD1 and TIM3. T memory stem cells (TSCMs) offer superior persistence, and IL15 promotes T cell memory. We engineered MSLN-CAR-T cells with a PD1/IL15Rβ switch receptor to convert PD1/PDL1 inhibitory signals into IL15-mediated STAT5 activation, enhancing T cell function. We developed MSLN-PD1/IL15Rβ-CAR-T cells, incorporating a PD1/IL15Rβ switch receptor, and evaluated their antitumor activity against pancreatic (AsPC-1, PANC-1) and cervical (HeLa) cancer cell lines. Proliferation, cytokine production (IL-2, IFN-γ), exhaustion markers (PD1, TIM3), and memory T cell phenotypes (CD45RO+/CCR7+) were assessed using flow cytometry, ELISA, and western blotting, with or without anti-PD1 antibody (Nivolumab) stimulation. MSLN-PD1/IL15Rβ-CAR-T cells exhibited enhanced STAT5 phosphorylation, significantly increased proliferation, and elevated IL-2 and IFN-γ secretion compared to MSLN-CAR-T cells when co-cultured with mesothelin- and PDL1-positive tumor cells or treated with Nivolumab. These cells exhibited reduced PD1 and TIM3 expression, along with a higher proportion of CD45RO+/CCR7 + memory T cells, suggesting decreased exhaustion and enhanced persistence. The PD1/IL15Rβ switch receptor overcomes PDL1-mediated immunosuppression in MSLN-CAR-T cells by activating STAT5 signaling, improving proliferation, cytokine production, and memory T cell formation while reducing exhaustion. This approach holds promise for enhancing CAR-T cell therapy in mesothelin-expressing solid tumors.