Abstract 3768: Development of novel MHC-II-restricted TCR-STEM CD4+ T cell immunotherapy for solid cancers

Abstract Despite recent advances in immune checkpoint inhibitors (ICI) for treating solid tumors, most patients fail to respond to ICI therapy, eventually relapse and die without further treatment options. Hence, the development of novel immunotherapy is urgently needed. While most studies focus on MHC-I-restricted T cell receptor (TCR)-engineered CD8+ T cell immunotherapy, we recently developed a novel MHC-II-restricted TCR-engineered CD4+ T cell immunotherapy. Because CT83 (KK-LC-1), a cancer-testis antigen, is highly expressed in 40-60% of lung and breast cancers, but not in normal tissues except testis, we used single-cell sequencing and identified a novel HLA-DR13-restricted CT83-specific TCR for tumor recognition. To improve the therapeutic potential of CD4+ TCR-T cells, we further engineered TCR with several novel technologies, including Synthetic TCR-signaling Enhancing for Memory T cells (STEM), thus markedly improving T cell persistence. We demonstrated that CD4+ TCR-STEM T cells specifically recognized and killed breast and lung cancer cells, with no T cell reactivity against a panel of HLA-DR13+ CT83- tumor cells. Surprisingly, we found that CD4+ TCR-STEM T cells could eliminate both breast and lung cancer cells in animal models. In contrast, TCR-engineered CD8+ T cells could only eliminate lung cancer, but not breast cancer, in an animal model. Notably, significantly high percentages (30-40%) of CD4+ TCR-STEM T cell infiltration were detected in the tumors by flow cytometry and immunohistochemistry. Imaging mass cytometry further revealed a substantial number of Th1 cells and M1 macrophages at the tumor site, suggesting a dual mechanism of action of CD4+ TCR-STEM T cells through direct tumor killing and indirect killing via recruitment of other immune cells. Indeed, we showed that CD4+ TCR-STEM T cells could kill antigen-negative tumor cells in a mixture of antigen-positive and negative tumor cells. In conclusion, we have developed a novel MHC-II-restricted CT83-specific CD4+ TCR-STEM T cell immunotherapy showing robust and therapeutic anti-tumor immunity against solid tumors. Given the high prevalence of HLA-DR13 expression across different ethnic groups (20-30%), particularly in African Americans (29.7%), CD4+ TCR-STEM T cells represent an entirely innovative approach to developing therapeutic T cell immunotherapy drugs for solid cancers and addressing cancer disparities. Citation Format: Jiayi Zhang, Chen Qian, Xin Liu, Tianhao Duan, Rongfu Wang. Development of novel MHC-II-restricted TCR-STEM CD4+ T cell immunotherapy for solid cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 3768.