ICAM1-specific chimeric costimulatory receptor enhances CAR T cell activity against HER2-expressing gastric cancer

Background:
Human epidermal growth factor receptor 2 (HER2) is amplified or overexpressed in approximately 15-30% of breast and gastrointestinal cancers, leading to rapid cell proliferation and metastasis through HER2-generated cell signaling. HER2-specific chimeric antigen receptor (CAR) T cells constructed with scFv derived from the FRP5 antibody have been proven safe against advanced sarcoma and brain cancer indications but have shown limited clinical response. In this study, we engineered HER2-specific CAR T cells that co-express a chimeric costimulatory receptor (CCR) targeting intercellular adhesion molecule-1 (ICAM1). The CCR is designed to provide complementary costimulation through OX40 and CD28 endodomains, which can synergize with the 4-1BB incorporated in the CAR construct. The combination of a CAR and a CCR aims to enhance T cell activation, expansion, and persistence, particularly when CAR activation alone is insufficient due to low or heterogeneous antigen expression in target cells. ICAM1 is selected as the target for costimulation because it is highly inducible by inflammatory cytokines such as interferon-gamma, which is released by activated T cells.

Methods:
HER2 CAR/ICAM1 CCR T cells (designated as HMJ01) were manufactured using the fully automated CliniMACS Prodigy system at cGMP and FACT accredited facility at Houston Methodist Research Institute. The antitumor activity and toxicity of HMJ01 were evaluated in a GLP/non-GLP hybrid study using HER2-positive human gastric cancer xenograft models.

Results:
Four batches of HMJ01 CAR T cells were successfully manufactured from healthy donor leukopak, achieving a transduction efficiency of 44.0 ± 8.7%. Compared to second-generation HER2 CAR T cells, HMJ01 exhibited increased sensitivity to recognize and lyse target cells with low levels of HER2 expression. Additionally, HMJ01 CAR T cells enabled the in vivo eradication of HER2-low tumor xenografts, which were otherwise resistant to treatment with conventional second-generation HER2 CAR T cells. We also observed increased cytokine secretion and clonal expansion of HMJ01 cells in vivo compared to conventional HER2 CAR T cells. Furthermore, HMJ01 CAR T cells were found to be safe in the toxicology study, which evaluated mortality, clinical signs, hematology and clinical chemistry, and histopathology at both intermediate and final time points, warranting further clinical evaluation.

Conclusions:
Our studies demonstrate the significant potential of ICAM1-specific CCR to improve the therapeutic outcomes of CAR T cells by enhancing cytotoxic efficacy and persistence. We plan to open a first-in-human phase I study to assess the safety and preliminary efficacy of HMJ01 cells in patients with HER2-positive or HER2-low unresectable or metastatic gastric cancer.