CRPA1A2: A novel TCR-based T-cell engager targeting MAGEA1-positive solid tumors.

e14589 Background: MAGEA1, identified as a cancer/testis antigen, is highly expression in various solid tumors, including hepatocellular carcinoma, non-small cell lung cancer, but absent in normal tissues except male germ cells and placenta, both of which lacking HLA class molecules. This selective expression of HLA-MAGEA1 epitope makes it a promising target for cancer therapy. However, its intracellular localization poses a challenge for conventional antibodies designed to target surface-expressed antigens. TCR-based T-cell engagers, such as Tebentafusp, overcome this hurdle by targeting intracellular protein-derived peptides presented on cancer cell surfaces via HLA, enabling precise cytotoxic T cell attacks. Notably, Tebentafusp has shown significant clinical benefits by improving survival rates in metastatic uveal melanoma, underscoring the efficacy of TCR-based T-cell engagers in treating MAGEA1-positive tumors. Methods: We have developed an advanced structural format, CR62, consisting of a anti-CD3 single chain fragment, a soluble modified TCR, and an Fc region. Additionally, the use of CorreGene's SMART-TCR system has facilitated the acquisition of TCRs with high affinities in the pico-molar range. By leveraging CR62 and a high-affinity TCR, we have conceptualized the TCR-based T-cell engager, CRPA1A2. Comprehensive preclinical assessments have been conducted to evaluate CRPA1A2's safety and efficacy. Results: CRPA1A2 is designed to specifically target the HLA-A*02:01-restricted MAGEA1 epitope, effectively inhibiting tumor growth. CRPA1A2 is characterized by its exceptional soluble expression in CHO cells, minimal homodimer miss-assembly and simplifying purification. It is strategically engineered with a high-affinity TCR and a low-affinity anti-CD3 scFv to optimize the efficacy and safety. In vitro studies, CRPA1A2 showed strong ability to eliminate tumor cells and induce IFN-γ release, effective even at low MAGEA1 epitope densities, with a therapeutic window that spans over three orders of magnitude, suggesting a 1000-fold greater activity against antigen-positive cancer cells compared to antigen-negative cells. In vivo, using a tumor-bearing mouse model, CRPA1A2 has been shown to recruit T cells into subcutaneous solid tumors, expand CD8+ T cell populations, and significantly reduce tumor mass. Notably, CRPA1A2 has an extended half-life of 120 hours and demonstrates preferential accumulation in tumor tissues, thereby enhancing its therapeutic potential. Moreover, the safety assessments for CRPA1A2 highlight its exceptional specificity, with in vitro studies showing no evidence of off-target toxicity, on-target off-tumor toxicity, or alloreactivity and favorable tolerance in mice during in vivo studies. Conclusions: CRPA1A2 has emerged as a superior TCR-based T-cell engager with exceptional antitumor efficacy and promising safety profile.