Abstract LB152: CAR-T cell therapy for melanoma targeting surface expression of TYRP-1

The success of adoptive T cell therapies for solid cancers is challenged, in part, by the lack of targets expressed at sufficient levels by the tumor. Tyrosinase-related protein-1 (TYRP-1) is an enzyme that plays an essential role in melanin biosynthesis, which occurs in the pigmented cells of the skin and the eye. TYRP-1 is expressed in 70% of melanoma patients (Log2 FPKM ≥ 1) and presents a high overexpression (Log2FPKM ≥ 7) in 30% of all melanoma lesions included in The Cancer Genome Atlas (TCGA) dataset. TYRP-1 is localized intracellularly in the melanosomes. However, as a result of the fusion of the melanosomes with the plasma membrane, a small fraction of the cellular TYRP-1 is located on the cell surface. We have shown that between 1-50% (depending on the cell line) of the cellular TYRP-1 is expressed on the cell surface in melanoma cell lines with high levels of TYRP-1 but cannot be detected in cell lines with low or intermediate levels of expression, and we have designed a new chimeric antigen receptor (CAR) to target this fraction of the total TYRP-1. Upon co-culture with a panel of human melanoma cell lines with high expression of TYRP-1, the newly developed CAR-T cell therapy leads to tumor cell growth inhibition (94.4% ±0.9 in M207 melanoma cells, 94.4% ±0.9 in M230, 99.2% ±0.2 in M249, and 83.1% ±1.1 in M285 at 96h after co-culture using an effector to target cell ratio of 1:1) and cytokine release (between 13,325 - 5,558pg IFNgamma/mL was secreted 24h after co-culture depending on the target cell line). Additionally, it induces tumor growth control or tumor elimination after adoptive transfer of CAR-T cells in immunocompromised mice bearing human tumors established from the same cell lines (100% Complete responses (CR) in M207 and 90% CR in M249 tumor models at the end of the experiment). The epitope targeted by the TYRP-1 CAR-T cells is conserved between mouse and human. As a result, similar antitumor activity is obtained in a murine melanoma model in vitro (73.1% ± 1.2 tumor growth inhibition at 48h with a 1:1 effector to target ratio and 300,925pg IFNgamma/mL ± 19,657 secretion at 24h with a 5:1 effector to target ratio in the B16 murine melanoma model) and in vivo in immunocompetent mice (20% CR at the end of the experiment). Moreover, we have confirmed the specificity of the TYRP-1 CAR-T cells using TYRP-1-knocked out melanoma cell lines. And we have observed a lack of toxicity in the eye after adoptive T cell therapy of TYRP-1 CAR-T cells in immunocompetent mouse models. In summary, we have shown the relevance of the TYRP-1 expression on the cell surface as a widespread target for CAR-T cell therapy for melanoma patients and have designed a highly efficacious candidate that we now plan on translating to the clinic. Additionally, our results unravel a new source of potential CAR targets for solid tumors based on highly abundant intracellular membrane proteins translocated to the plasma membrane as a consequence of the cell secretory pathway. Citation Format: Cristina Puig Saus, Sameeha Jilani, Justin Saco, Clement Ng, Jane Coffman, Roxana Radu, Yvonne Chen, Antoni Ribas. CAR-T cell therapy for melanoma targeting surface expression of TYRP-1 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr LB152.