Abstract 1542: ALK expression identifies a therapeutically targetable subset of Merkel cell carcinomas responsive to ALK.CAR-T cell therapy alone or in combination with ALK inhibitors

Abstract Background: Merkel cell carcinoma (MCC) is a rare and highly aggressive neuroendocrine skin cancer with limited treatment options. While chemo-immunotherapy remains the standard of care, nearly 50% of patients experience disease progression, with a median overall survival of 10 months. Anaplastic lymphoma kinase (ALK) has emerged as a promising therapeutic target in various malignancies, including MCC, where it is detected in 40-80% of cases. Our group recently developed novel chimeric antigen receptor T-cell against ALK (ALK.CAR-T), demonstrating potent anti-tumor activity against ALK+ neuroblastoma. This ALK.CAR-T product is currently under clinical investigation in a Phase I/II clinical trial (NCT06803875). In the present study, we evaluated the relevance of ALK.CAR-T immunotherapy in ALK+ MCC tumors. Methods: We tested ALK and Merkel cell polyomavirus antigen (MCPyV) expression in a cohort of 181 patients with MCC using immunohistochemistry. In addition, we characterized a panel of MCC human cell lines and two patient-derived xenografts (PDX) to identify potential immunotherapeutic targets (ALK, GD2, and HLA-I). ALK.CAR-T cells were co-cultured either in 2D with MCC cell lines or in 3D-microfluidic devices with xenograft-derived organotypic tumor spheroids (xDOTS) to assess their killing efficacy in vitro, either alone or in combination with ALK inhibitors. For in vivo testing, NSG mice were injected intravenously with human MCC cell lines and, after engraftment, treated with ALK.CAR-T cells, either alone or in combination with the ALK inhibitor lorlatinib. Tumor monitoring was performed weekly using IVIS imaging. Results: We found ALK expression in approximately 90% of MCC tumors and observed a significant association between ALK expression and poor clinical outcomes. In vitro, ALK.CAR-T treatment effectively killed ALK+ MCC cell lines and xDOTS, associated with an increased production of IFNγ and granzyme B. Moreover, the combination with an ALK inhibitor (lorlatinib or nadelalkib) enhanced ALK.CAR-T antitumor activity, even when the ALK inhibitor showed no effect alone. In vivo, ALK.CAR-T outperformed GD2.CAR-T, extending the overall survival of mice in two MCC metastatic models. Nonetheless, ALK.CAR-T efficacy was enhanced by lorlatinib, improving tumor control without altering the safety profile. Conclusions: We identified ALK as a clinically relevant target in MCC and demonstrated that ALK.CAR-T cells, especially when combined with ALK inhibitors, have a potent anti-tumor activity against ALK+ MCC. Our study provides a preclinical rationale for expanding the ongoing Phase I/II clinical trial in relapsed/refractory neuroblastoma patients to include patients with MCC, thus broadening the therapeutic indication of ALK.CAR-T. Citation Format: Alessandro Gasparetto, Jasna Metovic, Elisa Landoni, Carmen Mecca, Gabriele Saccu, Simone Piane, Nirmala Tilija Pun, Umberto Mortara, Chiara Anselmo, Marco Campisi, Haley Ohlson, Maria Vittoria Di Marco, Giulia Mura, Mauro Papotti, Rebecca Senetta, Claudia Voena, Gianpietro Dotti, Elisa Bergaggio, Roberto Chiarle. ALK expression identifies a therapeutically targetable subset of Merkel cell carcinomas responsive to ALK.CAR-T cell therapy alone or in combination with ALK inhibitors abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 1542.