The SPA17-AXL axis drives melanoma aggressiveness and SPA17-targeting vaccination exhibits antitumor efficacy.

INTRODUCTION: Sperm Autoantigenic Protein 17 (SPA17), a member of the cancer-testis antigen family, is frequently overexpressed in various malignancies, yet its biological functions, regulatory mechanisms, and clinical relevance in melanoma remain largely unexplored. This study aimed to investigate the expression pattern, prognostic value, and functional role of SPA17 in melanoma progression and immune modulation. METHODS: We analyzed SPA17 expression in melanoma clinical specimens and correlated it with patient prognosis, metastatic burden, and immunotherapy response. Functional assays, including migration and proliferation tests, were performed in SPA17-knockdown melanoma cells in vitro, and tumor growth was evaluated in a subcutaneous syngeneic mouse model in vivo. Mechanistic studies involved co-culture systems with activated human lymphocytes and molecular interrogation of downstream effectors, with particular focus on AXL. The therapeutic potential of a SPA17-targeting peptide vaccine was also assessed in vivo, with tumor-infiltrating lymphocyte populations characterized by immunohistochemistry. RESULTS: SPA17 was markedly upregulated in melanoma tissues, especially in metastatic lesions, and high expression correlated with poor prognosis, increased metastatic burden, and resistance to immunotherapy. Knockdown of SPA17 significantly suppressed melanoma cell migration in vitro and tumor growth in vivo, with no effect on proliferation. Mechanistically, SPA17 depletion enhanced intratumoral infiltration and cytotoxic activity of CD8+ T cells, and SPA17-knockdown melanoma cells showed reduced resistance to activated lymphocyte-mediated killing in co-culture. We identified AXL as a critical downstream effector, as SPA17 positively regulated AXL expression, and ectopic AXL overexpression rescued the migration defect and restored lymphocyte-mediated killing impaired by SPA17 knockdown. Therapeutically, administration of the SPA17-targeting peptide vaccine markedly restrained melanoma progression in vivo, accompanied by increased tumor-infiltrating CD8+ and GZMB+ CD8+ T cells. DISCUSSION: Collectively, our findings suggest that SPA17 promotes melanoma progression and immune evasion through upregulation of AXL, and that SPA17-directed peptide vaccination elicits antitumor immune responses and inhibits tumor growth. These data support SPA17 as a candidate prognostic biomarker and a potential therapeutic target warranting further clinical investigation.