SPP1+ Tumor-associated Macrophages Drive Immunotherapy Resistance via CD8+ T-Cell Dysfunction in Clear Cell Renal Cell Carcinoma.

Tumor-associated macrophages (TAMs) are key regulators of tumor immunity. With advances in single-cell analyses, SPP1+ TAMs have been observed across multiple tumor sites. However, their clinical relevance and phenotypic characteristics in clear cell renal cell carcinoma (ccRCC) have not been comprehensively delineated. Using patient-level data from two in-house cohorts (n=355) we explored the relationship between SPP1+ TAM infiltration and therapeutic response as well as prognosis in ccRCC. Four publicly available datasets consisting of 1,741 ccRCC patients were included for external validation. Cytometry by time-of-flight (CyTOF) and flow cytometry were utilized to phenotype SPP1+ TAMs and establish their impact on CD8+ T cells. Further, we established an ex vivo culture system to test the potential therapeutic value of targeting SPP1 alone and in conjunction with PD-1 inhibitors in ccRCC. We found that patients with high SPP1+ TAM infiltration exhibited worse response to immunotherapy and dismal prognosis in ccRCC. SPP1+ TAMs exhibited an immunosuppressive and pro-tumor phenotype, and were related to impaired effector function and terminal differentiation of CD8+ T cells. Blockade of SPP1 mitigated the pro-tumor tumor microenvironment and reinvigorated CD8+ T-cell function. Combining PD-1 blockade with SPP1 blockade boosted the expansion of CD8+ T cells and enhanced antitumor efficacy. Together, these data indicate that elevated infiltration of SPP1+ TAMs is related to worse response to immunotherapy and dysfunction of CD8+ T cells in ccRCC. We conclude that SPP1 may serve as a potential therapeutic target in ccRCC.