Olfactory receptor 2+ tumor-associated macrophages activate CD8+ T cells to suppress tumor growth

Introduction/Rationale: Olfactory receptor 2 (Olfr2 in mice; OR6A2 in humans) has emerged as a regulator of macrophage activity. We found that Olfr2+ tumor-associated macrophages (TAMs) are required for proper CD8+ T cell activation.

Methods: Using an orthotopic B16F10 melanoma model, we compared tumor growth in wild-type and Olfr2-/-mice. Bone marrow transplant experiments were performed to determine whether the phenotype was driven by loss of Olfr2 in hematopoietic cells. In vivo OT-I adoptive transfer assays were conducted to assess the ability of Olfr2+ TAMs to support CD8+ T cell priming and cytotoxicity. Additionally, RNA-seq analysis of sorted Olfr2+TAMs was performed to characterize their transcriptional programs. Gene set enrichment analysis (GSEA) was used to evaluate the transcriptional impact of Olfr2+ TAMs and their potential association with improves responses to immune checkpoint inhibitor (ICI) treatments.

Results: Olfr2-/- mice developed nearly twice the tumor burden of wild-type controls, a phenotype driven by loss of Olfr2 in hematopoietic cells. Tumors from Olfr2-/- mice exhibited reduced CCL2 and CXCL9 expression and diminished CD8+ T cell infiltration. In vivo OT-I adoptive transfer demonstrated that Olfr2+ TAMs are essential for supporting CD8+ T cell priming and cytotoxicity. RNA-seq of Olfr2+ TAMs revealed enrichment of antigen presentation, pro-inflammatory, and anti-tumor pathways, consistent with their enhanced antigen presentation capacity observed in vitro. GSEA further showed that the Olfr2+ TAM transcriptional signature was associated with CXCL9+ TAM–enriched tumors and improved ICI responsiveness in human melanoma datasets.

Conclusion: Together, these findings establish Olfr2+ TAMs as central regulators of CD8+ T cell immunity in melanoma, linking olfactory receptor signaling in macrophages to anti-tumor immune activation and potentially improved responses to ICI therapy.