CD103+ tumor-resident CD8+ T cells are associated with improved survival in immunotherapy naive melanoma patients and expand significantly during anti-PD1 treatment.

Purpose: Therapeutic blockade of immune checkpoints has revolutionized cancer treatment. Durable responses however, occur in less than half of those treated and efforts to improve treatment efficacy are confounded by a lack of understanding of the characteristics of the cells that initiate anti-tumor immune response. Experimental Design: We performed multi-parameter flow cytometry and quantitative multiplex immunofluorescence staining on tumor specimens from immunotherapy-naïve melanoma patients and longitudinal biopsy specimen obtained from patients undergoing anti-PD-1 therapy. Results: Increased numbers of CD69+CD103+ tumor-resident CD8+ T cells was associated with improved melanoma-specific survival in immunotherapy-naive melanoma patients. Local IL-15 expression levels strongly correlated with these tumor-resident T cell numbers. The expression of several immune checkpoints including PD-1 and LAG3 was highly enriched in this subset and these cells significantly expanded early during anti-PD-1 immunotherapy. Conclusions: Tumor-resident CD8+ T cell numbers are more prognostic than total CD8+ T cells in metastatic melanoma. In addition, they are likely to initiate response to anti-PD-1 and anti-LAG-3 treatments. We propose that the immune profile of these cells prior to treatment could inform strategies for immune checkpoint blockade.

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