Selection of CD8⁺PD-1⁺ Lymphocytes in Fresh Human Melanomas Enriches for Tumor-reactive T Cells

Abstract

CD8⁺ tumor-infiltrating lymphocytes (TILs) in human melanomas express high levels of PD-1 and are functionally impaired. However, adoptive cell therapy using in vitro-expanded TIL can be a highly effective therapy for patients with advanced melanoma. This discrepancy led us to further analyze the CD8⁺PD-1⁺ TILs. We found that the percentage of PD-1−expressing CD8⁺ T cells was higher in the tumor digests that generate tumor-reactive TILs after in vitro culture in interleukin-2 (P=0.0007). Also sorted and expanded CD8⁺PD-1⁺ T cells in tumor digests showed much higher tumor-specific interferon-γ production compared with CD8⁺PD-1⁻ T cells. These results suggested that tumor-specific CD8⁺ T cells in melanoma tumor digests are largely PD-1⁺, and this population can recover function after culturing in interleukin-2. PD-1 has been reported as an inhibitory receptor on T cells. We found that the in vitro functional suppression of cultured-TILs from native levels of PD-L1 expression on melanomas was minimal, and moreover expression level of PD-1 on CD8⁺ tumor-specific TILs decreased during the culture. As a consequence, the PD-1 receptor can be a useful biomarker for enriching tumor-specific T cells from fresh melanomas.