Detection of lymphocytes that target tumor-specific mutant neoantigens--derived from products encoded by mutated genes in the tumor--is mostly limited to tumor-resident lymphocytes, but whether these lymphocytes often occur in the circulation is unclear. We recently reported that intratumoral expression of the programmed cell death 1 (PD-1) receptor can guide the identification of the patient-specific repertoire of tumor-reactive CD8(+) lymphocytes that reside in the tumor. In view of these findings, we investigated whether PD-1 expression on peripheral blood lymphocytes could be used as a biomarker to detect T cells that target neoantigens. By using a high-throughput personalized screening approach, we identified neoantigen-specific lymphocytes in the peripheral blood of three of four melanoma patients. Despite their low frequency in the circulation, we found that CD8(+)PD-1(+), but not CD8(+)PD-1(-), cell populations had lymphocytes that targeted 3, 3 and 1 unique, patient-specific neoantigens, respectively. We show that neoantigen-specific T cells and gene-engineered lymphocytes expressing neoantigen-specific T cell receptors (TCRs) isolated from peripheral blood recognized autologous tumors. Notably, the tumor-antigen specificities and TCR repertoires of the circulating and tumor-infiltrating CD8(+)PD-1(+) cells appeared similar, implying that the circulating CD8(+)PD-1(+) lymphocytes could provide a window into the tumor-resident antitumor lymphocytes. Thus, expression of PD-1 identifies a diverse and patient-specific antitumor T cell response in peripheral blood, providing a novel noninvasive strategy to develop personalized therapies using neoantigen-reactive lymphocytes or TCRs to treat cancer.

Adoptive cell transfer, the infusion of large numbers of activated autologous lymphocytes, can mediate objective tumor regression in a majority of patients with metastatic melanoma (52 of 93; 56%). Addition and intensification of total body irradiation (TBI) to the preparative lymphodepleting chemotherapy regimen in sequential trials improved objective partial and complete response (CR) rates. Here, we evaluated the importance of adding TBI to the adoptive transfer of tumorinfiltrating lymphocytes (TIL) in a randomized fashion. Patients and MethodsA total of 101 patients with metastatic melanoma, including 76 patients with M1c disease, were randomly assigned to receive nonmyeloablative chemotherapy with or without 1,200 cGy TBI before transfer of tumor-infiltrating lymphcytes. Primary end points were CR rate (as defined by Response Evaluation Criteria in Solid Tumors v1.0) and overall survival (OS). Clinical and laboratory data were analyzed for correlates of response.Results CR rates were 24% in both groups (12 of 50 v 12 of 51), and OS was also similar (median OS, 38.2 v 36.6 months; hazard ratio, 1.11; 95% CI, 0.65 to 1.91; P = .71). Thrombotic microangiopathy was an adverse event unique to the TBI arm and occurred in 13 of 48 treated patients. With a median potential follow-up of 40.9 months, only one of 24 patients who achieved a CR recurred. ConclusionAdoptive cell transfer can mediate durable complete regressions in 24% of patients with metastatic melanoma, with median survival . 3 years. Results were similar using chemotherapy preparative regimens with or without addition of TBI.

Cancer immunotherapy is a rapidly evolving field that exploits T-cell responses to tumor-associated antigens to induce tumor rejection. Molecular identification of tumor rejection antigens has helped define several classes of antigens, including tissue-differentiation and tumor-germline antigens. The ability to genetically engineer antigen-specific receptors into T cells provides an opportunity to translate these findings into therapies. New immunotherapy agents, notably checkpoint inhibitors, have demonstrated unprecedented efficacy in certain cancers. Yet the nature of the antigens driving those beneficial immune responses remains unclear. New evidence suggests that tumors express immunogenic, tumor-specific epitopes generated from the same mutations that drive cancer development. Correlations between cancer types responding to immunotherapies and the frequency of somatic mutations may clarify what drives natural anti-tumor immune responses. This fusion of tumor immunology and genetics is leading to new ways to target this class of ideal tumor-specific antigens and could allow the application of immunotherapy to many cancers.