A mixed inflammatory peripheral signature defines clinical outcomes in a phase II trial combining pembrolizumab with paclitaxel and carboplatin in melanoma

Checkpoint blockade of PD-1 with pembrolizumab provides long-term survival to a significant proportion of patients with metastatic melanoma. Pembrolizumab has been successfully used in combination with chemotherapy in non-small-cell lung cancer to increase the response rate. This phase II trial combined pembrolizumab with carboplatin/paclitaxel (CP) to assess its safety and efficacy, and to identify correlates of responses. Thirty patients without prior immunotherapy for unresectable/metastatic melanoma were treated with pembrolizumab and CP. Peripheral blood was collected at baseline and after 2 cycles to characterize systemic immune activity by multiplex assays and flow cytometry. Seventy percent of patients received all 4 cycles of CP; 87% received pembrolizumab for 2 y or until progression. Grade 3 and higher adverse events (AEs) occurred in 50% of the patients. The overall response rate (ORR) and disease control rate (DCR) by irRC criteria were 43% and 53%, respectively. Median overall survival (OS) was 23.8 months. Objective response was associated with a lower frequency of naive CD8 T cells and low plasma CCL3 at baseline, along with a larger proportion of mature NK cells and of CD4 T cells expressing BTLA or LAIR-1. Survival rate was higher for patients with lower baseline of IL-6, IL-8, and CD4⁺CD39⁺ T cells. Following treatment, pro-inflammatory soluble factors increased in both responders and non-responders. Addition of CP to pembrolizumab in this study did not appear to result in a response or survival advantage and was less tolerable than immunotherapy alone. Correlative data point to peripheral signals to investigate further as potential biomarkers. Trial registration: clinicaltrials.gov, NCT02617849, registered on December 1st, 2015.