PURPOSE To evaluate first-line pembrolizumab monotherapy efficacy and safety in patients with unresectable cutaneous squamous cell carcinomas (CSCCs). PATIENTS AND METHODS Patients, predominantly men, with their CSSCs’ immunohistochemically determined programmed cell death-ligand 1 (PD-L1) status determined (tumor proportion score threshold, 1%), received pembrolizumab (200 mg every 3 weeks). The primary endpoint was the 39-patient primary cohort’s objective response rate at week 15 (ORRW15). Secondary objectives were best ORR, overall survival (OS), progression-free survival (PFS), duration of response (DOR), safety, ORR according to PD-L1 status and health-related quality of life using Functional Assessment of Cancer Therapy–General (FACT-G) score. An 18-patient expansion cohort, recruited to power the study to evaluate the ORRW15 difference between PD-L1+ and PD-L1– patients, was assessed for ORR, disease control rate, and safety, but not survival. RESULTS Median age of all patients was 79 years. The primary cohort’s ORRW15 was 41% (95% CI, 26% to 58%), including 13 partial and 3 complete responses. Best responses were 8 partial and 8 complete responses. At a median follow-up of 22.4 months, respective median PFS, DOR, and OS were 6.7 months, not reached, and 25.3 months, respectively. Pembrolizumab-related adverse events affected 71% of the patients, and 4 (7%) were grade ≥ 3. One death was related to rapid CSCC progression; another resulted from a fatal second aggressive head and neck squamous cell carcinoma diagnosed 15 weeks postinclusion. ORRW15 for the entire population was 42%; it was significantly higher for PD-L1+ patients (55%) versus PD-L1– patients (17%; P = .02). Responders’ W15 total FACT-G score had improved ( P = .025) compared with nonresponders. CONCLUSION First-line pembrolizumab monotherapy exhibited promising anti-CSCC activity, with durable responses and manageable safety. PD-L1 positivity appears to be predictive of pembrolizumab efficacy.

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The efficacy of immune checkpoint inhibitors has been shown to depend on preexisting antitumor immunity; thus, their combination with cancer vaccines is an attractive therapeutic approach. Plasmacytoid dendritic cells (PDC) are strong inducers of antitumor responses and represent promising vaccine candidates. We developed a cancer vaccine approach based on an allogeneic PDC line that functioned as a very potent antigen-presenting cell in pre-clinical studies. In this phase Ib clinical trial, nine patients with metastatic stage IV melanoma received up to 60 million irradiated PDC line cells loaded with 4 melanoma antigens, injected subcutaneously at weekly intervals. The primary endpoints were safety and tolerability. The vaccine was well tolerated and no serious vaccine-induced side effects were recorded. Strikingly, there was no allogeneic response toward the vaccine, but a significant increase in the frequency of circulating anti-tumor specific T lymphocytes was observed in two patients, accompanied by a switch from a naïve to memory phenotype, thus demonstrating priming of antigen-specific T-cells. Signs of clinical activity were observed, including four stable diseases according to IrRC and vitiligoïd lesions. Four patients were still alive at week 48. We also demonstrate the in vitro enhancement of specific T cell expansion induced by the synergistic combination of peptide-loaded PDC line with anti-PD-1, as compared to peptideloaded PDC line alone. Taken together, these clinical observations demonstrate the ability of the PDC line based-vaccine to prime and expand antitumor CD8+ responses in cancer patients. Further trials should test the combination of this vaccine with immune checkpoint inhibitors.