Safety and Efficacy of VB10.16 and Pembrolizumab in Patients With Head-Neck Squamous Cell Carcinoma

This is a multi-center study in patients with un-resectable Recurrent or Metastatic HPV16-positive oropharyngeal Head and Neck Squamous Cell Carcinoma (HNSCC). The trial is designed to investigate VB10.16, an investigational therapeutic DNA vaccine in combination with another medicine, pembrolizumab, which is the standard of care for patients with previously untreated metastatic or resectable recurrent PD-L1 positive HNSCC. The study is divided in 2 parts: * Phase 1: Dose escalation to evaluate safety and determine the recommended phase 2 dose (RP2D) of VB10.16 * Phase 2: Randomized comparison of VB10.16 in combination with pembrolizumab versus pembrolizumab monotherapy The goal of Phase 1 is to evaluate the safety and tolerability of the combined treatment and to decide on the dose of VB10.16 to be used in the second part of the trial. The randomized Phase 2 will consist of 2 parallel arms exploring VB10.16 at the selected RP2D from the escalation phase in combination with pembrolizumab SoC (experimental arm, Arm A), versus pembrolizumab alone (control arm, Arm B).