A Study of HB-202/HB-201 With Pembrolizumab in Patients With HPV16+ Recurrent/Metastatic Oropharyngeal Cancer

Inclusion Criteria:

* Participants at least 18 years of age.
* Confirmed recurrent and/or metastatic OPSCC that is considered incurable by local therapies.
* Must not have had prior systemic anticancer therapy, including investigational therapy and non-palliative radiotherapy, administered in the recurrent and/or metastatic setting.
* Confirmed HPV16+ AND PD-L1+ (with a CPS greater or equal to 20) tumor, based on tumor specimen, core, or excisional biopsy samples from a tumor lesion not previously irradiated.
* Must have measurable disease based on RECIST version 1.1 as determined by BICR.
* Eastern Cooperative Oncology Group performance status must be 0 to 1.
* Adequate organ function should be confirmed within 10 days prior to the first dose of study treatment.

Exclusion Criteria:

* Has progressive disease within 6 months of completion of curatively intended systemic treatment (including checkpoint inhibitors) for locoregionally advanced OPSCC.
* Life expectancy of less than 3 months and/or rapidly progressing disease, high burden of visceral metastatic disease, or significant tumor burden in anatomically critical areas (e.g., causing significant biliary or respiratory obstruction) who may benefit from a chemotherapy-based treatment regimen.
* History or current evidence of any condition, therapy, laboratory abnormality, or other circumstance that might confound the results of the trial or interfere with the participant's participation for the full duration of the trial, or such that it is not in the best interest of the patient to participate, in the opinion of the treating Investigator. This includes active cardiovascular disease within 6 months before study entry.
* Is pregnant or breastfeeding or expecting to conceive or father children starting with the screening visit through a minimum of 2 months after the last dose of trial treatment.
* Was discontinued due to a Grade 3 or 4 immune-related AE after receiving prior therapy with a checkpoint inhibitor agent, or with an agent directed to another stimulatory or coinhibitory T-cell receptor.
* Received systemic steroids at a dose of \>10 mg/day (prednisone equivalent) for \<30 days within 14 days or for ≥30 days within 28 days of the first dose of study treatment.
* Received live, or live-attenuated vaccine within 30 days of the planned first dose of treatment or anticipates that such a vaccine will be required during the study.
* Participating in or has participated in a study of an investigational agent, or has used an investigational device treatment, within 4 weeks before the first dose of study treatment.
* Has had an allogeneic tissue/solid organ transplant.
* Has known immunodeficiency OR is receiving long-term systemic steroid therapy or any other form of immunosuppressive therapy within 28 days before the first dose of study treatment.
* Known additional malignancy within 2 years before the first dose of study treatment.
* Known CNS metastases and/or carcinomatous meningitis.
* Has severe hypersensitivity (Grade 3 and/or 4) to pembrolizumab and/or any of its excipients.
* Has an active autoimmune disease that has required systemic treatment in the past 2 years.
* History or current evidence of (non-infectious) pneumonitis/interstitial lung disease.
* Has an active infection requiring systemic therapy.
* Known history of acquired immunodeficiency syndrome (AIDS). Testing for human immunodeficiency virus (HIV) is not mandatory.
* Known history of hepatitis B virus (defined as hepatitis B surface antigen reactive) or known active hepatitis C virus infection (defined as hepatitis C virus ribonucleic acid \[RNA\] is detected \[qualitative\]).