A Phase 1/2 Study in Patients With HPV16+ Recurrent/Metastatic Head and Neck Squamous Cell Carcinoma and Other Cancers

All Patients:

• Documentation of confirmed HPV 16+ cancer via genotype testing.
• ≥ 1 measurable lesion by imaging for tumor response following RECIST
• ECOG performance status of 0 to 1.
• Prior curative radiation therapy and prior focal palliative completed per protocol-specified wash-out windows.
• Screening laboratory values must meet protocol-specified criteria.
• Able to provide tumor tissue following last treatment, unless otherwise agreed. Treatment Group E or Group F:
• Documentation of confirmed head and neck squamous cell carcinoma.
• Eligible to receive pembrolizumab, per standard of care and product label.
• Group E: this group includes first line / 1L patients who have not yet received treatment in the metastatic/recurrent setting.
• Group F: Tumor progression or recurrence on standard of care therapy, including ≥1 systemic therapy. Imaging Sub-Study (for specific participants at Memorial Sloan Kettering Cancer Center only):

• At least 1 non-irradiated measurable lesion documented through imaging.

All patients:

• Metastatic central nervous system disease, and/or carcinomatous meningitis.
• Any serious or uncontrolled medical disorder that, in the opinion of the Investigator, may increase the risk associated with study participation / treatment administration.
• Concurrent malignancy that is clinically significant or requires active intervention, unless protocol-defined criteria are met.
• Active, known or suspected, autoimmune or inflammatory disorders requiring immunosuppressive therapy.
• Has a life expectancy of less than 3 months.
• Any toxicities attributed to systemic prior anticancer therapy o that have not resolved to Grade 1 or baseline prior to the first administration of study drug, unless protocol-defined criteria is met.
• Not meeting the protocol-specified washout periods for prohibited medications.
• Prior anaphylactic reaction to or known allergy or hypersensitivity to investigational product(s) or any of the excipients of the investigational product(s).
• Positive hepatitis B surface antigen (HBsAg) or hepatitis C virus (HCV) antibody, indicating acute or chronic infection.
• Known history of acquired immunodeficiency syndrome. For patients in Groups E or F and certain backfill cohorts:
• History of severe hypersensitivity reaction to or other contraindication to receiving pembrolizumab.
• History of/Presently having non-infectious pneumonitis requiring treatment.
• Was discontinued due to a Grade 3 or higher immune-related AE (irAE) after receiving prior therapy with check point inhibitors. Imaging Sub-Study (for specific participants at Memorial Sloan Kettering Cancer Center only):
• Having splenic disorders or prior splenectomy, and can compromise protocol objectives per Investigator and/or Sponsor.