Pepinemab in Combination With Pembrolizumab in Recurrent or Metastatic Squamous Cell Carcinoma of the Head and Neck

Inclusion Criteria: 1. Subjects must be ≥18 years of age. 2. Subjects or their legal representative must be able to provide written informed consent to participate in the trial prior to the performance of any study-specific procedures. 3. Subjects must have histologically or cytologically confirmed HNSCC; eligible histologies include SCC of the oropharynx, oral cavity, hypopharynx, and larynx. 4. Subjects must have PD-L1 IHC (including CPS score using an FDA approved test) testing completed within 6 months of screening or at screening. 5. Have measurable disease per RECIST 1.1 as assessed by the central imaging vendor or the local site investigator/radiology. Lesions situated in a previously irradiated area are considered measurable if progression has been demonstrated in such lesions. 6. Subjects must have locally advanced, recurrent or metastatic neoplastic disease that is not curable by currently available local therapies. 7. Subjects must have an Eastern Cooperative Oncology Group (ECOG) PS of 0 or1. 8. Subjects must have a life expectancy of at least 12 weeks. 9. Subjects must have adequate hematologic reserve based on the following: 1. ANC ≥1,500/μL 2. Platelet count \>100,000/μL 3. Hemoglobin \>9 g/dL 10. Subjects must have adequate hepatic function based on the following: 1. Total bilirubin \<1.5 × upper limit of normal (ULN) 2. Alanine aminotransferase (ALT)/aspartate aminotransferase (AST) ≤2.5 x ULN (≤5 x ULN for subjects with known hepatic metastases). 11. Subjects must have adequate renal function based on the following: 1. Serum creatinine ≤1.5 × ULN; or 2. Calculated creatinine clearance of \>30 mL/min. 12. Human immunodeficiency virus (HIV) infected subjects must be on antiretroviral therapy (ART) and have a well-controlled HIV infection/disease defined as: 1. Subjects on ART must have a CD4+ T cell count 350 cells/mm3 at time of screening 2. Subjects on ART must have achieved and maintained virologic suppression defined as confirmed HIV RNA level below 50 copies/mL or the lower limit of qualification (below the limit of detection) using the locally available assay at the time of screening and for at least 12 weeks prior to screening 3. Subjects on ART must have been on a stable regimen, without changes in drugs or dose modification, for at least 4 weeks prior to study entry (Day 1). 13. Subjects with oropharyngeal cancer must have archival tissue available for p16 testing or be willing to undergo pre-study biopsy to obtain tissue for p16 testing. 14. All subjects must have archival or recently obtained tissue available for biomarker analysis. 15. Female subjects of childbearing potential must have a negative pregnancy test within 72 hours of first dose of study treatment. Female subjects of childbearing potential must use a highly effective mode of contraception or abstain from heterosexual activity for the duration of the trial and for 120 days following the last dose of study medication. A female is NOT of childbearing potential if she has undergone bilateral salpingoophorectomy or is menopausal, defined as an absence of menses for 12 consecutive months. Male subjects must agree to use highly effective contraception. Exclusion Criteria: 1. Subjects with SCC of the nasopharynx. 2. Subjects who have received systemic treatment for recurrent or metastatic HNSCC; however, subjects who have received adjuvant systemic therapy or systemic therapy for locally advanced disease which was completed more than 6 months prior to study enrollment are eligible. 3. Subjects must have recovered from the effects of any prior radiation therapy or surgery. 4. Subjects who have received investigational therapy within 5 half-lives of the investigational agent or 4 weeks, whichever is shorter. 5. Subjects with primary immunodeficiency. 6. Subjects who require immunosuppressive therapy including, but not limited to, treatment with corticosteroids in pharmacologic doses (equivalent to ≥10 mg prednisone daily), cyclosporine, mycophenolate, azathioprine, methotrexate, adalimumab, infliximab, vedolizumab, tofacitinib, dupilumab, rituximab, etc. 7. Subjects with autoimmune conditions requiring treatment in the previous 2 years; however, subjects on replacement hormonal therapy alone for autoimmune endocrinopathies are eligible for enrollment. 8. Subjects with active central nervous system (CNS) metastases; however, subjects who have undergone radiation and/or surgery for the treatment of CNS metastases, who are neurologically stable and who are no longer taking pharmacologic doses of corticosteroids are eligible; subjects with leptomeningeal metastases are not eligible. 9. Has received prior radiotherapy within 2 weeks of start of study treatment. Subjects must have recovered from all radiation-related toxicities, not require corticosteroids, and not have had radiation pneumonitis. A 1-week washout is permitted for palliative radiation (≤2 weeks of radiotherapy) to non-CNS disease. 10. Subjects with a prior malignancy (other than the malignancy under study) in the 2 years prior to enrollment; however, subjects with curatively treated nonmelanoma skin cancers, intra-epithelial cervical neoplasia or in situ carcinoma of the breast are eligible for enrollment. 11. Subjects with prior allogenic transplants. 12. Has a history of (noninfectious) pneumonitis that required steroids or has current pneumonitis. 13. Subjects with an active infection requiring treatment with systemic antibiotics. 14. Subjects who are pregnant or lactating. 15. Subjects who have received treatment with a prior anti-PD-1 or anti-PD-L1, anti-CTLA-4, or anti-LAG3 agent or who have received prior treatment with pepinemab. 16. HIV-infected subjects with a history of Kaposi sarcoma and/or Multicentric Castleman Disease. 17. Subjects who are hepatitis B surface antigen positive are eligible if they have received hepatitis B virus (HBV) antiviral therapy for at least 4 weeks and have undetectable HBV viral load prior to enrollment. Note: Subjects should remain on antiviral therapy throughout study intervention and follow local guidelines for HBV antiviral therapy post completion of study intervention. Hepatitis B screening tests are not required unless: 1. Known history of HBV infection 2. As mandated by local health authority. 18. Subjects with a history of hepatitis C virus (HCV) infection are eligible if HCV viral load is undetectable at screening. Note: Subjects must have completed curative antiviral therapy at least 4 weeks prior to enrollment. Hepatitis C screening tests are not required unless: 1. Known history of HCV infection 2. As mandated by local health authority. 19. Subjects who have received a live vaccine within 30 days of study enrollment. 20. Current alcohol or drug abuse. 21. Subjects with any intercurrent medical condition where the known risks of participation in the trial outweigh any potential benefits; subjects with psychiatric or social circumstances that preclude responsible participation in the trial; subjects with severe nutritional deficiencies or marked hypoalbuminemia. 22. History of significant hypersensitivity, intolerance, or allergy to any drug compound, food, or other substance, unless approved by the investigator (or designee). 23. Inability to comply with visit schedule or other protocol requirements.