Inclusion Criteria:  Participants are eligible to be included in the study only if all of the criteria below apply.  Age ≥ 18 years of age. Ability to understand and the willingness to sign a written informed consent document. ECOG Performance Status 0-2. Histologically confirmed head and neck squamous cell carcinoma of the oropharynx, larynx, hypopharynx, or pharynx. Satisfies eligibility criteria for treatment with concurrent cisplatin with radiation for the definitive treatment of head and neck squamous cell carcinomas. Eligibility criteria are as follows: HPV-negative Stage III-IVB or HPV-positive Stages II-III and select stage I patients as per PI discretion.  Adequate organ and marrow function defined as the following:  Neutrophils ≥ 1500/μL (in absence of growth factor support) Platelets ≥ 100 x 103/μL without transfusion Hemoglobin ≥ 9.0 g/dL Serum creatinine ≤ 1.5 x upper limit of normal (ULN) or creatinine clearance ≥ 50 mL/min as determined by Cockcroft-Gault equation Aspartate aminotransferase (AST) ≤ 2.5 x ULN Alanine aminotransferase (ALT) ≤ 2.5 x ULN Direct bilirubin ≤ 1.5 x ULN (except participants with Gilbert's syndrome who must have direct bilirubin ≤ 3 x ULN). WBC count ≥ 2500/μL Lymphocyte count ≥ 500/μL Albumin ≥ 25 g/L (2.5 g/dL)  Exclusion Criteria:  Participants are excluded from the study if any of the criteria below apply.  Prior treatment for head and neck squamous cell carcinoma including systemic therapies, local therapies or radiation. Major medical or other conditions that might affect the study assays: major surgery or trauma in the past 28 days, known current pregnancy, poorly controlled diabetes (repeated glucose >250), history of or current clinically relevant coagulation abnormalities, as determined by the PI. Tracheostomy and feeding tube placement are permitted at any time. Known additional malignancy within the past 3 years (exceptions: basal cell carcinoma of the skin, squamous cell carcinoma of the skin, or carcinoma-in-situ that have undergone curative therapy). Active or documented history of autoimmune disease or history of a syndrome that required disease-modifying agents, systemic steroids (>10 mg prednisone per day or equivalent) or immunosuppressive medications, except for vitiligo, endocrinopathies in participants stable on hormone replacement therapy, or resolved childhood asthma/atopy within the past 2 years. Participants with asthma requiring intermittent use of bronchodilators (such as albuterol) will not be excluded from this study. Replacement therapy (e.g. thyroxine, insulin, or physiologic corticosteroid replacement for adrenal or pituitary insufficiencies) is not considered a form of systemic treatment and is allowed. This exclusion criteria applies only to Cohorts 1 and 2 but would be allowed on to Cohort 3. Uncontrolled intercurrent illness including, but not limited to ongoing or active infection requiring systemic antibiotic therapy, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, interstitial lung disease, or psychiatric illness/social situations that would limit compliance with study requirements in the opinion of the Investigator or PI. History of myocardial infarction within 6 months or history of arterial thromboembolic event within 3 months of the first dose of investigational agent. Known infection with hepatitis B virus, hepatitis C virus or human immunodeficiency virus (HIV). History of idiopathic pulmonary fibrosis, organizing pneumonia (eg, bronchiolitis obliterans), drug induced pneumonitis, or idiopathic pneumonitis, or evidence of active pneumonitis on screening chest computed tomography (CT) scan. Grade ≥ 3 hemorrhage or bleeding event within 28 days prior to initiation of study treatment. Cohort 2 only: Inability to swallow medications. Cohort 2 only: Malabsorption condition that would alter the absorption of orally administered medications. Evidence of inherited bleeding diathesis or significant coagulopathy at risk of bleeding (i.e., in the absence of therapeutic anticoagulation); INR or aPTT ≥ 1.5 ULN. Use of medications that are likely to significantly affect wound healing or clotting (e.g. steroids, anti-coagulants, aspirin > 325 mg per day or other NSAID more once per day).  Treatment with therapeutic oral or intravenous (IV) antibiotics within 2 weeks prior to initiation of study treatment. Patients receiving prophylactic antibiotics (eg, to prevent a urinary tract infection or chronic obstructive pulmonary disease exacerbation) are eligible for the study.  a. Topical antibiotics are not permitted within 24 hours from the collection "Skin biopsy Pair 1" if the areas of application are anticipated to interfere with the anticipated sites of biopsies.  Use of systemic steroids >10 mg prednisone (or equivalent) within 7 days prior to the collection of "Skin biopsy Pair 1" with the exception of pulse dose steroids the day prior to and after CT for prevention of a contrast allergy. Use of any live attenuated vaccines against infectious diseases (e.g., influenza, varicella) within 4 weeks (28 days) of initiation of investigational product. Prior treatment with an anti-PD-L1, anti-PD-1, anti-CTLA-4, or other immune checkpoint inhibitor or agonist as monotherapy or in combination.  Use of other investigational drugs (drugs not marketed for any indication) within 28 days or at least 5 half-lives (whichever is longer) before investigational product administration.  In addition, participants are excluded from Cohort 2 if any of the criteria below apply.  Prior treatment with an agent targeting the adenosine pathway. Treatment with known breast cancer resistance protein (BCRP) substrates with a narrow therapeutic window, administered orally (eg, prazosin, rosuvastatin) within 4 weeks or 5 half-lives of the drug (whichever is longer) prior to initiation of study treatment. Treatment with known P-glycoprotein (P-gp) substrates with a narrow therapeutic window, administered orally (eg, digoxin) within 4 weeks or 5 half-lives of the drug (whichever is longer) prior to initiation of study treatment Treatment with known strong CYP3A4 inducers (eg, rifampin, phenytoin, carbamazepine, phenobarbital, and St. John's Wort) and strong CYP3A4 inhibitors (eg, clarithromycin, grapefruit juice, itraconazole, ketoconazole, posaconazole, telithromycin, and voriconazole) within 4 weeks or 5 half lives of the drug (whichever is longer) prior to initiation of study treatment.