Inclusion Criteria:

          1. Age ≥18 years old

          2. Histologically confirmed HPV-positive Oropharyngeal squamous cell carcinoma (OPSCC)
             amenable to curative treatment with RT-CT (HPV status is defined on the basis of the
             combination of 2 assays: p16 protein overexpression assessed by immunohistochemistry
             (IHC) and high-risk HPV DNA identification by in-situ Hybridization (ISH) or PCR. An
             HPV-driven OPSCC is defined as a tumor that is positive for both p16 IHC and HPV-DNA
             ISH or PCR)

          3. According to the 8th TNM edition, eligible stages are as follow:

               -  Irrespective of tobacco consumption: Stage T4 (any N), N2 or N3 (any T)

               -  Only if tobacco consumption ≥10 pack- years: T1-3N1 and T3N0 (T1N0 and T2N0
                  irrespective of tobacco consumption are not eligible for the study)

          4. Planned date of chemoradiation allowing 2 treatment infusions, 2 weeks apart

          5. Eastern Cooperative Oncology Group (ECOG) performance status ≤1

          6. Screening laboratory values must meet the following criteria (using CTCAE v5.0) and
             should be obtained within 7 days prior to the randomisation:

               1. Polynuclear neutrophils ≥1.5 x 10⁹/L

               2. Platelets ≥100 x 10⁹/L

               3. Hemoglobin ≥9.0 g/dL

               4. Alanine aminotransferase (ALAT)/aspartate transaminase (ASAT) ≤2.5 x upper limit
                  of normal (ULN)

               5. Total Bilirubin ≤1.5 x ULN (except Gilbert Syndrome : <3.0 mg/dL)

               6. Creatinine clearance ≥60 mL/min (measured or calculated by Cockcroft and Gault
                  formula)

          7. Potentially reproductive patients must agree to use a highly effective contraceptive
             method while on treatment and up to 6 months after the end of chemoradiation

          8. Women of childbearing potential must have a negative serum or urine pregnancy test
             done within 72 hours before randomisation

          9. Patients must be willing and able to comply with scheduled visits, treatment plan,
             laboratory tests and other study procedures (including mandatory study-specific
             biopsies)

         10. Subjects must have at least one lesion amenable to biopsy

         11. Subjects must have at least one measurable lesion (different from the lesion amenable
             to biopsy) as per RECIST v1.1 to assess efficacy

         12. Consent to provide archived tumour tissue sample, if available

         13. Patients must be affiliated to a Social Security System

         14. Patient information and written informed consent form signed

        Exclusion Criteria:

          1. Prior treatment for OPSCC

          2. Prior treatment with anti PD-1/PD-L1 and CTLA-4

          3. Distant metastases

          4. Tumour embolization within 28 days prior to the first dose of study drug.

          5. Contra-indication(s) to receive high-dose cisplatin as listed in the most updated
             Summary of Product Characteristics (including creatinine clearance <60 mL/min,
             pre-existing hearing loss or neurological disorder)

          6. Uncontrolled intercurrent illness including, but not limited to, ongoing or active
             infection, symptomatic congestive heart failure, uncontrolled hypertension, unstable
             angina pectoris, cardiac arrhythmia, active peptic ulcer disease or gastritis, or
             psychiatric illness and social situations that would limit compliance with study
             requirement or compromise the ability of the subject to give written informed consent

          7. Current or prior use of immunosuppressive medication within 14 days before the first
             dose, including intranasal and inhaled corticosteroids or systemic corticosteroids

          8. Active or prior documented autoimmune or inflammatory disease within the 2 years prior
             to start of treatment (including inflammatory bowel disease [e.g., ulcerative colitis,
             Crohn's disease], celiac disease, irritable bowel disease, or other serious chronic
             gastrointestinal conditions associated with diarrhea; systemic lupus erythematosus;
             Wegener syndrome [granulomatosis with polyangiitis]; myasthenia gravis; Graves'
             disease; rheumatoid arthritis; hypophysitis, uveitis, etc.) The following are
             exceptions to these criteria:a) Subjects with vitiligo or alopecia, b) Subjects with
             hypothyroidism (e.g.,Hashimoto syndrome) stable on hormone replacement and c) Subjects
             with psoriasis not requiring systemic treatment (within the past 2 years)

          9. History of primary immunodeficiency or organ transplant requiring immunosuppressive
             drugs

         10. Patients with a known HIV, active hepatitis B or C infection

         11. Other invasive malignancy within 3 years except for noninvasive malignancies such as
             cervical carcinoma in situ, non-melanomatous carcinoma of the skin or ductal carcinoma
             in situ of the breast that has/have been surgically cured

         12. Pregnant women or women who are breast-feeding

         13. Patients with any psychological, familial, sociological or geographical condition
             potentially hampering compliance with the study protocol and follow-up schedule; those
             conditions should be discussed with the patient before registration in the study

         14. Individuals deprived of liberty or placed under the authority of a tutor

         15. Severe infection requiring parenteral antibiotics treatment

         16. Known history or active symptomatic interstitial lung disease

         17. Patients with major surgery within 28 days, or open biopsy within 7 days, prior to
             randomisation. Patients must have recovered from major side effects of the surgery
             before randomisation