This is a multi-center study in patients with un-resectable Recurrent or Metastatic HPV16-positive oropharyngeal Head and Neck Squamous Cell Carcinoma (HNSCC). The trial is designed to investigate VB10.16, an investigational therapeutic DNA vaccine in combination with another medicine, pembrolizumab, which is the standard of care for patients with previously untreated metastatic or resectable recurrent PD-L1 positive HNSCC. The study is divided in 2 parts: a phase 1, dose escalation part, testing 3 different doses of VB10.16 in combination with a standard fixed dose of pembrolizumab. The goal of this part is to evaluate the safety and tolerability of the combined treatment and to decide on the dose of VB10.16 to be used in the second part of the trial. In the second part of the trial, a phase 2a, dose expansion part, participants will receive either the highest safe dose of VB10.16 from part 1 or the 3 mg dose both in combination with pembrolizumab. The dose given to each participant will be decided in random.

The trial is designed to define the optimal dose of VB10.16 in combination with pembrolizumab for future clinical studies based on the safety, tolerability and anti-tumor effect data generated.

This phase 1/2a, open-label, dose-finding trial is designed to evaluate the safety, tolerability, immunogenicity, and anti-tumor activity of VB10.16 immunotherapy in patients with HPV16-positive R/M oropharyngeal HNSCC whose tumors express PDL1 (CPS ≥ 1) and who are eligible for pembrolizumab monotherapy as standard of care. The trial is designed to determine the biological optimal dose (BOD) of VB10.16 in combination with a fixed dose of pembrolizumab based on the totality of data (i.e., safety, tolerability, anti-tumor activity, and HPV16 E6/E7specific cellular immune response). The trial consists of 2 consecutive phases with separate patient groups in a seamless trial design: a dose escalation phase (phase 1) and a dose expansion phase (phase 2a). After completing 48 weeks of combination treatment, patients can either continue pembrolizumab treatment with 200 mg Q3W administration or change to 400 mg Q6W administration at the discretion of the investigator and after consultation with the Sponsor.

Inclusion Criteria:

GENERAL REQUIREMENTS

1. ≥18 years of age (or as per national legal age of trial consent, whichever is higher) at date of signing the informed consent form (ICF)

2. Histologically or cytologically confirmed R/M HNSCC, located in the oropharynx, considered incurable by local therapy and eligible for monotherapy with pembrolizumab

3. HPV16 positivity of R/M oropharyngeal HNSCC confirmed by designated central laboratory

4. PD-L1 positivity (CPS ≥1) using the validated PD-L1 IHC 22C3 pharmDx (DAKO) assay.

5. Primary tumor location in the oropharynx.

6. At least 1 measurable lesion per RECIST 1.1

   ORGAN FUNCTION

   Overall function:

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

   Hematological function:

8. Platelets ≥100 × 10^9/L (100,000/µL)

9. Neutrophils (absolute neutrophil count [ANC]) ≥1.5 × 10^9/L (1,500/µL)

10. Hemoglobin ≥5.6 mmol/L (9.0 g/dL)

    Hepatic and hemostatic function:

11. Bilirubin (BILI), total ≤1.5 × upper limit of normal (ULN) (except Gilbert syndrome, then direct BILI ≤2 × ULN) or direct bilirubin ≤ULN for participants with total bilirubin levels >1.5 × ULN.

12. Aspartate transaminase (AST) ≤ 2.5 × ULN or ≤5 × ULN for a patient with liver metastases.

13. Alanine transaminase (ALT) ≤ 2.5 × ULN or ≤5 × ULN for a patient with liver metastases.

14. Alkaline phosphatase ≤ 2.5 × ULN or ≤5 × ULN for a patient with liver metastases.

15. International normalized ratio (INR) or prothrombin time (PT) ≤1.5 × ULN unless the patient is receiving anticoagulant therapy, in which case PT and partial thromboplastin time (PTT)/activated PTT (aPTT) must be within therapeutic range of intended use of anticoagulants.

    Renal function:

16. Estimated glomerular filtration rate (eGFR) ≥45 mL/min/1.73 m^2 using the Cockroft-Gault formula

    OTHER TRIAL REQUIREMENTS

17. Female patients of childbearing potential: negative serum pregnancy test (≤72 hours)

18. Female patients of childbearing potential must agree to use highly effective contraception throughout the trial (14 days prior to initiation of treatment for oral contraception), and for at least 120 days (according to the current version of the IB for pembrolizumab) after the last dose of pembrolizumab and up to 6 months after the last dose of VB10.16, whichever comes last.

    Male patients must agree to use male condoms during intercourse throughout the trial, and up to 3 months after the last dose of VB10.16, and must refrain from sperm donation in the same period.

19. Patients capable of giving informed consent must provide signed and dated written informed consent prior to initiation of any study-related procedures.

Exclusion Criteria:

HNSCC DISEASE

1. Has disease that is suitable for local therapy with curative intent

2. Has progressive disease ≤6 months after completion of curatively intended concurrent chemoradiotherapy for locoregionally advanced R/M oropharyngeal HNSCC

3. Primary tumor site of the oral cavity, hypopharynx, larynx or nasopharynx (any histology)

4. Rapidly progressing disease (e.g., tumor bleeding, uncontrolled tumor pain) in the opinion of the investigator

   PRIOR, CONCURRENT, OR FUTURE INTERVENTIONS

5. Has received prior palliative radiotherapy within 2 weeks of start of trial treatment or has a prior history of radiation pneumonitis

6. Any prior investigational or approved systemic antineoplastic drug or invasive medical device (including ICIs), either as monotherapy or as part of a combination regimen administered in the R/M HNSCC setting

7. Prior solid organ or tissue transplantation (except corneal transplant)

8. Prior autologous or allogeneic hematopoietic stem cell transplantation (HSCT)

9. Prior chimeric antigen receptor T (CAR-T) cell therapy

10. Prior therapy with a monoclonal or bispecific antibody or antibody fragment (or other molecule with similar mechanism of action) that engages T-cells

11. Has received a live or live-attenuated vaccine within 30 days prior to the first dose of trial intervention

12. Administration of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine within 30 days prior to VB10.16 treatment start

13. Prior administration with a therapeutic HPV16 vaccine

14. Patients receiving systemic immunosuppression with immunosuppressive agents such as cyclosporine, azathioprine, methotrexate, or tumor necrosis factor alpha (TNF α) blockers for any concurrent condition

15. Chronic administration of systemic corticosteroids: prednisone >10 mg daily (or dose equivalent)

16. Administration of G-CSF/GM-CSF or transfusions with red blood cells, platelets, or plasma components ≤2 weeks prior to VB10.16 treatment start

17. Has received prior therapy with an anti-PD-1, anti-PD-L1, or anti-PD-L2 agent or with an agent directed to another stimulatory or co-inhibitory T-cell receptor (e.g., CTLA-4, OX 40, CD137)

18. Has received prior surgery within 4 weeks prior to treatment

19. Any planned major surgery

    PRIOR OR CONCURRENT MORBIDITY

    Malignancy:

20. Past or current malignancy other than inclusion diagnosis, except for:

    • Malignancy treated with curative intent and with no known active disease present and has not received chemotherapy for at least 3 years before screening and felt to be at low risk for recurrence by the treating physician
    • Adequately treated breast ductal carcinoma in situ without evidence of disease
    • Adequately treated cervical carcinoma in situ, without evidence of disease
    • Adequately treated non-melanoma skin cancer without evidence of disease
    • Adequately treated superficial or in situ carcinoma of the bladder without evidence of disease
    • Prostatic intraepithelial neoplasia without evidence of prostate cancer

    Hepatic and hemostatic function:

21. Any current bleeding disorder, active bleeding, or bleeding diathesis

    Cardiovascular function:

22. Symptomatic congestive heart failure (Grade III or IV as classified by the New York Heart Association), unstable angina pectoris, or cardiac arrhythmia

23. History of myocardial infarction ≤ 6 months prior to planned VB10.16 treatment start

24. Uncontrolled hypertension (systolic blood pressure ≥160 mmHg and/or diastolic blood pressure ≥100 mmHg), despite optimal medical management

25. Any other significant cardiac disease(s) that, in the opinion of the investigator, is/are clinically significant and/or unacceptable

    Pulmonary function:

26. Has a history of (non-infectious) pneumonitis / interstitial lung disease that required steroids or has current pneumonitis / interstitial lung disease

    Immune system and infectious diseases:

27. Primary immunodeficiency, other immunosuppressive disorder, and/or other causes of immunosuppression

28. Has an active autoimmune disease that has required systemic treatment in the past 2 years (i.e., with use of disease-modifying agents, corticosteroids, or immunosuppressive drugs). Replacement therapy (e.g., thyroxine, insulin, or physiologic corticosteroid replacement therapy for adrenal or pituitary insufficiency) is not considered a form of systemic treatment and is allowed

29. Has a known history of human immunodeficiency virus (HIV) infection.

30. Has a known history of Hepatitis B (defined as HBsAg reactive) or known active Hepatitis C virus (defined as HCV RNA [qualitative] is detected) infection

31. Any active, acute, or chronic infection that is uncontrolled and/or requires systemic treatment

32. Known allergies, sensitivity, or intolerance to VB10.16 (active substance or to any of the excipients), pembrolizumab (active substance or to any of the excipients), or aminoglycosides (especially kanamycin).

    Central nervous system (CNS) function:

33. Any history of intracerebral arteriovenous malformations, cerebral aneurysm, or stroke

34. Has known active CNS metastases and/or carcinomatous meningitis. Patients with previously treated brain metastases may participate provided they are radiologically stable, i.e., without evidence of progression for at least 4 weeks by repeat imaging (note that the repeat imaging should be performed during trial screening), clinically stable and without requirement of steroid treatment for at least 14 days prior to first dose of trial treatment

35. New (≤6 months), progressive and/or symptomatic brain metastases

    OTHER

36. Is currently participating in or has participated in a trial of an investigational agent or device in the R/M setting.

37. Has a history or current evidence of any condition, therapy, or laboratory abnormality, or other circumstance that might confound the results of the trial or interfere with the patient's participation for the full duration of the trial, such that it is not in the best interest of the patient to participate, in the opinion of the treating investigator

38. Has a known psychiatric or substance abuse disorder that would interfere with the patient's ability to cooperate with the requirements of the trial

39. Has a concomitant medical condition requiring receipt of a therapeutic anticoagulant that, in the opinion of the treating physician, would contraindicate administration of VB10.16 and tumor biopsies

40. Female patients who are pregnant or breastfeeding