Inclusion Criteria:

   1. Male or female ≥ 12 years of age

   2. Incurable, locally recurrent or metastatic EBV+NPC (World Health Organization type
   II/III)

   3. Subjects must have had prior receipt of platinum-containing regimen

   4. Phase 1B (Cohort 1):

      1. Checkpoint inhibitor naïve (have never received pembrolizumab or any other
      checkpoint/immuno-oncology agents) OR

      2. Refractory to an anti-programmed cell death protein-1 (PD-1) or anti-programmed
      death-ligand1 (PD-L1) monoclonal antibody approved by the local regulatory agency
      either as monotherapy or in combination with other checkpoint inhibitors or
      therapies according to their approved label.

   5. Phase 2 (Cohort 2): Checkpoint inhibitor naïve (have never received pembrolizumab or
   any other checkpoint/immuno-oncology agents

   6. Life expectancy ≥ 4 months at time of screening

   7. Measurable disease using RECIST 1.1. Tumor lesions situated in a previously irradiated
   area are considered measurable if progression has been documented in such lesions

   8. Eastern Cooperative Oncology Group (ECOG) performance status of < 2 for subjects aged
   > 16 years; Lansky score ≥ 70 for subjects aged 12 to 16 years

   9. Adequate organ function per the protocol.

10. Willing and able to provide written informed consent (pediatric subjects 12 to < 18
   years of age must provide assent along with consent from the subject's legally
   authorized representative)

Exclusion Criteria:

   1. Disease that is suitable for local therapy administered with curative intent

   2. Requires vasopressor or ventilator support

   3. Received antithymocyte globulin or similar anti-T-cell antibody therapy ≤ 4 weeks
   prior to Cycle 1 Day 1

   4. Diagnosis of immunodeficiency or is receiving systemic steroid therapy or any other
   form of immunosuppressive therapy within 7 days prior to Cycle 1 Day 1 of study
   treatment.

   5. Active autoimmune disease that has required systemic treatment in past 2 years (ie,
   with use of disease modifying agents, corticosteroids or immunosuppressive drugs).
   Replacement therapy (eg, thyroxine, insulin, or physiologic corticosteroid replacement
   therapy for adrenal or pituitary insufficiency) is not considered a form of systemic
   treatment and is allowed.

   6. History or evidence of interstitial lung disease

   7. History of severe hypersensitivity (Grade ≥ 3) to pembrolizumab and/or any of its
   excipients

   8. Active infection requiring systemic therapy

   9. History of (non-infectious) pneumonitis that required steroids or current pneumonitis

10. Received transfusion of blood products (including platelets or red blood cells) or
   administration of colony stimulating factors (including granulocyte-colony stimulating
   factor, granulocyte macrophage-colony stimulating factor or recombinant erythropoetin)
   within 4 weeks prior to study Day 1

11. Received any non-oncology vaccine therapy used for prevention of infectious diseases
   for up to 30 days prior to enrollment.

12. Known additional malignancy that is progressing or requires active treatment.
   Exceptions include basal cell carcinoma of the skin, squamous cell carcinoma of the
   skin that has undergone potentially curative therapy or in situ cervical cancer

13. Pregnancy or breastfeeding: females of childbearing potential must have a negative
   serum pregnancy test.

14. Female of childbearing potential or male with a female partner of childbearing
   potential unwilling to use a highly effective method of contraception (abstinence is
   acceptable) for the course of the study through 120 days after the last study dose

15. Inability to comply with study procedures

16. Received chemotherapy or targeted small molecule therapy within 2 weeks of Cycle 1 Day
   1. Subjects must have recovered (ie, grade ≤ 1 or at baseline) from adverse events
   (AEs) due to a previously administered agent. Subjects with grade ≤ 2 neuropathy or
   grade ≤ 2 alopecia are an exception to this criterion.

17. Received prior radiotherapy within 2 weeks of Cycle 1 Day 1. 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-central nervous system (CNS) disease.

18. Antibody/biologic therapy within 4 weeks of Cycle 1 Day 1 or not recovered (i.e.,
   grade ≤ 1 or at baseline) from AEs due to agents administered more than 4 weeks
   earlier

19. Carcinomatous meningitis; and/or active CNS metastases, unless metastases are treated
   and stable and the subject does not require systemic steroids.

20. Known history of human immunodeficiency virus (HIV), known active hepatitis B virus
   (HBV; e.g., hepatitis B surface antigen [HBsAg] reactive), or hepatitis C virus (HCV;
   e.g., HCV ribonucleic acid [RNA] is detected)

21. Prior treatment with any investigational product within 4 weeks of Cycle 1 Day 1

22. Prior treatment with EBV T cells