Inclusion Criteria:
 - -  Have histologically confirmed WHO grade I, II or III meningioma that is progressive
     or recurrent.
 
Metastatic meningiomas are allowed. Participants with grade I tumors
     must have failed radiation therapy.
 
- -  Prior therapy:
  -  There is no limit on the number of prior surgeries, radiation therapy, radiosurgery
     treatments or systemically administered therapeutic agents.
 
- -  Patients may have been treated with standard external beam radiation or
          radiosurgery in any combination, however, an interval of ≥ 12 weeks (84 days)
          must have elapsed from the completion of the radiation therapy to start of
          study therapy unless there is histopathologic confirmation of recurrent tumor
          or there is new enhancing tumor outside the radiation field (beyond the high
          dose region or the 80% isodose line).
 
- -  In addition, there must be subsequent evidence of tumor progression after
          completion of radiation therapy (grade I tumors only)
       -  An interval of ≥ 28 days and full recovery (no ongoing safety issues) from
          surgical resection.
 
- -  An interval of ≥ 7 days from stereotactic biopsy;
  -  For prior systemic agents, participants must be at least 4 weeks (or 5 half-lives,
     whichever is shorter) from other prior cytotoxic chemotherapy (6 weeks from
     nitrosoureas) or biologic therapies.
 
- -  Participants must have recovered to grade ≤ 1 or pretreatment baseline from
     clinically significant adverse events related to prior therapy (exclusions include
     but are not limited to alopecia, laboratory values listed per inclusion criteria and
     lymphopenia);
  -  Be 18 years of age on day of signing informed consent.
 
- -  Have a Karnofsky performance status (KPS) ≥ 70 (Appendix A).
 
- -  Participants must demonstrate adequate organ and marrow function as defined below
     (all screening labs to be performed within 14 days of treatment initiation):
       -  White blood cell (WBC) ≥ 2000/mm3.
 
- -  Absolute neutrophil count (ANC) ≥ 1,000/mm3.
 
- -  Platelet count ≥ 100,000/mm3.
 
- -  AST(SGOT)/ALT(SGPT) ≤ 3 x laboratory upper limit of normal (ULN)
       -  Serum creatinine ≤ 1.5 X ULN OR.
 
- -  creatinine clearance (meas or calc) ≥ 60 mL/min for participants with
          creatinine levels > 1.5 X ULN.
 
- -  (GFR can be used in place of creatinine or creatinine clearance)
       -  Total serum bilirubin ≤ 1.5 X ULN.
 
- -  (except participants with Gilbert's Syndrome, who can have a total bili < 5 X
          ULN)
       -  Resting baseline oxygen saturation ≥ 92% at rest by pulse oximetry.
 
- -  MRI (or CT if MRI contraindicated) within 14 days prior to start of study drug.
 
Corticosteroid dose must be stable or decreasing for at least 5 days prior to the
     scan. If steroids are added or the steroid dose is increased between the date of the
     screening MRI or CT scan and the start of treatment, a new baseline MRI or CT is
     required.
 
- -  Ability to understand and the willingness to comply with scheduled visits, treatment
     schedule, laboratory testing, and other requirements of the study, including disease
     assessment by MRI (or CT), as confirmed by signing a written informed consent
     document.
 
- -  For cohort 2, patients must be a candidate for external beam radiotherapy including
     either conventional fractionated conformal dosing or stereotactic radiosurgical
     boost dosing (participants may enroll if they are receiving radiotherapy or have
     completed it within 8 weeks of starting immunotherapy);
  -  For cohort 2 patients who are undergoing fractionated conformal re-irradiation to a
     tumor site that has been previously irradiated, an interval of at least 6 months
     must have passed since they completed their prior irradiation to be eligible unless
     the current course of radiation is targeting a new area of tumor growth outside the
     80% isodose line of the original radiation field as determined by the treating
     investigator.
 
- -  The effects of nivolumab on the developing human fetus are unknown.
 
For this reason:
 
- -  Women of childbearing potential (WOCPB; defined in Section 3.4) must have a negative
     serum or urine pregnancy test (minimum sensitivity 25 IU/L or equivalent units of
     HCG) within 24 hours of starting study therapy;
  -  Women must not be breastfeeding;
  -  WOCPB must agree to follow instructions for method(s) of contraception from the time
     of enrollment for the duration of treatment with study therapy plus 5 months after
     the last dose of Nivolumab.
 
- -  Should a woman become pregnant or suspect she is pregnant while she or her partner
     is participating in this study, she should inform her treating physician
     immediately.
 
- -  Men who are sexually active with WOCBP must agree to follow instructions for
     method(s) of contraception for the duration of treatment with study drug plus 7
     months after the last dose of Nivolumab.
 
- -  Investigators shall counsel WOCBP and male subjects who are sexually active with
     WOCBP on the importance of pregnancy prevention and the implications of an
     unexpected pregnancy Investigators shall advise WOCBP and male subjects who are
     sexually active with WOCBP on the use of highly effective methods of contraception.
 
Highly effective methods of contraception have a failure rate of < 1% per year when
     used consistently and correctly.
 
- -  At a minimum, subjects must agree to the use of two methods of contraception, with
     one method being highly effective and the other method being either highly effective
     or less effective as listed below:
       -  HIGHLY EFFECTIVE METHODS OF CONTRACEPTION.
 
- -  Male condoms with spermicide.
 
- -  Hormonal methods of contraception including combined oral contraceptive
               pills, vaginal ring, injectables, implants, and intrauterine devices
               (IUDs) such as Mirena by WOCBP subjects or male subject's WOCBP partner.
 
Female partners of male subjects participating in the study may use
               hormone based contraceptives as one of the acceptable methods of
               contraception since they will not be receiving study drug.           
- -  Progestogen only hormonal contraception associated with inhibition of
               ovulation.
 
- -  Intrauterine hormone-releasing system (IUS)
            -  Nonhormonal IUDs, such as ParaGard.
 
- -  Complete Abstinence - Complete abstinence is defined as complete avoidance
               of heterosexual intercourse and is an acceptable form of contraception for
               all study drugs.
 
Subjects who choose complete abstinence are not required
               to use a second method of contraception, but female subjects must continue
               to have pregnancy tests. Acceptable alternate methods of highly effective
               contraception must be discussed in the event that the subject chooses to
               forego complete abstinence.
      
- -  LESS EFFECTIVE METHODS OF CONTRACEPTION.
 
- -  Diaphragm with spermicide.
 
- -  Cervical cap with spermicide.
 
- -  Male Condom without spermicide.
 
- -  Progestin only pills by WOCBP subjects or male subject's WOCBP partner.
 
- -  Female Condom - A male and female condom must not be used together.
 
- -  UNACCEPTABLE METHODS OF CONTRACEPTION.
 
- -  Periodic abstinence (calendar, symptothermal, post-ovulation methods)
            -  Withdrawal (coitus interruptus)
            -  Spermicide only.
 
- -  Lactation amenorrhea method (LAM)
  -  NOTE: Azoospermic males and WOCBP who are continuously not heterosexually active are
     exempt from contraceptive requirements.
 
However, WOCBP participants must still
     undergo pregnancy testing as described.
Exclusion Criteria:
 - -  Current or planned participation in a study of an investigational agent or using an
     investigational device.
 
- -  Tumors that are primarily localized to the brainstem or spinal cord;
  -  Evidence of intratumoral or peritumoral hemorrhage on baseline MRI scan other than
     those that are grade ≤ 1 and either post-operative or stable on at least 2
     consecutive MRI scans;
  -  Prior Therapy:
  -  Prior treatment with systemic immunosuppressive treatments, aside from systemic
     dexamethasone therapy for cerebral edema, such as methotrexate, chloroquine,
     azathioprine, etc. within 3 months of start of study therapy;
  -  Prior treatment with interstitial brachytherapy within 6 months of start of study
     therapy;
  -  All patients: Previous treatment with PD-1 or PD-L1 directed therapy;
  -  Cohort 2 patients: Previous treatment with CTLA-4 directed therapy;
  -  Surgical procedure (including open biopsy, surgical resection, wound revision, or
     any other major surgery involving entry into a body cavity) or significant traumatic
     injury within 28 days prior to first study treatment, or anticipation of need for
     major surgical procedure during the course of the study;
  -  Minor surgical procedure (eg, stereotactic biopsy within 7 days of first study
     treatment; placement of a vascular access device within 2 days of first study
     treatment);
  -  Other Meds:
  -  Participants who are receiving any other investigational agents.
 
- -  Immunosuppressive medications / steroids:
       -  Subject must not require high dose systemic corticosteroids defined as
          dexamethasone > 4 mg/day or bioequivalent for at least 3 consecutive days
          within 2 weeks prior to Day 1of study therapy;
       -  Inhaled or topical steroids and adrenal replacement doses > 10 mg daily
          prednisone equivalents are permitted in the absence of active autoimmune
          disease.
 
- -  Subjects are permitted to use topical, ocular, intra-articular, intranasal, and
          inhalational corticosteroids (with minimal systemic absorption).
 
- -  Physiologic replacement doses of systemic corticosteroids are permitted, even
          if > 10 mg/day prednisone equivalents.
 
- -  A brief course of corticosteroids for prophylaxis (eg, contrast dye allergy) or
          for treatment of non-autoimmune conditions (eg, delayed-type hypersensitivity
          reaction caused by contact allergen) is permitted.
 
- -  Has received a live vaccine within 30 days prior to the first dose of study drug;
     seasonal influenza vaccination is permitted excluding the nasal spray formulation;
  -  No concurrent treatment on another clinical trial.
 
Supportive care trials or non-
     treatment trials, e.g. quality of life, are allowed;
 
- -  Concomitant Medical Illnesses: Uncontrolled intercurrent illness, including-but not
     limited to:
  -  Known additional malignancy that is progressing or requires active treatment within
     3 years of start of study drug.
 
Exceptions include basal cell carcinoma of the skin,
     squamous cell carcinoma of the skin, or in situ cervical cancer that has undergone
     potentially curative therapy;
 
- -  Has evidence of interstitial lung disease or active, non-infectious pneumonitis;
  -  Any serious or uncontrolled medical disorder that, in the opinion of the
     investigator, may increase the risk associated with study participation or study
     drug administration, impair the ability of the subject to receive protocol therapy,
     or interfere with the interpretation of study results examples include but are not
     limited to symptomatic congestive heart failure, unstable angina pectoris, cardiac
     arrhythmia or psychiatric illness/social situations that would limit compliance with
     study requirements;
  -  Has an active autoimmune disease requiring systemic treatment within the past 3
     months or a documented history of clinically severe autoimmune disease, or a
     syndrome that requires systemic steroids or immunosuppressive agents.
 
Subjects with
     vitiligo, type 1 diabetes mellitus, residual hypothyroidism due to autoimmune
     condition requiring hormone replacement, psoriasis not requiring systemic treatment,
     conditions not expected to recur in the absence of an external trigger or resolved
     childhood asthma/atopy would be exceptions to this rule. Subjects that require
     intermittent use of bronchodilators or local steroid injections would not be
     excluded from the study. Subjects with hypothyroidism stable on hormone replacement
     or Sjorgen's syndrome will not be excluded from the study;
 
- -  Has an active infection requiring intravenous therapy;
  -  Positive test for hepatitis B virus surface antigen (HBV sAg) or detectable
     hepatitis C virus ribonucleic acid (HCV RNA) indicating acute or chronic infection.
 
- -  Medical History:
  -  History of intracranial abscess within 6 months prior to start of study therapy;
  -  Known history of testing positive for human immunodeficiency virus (HIV) or known
     acquired immunodeficiency syndrome (AIDS);
  -  NOTE: HIV-positive participants on combination antiretroviral therapy are ineligible
     because of the potential for pharmacokinetic interactions with Nivolumab.
 
Appropriate studies will be undertaken in participants receiving combination
     antiretroviral therapy when indicated.
 
- -  History of allergy to study drug components.
 
- -  History of severe hypersensitivity reaction to any monoclonal antibody;
  -  Prisoners or participants who are involuntarily incarcerated;
  -  Pregnant women are excluded from this study because Nivolumab is an agent with the
     potential for teratogenic or abortifacient effects.
 
Because there is an unknown but
     potential risk for adverse events in nursing infants secondary to treatment of the
     mother with Nivolumab, breastfeeding should be discontinued if the mother is treated
     Nivolumab.