This two-arm randomized trial will evaluate the safety of nivolumab in combination with DC vaccinations for the treatment of bevacizumab-naïve subjects with first or second recurrent, resectable World Health Organization (WHO) Grade III and IV malignant gliomas (MGs). Up to 66 patients will be enrolled and treated with the goal of accruing 30 patients (15 per arm) that will receive nivolumab and at least 3 vaccines. After enrollment, leukapheresis will be done for generation of DC vaccines and immunologic monitoring. All subjects will undergo standard of care tetanus booster vaccination with 0.5 mL of Td (tetanus and diphtheria toxoids adsorbed) intramuscularly (I.M.) into the deltoid muscle to ensure adequate immunity to the tetanus antigen. Subjects will initially return every 2 weeks and receive approximately 3 infusions of nivolumab 3 mg/kg IV while the DC vaccines are being prepared from the initial leukapheresis and will then be randomized 1:1 to one of 2 arms (Group I: nivolumab only pre-surgery; Group II: nivolumab with DC vaccines pre-surgery). Patients who are unable to tolerate nivolumab will be withdrawn from the study and replaced. Patients whose DCs or Peripheral Blood Lymphocytes (PBLs) fail to meet release criteria will continue to receive nivolumab only and will not undergo repeat leukapheresis. For patients whose leukapheresis yields less than 4 vaccines, a repeat leukapheresis may be obtained a minimum of 2 weeks from the previous leukapheresis (and may be repeated as needed) if stable. Peripheral blood will be drawn for immune monitoring prior to treatment with the 4th cycle of nivolumab (first post-randomization infusion of nivolumab).

Group I Treatment Plan (Nivolumab Only Pre-Surgery) After randomization, patients in Group I will receive nivolumab 3 mg/kg IV every 2 weeks x approximately 8 weeks. The subject will then undergo surgical resection of tumor within approximately 1-3 weeks. Approximately 2-4 weeks later, leukapheresis is repeated for generation of DC vaccines and immunologic monitoring. Approximately 1 day to 2 weeks after leukapheresis, the subject will resume nivolumab 3mg/kg IV every two weeks with DC vaccine administration intradermally (i.d.) for a total of 3 vaccines. At the time of the third DC vaccine, patients will receive vaccine site pre-conditioning. A single dose of Td toxoid (1 flocculation unit (Lf) in 0.4 milliliters (mL) of saline) will be administered to a single side of the groin i.d. (as described above for all vaccine administrations 12-24 hours prior to the third DC vaccine, which is always given bilaterally at the groin site. At the vaccine #3 visit, prior to vaccine # 3 administration, erythema and induration measurements will be taken of pre-conditioning site. Group I subjects will then receive monthly DC vaccine administrations intradermally for 5 months or until progression (whichever comes first).Total vaccines to be administered will be 8 post-surgery unless subject is removed. Nivolumab will continue until progression. At the clinic visit following the last vaccine (#8), subjects will have peripheral blood drawn for immune monitoring prior to infusion of nivolumab.

Group II Treatment Plan (Nivolumab with DC Vaccines Pre-Surgery) After randomization, patients in Group II will receive the fourth cycle of nivolumab then receive nivolumab 3 mg/kg IV along with DC vaccines intradermally every 2 weeks x approximately 6 weeks for a total of 3 vaccines. At the time of the third DC vaccine, patients will receive vaccine site pre-conditioning. A single dose of Td toxoid (1 Lf in 0.4 mL of saline) will be administered to a single side of the groin i.d. 12-24 hours before the third DC vaccine, which is always given bilaterally at the groin site. At the vaccine #3 visit, prior to vaccine #3 administration, erythema and induration measurements will be taken of pre-conditioning site.The subject will then undergo surgical resection of tumor within approximately 1-3 weeks. Approximately 2-4 weeks later, leukapheresis is repeated for generation of DC vaccines and immunologic monitoring. Approximately 1 day to 2 weeks after leukapheresis, the subject will resume nivolumab 3mg/kg IV every two weeks. When DC vaccines have completed processing and are available for administration, monthly DC vaccine administrations as described above will be administered for 5 months or until progression (whichever comes first). Total vaccines to be administered will be 8 (3 pre- and 5 post-surgery) unless subject is removed. Nivolumab will continue until progression. At the clinic visit following the last vaccine (#8), subjects will have peripheral blood drawn for immune monitoring prior to infusion of nivolumab.