Inclusion Criteria:  Ability to understand the purpose of the study, provide signed and dated informed consent, and able to comply with all procedures Male or female subjects aged >= 18 years on the day of signing informed consent Has histologically confirmed supratentorial World Health Organization grade IV astrocytoma (glioblastoma or gliosarcoma) with any prior number of recurrences, and who have received prior radiation and temozolomide therapy. Participants will be eligible if the original histology was lower-grade glioma and a subsequent histological diagnosis of glioblastoma or variants is made Karnofsky performance status (KPS) of >= 70 at trial entry Must be at least 12 weeks from receiving conformal radiation, unless RANO criteria for early progression are met A baseline brain magnetic resonance imaging (MRI) must be obtained no more than 14 days (+/- 2 working days) prior to study registration Patients having undergone recent surgery are eligible as long as they are at least 3 weeks from resection or at least 1 week from stereotactic biopsy and recovered from any operative or perioperative complications. Patients with non-measurable tumor after resection will NOT be excluded; if they do not experience tumor progression while on trial, response will be labeled as "stable disease" (and not as "complete response") White blood cell (WBC) count >= 3 x 10^9/L Absolute neutrophil count (ANC) >= 1.5 x 10^9/L Lymphocyte count >= 0.5 x 10^9/L Platelet count >= 120 x 10^9/L Hemoglobin (Hgb) >= 9 g/dL (in absence of blood transfusion) Total bilirubin level =< 1.5 x upper limit of normal (ULN) Aspartate aminotransferase (AST) level =< 2.5 x ULN Alanine aminotransferase (ALT) level =< 2.5 x ULN International normalized ratio (INR) =< 1.5 Estimated creatinine clearance > 50 mL/min according to the Cockcroft-Gault formula or by measure of creatinine clearance from 24-hour urine collection Female subject of childbearing potential should have a negative serum pregnancy test within 14 days (+/- 2 working days) of study registration Female subjects of childbearing potential should be willing to use 2 methods of birth control or be surgically sterile, or abstain from heterosexual activity for the course of the study and for 3 months after the last dose of study therapy. Subjects of childbearing potential are those who have not been surgically sterilized or have not been free from menses for > 1 year Male subjects should agree to use highly effective 2 methods of contraception starting with the first dose of study therapy and for 3 months after the last dose of study therapy SURGICAL EXPANSION GROUP (GROUP 2): Have evaluable or measurable disease of >= 1 cm^2 of contrast enhancing disease at a surgically accessible site at baseline  Exclusion Criteria:  Has been treated previously with bevacizumab or Gliadel wafers Has received prior interstitial brachytherapy, implanted chemotherapy, or therapeutics delivered by local injection or convection enhanced delivery Is currently participating in or has participated in a study of an investigational agent or using an investigational device 4 weeks since last dose of agent administration, or is planning to continue or start treatment with Optune during participation in this trial Has known severe hypersensitivity reactions to monoclonal antibodies (grade >= 3 National Cancer Institute [NCI]-Common Terminology Criteria for Adverse Events [CTCAE] version [v]4.03), any history of anaphylaxis, or recent, within 5 months, history of uncontrolled asthma Has a known history of human immunodeficiency virus (HIV) (positive HIV 1/2 antibodies); human T-cell lymphotropic virus (HTLV)1 and/or HTLV2; active hepatitis B (e.g., hepatitis B surface antigen [HBsAg] reactive) or hepatitis C (e.g., hepatitis C virus [HCV] ribonucleic acid [RNA] [qualitative] is detected). Patients with prior hepatitis B virus (HBV) vaccination (anti-hepatitis B surface antibody [HBs] positive, HBsAg negative, anti-hepatitis B core antibody [HBc] negative) will NOT be excluded Has a diagnosis of immunodeficiency or is receiving any immunosuppressive therapy within 7 days prior to study registration  Has had prior chemotherapy or targeted small molecule therapy within 2 weeks prior to study day 1 or who has not recovered (i.e., =< grade 1 or at baseline) from adverse events due to a previously administered agent  Note: Subjects with =< grade 2 neuropathy are an exception to this criterion and may qualify for the study Note: If subject received major surgery (other than craniotomy), they must have recovered adequately from the toxicity and/or complications from the intervention prior to starting therapy Has had prior radiation therapy less than 12 weeks prior to enrollment; unless RANO criteria for early progression are met Has had prior therapy with any antibody/drug targeting T cell co-regulatory proteins (immune checkpoints) such as anti-PD-1, anti-PD-L1, or anti-CTLA-4 antibody Has a known additional malignancy that is progressing or requires active treatment. Exceptions include superficial tumors considered adequately treated locally with curative intent, including but not limited to basal cell carcinoma of the skin, squamous cell carcinoma of the skin, or in situ cervical cancer that has undergone potentially curative therapy. Any exceptions must be discussed with the protocol principal investigator (PI) Has known gliomatous meningitis or extracranial disease, or tumor localized primarily to the brainstem or spinal cord Midline shift greater than 0.5 cm or pending herniation 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 or resolved childhood asthma/atopy would be an exception 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 Sjogren's syndrome will not be excluded from the study Has evidence of interstitial lung disease or active, non-infectious pneumonitis Has an active infection requiring systemic therapy or that in the opinion of the PI may interfere with the subject's participation, assessment of experimental treatment toxicity or increase the subject's risk of side effects Has a history or current evidence of any condition, therapy, or laboratory abnormality that might confound the results of the trial, interfere with the subject's participation for the full duration of the trial, or is not in the best interest of the subject to participate in the opinion of the treating investigator Has known psychiatric or substance abuse disorders that would interfere with cooperation with the requirements of the trial Is pregnant or breastfeeding, or expecting to conceive or father children within the projected duration of the trial, starting with the screening visit Has received a live vaccine within 30 days prior to the first dose of trial treatment Has a contraindication for undergoing MRIs Has evidence of bleeding diathesis or coagulopathy Is on full dose anticoagulation or antiplatelet therapy Has significant hemorrhage on baseline scan defined as > 1 cm diameter of acute blood Has received any organ transplantation, including allogeneic stem-cell transplantation, but with the exception of transplants that do not require immunosuppression (e.g., corneal transplant, hair transplant)