In addition, information regarding demographics and treatment history will be collected as part of the larger study and used in this analysis. The MDASI-BT consists of symptoms rated on an 11-point scale (0 to 10) to indicate the presence and severity of the symptom, with 0 being “not present” and 10 being “as bad as you can imagine.” Each symptom is rated at its worst in the last 24 hours. Symptoms included on the instrument include those commonly associated with cancer therapies, those associated with increased intracranial pressure, and those related to focal deficits. The questionnaire also includes ratings of how much symptoms interfered with different aspects of a patient’s life in the last 24 hours. These interference items include: general activity, mood, work (includes both work outside the home and housework), relations with other people, walking, and enjoyment of life. 42 Abbreviated Title: GBM Pembro HSPPC Version Date: 03/26/2024 The interference items are also measured on 0 - 10 scales. The average time to complete these instruments is 5 minutes. The MDASI-BT has been translated into multiple languages, but the English language version will be used for this study. [43] 3.9 TELEHEALTH/REMOTE V ISITS In the extenuating event that a subject cannot travel to be seen in person at the study site, or any other crisis causing travel and staffing restriction, the provider assessment may occur via telehealth visits. Telehealth visits (synonyms: telemedicine, videoconferencing, virtual visits, video phone call or remote visits) will be allowed for patients on-study unless these visits are essential to maintaining patient safety while on-study, refer to study calendar section 3.11 for more details. Decisions regarding the use of telehealth will be based on the patient’s physician’s decision regarding the risk of an in-person clinic visit compared with the potential benefit of a comprehensive in-person evaluation. The medical record or progress note for the telehealth visit should state that the risks were greater than the benefit. Telehealth visits for clinical assessments will be conducted in compliance with local guidelines and FDA regulations. For example, to ensure privacy, the patients will confirm their identities before the interaction or exchange of private information begins; guidance on this issue can be found in the National Institute of Standards and Technology (NIST) Digital Identity Guidelines, Special Publication 800-63A —Enrollment and Identity Proofing Requirements When Developing an Identity Verification Plan. In addition, documentation of telehealth visits must comply with local requirements (e.g., date and time of the real-time video interaction, location of the subject, individuals present, assessments performed, etc.). General interviews may be conducted adequately via telehealth visits. For example, to obtain a patient’s medical history, check-in with a participant regarding their current health status, or to administer a questionnaire to a participant related to their level of functioning or activities of daily living. Clinical assessments via telehealth visits for patients on study will not compromise either the primary or secondary objectives and will likely have minimal impact on the ability to complete this study as long as administration of treatment (e.g., radiation, temozolomide, pembrolizumab and vaccine/placebo) is not compromised. Given that the study requires only standard, clinical laboratory assessments and imaging per routine radiologic parameters/procedures, any possible interlaboratory or facility variability is not expected to be a concern. If any question about possible progression, a patient may be asked to have repeat imaging and/or additional assessments to confirm response. Further, a patient may be referred to another local provider or asked to come to the NIH for an in-person assessment, if clinically indicated, and at the discretion of the investigator. In the case of any visits with participants’ local providers, records will be obtained for the research records. The following clinical assessments generally obtained during a physical examination (i.e., H&P) can be conducted via telehealth visits through discussion and remote/video observation: Karnofsky Performance Status. 43 Abbreviated Title: GBM Pembro HSPPC Version Date: 03/26/2024 Neurological exam to assess cognition remotely will use the American Academy of Neurology Telemedicine guidance document for evaluation of memory, attention, concentration, language, eye movements, facial weakness, strength, walking and coordination. Physical exam to observe rashes, thrust, surgical scar, and swelling will use the American Academy of Dermatology Teledermatology guidance document for physical evaluation during telehealth vistis. The following clinical assessments are not feasible via telehealth visits: Hearing and vision Listening to your heart and lungs Assessing weakness Checking reflexes Checking for abnormalities in sensation Feeling lymph nodes, areas of swelling 3.10 DOSE MODIFICATIONS If Pembrolizumab and/or HSPPC-96 are stopped or discontinued, the patient can continue treatment on TMZ alone. If TMZ is stopped or discontinued, Pembrolizumab or HSPPC- 96/placebo can continue. If HSPPC-96/Placebo is stopped or discontinued, TMZ and Pembrolizumab can continue. 3.10.1 Pembrolizumab Dose Modifications Adverse events (AE) (both non-serious and serious) associated with pembrolizumab exposure, including coadministration with additional compounds, may represent an immunologic etiology. These immune-related adverse events (irAEs) may occur shortly after the first dose or several months after the last dose of treatment and may affect more than one body system simultaneously. Pembrolizumab must be withheld for drug-related toxicities and severe or life- threatening AEs as per Table 1: Dose Modification and Toxicity Management Guidelines for Immune-related AEs Associated with Pembrolizumab. See Section 3.10.3 for supportive care guidelines, including use of corticosteroids. 3.10.1.1 Attribution of Toxicity: When study interventions are administered in combination, attribution of an adverse event to a single component is likely to be difficult. Therefore, while the investigator may attribute a toxicity event [to the combination, to Temozolomide alone or to pembrolizumab alone, for adverse events listed in [Table 1], both interventions must be held according to the criteria in [Table 1 Dose Modification and Toxicity Management Guidelines for Immune-Related Adverse Events Associated with Pembrolizumab]. 44 Abbreviated Title: GBM Pembro HSPPC Version Date: 03/26/2024 3.10.1.2 Holding Study Interventions: When study interventions are administered in combination, if the AE is considered immune- related, both interventions should be held according to recommended dose modifications. 3.10.1.3 Restarting Study Interventions: Participants may not have any dose modifications (no change in dose or schedule) of pembrolizumab in this study, as described in [Table 1]. If the toxicity does not resolve or the criteria for resuming treatment are not met, the participant must be discontinued from all study interventions. If the toxicities do resolve and conditions are aligned with what is defined in [Table 1], the combination of temozolomine and pembrolizumab may be restarted at the discretion of the investigator.[In these cases where the toxicity is attributed to [the combination or to temozolomine alone, re-initiation of pembrolizumab as a monotherapy may be considered at the principal investigator’s discretion . 45 Abbreviated Title: GBM Pembro HSPPC Version Date: 03/26/2024 Table 1: Dose Modification and Toxicity Management Guidelines for Immune-related AEs Associated with Pembrolizumab General instructions: 1. Severe and life-threatening irAEs should be treated with IV corticosteroids followed by oral steroids. Other immunosuppressive treatment should begin if the irAEs are not controlled by corticosteroids. 2.Study intervention must be permanently discontinued if the irAE does not resolve or the corticosteroid dose is not ≤10 mg/day within 12 weeks of the last study intervention treatment. 3.The corticosteroid taper should begin when the irAE is ≤ Grade 1 and continue at least 4 weeks. 4.If study intervention has been withheld, study intervention may resume after the irAE decreased to ≤ Grade 1 after corticosteroid taper. irAEsToxicity Grade (CTCAE v5.0)Action With PembrolizumabCorticosteroid and/or Other Therapies Monitoring and Follow-up Grade 2 Withhold Pneumonitis Recurrent Grade 2, Grade 3 or 4 Permanently discontinue Administer corticosteroids (initial dose of 1 to 2 mg/kg prednisone or equivalent) followed by taper  Add prophylactic antibiotics for opportunistic infections Monitor participants for signs and symptoms of pneumonitis  Evaluate participants with suspected pneumonitis with radiographic imaging and initiate corticosteroid treatment Diarrhea/Colitis Grade 2 or 3 Withhold  Administer corticosteroids (initial dose of 1 to 2 mg/kg prednisone or equivalent) followed by taper Monitor participants for signs and symptoms of enterocolitis (ie, diarrhea, abdominal pain, blood or mucus in stool with or without fever) 46 Abbreviated Title: GBM Pembro HSPPC Version Date: 03/26/2024 irAEsToxicity Grade (CTCAE v5.0)Action With PembrolizumabCorticosteroid and/or Other Therapies Monitoring and Follow-up Recurrent Grade 3 or Grade 4Permanently discontinueand of bowel perforation (ie, peritoneal signs and ileus)  Participants with ≥Grade 2 diarrhea suspecting colitis should consider GI consultation and performing endoscopy to rule out colitis  Participants with diarrhea/colitis should be advised to drink liberal quantities of clear fluids. If sufficient oral fluid intake is not feasible, fluid and electrolytes should be substituted via IV infusion Grade 2 aWithhold  Administer corticosteroids (initial dose of 0.5 to 1 mg/kg prednisone or equivalent) followed by taper AST or ALT Elevation or Increased BilirubinGrade 3 b or 4 cPermanently discontinue Administer corticosteroids (initial dose of 1 to 2 mg/kg prednisone or equivalent) followed by taper Monitor with liver function tests (consider weekly or more frequently until liver enzyme value returned to baseline or is stable) T1DM or HyperglycemiaNew onset T1DM or Grade 3 or 4 hyperglycemia associated with Withhold d Initiate insulin replacement therapy for participants with T1DM Monitor participants for hyperglycemia or other signs and symptoms of diabetes 47 Abbreviated Title: GBM Pembro HSPPC Version Date: 03/26/2024 irAEsToxicity Grade (CTCAE v5.0)Action With PembrolizumabCorticosteroid and/or Other Therapies Monitoring and Follow-up evidence of -cell failure Administer antihyperglycemic in participants with hyperglycemia Grade 2 Withhold HypophysitisGrade 3 or 4 Withhold or permanently discontinue d Administer corticosteroids and initiate hormonal replacements as clinically indicated Monitor for signs and symptoms of hypophysitis (including hypopituitarism and adrenal insufficiency) Grade 2 Continue HyperthyroidismGrade 3 or 4 Withhold or permanently discontinue d Treat with nonselective beta-blockers (eg, propranolol) or thionamides as appropriate Monitor for signs and symptoms of thyroid disorders HypothyroidismGrade 2, 3 or 4 Continue  Initiate thyroid replacement hormones (eg, levothyroxine or liothyronine) per standard of care Monitor for signs and symptoms of thyroid disorders Grade 2 Withhold Nephritis: grading according to increased creatinine or acute kidney injuryGrade 3 or 4 Permanently discontinue Administer corticosteroids (prednisone 1 to 2 mg/kg or equivalent) followed by taper Monitor changes of renal function Neurological Grade 2 Withhold  Based on severity of AE administer  Ensure adequate evaluation to confirm etiology 48 Abbreviated Title: GBM Pembro HSPPC Version Date: 03/26/2024 irAEsToxicity Grade (CTCAE v5.0)Action With PembrolizumabCorticosteroid and/or Other Therapies Monitoring and Follow-up ToxicitiesGrade 3 or 4 Permanently discontinuecorticosteroids and/or exclude other causes Grade 1 Withhold MyocarditisGrade 2, 3 or 4 Permanently discontinue Based on severity of AE administer corticosteroids Ensure adequate evaluation to confirm etiology and/or exclude other causes Suspected SJS, TEN, or DRESSWithhold Exfoliative Dermatologic Conditions Confirmed SJS, TEN, or DRESSPermanently discontinue Based on severity of AE administer corticosteroids Ensure adequate evaluation to confirm etiology or exclude other causes Persistent Grade 2 Withhold Grade 3 Withhold or discontinue based on the event e All Other irAEs Recurrent Grade 3 or Grade 4 Permanently discontinue Based on severity of AE administer corticosteroids Ensure adequate evaluation to confirm etiology or exclude other causes AE(s)=adverse event(s); ALT= alanine aminotransferase; AST=aspartate aminotransferase; CTCAE=Common Terminology Criteria for Adverse Events; DRESS=Drug Rash with Eosinophilia and Systemic Symptom; GI=gastrointestinal; IO=immuno-oncology; ir=immune related; IV=intravenous; SJS=Stevens-Johnson Syndrome; T1DM=type 1 diabetes mellitus; TEN=Toxic Epidermal Necrolysis; ULN=upper limit of normal. Note: Non-irAE will be managed as appropriate, following clinical practice recommendations. 49 Abbreviated Title: GBM Pembro HSPPC Version Date: 03/26/2024 irAEsToxicity Grade (CTCAE v5.0)Action With PembrolizumabCorticosteroid and/or Other Therapies Monitoring and Follow-up aAST/ALT: >3.0 to5.0 x ULN if baseline normal; >3.0 to 5.0 x baseline, if baseline abnormal; bilirubin:>1.5 to 3.0 x ULN if baseline normal; >1.5 to 3.0 x baseline if baseline abnormal bAST/ALT: >5.0 to 20.0 x ULN, if baseline normal; >5.0 to 20.0 x baseline, if baseline abnormal; bilirubin:>3.0 to 10.0 x ULN if baseline normal; >3.0 to 10.0 x baseline if baseline abnormal cAST/ALT: >20.0 x ULN, if baseline normal; >20.0 x baseline, if baseline abnormal; bilirubin: >10.0 x ULN if baseline normal; >10.0 x baseline if baseline abnormal dThe decision to withhold or permanently discontinue pembrolizumab is at the discretion of the investigator or treating physician. If control achieved or ≤ Grade 2, pembrolizumab may be resumed. eEvents that require discontinuation include, but are not limited to: encephalitis and other clinically important irAEs (eg, vasculitis and sclerosing cholangitis). 50 Abbreviated Title: GBM Pembro HSPPC Version Date: 03/26/2024 3.10.2 Guidelines for Drug-Related Adverse Events due to Pembrolizumab Dosing interruptions are permitted in the case of medical / surgical events or logistical reasons not related to study therapy (e.g., elective surgery, unrelated medical events, patient vacation, and/or holidays). Subjects should be placed back on study therapy within 3 weeks of the scheduled interruption, unless otherwise discussed with the Study Chair. The reason for interruption should be documented in the patient's study record. 3.10.3 Pembrolizumab Supportive Care Participants should receive appropriate supportive care measures as deemed necessary by the treating investigator. Suggested supportive care measures for the management of adverse events with potential immunologic etiology are outlined below. Where appropriate, these guidelines include the use of oral or intravenous treatment with corticosteroids as well as additional anti- inflammatory agents if symptoms do not improve with administration of corticosteroids. Note that several courses of steroid tapering may be necessary as symptoms may worsen when the steroid dose is decreased. For each disorder, attempts should be made to rule out other causes such as metastatic disease or bacterial or viral infection, which might require additional supportive care. The treatment guidelines are intended to be applied when the investigator determines the events to be related to pembrolizumab. Note: If after the evaluation the event is determined not to be related, the investigator does not need to follow the treatment guidance (as outlined below). Refer to Section 3.10 for dose modification. It may be necessary to perform conditional procedures such as bronchoscopy, endoscopy, or skin photography as part of evaluation of the event. Pneumonitis: oFor Grade 2 events, treat with systemic corticosteroids. When symptoms improve to Grade 1 or less, steroid taper should be started and continued over no less than 4 weeks. oFor Grade 3-4 events, immediately treat with intravenous steroids. Administer additional anti-inflammatory measures, as needed. oAdd prophylactic antibiotics for opportunistic infections in the case of prolonged steroid administration. Diarrhea/Colitis: Subjects should be carefully monitored for signs and symptoms of enterocolitis (such as diarrhea, abdominal pain, blood or mucus in stool, with or without fever) and of bowel perforation (such as peritoneal signs and ileus). oAll subjects who experience diarrhea/colitis should be advised to drink liberal quantities of clear fluids. If sufficient oral fluid intake is not feasible, fluid and electrolytes should be substituted via IV infusion. For Grade 2 or higher diarrhea, consider GI consultation and endoscopy to confirm or rule out colitis. oFor Grade 2 diarrhea/colitis, administer oral corticosteroids. 51 Abbreviated Title: GBM Pembro HSPPC Version Date: 03/26/2024 oFor Grade 3 or 4 diarrhea/colitis, treat with intravenous steroids followed by high dose oral steroids. oWhen symptoms improve to Grade 1 or less, steroid taper should be started and continued over no less than 4 weeks. Type 1 diabetes mellitus (if new onset, including diabetic ketoacidosis [DKA]) or ≥ Grade 3 Hyperglycemia, if associated with ketosis (ketonuria) or metabolic acidosis (DKA) oFor T1DM or Grade 3-4 Hyperglycemia Insulin replacement therapy is recommended for Type I diabetes mellitus and for Grade 3-4 hyperglycemia associated with metabolic acidosis or ketonuria. Evaluate patients with serum glucose and a metabolic panel, urine ketones, glycosylated hemoglobin, and C-peptide. Hypophysitis: oFor Grade 2 events, treat with corticosteroids. When symptoms improve to Grade 1 or less, steroid taper should be started and continued over no less than 4 weeks. Replacement of appropriate hormones may be required as the steroid dose is tapered. oFor Grade 3-4 events, treat with an initial dose of IV corticosteroids followed by oral corticosteroids. When symptoms improve to Grade 1 or less, steroid taper should be started and continued over no less than 4 weeks. Replacement of appropriate hormones may be required as the steroid dose is tapered. Hyperthyroidism or Hypothyroidism: Thyroid disorders can occur at any time during treatment. Monitor patients for changes in thyroid function (at the start of treatment, periodically during treatment, and as indicated based on clinical evaluation) and for clinical signs and symptoms of thyroid disorders. oGrade 2 hyperthyroidism events (and Grade 2-4 hypothyroidism): In hyperthyroidism, non-selective beta-blockers (e.g. propranolol) are suggested as initial therapy. In hypothyroidism, thyroid hormone replacement therapy, with levothyroxine or liothyronine, is indicated per standard of care. oGrade 3-4 hyperthyroidism Treat with an initial dose of IV corticosteroid followed by oral corticosteroids. When symptoms improve to Grade 1 or less, steroid taper should be started and continued over no less than 4 weeks. Replacement of appropriate hormones may be required as the steroid dose is tapered. 52 Abbreviated Title: GBM Pembro HSPPC Version Date: 03/26/2024 Hepatic: oFor Grade 2 events, monitor liver function tests more frequently until returned to baseline values (consider weekly). Treat with IV or oral corticosteroids oFor Grade 3-4 events, treat with intravenous corticosteroids for 24 to 48 hours. oWhen symptoms improve to Grade 1 or less, a steroid taper should be started and continued over no less than 4 weeks. Renal Failure or Nephritis: oFor Grade 2 events, treat with corticosteroids. oFor Grade 3-4 events, treat with systemic corticosteroids. oWhen symptoms improve to Grade 1 or less, steroid taper should be started and continued over no less than 4 weeks. Management of Infusion Reactions: Signs and symptoms usually develop during or shortly after drug infusion and generally resolve completely within 24 hours of completion of infusion. Refer to Infusion Reaction Treatment Guidelines Appendix 16.8 for subjects who experience an infusion reaction associated with administration of pembrolizumab. 3.10.4 Temozolomide Dose Modifications NOTE: TMZ dose is modified ONLY if toxicity is specifically attributed to TMZ. TMZ can be delayed at the beginning of a cycle (e.g., C2D1) and then restarted when the reason for a delay has resolved. If TMZ is held (e.g., for toxicity) at mid-cycle (e.g., C2D29) it can be delayed up to 2 weeks. When TMZ is restarted, for example, 1 week later (e.g., D36) the cycle date entered in the CRF will automatically be labelled as D36, not D29; please enter a comment in the CRF that TMZ was held for X amount of days. If during a TMZ dosing period, there is a drop in ANC to < 1.5 or platelets < 75 000 a dose reduction should occur in the subsequent cycle.