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 4 Permanently discontinue AST / ALT elevation or Increased bilirubin Grade 2 Withhold Administer corticosteroids (initial dose of 0.5 - 1 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 Grade 3 or 4 Permanently discontinue Administer corticosteroids (initial dose of 1 -2 mg/kg prednisone or equivalent) followed by taper Type 1 diabetes mellitus (T1DM) or Hyperglycemia Newly onset T1DM or Grade 3 or 4 hyperglycemia associated with Withhold Initiate insulin replacement therapy for participants with T1DM Administer anti- hyperglycemic in participants with hyperglycemia Monitor participants for hyperglycemia or other signs and symptoms of diabetes. SELLAS Life Sciences Group Galinpepimut -S Protocol : SLS17 -201/MK3475 -770 Protocol v1.1 (Amendment 1.0) 12 April 2019 Page 156 evidence of b- cell failure Hypophysitis Grade 2 Withhold Administer corticosteroids and initiate hormonal replacements as clinically indicated. Monitor for signs and symptoms of hypophysitis (including hypopituitarism and adrenal insufficiency) Grade 3 or 4 Withhold or permanently discontinue1 Hyperthyroidism Grade 2 Continue Treat with non -selective beta - blockers (e.g., propranolol) or thionamides as appropriate Monitor for signs and symptoms of thyroid disorders. Grade 3 or 4 Withhold or permanently discontinue1 Hypothyroidism Grade 2 -4 Continue Initiate thyroid replacement hormones (e.g., levothyroxine or liothyroinine) per standard of care Monitor for signs and symptoms of thyroid disorders. Nephritis and Renal dysfunction Grade 2 Withhold Administer corticosteroids (prednisone 1 -2 mg/kg or equivalent) followed by taper. Monitor changes of renal function Grade 3 or 4 Permanently discontinue Myocarditis Grade 1 or 2 Withhold Based on severity of AE administer corticosteroids Ensure adequate evaluation to confirm etiology and/or exclude other causes Grade 3 or 4 Permanently discontinue SELLAS Life Sciences Group Galinpepimut -S Protocol : SLS17 -201/MK3475 -770 Protocol v1.1 (Amendment 1.0) 12 April 2019 Page 157 All other immune-related AEs Intolerable/ persistent Grade 2 Withhold Based on type and severity of AE administer corticosteroids Ensure adequate evaluation to confirm etiology and/or exclude other causes Grade 3 Withhold or discontinue based on the type of event. Events that require discontinuation include and not limited to: Guillain -Barre Syndrome, encephalitis Grade 4 or recurrent Grade 3 Permanently discontinue 1Withhold or permanently discontinue pembrolizumab is at the discretion of the investigator or treating physician. NOTE: For participants with Grade 3 or 4 immune -related endocrinopathy where withhold of pembrolizumab is required, pembrolizumab may be resumed when AE resolves to ≤ Grade 2 and is controlled with hormonal replacement therapy or achieved metabolic control (in cas e of T1DM). SELLAS Life Sciences Group Galinpepimut -S Protocol : SLS17 -201/MK3475 -770 Protocol v1.1 (Amendment 1.0) 12 April 2019 Page 158 5.3.6.3.2. Dose Modification and Toxicity M anagement of Infusion-R eactions Related to Pembrolizumab Pembrolizumab may cause severe or life-threatening infusion-reactions including severe hypersensitivity or anaphylaxis. Signs and symptoms usually develop during or shortly after drug infusion and generally resolve completely within 24 hours of completion of infusion. Dose modification and toxicity management guidelines on pembrolizumab associated infusion reaction are provided in Table 6. Table 6 Pembrolizumab Infusion Reaction Dose Modification and Treatment Guidelines SELLAS Life Sciences Group Galinpepimut -S Protocol : SLS17 -201/MK3475 -770 Protocol v1.1 (Amendment 1.0) 12 April 2019 Page 159 NCI CTCAE Grade Treatment Premedication at Subsequent Dosing Grade 1 Mild reaction; infusion interruption not indicated; intervention not indicated • Increase monitoring of vital signs as medically indicated until the participant is deemed medically stable in the opinion of the investigator. None Grade 2 Requires therapy or infusion interruption but responds promptly to symptomatic treatment (e.g., antihistamines, NSAIDs, narcotics, IV fluids); prophylactic medications indicated for ≤24 hrs. • Stop Infusion. • Additional appropriate medical therapy may include but is not limited to: • IV fluids • Antihistamines • NSAIDs • Acetaminophen • Narcotics • Increase monitoring of vital signs as medically indicated until the participant is deemed medically stable in the opinion of the investigator. • If symptoms resolve within 1 hour of stopping drug infusion, the infusion may be restarte d at 50% of the original infusion rate (e.g. from 100 mL/hr. to 50 mL/hr.). Otherwise dosing will be held until symptoms resolve and the participant should be premedicated for the next scheduled dose. Participants who develop Grade 2 toxicity despite adequ ate premedication should be permanently discontinued from further study drug treatment Participant may be premedicated 1.5h (± 30 minutes) prior to infusion with: - Diphenhydramine 50 mg po (or equivalent dose of antihistamine). - Acetaminophen 500- 1000 mg po (or equivalent dose of analgesic). SELLAS Life Sciences Group Galinpepimut -S Protocol : SLS17 -201/MK3475 -770 Protocol v1.1 (Amendment 1.0) 12 April 2019 Page 160 Grades 3 or 4 Grade 3: Prolonged (i.e., not rapidly responsive to symptomatic medication and/or brief interruption of infusion); recurrence of symptoms following initial improvement; hospitalization indicated for other clinical sequelae (e.g., renal impairment, pulmonary infiltrates) Grade 4: Life-threatening; pressor or ventilator support indicated • Stop Infusion. • Additional appropriate medical therapy may include but is not limited to: • Epinephrine** • IV fluids • Antihistamines • NSAIDs • Acetaminophen • Narcotics • Oxygen • Pressors • Corticosteroids • Increase monitoring of vital signs as medically indicated until the participant is deemed medically stable in the opinion of the investigator. • Hospitalization may be i ndicated. **In cases of anaphylaxis, epinephrine should be used immediately. Participant is permanently discontinued from further study drug treatment. No subsequent dosing Appropriate resuscitation equipment should be available at the bedside and a physician readily available during the period of drug administration. For further information, please refer to the Common Terminology Criteria for Adverse Events v5.0 (CTCAE) at h ttps://ctep.cancer.gov/protocolDevelopment/electronic_applications/docs/CTCAE_v5_Q uick_Reference_5x7.pdf. Other allowed dose interruptions for pembrolizumab SELLAS Life Sciences Group Galinpepimut -S Protocol : SLS17 -201/MK3475 -770 Protocol v1.1 (Amendment 1.0) 12 April 2019 Page 161 Pembrolizumab may be interrupted for situations other than treatmen t-related AEs such as medical/surgical events or logistical reasons not related to study therapy. Patients should be placed back on study therapy within 3 weeks of the scheduled interruption, unless otherwise discussed with the sponsor. The reason for interruption should be documented in the patient's study record 5.3.7. Toxicity Management of Injection -reactions Related to Galinpepimut -S Expected AEs from study treatment injection (any component of galinpepimut-S, excluding GM-CSF) include local erythema, edema , itching, and persistent induration at the site of injection. These events are usually mild and may appear after each administration of the study treatment. These Grade 1 and Grade 2 local injection site reactions may resolve spontaneously but they can be treated with topical cr eams (e.g., aloe), analgesics and/or antihistamines as per investigative site guidelines and will not require treatment interruptions or discontinuation. Local injection site reactions of grade 3 or higher may require antihistamines, non -steroidal anti-inflammatory agents, and/or steroid therapy as per investigative site guidelines. Re-challenge of a patient after a local g rade 3 event will need to be discussed with the medical monitor. Premedication with diphenhydramine 50 mg (or equivalent) and/or paracetamol (325 to 1,000 mg) at least 30 minutes prior to the next treatment injection will be required for the re-challenge. If local toxicity of grade 3 or higher persists, the patient will be moved to the off- treatment follow-up period. Systemic events of grade 3 or grade 4 toxicity that are considered possibly related to study treatment (any component of galinpepimut-S, excluding GM-CSF) should be quickly discussed with the medical monitor. Autoimmune or hypersensitivity reactions to components of the study treatment or skin test antigens are possibilities. Patients who develop events of non-skin related autoimmune disorders or anaphylactic reaction s considered possibly related to the study treatment or any of its components (other than SELLAS Life Sciences Group Galinpepimut -S Protocol : SLS17 -201/MK3475 -770 Protocol v1.1 (Amendment 1.0) 12 April 2019 Page 162 GM-CSF) may require appropriate care with epinephrine, antihistamines, vasopressors, fluids, and/or steroid therapy as per investigative site guidelines. The medical monitor should be contacted, and these patients will be moved to the off- treatment follow-up period. Toxicity events related to GM-CSF should be discussed expeditiously with the medical monitor and consideration will be made to either allow the patient to continue the study treatment with or without GM-CSF or to move that particular patient to the off- treatment follow-up period. Treatment of GM-CSF related events are to be treated as per investigative site guidelines. Toxicity will be graded in accordance with CTCAE v5.0 developed by the NCI (https://ctep.cancer.g ov/protocolDevelopment/electronic_applications/docs/CTCAE_v5_Q uick_Reference_5x7.pdf). ).