j. Urine dipstick testing will be performed locally at the site. k. Patients will provide any historical docume ntation of HLA type at the pretreatment screening visit. The majority of patients will not have such information available and must undergo HLA typing assessment at participating sites. l. For AML patients ONLY : provide historical documentation of cytogenet ic and molecular analyses results (from initial diagnosis) at the pretreatment screening visit. Only patients with abnormal karyotype at initial diagnosis will require to repeat karyotype plus/minus fluor escence in situ hybridization (FISH) at pretreatment screening in this study. Full molecular analysis (i.e., FLT3 -ITD and NPM1 mutations , etc.) will also be performed on bone marrow biopsy samples collected during pretreatment screening in all AML patients. m. For AML patients ONLY : a bone marrow aspiration an d biopsy is required during pretreatment screening to confirm morphologic partial response (PR) or stable disease (SD) status, for MRD analysis, and for cytogenetic and molecular analyses as defined in footnote k. Additio nal bone marrow biopsies are requir ed as shown per schedule, as well as at the end -of-treatment/early termination visit to evaluate progression and MRD. If a peripheral blood differential result (including manual differentiation) at any study visit is suggestive of abnormal or immature cell s and a possible relapse, a bone marrow biopsy must be performed as part of a scheduled AML relapse visit. If the bone marrow biopsy confirms relapse, the patient wi ll be discontinued from the study and will need to return to the site 0 to 30 days after th eir last treatment injection for end- of-treatment/early termination procedures. The bone marrow aspiration performed as part of the scheduled relapse visit will serve as bone marrow aspiration procedure required at the end -of-treatment/early SELLAS Life Sciences Group Galinpepimut -S Protocol : SLS17 -201/MK3475 -770 Protocol v1.1 (Amendment 1.0) 12 April 2019 Page 183 termination vi sit. A bone marrow biopsy must be collected if an adequate aspiration is not attainable. Refer to the laboratory manual for c ollection and processing these samples. n. For AML patients ONLY : Analysis of MRD will be performed on samples of peripheral blood an d will be evaluated by molecular analysis of transcripts. Peripheral blood samples will be collected from patients according to the schedule shown. Samples must be collec ted before study treatment administration. Refer to the laboratory manual for collecti on and processing of samples. o. Peripheral blood samples for immunologic response (IR) assessment will be collected from a large subset of patients enrolled in each of the 5 arms of the study at select sites as per the schedule shown. The study is aiming to analyze IR profile in at least 50% of the enrolled patients. Samples must be collected before study treatment administrations. Refer to the laboratory manual for collection and processing these samples. p. Biopsies of malignant tissue deposit (or bone marrow , for AML patients) will be performed according to the schedule shown in a subset of patients at select sites. These tissue specimens will be used to study the presence and kinetics of host immunocytes infiltrating the abo ve tissues, as well as the expression of key markers of immune biological significance in the tumor microenvironment. All biopsies are in principle mandatory, as long as the tumor deposits are technically accessible and such biopsies can be conducted safely. q. For solid tumors only: CT or MR I staging assessment (both per RECIST and iRECIST). r. Prior to contacting IWRS to enroll a patient into the study and obtaining a patient number, the following must be reviewed an d verified: inclusion/exclusion criteria (including specific tumor histologic t ype verification, [e.g., TNBC]), laboratory and tissue pathology. s. GM-CSF will be administered 2 days before and on the day of each galinpepimut -S administration. A GM -CSF dose of 70 µg will be injected subcutaneously at the same anatomical site as the plan ned subsequent galinpepimut -S injection (to be given during the same cycle of therapy) . Before injection, study staff should assess the immunization site. On Day −1, patients will remain in the clinic for approximately 3 0 minutes following receipt of GM -CSF to monitor for any adverse reactions. Blood samples will be collected before study treatment administration. t. Immediately after the patient receives the GM -CSF injection, patients are to receive galinpepimut -S injected SC in the same anatomical location a s the GM-CSF injection. The injection site should be on the arm, leg, or torso of the patient, and should be positioned at least 5 cm away from the previous site of study treatment injection. u. Adverse event reporting begins from the time of signing the ICF to 30 days after the last injection of any study treatment (GPS/placebo or pembrolizumab). Adverse events collected before the first injection of GM -CSF will be reported as “pre -WT1 AEs”. All AEs will be graded by SELLAS Life Sciences Group Galinpepimut -S Protocol : SLS17 -201/MK3475 -770 Protocol v1.1 (Amendment 1.0) 12 April 2019 Page 184 CTCAE, Version 5.0. A follow -up phone cal l for serious adverse events will occur 90 days after the last dose of pembrolizumab or 30 days following cessation of study treatment if the patient begins new anticancer therapy, whichever is earlier. If the patient initiates new anticancer therapy, this must be reported by the investigator. v. Patients who complete the study, or who discontinue because of any reason other than recurrent/refractory/relapsed disease wi ll return to the site 30 days after their last injection for final safety follow -up and completion of EOT/ET visit. w.