Only to occur at Week 9. x. Only to occur at Week 36. y. Only to occur at Week 54. z. Only to occur at Weeks 72 and 84. aa. Only to occur at Weeks 27 and 36. bb. Only to occur at Weeks 45, 54, and 63. SELLAS Life Sciences Group Galinpepimut -S Protocol : SLS17 -201/ MK3475 -770 Protocol v1.1 (Amendment 1.0) 12 April 2019 Page 185 6.1. Study Visits 6.1.1. Screening Period and Enrollment Informed consent must be obtained before any study -related procedures are conducted. All study-specific screening procedures must be completed within 28 days (refer to Table 8 for screening procedures). At the baseline visit (Day −3), all pretreatment screening procedures/assessments must be completed and laboratory results confirmed prior to enrollment and the first injection of GM -CSF. If a patient does not meet inclusion/exclusion criteria within 28 days of signing the ICF, the patient will be considered a screen failure and may be allowed to re -screen with a newly signed ICF up to 2 times. 6.1.2. Open -Label Treatment Period Refer to Section 5 (Study Treatments) and Table 8 (Schedule of Assessments) for further details. 6.1.3. End of Treatment/Early Termination Visit Patients who complete the protocol-specified study injections or scheduled study visit evaluations, or who discontinue because of any reason other than recurrent/refractory/relapsed disease will return to the site 30 days after their last injection for final safety follow-up and completion of the EOT/early termination procedures. 6.1.4. Safety Follow -up Period Patients who complete the study treatment period or discontinue early (if they have received at least 1 treatment injection) will enter an off -treatment follow-up period to assess progression-free survival and overall survival. A follow -up telephone call 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 SELLAS Life Sciences Group Galinpepimut -S Protocol : SLS17 -201/ MK3475 -770 Protocol v1.1 (Amendment 1.0) 12 April 2019 Page 186 earlier. If the patient initiates new anticancer therapy, this mus t be reported by the investigator. Patients will be followed in accordance with standard guidelines, which suggest regular assessments every 3 months until study closure, defined as up to 2 years and 6 weeks, i.e., 111 weeks, after the first galinpepimut-S administration given to the last patient enrolled into the study (which corresponds to up to 2 years after the first injection of pembrolizumab) . 6.1.5. Relapse Visit In addition to the SOA above, one additional series of assessments will be performed at the time of tumor (or leukemia) relapse. Indeed, t o assess PFS, it is important to document disease relapse. At the time of the “relapse visit”, the following assessments will be performed: • Collect and update concomitant medication information • Collect and update AEs • Obtain ECOG performance score • Obtain vital signs and document weight • Collect blood samples for the central laboratory o Hematology (CBC with differential and platelet count) o Serum chemistry o Immune/exploratory correlates • Evaluate clinical endpoints For AML patients in specific, PB differentials from CBCs collected during every visit will be used to determine initially if the patient has relapsed, as defined by loss of CR status (if previously achieved) or further progression beyond initially ach ieved PR. For abnormal CBCs, a manual differential is required. If the differential is suggestive of abnormal or SELLAS Life Sciences Group Galinpepimut -S Protocol : SLS17 -201/ MK3475 -770 Protocol v1.1 (Amendment 1.0) 12 April 2019 Page 187 immature cells and a possible relapse, a BM aspiration must be performed as part of a scheduled relapse visit to confirm the diagnosis of recur rent/relapse/refractory AML. A BM biopsy must be performed if an adequate aspiration is not attainable. In patients with AML who achieve CR status while on investigational therapy (galinpepimut -S plus pemrolizumab – administered on top of their continuing HMA regimen), relapse (post-CR) will be defined as a reappearance of leukemic blasts in the PB or >5% blasts in the BM not attributable to any other cause (e.g., BM regeneration after chemotherapy [ Cheson et al, 2003]). If relapse is confirmed, the patient should be discontinued from the on-treatment portion of the study due to recurrent/refractory/relapsed AML and will need to return to the site 0 to 30 days after their last treatment injection for final safety follow -up and completion of the EOT/early termination visit procedures. The BM aspiration performed as part of the scheduled relapse visit will serve as BM aspiration procedure required at the EOT/early termination visit. Once EOT/early termination visit procedures have been completed, the physician can choose to treat the documented recurrent/refractory/relapsed disease with any subsequent therapy they choose. The patient will be moved to the off- treatment follow -up period and will be followed only for AEs and OS. 6.1.6. Unscheduled Visits As appropriate, assessments at any unscheduled visit should follow the assessments at the closest weekly/monthly/quarterly visit. 6.2. Efficacy Assessments Signal response for each a priori statistically defined clinical outcome (ORR per RECIST 1.1) for all patients enrolled in the solid tumor arms of the study or other appropriate instruments scales, such as attainment of morphologic CR in patients enrolled in the AML arm. In addition to RECIST 1.1, all scans will be read according to iRECIST immune response consensus guideline (Seymour et al, 2017) to ensure that patients are not discontinued from therapy due to the phenomenon of tumor “pseudoprogression”, and clinical decisions will be based on iRECIST ( Hodi et al, 2016). ORR per iRECIST will be an exploratory endpoint of this study. SELLAS Life Sciences Group Galinpepimut -S Protocol : SLS17 -201/ MK3475 -770 Protocol v1.1 (Amendment 1.0) 12 April 2019 Page 188 6.3. Exploratory Assessments Assessment of tumor response in solid tumor patients by iRECIST, as well as estimation of the rate of achievement of MRD negativity in AML patients are exploratory endpoints in this study. All patients will be followed and assessed for PFS and OS, as per the schedule of assessments and using the ITT principle. As an exploratory evaluation, this study will assess the effect of the study treatment on readouts of immunologic tests in PB samples (see below), as well as presence and density of immune cell infiltrates within the tumor stroma (or BM in AML patients) using at least one post-therapy tumor biopsy (and comparing the findings with those at baseline, i.e., prior to initiation of treatment). In more detail: In peripheral blood: The following parameters will be tested: • Galinpepimut-S -relevant immune resonse-relevant: • WT1 peptide--specific CD8 and CD4 cell frequencies: o Cell frequencies (absolute cell abundance/numbers/microliter of blood) of host CD8 and CD4 cells that react with increased production of intracellular interferon- g as detected by intracellular cytokine staining (ICS) after ex vivo re - stimulation (Pinella-Ibarz et al, 2006; Gomez-Nunez et al, 2006; Maslak et al, 2010) with the following peptides: • WT1A1 (heteroclitic) • WT1A (cognate native of the one above) SELLAS Life Sciences Group Galinpepimut -S Protocol : SLS17 -201/ MK3475 -770 Protocol v1.1 (Amendment 1.0) 12 April 2019 Page 189 • 122A1 (heteroclitic) • 122A (cognate native of the one above) • 331 (native) • 427 (native) • Complete lymphocyte population panel (non-antigen-specific) Cell frequencies (absolute cell abundance/numbers/microliter of blood) - for each patient at each timepoint of collection, as follows: o Naïve T cells: CD45RA+CD45RO-CCR7+CD62L+CD57- o Central memory T cells: CD45RA -CD45RO+CCR7+CD62L+CD57- o Effector memory T cells: CD45RA -CD45RO+CCR7-CD62L-CD57+ o Total effector cells: CD45RA+CD45RO-CCR7-CD62L-CD57+ o Tregs: FoxP3+, CD25+, PD1, ICOS o Myeloid-derived suppressor cells (MDSC’s): o PMN-MDSC’s: CD14-CD11b+CD15+(or CD66b+) and o M-MDSC’s: CD11b+CD14+HLA-DRlow/−CD15− § Thus, the following antibody “gates” would have to be utilized in methodology selected (see Laboratory Manual): CD3, CD4, CD8, CD45RA or CD45RO, CD57, and CCR7 or CD62L or CD27, FoxP3, CD25, PD1, ICOS, CD14, CD11b, CD15; HLA-DR • In tumoral biopsy samples (TBx): SELLAS Life Sciences Group Galinpepimut -S Protocol : SLS17 -201/ MK3475 -770 Protocol v1.1 (Amendment 1.0) 12 April 2019 Page 190 o Galinpepimut-S -relevant o The following parameters will be tested: • Intratumoral CD8 and CD4 (cells within tumor stroma versus surrounding the tumor proper) (Arlen and Arlen, 2013) • MDSC, T-regulatory cells (Treg), and tumor-associated macrophages (TAMs) General (non-antigen-specific) immunodynamics o PDL1 expression and Interferon- g tissue inflammatory gene expression ‘signature’ assessment Genetic (DNA) analyses o The application of new technologies, such as next generation sequencing, has provided scientists the opportunity to identify tumor -specific DNA changes (i.e., mutations, methylation status, microsatellite instability, etc.). Key molecular changes of interest to immune-oncology drug development include (for example) the mutational burden of tumors and the clonality of T cells in the tumor microenvironment.