5.2.4. Pembrolizumab Treatment for pembrolizumab is outlined below in Table 2. Table 2 Treatment with Pembrolizumab (irrespective of whether it is administered alone or concomitantly with galinpepimut-S) Drug Dose/Potency Dose Frequency Route of Administration Regimen Use Pembrolizumab 200 mg Every 3 weeks Intravenous Day 1 of each cycle (3 week cycles) and begins at Week 6 Experimental SELLAS Life Sciences Group Galinpepimut -S Protocol : SLS17 -201/MK3475 -770 Protocol v1.1 (Amendment 1.0) 12 April 2019 Page 136 Pembrolizumab will be administered as a dose of 200 mg using a 30-minute IV infusion. Sites should make every effort to target infusion timing to be as cl ose to 30 minutes as possible. However, given the variability of infusion pumps from site to site, a window between -5 minutes and +10 minutes is permitted (i.e., infusion time is 30 minutes -5 min/+10 min). The Pharmacy Manual contains specific instructions for the preparation of the pembrolizumab infusion and administration of infusion solution. Patients can receive up to 35 treatments (approximately 2 years) with pembrolizumab. During that time, patients may continue until disease progression, unacceptable toxicity, withdrawal of consent, physician's decision to stop therapy for the patient, or Sponsor’s decision to terminate the study. Discontinuation of treatment may be considered for patients who have attained a confirmed CR (either solid tumors or AML, using the corresponding response definitions), as follows: Such patients would have attained CR after having been treated for at least 10 cycles of galinpepimut-S, i.e., at least 30 weeks: 2 cycles of galinpepimut-S monotherapy (6 weeks) followed by 9 cycles of pembrolizumab (an additional 24 weeks). Such patients in CR should also receive 2-additional cycles of the combination (2 doses of pembrolizumab and galinpepimut-S [until Week 36]) beyond the date when the initial CR was declared, so that at least 12 of the total 16 (75%) planned doses of galinpepimut-S would have been administered. At that time, 12 out of a planned total of 36 treatments (2 years) with pembrolizumab (corresponding to approximately 33% of the total planned pembrolizumab treatments). Note: The number of treatment administrations is calculated starting with the first dose of galinpepimut-S. SELLAS Life Sciences Group Galinpepimut -S Protocol : SLS17 -201/MK3475 -770 Protocol v1.1 (Amendment 1.0) 12 April 2019 Page 137 5.3. Identity of Investigational Drug Product Table 3 provides a description for each of the investigational products . Table 3 Description of Investigational Products Product Supplied as: Galinpepimut -S 0.8 mg sterile, white preservative -free powder filled into a 2 -mL colorless glass vial provided by the sponsor. Lyophilized galinpepimut -S requires reconstitution with sterile water (not provided by the sponsor) Montanide ISA 51 VG 3-mL amber glass vial provided by the sponsor Sargramostim (GM -CSF) 250-µg sterile, white, preservative -free powder in a single -use vial provided by the sponsor. Lyophilized sa rgramostim requires reconstitution with sterile water (not provided by the sponsor) Pembrolizumab Solution for infusion is supplied by the sponsor as 100 mg/vial liquid DP (manufactured using the fully formulated DS with L -histidine as a buffering agent, polysorbate 80 as a surfactant, and sucrose as a stabilizer/tonicity modifier) in a s ingle use glass vial (will be provided by Merck) . Abbreviation s: GM -CSF, granulocyte -macrophage colony -stimulating factor ; USP, United States Pharmacopeia. 5.3.1. Galinpepimut -S Galinpepimut-S is a lyophilized preparation of 4 different WT1-derived synthetic analog peptides considered as a multicomponent single drug product. Each of the 4 peptides will be supplied at a concentration of 0.2 mg/vial. A fter reconstitution with 0.6 mL SWFI, each peptide will be at a concentration of 0.4 mg/mL (400 μg/mL of each peptide) combined in a single sterile solution (after reconstitution into liquid/soluble form) in a buffer consisting of SELLAS Life Sciences Group Galinpepimut -S Protocol : SLS17 -201/MK3475 -770 Protocol v1.1 (Amendment 1.0) 12 April 2019 Page 138 10 mM histidine, pH 6.0 + 0.05% EDTA. As galinpepimut-S Drug Product will comprise 50% (0.5 mL) of the study treatment injection administered, with the other 50% of the total injectate volume being Montanide, the actual dose of each peptide is 200 μg per inoculation (with the total 4 active peptides equaling in weight 800 μg per inoculation). The peptides include 1 WT1-derived peptide (A1) to stimulate CD8+ responses , 2 WT1 long peptides (WT1-427 L, WT1-331 L) to stimulate CD4+ responses, and 1 modified peptide (WT1-122A1 L) that is able to stimulate both CD4+ and CD8+ cells. The WT1-A1 and WT1-122A1 L contain a mutated aminoacid (aa) residue (R126Y), and are, therefore, heteroclitic. The sequence for the heteroclitic WT1-A1 peptide is embedded within the sequence of the longer WT1-122A1 L peptide. The structural formulas (aa sequences) of the vaccine administered are depicted in Table 4. Table 4 Structural Formula of Galinpepimut-S Abbreviations: DR, D-related; HLA, human leukocyte antigen; WT1, Wilms’ tumor 1 antigen. SELLAS Life Sciences Group Galinpepimut -S Protocol : SLS17 -201/MK3475 -770 Protocol v1.1 (Amendment 1.0) 12 April 2019 Page 139 Peptide abbreviations: A, alanine; C, cysteine; D, aspartic acid; E, glutamic acid; F, phenylalanine; G, glycine; H, histidine; K, lysine; L, leucine; M, methionine; N, asparagine; P, proline; Q, glutamine; R, arginine; S, serine; T, threonine; V, valine; Y, tyrosine. *Designates sing le amino acid substitution (R>Y) by deliberately designed mutations in the heteroclitic peptides The Drug Substance for the 4 peptides are manufactured at Polypeptide Laboratories, Inc. (Torrance, CA, USA). The lyophilization process, manufacturing of Drug Product (API) and sterile fill and finish under Good Manufacturing Practice conditions are performed by Corden Pharma S.p.A. (Caponago, Italy). Each lot of the lyophilized peptide powder are tested for physicochemical stability, sterility, and API content at PPD GMP Laboratories, Inc. (Middleton, WI, USA). Galinpepimut-S is considered as a multicomponent single drug product comprised of 4 peptides (described above) in a sterile lyophilized powder containing 0.8 mg peptides. Galinpepimut-S will be provided as a sterile, white, preservative-free powder filled into a 2 mL vial, for reconstitution with 0.6 mL SWFI. After reconstitution with SWFI, the peptides will be in a buffer of 10 mM histidine, pH 6.0 + 0.05% EDTA . Galinpepimut-S will be mixed in a water in oil emulsion with the oily adjuvant Montanide at a 1:1 ratio. The resulting final emulsion, which is administered as study treatment, will also be referred to as galinpepimut-S for practical product administration purposes in this pro tocol. The total amount of the finished product is 0.96 mg (overfill of 20%) filled into a 2-mL colorless glass vial. The vial should be stored at the site at or below −20°C until use. 5.3.2. Montanide ISA 51 VG Montanide ISA 51 VG is an adjuvant (NSC # 737063) produced by SEPPIC, Inc. (Fairfield, NJ) under Good Manufacturing Practice and is composed of a light oil and a surfactant system designed to make a water-in-oil emulsion. Montanide ISA 51 VG has been clinically tested based on a vegetable grade formulation used to emulsify the peptides. Montanide ISA 51 VG has proved to be a very efficient adjuvant, activating the cellular and the humoral SELLAS Life Sciences Group Galinpepimut -S Protocol : SLS17 -201/MK3475 -770 Protocol v1.1 (Amendment 1.0) 12 April 2019 Page 140 immune response. Montanide ISA 51 VG has been administered to more than 10,000 patients throughout the world. Montanide is packaged in 3-mL amber glass vials. The adjuvant is stored between 15°C to 30°C and must not be frozen. 5.3.3. Sargramostim (GM -CSF) Sargramostim (GM-CSF) is manufactured by Partner Therapeutics, Inc. (Lexington, MA) , under Good Manufacturing Practices and is provided in lyophilized form as a 250-µg sterile, white, preservative-free powder that requires reconstitution with SWFI . GM-CSF must be stored at 2°C to 8°C. For this study, the vial of GM-CSF is intended for single-use only. 5.3.4. Pembrolizumab The pembrolizumab treatment to be used in this trial is outlined in Table 2 in Section 5.2.4. above.