3. Has histologically or cytologically -confirmed advanced or metastatic solid tumors who have disease progression after treatment with available therapies for metastatic disease that are known to confer clinical benefit, or are intolerant to treatment, or refuse standard treatment in the context of the particular line of treatment defined in SELLAS Life Sciences Group Galinpepimut -S Protocol : SLS17 -201/MK3475 -770 Protocol v1.1 (Amendment 1.0) 12 April 2019 Page 117 this protocol (refer to #5 below) or, specifically for AML, demonstrate as their best observed response after 4 cycles of HMA therapy the status of “partial response” per European LeukemiaNet (ELN) criteria and meet the additional specified requirements for the cohort of the study they will enroll into. 4. All patients will be tested for WT1 expression via IHC in both their initial primary tumor and recent biopsy of metastatic disease at the time of screening for study entry, or, specifically for AML, leukemic blasts either in the BM or PB. Specifically: a. Testing of patient’s archived (paraffin embedded, unstained slides) as well as freshly biopsied tumor nodules prior to study entry must be positive for WT1 protein expression. b. WT1 expression: The IHC technique to be used for the detection of WT1 in tumor tissue (or AML blasts within the bone marrow - applicable only for subjects in the AML arm) is described in detail by Dupont et al. (Dupont et al, 2004) using the anti-WT1 monoclonal antibody H-1/ sc-393498 (Santa Cruz Biotechnology, Dallas, TX, USA). In more detail, formalin-fixed, paraffin- embedded tissue sections are subjected to immunohistochemical testing using the streptavidin-biotin method. WT1 is used at a dilution of 1:4,000. A heat-induced epitope retrieval system is used for the antibody, involving steam-heat incubation with citrate at pH 6 for 30 min at 97 oC. Human Wilms tumor or malignant pleural mesothelioma samples will used as a positive control for WT1, with appropriate negative controls. Positive WT1 nuclear staining is defined as the presence of any nuclear staining in >5% of tumor cells and positive WT1 cytoplasmic staining was defined as the presence of any cytoplasmic staining in >5% of tumor cells. WT1 expression is graded according to an adaptation of the German Immunoreactive Score (IRS) (Remmele and Stegner, 1986 & 1987). Briefly, the IRS assigns subscores for intensity of immunoreactivity (0–3) and distribution of immunoreactivity (0–4; based on percent positive cells within a cluster), which when multiplied, yield a product (IRS score, ranging from 0 to 12) that allows categorization of SELLAS Life Sciences Group Galinpepimut -S Protocol : SLS17 -201/MK3475 -770 Protocol v1.1 (Amendment 1.0) 12 April 2019 Page 118 weak, moderate, and strong immunoreactivity. For WT1, negat ive or weak immunoreactivity (scores 0–3) are considered negative, while moderate or strong immunoreactivity (scores 4–12) are considered positive. Assessment of all tumor/BM biopsies for WT1 expression using the German IRS assignment system will be performed centrally by an experienced Pathologist using a standardized form, which also depicts the IRS scale for ease of reference. This form is shows as Appendix 12.3 of this protocol. Due to essential non-expression of WT1 in normal tissues, the specificity for WT1 expression in tumors under study is essentially 100%. The sensitivity of the IHC assay is defined in relevant sections of the protocol for each tumor type under study, ranging from 40% in SCLC to >90% in AML cases. All above specimens will undergo central pathology review. 5. Patients may have received a specific maximum allowable number of prior lines of therapy for metastatic/advanced disease, as follows: a. CRC: 2 or 3 lines; b. OvC: 1 or 2 lines; c. SCLC: 1 line; d. TNBC: 1 line; and e. AML: 0 lines (allo-SCT-eligible status or patients with relapsed [2nd line] AML not allowed) 6. Patients should have experienced resolution of toxic effect(s) of the most recent prior chemotherapy to Grade 1 or less (except alopecia). If the patient received major surgery or radiation therapy of > 30 Gy, they must have recovered from the toxicity and/or complications from the intervention. 7. Specifically for patients in the AML arm, the following subject subgroups are eligible: a. Frontline (1 st line) patients treated with HMAs since their initial AML diagnosis b. Patients who have required cytoreductive therapy with hydroxyurea or leukapheresis at the time of their initial AML diagnosis, and who subsequently seamlessly transitioned to HMA therapy SELLAS Life Sciences Group Galinpepimut -S Protocol : SLS17 -201/MK3475 -770 Protocol v1.1 (Amendment 1.0) 12 April 2019 Page 119 c. Subjects who have experienced induction early failure after initial therapy with 1 - 2 cycles of a standard chemotherapy (“7+3” and similar regimens) and subsequently immediately treated with HMAs as long as such patients have achieved PR as their best ob servable response after 4 cycles of HMA therapy (per European LeukemiaNet [ELN] criteria). 8. AML patients should continue treatment with HMAs as long as they cannot achieve a response deeper than PR after the completion of administration of 4 cycles of HMAs. 9.