A Study of GV20-0251 Monotherapy and GV20-0251 in Combination with Pembrolizumab in Participants with Solid Tumor Malignancies

Inclusion Criteria:

1. Participants ≥18 years of age
2. Previously treated, histologically-confirmed advanced solid malignancy with progressive disease requiring therapy
3. Refractory or intolerant to standard therapy(ies)
4. Must have received, be not eligible or decline standard of care therapy
5. Participants must have measurable disease per Response Evaluation Criteria in Solid Tumors (RECIST version 1.1)
6. For participants who have received prior treatment with a checkpoint inhibitor there must be documented disease progression
7. ECOG performance status of 0 or 1
8. Life expectancy of ≥ 12 weeks in Parts A and C and ≥ 24 weeks in Parts B and D
9. Participants must be willing to provide fresh tumor biopsy (core biopsy) both pre-treatment (Parts A, B, C and D) and on-treatment (Parts A and B), if clinically feasible
10. Disease-free of active second/secondary or prior malignancies for ≥ 2 years
11. Laboratory test results within the required parameters
12. Women of child bearing potential (WOCBP) and men must agree to use adequate contraception
13. Parts B, C and D may include the following tumor types:

1. Endometrial carcinoma
2. Squamous head and neck carcinoma
3. Cutaneous melanoma
4. Non-small cell lung cancer
5. Proficient MMR (pMMR)/MSS adenocarcinoma of the colon or rectum (Parts C and D only)

Parts A, B, C and D Exclusion Criteria:

1. Participant with acute leukemia or CLL (Parts A and B only)
2. Participant with heart disease or unstable arrhythmia
3. Active, uncontrolled bacterial, viral, or fungal infections requiring systemic therapy
4. Participant has active autoimmune disease or other medical conditions requiring chronic systemic steroid or immunosuppressive therapy
5. History of major organ transplant
6. History of a bone marrow transplant
7. Symptomatic central nervous system (CNS) malignancy or metastasis
8. Serious nonmalignant disease
9. Pregnant or nursing women
10. Treatment with PD-1 and equivalent immune modulators or major surgery prior to the first dose of study medication
11. Participants who are currently receiving any other investigational agent or have received an investigational agent within 4 weeks prior to the first dose of study medication
12. Treatment with any anticancer treatments with 2-weeks prior to the first dose of study medication
13. Radiation for symptomatic lesions must have been completed prior to the first dose of study medication
14. Participants with liver metastases unless approved by the Sponsor
15. Any history of an immune related ≥ Grade 3 AE attributed to prior cancer immunotherapy
16. Has a known additional malignancy that is progressing or has required active treatment within the past 2 years from C1D1
17. Has received radiation therapy to the lung that is higher than 30 Gy within 6 months prior to C1D1 for NSCLC (Parts C and D only)
18. Has a known additional malignancy that is progressing or has required active treatment within the past 2 years from C1D1 (Parts C and D only)
19. Has severe hypersensitivity ( ≥ Grade 3) to Pembrolizumab and/or any of its excipients (Parts C and D only)
20. Has a history of (non-infectious) pneumonitis / interstitial lung disease that required steroids or has current pneumonitis / interstitial lung disease (Parts C and D only)
21. Has a condition, therapy, laboratory abnormality, or circumstance that could confound study results or interfere with full participation, making it unsuitable for the participant, as determined by the treating Investigator (Parts C and D only)
22. Active substance abuse