Neoadjuvant and Adjuvant Anti-PD1 or Combinations for Locoregionally Advanced Melanoma

Inclusion Criteria: * This study is divided into 2 sub-studies/parts designated Part 1 and Part 2 that will enroll in sequence starting with Part 1 followed by Part 2. In Part 2, Part 2 Cohort A and Part 2 Cohort B will enroll simultaneously. Inclusion criteria apply to Part 1 and Part 2 unless otherwise specified. * Voluntarily agree to participate by giving signed, dated, and written informed consent prior to any study-specific procedures. * 18 years of age or older * Histologic diagnosis of melanoma (cutaneous, acral, mucosal or unknown primary) belonging to the following American Joint Committee on Cancer (AJCC) 8th edition TNM stages (Tx or T1-4) and (N1b, N1c, N2b, N2c, N3b or N3c) and/or (M1a). * Requirements for prior systemic therapy for melanoma are as follows: 1. Sub-study Part 1: No prior systemic therapy for melanoma (N=30). 2. Sub-study Part 2 Cohort A: No prior systemic therapy for melanoma (N=20) 3. Sub-study Part 2 Cohort B: Locoregionally advanced melanoma that is refractory to systemic adjuvant therapy (anti-PD1-based or BRAF-MEK inhibitors) (N=40). This excludes patients who previously received adjuvant or neoadjuvant anti-PD1 plus anti-LAG3 or anti-PD1 plus anti-CTLA4. Participants who experienced progression or recurrence after anti-PD1 as monotherapy or other combinations or after BRAF-MEK inhibition would be eligible. Participants who have previously experienced prior high-grade (grade 3 or 4 by CTCAE criteria) immune related adverse events with immune checkpoint inhibitors are not eligible. * Must be considered surgically operable and may present as any of the following groups: 1. Primary melanoma with clinically apparent regional lymph node metastases, confirmed by pathological diagnosis. 2. Clinically detected recurrence of melanoma at regional lymph node basin(s), confirmed by pathological diagnosis. 3. Clinically or histologically detected primary melanoma involving multiple regional nodal groups, confirmed by pathological diagnosis. 4. Clinically detected single site of nodal metastatic melanoma arising from an unknown primary, confirmed by pathological diagnosis. 5. Participants with in-transit or satellite metastases with or without lymph node involvement are allowed if they are considered surgically resectable at Screening by the treating surgical oncologist. 6. Participants with distant cutaneous/subcutaneous, soft tissue or nodal metastases with or without regional lymph node involvement are allowed if they are considered potentially surgically resectable and can be biopsied at Screening by the treating surgical oncologist. Elevated LDH is not an exclusion. 7. Elevated LDH is not an exclusion. * Participants are eligible for this study either at presentation for primary melanoma with concurrent regional nodal and/or in-transit or distant metastasis, or at the time of clinically detected nodal, in transit, or distant recurrence. * Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1. * Adequate organ function within 28 days of Cycle 1 Day 1 (C1D1) * Participants must provide a sufficient and adequate formalin-fixed paraffin-embedded (FFPE) tumor tissue sample from the most recent biopsy of a tumor lesion, obtained within 90 days from signing informed consent form (ICF). If recent tumor tissue is unavailable or inadequate, a fresh biopsy will be required, unless the principal investigator agrees that it is not safe/feasible. * Participants must be evaluated by standard-of-care full body imaging studies, the choice of which is decided by the treating physician investigator. * Women of childbearing potential (WOCBP) must have a negative urine or serum pregnancy test at screening (within 72 hours of first dose of study medication) in accordance with the standard of care for WOCBP. * WOCBP must agree to use highly effective contraceptive measures starting with the screening visit through 5 months after the last dose of study treatment. Highly effective contraception is as stipulated in national or local guidelines. * Male participants with a female partner(s) of childbearing potential must agree to use highly effective contraceptive measures throughout the study starting with the screening visit through 5 months after the last dose of study treatment is received. Males with pregnant partners must agree to use a condom; no additional method of contraception is required for the pregnant partner. * Willing and able to comply with the requirements of the protocol. Exclusion Criteria: * Pregnancy or lactation. * Treatment with another investigational drug or other systemic intervention for melanoma within 4 weeks of initiation of study drugs. Patients must not have radiotherapy within the preceding 2 weeks. Patients must have recovered from adverse events due to agents administered more than 4 weeks earlier. * Participants must be at least 4 weeks from major surgery and have fully recovered from any effects of surgery and be free of significant detectable infection. * Ocular or uveal melanoma. * Bowel obstruction or impending bowel obstruction within the past 3 months. * Clinically significant (i.e., active) cardiovascular disease: cerebral vascular accident/stroke or myocardial infarction within 6 months of enrollment, unstable angina, congestive heart failure or serious uncontrolled cardiac arrhythmia requiring medication. * Active or history of brain metastases or leptomeningeal metastases. * Concurrent malignancy (present during screening) requiring treatment or history of prior malignancy active within 2 years prior to the first dose of study treatment, i.e., patients with a history of prior malignancy are eligible if treatment was completed at least 2 years before the first dose of study treatment and the patient has no evidence of disease. Participants with history of prior early-stage basal/squamous cell skin cancer, low-risk prostate cancer eligible for active surveillance or noninvasive or in situ cancers wh