• Diagnosis of histologically confirmed advanced or metastatic melanoma that has progressed after at least 12 weeks or a minimum of 2 doses of treatment with a standard of care PD1/PDL1 containing therapy (nivolumab, pembrolizumab, atezolizumab, or durvalumab).

• Age: ≥18 years of age

• Have an Eastern Cooperative Oncology Group Performance Status (ECOG) ≤ 2 at screening Form Arm 1 only: Patients must meet the eligibility criteria to undergo apheresis to obtain autlogous NK cells.

• For Arm 2 only: Patient must have an available allogeneic NK cell donor who meets the eligibility criteria.

• Adequate organ function as defined below:

‣ Total bilirubin \< 2 mg/dL

⁃ AST(SGOT)/ALT(SGPT) \< 3.0 x ULN

⁃ Creatinine within normal institutional limits OR creatinine clearance \> 40 mL/min/1.73 m\^2 by Cockcroft-Gault Formula

⁃ Oxygen saturation ≥ 90% on room air

⁃ Ejection fraction ≥ 45%

• Patients with a prior history of symptomatic CNS metastases must have received treatment and be neurologically stable for at least for 4 weeks and off anti-seizure medication and steroids for 7 days prior to initiation of LDC.

• Able to be off corticosteroids and any other immune suppressive medications for at least 14 days prior to apheresis or lymphodepletion and continuing until 30 days after the infusion of the ML NK cells. However, use of physiological dosing of corticosteroids (defined as ≤15mg prednisone or equivalent) is permitted if deemed medically necessary.

• Women of childbearing potential must have a negative pregnancy test within 28 days prior to study registration. Female and male patients (along with their female partners) must agree to use two forms of acceptable contraception, including one barrier method, throughout participation in the study and for at least 5 months after the last dose of relatlimab.

• Life expectancy \>12 weeks

• Ability to understand and willingness to sign an IRB approved written informed consent document