Inclusion Criteria:  Participants must have a histologically or cytologically confirmed diagnosis of unresectable or metastatic melanoma of cutaneous, acral or mucosal subtype Availability of a fresh tumour biopsy taken at screening Patient must have received at least 1 prior immunotherapy (anti-PD-(L)1 ± anti-CTLA-4) for a minimum of 6 weeks Patients must have confirmed progression during treatment with a PD-(L)1 inhibitor +/- a CTLA 4 inhibitor The interval between the last dose of anti-PD-(L)1, and the first dose of the study regimen must be a minimum of 14 days Measurable disease by RECIST 1.1. Patients must have a life expectancy ≥3 months from proposed first dose date. Biopsy Sub-study: Consent to the provision of 3 mandatory tumour biopsies.  Exclusion Criteria:  Patients must not have experienced a toxicity that led to permanent discontinuation of prior checkpoint inhibitors (CPI) treatment. History of another primary malignancy except for malignancy treated with curative intent with no known active disease ≥ 3 years before the first dose of study treatment Uveal melanoma Must not have experienced a Grade ≥ 3 immune-related AE or an immune-related neurologic or ocular AE of any grade while receiving prior immunotherapy History of organ transplant that requires use of immunosuppressive medications Inadequate bone marrow and impaired hepatic or renal function Known active hepatitis infection, positive hepatitis C virus antibody, hepatitis B virus (HBV) surface antigen or HBV core antibody (anti-HBc), at screening Patients with confirmed COVID-19 infection by polymearse chain reaction test who have not made a full recovery.