Phase 1b (dose-escalation): In the phase 1b/2 portion of this study, 12 patients will be enrolled in each dose cohort, with six patients administered omaveloxolone (RTA 408) plus ipilimumab and the remaining six administered rTA 408 plus nivolumab. Subsequent cohorts will assess escalating the doses of omaveloxolone (RTA 408) administered in combination with ipilimumab or nivolumab. Dose escalation decisions will be based on ongoing review of all available safety information for enrolled patients.