Proportions of IFNγ+ IL-17− CD4+ T (Th1) cells were similar between the two groups, whereas IFNγ− IL-17+ CD4+ T (Th17) cells were enriched in the combined ICI arthritis group (% within CD4+ T cells; PD-1 inhibitor arthritis vs. combined ICI arthritis; 0.79 ± 0.83 vs. 1.89 ± 0.64; P = 0.04). Here, CD4 is linked to arthritic joint disease.