We visualised T cells (CD3-positive) and CXCL9-positive macrophages along with beta cells (insulin-positive) and alpha cells (glucagon-positive) in the islets of a cancer patient who developed type 1 diabetes following anti-CTLA-4 antibody (ipilimumab) and anti-PD-1 antibody (nivolumab) combination therapy (Fig. 5). Here, CTLA4 is linked to type 1 diabetes mellitus.