Pancreatic islet tumors of RIP-Tag2 mice perfused with PBS after anesthesia and were removed, weighed, and digested in collagenase II and IV solution (625U/ml, Gibco) with DNase (60 U/ml, Roche), followed by erythrocyte lysis (24 (link)). Dissociated cells were counted and stained for flow cytometric assessment of CD4+, CD8+, Foxp3+, and NK1.1+ cells by FACS (BD LSR Fortessa™) and analyzed with FlowJo software (8.8.6 and X) (details in Supplementary Methods).