CD39SP precede autoantibody production. Whole blood and sera were collected from young (aged 2-3 months) HOD⁺OTII⁺ mice before, during (3 and 7 days), and at the cessation of ICPi or PBS treatment (∼14 days); (A-C) representative flow plots (A) and frequency of CD39SP in peripheral whole blood (B) and RBC autoantibodies (C) in sera are shown at each time point. (D) Representative flow plots of FoxP3 and CD25 staining in CD3⁺CD4⁺CD45RA^– gated T cells isolated from human patients with AIHA (n = 9) and healthy volunteers (n = 15). Expression of CD39 and CD73 on gated FoxP3⁺ Tregs (red box) and on gated FoxP3^–CD25^– T cells (blue box) were shown. (E-F) Frequencies of CD39SP with phenotype CD4⁺CD39⁺CD73^–FoxP3^–CD25^– (E) and FoxP3⁺ Tregs (F) were detected in PBMCs from patients with AIHA (not treated with ICPi) and healthy volunteers. Age-matched healthy volunteers are colored blue. Data presented in panels A-C are cumulative from 4 to 5 independent experiments with 3 to 4 mice per group. Statistical significance was determined by Mann-Whitney test: ∗P < .05; ∗∗P < .01; ∗∗∗∗P < .0001.