To determine if CPIs interfere with the establishment of B cell tolerance in humans, we tested the reactivity by ELISA of recombinant antibodies cloned from single CD19+CD27–CD10+IgMhiCD21lo new emigrant/transitional and CD19+CD27–CD10–IgM+CD21+ mature naive B cells isolated from frozen PBMCs of 4 patients with cancer before and after treatment with CPI. The gene discussed is CD19; the disease is cancer.