Since the transient production of autoreactive B cells induced by anti–CTLA-4 and anti–PD-1 combination therapy correlates with increased antitumor responses but also elevated risk of irAE, we intended to further characterize the reactivity of the recombinant antibodies cloned from single mature naive B cells isolated from patients with cancer at the 3 analyzed time points using Rapid Extracellular Antigen Profiling (REAP). The gene discussed is CTLA4; the disease is cancer.