CD19 and precursor B-cell acute lymphoblastic leukemia: However, CD19 loss, a well-described mechanism occurring in 30–70% of B-cell acute lymphoblastic leukemia (B-ALL) [1–3] and in 20–30% of B-cell non-Hodgkin lymphoma (B-NHL) cases [4–6] following CD19 CAR-T cell therapy, contributes to relapse and treatment failure.