CD19 and acute lymphoblastic leukemia: Although CAR T-cell therapy has been shown to be highly effective in treating ALL and that two CD19-CAR T-cell therapies (tisagenlecleucel and Brexucabtagene autoleucel) have been approved by the FDA for the treatment of refractory or relapsed ALL, relapsing ALL-blasts with down-regulated or abrogated CD19 expression remain a critical barrier to maintaining permanent remissions [73, 74].