ATM and mantle cell lymphoma: Importantly, using a PDX model generated from a patient with MCL who had ATM mutations and deletion of exon 7 in the TP53 at diagnosis and relapsed after CD19-directed CAR T-cell therapy, we observed that PRMT5 inhibitor treatment markedly attenuated the tumor growth (Fig. 5m, n), with decreased methylation of PRMT5 substrate histone H4R3me2s (Fig. 5o).