While the addition of the DHFR mutant in tumor cells resulted in a pronounced reduction of toxicity (106% viable MV4-11mut cells vs. 65% parental, 10 μM MTX + LV), it was only marginally beneficial in CAR T cells (82% viable DHFR mutant vs. 70%, 10 μM MTX + LV). This evidence concerns the gene DHFR and neoplasm.