CD81 mediates cell adhesion and BMC in ALL. (A) CRISPR guide sequence within the targeted exon 3 of CD81 gene in Nalm6 is shown. The biallelic mutant clone had 4-bp insertion in 1 allele and 1-bp insertion in the other, each generating a premature stop codon. (B) Flow cytometry analysis of CD81 surface expression in WT and CD81KO Nalm6 cells. (C) Western blot analysis of CD81 in WT and CD81KO Nalm6 cell lysates. GAPDH was used as a loading control. (D) Bar graph showing the average percentage of Nalm6 cells bound to Saos-2 cells with respect to input. Data from 2 independent experiments in quadruplicates is plotted. Error bar signifies standard deviation of the mean. *P < .05. (E) Nalm6 cells were treated with Ara-C in both monoculture (mono) and coculture (co) with Saos-2 cells to determine IC₅₀s for calculation of Drug Resistance Index (DRI) from 3 independent experiments. The coculture curves for WT and CD81KO are shown for reference.