Inhibitory effect of anti-CD38 antibody is mediated by Fc portion. Cord blood (A) or AML (B) mononuclear cells were incubated with whole antibody or F(ab′)2 fragments of anti-CD38 antibody (clone AT13/5) before washing and injection into mice. After 6 weeks, the percentage of human cells in the bone marrow was determined. Horizontal bars represent mean engraftment percentage per condition. (A) A total of 5 × 106 cord blood cells were injected per mouse. There was no significant difference in engraftment between control and F(ab′)2 groups (P = .45), whereas there were significant differences between the anti-CD38 antibody and F(ab′)2 groups (P < .001). (B) A total of 6 × 106 AML cells (sample 4) were injected per mouse. There was a significant difference between anti-CD38 antibody and F(ab′)2 groups (P < .001).
