Effect of antibody on engraftment of human cells. Human mononuclear cells were incubated with either test antibody or isotype control before washing and transplantation into mice. After 6 weeks, the percentage of human cells in the bone marrow was determined. Horizontal bars represent mean engraftment percentage. (A) A total of 3.5 × 10⁶ cord blood mononuclear cells were injected per mouse. There was a significant difference between control and anti-CD34 antibody (P < .001) and anti-CD38 antibody (P < .001). (B) A total of 5 × 10⁶ AML cells (sample 1) were transplanted per mouse. Only anti-CD38 antibody significantly inhibited engraftment (P < .001). Blasts from sample 1 express CD13 and CD123 but lack CD34.