8F4 inhibits CFU-L from AML patients, but does not inhibit CFU-L from ALL patients or CFU-E, BFU-E, CFU-GM, and CFU-GEMM from umbilical cord blood and normal bone marrow. (A) CFU-L inhibition by 8F4 from patients AML1, AML7, AML9 (see patient characteristics in Table 1). 8F4 inhibited day-10 CFU-L from AML1 (AML-M1) by 33% compared with the isotype control (P = .004). Similarly, 8F4 inhibited day 10 CFU-L from AML7 (AML-M7) by 44% (P = .03) and AML9 (AML-M1) by 41% (P = .008), respectively. 8F4 did not inhibit CFU-L from patient ALL1. (B) 8F4 had no effect on CFU-E, BFU-E, CFU-GM, or CFU-GEMM from HLA-A2⁺ umbilical cord blood units. The day-14 CFU-E count was not significantly different between 8F4- and isotype-treated mononuclear cells; results were similar for BFU-E, CFU-GM, and CFU-GEMM. A representative experiment of 3 performed with independent cord blood units is shown. (C) 8F4 had no effect on CFU-E, BFU-E, CFU-GM, or CFU-GEMM from fresh HLA-A2⁺ normal bone marrow. The day-14 CFU-E count was not significantly different between 8F4- and isotype-treated mononuclear cells; results were similar for BFU-E, CFU-GM, and CFU-GEMM. (A-C) Data represent mean colony counts ± SEM. (D) 8F4 inhibits CFU-L from AML1, but not normal progenitors from HLA-A2⁺ individual cord blood units (n = 5) in the presence of added rabbit complement. Data represent mean percent colony inhibition calculated for 5 individual cord blood units ± SEM. (A-D) Assays were performed in duplicate.