Treatment of NK cells with 5E6 F(ab′)₂.

Treatment of NK cells with 5E6 F(ab′)₂ results in decreased tumor growth in vitro. Various numbers of B6 SCID NK cells activated with rhIL-2 for 5 to 7 days were plated in U-bottom 96-well microtiter plates at 50 μL per well and pretreated with media alone (■) or 25 μg/mL F(ab′)₂ fragments of normal mouse IgG (NMG) (▨), 5E6 (Ly49C and I) (▪), or 4D11 (Ly49G2) (░) for 2 to 3 hours at 37°C. Then 100, 50, or 25 C1498, EL4, or P815 cells, respectively, were added at 50 μL per well, and the cells were cocultured for 48 hours. As controls, tumor cells were cultured alone. After the co-incubation, the cells were transferred into a semisolid matrix and cultured for 5 to 7 days for quantification of leukemic cell colonies. (A) C1498 (H2^b) cells at NK-to-tumor ratio of 2:1. (B) EL4 (H2^b) at NK-to-tumor ratio of 10:1. (C) P815 (H2^d) at NK-to-tumor ratio of 100:1. Data from a representative of 3 independent experiments are shown as a percentage of control cells, where tumor growth in the absence of NK and the antibody is used as 100%. The stars indicate significant differences in 5E6 or 4D11 F(ab′)₂–treated groups compared with NMG controls as determined by Studentt test.