Fig. 4. Lenalidomide enhances the ADCC activities of anti-β₂M mAbs both in vitro and in vivo.

(A) Viability of lenalidomide-resistant U266/R10R and -sensitive U266 WT MM cells in culture with different concentrations of lenalidomide for 48 hours. (B) ADCC activity detected as apoptosis of lenalidomide-resistant U266/R10R and -sensitive U266 WT MM cells. The MM cells and normal PBMCs were first incubated separately with lenalidomide for 48 hours, followed by washing and incubating together with anti-β₂M mAbs for 4 hours. Controls included medium alone (control), lenalidomide alone, and ADCC without lenalidomide. An E:T ratio of 40:1 was used. CD138⁺ MM cell apoptosis was detected using Annexin V and PI staining. (C) Tumor burden of ARP-1 tumor-bearing SCID mice (n=5) treated with lenalidomide alone, anti-β₂M mAbs alone, or in combination. (D, E) In situ TUNEL assay was performed to detect cell apoptosis in the tumors of treated mice. Representative images were given in (D). Average numbers of apoptotic tumor cells from 6 randomly chosen fields were given in (E). Summarized data from three performed independent experiments are shown. *P < 0.05, **P < 0.01.