To assess the effect of monoclonal antibodies anti-CD20 (Rituximab) and anti-CD52 (Campath-1H) on the viability of B cells from patients with B cell chronic lymphocytic leukemia (B-CLL) in comparison with a cytotoxic drug fludarabine (Fluda), and to determine the influence of these agents on the expression of cell cycle regulatory proteins in vitro. B-CLL cells were incubated in vitro in the presence of Rituximab, Campath-1H, and Fluda. The viability of the cells was measured by MTT test

more »

... -dimethylthiazol-2-yl)-2,5-dyphenyltetrazolium bromide). Gel electrophoresis and Western blotting were used to determine the effect of these agents on the expression of cell cycle regulatory proteins in vitro. Both monoclonal antibodies, Rituximab and Campath-1H, were less toxic than Fluda to B-CLL cells. Combination of Campath-1H or Rituximab with Fluda did not have a stronger effect on the cells than Fluda alone. Both antibodies decreased the expression of p27 protein and increased the expression of p23; Fluda had a similar effect. The extent of cyclin D3 and cyclin E expression did not change significantly. The expression of cyclin D2 was slightly increased in the presence of Campath-1H, but in the presence of Rituximab it either decreased slightly or remained the same. Treatment of B-CLL cells with Fluda alone induced significant decrease in cyclin D2 expression. These results demonstrated that monoclonal antibodies Campath-1H and Rituximab antibodies, as well as a cytotoxic drug fludarabine, had cytotoxic effects on B-CLL cells. They most likely induce apoptosis of B-CLL cells, but their activity is mediated through different pathways.