ERYTHROPOIETIN-LIKE ACTIVITY IN-VIVO OF THE FUSION PROTEIN RHLL-6 IL-2 (CH925)/

CH925 is a novel cytokine of a fusion protein interleukin-6 (IL-6)/IL- 2 exhibiting erythropoietin (Epo)-like effects in vivo and ex vivo, in addition to its enhanced effects compared to IL-2 and IL-6 reported b y us previously, which indicates its potential clinical use. Our prese nt study was undertaken to determine the Epo-like activity of CH925 in vivo. The reticulocyte response was observed in transfusion-induced p olycythemic mice by using flow cytometry with pyronin Y staining. On d ay 2 after injection of CH925, the average number of reticulocytes was 2.11% in the group given 250 mu g/kg/d and 1.01% for 100 mu g/kg/d. T he mean fluorescence intensity (MFI) also significantly increased. Lon gitudinal studies of CH925 were performed on days 2, 4, and 10, and re ticulocyte counts increased up to a peak on day 4. Activity of CH925 ( 100 mu g/kg/d) corresponds to 1 U of standard rhEpo in our study.