Typical comet images from plasma cells treated ex vivo with melphalan.

After irradiation (10 Gy) of nondrug-treated plasma cells, distinct comets were observed (B) when compared with nondrug-treated unirradiated plasma cells (A). After treatment with 50 μM melphalan for 1 hour followed by 16 hours drug-free after incubation, no DNA single strand breaks were observed (C). After irradiation of drug-treated plasma cells, comet tails were visible but with decreased length and intensity because of the presence of melphalan-induced ICL (D). All images stained with propidium iodide. Original magnification, × 20.