SEMA4D and plasma cell myeloma: After incubation for 24 and 48 h with stromal cell line HS5 (Sema4D and Plexin-B1 levels in the HS5 supernatant were not detectable), there was no alteration in the Sema4D levels of the supernatants of both the myeloma and the ovarian cancer cell lines (Fig. 2a), while there was a 5-fold to 8-fold increase in the Plexin-B1 levels in all studied cell lines except for SKOV3 cell line, where no alteration was noted (Fig. 2b).