Hybridoma and murine plasmacytoma cell lines. As for CHO cells, plasmacytoma and hybridoma cells produce IAPs and C-type particles (Table VI) (Spriggs and Krueger, 1979; Weiss, 1982) . As for CHO IAPs, hybridoma IAPs stay inside the cells and are noninfectious because they are devoid of intact open reading frames. However, unlike CHO C-type retroviral particles, hybridoma C-type particles have the ability to replicate in several different cell lines including a small number of human cell lines (lung fibroblasts, RD cells (Weiss, 1982; Levy, 1983; Adamson, 1998) ).