Combined effects of acyclovir and human interferon-alpha on herpes simplex virus replication in cultured neural cells

The combined effects of Acyclovir [9-(2'-hydroxyethoxymethyl)guanine; ACV] and human interferon-alpha (IFN-alpha) on replication of the herpes simplex virus type I (HSV-1) were determined in human neural cell lines, neuroblastoma (IMR), glioblastoma (118MGC), and glioma (U251MG). HSV-1 grew well in all these cells, with final yields of more than 1 x 10(6) PFU/ml. In terms of virus-yield reduction, ACV was found to be highly effective in IMR, moderately effective in U251MG, but ineffective in 118MGC. By contrast, IFN-alpha reduced the virus yield significantly in 118MGC and in U251MG, but did not in IMR. Combined application of ACV and IFN-alpha strongly inhibited the virus replication in all three cell lines with various degrees of synergism or additive effect. These results were also confirmed by immunofluorescent examinations. The sensitivity of HSV-1 to ACV or IFN-alpha was found to be different among the three different cell types. By combining the two agents, the virus growth was strongly suppressed in all the cells. These results suggest the importance of combination therapy for severe type of herpes simplex encephalitis in clinical practice.