Cyclosporin A inhibits vaccinia virus replication in vitro

Summary The effect of the immune modulator, Cyclosporin A (CsA) on vaccinia virus replication has been examined in cell cultures. In the present study we report that CsA is anti-viral towards vaccinia virus. Viral yield was inhibited by more than 97% after 24 h postinfection in the presence of 16 µM to 40 µM CsA. An analysis of the infectious cycle in greater detail revealed that CsA did not effect the total level of [³⁵S] methionine incorporation into vaccinia infected cells. However, both early and late viral gene expression were inhibited by CsA. Late viral protein synthesis appeared to be more sensitive to the drug. At least one late viral polypeptide of approximately Mr 38 000 was virtually undetected up to 8 h postinfection in the presence of 40 µM CsA. Host protein synthesis which is normally inhibited by the virus was not turned off until very late in infection. Viral DNA replication was also inhibited by the addition of CsA at levels comparable to those observed for late protein synthesis.