In vitro lymphotoxicity and selective T cell immunotoxicity of high doses of acyclovir and its derivatives in mice

The antiviral drug acyclovir [9-(2-hydroxyethoxymethyl)guanine (ACV)], its 7-isomer (7-ACV) and its two derivatives: N₂-acetyl ACV (ac-ACV) and N₂,O-diacetyl ACV (diac-ACV) were examined for their potential in vitro lymphotoxicity and in vivo immunotoxicity in mice. In vitro lymphotoxicity of ACV and its acetylated derivatives was low, whereas the 7-ACV isomer enhanced the in vitro cell proliferation in PHA-stimulated cultures. Addition of 2'-deoxyguanosine (dGuo) did not exhibit any inhibitory potential of ACV. However, reduction in the absolute number of CD³⁺, CD8⁺, and CD25⁺ cells, but not Ig⁺ cells, was noted at high concentrations of ACV and its derivatives, suggesting a selective T cell cytotoxicity. Similarly, the in vivo exposure revealed selective T cell immunotoxicity of ACV and its derivatives since the reduced number of Thy 1.2⁺ and CD8⁺ cells was not accompanied with any marked changes in the Ig⁺ population. The CD4⁺/CD8⁺ ratio was affected both in vitro and in vivo by high concentrations of ACV.