Inhibition of human immunodeficiency virus 1 (HIV-1) by variant B of human herpesvirus 6 (HHV-6).

Four HHV-6 strains were initially isolated during attempts to observe HIV-1 replication in cultured primary lymphocytes from 48 patients with AIDS. HHV-6 DNA from each strain was extracted from primary cell cultures and amplified using specific primers in a nested polymerase chain reaction (PCR) assay. All HHV-6 strains were classified as B variants by submitting the PCR products to the digestion of two restriction enzymes (Hind III and Bgl II). Since in primary cultures, the appearance of HHV-6 cytopathic effect was followed by a progressive reduction of HIV-1 replication, we tried to reproduce the observed inhibition in vitro. Two HHV-6 strains, used throughout the experiments, showed their ability to suppress HIV-1 replication when the viruses co-infected CD4+T lymphocyte cultures. While the intrinsic mechanism of this finding still remains unclear, the inhibition of HIV-1 replication was observed only when a high multiplicity of infection (m.o.i.) of HHV-6 and a low m.o.i. of HIV-1 were used in dually infected cell cultures. By using a semiquantitative determination of HIV-1 cDNA by PCR, it appears that the inhibition begins in infected cell cultures and, once established, does not allow any further HIV-1 replication.