Evidence for a post-entry barrier to R5 HIV-1 infection of CD4 memory T cells

Background: HIV-1 strains R5 and X4 can infect CD4 memory T cells in vivo. Anti-CD3/28 stimulation induces beta -chemokines and CCR5 down-regulation a nd renders these cells resistant to R5 HIV-1 infection. Here we describe an additional cellular mechanism that blocks productive R5 HIV-1 infection of CD4 memory T cells. Methods: Blood-derived CD4 memory T cells and CD4 T-cell clones were infect ed with primary R5 and X4 HIV-1 strains. Virus replication was correlated w ith CCR5 expression and beta -chemokine production. Virus entry and infecti vity were measured by PCR for early and late products of HIV reverse transc ription respectively. Results: R5 strains were up to 1000-fold less infectious than X4 viruses fo r CD4 memory T cells. This resistance was independent of CCR5 levels and of the Delta -32 mutation and the CCR2-V641/CCR5-59653T linked mutations. Blo cking endogenous beta -chemokines relieved minimally this restriction. At t he single cell level, CD4 memory cells were either permissive or non-permis sive for R5 HIV-1 infection. R5 HIV titre was up to 10-fold lower than X4 v irus titre even in a permissive clone. However, R5 viruses replicated as ef ficiently as X4 viruses in the permissive clone when neutralizing anti-beta chemokine antibodies were added. Non-permissive cells blocked a post-entry step of the virus life-cycle and expressed early but not late HIV transcri pts. Neutralizing anti-beta chemokine antibodies promoted R5 virus replicat ion marginally in the non-permissive clone. Conclusion: Some blood memory CD4 T cells retard R5 HIV-1 replication via e ndogenous beta -chemokines whereas others block productive R5 HIV-1 infecti on by an additional mechanism that interferes with a post-entry step of the virus life cycle. These natural barriers might contribute to lower pathoge nicity of R5 HIV-1 strains for CD4 memory T cells than X4 viruses that emer ge late in disease. (C) 2001 Lippincott Williams &Wilkins.