A new study from the laboratory of Elizabeth Connick at the University of Colorado takes a detailed look at HIV replication in activated T cells. The study demonstrates that the chemokine receptor CCR5 is highly expressed by CD4 T cells displaying dual activation markers, HLA-DR and CD38, and that these cells are the major source of virus in lymph node samples from infected individuals. Importantly, there were differences observed between viral replication studied in lab culture conditions (in vitro) compared to the lymph node samples: the bulk of the CD4 cells replicating HIV in vitro were CD38+ but lacked HLA-DR and did not preferentially express CCR5.
The researchers also extend the findings of prior studies suggesting that CD4 downregulation is common among activated, HIV-infected cells. The DR+CD38+ T cells could be sorted into the following subsets:
- CD4-CD8- T cells (contributing a median of 48% of the total HIV RNA copies detected)
- CD4+CD8- T cells (median HIV RNA copies, 15%)
- CD4+CD8+ T cells (median HIV RNA copies, 29%)
- CD4-CD8+ T cells (HIV RNA copies, 8%)
Thus the bulk of HIV RNA in the lymph node samples was coming from cells that had downregulated their CD4 receptors, similar to the previously reported results obtained from the blood of untreated HIV-positive individuals. CD4 cells co-expressing CD8 are an unusual subset and the authors note they need further study; whether the observed CD8 expression is stable or a transient activation-related phenomena is unclear. The amount of HIV RNA produced by each of the DR+CD38+ T cell subsets correlated with the amount of CCR5 they expressed.
The importance of CCR5 expression in facilitating viral replication is also underscored by a recent Nature Medicine paper from Miko Paiardini and colleagues. The researchers document that non-pathogenic SIV infection of sooty mangabeys is associated with greatly reduced CCR5 expression on long-lived central memory CD4 T cells. A consequence of the reduced CCR5 expression is that the amount of SIV found in central memory CD4 T cells in sooty mangabeys is a log lower than in rhesus macaques, whereas there is no significant difference when SIV infection of short-lived effector memory CD4 T cells is compared. The authors argue that this sparing of central memory CD4 T cell allows sooty mangabeys to co-exist peacefully with SIV, because the short-lived effector memory CD4 T cells the virus does infect are relatively dispensable.
JVI Accepts, published online ahead of print on 3 August 2011
J. Virol. doi:10.1128/JVI.02529-10
Amie L. Meditz1, Michelle K. Haas1, Joy M. Folkvord1, Kelsey Melander1, Russ Young1, Martin McCarter3, Samantha MaWhinney4, Thomas B. Campbell1, Yolanda Lie5, Eoin Coakley5, David N. Levy7, and Elizabeth Connick1
1 Division of Infectious Diseases, Department of Medicine, University of Colorado Denver, Aurora, CO
3 Department of Surgery, University of Colorado Denver, Aurora, CO
4 Department of Biostatistics and Informatics, University of Colorado Denver, Aurora, CO
5 Monogram Biosciences, South San Francisco, CA
7 New York University, College of Dentistry, New York City, NY
Percentages of activated T-cells correlate with HIV-1 disease progression, but underlying mechanisms are not fully understood. We hypothesized that HLA-DR+CD38+ (DR+38+) CD4+ T-cells produce the majority of HIV-1 due to elevated expression of CCR5 and CXCR4. In PHA-stimulated CD8-depleted PBMC infected with HIV-1 GFP reporter viruses, DR-38+ T-cells constituted the majority of R5-tropic (median, 62%) and X4-tropic HIV-1-producing cells (median, 61%), although cell surface CCR5 and CXCR4 were not elevated on this subset. In lymph nodes from untreated individuals infected with R5-tropic HIV-1, percentages of CCR5+ cells were elevated in DR+38+CD4+ T-cells (median, 36.4%) compared to other CD4+ T-cell subsets (median, DR-38- 5.7%; DR+38- 19.4%; DR-38+ 7.6%; n=18; p<0.001). In sorted CD8- lymph node T-cells, median HIV-1 RNA copies/105 cells was higher for DR+38+ (1.8x106) compared to DR-38- (0.007x106), DR-38+ (0.064x106), and DR+38- (0.18x106) subsets (n=8; p<0.001 for all). After adjusting for percentages of subsets, a median of 87% of viral RNA was harbored by DR+38+ cells. Percentages of CCR5+ CD4+ T-cells and concentrations of CCR5 molecules among subsets predicted HIV-1 RNA levels among CD8- DR/38 subsets (p<0.001 for both). Median HIV-1 DNA copies/105 cells was higher in DR+38+ (5, 360) compared to DR-38- (906), DR-38+ (814), and DR+38- (1, 984) subsets (n=7, p<=0.031). Thus, DR+38+CD4+ T-cells in lymph nodes have elevated CCR5 expression, are highly susceptible to infection with R5-tropic virus, and produce the majority of R5-tropic HIV-1. PBMC assays failed to recapitulate in vivo findings, suggesting limited utility. Strategies to reduce numbers of DR+38+CD4+ T-cells may substantially inhibit HIV-1 replication.
Nat Med. 2011 Jun 26;17(7):830-6. doi: 10.1038/nm.2395.
Paiardini M, Cervasi B, Reyes-Aviles E, Micci L, Ortiz AM, Chahroudi A, Vinton C, Gordon SN, Bosinger SE, Francella N, Hallberg PL, Cramer E, Schlub T, Chan ML, Riddick NE, Collman RG, Apetrei C, Pandrea I, Else J, Munch J, Kirchhoff F, Davenport MP, Brenchley JM, Silvestri G.
Naturally simian immunodeficiency virus (SIV)-infected sooty mangabeys do not progress to AIDS despite high-level virus replication. We previously showed that the fraction of CD4(+)CCR5(+) T cells is lower in sooty mangabeys compared to humans and macaques. Here we found that, after in vitro stimulation, sooty mangabey CD4(+) T cells fail to upregulate CCR5 and that this phenomenon is more pronounced in CD4(+) central memory T cells (T(CM) cells). CD4(+) T cell activation was similarly uncoupled from CCR5 expression in sooty mangabeys in vivo during acute SIV infection and the homeostatic proliferation that follows antibody-mediated CD4(+) T cell depletion. Sooty mangabey CD4(+) T(CM) cells that express low amounts of CCR5 showed reduced susceptibility to SIV infection both in vivo and in vitro when compared to CD4(+) T(CM) cells of rhesus macaques. These data suggest that low CCR5 expression on sooty mangabey CD4(+) T cells favors the preservation of CD4(+) T cell homeostasis and promotes an AIDS-free status by protecting CD4(+) T(CM) cells from direct virus infection.