R5 Human Immunodeficiency Virus Type 1 (HIV-1) Replicates More Efficiently in Primary CD4 ⁺ T-Cell Cultures Than X4 HIV-1

Abstract

In this report, we present evidence that R5 human immunodeficiency virus type 1 (HIV-1) replicates more efficiently in primary CD4؉ T cells than X4 HIV-1. By comparing CD3/CD28-costimulated CD4 ؉ T-cell cultures infected by several X4 and R5 HIV-1 strains, we determined that R5-infected CD4 ؉ T cells produce more virus over time than X4-infected CD4 ؉ T cells. In the first comparison, we found that more cells were infected by the X4-tropic strain LAI than by the R5-tropic strain JR-CSF and yet that higher levels of viral production were detected in the R5-infected cultures. The differential viral production was partially due to the severe cytopathic effects of the X4 virus. We also compared cultures infected with the isogenic HIV-1 strains NL4-3 (X4) and 49.5 (R5). We found that fewer cells were infected by the R5 strain, and yet similar levels of viral production were detected in both infected cultures. Cell death played less of a role in the differential viral production of these strains, as the cell viability remained comparable in both X4-and R5-infected cultures over time. The final comparison involved the primary R5-tropic isolate KP1 and the primary dual-tropic isolate KP2. Although both strains infected similar numbers of cells and induced comparable levels of cytopathicity, viral production was considerably higher in the R5-infected culture. In summary, these data demonstrate that R5 HIV-1 has an increased capacity to replicate in costimulated CD4؉ T cells compared to X4 HIV-1.Human immunodeficiency virus type 1 (HIV-1) infects cells by binding to the CD4 receptor and to one of several coreceptors expressed on the surface of target cells (2,13,15,16,18,26). The chemokine receptors CCR5 and CXCR4 serve as the major coreceptors for HIV-1, although several other chemokine receptors have been linked to minor HIV-1 coreceptor usage (2,8,15,18,32,52). Characteristically, non-syncytiuminducing (NSI) isolates utilize CCR5 as a coreceptor and are referred to as R5 strains (2, 14-16). R5 strains often represent the dominant viral population detected during the early stages of clinical HIV-1 infection (9,14,41,43,46,53). In contrast, syncytium-inducing (SI) isolates utilize CXCR4 as a coreceptor and are referred to as X4 strains (18,20,24,25,28,30,40,45,48). X4 strains are typically detected in the later stages of infection and are associated with rapid CD4 ϩ T-cell loss (11,14,24,25,46,48,49). Despite the link between X4 emergence and disease progression, approximately half of all individuals with AIDS continue to harbor predominantly R5 viruses, suggesting that CXCR4 coreceptor usage alone is not responsible for disease progression (9,43,46,53).Several mechanisms have been proposed to explain the R5 dominance of early HIV-1 infection. There is evidence that R5 strains may be transmitted at an increased frequency compared to X4 strains. For example, individuals that carry a 32-bp deletion mutation (⌬32) in the CCR5 gene are highly resistant to HIV-1 infection (10,33,38,44). Although these individuals are suscepti...

Enhanced Replication of R5 HIV-1 Over X4 HIV-1 in CD4+CCR5+CXCR4+ T Cells

“…As a function of time thereafter, CD4 + T cells in these cultures showed evidence of stimulation, expressing CXCR4 (98%), CCR5 (10%), and a number of activation markers (eg, 29% were positive for CD38 + and CD69 + ). 25 A comparable level of activation was seen in HLACs (ie, 20% of CD4 + T cells in HLACs were CD69 + [data not shown]). After 72 hours of stimulation, the cultures were thoroughly rinsed and then infected with X4 HIV-1 (NL4-3) or an R5 isolate (49-5) isogenic in the V3 loop at an moi of 0.001.…”

“…This study demonstrated that such cultures produced more virus over the course of a 10-day in vitro infection (as measured by p24 production in the supernatant) when infected by R5 as compared with X4 HIV-1, a difference in virus production that did not seem to be the result of enhanced X4 HIV-1 cytopathicity in vitro. 25 We have extended these observations in the current study using ex vivo lymphoid histoculture and a quantitative approach that assesses not simply p24 production but the production of infectious virions. We directly addressed the possibility that CD4+CCR5 + CXCR4 + T cells may produce a larger number of virions per infected cell after R5 HIV-1 infection than after X4 HIV-1 infection.…”

Human immunodeficiency virus type 1 (HIV-1) circulating recombinant form 02_AG (CRF02_AG) has a higher in vitro replicative capacity than its parental subtypes A and G

“…In the current study, the mono-infection assay showed a significantly higher in vitro replicative capacity of CRF02_AG compared to the parental subtypes A and G of 1.4 times based on p24 production and 1.4-1.9 times based on the mean RT activity at day 11 p.i. Monoinfection experiments are used widely to determine differences in in vitro replication between HIV-1 strains [Bleiber et al, 2001;Campbell et al, 2003;Schweighardt et al, 2004;van Opijnen et al, 2004]. Recently, virus competition assays have been employed more often since this technique allows for the detection of smaller differences in replication Arts, 2001, 2002] and these kinds of experiments need to be performed to confirm observations.…”

Humanized mice dually challenged with R5 and X4 HIV-1 show preferential R5 viremia and restricted X4 infection of CCR5+CD4+ T cells

“…Here, we found that both R5 and X4 HIV-1 were cytopathic, and that the cytopathic effects of X4 HIV-1 may be higher than those of R5 HIV-1 in vivo (as evidenced by the effects in dually challenged mice). It is possible that the potential replicative advantage that R5 HIV-1 holds over X4 HIV-1 [34,35] is due to the lower cytopathic effect of R5 HIV-1, such that R5 HIV-1 is able to propagate more readily than X4 HIV-1 in vivo. However, cytopathic effects alone do not fully explain the restricted infection of CCR5 þ CD4 þ T cells by X4 HIV-1 because this cell type was not selectively targeted and damaged by X4 HIV-1.…”

“…Some groups report that X4 HIV-1 is more cytopathic than R5 HIV-1 in vitro [35,36]. Indeed, X4 (or syncytiuminducing) virus was believed to be more cytopathic than R5 (or non-syncytium-inducing) virus in vivo [37e39], even though R5 HIV-1 is highly cytopathic to CCR5 þ CD4 þ T cells [40].…”