Raj Shankarappa

To understand the high variability of the asymptomatic interval between primary human immunodeficiency virus type 1 (HIV-1) infection and the development of AIDS, we studied the evolution of the C2-V5 region of the HIV-1 env gene and of T-cell subsets in nine men with a moderate or slow rate of disease progression. They were monitored from the time of seroconversion for a period of 6 to 12 years until the development of advanced disease in seven men. Based on the analysis of viral divergence from the founder strain, viral population diversity within sequential time points, and the outgrowth of viruses capable of utilizing the CXCR4 receptor (X4 viruses), the existence of three distinct phases within the asymptomatic interval is suggested: an early phase of variable duration during which linear increases ( approximately 1% per year) in both divergence and diversity were observed; an intermediate phase lasting an average of 1.8 years, characterized by a continued increase in divergence but with stabilization or decline in diversity; and a late phase characterized by a slowdown or stabilization of divergence and continued stability or decline in diversity. X4 variants emerged around the time of the early- to intermediate-phase transition and then achieved peak representation and began a decline around the transition between the intermediate and late phases. The late-phase transition was also associated with failure of T-cell homeostasis (defined by a downward inflection in CD3(+) T cells) and decline of CD4(+) T cells to </=200 cells/microliter. The strength of these temporal associations between viral divergence and diversity, viral coreceptor specificity, and T-cell homeostasis and subset composition supports the concept that the phases described represent a consistent pattern of viral evolution during the course of HIV-1 infection in moderate progressors. Recognition of this pattern may help explain previous conflicting data on the relationship between viral evolution and disease progression and may provide a useful framework for evaluating immune damage and recovery in untreated and treated HIV-1 infections.

Early in infection, human immunodeficiency virus type 1 (HIV-1) generally uses the CCR5 chemokine receptor (along with CD4) for cellular entry. In many HIV-1-infected individuals, viral genotypic changes arise that allow the virus to use CXCR4 (either in addition to CCR5 or alone) as an entry coreceptor. This switch has been associated with an acceleration of both CD3(+) T-cell decline and progression to AIDS. While it is well known that the V3 loop of gp120 largely determines coreceptor usage and that positively charged residues in V3 play an important role, the process of genetic change in V3 leading to altered coreceptor usage is not well understood. Further, the methods for biological phenotyping of virus for research or clinical purposes are laborious, depend on sample availability, and present biosafety concerns, so reliable methods for sequence-based "virtual phenotyping" are desirable. We introduce a simple bioinformatic method of scoring V3 amino acid sequences that reliably predicts CXCR4 usage (sensitivity, 84%; specificity, 96%). This score (as determined on the basis of position-specific scoring matrices [PSSM]) can be interpreted as revealing a propensity to use CXCR4 as follows: known R5 viruses had low scores, R5X4 viruses had intermediate scores, and X4 viruses had high scores. Application of the PSSM scoring method to reconstructed virus phylogenies of 11 longitudinally sampled individuals revealed that the development of X4 viruses was generally gradual and involved the accumulation of multiple amino acid changes in V3. We found that X4 viruses were lost in two ways: by the dying off of an established X4 lineage or by mutation back to low-scoring V3 loops.

Immune responses induced during the early stages of chronic viral infections are thought to influence disease outcome. Using HIV as a model, we examined virus-specific cytotoxic T lymphocytes (CTLs), T helper cells, and viral genetic diversity in relation to duration of infection and subsequent response to antiviral therapy. Individuals with acute HIV-1 infection treated before seroconversion had weaker CTL responses directed at fewer epitopes than persons who were treated after seroconversion. However, treatment-induced control of viremia was associated with the development of strong T helper cell responses in both groups. After 1 yr of antiviral treatment initiated in acute or early infection, all epitope-specific CTL responses persisted despite undetectable viral loads. The breadth and magnitude of CTL responses remained significantly less in treated acute infection than in treated chronic infection, but viral diversity was also significantly less with immediate therapy. We conclude that early treatment of acute HIV infection leads to a more narrowly directed CTL response, stronger T helper cell responses, and a less diverse virus population. Given the need for T helper cells to maintain effective CTL responses and the ability of virus diversification to accommodate immune escape, we hypothesize that early therapy of primary infection may be beneficial despite induction of less robust CTL responses. These data also provide rationale for therapeutic immunization aimed at broadening CTL responses in treated primary HIV infection.

Human immunodeficiency virus type 1 (HIV-1)-associated dementia (HAD) is correlated with increased monocyte migration to the brain, and the incidence of HAD among otherwise asymptomatic subjects appears to be lower in India than in the United States and Europe (1 to 2% versus 15 to 30%). Because of the genetic differences between HIV-1 strains circulating in these regions, we sought to identify viral determinants associated with this difference. We targeted Tat protein for these studies in view of its association with monocyte chemotactic function. Analyses of Tat sequences representing nine subtypes revealed that at least six amino acid residues are differentially conserved in subtype C Tat (C-Tat). Of these, cysteine (at position 31) was highly (>99%) conserved in non-subtype C viruses and more than 90% of subtype C viruses encoded a serine. We hypothesized a compromised chemotactic function of C-Tat due to the disruption of CC motif and tested it with the wild type C-Tat (CS) and its two isogenic variants (CC and SC) derived by site-directed mutagenesis. We found that the CS natural variant was defective for monocyte chemotactic activity without a loss in the transactivation property. While the CC mutant is functionally competent for both the functions, in contrast, the SC mutant was defective in both. Therefore, the loss of the C-Tat chemotactic property may underlie the reduced incidence of HAD; although not presenting conclusive evidence, this study provides the first evidence for a potential epidemiologic phenomenon associated with biological differences in the subtype C viruses.

Letters from: [ Shan-Lu Liu, et al . ][1] [ Barton F. Haynes, et al . ][1] Human immunodeficiency virus (HIV) behaves as an evolving quasispecies in infected individuals. When the populations of genetic variants that make up this quasispecies are characterized, it is common practice to obtain