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Letvin, Norman Lee

We characterized the evolution of simian immunodeficiency virus (SIV) in the male genital tract by examining blood- and semen-associated virus from experimentally and sham vaccinated rhesus monkeys during primary infection. At the time of peak virus replication, SIV sequences were intermixed between the blood and semen supporting a scenario of high-level virus "spillover" into the male genital tract. However, at the time of virus set point, compartmentalization was apparent in 4 of 7 evaluated monkeys, likely as a consequence of restricted virus gene flow between anatomic compartments after the resolution of primary viremia. These findings suggest that SIV replication in the male genital tract evolves to compartmentalization after peak viremia resolves.

Poster presentation. Conclusion: Our results indicate that env vaccination is associated with an accelerated development of autologous neutralizing antibodies. These antibodies were focused at least in part on the V1 region of Env, since there was selective pressure in this region of the envelope for the evolution of mutational changes.

CCL3 is a ligand for the HIV-1 co-receptor CCR5. There have recently been conflicting reports in the literature concerning whether CCL3-like gene (CCL3L) copy number variation (CNV) is associated with resistance to HIV-1 acquisition and with both viral load and disease progression following infection with HIV-1. An association has also been reported between CCL3L CNV and clinical sequelae of the simian immunodeficiency virus (SIV) infection in vivo in rhesus monkeys. The present study was initiated to explore the possibility of an association of CCL3L CNV with the control of virus replication and AIDS progression in a carefully defined cohort of SIVmac251-infected, Indian-origin rhesus monkeys. Although we demonstrated extensive variation in copy number of CCL3L in this cohort of monkeys, CCL3L CNV was not significantly associated with either peak or set-point plasma SIV RNA levels in these monkeys when MHC class I allele Mamu-A*01 was included in the models or progression to AIDS in these monkeys. With 66 monkeys in the study, there was adequate power for these tests if the correlation of CCL3L and either peak or set-point plasma SIV RNA levels was 0.34 or 0.36, respectively. These findings call into question the premise that CCL3L CNV is important in HIV/SIV pathogenesis.

The role of CD8 T cells in anti-tuberculosis immunity in humans remains unknown, and studies of CD8 T cell–mediated protection against tuberculosis in mice have yielded controversial results. Unlike mice, humans and nonhuman primates share a number of important features of the immune system that relate directly to the specificity and functions of CD8 T cells, such as the expression of group 1 CD1 proteins that are capable of presenting Mycobacterium tuberculosis lipids antigens and the cytotoxic/bactericidal protein granulysin. Employing a more relevant nonhuman primate model of human tuberculosis, we examined the contribution of BCG- or M. tuberculosis-elicited CD8 T cells to vaccine-induced immunity against tuberculosis. CD8 depletion compromised BCG vaccine-induced immune control of M. tuberculosis replication in the vaccinated rhesus macaques. Depletion of CD8 T cells in BCG-vaccinated rhesus macaques led to a significant decrease in the vaccine-induced immunity against tuberculosis. Consistently, depletion of CD8 T cells in rhesus macaques that had been previously infected with M. tuberculosis and cured by antibiotic therapy also resulted in a loss of anti-tuberculosis immunity upon M. tuberculosis re-infection. The current study demonstrates a major role for CD8 T cells in anti-tuberculosis immunity, and supports the view that CD8 T cells should be included in strategies for development of new tuberculosis vaccines and immunotherapeutics.

We recently developed a novel strategy to identify transmitted HIV-1 genomes in acutely infected humans using single-genome amplification and a model of random virus evolution. Here, we used this approach to determine the molecular features of simian immunodeficiency virus (SIV) transmission in 18 experimentally infected Indian rhesus macaques. Animals were inoculated intrarectally (i.r.) or intravenously (i.v.) with stocks of SIVmac251 or SIVsmE660 that exhibited sequence diversity typical of early-chronic HIV-1 infection. 987 full-length SIV env sequences (median of 48 per animal) were determined from plasma virion RNA 1–5 wk after infection. i.r. inoculation was followed by productive infection by one or a few viruses (median 1; range 1–5) that diversified randomly with near starlike phylogeny and a Poisson distribution of mutations. Consensus viral sequences from ramp-up and peak viremia were identical to viruses found in the inocula or differed from them by only one or a few nucleotides, providing direct evidence that early plasma viral sequences coalesce to transmitted/founder viruses. i.v. infection was >2,000-fold more efficient than i.r. infection, and viruses transmitted by either route represented the full genetic spectra of the inocula. These findings identify key similarities in mucosal transmission and early diversification between SIV and HIV-1, and thus validate the SIV–macaque mucosal infection model for HIV-1 vaccine and microbicide research.

Background: Systemic events in acute HIV infection (AHI) are associated with disease severity and progression to AIDS. Timely identification of AHI patients has posed a significant challenge to identifying the underlying mechanisms driving these events. The aim of this study is to elucidate these pathways by characterizing the genome-wide transcriptional signature expressed by whole blood during early AHI. Methods: Longitudinal whole blood samples from ART treated and untreated patients from both the United States (n = 16) and Africa (n = 16) were collected at study enrollment and weeks 1, 2, 4, 12, and 24. AHI and non-infected controls were analyzed using Illumina HT-12 microarrays. Both gene and module level analysis were conducted to identify biologic pathways active in AHI. Results: Nineteen annotated and 24 undefined transcriptional modules constitute a robust transcriptional signature that collectively distinguished early AHI patients from noninfected controls. The activity of transcriptional modules related to interferon, cell cycle, cytotoxic, and mitochondrial responses were significantly increased in AHI patients. At study enrollment, the intensity of this signature was not correlated with viral load and exhibited heterogeneity between patients. Association between viral load and signature intensity was found over time. However, three patients exhibited little change in transcriptional activity despite high viral loads. When compared to acute RSV and Influenza infections, only interferon signatures were conserved across all three infections while cell cycle, cytotoxic, and mitochondrial responses were unique to AHI. The AHI signature of untreated patients regressed to non-infected control levels by 12–24 weeks post enrollment. The initiation of ART accelerated the dissipation of this signature, returning the core AHI signature to normal levels within 4 weeks. Conclusion: The whole blood AHI transcriptional signature is unique, transient, and capable of classifying individual responses to infection. This signature is responsive to ART and contains pathways with both defined and novel associations with HIV infection.

Breast milk transmission remains a major mode of infant HIV acquisition, yet anatomic and immunologic forces shaping virus quasispecies in milk are not well characterized. In this study, phylogenic analysis of envelope sequences of milk SIV variants revealed groups of nearly identical viruses, indicating local virus production. However, comparison of the patterns and rates of CTL escape of blood and milk virus demonstrated only subtle differences between the compartments. These findings suggest that a substantial fraction of milk viruses are produced by locally-infected cells, but are shaped by cellular immune pressures similar to that in the blood.

Background: The ability of CD8+ T lymphocytes to recognize a diversity of mutant forms of an HIV epitope is of central importance in the immune containment of this virus. The present studies were pursued to determine the mechanism employed by CD8+ T lymphocytes to recognize mutant viruses. In particular, we sought to determine whether mutant sequences are recognized by distinct CD8+ T lymphocyte populations or whether individual clonal populations of CD8+ T lymphocytes recognize a diversity of mutant sequences. Methods: We employed flow cytometry, Vβ repertoire analysis, and CDR3 sequencing methodologies to characterize the clonal diversity of CD8+ T lymphocytes that recognize variant forms of the HIV-1 envelope (Env) p41A epitope generated after infection by SHIV-89.6P or elicited by HIV-1 89.6P Env immunization of Mamu-A*01+ rhesus monkeys. To evaluate the capacity of the CD8+ T lymphocytes to recognize genetically diverse isolates of HIV-1, we employed a series of tetramers constructed with variants of the p41A epitope of HIV-1 Env. To define which T cell receptor mediated the recognition of each specific variant p41A, we isolated variant p41A-specific CD8+ T lymphocyte populations and analyzed the expression of 46 Vβ families and subfamilies genes. We then determined the precise clones employed for the recognition of each variant epitope peptide through CDR3 sequencing. Results: In both the infected and the vaccinated monkeys, we observed clonotypes capable of recognizing the majority of the variant epitope peptides. Conclusion: These data show that exposure to a single HIV-1 Env sequence can generate clonotypes capable of recognizing multiple variant forms of HIV-1 Env. Such Env-specific CD8+ T lymphocytes should be able to confer potent, effective protection against a diverse spectrum of circulating viruses.