Constraints on HIV-1 evolution and immunodominance revealed in monozygotic adult twins infected with the same virus.

The predictability of virus-host interactions and disease progression in rapidly evolving human viral infections has been difficult to assess because of host and genetic viral diversity. Here we examined adaptive HIV-specific cellular and humoral immune responses and viral evolution in adult monozygotic twins simultaneously infected with the same virus. CD4 T cell counts and viral loads followed similar trajectories over three years of follow up. The initial CD8 T cell response targeted 17 epitopes, 15 of which were identical in each twin, including two immunodominant responses. By 36 months after infection, 14 of 15 initial responses were still detectable in both, whereas all new responses were subdominant and remained so. Of four responses that declined in both twins, three demonstrated mutations at the same residue. In addition, the evolving antibody responses cross-neutralized the other twin's virus, with similar changes in the pattern of evolution in the envelope gene. These results reveal considerable concordance of adaptive cellular and humoral immune responses and HIV evolution in the same genetic environment, suggesting constraints on mutational pathways to HIV immune escape.

Expansion of pre-existing, lymph node-localized CD8+ T cells during supervised treatment interruptions in chronic HIV-1 infection.

To date, most studies have focused on the characterization of HIV-1-specific cellular immune responses in the peripheral blood (PB) of infected individuals. Much less is known about the comparative magnitude and breadth of responses in the lymphoid tissue. This study analyzed HIV-1-specific CD8+ T cell responses simultaneously in PB and lymph nodes (LNs) of persons with chronic HIV-1 infection and assessed the dynamics of these responses during antiretroviral treatment and supervised treatment interruption (STI). In untreated chronic infection, the magnitude of epitope-specific CD8+ T cell activity was significantly higher in LNs than in PB. Responses decreased in both compartments during highly active antiretroviral therapy, but this decline was more pronounced in PB. During STI, HIV-1-specific CD8+ T cell responses in PB increased significantly. Enhancement in breadth and magnitude was largely due to the expansion of pre-existing responses in the LNs, with new epitopes infrequently targeted. Taken together, these data demonstrate that HIV-1-specific CD8+ T cells are preferentially located in the LNs, with a subset of responses exclusively detectable in this compartment. Furthermore, the enhanced CD8+ T cell responses observed during STI in chronically infected individuals is largely due to expansion of pre-existing virus-specific CD8+ T cells, rather than the induction of novel responses.

Important contribution of p15 Gag-specific responses to the total Gag-specific CTL responses.

OBJECTIVES: HIV-1 p15 Gag and its protease cleavage products, NCp7 and p6, are believed to play a major role in viral infectivity and assembly during the early and late stages of the retroviral life cycle. However, the extent to which p15 Gag is targeted by the host immune system in natural infection as well as precise cytotoxic T lymphocyte (CTL) epitopes within this protein remains to be defined. METHODS: In this study, 57 HIV-1 infected individuals and 10 HIV-1 negative controls were screened for CD8 and CD4 T-cell responses using overlapping peptides spanning the entire p15 Gag protein as well as the p17 Gag and p24 Gag proteins. Peptide-specific interferon-gamma production was measured by Elispot assay and flow-based intracellular cytokine quantification, and cytotoxic activity was confirmed after isolation of peptide-specific CD8 T-cell lines. RESULTS: CD8 T lymphocytes specific to p15 Gag were found in 46% (26/57) of HIV-1 infected individuals studied and contributed on average 17% (range, 0-100%) to the total Gag-specific T-cell responses. Responses were clustered within three immunodominant regions of p15 Gag, mapping to important functional sites. These studies also include the description of the first three optimally defined CTL epitopes within p15 Gag. CONCLUSIONS: These results indicate that p15 Gag is frequently recognized by HIV-1-specific CD8 T cells in HIV-1 infection and will be important in the comprehensive assessments of CTL responses in infected persons, as well as the design and testing of future HIV-1 vaccines and immunotherapeutic interventions.

Selective escape from CD8+ T-cell responses represents a major driving force of human immunodeficiency virus type 1 (HIV-1) sequence diversity and reveals constraints on HIV-1 evolution.

The sequence diversity of human immunodeficiency virus type 1 (HIV-1) represents a major obstacle to the development of an effective vaccine, yet the forces impacting the evolution of this pathogen remain unclear. To address this issue we assessed the relationship between genome-wide viral evolution and adaptive CD8+ T-cell responses in four clade B virus-infected patients studied longitudinally for as long as 5 years after acute infection. Of the 98 amino acid mutations identified in nonenvelope antigens, 53% were associated with detectable CD8+ T-cell responses, indicative of positive selective immune pressures. An additional 18% of amino acid mutations represented substitutions toward common clade B consensus sequence residues, nine of which were strongly associated with HLA class I alleles not expressed by the subjects and thus indicative of reversions of transmitted CD8 escape mutations. Thus, nearly two-thirds of all mutations were attributable to CD8+ T-cell selective pressures. A closer examination of CD8 escape mutations in additional persons with chronic disease indicated that not only did immune pressures frequently result in selection of identical amino acid substitutions in mutating epitopes, but mutating residues also correlated with highly polymorphic sites in both clade B and C viruses. These data indicate a dominant role for cellular immune selective pressures in driving both individual and global HIV-1 evolution. The stereotypic nature of acquired mutations provides support for biochemical constraints limiting HIV-1 evolution and for the impact of CD8 escape mutations on viral fitness.