A high viral burden predicts the loss of CD8 T-cell responses specific for subdominant gag epitopes during chronic human immunodeficiency virus infection

Defining Kinetic Properties of HIV-Specific CD8⁺ T-Cell Responses in Acute Infection

Multiple lines of evidence indicate that CD8 + T cells are important in the control of HIV-1 (HIV) replication. However, CD8 + T cells induced by natural infection cannot eliminate the virus or reduce viral loads to acceptably low levels in most infected individuals. Understanding the basic quantitative features of CD8 + T-cell responses induced during HIV infection may therefore inform us about the limits that HIV vaccines, which aim to induce protective CD8 + T-cell responses, must exceed. Using previously published experimental data from a cohort of HIV-infected individuals with sampling times from acute to chronic infection we defined the quantitative properties of CD8 + T-cell responses to the whole HIV proteome. In contrast with a commonly held view, we found that the relative number of HIV-specific CD8 + T-cell responses (response breadth) changed little over the course of infection (first 400 days post-infection), with moderate but statistically significant changes occurring only during the first 35 symptomatic days. This challenges the idea that a change in the T-cell response breadth over time is responsible for the slow speed of viral escape from CD8 + T cells in the chronic infection. The breadth of HIV-specific CD8 + T-cell responses was not correlated with the average viral load for our small cohort of patients. Metrics of relative immunodominance of HIV-specific CD8 + T-cell responses such as Shannon entropy or the Evenness index were also not significantly correlated with the average viral load. Our mathematical-model-driven analysis suggested extremely slow expansion kinetics for the majority of HIV-specific CD8 + T-cell responses and the presence of intra- and interclonal competition between multiple CD8 + T-cell responses; such competition may limit the magnitude of CD8 + T-cell responses, specific to different epitopes, and the overall number of T-cell responses induced by vaccination. Further understanding of mechanisms underlying interactions between the virus and virus-specific CD8 + T-cell response will be instrumental in determining which T-cell-based vaccines will induce T-cell responses providing durable protection against HIV infection.

Therapeutic conserved elements (CE) DNA vaccine induces strong T-cell responses against highly conserved viral sequences during simian-human immunodeficiency virus infection

HIV-specific T-cell responses play a key role in controlling HIV infection, and therapeutic vaccines for HIV that aim to improve viral control will likely need to improve on the T-cell responses induced by infection. However, in the setting of chronic infection, an effective therapeutic vaccine must overcome the enormous viral genetic diversity and the presence of pre-existing T-cell responses that are biased toward immunodominant T-cell epitopes that can readily mutate to evade host immunity and thus potentially provide inferior protection. To address these issues, we investigated a novel, epidermally administered DNA vaccine expressing SIV capsid (p27^Gag) homologues of highly conserved elements (CE) of the HIV proteome in macaques experiencing chronic but controlled SHIV infection. We assessed the ability to boost or induce de novo T-cell responses against the conserved but immunologically subdominant CE epitopes. Two groups of animals were immunized with either the CE DNA vaccine or a full-length SIV p57^gag DNA vaccine. Prior to vaccination, CE responses were similar in both groups. The full-length p57^gag DNA vaccine, which contains the CE, increased overall Gag-specific responses but did not increase CE responses in any animals (0/4). In contrast, the CE DNA vaccine increased CE responses in all (4/4) vaccinated macaques. In SIV infected but unvaccinated macaques, those that developed stronger CE-specific responses during acute infection exhibited lower viral loads. We conclude that CE DNA vaccination can re-direct the immunodominance hierarchy towards CE in the setting of attenuated chronic infection and that induction of these responses by therapeutic vaccination may improve immune control of HIV.

Relationship between chemokine receptor expression, chemokine levels and HIV-1 replication in the lungs of persons exposed to Mycobacterium tuberculosis

Increased susceptibility to tuberculosis following HIV-1 seroconversion contributes significantly to the tuberculosis epidemic in sub-Saharan Africa. Lung-specific mechanisms underlying the interaction between HIV-1 and Mycobacterium tuberculosis infection are incompletely understood. Here we address these questions by examining the effect of HIV-1 and latent M. tuberculosis co-infection on the expression of viral-entry receptors and ligands in bronchoalveolar lavage (BAL) of HIV-1-infected and -uninfected patients with and without latent M. tuberculosis infection. Irrespective of HIV-1 status, T cells from BAL expressed higher levels of the beta-chemokine receptor (CCR)5 than peripheral blood T cells, in particular the CD8⁺ T cells of HIV-1-infected persons showed elevated CCR5 expression. The concentrations of the CCR5 ligands RANTES and MIP-1β were elevated in the BAL of HIV-1-infected persons compared with that in HIV-1-uninfected controls. CCR5 expression and RANTES concentration correlated strongly with HIV-1 viral load in the BAL. In contrast, these alterations were not associated with M. tuberculosis sensitisation in vivo, nor did M. tuberculosis infection of BAL cells ex vivo change RANTES expression. These data suggest ongoing HIV-1 replication predominantly drives local pulmonary CCR5⁺ T-cell activation in HIV/latent M. tuberculosis co-infection.

Interleukin-12p70 expression by dendritic cells of HIV-1-infected patients fails to stimulate gag-specific immune responses

A variety of immune-based therapies has been developed in order to boost or induce protective CD8⁺ T cell responses in order to control HIV replication. Since dendritic cells (DCs) are professional antigen-presenting cells (APCs) with the unique capability to stimulate naïve T cells into effector T cells, their use for the induction of HIV-specific immune responses has been studied intensively. In the present study we investigated whether modulation of the activation state of DCs electroporated with consensus codon-optimized HxB2 gag mRNA enhances their capacity to induce HIV gag-specific T cell responses. To this end, mature DCs were (i) co-electroporated with mRNA encoding interleukin (IL)-12p70 mRNA, or (ii) activated with a cytokine cocktail consisting of R848 and interferon (IFN)-γ. Our results confirm the ability of HxB2 gag-expressing DCs to expand functional HIV-specific CD8⁺ T cells. However, although most of the patients had detectable gag-specific CD8⁺ T cell responses, no significant differences in the level of expansion of functional CD8⁺ T cells could be demonstrated when comparing conventional or immune-modulated DCs expressing IL-12p70. This result which goes against expectation may lead to a re-evaluation of the need for IL-12 expression by DCs in order to improve T-cell responses in HIV-1-infected individuals.

Strenuous resistance to natural HIV-1 disease progression: viral controllers and long-term nonprogressors

HIV-1 infection leads to AIDS and death within 8–10 years for most individuals in the absence of antiretroviral therapy (ART). However, a minority of infected individuals show the unusual capacity to spontaneously control disease progression after infection in the absence of any ART. So-called ‘long-term nonprogressors’ are defined by maintenance of peripheral CD4+ T-cell counts >500 cells/µl and good health without ART for >7 years since infection. More recently, ART-naive individuals who spontaneously control their viremia levels at either <50 or <2000 copies of RNA/ml for at least 12 months in the absence of ART have been named ‘elite controllers’ and ‘HIV controllers’, respectively. The overlap between long-term nonprogressors and elite controllers/HIV controllers is partial, and both groups collectively account for <5% of all infected individuals. Unraveling the nature of their relative resistance to HIV-1 disease progression would be of great value for HIV-prevention strategies.

Fluidity of HIV-1-specific T-cell responses during acute and early subtype C HIV-1 infection and associations with early disease progression

Deciphering immune events during early stages of human immunodeficiency virus type 1 (HIV-1) infection is critical for understanding the course of disease. We characterized the hierarchy of HIV-1-specific T-cell gamma interferon (IFN-γ) enzyme-linked immunospot (ELISPOT) assay responses during acute subtype C infection in 53 individuals and associated temporal patterns of responses with disease progression in the first 12 months. There was a diverse pattern of T-cell recognition across the proteome, with the recognition of Nef being immunodominant as early as 3 weeks postinfection. Over the first 6 months, we found that there was a 23% chance of an increased response to Nef for every week postinfection (P = 0.0024), followed by a nonsignificant increase to Pol (4.6%) and Gag (3.2%). Responses to Env and regulatory proteins appeared to remain stable. Three temporal patterns of HIV-specific T-cell responses could be distinguished: persistent, lost, or new. The proportion of persistent T-cell responses was significantly lower (P = 0.0037) in individuals defined as rapid progressors than in those progressing slowly and who controlled viremia. Almost 90% of lost T-cell responses were coincidental with autologous viral epitope escape. Regression analysis between the time to fixed viral escape and lost T-cell responses (r = 0.61; P = 0.019) showed a mean delay of 14 weeks after viral escape. Collectively, T-cell epitope recognition is not a static event, and temporal patterns of IFN-γ-based responses exist. This is due partly to viral sequence variation but also to the recognition of invariant viral epitopes that leads to waves of persistent T-cell immunity, which appears to associate with slower disease progression in the first year of infection.

Proliferation, but not interleukin 2 production, of Gag-specific CD8+ T cells is associated with low HIV viremia and high CD4 counts in HIV-1-infected Chinese individuals

BACKGROUND

To control HIV globally, a comprehensive understanding of host immunity to HIV in different human populations is needed. Relatively, little is known on the quantity and quality of HIV-specific T-cell responses in Chinese patients.

METHODS

We quantified HIV Gag-specific CD8+ and CD4+ T cells that are capable of producing interferon (IFN)-gamma and interleukin 2 and assessed their proliferative capacity in a cohort of 53 antiretroviral-naive chronically HIV-1-infected Chinese patients.

RESULTS

The proliferation of Gag-specific CD8+ T cells, but not their IFN-gamma or interleukin 2 production, was inversely proportional to HIV viral load and directly proportional to CD4+ T-cell counts. Gag-specific CD8+ T-cell proliferation was proportionate to the frequency of IFN-gamma-secreting CD8+ T cells. Such correlations, however, did not exist for Gag-specific CD4 T cells.

CONCLUSIONS

These results suggest that good quality and large quantities of HIV Gag-specific T-cell responses are associated with virologic control in HIV-1-infected Chinese patients. We infer that protective T-cell vaccines tested in other populations should also provide benefit to the Chinese population.

Magnitude and complexity of rectal mucosa HIV-1-specific CD8+ T-cell responses during chronic infection reflect clinical status

Background

The intestinal mucosa displays robust virus replication and pronounced CD4+ T-cell loss during acute human immunodeficiency virus type 1 (HIV-1) infection. The ability of HIV-specific CD8+ T-cells to modulate disease course has prompted intensive study, yet the significance of virus-specific CD8+ T-cells in mucosal sites remains unclear.

Methods and Findings

We evaluated five distinct effector functions of HIVgag-specific CD8+ T-cells in rectal mucosa and blood, individually and in combination, in relationship to clinical status and antiretroviral therapy (ART). In subjects not on ART, the percentage of rectal Gag-specific CD8+ T-cells capable of 3, 4 or 5 simultaneous effector functions was significantly related to blood CD4 count and inversely related to plasma viral load (PVL) (p<0.05). Polyfunctional rectal CD8+ T-cells expressed higher levels of MIP-1β and CD107a on a per cell basis than mono- or bifunctional cells. The production of TNFα, IFN-γ, and CD107a by Gag-specific rectal CD8+ T-cells each correlated inversely (p<0.05) with PVL, and MIP-1β expression revealed a similar trend. CD107a and IFN-γ production were positively related to blood CD4 count (p<0.05), with MIP-1β showing a similar trend. IL-2 production by rectal CD8+ T-cells was highly variable and generally low, and showed no relationship to viral load or blood CD4 count.

Conclusions

The polyfunctionality of rectal Gag-specific CD8+ T-cells appears to be related to blood CD4 count and inversely related to PVL. The extent to which these associations reflect causality remains to be determined; nevertheless, our data suggest a potentially important role for mucosal T-cells in limiting virus replication during chronic infection.

Human immunodeficiency virus-specific gamma interferon enzyme-linked immunospot assay responses targeting specific regions of the proteome during primary subtype C infection are poor predictors of the course of viremia and set point

It is unknown whether patterns of human immunodeficiency virus (HIV)-specific T-cell responses during acute infection may influence the viral set point and the course of disease. We wished to establish whether the magnitude and breadth of HIV type 1 (HIV-1)-specific T-cell responses at 3 months postinfection were correlated with the viral-load set point at 12 months and hypothesized that the magnitude and breadth of HIV-specific T-cell responses during primary infection would predict the set point. Gamma interferon (IFN-gamma) enzyme-linked immunospot (ELISPOT) assay responses across the complete proteome were measured in 47 subtype C HIV-1-infected participants at a median of 12 weeks postinfection. When corrected for amino acid length and individuals responding to each region, the order of recognition was as follows: Nef > Gag > Pol > Rev > Vpr > Env > Vpu > Vif > Tat. Nef responses were significantly (P < 0.05) dominant, targeted six epitopic regions, and were unrelated to the course of viremia. There was no significant difference in the magnitude and breadth of responses for each protein region with disease progression, although there was a trend of increased breadth (mean, four to seven pools) in rapid progressors. Correlation of the magnitude and breadth of IFN-gamma responses with the viral set point at 12 months revealed almost zero association for each protein region. Taken together, these data demonstrate that the magnitude and breadth of IFN-gamma ELISPOT assay responses at 3 months postinfection are unrelated to the course of disease in the first year of infection and are not associated with, and have low predictive power for, the viral set point at 12 months.

Potent specific immune responses induced by prime-boost-boost strategies based on DNA, adenovirus, and Sendai virus vectors expressing gag gene of Chinese HIV-1 subtype B

To study the immune responses elicited by multiple vectors and develop vaccines strategies against prevalent HIV-1 strains in China, we have examined the potency of vaccine regimens of plasmid DNA, adenovirus, and Sendai virus vectors expressing HIV-1 gag consensus sequence of HIV-1 isolates from China for inducing specific immune responses. In BALB/c mice, combination of these vectors induced higher Gag-specific cellular immune response than any regimen using single vector alone. The prime-boost-boost regimen consisting of the triple heterologous vectors induced Gag-specific T-cell responses the most efficiently. In rhesus macaques, the prime-boost-boost regimen induced potent Gag-specific cellular immune responses as well as long lasting humoral immune response, and each booster resulted in rapid and efficient expansion of Gag-specific T cells. These results indicate that this prime-boost-boost regimen using triple heterologous vectors is a promising AIDS vaccine candidate for efficiently inducing HIV-1-specific cellular and humoral immune responses. Its further studies as a promising scheme for therapeutic and/or prophylactic HIV-1 vaccines should be grounded.

Crippling HIV one mutation at a time

Accumulating data suggest that not all human immunodeficiency virus (HIV)-1–specific immune responses are equally effective at controlling HIV-1 replication. A new study now demonstrates that multiple immune-driven sequence polymorphisms in the highly conserved HIV-1 Gag region of transmitted viruses are associated with reduced viral replication in newly infected humans. These data suggest that targeting these and other conserved viral regions may be the key to developing an effective HIV-1 vaccine.