A low CD4/CD8 ratio in elderly HIV-uninfected adults is associated with increased morbidity and mortality. A subset of HIV-infected adults receiving effective antiretroviral therapy (ART) fails to normalize this ratio, even after they achieve normal CD4+ T cell counts. The immunologic and clinical characteristics of this clinical phenotype remain undefined. Using data from four distinct clinical cohorts and three clinical trials, we show that a low CD4/CD8 ratio in HIV-infected adults during otherwise effective ART (after CD4 count recovery above 500 cells/mm³) is associated with a number of immunological abnormalities, including a skewed T cell phenotype from naïve toward terminally differentiated CD8+ T cells, higher levels of CD8+ T cell activation (HLADR+CD38+) and senescence (CD28− and CD57+CD28−), and higher kynurenine/tryptophan ratio. Changes in the peripheral CD4/CD8 ratio are also reflective of changes in gut mucosa, but not in lymph nodes. In a longitudinal study, individuals who initiated ART within six months of infection had greater CD4/CD8 ratio increase compared to later initiators (>2 years). After controlling for age, gender, ART duration, nadir and CD4 count, the CD4/CD8 ratio predicted increased risk of morbidity and mortality. Hence, a persistently low CD4/CD8 ratio during otherwise effective ART is associated with increased innate and adaptive immune activation, an immunosenescent phenotype, and higher risk of morbidity/mortality. This ratio may prove useful in monitoring response to ART and could identify a unique subset of individuals needed of novel therapeutic interventions. The CD4/CD8 ratio, a hallmark of the collection of T cell defects related to aging –“immunosenescence”- and a predictor of mortality in the general population, often fails to normalize in an important proportion of HIV-infected individuals with adequate CD4+ T cell recovery after ART initiation. However, the immunological and clinical characteristics of this clinical phenotype have not been elucidated. Herein we show that during treated HIV infection, expansion of CD8+ T cells, reflected as a low CD4/CD8 ratio, identifies a subgroup of individuals with a number of immunological abnormalities and a poor prognosis. These subjects exhibit increased innate and adaptive immune activation, an immunosenescent phenotype, CD4+ and CD8+ imbalance in the gut mucosa and higher risk of morbidity and mortality. In contrast, those who normalize the CD4/CD8 ratio have traits of a healthy immune system. We observed that early ART initiation might contribute to more rapid and robust CD4/CD8 ratio normalization compared to later initiation. Hence, the CD4/CD8 ratio might help to further discriminate the risk of disease progression of successfully treated HIV-infected individuals, and a successful response to ART may require both normalization of the peripheral CD4+ T cell count and the ratio of CD4+ to CD8+ T cell counts.

Key Points: Antimicrobial CD8+ MAIT cells are activated, exhausted, and progressively and persistently depleted during chronic HIV-1 infection. This decline in MAIT cell level and function may seriously impair the ability to mount immune responses to bacterial and fungal pathogens.

Although the gut-associated lymphoid tissue (GALT) is an important early site for human immunodeficiency virus (HIV) replication and severe CD4⁺T-cell depletion, our understanding is limited about the restoration of the gut mucosal immune system during highly active antiretroviral therapy (HAART). We evaluated the kinetics of viral suppression, CD4⁺T-cell restoration, gene expression, and HIV-specific CD8⁺T-cell responses in longitudinal gastrointestinal biopsy and peripheral blood samples from patients initiating HAART during primary HIV infection (PHI) or chronic HIV infection (CHI) using flow cytometry, real-time PCR, and DNA microarray analysis. Viral suppression was more effective in GALT of PHI patients than CHI patients during HAART. Mucosal CD4⁺T-cell restoration was delayed compared to peripheral blood and independent of the time of HAART initiation. Immunophenotypic analysis showed that repopulating mucosal CD4⁺T cells were predominantly of a memory phenotype and expressed CD11α, α_Eβ₇, CCR5, and CXCR4. Incomplete suppression of viral replication in GALT during HAART correlated with increased HIV-specific CD8⁺T-cell responses. DNA microarray analysis revealed that genes involved in inflammation and cell activation were up regulated in patients who did not replenish mucosal CD4⁺T cells efficiently, while expression of genes involved in growth and repair was increased in patients with efficient mucosal CD4⁺T-cell restoration. Our findings suggest that the discordance in CD4⁺T-cell restoration between GALT and peripheral blood during therapy can be attributed to the incomplete viral suppression and increased immune activation and inflammation that may prevent restoration of CD4⁺T cells and the gut microenvironment.

There exists a unique group of persons who are able to durably control HIV in the absence of therapy. The mechanisms of control in these persons remain poorly defined. In this study, we examined CD8+ T-cell responses in blood and rectal mucosa from 17 “elite controllers” (viral load < 75 copies/mL), 11 “viremic controllers” (75-2000 copies/mL), 14 noncontrollers (> 10 000 copies/mL), and 10 antiretroviral-treated persons (< 75 copies/mL). Production of interferon-γ, interleukin-2, tumor necrosis factor-α, macrophage inflammatory protein-1β, and CD107a by CD8+ T cells in response to HIV-1 Gag stimulation was measured using flow cytometry. Our hypothesis was that “polyfunctional” T cells producing multiple antiviral factors would be most abundant in mucosal tissues of HIV controllers. Mucosal CD8+ T-cell responses were significantly stronger and more complex in controllers than in antiretroviral-suppressed persons (P = .0004). The frequency of 4-function responses in rectal mucosa was higher in controllers than in noncontrollers and patients on therapy (P < .0001). Mucosal responses in controllers were frequently stronger and more complex than blood responses. These findings demonstrate that many controllers mount strong, complex HIV-specific T-cell responses in rectal mucosa. These responses may play an important role in mucosal immune surveillance, as suggested by their relative enrichment among persons who control HIV in the absence of therapy.

A rare subset of human immunodeficiency virus (HIV)-infected individuals maintains undetectable HIV RNA levels without therapy (“elite controllers”). To clarify the role of T-cell responses in mediating virus control, we compared HLA class I polymorphisms and HIV-specific T-cell responses among a large cohort of elite controllers (HIV-RNA < 75 copies/ml), “viremic” controllers (low-level viremia without therapy), “noncontrollers” (high-level viremia), and“antiretroviral therapy suppressed” individuals (undetectable HIV-RNA levels on antiretroviral therapy). The proportion of CD4⁺and CD8⁺T cells that produce gamma interferon (IFN-γ) and interleukin-2 (IL-2) in response to Gag and Pol peptides was highest in the elite and viremic controllers (P< 0.0001). Forty percent of the elite controllers were HLA-B*57 compared to twenty-three percent of viremic controllers and nine percent of noncontrollers (P< 0.001). Other HLA class I alleles more common in elite controllers included HLA-B*13, HLA-B*58, and HLA-B*81 (P< 0.05 for each). Within elite and viremic controller groups, those with protective class I alleles had higher frequencies of Gag-specific CD8⁺T cells than those without these alleles (P= 0.01). Noncontrollers, with or without protective alleles, had low-level CD8⁺responses. Thus, certain HLA class I alleles are enriched in HIV controllers and are associated with strong Gag-specific CD8⁺IFN-γ⁺IL-2⁺T cells. However, the absence of evidence of T cell-mediated control in many controllers suggests the presence of alternative mechanisms for viral control in these individuals. Defining mechanisms for virus control in “non-T-cell controllers” might lead to insights into preventing HIV transmission or preventing virus replication.

Some human immunodeficiency virus (HIV)-infected individuals are not able to achieve a normal CD4(+) T cell count despite prolonged, treatment-mediated viral suppression. We conducted an intensification study to assess whether residual viral replication contributes to replenishment of the latent reservoir and whether mucosal HIV-specific T cell responses limit the reservoir size. Thirty treated subjects with CD4(+) T cell counts of <350 cells/mm(3) despite viral suppression for ≥ 1 year were randomized to add raltegravir (400 mg twice daily) or matching placebo for 24 weeks. The primary end points were the proportion of subjects with undetectable plasma viremia (determined using an ultrasensitive assay with a lower limit of detection of <.3 copy/mL) and a change in the percentage of CD38(+)HLA-DR(+)CD8(+) T cells in peripheral blood mononuclear cells (PBMCs). The proportion of subjects with undetectable plasma viremia did not differ between the 2 groups (P = .42). Raltegravir intensification did not have a significant effect on immune activation or HIV-specific responses in PBMCs or gut-associated lymphoid tissue. Low-level viremia is not likely to be a significant cause of suboptimal CD4(+) T cell gains during HIV treatment. NCT00631449.