HIV-infected individuals with low CD4/CD8 ratio despite effective antiretroviral therapy exhibit altered T cell subsets, heightened CD8+ T cell activation, and increased risk of non-AIDS morbidity and mortality

Abstract

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.

Figure 1. Percentages and absolute counts of CD8+ T cell maturation subsets among HIV-/CMV+ individuals and ART-suppressed HIV-infected patients with CD4 counts >500 cells/mm³ stratified by a normal (4th quartile, ≥1) or low (1st quartile, ≤0.4) CD4/CD8 ratio.

HIV-infected individuals with low CD4/CD8 ratio had lower percentages of T_N, T_CM, and T_TR CD8+ cells, higher T_EM and T_EMRA (A), and higher absolute counts (B) of all subsets compared to those with higher CD4/CD8 ratio and with healthy controls.

Figure 2. Percentages and absolute counts of CD8+ activation phenotypes among HIV-/CMV+ individuals and ART-suppressed HIV-infected patients with CD4 counts >500 cells/mm³ stratified by a normal (4th quartile, ≥1, in green) or low (1st quartile, ≤0.4, in red) CD4/CD8 ratio.

Subjects with low CD4/CD8 ratio showed higher percentages (A) and absolute counts (B) of HLADR+, CD28− and CD28−CD57+, and higher absolute counts of PD1+ cells (B). There were no differences in HIV-infected individuals in the proportion of CD28−CD8+ T cells expressing CD57, being significantly lower in both groups compared to HIV-/CMV+ controls.

Figure 3. Association between the CD4/CD8 ratio and the % of CD28−CD8+ T cells with indoleamine 2,3-dioxygenase-1 (IDO-1) activity (kinurenine/tryptophan ratio) among participants in the SOCA cohort with 500 CD4+ T cells/mm³.

The KT ratio significantly correlated with the CD4/CD8 ratio and the % of CD28+CD8+ T cells. The between the CD4/CD8 ratio and the KT ratio was confirmed in a linear regression analysis adjusted by age, gender and cumulative ART exposure (Beta = −0.72, P = 0.009). The red line represents a linear prediction.

Figure 4. Association between the CD4/CD8 ratio in blood and in lymph nodes or in GALT.

While no association with the CD4/CD8 ratio in lymph nodes was detected (A), it correlated positively with the ratio in GALT (B). The red line represents a linear prediction.

Figure 5. Impact of early or later ART initiation in peripheral CD4+ T cell counts, CD8+ T cell counts and CD4/CD8 ratio in the OPTIONS cohort.

The CD4/CD8 ratio was compared between HIV-uninfected individuals (blue) and HIV-infected individuals initiating ART “early,” ≤6 months of infection (green), or “later,” ≥2 years after initial infection (red), at acute HIV diagnosis and after 1 year of ART. Median CD4/CD8 ratio was significantly higher after one year in early ART initiators compared to later initiators. (A). Early ART initiators experienced higher CD4+ T cell increase (B) than later initiators (C) after one year of ART (221 cells/mm³ vs. 130, respectively, P<0.001). No differences were observed in CD8+ T cell counts between early (D) and later ART initiators (E) after one year of ART (−212 cells/mm³ vs. −114, respectively, P = 0.098) but CD8+ T cells were significantly different between groups beyond one year of ART (−309 cells/mm³ vs. −114, respectively, P = 0.014). Changes in the CD4/CD8 ratio among recently HIV-infected individuals initiating ART early (F) and later (G) were also assessed over time. Early ART initiators experienced a higher increase at one year of ART than later initiators (+0.43 vs. +0.25, P<0.001). Individual participant trajectories shown with red lines, estimated mean values over time from linear mixed models adjusted by age, sex, baseline CD4+ T cells shown in thick black lines.