Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. Research Letter AIDS 2013, 27:1513–1519 The CD4/CD8 ratio as a marker T-cell activation, senescence and activation/exhaustion in treated HIV-infected children and young adults Talı ´a Sainz a,M , Sergio Serrano-Villar c,M , Laura Dı ´az a,b , Marı ´a Isabel Gonza ´lez Tome ´ d , Marı ´a Dolores Gurbindo a , Marı ´a Isabel de Jose ´ e , Marı ´a Jose ´ Mellado f , Jose ´ T. Ramos g , Javier Zamora c , Santiago Moreno c and Marı ´a A ´ ngeles Mun ˜ oz-Ferna ´ndez a,b We explored the associations of the CD4/CD8 ratio with markers of immunoactivation, immunosenes- cence and T-cell subsets, in 37 vertically HIV- infected children and adolescents. CD4/CD8 ratio inversion was associated with higher frequencies of activated, senescent and activated/exhausted CD4 R and CD8 R T-cells, and a skewed T-cell phe- notype from naive toward effector memory which persisted after the multivariate analysis. Thus, the CD4/CD8 ratio may identify patients with higher immunoactivation despite ART. Immunoactivation has demonstrated to be a strong predictor of disease progression in HIV-infection, and one of the underlying causes leading to immunosenes- cence, premature aging and adverse outcomes among patients with access to modern ART regimens [1]. The effects of chronic immunoactivation and immunosenes- cence are likely to be more pernicious in vertically HIV- infected individuals, since their immune system coevolves since birth with the virus. Inversion of the CD4/CD8 ratio (<1), a hallmark of untreated HIV infection, is a surrogate marker of immunosenescence and independently predicts all-cause mortality in the general population [2–5]. Although a failure to normalize the CD4/CD8 ratio is commonly observed HIV-infected patients after starting ART, its biological significance and clinical relevance remain unknown. We hypothesized that a low CD4/CD8 ratio despite ART could be a predictor of increased immunoactivation and immunosenescence in vertically-HIV infected children and adolescents. HIV-infected children and adolescents on stable ART were enrolled in a cross-sectional multicenter study. Exclusion criteria included acute or opportunistic infections and chronic inflammatory diseases. The study was approved by the Ethics Committee and all parents or legal guardians and children over 12 years gave written informed consent. Plasma viral load was measured using the Cobas TaqMan HIV-1 assay (Roche Diagnostics Systems, Inc., Branchburg, New Jersey, USA) with a detection limit of 50 copies/ml. CD4 þ and CD8 þ T-cell counts were determined using a Gallios flow cytometer and data analyzed using Kaluza software (Beckman Coulter, Fullerton, California, USA). T-cell activation was characterized by HLADR þ CD38 þ expression, senescence by CD57 þ CD28  , and activation/exhaustion by HLADR þ PD-1 þ , in CD4 þ and CD8 þ T-cells. T-cell subsetswere defined as follows: naive (CD45RA þ CD27 þ ), central memory (CD45RO þ CD27 þ ) and effector memory (CD45RO þ CD27  ). Patients were classified according to the presence of a normal (1) or an inverted (<1) CD4/CD8 ratio. Mann–Whitney tests were used for independent two- group comparisons and the Spearman correlation coefficient to analyze the correlation between continuous variables. Independent associations between CD4 þ and CD8 þ T-cells expressing markers of activation, senes- cence and activation/exhaustion (as dependent variables), with a limited subset of independent variables (including the CD4/CD8 ratio) were explored by a series of multivariate linear regression models. The crude corre- lation coefficients between the percentage of CD4 þ and CD8 þ T-cells with phenotypes of activation, senescence and activation/exhaustion and the CD4/CD8 ratio were calculated, followed by consecutive multivariate analyses adjusting by age, time on viral suppression, HIV-1 RNA less than 50 copies/ml, CD4 þ T-cell nadir and accumu- lated ARTexposure for all dependent variables. Statistical analyses were performed using SPSS 18.0 (SPSS Inc., Chicago, Illinois, USA). Thirty-seven vertically HIV-infected children and adolescents were included, with a mean age of 16.4  3.8years. Twenty-eight patients (75.7%) presented viral load less than 50 copies/ml. Median accumulated exposure to ART was 13.8 years (8.6–15.5), and mean time on viral suppression 4.8 years (1.8–7.3). Median CD4 nadir was 310 cells/ml, median CD4 cell count 783 cells/ml and median CD4/CD8 ratio 1.24. Sixteen (43.2%) patients showed CD4/CD8 ratio inversion (<1). Main correlations between the CD4/CD8 ratio and clinical and immunological variables are shown in Fig. 1. The CD4/CD8 ratio positively correlated with CD4 þ T-cell count, accumulated ARTexposure and time on viral suppression. In contrast, the CD4/CD8 ratio inversely correlated with age and CD8 þ T-cell count. No significant correlation was observed with the CD4 þ ISSN 0269-9370 Q 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins 1513