Mitochondrial haplogroup H is related to CD4+ T cell recovery in HIV infected patients starting combination antiretroviral therapy

The human immunodeficiency virus (HIV) infects and destroys the CD4+ T cell, promoting a continuous loss of CD4+ T cells that leads to immunodeficiency, opportunistic diseases, and death [1, 2]. The cART reduces the plasma HIV-RNA to undetectable levels and restores immunologic function, decreasing clinical progression and prolonging life [3]. However, despite suppression of HIV replication, a fraction of cART-treated patients fail to reconstitute CD4+ T-cell numbers sufficiently [4].

Mitochondrial dysfunction is related to acquired immune deficiency syndrome (AIDS) progression, in which there is mitochondrial DNA (mtDNA) depletion, increased reactive oxygen species (ROS) formation, antioxidant enzyme deficiency, and increased oxidative damage in patients with accelerated AIDS disease [5]. Additionally, mitochondrial toxicity due to nucleoside reverse transcriptase inhibitors may contribute to severe side effects observed in HIV-infected individuals on combination antiretroviral therapy (cART) [5].

Variations in mtDNA sequence are associated with several disorders [6], including HIV infection [5]. The combinations of mtDNA polymorphisms define mitochondrial haplogroups, which have a well-defined phylogeny among human populations [7]. In European Caucasians (N macro-cluster), people stratify in 4 cluster or major-haplogroups (HV, U, JT, and IWX) and several main haplogroups (H, V, pre-V, J, T, U, W, X, I) [7]. In European HIV-infected patients, mtDNA haplogroup has been associated with viroimmunological parameters, metabolic alterations, and AIDS progression [5, 8‐10]. To our knowledge, only a previous study of our group has reported data about European mtDNA haplogroups and immune recovery in a cohort of HIV-infected patients starting cART with CD4+ count < 350 cells/mm³ in a tertiary hospital in Madrid (Spain) [11]. In the current multicentric study, we analyzed the association between European haplogroups and CD4+ T-cell recovery in naïve HIV-infected patients starting cART with CD4+ count < 200 cells/mm³ collected throughout the Spanish national territory.

In this study, haplogroup H was related to better CD4+ T-cells counts recovery in HIV-infected patients starting cART with low CD4 counts and followed during the first 24 months after initiating cART. This association was found both in the univariate and in the multivariate analysis adjusted by the most important baseline characteristics. However, we did not find any association when the continuous outcome measure (slope of CD4+ T-cells recovery) was used, possibly because there is no linear relationship between the analyzed variables.

The data found in this study confirm the positive influence of European haplogroup H on CD4+ T-cells count recovery in cART-treated patients, which was previously described by our group in a different cohort [11]. In addition to the influence of haplogroup H, in this previous article of Guzmán-Fulgencio et al. [11], we also found a worse CD4+ recovery in patients with haplogroup J and T. However, we did not observe any significant association for haplogroups J and T in the current study. The small sample size could explain this discrepancy in these haplogroups, which may have impaired the ability to detect less robust associations. However, we must also consider other factors. On the one hand, the article of Guzmán-Fulgencio et al. [11] studied a cohort of HIV-infected patients provided by a tertiary referral hospital center (Spain), with baseline CD4+ values < 350 cells/mm³, and followed during at least 24 months. On the other hand, we now analyzed a cohort of HIV-infected patients provided by a large number of hospitals spread throughout Spain (a sample more representative of Spanish population), with baseline CD4+ values < 200 cells/mm³ (a more restricted criteria), and followed during the first 24 months after starting cART (the same follow-up in all patients). Moreover, the type of statistical analysis applied was different in our previous study. In the article of Guzmán-Fulgencio et al. [11], a survival analysis was performed with CD4+ > 500 cells/mm³ as the primary outcome, whereas in the present study, we calculated the slope of CD4+ T-cells count for each patient and compared groups by logistic regression analysis.

Moreover, mtDNA haplogroups in other cohort have also been related to CD4+ T-cells recovery in HIV-infected patients who started cART. Grady et al. found that African L2 haplogroup was associated with decreased odds of CD4+ T-cells recovery after cART (CD4+ count change of ≥ 100 cells/mm³ and median CD4+ T-cell increases at 48 weeks of follow-up) in the AIDS Clinical Trials Group study 384 [12]. However, they did not find any significant association with European mitochondrial haplogroups in non-Hispanic white participants.

In the present study, the age of HIV-infected patients with worse CD4+ T-cells recovery was higher than patients with better CD4+ T-cells recovery, which could have had a negative impact since a poorer CD4+ T-cell counts recovery has been found in older HIV-infected patients starting cART [13]. However, we think that only 3 years of difference between groups is not relevant in adults of 35–45 years. In fact, we included the age in the multivariate analysis, and the significant association between haplogroup H and CD4+ T-cells recovery was maintained.

Variants in mtDNA which are not silent may have an essential role in adaptation to environmental conditions, by modulating specific mitochondrial functions [14]. Thus, the differences found in mtDNA haplogroups distribution among the different groups of patients in our study may be because haplogroup H is related to higher activity in the electron transport chain, producing higher levels of ATP and ROS than other haplogroups [15‐17], increasing the immune response against HIV infection [9]. Furthermore, ROS production may lead to an up-regulation of antioxidant defenses without causing severe immune damage [18], contributing to proper immune function, ensuring control of HIV replication and, in turn, decreasing oxidative stress and apoptosis [19, 20]. Additionally, a higher degree of energetic efficiency could have a substantial impact on HIV infection since the efficiency of the metabolism regulate T-cell function and susceptibility to infection [21]. The functional role of mtDNA haplogroups is controversial, but it is possible that the effects of mitochondrial haplogroups may emerge under special conditions such as CD4+ T-cells recovery in HIV-infected patients starting cART. However, we could not perform functional experiments to determinate the energetic efficiency in isolated mitochondria of T-cells from patients.

Nowadays or in the future, our results may have an impact on clinical practice in those cases where cART starts with very low CD4+ T-cells. cART should begin in all HIV-infected patients, regardless of the CD4+ T-cells count in order to decrease the risk of HIV transmission and prevent AIDS-related illness [22]. However, late presentation for HIV care is a significant and persistent issue throughout the world [23‐25], including developed countries with health systems with good access to health services [24]. Late presenters have delayed initiation of cART, CD4 values below 350 cells/mm³ and below 200 cells/mm³ in many cases [26], and higher risk of AIDS progression and death [27]. The initiation of cART with very low CD4+ T-cell counts is consistently associated with poorer outcomes of cART [28]. Thus, our data could provide information to improve the management of HIV-infected patients with poorer prognosis of CD4+ T-cells recovery.

Our study has some limitations that we should take into account to make a correct interpretation of the results. Firstly, this is a retrospective study and, therefore, the case record is selected a priori from patients surviving long enough to yield sufficient follow-up (at least 24 months after cART). Secondly, the sample size is limited, particularly in some haplogroups, which may have impaired the ability to detect less robust associations. Thirdly, although our results suggest that some variants in mtDNA may influence CD4+ T-cell recovery, it would be necessary to perform functional ROS and ATP measurement in the patients to provide additional confirmatory data. Fourthly, this study was carried out on Caucasian patients, and our conclusions are only truly applicable to this population.

In conclusion, European haplogroup H was associated with the improved CD4+ recovery in HIV-infected patients starting cART with CD4+ < 200 cells/mm³. This finding could be useful to understand the host genetic factors involved in the immune recovery of cART-treated patients. Additionally, it also may help to improve the management of patients with a poorer prognosis of immune recovery.