CD4+CD28null T lymphocytes resemble CD8+CD28null T lymphocytes in their responses to IL-15 and IL-21 in HIV-infected patients

HIV-infected individuals suffer from accelerated immunologic aging. One of the most prominent changes during T lymphocyte aging is the accumulation of CD28 T lymphocytes, mainly CD8 but also CD4 T lymphocytes. Enhancing the functional properties of these cells may be important because they provide antigen-specific defense against chronic infections. The objective of this study was to compare the responses of CD4CD28 and CD8CD28 T lymphocytes from HIV-infected patients to the immunomodulatory effects of cytokines IL-15 and IL-21. We quantified the frequencies of CD4CD28 and CD8CD28 T lymphocytes in peripheral blood from 110 consecutive, HIV-infected patients and 25 healthy controls. Patients showed increased frequencies of CD4CD28 and CD8CD28. Both subsets were positively correlated to each other and showed an inverse correlation with the absolute counts of CD4 T lymphocytes. Higher frequencies of HIV-specific and CMV-specific cells were found in CD28 than in CD28 T lymphocytes. Activation of STAT5 by IL-15 and STAT3 by IL-21 was higher in CD28 compared with CD28 T lymphocytes. Proliferation, expression of CD69, and IFN-g production in CD28 T lymphocytes were increased after treatment with IL-15, and IL-21 potentiated most of those effects. Nevertheless, IL-21 alone reduced IFN-g production in response to anti-CD3 stimulation but increased CD28 expression, even counteracting the inhibitory effect of IL-15. Intracytoplasmic stores of granzyme B and perforin were increased by IL-15, whereas IL21 and simultaneous treatment with the 2 cytokines also significantly enhanced degranulation in CD4CD28 and CD8CD28 T lymphocytes. IL-15 and IL-21 could have a role in enhancing the effector response of CD28 T lymphocytes against their specific chronic antigens in HIV-infected patients. J. Leukoc. Biol. 98: 000–000; 2015. Introduction Aging is associated with phenotypic and functional alterations in the immune system, which particularly affect the T lymphocyte compartment. These changes, associated with morbidity and mortality, are often referred to as immunosenescence. Increasing evidence suggests that HIV-infected individuals experience similar immunologic changes as uninfected elderly persons [1, 2]. Therefore, HIV-infected individuals suffer from accelerated aging, probably from immune activation and inflammation from chronic infection [3–5]. The persistent infection leads to constant stimulation of the immune system. HIV-infected individuals also lose CD4 T lymphocytes by activation-induced cell death. On the other hand, thymus involution reduces the capacity to produce new cells, resulting in a reduction of circulatory, naive T lymphocytes [6]. These events lead to impaired T lymphocyte homeostasis, resulting in progressive accumulation of highly differentiated T lymphocytes, one of the hallmarks of early aging in HIV infection [7]. The increase in the proportion of highly differentiated T lymphocytes limits T lymphocyte diversity, altering the overall immune response to pathogens by their reduced susceptibility to apoptosis and their oligoclonal expansions against chronic infection [8]. Loss of CD28 expression in highly differentiated T lymphocytes is a key predictor of immune incompetence in the elderly and HIV-infected individuals [9]. These subpopulations are thought to show the propensity to secrete proinflammatory cytokines, such as TNF-a and IFN-g, and to lose the capacity to produce IL-2 [10]. Moreover, they showed a decline in proliferative capacity associated with short telomere length and partial activation, and even an anergic state by the absence of costimulatory signal during immune activation. Other characteristics of CD28 T lymphocytes are an altered capacity to help B cell proliferation and antibody production, thus affecting vaccine responses [11]. Nevertheless, these CD28 cells are able to be activated, maybe through the expression of 1. Correspondence: Immunology Department, Hospital Universitario Central de Asturias, 33006 Oviedo, Spain. E-mail: ralonsoarias@hotmail.es Abbreviations: CD = cluster of differentiation, gc = g chain, HAART = highly active antiretroviral therapy, IR = interquartile range, KLRG-1 = killer-cell lectin-like receptor G1, LAMP-1 = CD107a lysosome-associated membrane protein-1, MFI = mean fluorescence intensity, NKG2D = natural-killer group 2-member D, NKG = NK cell-related receptors 0741-5400/15/0098-0001 © Society for Leukocyte Biology Volume 98, September 2015 Journal of Leukocyte Biology 1 Epub ahead of print June 1, 2015 doi:10.1189/jlb.1A0514-276RR Copyright 2015 by The Society for Leukocyte Biology. several NKRs. Among NKG2 receptors, only NKG2D has been shown to express in CD4CD28-aged T lymphocytes. In this way, augmented costimulation through NKG2D is effective in rescuing CD4-unhelped CD8 and CD28 T lymphocytes from their pathophysiological fate [12, 13]. Despite the accumulation of CD28 T lymphocytes being more marked within the CD8 subset, the increase of the percentage of CD4 T lymphocytes that lack CD28 expression is common in elderly persons and in patients with chronic infections and autoimmune diseases [14–17]. CD4CD28 T lymphocytes are phenotypically and functionally distinct from CD4CD28 T lymphocytes but exhibit similarities with CD8CD28 T lymphocytes, for example, in relation to activation and cytotoxic function [18]. In HIV-infected patients, high levels of CD4 and CD8 T lymphocytes lacking expression of CD28 have been reported [19, 20]. Low levels of CD4CD28 T lymphocytes, but not CD8CD28 T lymphocytes, are independent predictors for progression to AIDS and of high mortality in HIV-infected patients, whereas effective antiretroviral therapy reduces the proportion of those subsets [21–23]. Moreover, nadir CD4 T lymphocyte count and numbers of CD4CD28 T lymphocytes predict functional responses to immunizations in chronic HIV-1 infection [24]. Generation of highly differentiated T lymphocytes is dependent on antigen stimulation, but their survival is antigenindependent and requires peripherally produced cytokines, particularly those that use the common g-chain for signaling, such as IL-15 [25–27]. IL-15 not only stimulates the proliferation of CD8CD28 and CD4CD28 T lymphocytes, but also promotes both their effector function and their cytotoxic properties [28–30]. Meanwhile, IL-21 could be useful for up-regulating the cytotoxic effector function of CD8 T lymphocytes without inducing HIV-1 replication in vitro [29, 31]. This fact makes it very interesting as a therapeutic option for HIV-infected patients. As the accumulation of CD28 T lymphocyte is one of the most prominent changes in HIV-infected individuals, enhancing the functional properties of these cells with the above-described cytokines may be important as they provide antigen-specific defense against chronic infections. Therefore, our objectives were to evaluate the effects of IL-15 and IL-21 on CD4CD28 and CD8CD28 T lymphocytes and verify if the 2 CD28 T lymphocyte subsets showed similar patterns in response to these activating cytokines. MATERIALS AND METHODS