HIV-specific CD8+ T-cell proliferation is prospectively associated with delayed disease progression

Human immunodeficiency virus (HIV)-specific CD8(+) T-cell proliferation is consistently correlated with enhanced host HIV immune control, but whether proliferative responses are a cause or consequence of immune protection is unclear. We measured Env-specific CD8(+) T-cell proliferation and interferon (IFN)-γ secretion in HIV-infected participants with CD4 counts >200, who then completed 121 person-years of prospective follow-up to monitor HIV disease progression. In all, 13 of 31 participants (42%) reached end point during longitudinal follow-up. Strong Env-specific CD8(+) T-cell proliferation (>10% of CD8(+) T cells) was observed in 14/31 participants at baseline, and this was associated with a longer time to HIV disease progression end point, stratified baseline CD4 count (P=0.016). No associations were observed for IFN-γ ELISPOT responses and progression (P>0.2). Strong proliferation remained significant in multivariate Cox regression analyses (P=0.044) as an independent predictor of delayed HIV disease progression, along with baseline CD4 count (P=0.04). Duration of HIV infection was associated with more rapid progression in univariate, but not multivariate, analysis (P=0.112). Age and baseline viral load were not predictive of progression. HIV-specific CD8(+) T-cell proliferation was a correlate of protective immunity in this prospective study; such responses may be important for HIV vaccine protection.     

The mitogenic activity of human T-cell leukemia virus type I is T-cell associated and requires the CD2/LFA-3 activation pathway.

The presence of a high number of activated T cells in the bloodstream and spontaneous proliferation of peripheral blood mononuclear cells in vitro are striking characteristics of human T-cell leukemia virus type I (HTLV-I) infection. The HTLV-I regulatory protein Tax and the envelope protein gp46 have been implicated in mediating the activation process. In this study, HTLV-I-producing cell lines and purified virus from the cell lines were examined for the ability to activate peripheral blood lymphocytes (PBLs) and Jurkat cells. Antisera and monoclonal antibodies against several cellular adhesion proteins involved in T-cell activation and against viral proteins were used to identify which molecules may be participating in the activation process. First, neither virus from a T-cell line, MT2, nor virus produced from the human osteosarcoma cell line HOS/PL was able to induce PBLs to proliferate. In contrast, both fixed and irradiated HTLV-I-producing T-cell lines induced proliferation of PBLs; HOS/PL cells did not activate PBLs. Second, HTLV-I-positive T-cell lines were capable of activating interleukin-2 mRNA expression in Jurkat cells. Induction of interleukin-2 expression was inhibited by anti-CD2 and anti-lymphocyte function-associated antigen 3 (LFA-3) monoclonal antibodies but not anti-human leukocyte antigen-DR, anti-CD4, anti-LFA-1, or anti-intercellular adhesion molecule 1. Similar results were obtained with PBLs as the responder cells. Furthermore, monoclonal antibodies and antisera against various regions of the HTLV-I envelope proteins gp46 and gp21 as well as p40tax did not block activation. These data indicate that HTLV-I viral particles are not intrinsically mitogenic and that infection of target T cells is not necessary for activation. Instead, the mitogenic activity is restricted to virus-producing T cells, requires cell-to-cell contact, and may be mediated through the LFA-3/CD2 activation pathway.     

Lack of CD28 expression on HIV-specific cytotoxic T lymphocytes is associated with disease progression

During HIV infection, CD8+ T cells lacking the costimulatory molecule CD28 increase in number and proportion. This accumulation is associated with disease activity and possibly with CD8+ T-cell dysfunction. In this study, CD8+CD28+ and CD8+CD28- T cells from 41 HIV-infected individuals at various stages of disease were compared in terms of HIV-specific cytotoxicity, TCR beta V repertoire diversity, and cytokine production. We found that the CD28 phenotype of anti-HIV CTL evolves in parallel with disease progression and disease activity. Absolute numbers of CD4+ T cells and CD4+/CD8+ T-cell ratios progressively decreased in 3 groups with an increasing prevalence of CD28- HIV-specific CTL. Conversely, HIV replication levels progressively increased in parallel with the prevalence of CD28- HIV-specific CTL. Repertoire diversity at the level of TCR beta V gene family expression was maintained at normal levels for both CD28+ and CD28- T cells at all stages of infection. Diversity at the level of junctional length polymorphism was more restricted in the CD8+CD28- T-cell population, but this difference remained relatively constant through different stages of infection. Both CD28+ and CD28- T cells produced IL-2 and IFN-gamma, regardless of disease stage and/or the predominant CD28 phenotype of anti-HIV CTL.     

Human B-cell proliferation in response to recombinant interleukin 2 is not due to T-cell help

Positively selected human B-cell suspensions with no detectable T cells and containing more than 99.5% B cells both at the initiation and termination of culture were shown to proliferate in response to interleukin 2 (IL-2) in a dose-dependent fashion. The lack of influence of residual T cells on this proliferative response was demonstrated in experiments where T cells were added back in increasing numbers to B-cell suspensions. No detectable enhancing effect on B-cell proliferation was noted when 2.5% T cells were purposely added back to culture, a proportion far in excess of that which might be expected to contaminate B-cell suspensions under the present methodology. In contrast, when 10% T cells were added back to B-cell cultures, an enhanced proliferation of B cells was observed suggesting that the lack of effect of lower numbers of T cells was due to their inefficiency in helping B-cell proliferation in response to IL-2. Therefore, it is concluded that highly purified IL-2 is capable of triggering human peripheral blood B cells to proliferate and that this proliferation is not due to T-cell help.     

Mesenchymal stromal cells augment CD4+ and CD8+ T-cell proliferation through a CCL2 pathway

Background aimsMesenchymal stromal cells (MSC) derived from bone marrow are immunosuppressive in vitro and in vivo. Recent evidence, however, has shown that in certain settings, MSC can also be immunostimulatory. The mechanisms involved in this process are largely unknown.MethodsMouse spleen T cells were stimulated with allogeneic mixed lymphocyte reaction (MLR) or anti-CD3/CD28 beads and treated with autologous bone marrow MSC or MSC-conditioned medium. CD4+ and CD8+ T-cell proliferation was analyzed after treatment.ResultsWe show that MSC have both suppressive and stimulatory functions toward T cells after stimulation with anti-CD3/CD28 beads or in an MLR. This depended on the ratio of MSC to responder T cells, with low numbers of MSC increasing and higher numbers inhibiting T-cell proliferation. Immunostimulatory function was mediated, in part, by soluble factors. MSC immunosuppression of the MLR was indirect and related to inhibition of antigen-presenting cell maturation. Direct effects of MSC-conditioned medium during anti-CD3/CD28 stimulated proliferation were entirely stimulatory and required the presence of the T-cell receptor. MSC supernatant contained both CCL2 and CCL5 at high levels, but only CCL2 level correlated with the ability to augment proliferation. An anti-CCL2 antibody blocked this proliferative activity.ConclusionsCCL2 plays an important role in the immunostimulatory function of MSC, and we further hypothesize that the immunomodulatory role of MSC is determined by a balance between inhibitory and stimulatory factors, suggesting the need for caution when these cells are investigated in clinical protocols.     

The inhibitory effect of human syncytiotrophoblast plasma membrane vesicles on in vitro lymphocyte proliferation is associated with reduced interleukin 2 receptor expression

The mechanisms by which vesicles of syncytiotrophoblast plasma membranes (STPM) prepared from full-term human placentas inhibit lymphocyte proliferation have been investigated. In the presence of STPM, IL-2 secretion and the expression of protein P55 (IL-2R P55) from its receptor were examined in two models of PBMC proliferation: induced by PHA in 3-day-old cultures, and induced by IL-2 in 6-day-old cultures. In the case of PHA stimulation, STPM strongly inhibited IL-2 (but not IL-1) secretion and IL-2R P55 expression at a concentration where lymphocyte proliferation was also blocked. In these conditions, the addition of excess recombinant IL-2 (rIL-2) only partially restored proliferation and IL-2R P55 expression. In addition, STPM inhibited proliferation and IL-2R P55 expression when resting PBMC were stimulated by a high concentration of rIL-2. These results suggest that STPM inhibit lymphocyte proliferation by affecting one or several events occurring in the synthesis and/or expression of IL-2R P55 by a mechanism which is at least partially independent of its inhibitory effect on IL-2 secretion. The significance of these results is discussed in the context of the survival of the fetal allograft.     

Threshold of pre-T-cell-receptor surface expression is associated with alphabeta T-cell lineage commitment.

BACKGROUND: The development of immature thymocytes is regulated by the pre-T-cell receptor (pre-TCR). The pre-TCR is involved in several developmental processes including rescuing cells from programmed cell death, allelic exclusion and alphabeta versus gammadelta T-cell lineage commitment. A major issue is how the pre-TCR functions to integrate these processes in developing thymocytes. RESULTS: We have used a sensitive immunofluorescence technique to reveal the surface-expression profile of the pre-TCR on immature thymocyte subsets. We show that early pre-T cells (CD25(+)CD44(-)) can be subdivided on the basis of the level of surface pre-TCR expression. Detectable surface pre-TCR expression identified a rapidly cycling population of early pre-T cells which had successfully undergone beta-selection and been rescued from programmed cell death. Late pre-T cells (CD25(-)CD44(-)), which had traversed the beta-selection checkpoint, expressed surprisingly heterogeneous surface levels of the pre-TCR: high levels of surface pre-TCR expression were associated with commitment to the alphabeta T-cell lineage, whereas late pre-T cells with lower levels of surface pre-TCR could develop along both the alphabeta or gammadelta T-cell lineages. CONCLUSIONS: These data demonstrate that the surface expression of the pre-TCR can be used to reveal newly identified stages of T-cell development and to provide insights into alphabeta T-cell lineage commitment. They show that, although pre-TCR expression does not act as a developmental switch per se, its level of surface expression on late pre-T cells predicts their developmental potential.     

NF-kappaB signaling pathway governs TRAIL gene expression and human T-cell leukemia virus-I Tax-induced T-cell death.

The Tax oncoprotein encoded by human T-cell leukemia virus induces both T-cell activation and apoptosis. The mechanism by which Tax induces apoptosis has remained unclear. Using genetically manipulated T-cell lines, we demonstrate that Tax-induced T-cell death is dependent on NF-kappaB signaling. Tax fails to induce apoptosis in T cells lacking IkappaB kinase gamma (IKKgamma), an essential component of the NF-kappaB signaling pathway. This defect was rescued when the mutant cells were reconstituted with exogenous IKKgamma. We further demonstrate that the Tax-induced T-cell death is mediated by TNF (tumor necrosis factor)-related apoptosis-inducing ligand (TRAIL), because this event can be effectively inhibited by a TRAIL-blocking antibody. Consistent with this functional aspect, Tax stimulates the expression of TRAIL mRNA. Finally, we provide genetic evidence demonstrating that the NF-kappaB signaling pathway is essential for TRAIL gene induction by both Tax and T-cell activation signals. These studies reveal a novel function of the NF-kappaB signaling pathway and suggest a key mechanism by which Tax induces T-cell death.     

CD7 augments T cell proliferation via the interleukin-2 autocrine pathway.

The role of CD7, a T cell differentiation antigen, in T cell function is not known at present; this study evaluates the effect of anti-CD7 mAb in PMBC cultures activated with suboptimal concentrations of lectins, antigens, and anti-CD3 mAb. We found that the inclusion of anti-CD7 resulted in increased IL-2 production and IL-2R-alpha expression in these cultures. H-7, a protein kinase C (PKC) inhibitor, and genistein, a protein tyrosine kinase (PTK) inhibitor, significantly suppressed the proliferation of T cells in comitogenic assays. This suggested that the comitogenic effect mediated by CD7 molecule involved both the PKC and the PTK pathways of T cell activation. These drugs appeared to affect the CD7-mediated effects by inhibiting the IL-2 autocrine pathway, especially the up-regulation of IL-2R-alpha since inhibition was not relieved with exogenous rIL-2. Taken together, our results suggest that CD7 augments T cell function by up-regulating IL-2R-alpha expression and IL-2 production via multiple pathways of protein phosphorylation.