The CD31 ؉ subset of human naive CD4 ؉ T cells is thought to contain the population of cells that have recently emigrated from the thymus, while their CD31 ؊ counterparts have been proposed to originate from CD31 ؉ cells after homeostatic cell division. Naive T-cell maintenance is known to involve homeostatic cytokines such as interleukin-7 (IL-7). It remains to be investigated what role this cytokine has in the homeostasis of naive CD4 ؉ T-cell subsets defined by CD31 expression. We provide evidence that IL-7 exerts a preferential proliferative effect on CD31 ؉ naive CD4 ؉ T cells from adult peripheral blood compared with the CD31 ؊ subset. IL-7-driven proliferation did not result in loss of CD31 expression, suggesting that CD31 ؉ naive CD4 ؉ T cells can undergo cytokine-driven homeostatic proliferation while preserving CD31. Furthermore, IL-7 sustained or increased CD31 expression even in nonproliferating cells. Both proliferation and CD31 maintenance were dependent on the activation of phosphoinositide 3-kinase (PI3K) signaling. Taken together, our data suggest that during adulthood CD31 ؉ naive CD4 ؉ T cells are maintained by IL-7 and that IL-7-based therapies may exert a preferential effect on this population. (Blood. 2009;113: 2999-3007) IntroductionHuman naive CD4 ϩ T cells have recently been shown to contain 2 subpopulations distinguished by the expression of CD31 (platelet endothelial cell adhesion molecule-1, PECAM-1). The CD31 ϩ subset is thought to incorporate the population of cells recently emigrated from the thymus, whereas the CD31 Ϫ subset has been proposed to derive from CD31 ϩ after homeostatic cell division. 1 During T-cell development in the thymus, rearrangement of the T-cell receptor (TCR) genes generates stable episomal DNA excision circles (TRECs) that are progressively diluted with cell division. 2-4 Accordingly, CD31 ϩ naive CD4 ϩ T cells have higher TREC content compared with the CD31 Ϫ naive subset. 1 Moreover, the progressive age-associated decline in naive CD4 ϩ T cells is mainly due to a reduction in the CD31 ϩ naive subset while the CD31 Ϫ subset persists, 5,6 further supporting the contribution of thymic output to the maintenance of CD31 ϩ cells. However, the decrease in TREC levels observed during aging is disproportionally greater compared with the decline in CD31 ϩ naive T cells, implicating other mechanisms, in addition to thymic output, in the persistence of these cells into old age. 4 Cytokine-driven expansion has been proposed to significantly contribute to a low level of homeostatic proliferation that maintains naive T-cell numbers. 7 Besides its established importance in thymopoiesis, interleukin-7 (IL-7) is considered to play a key role in naive T-cell survival and proliferation in the periphery. 2,7 In vitro studies of human naive CD4 ϩ T cells cultured in the presence of IL-7 revealed, alongside with its antiapoptotic properties, an ability to induce proliferative responses without a switch to a memory phenotype. 8 IL-7 seems to exert a preferential effect on umbilic...

Until recently, hematopoietic stem cell transplantation was the only curative option for Wiskott-Aldrich syndrome (WAS). The first attempts at gene therapy for WAS using a ϒ-retroviral vector improved immunological parameters substantially but were complicated by acute leukemia as a result of insertional mutagenesis in a high proportion of patients. More recently, treatment of children with a state-of-the-art self-inactivating lentiviral vector (LV-w1.6 WASp) has resulted in significant clinical benefit without inducing selection of clones harboring integrations near oncogenes. Here, we describe a case of a presplenectomized 30-year-old patient with severe WAS manifesting as cutaneous vasculitis, inflammatory arthropathy, intermittent polyclonal lymphoproliferation, and significant chronic kidney disease and requiring long-term immunosuppressive treatment. Following reduced-intensity conditioning, there was rapid engraftment and expansion of a polyclonal pool of transgene-positive functional T cells and sustained gene marking in myeloid and B-cell lineages up to 20 months of observation. The patient was able to discontinue immunosuppression and exogenous immunoglobulin support, with improvement in vasculitic disease and proinflammatory markers. Autologous gene therapy using a lentiviral vector is a viable strategy for adult WAS patients with severe chronic disease complications and for whom an allogeneic procedure could present an unacceptable risk. This trial was registered at www.clinicaltrials.gov as #NCT01347242.

Summary Common variable immunodeficiency disorders (CVID),

Viremia is significantly lower in HIV-2 than in HIV-1 infection, irrespective of disease stage. Nevertheless, the comparable proviral DNA burdens observed for these two infections indicate similar numbers of infected cells. Here we investigated this apparent paradox by assessing cell-associated viral replication. We found that untreated HIV-1-positive (HIV-1 ؉ ) and HIV-2 ؉ individuals, matched for CD4 T cell depletion, exhibited similar gag mRNA levels, indicating that significant viral transcription is occurring in untreated HIV-2 ؉ patients, despite the reduced viremia (undetectable to 2.6 ؋ 10 4 RNA copies/ml). However, tat mRNA transcripts were observed at significantly lower levels in HIV-2 ؉ patients, suggesting that the rate of de novo infection is decreased in these patients. Our data also reveal a direct relationship of gag and tat transcripts with CD4 and CD8 T cell activation, respectively. Antiretroviral therapy (ART)-treated HIV-2 ؉ patients showed persistent viral replication, irrespective of plasma viremia, possibly contributing to the emergence of drug resistance mutations, persistent hyperimmune activation, and poor CD4 T cell recovery that we observed with these individuals. In conclusion, we provide here evidence of significant ongoing viral replication in HIV-2 ؉ patients, further emphasizing the dichotomy between amount of plasma virus and cell-associated viral burden and stressing the need for antiretroviral trials and the definition of therapeutic guidelines for HIV-2 infection.

Haploidentical hematopoietic stem cell transplantation (HSCT) constitutes an important alternative for patients lacking a human leukocyte antigen (HLA)-matched donor. Although the use of haploidentical donors is increasingly common, the long-term impact of generating a donor-derived immune system in the context of an HLA-mismatched thymic environment remains poorly characterized. We performed an in-depth assessment of immune reconstitution in a group of haploidentical HSCT recipients 4 to 6 years posttransplantation, in parallel with the respective parental donors and age-matched healthy control subjects. Our data show that the proportion of naive and memory subsets in the recipients, both within CD8(+) and CD4(+) T cells, more closely resembled that observed in age-matched control subjects than in the donors. HSCT recipients displayed relatively high signal-joint T cell-receptor excision circle levels and a high frequency of the recent thymic emigrant-enriched CD31(+) subset within naive CD4(+) and naive regulatory T cells. Moreover, CD8(+), CD4(+), and regulatory T cells from HSCT recipients displayed a diverse T cell repertoire. These results support a key role for thymic output in T cell reconstitution. Nevertheless, HSCT recipients had significantly shorter telomeres within a naive-enriched CD4(+) T cell population than age-matched control subjects, despite the similar telomere length observed within the most differentiated CD8(+) and CD4(+) T cell subsets. Overall, our data suggest that long-term immune reconstitution was successfully achieved after haploidentical HSCT, a process that appears to have largely relied on de novo T cell production.

Monocytes and myeloid dendritic cells (mDCs) are important orchestrators of innate and human immunodeficiency virus (HIV)-specific immune responses and of the generalized inflammation that characterizes AIDS progression. To our knowledge, we are the first to investigate monocyte and mDC imbalances in HIV type 2 (HIV-2)-positive patients, who typically feature reduced viremia and slow disease progression despite the recognized ability of HIV-2 to establish viral reservoirs and overcome host restriction factors in myeloid cells. We found a heightened state of monocyte and mDC activation throughout HIV-2 infection (characterized by CD14(bright)CD16(+) expansion, as well as increased levels of soluble CD14, HLA-DR, and CD86), together with progressive mDC depletion. Importantly, HIV-2-positive patients also featured overexpression of the inhibitory molecule PD-L1 on monocytes and mDCs, which may act by limiting the production of proinflammatory molecules. These data, from patients with a naturally occurring form of attenuated HIV disease, challenge current paradigms regarding the role of monocytes in HIV/AIDS and open new perspectives regarding potential strategies to modulate inflammatory states.

Cell activation is a vital step for T-cell memory/effector differentiation as well as for productive HIV infection. To identify novel regulators of this process, we used next-generation sequencing to profile changes in microRNA expression occurring in purified human naive CD4 T cells in response to TCR stimulation and/or HIV infection. Our results demonstrate, for the first time, the transcriptional up-regulation of miR-34c-5p in response to TCR stimulation in naive CD4 T cells. The induction of this miR was further consistently found to be reduced by both HIV-1 and HIV-2 infections. Overexpression of miR-34c-5p led to changes in the expression of several genes involved in TCR signaling and cell activation, confirming its role as a novel regulator of naive CD4 T-cell activation. We additionally show that miR-34c-5p promotes HIV-1 replication, suggesting that its down-regulation during HIV infection may be part of an anti-viral host response.

Plasmacytoid dendritic cells (pDC) provide an important link between innate and acquired immunity, mediating their action mainly through IFN-α production. pDC suppress HIV-1 replication, but there is increasing evidence suggesting they may also contribute to the increased levels of cell apoptosis and pan-immune activation associated with disease progression. Although having the same clinical spectrum, HIV-2 infection is characterized by a strikingly lower viremia and a much slower rate of CD4 decline and AIDS progression than HIV-1, irrespective of disease stage. We report here a similar marked reduction in circulating pDC levels in untreated HIV-1 and HIV-2 infections in association with CD4 depletion and T cell activation, in spite of the undetectable viremia found in the majority of HIV-2 patients. Moreover, the same overexpression of CD86 and PD-L1 on circulating pDC was found in both infections irrespective of disease stage or viremia status. Our observation that pDC depletion occurs in HIV-2 infected patients with undetectable viremia indicates that mechanisms other than direct viral infection determine the pDC depletion during persistent infections. However, viremia was associated with an impairment of IFN-α production on a per pDC basis upon TLR9 stimulation. These data support the possibility that diminished function in vitro may relate to prior activation by HIV virions in vivo, in agreement with our finding of higher expression levels of the IFN-α inducible gene, MxA, in HIV-1 than in HIV-2 individuals. Importantly, serum IFN-α levels were not elevated in HIV-2 infected individuals. In conclusion, our data in this unique natural model of “attenuated” HIV immunodeficiency contribute to the understanding of pDC biology in HIV/AIDS pathogenesis, showing that in the absence of detectable viremia a major depletion of circulating pDC in association with a relatively preserved IFN-α production does occur.