Progressive contraction of the latent HIV reservoir around a core of less-differentiated CD4⁺ memory T Cells.

In patients who are receiving prolonged antiretroviral treatment (ART), HIV can persist within a small pool of long-lived resting memory CD4(+) T cells infected with integrated latent virus. This latent reservoir involves distinct memory subsets. Here we provide results that suggest a progressive reduction of the size of the blood latent reservoir around a core of less-differentiated memory subsets (central memory and stem cell-like memory (TSCM) CD4(+) T cells). This process appears to be driven by the differences in initial sizes and decay rates between latently infected memory subsets. Our results also suggest an extreme stability of the TSCM sub-reservoir, the size of which is directly related to cumulative plasma virus exposure before the onset of ART, stressing the importance of early initiation of effective ART. The presence of these intrinsic dynamics within the latent reservoir may have implications for the design of optimal HIV therapeutic purging strategies.

Role of glucocorticoid-induced leucine zipper (GILZ) expression by dendritic cells in tolerance induction.

Dendritic cells (DCs) play a crucial role in T cell allorecognition in the context of organ transplantation and allogeneic hematopoietic stem cell transplantation (allo-HSCT). This DC function is believed to be directly involved in allo-HSCT morbidity and mortality. DC functions range from immunoaggressive responses to the promotion of tolerance, reflecting functional plasticity. This unique characteristic offers a rationale to propose generation of tolerogenic DCs as a therapeutic tool for graft-versus-host disease (GVHD). The accumulated preclinical findings support the concept that glucocorticoid-induced leucine zipper (GLIZ) expression redirects mature DC function toward a tolerogenic mode, driving differentiation of antigen-specific regulatory T cells. Taking into account the unique role of DCs within the allo-HSCT context, novel preventive and curative therapeutics for GVHD might be based on the selective induction of GILZ expression in vivo.

Impact of highly active antiretroviral therapy on the maturation of anti-HIV-1 antibodies during primary HIV-1 infection.

OBJECTIVES: To study the impact of highly active antiretroviral therapy (HAART) on isotype switching and avidity maturation of HIV-1-specific immunoglobulin G (IgG) in patients with primary HIV-1 infection (PHI). METHODS: We studied the emergence and the evolution of anti-HIV IgG antibodies by quantitative immunoblotting to analyse IgG subclasses and IgG avidity. Serum samples were obtained from 16 PHI patients from the French PRIMO Cohort Study at various points in the first year of infection: eight patients received no treatment (group I), and eight patients received efficient HAART (group II) during the study period. RESULTS: Early initiation of HAART in PHI patients partially prevented an increase in anti-HIV-1 IgG levels. Within IgG subclasses, the amount of anti-HIV-1 IgG1 gradually increased with time in both groups, although levels remained lower in treated patients. The anti-p24 IgG2 level was always lower in group II. We observed a decrease in anti-p24 IgG3 over time in both groups. Treatment did not affect the maturation of HIV-1 IgG avidity, which increased in both groups until month 3 and then remained high until the end of the 12-month follow-up period. CONCLUSIONS: HAART in PHI partially prevents the emergence of HIV-1 IgG antibodies, but does not affect the quality of these antibodies, as reflected in their isotype and avidity.

Stromal-derived factor-1 in human tumors recruits and alters the function of plasmacytoid precursor dendritic cells.

Dendritic-cell (DC) trafficking and function in tumors is poorly characterized, with studies confined to myeloid DCs (DC1s). Tumors inhibit DC1 migration and function, likely hindering specific immunity. The role of plasmacytoid DCs (DC2s) in tumor immunity is unknown. We show here that malignant human ovarian epithelial tumor cells express very high levels of stromal-derived factor-1, which induces DC2 precursor (preDC2) chemotaxis and adhesion/transmigration, upregulates preDC2 very late antigen (VLA)-5, and protects preDC2s from tumor macrophage interleukin-10-induced apoptosis, all through CXC chemokine receptor-4. The VLA-5 ligand vascular-cell adhesion molecule-1 mediated preDC2 adhesion/transmigration. Tumor preDC2s induced significant T-cell interleukin-10 unrelated to preDC2 differentiation or activation state, and this contributed to poor T-cell activation. Myeloid precursor DCs (preDC1s) were not detected. Tumors may weaken immunity by attracting preDC2s and protecting them from the harsh microenvironment, and by altering preDC1 distribution.

Preferential and persistent depletion of CCR5+ T-helper lymphocytes with nonlymphoid homing potential despite early treatment of primary HIV infection.

Strains of human immunodeficiency virus (HIV) transmitted between individuals use the CCR5 coreceptor, but no preferential depletion of particular Th-lymphocyte subpopulations has been reported during primary HIV infection (PHI). In contrast, gut-associated Th lymphocytes are preferentially depleted in macaques recently infected by simian immunodeficiency virus. The expression of CCR5 and the intestinal homing receptor integrin alpha4beta7 on subpopulations of Th lymphocytes was studied in 12 patients with PHI. There was a profound decrease of circulating alpha4beta7+ Th lymphocytes and CCR5+ memory Th lymphocytes with nonlymphoid homing potential (CD62L-CD45RO+). Unlike other Th lymphocytes, this cell population remained depleted despite early control of viral replication under antiretroviral treatment. Therefore, HIV preferentially targets a specific CCR5+ subpopulation of Th lymphocytes early during infection, inducing its persistent depletion despite treatment. Protective immunity in vivo depends on Th lymphocytes carrying homing capacity to nonlymphoid tissue, and therefore these data may explain the persistent abnormalities of immune functions in patients infected with HIV.

Deregulation of the expression of the fractalkine/fractalkine receptor complex in HIV-1-infected patients.

Fractalkine is the only member of the CX3C chemokine family. Polymorphism of the fractalkine receptor gene may influence the prognosis of human immunodeficiency virus (HIV) infection, but the nature of the cells expressing fractalkine or its receptor in HIV-infected patients remains unknown. We show that, in contrast to HIV-uninfected individuals, a large number of cells expressed fractalkine in T-cell zones of lymph nodes from HIV-infected patients. CD83(+) mature and CD123(+) plasmacytoid dendritic cells as well as plasma cells are involved in this increased expression of fractalkine. Increased numbers of plasmacytoid dendritic cells and plasma cells were present in T-cell zones of HIV-infected patients. CD83(+) dendritic cells were present in similar number in HIV-infected patients and controls, but an increased fraction of these cells produced fractalkine in HIV-infected patients. Many plasma cells in the gut-associated lymphoid tissue from HIV-infected patients also produced fractalkine, whereas few cells produced fractalkine in the gut of controls. The fraction of CD45RO(+) and CD45RO(-) T helper (Th) cells expressing the fractalkine receptor CX3CR1 was higher in HIV-infected patients than in healthy individuals, and these cells were abnormally sensitive to fractalkine stimulation. This increased response correlated with HIV viremia, and it returned to normal levels in patients successfully treated with antiretroviral drugs. The increased expression of the fractalkine/fractalkine receptor complex associated with HIV infection may affect adhesion and migration of Th lymphocytes and their interaction with dendritic cells. Thus, it may influence the equilibrium between depletion and renewal of the Th lymphocyte compartment.

Early control of HIV replication in primary HIV-1 infection treated with antiretroviral drugs and pegylated IFN alpha: results from the Primoferon A (ANRS 086) Study.

IFN alpha has both antiviral and immunostimulating properties. The ANRS086 Primoferon A Study evaluated in 12 patients with primary HIV infection the tolerance and efficacy of an early and transient administration of pegylated IFN alpha, in addition to highly active antiretroviral therapy. Tolerance was good, and this regimen allowed the early control of HIV replication and rapid decay of the viral reservoir. These results support the initiation of comparative studies with pegylated INF alpha in primary HIV infection.

Regulation of CCR6 chemokine receptor expression and responsiveness to macrophage inflammatory protein-3alpha/CCL20 in human B cells.

The regulation of CCR6 (chemokine receptor 6) expression during B-cell ontogeny and antigen-driven B-cell differentiation was analyzed. None of the CD34(+)Lin(-) hematopoietic stem cell progenitors or the CD34(+)CD19(+) (pro-B) or the CD19(+)CD10(+) (pre-B/immature B cells) B-cell progenitors expressed CCR6. CCR6 is acquired when CD10 is lost and B-cell progeny matures, entering into the surface immunoglobulin D(+) (sIgD(+)) mature B-cell pool. CCR6 is expressed by all bone marrow-, umbilical cord blood-, and peripheral blood-derived naive and/or memory B cells but is absent from germinal center (GC) B cells of secondary lymphoid organs. CCR6 is down-regulated after B-cell antigen receptor triggering and remains absent during differentiation into immunoglobulin-secreting plasma cells, whereas it is reacquired at the stage of post-GC memory B cells. Thus, within the B-cell compartment, CCR6 expression is restricted to functionally mature cells capable of responding to antigen challenge. In transmigration chemotactic assays, macrophage inflammatory protein (MIP)-3alpha/CC chemokine ligand 20 (CCL20) induced vigorous migration of B cells with differential chemotactic preference toward sIgD(-) memory B cells. These data suggest that restricted patterns of CCR6 expression and MIP-3alpha/CCL20 responsiveness are integral parts of the process of B-lineage maturation and antigen-driven B-cell differentiation.

Fractalkine receptor expression by T lymphocyte subpopulations and in vivo production of fractalkine in human.

Expression and function of the fractalkine receptor CX3CR1 by T lymphocyte subpopulations was evaluated in healthy individuals. In CD8(+) T lymphocytes, CX3CR1 was expressed by and functional in both CD45RO(-) and CD45RO(+) cells. In CD4(+) T lymphocytes, CX3CR1 was expressed mainly by CD45RO(+) cells, and almost exclusively by activated HLA-DR(+) T lymphocytes. This receptor was functional in CD45RO(+) cells, but not in CD45RO(-) cells. Expression of fractalkine was detected by in situ hybridization and immunohistochemistry in endothelial cells of normal lung and thymus. In hyperplastic lymph nodes, fractalkine was expressed by endothelial cells of high endothelial venules and of subcapsular vessels, by follicular dendritic cells (FDC) and by some follicle lymphocytes. Fractalkine mRNA was constitutively present in the HK FDC-like cell line, and it was induced in vitro in B lymphocytes stimulated by an anti-micro or by a CD40 mAb. These findings indicate that fractalkine may contribute to the recruitment of effector T helper lymphocytes, either in peripheral tissues or in lymphoid organs. In these tissues, fractalkine and its receptor may favor contact within follicles between activated T helper lymphocytes, activated B lymphocytes and FDC, thus contributing to the maturation of the B lymphocyte response.

Cutting edge: HIV-1 Tat protein differentially modulates the B cell response of naive, memory, and germinal center B cells.

Critical steps of B cell differentiation occur within lymphoid organs that are also major sites of HIV-1 replication. Because Tat can be released by infected cells, we investigated whether extracellular HIV-1 Tat modulates cell proliferation of B cells at critical stages of their differentiation. Here we show that extracellular Tat inhibited the proliferation of B cell receptor-triggered naive and memory B cells by >80% but had no effect on their CD40 mAb and IL-4-mediated proliferation. In striking contrast, Tat doubled the germinal center B cell proliferation induced by CD40 mAb and IL-4. These effects were dose dependent and required the addition of Tat at the initiation of the culture, suggesting that Tat acts on early stages of cell cycle progression. By its effects on B cell subsets, Tat might directly affect the normal B cell differentiation process in HIV-positive patients and favor the occurrence of AIDS-associated B cell lymphomas.

Antigen receptor engagement selectively induces macrophage inflammatory protein-1 alpha (MIP-1 alpha) and MIP-1 beta chemokine production in human B cells.

We show herein that B cell Ag receptor (BCR) triggering, but not stimulation by CD40 mAb and/or IL-4, rapidly induced the coordinated expression of two closely related T cell chemoattractants, macrophage inflammatory protein-1 beta (MIP-1 beta) and MIP-1 alpha, by human B cells. Naive, memory, and germinal center B cells all produced MIP-1 alpha/beta in response to BCR triggering. In contrast to MIP-1 alpha/beta, IL-8, which is spontaneously produced by germinal center B cells but not by naive and memory B cells, was not regulated by BCR triggering. Culturing follicular dendritic cell-like HK cells with activated B cells did not regulate MIP-1 alpha/beta production, but it did induce production of IL-8 by HK cells. Microchemotaxis assays showed that CD4+CD45RO+ T cells of the effector/helper phenotype actively migrated along a chemotactic gradient formed by BCR-stimulated B cells. This effect was partially blocked by anti-MIP-1 beta and anti-CC chemokine receptor 5 Ab, but not by anti-MIP-1 alpha Ab suggesting that MIP-1 beta plays a major role in this chemoattraction. Since maturation of the B cell response to a peptide Ag is mostly dependent on the availability of T cell help, the ability of Ag-stimulated B cells to recruit T cells via MIP-1 alpha/beta, may represent one possible mechanism enabling cognate interactions between rare in vivo Ag-specific T and B cells.

B cell-driven HIV type 1 expression in T cells: an essential role of CD86 costimulatory molecule.

During HIV-1 infection, HIV-1 is sequestered and actively replicates within lymphoid organs, mainly in areas essential for antigen-specific T-B interactions. We investigated whether cognate T-B interactions not only drive humoral response to HIV-1 but also enhance viral replication. Costimulation of in vitro HIV-1-infected tonsillar T cells with autologous or allogeneic activated B cells increased both viral replication and T cell proliferation. Addition of CD86 MAb to cocultures inhibited most p24 (84 +/- 12%, n = 13) and IL-2 (99 +/- 2%, n = 6) production, decreased T cell proliferation by 46 +/- 15% (n = 13), and decreased TNF-alpha and IFN-gamma production by 67 +/- 17% (n = 6) and 53 +/- 6% (n = 6), respectively. In contrast, CD80 MAb, which strongly inhibited IL-2 production (77 +/- 10%, n = 6), moderately downregulated p24 and TNF-alpha production (29 +/- 21%, n = 13 and 34 +/- 10%, n = 6, respectively) and did not decrease T cell proliferation (8 +/- 10%, n = 13) or IFN-gamma production (14 +/- 13%, n = 6). We thus showed that B cells deliver a potent CD86/CD28 costimulatory signal that induces T cell proliferation and simultaneously enhances HIV-1 replication. CD86+ B cells, mainly localized within the light zone of germinal centers, might thus favor active in situ replication of HIV-1 in response to each new challenge by T-dependent antigens.

CD40/CD40L interactions and cytokines regulate HIV replication in B cells in vitro.

Using our in vitro model of normal B cell infection, we investigated whether cellular interactions and/or cytokines directing the B cell response also regulate HIV replication. Phorbol esters and CD40 Ab plus IL4, added prior to infection, substantially increased subsequent viral replication. Postinfection, IL2 with or without IL4 and, to a lesser extent, CD40/CD40L interactions enhanced viral replication. In contrast, IL10 down-regulated HIV replication induced by cytokines, without affecting spontaneous or CD40 Ab-induced replication. Both enhancing and inhibitory effects of cytokines on viral replication were independent of their ability to modulate B cell proliferation. Thus, these two phenomena seem to be independently regulated in human B cells.

Mechanisms of opsonized HIV entry in normal B lymphocytes.

Using our in vitro model of normal B cell infection that functions with low doses of HIV but requires virus opsonization by seropositive patient serum, and complement, we analyzed what receptors allowed virus entry. Here, we show that HIV infection of B cells occurs through 2 major receptors: the CD4 antigen and the CR1/CR2 complex. These 2 pathways work independently since a complete inhibition of virus entry requires both CD4 and CD21/CD35 blockade on CD4dim tonsillar B cells whereas only the latter is critical on CD4-negative B cells.