Current perspectives on mesenchymal stromal cell therapy for graft versus host disease.

Graft versus host disease (GvHD) is the clinical condition in which bone marrow-derived mesenchymal stromal cells (MSCs) have been most frequently studied. In this review, we summarize the experience from clinical trials that have paved the way to translation. While MSC-based therapy has shown an exceptional safety profile, identifying potency assays and disease biomarkers that reliably predict the capacity of a specific MSC batch to alleviate GvHD has been difficult. As GvHD diagnosis and staging are based solely on clinical criteria, individual patients recruited in the same clinical trial may have vastly different underlying biology, obscuring trial outcomes and making it difficult to determine the benefit of MSCs in subgroups of patients. An accumulating body of evidence indicates the importance of considering not only the cell product but also patient-specific biomarkers and/or immune characteristics in determining MSC responsiveness. A mode of action where intravascular MSC destruction is followed by monocyte-efferocytosis-mediated skewing of the immune repertoire in a permissive inflammatory environment would both explain why cell engraftment is irrelevant for MSC efficacy and stress the importance of biologic differences between responding and nonresponding patients. We recommend a combined analysis of clinical outcomes and both biomarkers of disease activity and MSC potency assays to identify patients with GvHD who are likely to benefit from MSC therapy.

Cancer Immunotherapy with Immune Checkpoint Inhibitors-Biomarkers of Response and Toxicity; Current Limitations and Future Promise.

Immune checkpoint inhibitors are monoclonal antibodies that are used to treat over one in three cancer patients. While they have changed the natural history of disease, prolonging life and preserving quality of life, they are highly active in less than 40% of patients, even in the most responsive malignancies such as melanoma, and cause significant autoimmune side effects. Licenced biomarkers include tumour Programmed Death Ligand 1 expression by immunohistochemistry, microsatellite instability, and tumour mutational burden, none of which are particularly sensitive or specific. Emerging tumour and immune tissue biomarkers such as novel immunohistochemistry scores, tumour, stromal and immune cell gene expression profiling, and liquid biomarkers such as systemic inflammatory markers, kynurenine/tryptophan ratio, circulating immune cells, cytokines and DNA are discussed in this review. We also examine the influence of the faecal microbiome on treatment outcome and its use as a biomarker of response and toxicity.

Impact of chemokine C-C ligand 27, foreskin anatomy and sexually transmitted infections on HIV-1 target cell availability in adolescent South African males.

We compared outer and inner foreskin tissue from adolescent males undergoing medical male circumcision to better understand signals that increase HIV target cell availability in the foreskin. We measured chemokine gene expression and the impact of sexually transmitted infections (STIs) on the density and location of T and Langerhans cells. Chemokine C-C ligand 27 (CCL27) was expressed 6.94-fold higher in the inner foreskin when compared with the outer foreskin. We show that the density of CD4+CCR5+ cells/mm2 was higher in the epithelium of the inner foreskin, regardless of STI status, in parallel with higher CCL27 gene expression. In the presence of STIs, there were higher numbers of CD4+CCR5+ cells/mm2 cells in the sub-stratum of the outer and inner foreskin with concurrently higher number of CD207+ Langerhans cells (LC) in both tissues, with the latter cells being closer to the keratin surface of the outer FS in the presence of an STI. When we tested the ability of exogenous CCL27 to induce T-cell migration in foreskin tissue, CD4 + T cells were able to relocate to the inner foreskin epithelium in response. We provide novel insight into the impact CCL27 and STIs on immune and HIV-1 target cell changes in the foreskin.

Addition of a Viral Immunomodulatory Domain to Etanercept Generates a Bifunctional Chemokine and TNF Inhibitor.

The inhibition of tumor necrosis factor (TNF) through the use of either antibodies or soluble receptors is a highly effective strategy for the clinical control of chronic inflammatory conditions such as rheumatoid arthritis. Different viruses have similarly exploited this concept by expressing a set of specifically tailored secreted TNF decoy receptors to block host inflammatory responses. Poxviruses have been shown to encode at least two distinct molecules, termed Cytokine response modifier D (CrmD) and CrmB, in which a TNF inhibitor is combined with a chemokine inhibitor on the same molecule. The ectromelia virus CrmD protein was found to be a critical determinant of virulence in vivo, being able to control local inflammation to allow further viral spread and the establishment of a lethal infection. Strikingly, both the TNF and the chemokine inhibitory domains are required for the full activity of CrmD, suggesting a model in which inhibition of TNF is supported by the concomitant blockade of a reduced set of chemokines. Inspired by this model, we reasoned that a similar strategy could be applied to modify the clinically used human TNF receptor (etanercept), producing a generation of novel, more effective therapeutic agents. Here we show the analysis of a set of fusion proteins derived from etanercept by addition of a viral chemokine-binding protein. A bifunctional inhibitor capable of binding to and blocking the activity of TNF as well as a set of chemokines is generated that is active in the prevention of arthritis in a murine disease model.

Immunomodulatory Therapeutic Strategies in Stroke.

The role of immunity in all stages of stroke is increasingly being recognized, from the pathogenesis of risk factors to tissue repair, leading to the investigation of a range of immunomodulatory therapies. In the acute phase of stroke, proposed therapies include drugs targeting pro-inflammatory cytokines, matrix metalloproteinases, and leukocyte infiltration, with a key objective to reduce initial brain cell toxicity. Systemically, the early stages of stroke are also characterized by stroke-induced immunosuppression, where downregulation of host defences predisposes patients to infection. Therefore, strategies to modulate innate immunity post-stroke have garnered greater attention. A complementary objective is to reduce longer-term sequelae by focusing on adaptive immunity. Following stroke onset, the integrity of the blood-brain barrier is compromised, exposing central nervous system (CNS) antigens to systemic adaptive immune recognition, potentially inducing autoimmunity. Some pre-clinical efforts have been made to tolerize the immune system to CNS antigens pre-stroke. Separately, immune cell populations that exhibit a regulatory phenotype (T- and B- regulatory cells) have been shown to ameliorate post-stroke inflammation and contribute to tissue repair. Cell-based therapies, established in oncology and transplantation, could become a strategy to treat the acute and chronic stages of stroke. Furthermore, a role for the gut microbiota in ischaemic injury has received attention. Finally, the immune system may play a role in remote ischaemic preconditioning-mediated neuroprotection against stroke. The development of stroke therapies involving organs distant to the infarct site, therefore, should not be overlooked. This review will discuss the immune mechanisms of various therapeutic strategies, surveying published data and discussing more theoretical mechanisms of action that have yet to be exploited.

The immune system and stroke: from current targets to future therapy.

Stroke is a major cause of morbidity and mortality worldwide. Despite the intensive search for new therapies, hundreds of agents targeting various pathophysiological mechanisms have failed clinical trials, and the thrombolytic agent tissue plasminogen activator is currently the only FDA-approved medication for the treatment of acute ischemic stroke. The immune system is involved in all stages of stroke, from the pathogenesis of risk factors to neurotoxicity, to tissue remodeling and repair. There is a bidirectional interaction between the brain and the immune system, with stroke-induced immunosuppression and subsequent infection a principal source of patient mortality. Newer work also points to a role for the gut microbiota in the immune response to stroke, while clinical sequelae such as dementia might now also be explained in immune terms. However, the exact roles of innate and adaptive components have not been fully elucidated, with studies reporting both detrimental and beneficial functions. Time is a key determinant in defining whether immunity and inflammation are neuroprotective or neurotoxic. The local inflammatory milieu also has a clear influence on many proposed treatments. This review examines the individual components of the immune response to stroke, highlighting the most promising future stroke immunotherapies.

Composition of the Schistosoma mansoni worm secretome: Identification of immune modulatory Cyclophilin A.

The helminth Schistosoma mansoni modulates the infected host's immune system to facilitate its own survival, by producing excretory/secretory molecules that interact with a variety of the host's cell types including those of the immune system. Herein, we characterise the S. mansoni adult male worm secretome and identify 111 proteins, including 7 vaccine candidates and several molecules with potential immunomodulatory activity. Amongst the molecules present in the secretome, a 17-19kDa protein analogous to human cyclophilin A was identified. Given the ability of cyclophilin A to modulate the immune system by regulating antigen presenting cell activity, we sought to determine whether recombinant S. mansoni Cyclophilin A (rSmCypA) is capable of modulating bone-marrow derived dendritic cell (BMDC) and T cell responses under in vitro conditions. rSmCypA was enzymatically active and able to alter the pro-inflammatory cytokine profile of LPS-activated dendritic cells. rSmCypA also modulated DC function in the induction of CD4+ T cell proliferation with a preferential expansion of Treg cells. This work demonstrates the unique protein composition of the S. mansoni male worm secretome and immunomodulatory activity of S. mansoni Cyclophilin A.

Immunogenicity is preferentially induced in sparse dendritic cell cultures.

We have previously shown that human monocyte-derived dendritic cells (DCs) acquired different characteristics in dense or sparse cell cultures. Sparsity promoted the development of IL-12 producing migratory DCs, whereas dense cultures increased IL-10 production. Here we analysed whether the density-dependent endogenous breaks could modulate DC-based vaccines. Using murine bone marrow-derived DC models we show that sparse cultures were essential to achieve several key functions required for immunogenic DC vaccines, including mobility to draining lymph nodes, recruitment and massive proliferation of antigen-specific CD4+ T cells, in addition to their TH1 polarization. Transcription analyses confirmed higher commitment in sparse cultures towards T cell activation, whereas DCs obtained from dense cultures up-regulated immunosuppressive pathway components and genes suggesting higher differentiation plasticity towards osteoclasts. Interestingly, we detected a striking up-regulation of fatty acid and cholesterol biosynthesis pathways in sparse cultures, suggesting an important link between DC immunogenicity and lipid homeostasis regulation.

Dendritic Cell Response to HIV-1 Is Controlled by Differentiation Programs in the Cells and Strain-Specific Properties of the Virus.

Dendritic cells (DCs) are potent antigen-presenting cells that might play contradictory roles during HIV-1 infection, contributing not only to antiviral immunity but also to viral dissemination and immune evasion. Although DCs are characterized by enormous functional diversity, it has not been analyzed how differentially programmed DCs interact with HIV-1. We have previously described the reprogramming of DC development by endogenously produced lactic acid that accumulated in a cell culture density-dependent manner and provided a long-lasting anti-inflammatory signal to the cells. By exploiting this mechanism, we generated immunostimulatory DCs characterized by the production of TH1 polarizing and inflammatory mediators or, alternatively, suppressed DCs that produce IL-10 upon activation, and we tested the interaction of these DC types with different HIV-1 strains. Cytokine patterns were monitored in HIV-1-exposed DC cultures. Our results showed that DCs receiving suppressive developmental program strongly upregulated their capacity to produce the TH1 polarizing cytokine IL-12 and the inflammatory chemokines CCL2 and CCL7 upon interaction with HIV-1 strains IIIB and SF162. On the contrary, HIV-1 abolished cytokine production in the more inflammatory DC types. Preincubation of the cells with the HIV-1 proteins gp120 and Nef could inhibit IL-12 production irrespectively of the tested DC types, whereas MyD88- and TRIF-dependent signals stimulated IL-12 production in the suppressed DC type only. Rewiring of DC cytokines did not require DC infections or ligation of the HIV-1 receptor CD209. A third HIV-1 strain, BaL, could not modulate DC cytokines in a similar manner indicating that individual HIV-1 strains can differ in their capacity to influence DCs. Our results demonstrated that HIV-1 could not induce definite and invariable modulatory programs in DCs. Instead, interaction with the virus triggered different responses in different DC types. Thus, the outcome of DC-HIV-1 interactions might be highly variable, shaped by endogenous features of the cells and diversity of the virus.

Impaired B cells survival upon production of inflammatory cytokines by HIV-1 exposed follicular dendritic cells.

BACKGROUND: Follicular dendritic cells (FDCs) are important components in the organization of germinal centers in lymphoid tissue where, following antigen presentation, B cells differentiate into memory B cells. The possibility of establishing primary cell lines from FDCs isolated from lymphoid tissue paved the way for characterization of FDC biological properties. We exposed primary FDC cell lines to HIV-1 strains in vitro and studied changes in the chemo-attractive properties of FDCs and release of inflammatory cytokines. RESULTS: FDC lines expressed several known and putative HIV-1 receptors; viral genome was amplified in HIV-1 exposed FDCs which released low levels of p24 HIV-1 protein in culture supernatants, but were not definitely proven to be productively infected. Exposure of FDCs to HIV-1 strains did not change the expression of markers used to characterize these cells. HIV-1 exposed FDCs, however, changed the expression of chemo-attractants involved in cell recruitment at inflammatory sites and increased the production of several inflammatory cytokines. The inflammatory milieu created upon HIV-1 exposure of FDCs led to impaired B cell survival in vitro and reduced Ig production. CONCLUSIONS: FDC lines exposed to different HIV-1 strains, although not able to support productive HIV-1 replication, show an increased production of inflammatory cytokines. Our in vitro model of interactions between HIV-1 exposed FDC lines and B cells suggest that exposure of FDCs to HIV-1 in vivo can contribute to inflammation within germinal centers and that this pathological event may impair B cell survival and contribute to impaired B cell responses during HIV-1 infection.

Dysfunctions in the migratory phenotype and properties of circulating immature transitional B cells during HIV-1 infection.

OBJECTIVE: The frequency of immature transitional B cells is increased in blood of HIV-1-infected individuals. We investigated whether HIV-1 infection affects expression and function of chemokine receptors important for egress of immature transitional B cells from bone marrow and migration to lymphoid organs. DESIGN: This is a cross-sectional study analysing the migratory phenotype and function of immature transitional B cells in HIV-1-infected individuals, in relation to antiretroviral treatment and age. METHODS: Frequency of blood immature transitional B cells and their phenotypic characteristics, including chemokine receptors and a maturation marker, were determined by immunostainings. Migratory capacities were studied in a migration assay. RESULTS: The increased frequency of immature transitional B cells in untreated HIV-1 infection was normalized in patients receiving antiretroviral treatment; in our cohorts, age did not have an impact on the frequency of circulating immature transitional B cells. Immature transitional B cells from nontreated patients expressed low levels of CD21 molecule. We found an elevated frequency of CXCR3 and CXCR4 expressing immature transitional B cells in treated and nontreated patients. CXCR4 receptor was unresponsive to CXCL12 ligand in in-vitro migration and internalization assays. In addition, CXCR5 expression was downregulated on immature transitional B cells from infected patients, and these cells migrated poorly in response to CXCR5 ligand. CONCLUSION: Circulating immature transitional B cells from HIV-1-infected patients are not fully mature, probably due to premature egress from bone marrow; these cells showed a phenotype which could impair entry into secondary lymphoid organs. Changes in migratory capacity of immature transitional B cells may affect B-cell maturation during HIV-1 infection.

Dysfunctional phenotypes of CD4+ and CD8+ T cells are comparable in patients initiating ART during early or chronic HIV-1 infection.

Early initiation of antiretroviral therapy (ART) is becoming a common clinical practice according to current guidelines recommending treatment to all HIV-1-infected patients. However, it is not known whether ART initiated during the early phase of infection prevents the establishment of abnormal phenotypic features previously reported in CD4+ and CD8+T cells during chronic HIV-1 infection. In this cross-sectional study, blood specimens were obtained from 17 HIV-1-infected patients who began ART treatment shortly after infection (early ART [EA]), 17 age-matched HIV-1-infected patients who started ART during chronic phase of infection (late ART [LA]), and 25 age-matched non-HIV-1-infected controls. At collection of specimens, patients in EA and LA groups had received ART for comparable periods of time. Total HIV-1 DNA was measured in white blood cells by quantitative PCR. The concentration of 9 inflammatory parameters and 1 marker of fibrosis, including sCD14 and ß-2 microglobulin, was measured in plasma. Furthermore, expression of markers of abnormal immune activation (human leukocyte antigen - antigen D related [HLA-DR] and CD38), exhaustion (programmed death 1, CD28, CD57) and terminal differentiation (CD127) was measured on CD4+ and CD8+T cells. T-cell proliferation was measured through Ki67 expression. The copies of total HIV-1 DNA in blood were significantly lower (P = 0.009) in EA compared with that in LA group. Only the expression of HLA-DR on naïve CD4+ T cells distinguished EA from LA, whereas expression of 3 surface markers distinguished T-cell populations of HIV-1-infected patients from controls. These included HLA-DR distinguishing CD4+ T cells from EA compared with controls, and also CD38 and CD127 on CD4+ and CD8+ T cells, respectively, distinguishing both groups of patients from controls. The sCD14 levels were significantly higher in EA patients, and ß-2 microglobulin levels were higher in LA group compared with that in controls. Our results demonstrate an equivalent abnormal expression of activation (HLA-DR and CD38 on CD4+ T cells) and terminal differentiation (CD127 on CD8+ T cells) markers in T cells from both EA and LA patients. The size of total HIV-1 DNA copies in blood of EA was lower compared with LA patients. These findings suggest that some abnormalities taking place in the T-cell compartment during primary HIV-1 infection may not be corrected by early ART.

New Insights into IL-10 Dependent and IL-10 Independent Mechanisms of Regulatory B Cell Immune Suppression.

Regulatory B (Breg) cells are important regulators of immune responses and in recent years our understanding of their phenotypical and functional characteristics has improved considerably. Initially all suppressive capabilities of Breg cells were attributed to the actions of the anti-inflammatory cytokine interleukin (IL)-10 secreted by Breg cells. Recent studies however, highlight additional and novel mechanisms that influence both the expansion of Breg cells and their capacity to suppress immunity. Here we provide an overview of the complexity of Breg cell populations and address the newly discovered IL-10 independent mechanisms of Breg cell expansion and immune-suppression.

Increased extrafollicular expression of the B-cell stimulatory molecule CD70 in HIV-1-infected individuals.

OBJECTIVE: CD70 molecules expressed by activated T cells provide potent B cell stimulatory signals. We hypothesized that an altered CD70 expression might contribute to B cell abnormalities during HIV-1 infection. DESIGN: CD70 expression and the functional and migratory properties of the CD4CD70 T lymphocytes were analyzed in HIV-1-infected patients and in humanized mice. Correlations were tested between CD70 expression and features of B-cell activation, apoptosis sensitivity and functional exhaustion. METHODS: CD4CD70 T cells were analyzed in cohorts of CD4 T-cell lymphopenic, viremic or nonlymphopenic, nonviremic HIV-1-infected patients and in noninfected individuals. CD70 upregulation was also followed in HIV-1-infected humanized mice. CD38, CD95, LAIR1 and PD-1 expressions were monitored on B-cell subpopulations, Ki67 was assessed to estimate B-cell proliferation and antibody levels were measured in plasma. RESULTS: Blood CD4CD70 T-cell frequencies increased in response to CD4 T-cell depletion or high viremia levels as a possible consequence of increased activation and proliferation in this subset. CD4CD70 T cells produced T-helper 1-type cytokines and expressed chemokine receptors mobilizing toward sites of inflammation but not to lymphoid follicles. High CD70 expression was observed in HIV-1-infected humanized mice at extrafollicular sites (peritoneum, bone-marrow). CD4CD70 T-cell frequencies correlated with the expression of the activation marker CD38 and the death receptor CD95 on various memory B-cell subsets, with B-cell proliferation and with plasma IgG levels. CONCLUSIONS: CD4CD70 T cells may contribute to B cell hyperactivation and accelerated memory B-cell turnover during HIV-1 infection.

Suppressed diversity of survivin splicing in active rheumatoid arthritis.

INTRODUCTION: Alternative splicing distinguishes normal and pathologic cells. High levels of oncoprotein survivin recognise patients with severe rheumatoid arthritis (RA). Here, we assess clinical relevance of alternative splicing of survivin in leukocytes of peripheral blood (PBMC) and bone marrow (BM) in RA patients. METHOD: Transcription of survivin wild-type (survivin-WT), survivin-2B and survivin-ΔEx3 was measured in 67 randomly selected RA patients and in 23 patients before and after B cell depletion with rituximab. Analysis was done in relation to disease activity, anti-rheumatic treatment and serum levels of rheumatoid factor (RF) and survivin. RESULTS: Survivin-WT was the dominant splice variant equally expressed in T and B cells, while survivin-2B and survivin-ΔEx3 were higher in B cells. High disease activity (DAS28>5.1) was associated with an excess of survivin-WT and low ratios between survivin-2B/WT (p=0.035) and survivin-ΔEx3/WT in PBMC. Depletion of B cells by rituximab caused a decrease in survivin-WT (p=0.005) in PBMC, increasing the ratio between survivin-2B/WT (p=0.009) and survivin-ΔEx3/WT (p=0.001) in BM. This increase in survivin-2B/WT was associated with reduction in CD19+ BM cells (r=0.929, p=0.007), RF (IgM, r=0.857, p=0.024; IgA, r=0.739, p=0.021), and DAS28 (0.636, p=0.054). The increase in survivin-ΔEx3 in BM was associated with a reduction of CD19+ BM cells (r=0.714, p=0.058) and DAS28 (r=0.648, p=0.049), while survivin-ΔEx3/WT was associated with RF (IgG, r=0.882, p=0.016). CONCLUSION: This study demonstrates that the suppressed diversity of survivin splicing in leukocytes may attribute to adverse self-recognition in RA. Depletion of autoantibody producing B cells improves the balance of survivin splicing.

Impaired Phenotype and Function of T Follicular Helper Cells in HIV-1-Infected Children Receiving ART.

T follicular helper (Tfh) cells are important components in development of specific humoral immune responses; whether the number and biology of Tfh cells is impaired in HIV-1-infected children is not yet studied.The frequency, phenotype, and function of Tfh cells and B cells were determined in blood of HIV-1-infected children receiving antiretroviral therapy (ART) and age-matched controls. Flow cytometry was used to characterize the frequency of Tfh cells and B cell subsets. Cytokine expression was measured after in vitro activation of Tfh cells.A reduced frequency of memory Tfh cells (P < 0.001) was identified in HIV-1-infected children and, on these cells, a reduced expression of programmed death-1 (PD-1) and inducible T cell costimulator (ICOS) (P < 0.001 and P < 0.01). Upon activation, the capacity of Tfh cells to express IL-4, an important cytokine for B cell function, was impaired in HIV-1-infected children.B cell subpopulations in HIV-1-infected children displayed significant differences from the control group: the frequency of resting memory (RM) B cells was reduced (P < 0.01) whereas the frequency of exhausted memory B cells increased (P < 0.001). Interestingly, the decline of RM cells correlated with the reduction of memory Tfh cells (P = 0.02).Our study shows that function and phenotype of Tfh cells, pivotal cells for establishment of adaptive B cell responses, are impaired during HIV-1 infection in children. A consistent reduction of memory Tfh cells is associated with declined frequencies of RM B cells, creating a novel link between dysfunctional features of these cell types, major players in establishment of humoral immunity.

Ligation of TLR7 on CD19(+) CD1d(hi) B cells suppresses allergic lung inflammation via regulatory T cells.

B cells have been described as having the capacity to regulate cellular immune responses and suppress inflammatory processes. One such regulatory B-cell population is defined as IL-10-producing CD19(+) CD1d(hi) cells. Previous work has identified an expansion of these cells in mice infected with the helminth, Schistosoma mansoni. Here, microarray analysis of CD19(+) CD1d(hi) B cells from mice infected with S. mansoni demonstrated significantly increased Tlr7 expression, while CD19(+) CD1d(hi) B cells from uninfected mice also demonstrated elevated Tlr7 expression. Using IL-10 reporter, Il10(-/-) and Tlr7(-/-) mice, we formally demonstrate that TLR7 ligation of CD19(+) CD1d(hi) B cells increases their capacity to produce IL-10. In a mouse model of allergic lung inflammation, the adoptive transfer of TLR7-elicited CD19(+) CD1d(hi) B cells reduced airway inflammation and associated airway hyperresponsiveness. Using DEREG mice to deplete FoxP3(+) T regulatory cells in allergen-sensitized mice, we show that that TLR7-elicited CD19(+) CD1d(hi) B cells suppress airway hyperresponsiveness via a T regulatory cell dependent mechanism. These studies identify that TLR7 stimulation leads to the expansion of IL-10-producing CD19(+) CD1d(hi) B cells, which can suppress allergic lung inflammation via T regulatory cells.

Frequency and phenotype of B cell subpopulations in young and aged HIV-1 infected patients receiving ART.

BACKGROUND: Aged individuals respond poorly to vaccination and have a higher risk of contracting infections in comparison to younger individuals; whether age impacts on the composition and function of B cell subpopulations relevant for immune responses is still controversial. It is also not known whether increased age during HIV-1 infection further synergizes with the virus to alter B cell subpopulations. In view of the increased number of HIV-1 infected patients living to high age as a result of anti-retroviral treatment this is an important issue to clarify. RESULTS: In this work we evaluated the distribution of B cell subpopulations in young and aged healthy individuals and HIV-1 infected patients, treated and naïve to treatment. B cell populations were characterized for the expression of inhibitory molecules (PD-1 and FcRL4) and activation markers (CD25 and CD69); the capacity of B cells to respond to activation signals through up-regulation of IL-6 expression was also evaluated. Increased frequencies of activated and tissue-like memory B cells occurring during HIV-1 infection are corrected by prolonged ART therapy. Our findings also reveal that, in spite of prolonged treatment, resting memory B cells in both young and aged HIV-1 infected patients are reduced in number, and all memory B cell subsets show a low level of expression of the activation marker CD25. CONCLUSIONS: The results of our study show that resting memory B cells in ART-treated young and aged HIV-1 infected patients are reduced in number and memory B cell subsets exhibit low expression of the activation marker CD25. Aging per se in the HIV-1 infected population does not worsen impairments initiated by HIV-1 in the memory B cell populations of young individuals.