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The half-life of human neutrophils is still controversial, with estimates ranging from 7-9 h to 3.75 days. This debate should be settled to understand neutrophil production in the bone marrow (BM) and the potential and limitations of emergency neutropoiesis following infection or trauma. Furthermore, cellular lifespan greatly influences the potential effect(s) neutrophils have on the adaptive immune response. We posit that blood neutrophils are in exchange with different tissues, but particularly the BM, as it contains the largest pool of mature neutrophils. Furthermore, we propose that the oldest neutrophils are the first to die following a so-called conveyor belt model. These guiding principles shed new light on our interpretation of existing neutrophil lifespan data and offer recommendations for future research.

Supplementary Table 2 from In vivo Dynamics of Stable Chronic Lymphocytic Leukemia Inversely Correlate with Somatic Hypermutation Levels and Suggest No Major Leukemic Turnover in Bone Marrow

Supplementary Table 1 from In vivo Dynamics of Stable Chronic Lymphocytic Leukemia Inversely Correlate with Somatic Hypermutation Levels and Suggest No Major Leukemic Turnover in Bone Marrow

Systemic inflammation (SI) plays a detrimental role in various conditions with high mortality rates1–4. SI manifests an acute hyperinflammation followed by long-lasting immunosuppression, increasing patients’ risks for secondary infections and impaired clinical outcomes5–7. Due to the extensive heterogeneity in SI etiology, the mechanisms governing these states are incompletely understood. Here, we characterized acute and late effects of lipopolysaccharide (LPS)-induced SI (LPS-SI8) on blood monocytes and bone marrow (BM) cells of healthy volunteers. Like clinical SI, LPS administration elicited a profound but transient acute response. Single-cell transcriptomic analysis of acute LPS-SI unveiled loss of BM monocytes and appearance of an inflammatory monocyte-like (i-Mono’s) population, expressing gene programs similar to early-stage sepsis patients9. In the ensuing late phase of LPS-SI, we observed reduced expression of interferon type I (IFN-I) responsive genes in monocytes and profound attenuation of in vivo response to a second LPS challenge. Furthermore, late LPS-SI led to impaired myelopoiesis with a loss of intermediate and non-classical monocytes. In accordance, we show compromised myelopoiesis also occurs in late-stage sepsis. Finally, IFNβ treatment reversed LPS-induced immunosuppression in monocytes. Our results reveal long-lasting effects of SI on myelopoiesis and substantiate the importance of IFN-I in the pathophysiology of SI-induced immunosuppression.

The potential of memory T-cells to provide protection against re-infection is beyond question. Yet, it remains debated whether long-term T-cell memory is due to long-lived memory cells. There is ample evidence that blood-derived memory phenotype CD8+ T-cells maintain themselves through cell division, rather than through longevity of individual cells. It has recently been proposed, however, that there may be heterogeneity in the lifespans of memory T-cells, depending on factors such as exposure to cognate antigen. Cytomegalovirus (CMV) infection induces not only conventional, contracting T-cell responses, but also inflationary CD8+ T-cell responses, which are maintained at unusually high numbers, and are even thought to continue to expand over time. It has been proposed that such inflating T-cell responses result from the accumulation of relatively long-lived CMV-specific memory CD8+ T-cells. Using in vivo deuterium labelling and mathematical modelling, we found that the average production rates and expected lifespans of mouse CMV-specific CD8+ T-cells are very similar to those of bulk memory-phenotype CD8+ T-cells. Even CMV-specific inflationary CD8+ T-cell responses that differ three-fold in size, were found to turn over at similar rates.

The potential of memory T cells to provide protection against reinfection is beyond question. Yet, it remains debated whether long-term T cell memory is due to long-lived memory cells. There is ample evidence that blood-derived memory phenotype CD8

HIV-1 cell entry is mediated by binding to the CD4-receptor and chemokine co-receptors CCR5 (R5) or CXCR4 (X4). R5-tropic viruses are predominantly detected during early infection. A switch to X4-tropism often occurs during the course of infection. X4-tropism switching is strongly associated with accelerated disease progression and jeopardizes CCR5-based HIV-1 cure strategies. It is unclear whether host immunological factors play a causative role in tropism switching. We investigated the relationship between immunological factors and X4-tropism in a cross-sectional study in HIV-1 subtype C (HIV-1C)-infected patients and in a longitudinal HIV-1 subtype B (HIV-1B) seroconverter cohort. Principal component analysis identified a cluster of immunological markers (%HLA-DR+ CD4+ T-cells, %CD38+HLA-DR+ CD4+ T-cells, %CD38+HLA-DR+ CD8+ T-cells, %CD70+ CD4+ T-cells, %CD169+ monocytes, and absolute CD4+ T-cell count) in HIV-1C patients that was independently associated with X4-tropism (aOR 1.044, 95% CI 1.003–1.087, p = 0.0392). Analysis of individual cluster contributors revealed strong correlations of two markers of T-cell activation (%HLA-DR+ CD4+ T-cells, %HLA-DR+CD38+ CD4+ T-cells) with X4-tropism, both in HIV-1C patients (p = 0.01;p = 0.03) and HIV-1B patients (p = 0.0003;p = 0.0001). Follow-up data from HIV-1B patients subsequently revealed that T-cell activation precedes and independently predicts X4-tropism switching (aHR 1.186, 95% CI 1.065–1.321, p = 0.002), providing novel insights into HIV-1 pathogenesis and CCR5-based curative strategies.

Lymphocyte numbers need to be quite tightly regulated. It is generally assumed that lymphocyte production and survival rates increase homeostatically when lymphocyte numbers decrease. This widely-accepted concept is largely based on experiments in mice. In humans, lymphocyte reconstitution usually occurs very slowly, which challenges the idea that density dependent homeostasis aids recovery from lymphopenia. Using in vivo deuterium labelling, we quantified lymphocyte production and survival rates in patients who underwent an autologous hematopoietic stem cell transplantation (autoHSCT). We indeed found that the production rates of most T-cell and B-cell subsets in autoHSCT-patients were 2 to 8-times higher than in healthy controls. These increased lymphocyte production rates went hand in hand with a 3 to 9-fold increase in cell loss rates, and both rates did not normalize when cell numbers did. This challenges the concept of homeostatic regulation of lymphocyte production and survival rates in humans.

An association between T‐cell lymphopenia and autoimmunity has long been proposed, but it remains to be elucidated whether T‐cell lymphopenia affects B‐cell responses to autoantigens. Human neonatal thymectomy (Tx) results in a decrease in T‐cell numbers and we used this model to study the development of autoreactivity. Two cohorts of neonatally thymectomized individuals were examined, a cohort of young (1–5 years post‐Tx, n = 10–27) and older children (>10 years, n = 26), and compared to healthy age‐matched controls. T‐cell and B‐cell subsets were assessed and autoantibody profiling performed. Early post‐Tx, a decrease in T‐cell numbers (2.75 × 109/L vs. 0.71 × 109/L) and an increased proportion of memory T cells (19.72 vs. 57.43%) were observed. The presence of autoantibodies was correlated with an increased proportion of memory T cells in thymectomized children. No differences were seen in percentages of different B‐cell subsets between the groups. The autoantigen microarray showed a skewed autoantibody response after Tx. In the cohort of older individuals, autoantibodies were present in 62% of the thymectomized children, while they were found in only 33% of the healthy controls. Overall, our data suggest that neonatal Tx skews the autoantibody profile. Preferential expansion and preservation of Treg (regulatory T) cell stability and function, may contribute to preventing autoimmune disease development after Tx.

Plasmacytoid dendritic cells (PDCs) and their production of interferon-alpha (IFN-α) are believed to play an important role in human immunodeficiency virus, type I (HIV-1) pathogenesis. PDCs produce IFN-α and other proinflammatory cytokines through stimulation of Toll-like receptor 7 (TLR7) and TLR9 present in endosomal compartments. TLR7 recognizes single-stranded viral RNA, while TLR9 recognizes unmethylated DNA. In this study, we examined the mechanisms that may underlie variations in IFN-α production in response to HIV, and the impact of these variations on HIV pathogenesis. In four distinct cohorts, we examined PDC production of IFN-α upon stimulation with inactivated HIV-1 particles and unmethylated DNA. The signaling cascade of TLR7 bifurcates at the myeloid differentiation protein 88 (MyD88) adaptor protein to induce expression of either IFN-α or TNF-α. To determine whether variations in IFN-α production are modulated at the level of the receptor complex or downstream of it, we correlated production of IFN-α and TNF-α following stimulation of TLR7 or TLR9 receptors. Flow cytometry detection of intracellular cytokines showed strong, direct correlations between IFN-α and TNF-α expression in all four cohorts, suggesting that variations in IFN-α production are not due to variations downstream of the receptor complex. We then investigated the events upstream of TLR binding by using lipid-like vesicles to deliver TLR ligands directly to the TLR receptors, bypassing the need for CD4 binding and endocytosis. Similar tight correlations were found in IFN-α and TNF-α production in response to the TLR ligands. Taken together, these results strongly suggest that differences in IFN-α production depend on the regulatory processes at the level of the TLR7 receptor complex. Additionally, we found no association between IFN-α production before HIV infection and disease progression.

Effector-memory T-cells (TEM) are assumed to be short-lived cells that poorly proliferate upon antigenic restimulation, thus depending on central-memory T-cells (TCM) to replenish their numbers during homeostasis, largely depending on adoptive transfer evidence. Here we analyzed T cells in their natural environment and observed robust long-term in vivo cycling within the TEM subset that was stronger than the one in the TCM subset. We compared the non-persistent vaccinia virus and the persisting murine Cytomegalovirus (MCMV), which induces inflationary TEM responses that remain high during viral latency. We analyzed Ki67 expression during acute, resolved and latent infection and found Ki67hiBcl2lo TEM in acutely or latently infected mice, arguing for antigen-driven TEM proliferation. In vivo labeling with deuterium showed that TEM acquired deuterium more rapidly than TCM, and were rapidly lost during chase. Similarly, antibody-mediated depletion of primed CD8 T cells in latenly infected mice revealed that TEM replenished more rapidly than TCM, suggesting that TEM cycle faster than TCM. Finally, we utilized the ability of Tamoxifen-induced Cre-ERT2 recombinase to induce chromosomal translocations when large amounts of Tamoxifen are administered for an extended time, which resulted in a selective depletion of proliferating Ki67hi cells that hardly affected the TCM subset, but drove a selective loss of Ki67hiBcl2lo effector T-cells, and an increase in the death of TEM in the spleen, arguing that TEM preferentially proliferate in the spleen. Since our results contradicted previous evidence from adoptive transfer experiments, we tested T cell homing to the spleen upon adoptive transfer. TEM homing was substantially poorer than the one of TCM, likely explaining the previously reported expansions of TCM, but not TEM, upon transfer into latently infected mice. In conclusion, our data suggest that memory inflation is largely maintained by splenic proliferation of antigen-specific TEM, rather than by continued expansion and differentiation of TCM.

The maintenance and dynamics of memory T-cells in the bone marrow are a matter of ongoing debate. It has been suggested that memory T-cells in the bone marrow are maintained as long-lived, quiescent cells. We have recently shown that memory T-cells isolated from goat bone marrow undergo self-renewal and recirculate via the blood and lymph. Using the well-established memory T-cell markers CD44 and CD62L we here show very similar results in mice. This provides further support for the concept that memory T-cells are continuously self-renewing and recirculating between blood, bone marrow, spleen and lymph nodes.

Objective: Lipid management is one of the cornerstones of cardiovascular risk reduction. Treatment of HIV infection with protease inhibitors (PIs) may cause dyslipidaemia, whilst the integrase inhibitor raltegravir (RAL) has a relatively favorable effect on plasma lipids. We examined the effect of switching from PIs to RAL on endothelial function, and its effect on immunological and inflammatory parameters. Methods: We performed a 16-week open-label prospective crossover study: 8 weeks intervention (switch PIs to RAL) and 8 weeks control (unchanged cART regimen). Flow-mediated dilatation (FMD), inflammatory plasma, and cellular markers of immune activation were measured at weeks 0, 8, and 16. Results: Study participants (n = 22) with a median age of 50 years (IQR 42–60) and known HIV infection of 6.5 years (IQR 5.0–17.3) were on stable cART with undetectable HIV viral loads. After 8 weeks of RAL therapy, a reduction in FMD of −0.81% was seen, compared to +0.54% control (pairwise, p = 0.051), while fasting total cholesterol (−17% versus +10%; p

The generation of naive T cells is dependent on thymic output, but in adults, the naive T cell pool is primarily maintained by peripheral proliferation. Naive T cells have long been regarded as relatively quiescent cells; however, it was recently shown that IL-8 production is a signatory effector function of naive T cells, at least in newborns. How this functional signature relates to naive T cell dynamics and aging is unknown. Using a cohort of children and adolescents who underwent neonatal thymectomy, we demonstrate that the naive CD4+ T cell compartment in healthy humans is functionally heterogeneous and that this functional diversity is lost after neonatal thymectomy. Thymic tissue regeneration later in life resulted in functional restoration of the naive T cell compartment, implicating the thymus as having functional regenerative capacity. Together, these data shed further light on functional differentiation within the naive T cell compartment and the importance of the thymus in human naive T cell homeostasis and premature aging. In addition, these results affect and alter our current understanding on the identification of truly naive T cells and recent thymic emigrants.

To the editor: Monocytes originate from the bone marrow (BM), are distributed in the bloodstream, and can differentiate in the tissue into skin macrophages or intestinal dendritic cells (DCs).[1][1] They play an essential role in the defense against pathogens[2][2] and are implicated in a range of

BackgroundThe largest proportion of people living with HIV resides in sub-Saharan Africa (SSA). Evidence from developed countries suggests that HIV infection increases the relative risk of cardiovascular disease (CVD) by up to 50%. Differences in lifestyle, gender distribution, routes of HIV transmission and HIV subtype preclude generalisation of data from Western countries to the SSA situation. The Ndlovu Cohort Study aims to provide insight into the burden of cardiovascular risk factors and disease, the mechanisms driving CVD risk and the contribution of HIV infection and its treatment to the development of CVD in a rural area of SSA.DesignThe Ndlovu Cohort Study is a prospective study in the Moutse area, Limpopo Province, South Africa.MethodsA total of 1000 HIV-positive and 1000 HIV-negative participants aged 18 years and older with a male to female ratio of 1:1 will be recruited. Measurements of CVD risk factors and HIV-related characteristics will be performed at baseline, and participants will be followed-up over time at 6–month intervals. The burden of CVD will be assessed with repeated carotid intima–media thickness and pulse wave velocity measurements, as well as by recording clinical cardiovascular events that occur during the follow-up period.ConclusionThis project will contribute to the understanding of the epidemiology and pathogenesis of CVD in the context of HIV infection in a rural area of SSA. The ultimate goal is to improve cardiovascular risk prediction and to indicate preventive approaches in the HIV-infected population and, potentially, for non-infected high-risk populations in a low-resource setting.

Background: A higher risk of developing osteopenia/ osteoporosis has been seen in HIV-infected patients. We compared HIV-infected patients, all treated with combination antiretroviral therapy (cART), with a low bone mineral density (BMD) (T-score -I), examining the relation with T-cell activation and bone turnover markers (c-terminal telopeptide (CTX) and procollagen type I amino-terminal propeptide (PINP)). Methods: In this single visit pilot study, bone turnover markers, T-cell activation (CD38 + HLA - DR +) and senescence (CD57+) of T cells were measured in patients who had previously undergone dual energy X-ray absorptiometry scanning. Results: All study participants (n = I6) were male, on cART, with a median age of 6I years (IQR 56-66). Nine patients had osteopenia/osteoporosis. When comparing the patients with osteopenia/osteoporosis with those with a normal BMD, no differences in activation and senescence were found. A relation was seen between higher bone formation (PINP) and patients who were on cART for longer. The median length of cART use was 5.5 years (IQR 4.5-7.8), with all patients on nucleoside reverse transcriptase inhibitors, 88% on tenofovir, 63% on non-nucleoside reverse transcriptase inhibitors (NNRTIs) and 38% on protease inhibitors. Osteopenia/osteoporosis was seen in 100% of the patients on protease inhibitors versus 30% of those on NNRTIs. Conclusion: This study did not find an association between activated T cells and BMD, thus did not explain the higher prevalence of osteopenia/osteoporosis in HIV-infected patients. Interestingly, this small pilot showed that cART might influence BMD, with a possible negative effect for protease inhibitors and a possible protective effect for NNRTIs. These results warrant further investigation.

Cardiovascular disease (CVD) is highly prevalent in HIV-infected patients. Besides the classical cardiovascular risk factors, HIV related factors play a role, such as immune activation and treatment with highly active antiretroviral therapy (HAART). The resulting T cell activation is regarded as one of the driving forces behind this accelerated atherogenesis. Interventions, such as early treatment and anti-inflammatory therapy, decreasing T cell activation might lead to a lower incidence of CVD in future HIV infected patients. This review specifically explores the role of T cells in the development of atherosclerosis in HIV-infected patients.

Progressive multifocal leukoencephalopathy (PML) is a rare but generally fatal disease due to JC virus (JCV) reactivation, mainly occurring in immunosuppressed patients.(1) Therapeutic options are limited to blocking glial cell infection by mirtazapine or restoring cell-mediated immunity to acquire viral control.(2)

Neutrophils are the most abundant white blood cells and are indispensable for host defense. Recently, they have also been implicated in immune regulation and suppression. The latter functions seem hard to reconcile with the widely held view that neutrophils are very short-lived, with a circulatory half-life of

Quantitative knowledge of the turnover of different leukocyte populations is a key to our understanding of immune function in health and disease. Much progress has been made thanks to the introduction of stable isotope labeling, the state-of-the-art technique for in vivo quantification of cellular life spans. Yet, even leukocyte life span estimates on the basis of stable isotope labeling can vary up to 10-fold among laboratories. We investigated whether these differences could be the result of variances in the length of the labeling period among studies. To this end, we performed deuterated water-labeling experiments in mice, in which only the length of label administration was varied. The resulting life span estimates were indeed dependent on the length of the labeling period when the data were analyzed using a commonly used single-exponential model. We show that multiexponential models provide the necessary tool to obtain life span estimates that are independent of the length of the labeling period. Use of a multiexponential model enabled us to reduce the gap between human T-cell life span estimates from 2 previously published labeling studies. This provides an important step toward unambiguous understanding of leukocyte turnover in health and disease.

Background The increased risk of abacavir in cardiovascular disease (CVD) in HIV-infected patients is still being debated. Maraviroc, a CCR5 blocker, has been shown to decrease immune activation and monocyte infiltration in atherosclerotic plaques in murine experiments. Therefore, we examined the effect of maraviroc intensification on flow-mediated dilatation (FMD) in abacavir-treated HIV-infected patients and its effect on immunological and inflammatory parameters. Methods A open-label prospective crossover study with a duration of 16 weeks: 8 weeks of intervention (maraviroc intensification) and 8 weeks of control (unchanged cART regimen). FMD, HIV-specific variables, expression of HIV co-receptors, markers of inflammation and coagulation and cellular markers of immune activation were measured at weeks 0, 8 and 16. The changes (Δ) in these variables were compared between intervention and control periods using non-parametric tests. To evaluate the relation with the change in FMD, linear regression modeling was used. Results Twenty-one male patients with suppressed plasma HIV-RNA, on cART, had a known HIV infection for 9.2 years (IQR 6.9–13.5) with abacavir use for 6.5 years (2.8–9.3). A significantly increased FMD of 0.73% (IQR −0.25 to 1.70) was seen after maraviroc intensification compared to a decrease of −0.42% (IQR −1.89 to 0.25; p = 0.049) in the control period. There was a negative relation between ΔFMD with ΔD-dimer (β −22.70, 95% CI −39.27; −6.13, p = 0.011) and ΔCD95+ CD4+ T cells (β −0.16, 95% CI −0.28; −0.04, p = 0.013), adjusted for age and duration of HIV. Conclusion Maraviroc intensification modestly improves endothelial function in HIV-infected patients on an abacavir-containing regimen. Trial registration NCT01389063. Electronic supplementary material The online version of this article (doi:10.1007/s40121-016-0115-0) contains supplementary material, which is available to authorized users.

During acute inflammation, 3 neutrophil subsets are found in the blood: neutrophils with a conventional segmented nucleus, neutrophils with a banded nucleus, and T-cell-suppressing CD62L

The efficiency of the adaptive immune system is dependent on the diversity of T- and B-cell receptors, which is created by random rearrangement of receptor gene segments. AmpliCot is an experimental technique that allows the measurement of the diversity of the T- and B-cell repertoire. This procedure has the advantage over other cloning and sequencing techniques of being time- and expense-effective. In previous studies, receptor diversity, measured with AmpliCot, has been inferred assuming a second-order kinetics model. The latter implies that the relation between diversity and concentration × time (Cot) values is linear. We show that a more detailed model, involving heteroduplex and transient-duplex formation, leads to significantly better fits of experimental data and to nonlinear diversity-Cot relations. We propose an alternative fitting procedure, which is straightforward to apply and which gives an improved description of the relationship between Cot values and diversity.

Early human herpesvirus 6 (HHV6) reactivation after hematopoietic stem cell transplantation (HSCT) is associated with poor survival. We characterized HHV6 immuneresponses in HSCT patients during lymphopenia. Prospectively, HHV6 DNA-load was measured weekly by realtime-PCR. Numbers of IFNγ-producing HHV6-T-cells were retrospectively determined by enzyme-linked immunospot assay 2 months after HSCT. HHV6-specific T-cell proliferative capacity was analyzed with a newly developed assay using antigen-presenting autologous HHV6-infected PBMC. Fifty-six patients were included (median age 4.6 years; range 0.2-21.2 years). HHV6-reactivation occurred in 29/56 (52%) patients with a median time of 14 (range 1-41) days after HSCT. The median number of IFN-γ producing HHV6-specific T-cells at 2 months and the HHV6-specific CD8+ T-cell proliferative capacity at 6 months after HSCT was increased after HHV6-reactivation compared to non-reactivating patients (P=0.006 and p=0.019). In conclusion, HHV6-specific immuneresponses can be initiated during lymphopenia early after HSCT, which implicates a potential window for development of HHV6-specific (immuno)therapy.

SummaryParallels between T cell kinetics in mice and men have fueled the idea that a young mouse is a good model system for a young human, and an old mouse, for an elderly human. By combining in vivo kinetic labeling using deuterated water, thymectomy experiments, analysis of T cell receptor excision circles and CD31 expression, and mathematical modeling, we have quantified the contribution of thymus output and peripheral naive T cell division to the maintenance of T cells in mice and men. Aging affected naive T cell maintenance fundamentally differently in mice and men. Whereas the naive T cell pool in mice was almost exclusively sustained by thymus output throughout their lifetime, the maintenance of the adult human naive T cell pool occurred almost exclusively through peripheral T cell division. These findings put constraints on the extrapolation of insights into T cell dynamics from mouse to man and vice versa.

BACKGROUND: UNC13D, encoding the protein munc13-4, is essential in intracellular trafficking and exocytosis of lytic granules. Mutations in this gene are associated with familial hemophagocytic lymphohistiocytosis type 3 (FHL3), a genetically heterogeneous, rare autosomal recessive immune disorder. How mutations affect function of munc13-4 is poorly understood. Since 2006 we genetically identified seven FHL patients with mutations in UNC13D. PROCEDURES: Here, we report for the first time a c.2695C>T (p.Arg899X) mutation in exon 28 of UNC13D in three young unrelated Dutch patients. The mutation causes a premature stop codon and encodes munc13-4(1-899), which lacks the C-terminal C2 domain. Genealogical research and haplotyping of the patient families demonstrated that a single ancestral founder introduced the mutation in the Netherlands. We then characterized the mutant protein phenotypically in cell biological and immunological assays. RESULTS: Munc13-4(1-899) was correctly targeted to CD63-positive secretory lysosomes, although its stability was reduced and dynamic turnover on the granule membrane became uncoupled from receptor signaling. In accord, and in contrast to wild-type munc13-4, ectopically expressed mutant failed to rescue degranulation in cells with silenced endogenous munc13-4. CONCLUSIONS: The functional and clinical data showed that this novel Dutch founder mutation leads to severe early onset of FHL3 due to misfolding and degradation of munc13-4(1-899).

Children with Down syndrome (DS) have low numbers of naive T cells and abnormal thymus development and function. Because next to thymic production, peripheral proliferation greatly contributes to naive T cell generation in healthy children, we examined the cause of reduced naive T cell numbers in children with DS. Compared with aged matched controls, the total number of signal joint TCR excision circles (sjTREC) per ml blood was reduced in DS. Reduced frequencies and absolute numbers of protein tyrosine kinase 7-positive recent thymic emigrants, but similar levels of naive T cell apoptosis and Ag-driven activation in DS, suggested that reduced thymic output and not increased peripheral loss of naive T cells caused the reduced sjTREC numbers. We found no support for defective peripheral generation of naive T cells in DS. In DS the naive T cells responded to IL-7 and, based on Ki-67 expression, had similar proliferation rates as in healthy controls. sjTREC content per naive CD8+ T cells was not increased, but even decreased, pointing to increased survival or peripheral generation of naive T cells in DS. In conclusion, we show in this study that reduced thymic output, but not reduced peripheral generation nor increased loss of naive T cells, results in the low naive T cell numbers found in DS.

Modern intensive chemotherapy for childhood haematological malignancies has led to high cure rates, but has detrimental effects on the immune system. There is little knowledge concerning long-term recovery of the adaptive immune system. Here we studied the long-term reconstitution of the adaptive immune system in 31 children treated for haematological malignancies between July 2000 and October 2006. We performed detailed phenotypical and functional analyses of the various B and T cell subpopulations until 5 years after chemotherapy. We show that recovery of newly-developed transitional B cells and naive B and T cells occurred rapidly, within months, whereas recovery of the different memory B and T cell subpopulations was slower and incomplete, even after 5 years post-chemotherapy. The speed of B and T cell recovery was age-independent, despite a significant contribution of the thymus to T cell recovery. Plasmablast B cell levels remained above normal and immunoglobulin levels normalised within 1 week. Functional T cell responses were normal, even within the first year post-chemotherapy. This study shows that after intensive chemotherapy for haematological malignancies in children, numbers of several memory B and T cell subpopulations were decreased on the long term, while functional T cell responses were not compromised.

The diagnosis of common variable immunodeficiency (CVID) is reserved for patients who suffer from undefined B cell dysfunction. Division of the CVID population into subgroups enables research for underlying disease causes. We studied clinical features and lymphocyte characteristics in 38 children with CVID and compared them to 30 children with less severe antibody deficiencies (e.g. specific antibody deficiency combined with IgG subclass deficiency) and with 65 pediatric controls. Most pediatric immune phenotypes were comparable to adult CVID phenotypes, including a selective increase in newly formed B cells and a decrease in memory B cells and CD4(+) T cells. Eighteen percent of pediatric patients had a mutation in the TNFRSF13B gene, which requires further investigation. Finally, pediatric patients with decreased class-switched memory B cells had significantly more complications. A pediatric classification for CVID may enable prediction and early diagnosis of disease related complications and provide a framework for further etiologic research.

Although accumulating evidence indicates that chronic lymphocytic leukemia (CLL) is a disease with appreciable cell dynamics, it remains uncertain whether this also applies to patients with stable disease. In this study, 2H2O was administered to a clinically homogeneous cohort of nine stable, untreated CLL patients. CLL dynamics in blood and bone marrow were determined and compared with normal B-cell dynamics in blood from five healthy individuals who underwent a similar 2H2O labeling protocol. Average CLL turnover rates (0.08–0.35% of the clone per day) were ∼2-fold lower than average B-cell turnover rates from healthy individuals (0.34–0.89%), whereas the rate at which labeled CLL cells in blood disappeared (0.00–0.39% of B cells per day) was ∼10-fold lower compared with labeled B cells from healthy individuals (1.57–4.24% per day). Leukemic cell turnover variables inversely correlated with the level of somatic hypermutation of the CLL clone (IgVH mutations). Although CLL cells in bone marrow had a higher level of label enrichment than CLL cells in blood, no difference between proliferation rates and proapoptotic and antiapoptotic profiles of CLL cells from these compartments was observed. These data suggest that, in stable disease, there is a biological relationship between the degree of somatic hypermutation of the CLL clone and its dynamics in vivo. Furthermore, in contrast to lymph nodes, the bone marrow does not seem to be a major CLL proliferation site. [Cancer Res 2008;68(24):10137–44]

Concomitant with an increased number of memory-type cells, the amount of naive T cells steadily declines with age. Although the regulatory mechanisms behind this conversion are not fully understood, the suggestion is that both alterations in thymic output and homeostatic signals mold the naive T cell pool. In this study, we identify a new subset of circulating CD27highCD45RAhigh CD8+ T cells characterized by low IL-7Rα message and protein expression. Analysis of TCR repertoire and TCR excision circle content together with ex vivo recovery of IL-7Rα expression indicated that these cells should be placed into the naive T cell pool. Compared with conventional IL-7Rαhigh naive T cells, this subset displayed significantly lower levels of CD28 and higher levels of HLA-DR. Proliferative responses to anti-CD3/CD28 mAbs were indistinguishable from conventional naive T cells, but the responsiveness to IL-7 was limited. Strikingly, IL-7Rαlow naive T cells were particularly increased in circumstances of naive CD8+ T cells shortage, as in the elderly, in patients early after hemopoietic stem cell transplantation, and in HIV-infected individuals. As common γ chain cytokines induce rapid down-regulation of IL-7Rα, we propose that this new subset of naive T cells may encompass cells that have recently received homeostatic signals.

The development of novel vaccines against Neisseria meningitidis recently gained momentum by the generation of penta-acylated lpxL1 LPS which has similar adjuvant activity, but reduced endotoxic activity as compared to hexa-acylated wild type (H44/76) LPS. We investigated the costimulation requirements for the adjuvant activity of both forms of LPS by immunizing CD28-, ICOS- and B7.1/2/ICOS-deficient mice. Both ICOS and CD28 appeared essential for optimal adjuvant activity of H44/76 LPS or lpxL1 LPS. Interestingly, ICOS-mediated costimulation predominates in the adjuvant activity of lpxL1 LPS, while both ICOS and CD28 are required for H44/76 LPS adjuvant activity.