A Murine Intestinal Intraepithelial NKp46-Negative Innate Lymphoid Cell Population Characterized by Group 1 Properties

The Ly49E receptor is preferentially expressed on murine innate-like lymphocytes, such as epidermal Vγ3 T cells, intestinal intraepithelial CD8αα⁺ T lymphocytes, and CD49a⁺ liver natural killer (NK) cells. As the latter have recently been shown to be distinct from conventional NK cells and have innate lymphoid cell type 1 (ILC1) properties, we investigated Ly49E expression on intestinal ILC populations. Here, we show that Ly49E expression is very low on known ILC populations, but it can be used to define a previously unrecognized intraepithelial innate lymphoid population. This Ly49E-positive population is negative for NKp46 and CD8αα, expresses CD49a and CD103, and requires T-bet expression and IL-15 signaling for differentiation and/or survival. Transcriptome analysis reveals a group 1 ILC gene profile, different from NK cells, iCD8α cells, and intraepithelial ILC1. Importantly, NKp46^-CD8αα^-Ly49E⁺ cells produce interferon (IFN)-γ, suggesting that this previously unrecognized population may contribute to Th1-mediated immunity.

The role of Ly49E receptor expression on murine intraepithelial lymphocytes in intestinal cancer development and progression

Ly49E is a member of the Ly49 family of NK receptors and is distinct from other members of this family on the basis of its structural properties, expression pattern and ligand recognition. Importantly, Ly49E receptor expression is high on small intestinal and colonic intraepithelial lymphocytes (IELs). Intestinal IELs are regulators of the mucosal immune system and contribute to front-line defense at the mucosal barrier, including anti-tumor immune response. Whereas most Ly49 receptors have MHC class-I ligands, we showed that Ly49E is instead triggered by urokinase plasminogen activator (uPA). uPA has been extensively implicated in tumor development, where increased uPA expression correlates with poor prognosis. As such, we investigated the role of Ly49E receptor expression on intestinal IELs in the anti-tumor immune response. For this purpose, we compared Ly49E wild-type mice to Ly49E knockout mice in two established tumor models: ApcMin/+-mediated and azoxymethane-induced intestinal cancer. Our results indicate that Ly49E expression on IELs does not influence the development or progression of intestinal cancer.

Expression of the inhibitory Ly49E receptor is not critically involved in the immune response against cutaneous, pulmonary or liver tumours

Natural killer (NK) lymphocytes are part of the innate immune system and are important in immune protection against tumourigenesis. NK cells display a broad repertoire of activating and inhibitory cell surface receptors that regulate NK cell activity. The Ly49 family of NK receptors is composed of several members that recognize major histocompatibility complex class I (MHC-I) or MHC-I-related molecules. Ly49E is a unique inhibitory member, being triggered by the non-MHC-I-related protein urokinase plasminogen activator (uPA) in contrast to the known MHC-I-triggering of the other inhibitory Ly49 receptors. Ly49E also has an uncommon expression pattern on NK cells, including high expression on liver DX5⁻ NK cells. Furthermore, Ly49E is the only Ly49 member expressed by epidermal γδ T cells. As γδ T cells and/or NK cells have been shown to be involved in the regulation of cutaneous, pulmonary and liver malignancies, and as uPA is involved in tumourigenesis, we investigated the role of the inhibitory Ly49E receptor in the anti-tumour immune response. We demonstrate that, although Ly49E is highly expressed on epidermal γδ T cells and liver NK cells, this receptor does not play a major role in the control of skin tumour formation or in lung and liver tumour development.

Notch3 activation is sufficient but not required for inducing human T-lineage specification

Although the role for the individual Notch receptors in early hematopoiesis have been thoroughly investigated in mouse, studies in human have been mostly limited to the use of pan-Notch inhibitors. However, such studies in human are important to predict potential side effects of specific Notch receptor blocking reagents because these are currently being considered as therapeutic tools to treat various Notch-dependent diseases. In this study, we studied the individual roles of Notch1 and Notch3 in early human hematopoietic lineage decisions, particularly during T-lineage specification. Although this process in mice is solely dependent on Notch1 activation, we recently reported Notch3 expression in human uncommitted thymocytes, raising the possibility that Notch3 mediates human T-lineage specification. Although expression of a constitutive activated form of Notch3 (ICN3) results in the induction of T-lineage specification in human CD34(+) hematopoietic progenitor cells, similar to ICN1 overexpression, loss-of-function studies using blocking Abs reveal that only Notch1, but not Notch3, is critical in this process. Blocking of Notch1 activation in OP9-DLL4 cocultures resulted in a complete block in T-lineage specification and induced monocytic and plasmacytoid dendritic cell differentiation instead. In fetal thymus organ cultures, impeded Notch1 activation resulted in B and dendritic cell development. In contrast, Notch3 blocking Abs only marginally affected T-lineage specification and hematopoietic differentiation with a slight increase in monocyte development. No induction of B or dendritic cell development was observed. Thus, our results unambiguously reveal a nonredundant role for Notch1 in human T-lineage specification, despite the expression of other Notch receptors.

Ly49E expression on CD8αα-expressing intestinal intraepithelial lymphocytes plays no detectable role in the development and progression of experimentally induced inflammatory bowel diseases

The Ly49E NK receptor is a unique inhibitory receptor, presenting with a high degree of conservation among mouse strains and expression on both NK cells and intraepithelial-localised T cells. Amongst intraepithelial-localised T cells, the Ly49E receptor is abundantly expressed on CD8αα-expressing innate-like intestinal intraepithelial lymphocytes (iIELs), which contribute to front-line defense at the mucosal barrier. Inflammatory bowel diseases (IBDs), encompassing Crohn's disease and ulcerative colitis, have previously been suggested to have an autoreactive origin and to evolve from a dysbalance between regulatory and effector functions in the intestinal immune system. Here, we made use of Ly49E-deficient mice to characterize the role of Ly49E receptor expression on CD8αα-expressing iIELs in the development and progression of IBD. For this purpose we used the dextran sodium sulphate (DSS)- and trinitrobenzenesulfonic-acid (TNBS)-induced colitis models, and the TNFΔARE ileitis model. We show that Ly49E is expressed on a high proportion of CD8αα-positive iIELs, with higher expression in the colon as compared to the small intestine. However, Ly49E expression on small intestinal and colonic iIELs does not influence the development or progression of inflammatory bowel diseases.

Contribution of the Ly49E natural killer receptor in the immune response to Plasmodium berghei infection and control of hepatic parasite development

Natural killer (NK) cells have different roles in the host response against Plasmodium-induced malaria depending on the stage of infection. Liver NK cells have a protective role during the initial hepatic stage of infection by production of the T_H1-type cytokines IFN-γ and TNF-α. In the subsequent erythrocytic stage of infection, NK cells also induce protection through Th1-type cytokines but, in addition, may also promote development of cerebral malaria via CXCR3-induction on CD8⁺ T cells resulting in migration of these cells to the brain. We have recently shown that the regulatory Ly49E NK receptor is expressed on liver NK cells in particular. The main objective of this study was therefore to examine the role of Ly49E expression in the immune response upon Plasmodium berghei ANKA infection, for which we compared wild type (WT) to Ly49E knockout (KO) mice. We show that the parasitemia was higher at the early stage, i.e. at days 6–7 of Plasmodium berghei ANKA infection in Ly49E KO mice, which correlated with lower induction of CD69, IFN-γ and TNF-α in DX5⁻ liver NK cells at day 5 post-infection. At later stages, these differences faded. There was also no difference in the kinetics and the percentage of cerebral malaria development and in lymphocyte CXCR3 expression in WT versus Ly49E KO mice. Collectively, we show that the immune response against Plasmodium berghei ANKA infection is not drastically affected in Ly49E KO mice. Although NK cells play a crucial role in Plasmodium infection and Ly49E is highly expressed on liver NK cells, the Ly49E NK receptor only has a temporarily role in the immune control of this parasite.

Specific Notch receptor-ligand interactions control human TCR-αβ/γδ development by inducing differential Notch signal strength

Jagged2 preferentially signals through Notch3 to promote γδ T cell development.

In humans, high Notch activation promotes γδ T cell development, whereas lower levels promote αβ-lineage differentiation. How these different Notch signals are generated has remained unclear. We show that differential Notch receptor–ligand interactions mediate this process. Whereas Delta-like 4 supports both TCR-αβ and -γδ development, Jagged1 induces mainly αβ-lineage differentiation. In contrast, Jagged2-mediated Notch activation primarily results in γδ T cell development and represses αβ-lineage differentiation by inhibiting TCR-β formation. Consistently, TCR-αβ T cell development is rescued through transduction of a TCR-β transgene. Jagged2 induces the strongest Notch signal through interactions with both Notch1 and Notch3, whereas Delta-like 4 primarily binds Notch1. In agreement, Notch3 is a stronger Notch activator and only supports γδ T cell development, whereas Notch1 is a weaker activator supporting both TCR-αβ and -γδ development. Fetal thymus organ cultures in JAG2-deficient thymic lobes or with Notch3-blocking antibodies confirm the importance of Jagged2/Notch3 signaling in human TCR-γδ differentiation. Our findings reveal that differential Notch receptor–ligand interactions mediate human TCR-αβ and -γδ T cell differentiation and provide a mechanistic insight into the high Notch dependency of human γδ T cell development.

Abundant stage-dependent Ly49E expression by liver NK cells is not essential for their differentiation and function

The NKR Ly49E has several unique characteristics. Unlike most NKRs, Ly49E is highly expressed on fetal NK cells, whereas expression is decreased on bone marrow-derived NK cells in adult mice. To investigate a possible role for Ly49E in NK cell differentiation and function, we have generated an Ly49E KO mouse. Our results show that bone marrow and splenic NK cells are present in normal numbers in Ly49E KO mice, expressing an unaltered panel of NKRs and differentiation markers. Furthermore, cytokine production and cytotoxicity by these cells are unaffected. Surprisingly, WT DX5(-) liver NK cells express high Ly49E levels in fetal and adult mice. Ly49E(+)DX5(-) liver NK cells transferred into Rag-2(-/-)/gc(-/-) mice maintain high Ly49E expression in the liver and differentiate into DX5(+) NK cells in spleen and bone marrow. Ly49E expression is not crucial for liver NK cell differentiation during ontogeny, as the DX5(-)/DX5(+) ratio, the NKR repertoire, and the granzyme B and TRAIL levels are comparable in Ly49E KO versus WT mice, except for lower TRAIL expression on DX5(-) liver NK cells in 20-day-old mice. The TRAIL-, perforin-, and FasL-mediated cytolysis by liver NK cells is unaffected in Ly49E KO mice. Collectively, we show that in addition to high Ly49E expression on fetal NK cells versus low Ly49E expression on conventional NK cells in adult life, Ly49E remains highly expressed on DX5(-) liver NK cells. However, Ly49E expression does not have a crucial role in differentiation and/or function of these NK cells.

Differential Ly49e expression pathways in resting versus TCR-activated intraepithelial γδ T cells

The Ly49 NK receptor family in mice is composed of several members that recognize MHC class I (MHC-I) or MHC-I-related molecules. We and others have shown before that Ly49E is a unique member, with a different expression pattern on NK cells and being triggered by the non-MHC-I-related protein urokinase plasminogen activator. Among the entire Ly49 receptor family, Ly49E is the only Ly49 member expressed by epidermal-localized γδ T cells and their fetal thymic TCRγδ precursors, and it is the most abundantly expressed member on intestinal intraepithelial γδ T cell lymphocytes. In this study, we provide mechanistic insights into the regulation of Ly49e expression in γδ T cells. First, we demonstrate that TCR-mediated activation of intraepithelial γδ T cells significantly increases Ly49E expression. This results from de novo Ly49E expression and is highly selective, because no other Ly49 family members are induced. TCR-mediated Ly49E induction is a conserved feature of skin- and gut-residing intraepithelial-localized γδ T cell subsets, whereas it is not observed in spleen γδ T cells. By investigating Ly49e promoter activities and lymphotoxin (LT) αβ dependency in resting versus TCR-activated intraepithelial γδ T cells, we reveal two separate regulatory pathways for Ly49E expression, as follows: a LTαβ-dependent pathway leading to basal Ly49E expression in resting cells that is induced by Pro2-mediated Ly49e transcription, and a LTαβ-independent pathway leading to elevated, Pro3-driven Ly49E expression in TCR-stimulated cells.

Notch ligands control the human αβ/γδ lineage choice through receptor-specific induction of differential Notch signal strength. (111.29)

Differential Notch signal strength influences the αβ versus γδ T-cell lineage decision in both mouse and human. Here, we show that the Notch ligands Delta-like-4, Jagged1 and Jagged2, differentially impact this lineage decision in human. Whereas Delta-like-4 supports both αβ and γδ T-cell development, Jagged1 induces αβ-lineage differentiation and Jagged2 primarily γδ T-cell development. Jagged2 induces the strongest Notch signal in human thymocytes as a result of interactions with both Notch1 and Notch3, whereas Delta-like-4 only binds Notch1. In agreement, Notch3 is a stronger activator of Notch target genes and only supports γδ-lineage development, whereas Notch1 is a weaker activator supporting both αβ and γδ T cell development. Blockage of Notch3 activation in Jagged2 cocultures rescues αβ-lineage differentiation, showing the importance of this interaction for driving γδ-lineage differentiation. Further analysis revealed that Jagged2-mediated Notch3 activation blocks αβ-lineage differentiation as a result of inhibition of TCR-β chain expression. Consistently, TCR-αβ T cell development is restored in Jagged2 cocultures by providing immature human T cell progenitors with a TCR-β chain. Our results show that Notch ligands control the human αβ/γδ lineage choice through receptor-specific induction of differential Notch signal strength and that Jagged2-mediated Notch3 activation drives human γδ-lineage differentiation as a result of inhibition of αβ-lineage differentiation.

RHAMM/HMMR (CD168) is not an ideal target antigen for immunotherapy of acute myeloid leukemia

BACKGROUND

Criteria for good candidate antigens for immunotherapy of acute myeloid leukemia are high expression on leukemic stem cells in the majority of patients with acute myeloid leukemia and low or no expression in vital tissues. It was shown in vaccination trials that Receptor for Hyaluronic Acid Mediated Motility (RHAMM/HMMR) generates cellular immune responses in patients with acute myeloid leukemia and that these responses correlate with clinical benefit. It is not clear however whether this response actually targets the leukemic stem cell, especially since it was reported that RHAMM is expressed maximally during the G2/M phase of the cell cycle. In addition, tumor specificity of RHAMM expression remains relatively unexplored.

DESIGN AND METHODS

Blood, leukapheresis and bone marrow samples were collected from both acute myeloid leukemia patients and healthy controls. RHAMM expression was assessed at protein and mRNA levels on various sorted populations, either fresh or after manipulation.

RESULTS

High levels of RHAMM were expressed by CD34(+)CD38(+) and CD34(-) acute myeloid leukemia blasts. However, only baseline expression of RHAMM was measured in CD34(+)CD38(-) leukemic stem cells, and was not different from that in CD34(+)CD38(-) hematopoietic stem cells from healthy controls. RHAMM was significantly up-regulated in CD34(+) cells from healthy donors during in vitro expansion and during in vivo engraftment. Finally, we demonstrated an explicit increase in the expression level of RHAMM after in vitro activation of T cells.

CONCLUSIONS

RHAMM does not fulfill the criteria of an ideal target antigen for immunotherapy of acute myeloid leukemia. RHAMM expression in leukemic stem cells does not differ significantly from the expression in hematopoietic stem cells from healthy controls. RHAMM expression in proliferating CD34+ cells of healthy donors and activated T cells further compromises RHAMM-specific T-cell-mediated immunotherapy.

Notch induces human T-cell receptor γδ+ thymocytes to differentiate along a parallel, highly proliferative and bipotent CD4 CD8 double-positive pathway

In wild-type mice, T-cell receptor (TCR) γδ(+) cells differentiate along a CD4 CD8 double-negative (DN) pathway whereas TCRαβ(+) cells differentiate along the double-positive (DP) pathway. In the human postnatal thymus (PNT), DN, DP and single-positive (SP) TCRγδ(+) populations are present. Here, the precursor-progeny relationship of the various PNT TCRγδ(+) populations was studied and the role of the DP TCRγδ(+) population during T-cell differentiation was elucidated. We demonstrate that human TCRγδ(+) cells differentiate along two pathways downstream from an immature CD1(+) DN TCRγδ(+) precursor: a Notch-independent DN pathway generating mature DN and CD8αα SP TCRγδ(+) cells, and a Notch-dependent, highly proliferative DP pathway generating immature CD4 SP and subsequently DP TCRγδ(+) populations. DP TCRγδ(+) cells are actively rearranging the TCRα locus, and differentiate to TCR(-) DP cells, to CD8αβ SP TCRγδ(+) cells and to TCRαβ(+) cells. Finally, we show that the γδ subset of T-cell acute lymphoblastic leukemias (T-ALL) consists mainly of CD4 SP or DP phenotypes carrying significantly more activating Notch mutations than DN T-ALL. The latter suggests that activating Notch mutations in TCRγδ(+) thymocytes induce proliferation and differentiation along the DP pathway in vivo.

Association of haptoglobin phenotypes with the development of Kaposi's sarcoma in HIV patients

Kaposi's sarcoma (KS) is a rare cutaneous tumor caused by human herpes virus-8 (HHV-8) infection that preferentially develops in case of severe immunosuppression, such as in HIV/AIDS disease. Haptoglobin (Hp), a polymorphic multifunctional plasma protein, exerts several immunomodulatory effects and is characterized by a genetic polymorphism leading to three major phenotypes (Hp 1-1, Hp 2-1 and Hp 2-2). This study investigated the influence of Hp genetic polymorphism on the development of KS in HIV-positive patients. 661 HIV patients were enrolled in the study with a median age of 35 years and a median follow-up time of 57 months. Hp phenotyping was performed using hemoglobin-supplemented starch gel electrophoresis. In case of low Hp concentration high pressure gel permeation chromatography (HPGPC) was used. The Hp 1-1 phenotype was associated with a significant higher risk of KS compared to the combined group of Hp 2-1 and Hp 2-2 patients (p < 0.0005) which remained significant after adjustment for possible confounding variables (age, gender and AIDS status) (p < 0.001). In contrast, the Hp 2-1 phenotype carried the lowest risk. These findings point to the involvement of Hp phenotypes in the pathogenesis of KS, which may be due to a difference in skin immunosurveillance between the Hp phenotypes.

Langerhans cells are not required for epidermal Vgamma3 T cell homeostasis and function

This study tested the hypothesis that Vγ3 TCR-bearing T cells are influenced by LCs. Vγ3 T cells and LCs are located in the epidermis of mice. Vγ3 T cells represent the main T cell population in the skin epithelium and play a crucial role in maintaining the skin integrity, whereas LCs are professional APCs. Although Vγ3 T cells and LCs form an interdigitating network in the epidermis, not much is known about their reciprocal influence and/or interdependence. We used two different LC-deficient mouse models, in which LCs are constitutively or inducibly depleted, to investigate the role of LCs in maturation, homeostasis, and function of Vγ3 T cells. We show that Vγ3 T cell numbers are unaltered by LC deficiency, and Vγ3 T cells isolated from LC-deficient mice are phenotypically and upon in vitro stimulation, functionally indistinguishable from Vγ3 T cells isolated from WT mice based on their cytotoxic potential and cytokine production. Additionally, in vivo skin-wounding experiments show no major difference in response of Vγ3 T cells to wounding in the absence or presence of LCs. These observations indicate that Vγ3 T cells develop and function independently of LCs.

T-lymphoid differentiation potential measured in vitro is higher in CD34+CD38-/lo hematopoietic stem cells from umbilical cord blood than from bone marrow and is an intrinsic property of the cells

BACKGROUND

Human bone marrow and umbilical cord blood are sources of allogeneic hematopoietic stem cells for transplantation, which is a life-saving treatment in a variety of diseases but is burdened by delayed T-cell reconstitution. Observational studies evaluating T-cell reconstitution in post-transplant recipients suggest that cord blood hematopoietic stem cells have a more effective capacity for T-cell reconstitution. This study focuses on the comparison of the capacity of cord blood and bone marrow hematopoietic stem cells to generate T cells in vitro.

DESIGN AND METHODS

Hematopoietic stem cells were cultured in OP9-delta-like-1 and OP9-green fluorescent protein co-cultures to estimate T and myeloid generation capacity, respectively. Phenotypic markers of T-lineage or myeloid differentiation were measured by flow cytometry and used to analyze their kinetics as a function of culture time. Hematopoietic stem cells were labeled with carboxyfluorescein diacetate succinamidyl ester and analyzed after culture to track their phenotypic progression in consecutive generations. Mixed OP9-delta-like-1 co-cultures were done with either carboxyfluorescein diacetate succinamidyl ester-labeled bone marrow and unlabeled cord blood hematopoietic stem cells, or vice versa, to evaluate their mutual influence on T-lineage differentiation. The T-cell potential of hematopoietic stem cells was addressed quantitatively by limiting dilution analysis.

RESULTS

Bulk cultures showed faster and more extensive T-cell differentiation by cord blood hematopoietic stem cells. Furthermore, the T-lymphoid differentiation capacity of cord blood and bone marrow hematopoietic stem cells can be discriminated very early based on the coordinated expression of CD34 and CD7. Mixing experiments with cord blood hematopoietic stem cells and bone marrow hematopoietic stem cells showed that these differences are cell intrinsic. Quantitative clonal analyses demonstrated that CD34(+)CD38(-/lo) hematopoietic stem cells from cord blood contained a two-fold higher T-lineage generation capacity than CD34(+)CD38(-/lo) bone marrow hematopoietic stem cells, whereas the myeloid differentiation was similar.

CONCLUSIONS

Our data shows that cord blood hematopoietic stem cells have higher T-lymphoid differentiation potential than bone marrow hematopoietic stem cells and that this property is cell autonomous.

CD27-deficient mice show normal NK-cell differentiation but impaired function upon stimulation

Natural killer (NK) cells are part of the first line defense against tumors, parasites and virus-infected cells. Therefore, factors that control NK-cell numbers and their function are important. CD27 is constitutively expressed on NK cells and its expression correlates with sequential phases in NK-cell development, discriminating phenotypically and functionally different subsets within the NK-cell population. Although CD27 has been described to have an important regulatory role in effector and memory T and B lymphocytes, its role in NK-cell biology remains to be addressed. In this study, we used CD27(-/-) mice to investigate the role of CD27 in NK-cell development and function, both during the resting state and upon stimulation. The results show that NK-cell numbers are not impaired in CD27(-/-) mice. Moreover, CD27(-/-) NK cells reach full phenotypic maturity, evidenced by normal expression of CD49b, CD43 and CD11b. Expression of activating receptors is unaltered, whereas expression of several inhibitory receptors is increased. Cytotoxicity and interferon-γ production by NK cells from CD27(-/-) mice in the resting state are normal. However, upon in vivo anti-CD40- or poly-I:C-mediated activation, or in vitro interleukin-15 priming plus anti-NKp46 stimulation, the absence of CD27 results in decreased cytolytic activity and cytokine production by spleen and liver NK cells. In conclusion, this study demonstrates that CD27 is dispensable for the development of functional NK cells. However, upon stimulation of NK cells, CD27 displays an important role in their activation and functionality.

In vitro generation of immune cells from pluripotent stem cells

Stem cell transplant recipients and acquired or inherited immune-deficiency patients could benefit from the infusion of B, T and/or NK cells. These lymphoid cells can be generated in vitro from bone marrow derived CD34+CD45+ hematopoietic stem cells (HSC). The number of cells that can be obtained in this way is limited especially in the adult. An alternative source may therefore constitute human pluripotent stem cells (PSC) such as embryonic (hESC) or induced pluripotent stem cells (hiPSC). Here, we focus on present knowledge on the generation of lymphoid cells from hESC. The two main obstacles for the generation of clinically relevant immune cells are the failure to generate from hESC long-term repopulating HSC which could be kept in culture for prolonged time; and insufficient knowledge of the selection process which generates mature T cells from CD4 CD8 double positive (DP) precursors in vitro.

Comparison of phenotypic and genotypic tropism determination in triple-class-experienced HIV patients eligible for maraviroc treatment

Background

Determination of HIV-1 tropism is a pre-requisite to the use of CCR5 antagonists. This study evaluated the potential of population genotypic tropism tests (GTTs) in clinical practice, and the correlation with phenotypic tropism tests (PTTs) in patients accessing routine HIV care.

Methods

Forty-nine consecutive plasma samples for which an original Trofile^TM assay was performed were obtained from triple-class-experienced patients in need of a therapy change. Viral tropism was defined as the consensus of three or more tropism calls obtained from the combination of two independent population PTT assays (Trofile Biosciences, San Francisco, CA, USA, and Virco, Beerse, Belgium), population GTTs and GTTs based on ultra-deep sequencing. If no consensus was reached, a clonal PTT was performed in order to finalize the tropism call. This two-step approach allowed the definition of a reference tropism call.

Results

According to the reference tropism result, 35/49 samples were CCR5 tropic (R5) (patients eligible for maraviroc treatment) and 14/49 were assigned as non-R5 tropic. The non-R5 samples [patients not eligible for maraviroc treatment according to the FDA/European Medicines Agency (EMEA) label] group included both the CXCR4 (X4) samples and the dual and mixed CCR5/CXCR4 (R5/X4) samples. Compared with Trofile^TM population PTTs, population GTTs showed a higher sensitivity (97%) and a higher negative predictive value (91%), but almost equal specificity and an equal positive predictive value.

Conclusions

In line with recent reports from clinical trial data, our data support the use of population genotypic tropism testing as a tool for tropism determination before the start of maraviroc.

Epidemiological study of phylogenetic transmission clusters in a local HIV-1 epidemic reveals distinct differences between subtype B and non-B infections

Background

The number of HIV-1 infected individuals in the Western world continues to rise. More in-depth understanding of regional HIV-1 epidemics is necessary for the optimal design and adequate use of future prevention strategies. The use of a combination of phylogenetic analysis of HIV sequences, with data on patients' demographics, infection route, clinical information and laboratory results, will allow a better characterization of individuals responsible for local transmission.

Methods

Baseline HIV-1 pol sequences, obtained through routine drug-resistance testing, from 506 patients, newly diagnosed between 2001 and 2009, were used to construct phylogenetic trees and identify transmission-clusters. Patients' demographics, laboratory and clinical data, were retrieved anonymously. Statistical analysis was performed to identify subtype-specific and transmission-cluster-specific characteristics.

Results

Multivariate analysis showed significant differences between the 59.7% of individuals with subtype B infection and the 40.3% non-B infected individuals, with regard to route of transmission, origin, infection with Chlamydia (p = 0.01) and infection with Hepatitis C virus (p = 0.017). More and larger transmission-clusters were identified among the subtype B infections (p < 0.001). Overall, in multivariate analysis, clustering was significantly associated with Caucasian origin, infection through homosexual contact and younger age (all p < 0.001). Bivariate analysis additionally showed a correlation between clustering and syphilis (p < 0.001), higher CD4 counts (p = 0.002), Chlamydia infection (p = 0.013) and primary HIV (p = 0.017).

Conclusions

Combination of phylogenetics with demographic information, laboratory and clinical data, revealed that HIV-1 subtype B infected Caucasian men-who-have-sex-with-men with high prevalence of sexually transmitted diseases, account for the majority of local HIV-transmissions. This finding elucidates observed epidemiological trends through molecular analysis, and justifies sustained focus in prevention on this high risk group.

Continuous CD27 triggering in vivo strongly reduces NK cell numbers

NK cells are important mediators of the early defense. In mice, immature and mature NK (mNK) cells constitutively express the TNF receptor family member CD27; however, mNK cells eventually lose CD27 expression and become resting NK cells. Interaction of CD27 with its ligand, CD70, enhances proliferation and effector functions of NK cells. We used mice that constitutively express CD70 on B cells (CD70-Tg) to study the in vivo effects of continuous triggering of CD27 on NK cells. Continuous CD70-CD27 interaction resulted in strongly down-modulated CD27 expression on NK cells and gradually reduced absolute NK cell numbers. This reduction was most prominent in the mNK cell subpopulation and was at least partially due to increased apoptosis. Residual NK cells showed lower expression of activating Ly49 receptors and normal (liver) or decreased (spleen) IFN-gamma production. Nevertheless, NK cells from CD70-Tg mice displayed higher YAC-1 killing capacities. CD70-Tg NK cells exhibited up-regulated expression of NKG2D, which is in accordance with the increased YAC-1 lysis, as this is mainly NKG2D-dependent. Taken together, this study is the first to demonstrate that continuous CD70 triggering of CD27 on NK cells in vivo results in a severe reduction of NK cells. On a single cell basis, however, residual NK cells display enhanced cytotoxicity.

Rho GTPase Cdc42 is essential for human T-cell development

BACKGROUND

Rho GTPases are involved in the regulation of many cell functions, including some related to the actin cytoskeleton. Different Rho GTPases have been shown to be important for T-cell development in mice. However, their role in human T-cell development has not yet been explored.

DESIGN AND METHODS

We examined the expression and activation of Rho GTPases along different stages of T-cell development in the human thymus. Early stage human thymocytes were transduced with constitutively active and dominant negative mutants of different Rho GTPases to explore their role in human T-cell development, as analyzed in fetal thymus organ cultures. The use of these mutants as well as Rho GTPase-specific inhibitors allowed us to explore the role of GTPases in thymocyte migration.

RESULTS

We found that the expression of several Rho GTPases is differently regulated during successive stages of T-cell development in man, suggesting a specific role in human thymopoiesis. In chimeric fetal thymus organ culture, T-cell development was not or only mildly affected by expression of dominant negative Rac1 and Rac2, but was severely impaired in the presence of dominant negative Cdc42, associated with enhanced apoptosis and reduced proliferation. Kinetic analysis revealed that Cdc42 is necessary in human T-cell development both before and after expression of the pre-T-cell receptor. Using inhibitors and retrovirally transferred mutants of the aforementioned Rho GTPases, we showed that only Rac1 is necessary for migration of different thymocyte subsets, including the early CD34(+) fraction, towards stromal cell-derived factor-1 alpha. Constitutively active mutants of Rac1, Rac2 and Cdc42 all impaired migration towards stromal cell-derived factor-1 alpha and T-cell development to different degrees.

CONCLUSIONS

This is the first report on Rho GTPases in human T-cell development, showing the essential role of Cdc42. Our data suggest that enhanced apoptotic death and reduced proliferation rather than disturbed migration explains the decreased thymopoiesis induced by dominant negative Cdc42.

Viral load assay sensitivity and low level viremia in HAART treated HIV patients

BACKGROUND

The recent introduction of highly sensitive viral load assays resulted in a significant increase in number of treated HIV-infected patients with a detectable viral load. The significance of a viral load between 20 and 50 copies/mL remains unclear.

OBJECTIVES

To compare the performance of three viral load assays, with special attention for specificity and sensitivity at the lowest level of quantification.

STUDY DESIGN

Samples (n=181) were selected from 62 HIV-positive individuals that experience viral blips or episodes of low but detectable viremia under antiretroviral treatment, and from 216 HIV-negative individuals. Each sample was tested in at least two of three assays: the Cobas Amplicor HIV-1 Monitor (CAP/CA), the Cobas Ampliprep/Cobas TaqMan HIV-1 version 1 (CAP/CTM1) and the Cobas Ampliprep/Cobas TaqMan HIV-1 version 2 (CAP/CTM2).

RESULTS

No false positive results were recorded. Kappa statistics revealed fair to moderate agreement between the results of the three assays, but important differences in sensitivity were observed, with the highest sensitivity reported for CAP/CTM2 followed by CAP/CTM1 and CAP/CA. The differences in sensitivity remained after equalization of the detection limit for all assays at 50 copies/mL. Analysis of samples collected over time showed that patients with single blips in CAP/CA present with recurrent blips in CAP/CTM1 and persistent detectable viremia in CAP/CTM2.

CONCLUSIONS

Viral load results between 20 and 50 copies/mL in either CAP/CTM1 or CAP/CTM2, indicate true viremia. The availability of highly sensitive assays force reconsideration of the terms 'undetectable' viral load and 'virological success' of antiretroviral treatment.

Functionally mature CD4 and CD8 TCRalphabeta cells are generated in OP9-DL1 cultures from human CD34+ hematopoietic cells

Human CD34(+) hematopoietic precursor cells cultured on delta-like ligand 1 expressing OP9 (OP9-DL1) stromal cells differentiate to T lineage cells. The nature of the T cells generated in these cultures has not been studied in detail. Since these cultures do not contain thymic epithelial cells which are the main cell type mediating positive selection in vivo, generation of conventional helper CD4(+) and cytotoxic CD8(+) TCRalphabeta cells is not expected. Phenotypically mature CD27(+)CD1(-) TCRgammadelta as well as TCRalphabeta cells were generated in OP9-DL1 cultures. CD8 and few mature CD4 single-positive TCRalphabeta cells were observed. Mature CD8 single-positive cells consisted of two subpopulations: one expressing mainly CD8alphabeta and one expressing CD8alphaalpha dimers. TCRalphabeta CD8alphaalpha and TCRgammadelta cells both expressed the IL2Rbeta receptor constitutively and proliferated on IL-15, a characteristic of unconventional T cells. CD8alphabeta(+) and CD4(+) TCRalphabeta cells were unresponsive to IL-15, but could be expanded upon TCR stimulation as mature CD8alphabeta(+) and CD4(+) T cells. These T cells had the characteristics of conventional T cells: CD4(+) cells expressed ThPOK, CD40L, and high levels of IL-2 and IL-4; CD8(+) cells expressed Eomes, Runx3, and high levels of granzyme, perforin, and IFN-gamma. Induction of murine or human MHC class I expression on OP9-DL1 cells had no influence on the differentiation of mature CD8(+) cells. Similarly, the presence of dendritic cells was not required for the generation of mature CD4(+) or CD8(+) T cells. These data suggest that positive selection of these cells is induced by interaction between T precursor cells.

Endothelial progenitor cells: identity defined?

In the past decade, researchers have gained important insights on the role of bone marrow (BM)-derived cells in adult neovascularization. A subset of BM-derived cells, called endothelial progenitor cells (EPCs), has been of particular interest, as these cells were suggested to home to sites of neovascularization and neoendothelialization and differentiate into endothelial cells (ECs) in situ, a process referred to as postnatal vasculogenesis. Therefore, EPCs were proposed as a potential regenerative tool for treating human vascular disease and a possible target to restrict vessel growth in tumour pathology. However, conflicting results have been reported in the field, and the identification, characterization, and exact role of EPCs in vascular biology is still a subject of much discussion. The focus of this review is on the controversial issues in the field of EPCs which are related to the lack of a unique EPC marker, identification challenges related to the paucity of EPCs in the circulation, and the important phenotypical and functional overlap between EPCs, haematopoietic cells and mature ECs. We also discuss our recent findings on the origin of endothelial outgrowth cells (EOCs), showing that this in vitro defined EC population does not originate from circulating CD133⁺ cells or CD45⁺ haematopoietic cells.

Generation of T cells from human embryonic stem cell-derived hematopoietic zones

Human embryonic stem cells (hESC) are pluripotent stem cells. A major challenge in the field of hESC is the establishment of specific differentiation protocols that drives hESC down a particular lineage fate. So far, attempts to generate T cells from hESC in vitro were unsuccessful. In this study, we show that T cells can be generated in vitro from hESC-derived hematopoietic precursor cells present in hematopoietic zones (HZs). These zones are morphologically similar to blood islands during embryonic development, and are formed when hESC are cultured on OP9 stromal cells. Upon subsequent transfer of these HZs on OP9 cells expressing high levels of Delta-like 1 and in the presence of growth factors, cells expand and differentiate to T cells. Furthermore, we show that T cells derive exclusively from a CD34(high)CD43(low) population, further substantiating the notion that hESC-derived CD34(high)CD43(low) cells are formed in HZs and are the only population containing multipotent hematopoietic precursor cells. Differentiation to T cells sequentially passes through the physiological intermediates: CD34(+)CD7(+) T/NK committed, CD7(+)CD4(+)CD8(-) immature single positive, CD4(+)CD8(+) double positive, and finally CD3(+)CD1(-)CD27(+) mature T cell stages. TCRalphabeta(+) and TCRgammadelta(+) T cells are generated. Mature T cells are polyclonal, proliferate, and secrete cytokines in response to mitogens. This protocol for the de novo generation of T cells from hESC could be clinically and scientifically relevant.

Effectiveness of antiretroviral therapy and development of drug resistance in HIV-1 infected patients in Mombasa, Kenya

Access to antiretroviral therapy (ART) is increasing in resource-limited settings (RLS) and can successfully reduce HIV-related morbidity and mortality. However, virologic failure and development of viral drug resistance can result in reduced treatment options and disease progression. Additionally, transmission of resistant virus, and particularly multi-drug resistance, could become a public health concern. This study evaluated treatment success and development of ART drug resistance after short-term treatment among patients attending the Comprehensive HIV Care Centre (CCC) of Coast Province General Hospital, Mombasa, Kenya. One hundred and fifty HIV-infected individuals receiving ART were consecutively recruited to participate in the study. After determination of plasma viral load, patients with detectable viral load levels were subjected to genotypic drug resistance testing. At the time of sampling, 132 of the 150 participants were on ART for more than 6 months (median 21 months, IQR = 12–26). An efficient viral load reduction to below 50 copies/ml was observed in 113 (85.6%) of them. Of the 19 patients with a detectable viral load, sequencing of the protease (PR) and reverse transcriptase (RT) gene was successful in 16. Eleven (11) of these 16 patients were infected with a subtype A1 virus. Major PR mutations were absent, but mutations associated with drug resistance in RT were detected in 14 of the 16 patients (87.5%). High-level resistance against at least 2 drugs of the ART regimen was observed in 9/14 (64.3%). The 3TC mutation M184V and the NNRTI mutation K103N were most frequent but also the multi-drug resistance Q151M and the broad NRTI cross-resistance K65R were observed. The results of this study revealed a high rate of treatment success after short term ART in patients treated at a public provincial hospital in a RLS. Nevertheless, the observed high risk of accumulation of resistance mutations among patients failing treatment and the selection of multi-drug resistance mutations in some, remains of great concern for future treatment options and potential transmission to partners.

Impact of Delta 32-CCR5 heterozygosity on HIV-1 genetic evolution and variability--a study of 4 individuals infected with closely related HIV-1 strains

A cluster of four patients acutely infected with a genetically almost identical virus, allowed us to investigate genetic variability and disease progression in early HIV-1 infection with minimal interference of virus specific factors. Two of the patients were heterozygous for the 32-bp deletion in the CCR5 coreceptor gene. Both showed a slower disease progression with lower viral load levels and a reduced rate of genetic evolution compared to the patients with normal CCR5 alleles. During 3 years of treatment-free follow-up, the mean pairwise genetic distance increased with 1.45% and 1.58% in the two patients with a 32-bp deletion allele compared to 3.05% and 3.57% in the two patients with normal CCR5 alleles. The observed relation between slower disease progression and a reduced evolutionary rate illustrates the influence of the virus replicative capacity, here most possibly hampered by the CCR5 heterozygosity in two of the four individuals, on the genetic evolution of the virus in the host.

Continuous venovenous haemofiltration using a citrate buffered substitution fluid

Different methods of regional anticoagulation using citrate in continuous renal replacement therapy have been described in the past. However, these procedures were usually very complex or did not reach modem requirements for effective continuous renal replacement therapy. Furthermore, little is known about long-term acid-base stability and citrate levels during the treatment. We describe a system in which citrate is used both as anticoagulant and as the sole buffer substance in continuous venovenous haemofiltration. Our citrate-containing, calcium-free substitution fluid was used in predilution mode with a constant ratio between blood flow (120 to 150 ml/min) and substitution flow (2400 to 3000 ml/hour). Anticoagulation was limited to the extracorporeal circuit. Twenty patients with acute renal failure on mechanical ventilation were treated, four for eight hours, four for 24 hours and 12 as long they needed continuous renal replacement therapy (9.6 +/- 5.0 days, range 4.0 to 39.3 days). We achieved stable acid-base and electrolyte balance in all patients. We observed no bleeding complications (patient activated clotting time 112.4 +/- 17.1 s, post-filter circuit activated clotting time 270.5 +/- 80.3 s) and achieved appropriate filter life times (48.6 +/- 13.2 h). Predilution, citrate-based substitution fluid provides both anticoagulation within the extracorporeal circuit and control of acid-base balance in critically ill patients at risk of bleeding in acute renal failure. It is easy to apply and safe. Clearance can be varied as long as a constant ratio between blood and substitution flow is maintained.

Evaluation of two commercially available alternatives for HIV-1 viral load testing in resource-limited settings

There is an urgent need for low-cost assays for HIV-1 quantitation to ensure adequate follow-up of HIV-infected patients on antiretroviral therapy (ART) in resource-limited countries. Two low-cost viral load assays are evaluated, a reverse transcriptase activity assay (ExavirLoad v2, Cavidi) and a real-time reverse transcriptase PCR assay (Generic HIV viral load, Biocentric). Both tests were compared with the ultrasensitive HIV Amplicor Monitor assay. Samples were collected in Mombasa, Kenya, from 20 HIV-1 seronegative and 150 HIV-1 seropositive individuals of whom 50 received antiretroviral treatment (ART). The ExavirLoad and the Generic HIV viral load assay were performed in a local laboratory in Mombasa, the Amplicor Monitor assay (version 1.5, Roche Diagnostics) was performed in Ghent, Belgium. ExavirLoad and Generic HIV viral load reached a sensitivity of 98.3% and 100% and a specificity of 80.0% and 90.0%, respectively. Linear regression analyses revealed good correlations between the Amplicor Monitor and the Generic HIV viral load (r=0.935, p<0.001) with high accuracy (100.1%), good precision (5.5%) and a low percent similarity coefficient of variation (5.4%). Bland-Altman analysis found 95% of the samples within clinically acceptable limits of agreement (-1.19 to 0.87logcopies/ml). Although, the ExavirLoad also showed a good linear correlation with the Amplicor Monitor (r=0.901, p<0.001), a problem with false positive results was more significant. The cost per test remains relatively high (US$ 30 for ExavirLoad and US$ 20 for the Generic HIV viral load). Hence, false positive results and the need for an expensive PCR instrument for the Generic HIV viral load assays still limit the implementation of these tests in less equipped, less experienced laboratories.

Feasibility of detecting human immunodeficiency virus type 1 drug resistance in DNA extracted from whole blood or dried blood spots

Due to high cost, availability of human immunodeficiency virus type 1 (HIV-1) drug resistance testing in resource-poor settings is still limited. We therefore evaluated the usefulness of viral DNA extracted from either whole blood or dried blood spots (DBS). Samples were collected from 50 patients receiving therapy and 10 therapy-naïve patients. Amplification and sequencing of RNA and DNA was performed using an in-house assay. Protease (PR) and reverse transcriptase (RT) sequences of plasma viral RNA were obtained for 96.6% and 89.7%, respectively, of the 29 patients with a detectable viral load. For cellular viral DNA, useful PR and RT sequences were obtained for 96.6% and 93.1% of the whole-blood-cell samples and for 93.1% and 93.1% of the DBS samples, respectively. For the 31 patients with an undetectable viral load, PR and RT sequences were obtained for 67.7% and 61.3% of the whole-blood-cell DNA preparations and for 54.8% and 58.1% of the DBS DNA preparations, respectively. A good correlation between RNA and DNA sequences was found; most discordances were caused by the detection of mixed amino acids. Of the RT drug-resistant mutations, 13 (38.2%) were seen in RNA only, 6 (17.6%) in DNA only, and 15 (44.1%) in both. Repeated amplification and sequencing of DNA extracts revealed a lack of reproducibility for the detection of drug resistance mutations in a number of samples, indicating a possible founder effect. In conclusion, this study shows the feasibility of genotypic drug resistance testing on whole blood cells or DBS and its possible usefulness for HIV-1 subtyping or examining the overall distribution of drug resistance in a population. For individual patients, RNA sequencing was shown to be superior to DNA sequencing, especially for patients who experienced early treatment failure. The use of DNA extracted from whole blood or DBS for the detection of archived drug resistance mutations deserves further study.

Notch signaling induces cytoplasmic CD3 epsilon expression in human differentiating NK cells

It has been proposed that heterogeneity in natural killer (NK)-cell phenotype and function can be achieved through distinct thymic and bone marrow pathways of NK-cell development. Here, we show a link between Notch signaling and the generation of intracellular CD3epsilon (cyCD3)-expressing NK cells, a cell population that can be detected in vivo. Differentiation of human CD34(+) cord blood progenitors in IL-15-supplemented fetal thymus organ culture or OP9-Delta-like 1 (DL1) coculture resulted in a high percentage of cyCD3(+) NK cells that was blocked by the gamma-secretase inhibitor DAPT. The requirement for Notch signaling to generate cyCD3(+) NK cells was further illustrated by transduction of CD34(+) cord blood (CB) cells with either the active intracellular part of Notch or the dominant-negative mutant of mastermind-like protein 1 that resulted in the generation of NK cells with respectively high or low frequencies of cyCD3. Human thymic CD34(+) progenitor cells displayed the potential to generate cyCD3(+) NK cells, even in the absence of Notch/DL1 signaling. Peripheral blood NK cells were unable to induce cyCD3 expression after DL1 exposure, indicating that Notch-dependent cyCD3 expression can only be achieved during the early phase of NK-cell differentiation.

Tumor necrosis factor promotes T-cell at the expense of B-cell lymphoid development from cultured human CD34+ cord blood cells

OBJECTIVE

Human CD34+ cord blood (CB) cells are hematopoietic progenitors useful for stem cell transplantation, even after ex vivo expansion. We investigated the effect of tumor necrosis factor (TNF) on lymphoid development from cultured CD34+ CB cells.

MATERIALS AND METHODS

Human CD34+ CB cells were cultured in cytokine mixes with or without TNF. Preculture during 60 hours was followed by in vitro differentiation assays, including fetal thymus organ culture and coculture on murine stromal MS-5 cells. In a next step, experiments were extended to CD34+CD38- and CD34+CD38+ CB cells and prolonged preculture.

RESULTS

Preculture in the presence of TNF improved differentiation into T cells and diminished the ability to generate B cells, while NK potential and myeloid development were unaffected. Sorted CD34+CD38- CB cells were more potent T-cell precursors after preculture in TNF, compared to CD34+CD38+ CB cells. In precultured CD34+CD38- CB cells, TNF increased GATA3 but decreased EBF1 expression, in line with the skewed lymphoid differentiation induced by TNF. However, when preculture in the presence of TNF was extended to 1 week, T-cell precursors were lost.

CONCLUSION

After short-term culture of CD34+ CB cells in the presence of TNF, T-cell generation is stimulated at the expense of B-cell generation. T-cell progenitors are enriched in the CD34+CD38- fraction. These results have implications on the culture conditions to be used for CB CD34+ cells prior to transplantation.

Endothelial outgrowth cells are not derived from CD133+ cells or CD45+ hematopoietic precursors

OBJECTIVE

Two types of endothelial progenitor cells (EPCs), early EPCs and late EPCs (also called endothelial outgrowth cells [EOCs]), were described in vitro previously. In this report, we dissect the phenotype of the precursor(s) that generate these cell types with focus on the markers CD34, CD133, and vascular endothelial growth factor receptor-2 (VEGFR2) that have been used to identify putative circulating endothelial precursors. We also included CD45 in the analysis to assess the relation between CD34+ hematopoietic progenitors (HPC), CD34+ endothelial precursors, and both in vitro generated EPC types. Addressing this issue might lead to a better understanding of the lineage and phenotype of the precursor(s) that give rise to both cell types in vitro and may contribute to a consensus on their flowcytometric enumeration.

METHODS AND RESULTS

Using cell sorting of human cord blood (UCB) and bone marrow (BM) cells, we demonstrate that EOC generating precursors are confined to a small CD34+ CD45- cell fraction, but not to the CD34+ CD45+ HPC fraction, nor any other CD45+ subpopulation. CD34+ CD45+ HPC generated monocytic cells that displayed characteristics typical for early EPCs. Phenotypic analysis showed that EOC generating CD34+ CD45- cells express VEGFR2 but not CD133, whereas CD34+ CD45+ HPC express CD133 as expected, but not VEGFR2.

CONCLUSION

EOCs are not derived from CD133+ cells or CD45+ hematopoietic precursors.

Detection of drug resistance mutations as a predictor of subsequent virological failure in patients with HIV-1 viral rebounds of less than 1,000 RNA copies/ml

In order to evaluate the usefulness of resistance testing after a viral rebound with plasma HIV RNA levels of less than 1,000 copies (c)/ml, genotyping was performed on 39 samples from patients on highly active antiretroviral therapy (HAART) showing a viremia of over 50 c/ml up to a maximum of 1,000 c/ml after at least one undetectable viral load result. Protease and reverse transcriptase (RT) sequences were obtained for all 39 samples. In 10 (25.6%) of the samples, mutations not seen before the initiation of the regimen were observed. The M184V/I mutation was the most prevalent but in several patients a combination of multiple mutations was detected. Follow-up samples were available for 34 patients. In six (85.71%) out of seven patients with new mutations, the viral load on the follow-up visit remained detectable, indicating true failure, compared to 6 (31.6%) true failures out of 19 patients in whom only wild type virus was detected (P = 0.02) and three (37.5%) out of eight patients in whom only the mutations already present at the initiation of HAART were seen (P = 0.08). The results indicate that reliable resistance testing can be performed on samples with a viral burden of less than 1,000 c/ml and demonstrate that multiple drug resistance mutations can be selected at low viral load rebounds. Most importantly, detection of resistance mutations in viral rebound samples was predictive of subsequent virological failure.

T-, B- and NK-lymphoid, but not myeloid cells arise from human CD34+CD38−CD7+ common lymphoid progenitors expressing lymphoid-specific genes

Hematopoietic stem cells in the bone marrow (BM) give rise to all blood cells. According to the classic model of hematopoiesis, the differentiation paths leading to the myeloid and lymphoid lineages segregate early. A candidate 'common lymphoid progenitor' (CLP) has been isolated from CD34(+)CD38(-) human cord blood cells based on CD7 expression. Here, we confirm the B- and NK-differentiation potential of CD34(+)CD38(-)CD7(+) cells and show in addition that this population has strong capacity to differentiate into T cells. As CD34(+)CD38(-)CD7(+) cells are virtually devoid of myeloid differentiation potential, these cells represent true CLPs. To unravel the molecular mechanisms underlying lymphoid commitment, we performed genome-wide gene expression profiling on sorted CD34(+)CD38(-)CD7(+) and CD34(+)CD38(-)CD7(-) cells. Interestingly, lymphoid-affiliated genes were mainly upregulated in the CD7(+) population, while myeloid-specific genes were downregulated. This supports the hypothesis that lineage commitment is accompanied by the shutdown of inappropriate gene expression and the upregulation of lineage-specific genes. In addition, we identified several highly expressed genes that have not been described in hematopoiesis before.

Differentiation assays of bone marrow-derived Multipotent Adult Progenitor Cell (MAPC)-like cells towards neural cells cannot depend on morphology and a limited set of neural markers

There are accumulating studies that report a neurogenic potential of bone marrow-derived cells both in vitro as well as in vivo. Most claims of neural "transdifferentiation" have based their conclusions on morphology and neural gene expression. Recently, doubts have been raised about the validity of both outcome parameters since non-neural cells can extend neurites and show aberrant neural gene expression as a response to stress inducing factors. In this study, we compared bone marrow-derived Multipotent Adult Progenitor Cell (MAPC)-like cells and neural stem cells (NSC) in their morphology and neural gene expression profile after neural differentiation using three differentiation protocols. We evaluated the expression of five neuroglial antigens [neurofilament 200 (NF200); beta III tubulin (beta3 tub); tau; Glial Fibrillary Acidic Protein (GFAP); Myelin Basic Protein (MBP) and RIP antigen] using real-time PCR (RT-PCR) and immunocytochemistry (ICC). MAPC-like cells adopted a neural-like morphology in one protocol but a fibroblast-like morphology in the two other protocols. RT-PCR and ICC show that MAPC-like cells already express the neural antigens beta III tubulin and NF200 at baseline, but no upregulation of these genes after exposure to three distinct differentiation protocols was seen. In contrast, NSC adopt neural and glial morphologies with a clear increase in expression of all neuroglial genes in all differentiation protocols used. In conclusion, our data demonstrate that neural-like morphology and expression of a limited set of neural marker genes by MAPC-like cells after differentiation are not absolute proof of neural transdifferentiation because MAPC-like cells only partially meet the criteria which are fulfilled by NSC after neural differentiation.

In vitro expanded cells contributing to rapid severe combined immunodeficient repopulation activity are CD34+38-33+90+45RA-

Expansion of hematopoietic stem cells could be used clinically to shorten the prolonged aplastic phase after umbilical cord blood (UCB) transplantation. In this report, we investigated rapid severe combined immunodeficient (SCID) repopulating activity (rSRA) 2 weeks after transplantation of CD34(+) UCB cells cultured with serum on MS5 stromal cells and in serum- and stroma-free cultures. Various subpopulations obtained after culture were studied for rSRA. CD34(+) expansion cultures resulted in vast expansion of CD45(+) and CD34(+) cells. Independent of the culture method, only the CD34(+)33(+)38(-) fraction of the cultured cells contained rSRA. Subsequently, we subfractionated the CD34(+)38(-) fraction using stem cell markers CD45RA and CD90. In vitro differentiation cultures showed CD34(+) expansion in both CD45RA(-) and CD90(+) cultures, whereas little increase in CD34(+) cells was observed in both CD45RA(+) and CD90(-) cultures. By four-color flow cytometry, we could demonstrate that CD34(+)38(-)45RA(-) and CD34(+)38(-)90(+) cell populations were largely overlapping. Both populations were able to reconstitute SCID/nonobese diabetic mice at 2 weeks, indicating that these cells contained rSRA activity. In contrast, CD34(+)38(-)45RA(+) or CD34(+)38(-)90(-) cells contributed only marginally to rSRA. Similar results were obtained when cells were injected intrafemorally, suggesting that the lack of reconstitution was not due to homing defects. In conclusion, we show that after in vitro expansion, rSRA is mediated by CD34(+)38(-)90(+)45RA(-) cells. All other cell fractions have limited reconstitutive potential, mainly because the cells have lost stem cell activity rather than because of homing defects. These findings can be used clinically to assess the rSRA of cultured stem cells.

Overexpression of HES-1 is not sufficient to impose T-cell differentiation on human hematopoietic stem cells

By retroviral overexpression of the Notch-1 intracellular domain (ICN) in human CD34+ hematopoietic stem cells (HSCs), we have shown previously that Notch-1 signaling promotes the T-cell fate and inhibits the monocyte and B-cell fate in several in vitro and in vivo differentiation assays. Here, we investigated whether the effects of constitutively active Notch-1 can be mimicked by overexpression of its downstream target gene HES1. Upon HES-1 retroviral transduction, human CD34+ stem cells had a different outcome in the differentiation assays as compared to ICN-transduced cells. Although HES-1 induced a partial block in B-cell development, it did not inhibit monocyte development and did not promote T/NK-cell-lineage differentiation. On the contrary, a higher percentage of HES-1-transduced stem cells remained CD34+. These experiments indicate that HES-1 alone is not able to substitute for Notch-1 signaling to induce T-cell differentiation of human CD34+ hematopoietic stem cells.

Ex vivo characterization of allo-MHC-restricted T cells specific for a single MHC-peptide complex

Alloreactive T cells are thought to be a potentially rich source of high-avidity T cells with therapeutic potential since tolerance to self-Ags is restricted to self-MHC recognition. Given the particularly high frequency of alloreactive T cells in the peripheral immune system, we used numerous MHC class I multimers to directly visualize and isolate viral and tumor Ag-specific alloreactive CD8 T cells. In fact, all but one specificities screened were undetectable in ex vivo labeling. In this study, we report the occurrence of CD8 T cells specifically labeled with allo-HLA-A*0201/Melan-A/MART-1(26-35) multimers at frequencies that are in the range of 10(-4) CD8 T cells and are thus detectable ex vivo by flow cytometry. We report the thymic generation and shaping of tumor Ag-specific, alloreactive T cells as well as their fate once seeded in the periphery. We show that these cells resemble their counterparts in HLA-A*0201-positive individuals, based on their structural and functional attributes.

A sensitive in-house RT-PCR genotyping system for combined detection of plasma HIV-1 and assessment of drug resistance

Quantification of the viral burden and identification of drug resistant mutations are important laboratory tools in the management of HIV-1 infected patients. However, widespread use of assays for viral load determination and genotyping is still hampered by the high cost. Here, an in-house RT-PCR-sequencing assay for HIV-1 drug resistance monitoring with the potential to be used both as a qualitative assay to detect the virus in plasma and as a genotyping system is described. A total of 377 clinical samples, collected from 374 HIV-infected patients of diverse geographic origin, were tested. The nested RT-PCR for amplification of the protease reverse transcriptase gene was found positive for 350 (92.8%) and 346 (91.8%) of 377 samples, respectively. All amplification-failures were due to viral loads of below 500 copies/ml. However, low viral load does not exclude amplification since 80.2 and 76% of 121 samples with viral loads of less than 500 copies/ml were amplified successfully for protease and reverse transcriptase, respectively. The high sensitivity of the assay was independent of the HIV-subtype, with a broad range of different HIV-1 subtypes tested. In conclusion the RT-PCR-direct sequencing method is convenient for the sensitive detection and subsequent genotyping of plasma RNA from a broad range of different HIV-1 subtypes. The assay enables the accurate follow-up of patients under treatment at a significantly reduced cost compared to the currently available commercial assays for viral load assessment and genotyping.

Biocompatibility parameters in in-vitro simulated automated versus continuous ambulatory peritoneal dialysis

BACKGROUND

In peritoneal dialysis, the usage of automated peritoneal dialysis (APD) has been steadily increased. As APD means larger volumes of solution and more frequent contact times with fresh dialysate, an additive negative impact on biocompatibility data, exceeding the known effect of conventional PD fluids, seems possible. For an in-vitro comparison of APD and CAPD, a new cell culture system has recently been established.

METHODS

A double chamber cell culture system with human mesothelial cells on top of a permeable membrane and growth medium beyond was used for mimicking CAPD and APD. Reflecting the in vivo equilibration pattern, we compared an eight-hour CAPD with a CCPD setting, using a conventional PD solution. Cell viability was assessed with a MTT assay and cell function via constitutive and stimulated IL-6 release. CA125 was measured as a parameter of mesothelial cell integrity, and TGF-1beta was measured as an index of induction of fibrosis.

RESULTS

Both the CAPD and the CCPD mode resulted in a significantly lower MTT assay and stimulated IL-6 release compared to growth medium. TGF-1beta and CA125 release did not differ between the PD modes and control. The CAPD and the CCPD mode itself did not differ with regard to MTT assay, IL-6 release, TGF-1beta and CA125 generation.

CONCLUSION

From the in-vitro model imitating the acute exposure of mesothelial cells with conventional PD fluid in a CCPD and CAPD mode, there is no evidence that APD, due to the larger volumes of solution and more frequent contact times with fresh dialysate, has an acute, additive negative impact on biocompatibility parameters indicative for peritoneal host defense, mesothelial cell integrity and peritoneal fibrosis.