Dominique Charron

Acute graft-versus-host disease transiently impairs thymic output in young patients after allogeneic hematopoietic stem cell transplantation

Long-term T-cell reconstitution after hematopoietic stem cell transplantation (HSCT) is dependent on patient thymic function and affected by graft-versus-host disease (GVHD). To assess the impact of acute GVHD (aGVHD) on thymic function, we followed a cohort of 93 patients who received HSCT from a human histocompatibility leukocyte antigen-identical sibling, mainly for hematologic malignancies. Thymic output was measured by signal-joint T-cell receptor excision circles (sjTREC) real-time polymerase chain reaction. Absolute sjTREC number was lower at 6 months in patients with aGVHD (P = .014), associated with lower absolute counts of naive CD4 T cells at 6 and 12 months (P = .04 and .02), and persistent abnormalities in T-cell repertoire diversity. Age and aGVHD affected thymic function independently in multivariate analysis. In patients less than 25 years of age, thymic function recovered almost totally at 1 year. As a marker of thymocyte proliferation, we quantified the betaTREC generated during the T-cell receptor beta-chain recombination, in a group of 20 age-matched patients. Mean betaTREC level was reduced at 6 months in patients with aGVHD, indicating an impact on early thymic differentiation rather than on intrathymic proliferation. These data show that aGVHD or its treatment has a transient impact on thymic function in younger patients in the first months after HSCT.

Predictive, preventive, personalized and participatory medicine: back to the future

The pioneering work of Jean Dausset on the HLA system established several principles that were later reflected in the Human Genome Project and contributed to the foundations of predictive, preventive, personalized and participatory (P4) medicine. To effectively develop systems medicine, we should take advantage of the lessons of the HLA saga, emphasizing the importance of exploring a fascinating but mysterious biology, now using systems principles, pioneering new technology developments and creating shared biological and information resources.

MHC Class II Engagement by Its Ligand LAG-3 (CD223) Contributes to Melanoma Resistance to Apoptosis

Melanoma is the most aggressive skin cancer in humans that often expresses MHC class II (MHC II) molecules, which could make these tumors eliminable by the immune system. However, this MHC II expression has been associated with poor prognosis, and there is a lack of immune-mediated eradication. The lymphocyte activation gene-3 (LAG-3) is a natural ligand for MHC II that is substantially expressed on melanoma-infiltrating T cells including those endowed with potent immune-suppressive activity. Based on our previous data showing the signaling capacity of MHC II in melanoma cells, we hypothesized that LAG-3 could contribute to melanoma survival through its MHC II signaling capacity in melanoma cells. In this study, we demonstrate that both soluble LAG-3 and LAG-3–transfected cells can protect MHC II-positive melanoma cells, but not MHC II-negative cells, from FAS-mediated and drug-induced apoptosis. Interaction of LAG-3 with MHC II expressed on melanoma cells upregulates both MAPK/Erk and PI3K/Akt pathways, albeit with different kinetics. Inhibition studies using specific inhibitors of both pathways provided evidence of their involvement in the LAG-3–induced protection from apoptosis. Altogether, our data suggest that the LAG-3–MHC II interaction could be viewed as a bidirectional immune escape pathway in melanoma, with direct consequences shared by both melanoma and immune cells. In the future, compounds that efficiently hinder LAG-3–MHC II interaction might be used as an adjuvant to current therapy for MHC II-positive melanoma.

Biochemical and histological analysis of bone marrow collagen in myelofibrosis.

Summary. Total protein, collagen (hydroxyproline) and glycoproteins (hexosamine) content of control and myelofibrosis (MF) bone marrow samples was determined using a sequential extraction procedure. MF marrow extracts contained higher amounts of collagen than control extracts. The collagen content appeared to increase with the duration of the disease. In more recent MF cases (<2 years) at least 60% of the total collagen was extracted in 0.5 m NaCl. this proportion decreases to 33% in older cases (> 4 years), indicating a progressive insolubilization (crosslinking) of collagen.

Immunogenicity and allogenicity: a challenge of stem cell therapy.

As age progresses, the regenerative power of one’s own pluripotent stem cells is often inadequate to sustain normal tissue function. Consequently, the incidence of chronic and degenerative diseases has significantly increased. The derivation of adult tissues and organs from a variety of stem cell sources represents the starting mark for regenerative medicine. It is currently considered a developing mean to repair, restore, maintain, or enhance organ functioning through life span. Recent advances in human embryonic stem cells (hESC) research, however, made the prospect of cell replacement therapy even more compelling and highlighted hESC as a fast track in the therapeutic hope. Among the hurdles which have been largely overlooked in the excitement over the expected benefit is the immunogenicity. Indeed, beyond the clear need to establish the safety of hESC and their derived tissues in terms of tumorogenicity and potential to transmit infections, the challenge is to overcome the immunological barriers to their transplantation.

HLA Class II Antibody Activation of Endothelial Cells Promotes Th17 and Disrupts Regulatory T Lymphocyte Expansion.

Kidney transplantation is the most successful treatment option for patients with end‐stage renal disease, and chronic antibody‐mediated rejection is the principal cause of allograft loss. Predictive factors for chronic rejection include high levels of HLA alloantibodies (particularly HLA class II) and activation of graft endothelial cells (ECs). The mechanistic basis for this association is unresolved. We used an experimental model of HLA‐DR antibody stimulation of microvascular ECs to examine the mechanisms underlying the association between HLA class II antibodies, EC activation and allograft damage. Activation of ECs with the F(Ab′)2 fragment of HLA‐DR antibody led to phosphorylation of Akt, ERK and MEK and increased IL‐6 production by ECs cocultured with allogeneic peripheral blood mononuclear cells (PBMCs) in an Akt‐dependent manner. We previously showed that HLA‐DR–expressing ECs induce polarization of Th17 and FoxP3bright regulatory T cell (Treg) subsets. Preactivation of ECs with anti‐HLA‐DR antibody redirected EC allogenicity toward a proinflammatory response by decreasing amplification of functional Treg and by further increasing IL‐6–dependent Th17 expansion. Alloimmunized patient serum containing relevant HLA‐DR alloantibodies selectively bound and increased EC secretion of IL‐6 in cocultures with PBMCs. These data contribute to understanding of potential mechanisms of antibody‐mediated endothelial damage independent of complement activation and FcR‐expressing effector cells.

Regulation of the CD4+ T cell allo-immune response by endothelial cells.

Recent studies have revealed the presence of pro-inflammatory and/or regulatory CD4(+) T cells within allografts promoting either graft rejection or tolerance. Histological evidence has identified the microvascular endothelium as the primary site of allograft damage as it is the first site of encounter with the recipients immune system. The initial view of the human endothelial cell inducing an effector Th1 response leading to graft rejection has been extended by recent results which demonstrate the endothelial cell ability to generate other CD4(+) T cell sub-populations including Th17 and Treg cells. In the transplantation setting, the allo-reactivity of the endothelium with the CD4(+) T cell populations is likely to depend upon multiple factors including the vascular origin of the endothelial cell, the cytokine environment, the presence or absence of pro-inflammatory stimuli including ligands of Toll like receptors and alloantibodies. This review provides an update on the characteristics of the endothelial cell activation of the CD4(+) T cell response and an analysis of the factors, which can modify this activity in favor of either graft rejection or tolerance.

Anti-HLA antibodies in regenerative medicine stem cell therapy

Research on stem cell therapies for regenerative medicine is progressing rapidly. Although the use of autologous stem cells is a tempting choice, there are several instances in which they are either defective or not available in due time. Allogenic stem cells derived from healthy donors presents a promising alternative. Whether autologous or allogenic, recent advances have proven that stem cells are not as immune privileged as they were thought. Therefore understanding the interactions of these cells with the recipient immune system is paramount to their clinical application. Transplantation of stem cells induces humoral as well as cellular immune response. This review focuses on the humoral response elicited by stem cells upon their administration and consequences on the survival and maintenance of the graft. Current transplantation identifies pre- and post-transplantation anti-HLA antibodies as immune rejection and cell signaling effectors. These two mechanisms are likely to operate similarly in the context of SC therapeutics. Ultimately this knowledge will help to propose novel strategies to mitigate the allogenic barriers. Immunogenetics selection of the donor cell and immunomonitoring are key factors to allow the implementation of regenerative stem cell in the clinics.

Resolution of a manic episode treated with activated charcoal: Evidence for a brain-gut axis in bipolar disorder.

A 46-year-old woman was admitted to our intensive care unit for a inaugural episode of mania (Diagnostic and Statistical Manual of Mental Disorders [4th ed.; DSM-IV]); the episode was characterized by agitation, irritability, logorrhoea, reckless spending associated with delusional ideas and hallucinations (Positive and Negative Syndrome Scale [PANSS] = 76 and Young Mania Rating Scale [YMRS] = 28). The patient had, 15 days earlier, undergone a subtotal gastrectomy for morbid obesity. The pre-operative psychiatric evaluation revealed no personal or familial psychiatric history. On admission, the neurological examination was normal with no signs of encephalopathy or Wernicke–Korsakoff syndrome. The body mass index (BMI) was 36 kg/m2 on admission and remained stable. Post-operative serum levels of vitamins D and B, folates and zinc were normal excluding the possibility of postgastrectomy syndrome (by deprivation). Full blood count and brain magnetic resonance imaging were also normal, and serology for hepatitis B/C and HIV were negative. There is substantial evidence that bipolar disorder can be associated with an abnormal immuno-inflammatory background (Goldstein et al., 2009); therefore, we suspected that this inaugural manic episode occurring shortly after gastrectomy could have been induced by altered gut microbiota and intestinal barrier dysfunction (Collins and Bercik, 2009). Consequently, we hypothesized that activated charcoal, a potent adsorbent of inflammatory cytokines (Howell et al., 2006) that neutralizes the effect of inflammatory mediators in the gut, may improve both systemic inflammation and manic symptoms. After obtaining written informed consent, we collected samples from the patient for immuno-inflammatory testing and prescribed oral activated charcoal treatment at 1 g/day on the basis of calculated adsorption potential (Howell et al., 2006) without any adjunctive psychotropic treatment. The following markers were tested before treatment and confirmed acute inflammation: (a) circulating proinflammatory cytokines (tumour necrosis factor [TNF-α], interleukin [IL]-6, IL-1β and IL-17) and chemokines (IL-8, macrophage inflammatory protein [MIP]-1α and MIP-1β); (b) soluble CD14 isoform (Presepsin®, sCD14subtype), a pattern recognition receptor that senses and reacts to lipopolysaccharide (LPS) and an inflammation process inducer produced by the commensal gut microflora (Gram-negative bacteria); (c) immunoglobulin-A (IgA) that is directed against mucosal microbiota (Tlaskalová-Hogenová et al., 2004); and (d) monocyte chemoattractant protein 1 (MCP-1), a key regulator of the immune cells involved in inflammatory processes. Fifteen days after the initiation of charcoal treatment, the patient became asymptomatic (PANSS = 45 and YMRS = 8). The improvement of manic symptoms was substantial and persisted during follow-up (PANSS = 33 and YMRS = 0 at 4 and 8 months) during which the same charcoal treatment was maintained without any psychotropic drugs (Figure 1(a)). In parallel, the titers of all the immuno-inflammatory markers listed above progressively normalized (Figure 1(b)). In the present case, severe disruption of the local beneficial commensal equilibrium following gastrectomy may have led to a pro-inflammatory ‘cytokine storm’; inflammatory mediators may have been adsorbed by the activated charcoal, consequently reducing local cytokine transfer from the gut to the bloodstream circulation and thereby to the brain. To our knowledge, this is the first unambiguous evidence of the efficacy Letters

Contrasting cytoskeletal regulation of MHC class II peptide presentation by human B cells or dendritic cells

MHC classu2004II‐mediated antigen presentation by Bu2004lymphocytes or dendritic cells (DC) initiates CD4+ Tu2004lymphocyte activation. In Bu2004lymphocytes, MHC classu2004II peptide presentation has been characterised by recruitment of MHC classu2004II, F‐actin and lipid rafts to the B cell–T cell immunological synapse. We now show that MHC classu2004II engagement in Bu2004lymphocytes induced lipid raft‐independent Rho and Rac activation and that inhibition of either Rho‐GTPase activation or actin polymerisation in the B cell abrogated T cell activation without altering B cell–T cell conjugate formation. Short‐hairpin RNA studies excluded a role for the Cdc42 effector Wiskott–Aldrich syndrome protein. In contrast, antigen presentation by DC was Rho‐GTPase‐independent although actin was recruited to the DC–T cell interaction site. Moreover, actin depolymerisation in the DC significantly increased T cell activation without altering the number of DC–T cell conjugates. Finally we show that stable recruitment of HLA‐DR to the site of the immunological synapse is not a uniform observation in DC and demonstrate reduced HLA‐DR expression at the site of microtubule organising centre polarization. Therefore although actin accumulates in DC and Bu2004lymphocytes at the immunological synapse with antigen‐specific Tu2004lymphocytes, this does not reflect comparable functional roles of their actin cytoskeletons in antigen presentation.