Antoine Toubert

Binding of Escherichia coli adhesin AfaE to CD55 triggers cell-surface expression of the MHC class I-related molecule MICA

MICA are distant homologs of MHC class I molecules expressed in the normal intestinal epithelium. They are ligands of the NKG2D activating receptor expressed on most γδ T cells, CD8+ αβ T cells, and natural killer cells and therefore play a critical role in innate immune responses. We investigated MICA cell-surface expression on infection of epithelial cell lines by enteric bacteria and show here that MICA expression can be markedly increased by bacteria of the diffusely adherent Escherichia coli diarrheagenic group. This effect is mediated by the specific interaction between bacterial adhesin AfaE and its cellular receptor, CD55, or decay-accelerating factor. It is extremely rapid after AfaE binding, consistent with a stress-induced signal. MICA induction on epithelial cells triggered IFN-γ release by the NKG2D expressing natural killer cell line NKL. This host–bacteria interaction pathway could play a role in the pathogenesis of inflammatory bowel disease, a condition that implicates a bacterial trigger in genetically susceptible individuals. This was supported by the increased MICA expression at the surface of epithelial cells in colonic biopsies from Crohns disease-affected patients compared with controls.

Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS): A Multiorgan Antiviral T Cell Response

A dangerous drug reaction may be caused by a severe immune response to reactivated resident herpes viruses. Drug Sensitivity: Don’t Wake Up the Baby (Virus) The benefits of drugs almost always come with a cost. Anticonvulsants and antibiotics are no exception. Some of these commonly used drugs can cause a skin reaction so severe, appearing several weeks after use, that the patient is treated as a burn victim. Called DRESS (drug reaction with eosinophilia and systemic symptoms), this response results in death 10% of the time. A better understanding of DRESS would be a boon to diagnosis and treatment. Data from 40 DRESS patients gathered by Picard and his colleagues now move us a few steps closer to this goal. They find that the symptoms of DRESS are largely a result of activated immune cells directed at herpes virus–related antigens, which home to the skin and visceral organs. The culprit drugs may reactivate quiescent herpes viruses lurking in the patients’ genomes, triggering expansion of these misguided cells. A careful look at the T lymphocytes from 40 patients with DRESS—induced by carbamazepine, allopurinol, or sulfamethoxazole—revealed excess numbers of activated cytotoxic CD8+ T cells, which had surface proteins directing them to skin and other organs. The cells secreted cytokines such as tumor necrosis factor–α (TNF-α) and interferon-γ (IFN-γ) and expressed genes characteristic of inflammation. To get a better handle on the antigen targets of these activated T cells, the authors tested whether the patients showed viral reactivation, which had been noted before in some patients with DRESS. Not only did 76% of the patients show activation of previously quiescent Epstein-Barr virus (EBV) or human herpes viruses 6 or 7 (HHV-6, HHV-7), but a large proportion of the activated CD8 T cells in blood and affected organs carried T cell receptor sequences known to be specific for antigens from EBV. (Specific sequences for HHV-6 or HHV-7 are not available.) Cellular stimulation by antigenic peptides from EBV confirmed this result. The authors propose that DRESS is caused by an EBV (or other similar virus)–driven selection of CD8+ T lymphocytes, which in turn inappropriately attack multiple organs. They think that the culprit drugs may trigger activation of the patients’ dormant EBV by an as yet undefined mechanism, possibly directly. Indeed, they found that the three culprit drugs induce EBV production in EBV-transformed cells from DRESS patients but not from healthy controls, setting the stage for discovering just what it is that makes some people susceptible to DRESS. Drug reaction with eosinophilia and systemic symptoms (DRESS) is a severe, drug-induced reaction that involves both the skin and the viscera. Evidence for reactivation of herpes family viruses has been seen in some DRESS patients. To understand the immunological components of DRESS and their relationship to viral reactivation, we prospectively assessed 40 patients exhibiting DRESS in response to carbamazepine, allopurinol, or sulfamethoxazole. Peripheral blood T lymphocytes from the patients were evaluated for phenotype, cytokine secretion, and repertoire of CD4+ and CD8+ and for viral reactivation. We found Epstein-Barr virus (EBV), human herpes virus 6 (HHV-6), or HHV-7 reactivation in 76% of the patients. In all patients, circulating CD8+ T lymphocytes were activated, exhibited increased cutaneous homing markers, and secreted large amounts of tumor necrosis factor–α and interferon-γ. The production of these cytokines was particularly high in patients with the most severe visceral involvement. In addition, expanded populations of CD8+ T lymphocytes sharing the same T cell receptor repertoire were detected in the blood, skin, liver, and lungs of patients. Nearly half of these expanded blood CD8+ T lymphocytes specifically recognized one of several EBV epitopes. Finally, we found that the culprit drugs triggered the production of EBV in patients’ EBV-transformed B lymphocytes. Thus, cutaneous and visceral symptoms of DRESS are mediated by activated CD8+ T lymphocytes, which are largely directed against herpes viruses such as EBV.

Prolonged immune deficiency following allogeneic stem cell transplantation: risk factors and complications in adult patients.

To evaluate the long‐term immune reconstitution after allogeneic haematopoietic stem cell transplantation (SCT), we prospectively screened standard immune parameters in a series of 105 patients, at a median time of 15u2003months after SCT. Analysing lymphoid phenotypes, in vitro immune functions and immunoglobulin levels, we found that, more than 1u2003year post SCT, cellular and humoral immunity was still altered in a significant number of patients. CD4+ T cells were <u200a200/µl in one third of patients, and the CD4/CD8 ratio was still reversed in 78% of patients. Almost all patients showed positive T‐cell responses against mitogens, but antigen‐specific proliferation assays identified 20% to 80% of non‐responders. B‐cell counts were reconstituted in 61% of the patients, but levels of total immunoglobulins were still low in 59%. In multivariate analyses, human leucocyte antigen (HLA) disparity between donor and recipient and chronic graft‐versus‐host disease were the leading causes affecting immune reconstitution. Interestingly, cytomegalovirus (CMV) infections were strongly associated with normal CD8+ T‐cell counts. Studying the impact of impaired immune reconstitution on the rate of infections occurring in the 6u2003years following screening, we identified three parameters (low B‐cell count, inverted CD4/CD8 ratio, and negative response to tetanus toxin) as significant risk factors for developing such late infections.

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.

Epstein-Barr virus (EBV) reactivation in allogeneic stem-cell transplantation: relationship between viral load, EBV-specific T-cell reconstitution and rituximab therapy.

Background. Monitoring of Epstein-Barr virus (EBV) reactivation after allogeneic hematopoietic stem-cell transplantation markedly improved with quantitative real-time polymerase chain reaction amplification of EBV DNA and visualization of EBV-specific CD8+ T cells with peptide-human leukocyte antigen (HLA) class I tetramers. We decided to combine these methods to evaluate posttransplant EBV reactivation and rituximab therapy. Methods. We followed 56 patients treated with an HLA-genoidentical sibling (n=32), an HLA-matched unrelated donor (MUD, n=19), or an unrelated cord-blood transplant (n=5). EBV DNA was quantified in plasma and in peripheral blood mononuclear cells (PBMC). Patient CD8+ T cells were stained with a panel of eight tetramers. Results. EBV DNA was detected in half of the patients, mainly in the MUD group (17/19). In 19 patients, viral DNA was detected only in the cellular compartment. All patients who controlled reactivation without rituximab and despite a viral load of greater than 500 genome equivalents (gEq)/150,000 PBMC mounted an EBV-specific CD8+ T-cell response in greater than 1.4% of CD3+CD8+ T cells. Plasmatic EBV genome was found in nine patients preceded by a high cellular viral load. Three of these patients controlled the reactivation before or without the introduction of rituximab, and they all developed a significant and increasing EBV-specific T-cell response. Patients with EBV-specific T cells at the onset of reactivation controlled viral reactivation without rituximab. Conclusion. This study emphasizes the benefit of an early and close monitoring of EBV reactivation and CD8+-specific immune responses to initiate rituximab only when necessary and before the immune response becomes overwhelmed by the viral burden.

An Unusual CD56brightCD16low NK Cell Subset Dominates the Early Posttransplant Period following HLA-Matched Hematopoietic Stem Cell Transplantation

The expansion of the cytokine-producing CD56bright NK cell subset is a main feature of lymphocyte reconstitution after allogeneic hematopoietic stem cell transplantation (HSCT). We investigated phenotypes and functions of CD56bright and CD56dim NK subsets from 43 HLA-matched non-T cell-depleted HSCT donor-recipient pairs. The early expansion of CD56bright NK cells gradually declined in the posttransplant period but still persisted for at least 1 year and was characterized by the emergence of an unusual CD56brightCD16low subset with an intermediate maturation profile. The activating receptors NKG2D and NKp46, but also the inhibitory receptor NKG2A, were overexpressed compared with donor CD56bright populations. Recipient CD56bright NK cells produced higher amounts of IFN-γ than did their respective donors and were competent for degranulation. Intracellular perforin content was increased in CD56bright NK cells as well as in T cells compared with donors. IL-15, the levels of which were increased in the posttranplant period, is a major candidate to mediate these changes. IL-15 serum levels and intracellular T cell perforin were significantly higher in recipients with acute graft-vs-host disease. Altogether, CD56bright NK cells postallogeneic HSCT exhibit peculiar phenotypic and functional properties. Functional interactions between this subset and T cells may be important in shaping the immune response after HSCT.

MICA-129 genotype, soluble MICA, and anti-MICA antibodies as biomarkers of chronic graft-versus-host disease

The MHC class I-related chain A (MICA) molecules exist as membrane-bound and soluble isoforms and are encoded by a polymorphic gene. Their genetic and phenotype characteristics have been studied in various pathologic settings but not in the context of hematopoietic stem cell transplantation (HSCT). Here, we evaluated whether MICA-related features namely MICA-129 gene polymorphism, serum levels of soluble MICA (sMICA) and anti-MICA antibodies (MICA Abs) before and after HSCT could influence the incidence of chronic graft-versus-host disease (cGVHD) and relapse of their disease in 211 HLA-identical sibling pairs and in a subset of 116 recipients, respectively. Although the MICA-129 val/val genotype and elevated sMICA serum levels after HSCT are independently associated with the incidence of cGVHD (P = .002 and .001) regardless of history of acute GVHD, the presence of MICA Abs before transplantation confers protection against cGVHD (P = .04). There is an inverse relationship between MICA Abs and sMICA, suggesting an antibody-based neutralization of deleterious effects of sMICA. Similarly, these genetic and phenotype characteristics of MICA influence the incidence of relapse. Altogether, these data suggest that the studied MICA genotype and phenotype specificities could be used as relevant biomarkers for cGVHD monitoring.

Functional Analysis via Standardized Whole-Blood Stimulation Systems Defines the Boundaries of a Healthy Immune Response to Complex Stimuli

Standardization of immunophenotyping procedures has become a high priority. We have developed a suite of whole-blood, syringe-based assay systems that can be used to reproducibly assess induced innate or adaptive immune responses. By eliminating preanalytical errors associated with immune monitoring, we have defined the protein signatures induced by (1) medically relevant bacteria, fungi, and viruses; (2) agonists specific for defined host sensors; (3) clinically employed cytokines; and (4) activators of T cell immunity. Our results provide an initial assessment of healthy donor reference values for induced cytokines and chemokines and we report the failure to release interleukin-1α as a common immunological phenotype. The observed naturally occurring variation of the immune response may help to explain differential susceptibility to disease or response to therapeutic intervention. The implementation of a general solution for assessment of functional immune responses will help support harmonization of clinical studies and data sharing.

Thymus and immune reconstitution after allogeneic hematopoietic stem cell transplantation in humans: never say never again.

Assessment of the host immune status is becoming a key issue in allogeneic hematopoietic stem cell transplantation (allo-HSCT). In the long-term follow-up of these patients, severe post-transplant infections, relapse or secondary malignancies may be directly related to persistent immune defects. In allo-HSCT, T-cell differentiation of donor progenitors within the recipient thymus is required to generate naive recent T-cell emigrants (RTE). These cells account for a durable T-cell reconstitution, generating a diverse T-cell receptor (TCR) repertoire and robust response to infections. It is now possible to quantify the production of RTE by measuring thymic T-cell receptor excision circles or TREC which are small circular DNA produced during the recombination of the genomic segments encoding the TCR alpha chain. Here we discuss the role of thymic function in allo-HSCT. The pre-transplant recipient thymic function correlates with clinical outcome in terms of survival and occurrence of severe infections. Post-transplant, TREC analysis showed that the thymus is a sensitive target to the allogeneic acute graft-versus-host disease (GvHD) reaction but is also prone to recovery in young adult patients. In all, thymus is a key player for the quality of immune reconstitution and clinical outcome after allo-HSCT. Thymic tissue is plastic and it is a future challenge to halt or reverse thymic GVHD therapeutically by acting at the level of T-cell progenitors generation, thymic homing and/or epithelial thymic tissue preservation.

NK-cell education is shaped by donor HLA genotype after unrelated allogeneic hematopoietic stem cell transplantation

The rules governing natural killer (NK)-cell education in the allogeneic environment created by unrelated hematopoietic stem-cell transplantation (HSCT) are still largely elusive, especially in an unrelated donor setting. NK-cell inhibitory receptors for self-human leukocyte antigen (HLA) play a central role in the acquisition or maintenance of NK-cell functional competence. Therefore, the responsiveness of different NK-cell subsets was assessed as a function of their expression or absence of expression of self-HLA-specific inhibitory receptors, in a large cohort (n = 60) of unrelated HSCT recipients. A fully effective NK-cell education process was achieved within the first year after allogeneic HSCT and lasted for at least 3 years thereafter. In addition, HLA-mismatched HSCT led to a stable education pattern that was determined by the donors HLA ligands. These data suggest that the NK cells education partner could be of hematopoietic rather than extrahematopoietic origin. This donor-ligand-driven NK-cell education model would suggest a sustained graft-versus-leukemia effect after HLA-mismatched HSCT.