[Novel vaccines. Vaccinations in the near and distant future]. / Neuartige Impfstoffe. Impfen in naher und ferner Zukunft.

Easy-to-develop vaccines usually induce antibodies against acute, self-limiting infections by stable pathogens. Today, most of these vaccines have been made, and the future diseases to tackle are more challenging: highly variable pathogens, rapidly emerging new infections with the potential of developing into pandemics, or therapeutic applications for chronic infections and cancer which most likely require complex immune responses beyond the induction of antibodies. The impact of scientific and technological progress on vaccinology has multiplied the strategies to improve vaccines. Here, we describe how genome-based approaches have revolutionized the way to identify vaccine antigen candidates, how the vast numbers of candidates can be further ranked by sophisticated gene- and protein-array based screening methods, and how surface proteomics may accelerate this target identification process. Increased structural knowledge of antigens will allow exposing or stabilizing those antigen parts relevant for protection and thereby direct the immune response to them. Improved adjuvants will enhance and bias the immune response to induce the relevant arms of the immune system. In conclusion, thanks to conceptual and biotechnological progress, future vaccines will be safer, more efficient and more complex than those today.

[Infectious complications and misuse of high-dose buprenorphine]. / Complications infectieuses et mésusage de la buprénorphine à haut dosage.

BACKGROUND: High-dose buprenorphine (HDB) treatment began in France in 1996 according to relatively unrestricted prescription rules. Continued heroin injection by patients on HDB maintenance treatment and even HDB injection remain underestimated and may lead to a variety of infectious diseases. OBJECTIVES: Description of infectious complications occurring in patients receiving HDB maintenance treatment. METHODS: Retrospective study of drug addicts receiving HDB maintenance treatment, injecting (or highly suspected of injecting) it, and hospitalized for infections (other than HIV or viral hepatitis) in the department of infectious and tropical diseases in Nancy University Hospital. Data collection covered 1998 through 2003. RESULTS: We identified 21 case reports, 9 concerning infectious endocarditis, 8 cutaneous abscesses, 2 osteoarticular infections, 1 meningitis and 1 Candida retinitis. The sex-ratio was of 1 woman for 2 men, and the patients' mean age was 29.8 years. Globally 13 patients had systemic infections. Nine patients admitted having injected HDB (and no other drugs) (including the case of Candida retinitis), while in the other 12 cases, the patients continued injecting heroin as well. The role of misused HDB was strongly suspected in those 12 infections, but was not clearly confirmed. All patients recovered from the infections. The long-term psychosocial outcome remains unknown. CONCLUSION: The cases analyzed illustrate the dual reality that HDB is often ineffective as a maintenance treatment, since some patients continue to inject heroin, and that its misuse can have infectious consequences. The results of HDB maintenance treatment substitution are mixed. The individual benefit/risk ratio must be improved. Networking is crucial, notably between physician and pharmacist, and the monitoring system must be reinforced.

Binding of the hepatitis C virus envelope protein E2 to CD81 provides a co-stimulatory signal for human T cells.

Chronic hepatitis C virus (HCV) infection frequently develops into liver disease and is accompanied by extra-hepatic autoimmune manifestations. The tetraspanin CD81 is a putative HCV receptor as it binds the E2 envelope glycoprotein of HCV and bona fide HCV particles. Here we show that HCV E2 binding to CD81 on human cells in vitro lowers the threshold for IL-2 receptor alpha expression and IL-2 production, resulting in strongly increased T cell proliferation. HCV E2-induced co-stimulation also enhances the production of IFN-gamma and IL-4 and causes increased TCR down-regulation. This suggests that binding of HCV particles to CD81 on T cells in vivo may lead to activation by otherwise suboptimal stimuli. Therefore, co-stimulation of autoreactive T cells by HCV may contribute to liver damage and autoimmune phenomena observed in HCV infection.

Life, activation and death of intrahepatic lymphocytes in chronic hepatitis C.

The healthy liver of adult humans has little or no lymphocyte component and the histological finding of intrahepatic lymphocytes (IHL) is evidence of liver pathology. In a liver injured by chronic hepatitis C, the most common chronic liver disease, most IHL are activated/pro-inflammatory cells, which are particularly enriched for effectors of innate immunity (natural killer (NK), natural T, and other NK-like T cells). IHL do not undergo clonal expansion in the liver but migrate from extrahepatic sites to the chronically infected liver, where they display effector function and subsequently die, suggesting that maintenance of the IHL pool depends on continuous lymphocyte migration. The cytotoxic and inflammatory functions of these IHL have three potential outcomes: 1) they could be helpful in clearing the virus (a rare case in hepatitis C virus (HCV) infection); 2) they could be useless and have no effect on the infection; or 3) they could be harmful, whereby overaggressive lymphocyte responses destroy the liver in a continuous and unsuccessful attempt to clear the virus. Unfortunately, we do not know as of yet which of these possibilities is the case and, therefore, a more complete picture of the intrahepatic immune response will be relevant to the development of new therapeutic strategies against HCV. Additionally and from a more general perspective, due to the availability of biopsied material and the high prevalence (approximately 3%) of HCV infection worldwide, studying the chronically inflamed liver of hepatitis C patients is an ideal model to investigate the poorly understood processes of lymphocyte trafficking, activation and death to non-lymphoid sites of chronic inflammation in man.

Th cells and Th2 responses can develop in the absence of MHC class II-CD4 interactions.

In this paper, we address the question whether CD4 and MHC class II expression are necessary for the development of the T helper lineage during thymocyte maturation and for activation-induced Th2 responses. To bypass the CD4-MHC class II interaction requirements for positive selection and activation, we used mice that are doubly transgenic for CD8 and for the MHC class I-restricted TCR F5. This transgene combination leads to MHC class I-dependent maturation of CD4 lineage cells. Upon activation, these CD4 lineage T cells secrete IL-4 and give help to B cells but show no cytotoxic activity. Remarkably, neither MHC class II nor CD4 expression are necessary for the generation and helper functions of these cells. This suggests that under normal conditions, coreceptor-MHC interactions are necessary to ensure the canonical combinations of coreceptor and function in developing thymocytes, but that they do not determine functional commitment. Our results also imply that expression of the CD4 gene does not influence, but is merely associated with the decision to establish the T helper program. In addition, we show that activation through TCR-MHC class I interactions can induce Th2 responses independently of CD4 and MHC class II expression.

Interactions with multiple peptide ligands determine the fate of developing thymocytes.

Thymocytes are positively or negatively selected depending on interactions between their T cell receptors (TCR) and peptides presented by major histocompatibility complex molecules. We have previously shown that apoptosis of thymocytes from an alpha beta TCR-transgenic mouse (F5), induced by antigenic peptide, can be inhibited specifically by an antagonist peptide variant in an in vitro culture model. We have now extended these experiments by demonstrating that the antagonist peptide can inhibit natural negative selection of maturing thymocytes, induced by endogenously expressed antigen, in fetal thymic organ cultures (FTOC). This inhibition resulted in the rescue and maturation of thymocytes that would otherwise have been deleted. Mature T cells generated in these cultures were able to respond to antigen by producing limited quantities of interferon-gamma, but unlike T cells from control FTOC, they required exogenous interleukin-2 to generate cytolytic effector cells. Interestingly, the antagonist peptide also accelerated the development of F5 thymocytes in the absence of the negatively selecting ligand. These data suggest that the developmental fate of a thymocyte may be determined by the recognition of multiple distinct peptide ligands during thymic selection. Alterations in the profiles of selecting peptides presented in the thymus would thus have profound effects on the size and autoreactive potential of the T cell repertoire generated.

Susceptibility and resistance to antigen-induced apoptosis in the thymus of transgenic mice.

Injection of TCR transgenic mice with antigenic peptide results in the deletion of immature thymocytes expressing the transgenic TCR. We have analyzed this process in mice transgenic for a TCR (F5) that recognizes a peptide from the influenza nucleoprotein (NP68). To determine whether deletion of immature thymocytes is the result of specific recognition of the antigenic peptide by the thymocytes or mature T cell activation, bone marrow chimeric mice were generated using a mixture of cells from F5 transgenic and nontransgenic mice. Injection of these mice with antigenic peptide leads to the preferential depletion of F5 transgenic thymocytes, whereas nontransgenic thymocytes remain largely unaffected. Furthermore, exposure of F5 fetal thymic lobes to peptide leads to thymocyte deletion even though no mature single positive T cells are present at this stage. These data suggest that Ag-induced death of immature thymocytes is due to peptide-specific recognition, although activated mature T cells appear to potentiate such deletion. Further administration of antigenic peptide to F5 mice results in the appearance of double-positive thymocytes that are resistant to Ag or anti-CD3-induced apoptosis. These data suggest a change in the ability of the cells to signal through the TCR-CD3 complex, resembling the state of anergy induced in peripheral T cells following chronic exposure to Ag.

In vitro positive selection of alpha beta TCR transgenic thymocytes by a conditionally immortalized cortical epithelial clone.

Development of mature CD4 and CD8 single-positive T cells requires a process known as positive selection, which depends on the specific recognition of self-peptide-MHC complexes on thymic stromal cells by immature CD4+CD8+ thymocytes. We have used an in vitro reaggregate system to study the positive selection of thymocytes by conditionally immortalized thymic epithelial clones. Thymocytes from mice transgenic for the F5 alpha beta TCR, specific for a peptide from the influenza nucleoprotein in the context of H-2Db, are positively selected in the H-2b MHC background, but fail to mature in mice expressing the H-2q haplotype. Development of embryonic day 15 F5 H-2q transgenic thymocytes was followed in reaggregate cultures supplemented with H-2b-expressing epithelial clones. A conditionally immortalized cortical epithelial clone, derived from H-2Kb-tsA58 transgenic mice, was found to be as efficient as freshly isolated thymic stromal cells in positively selecting CD8 transgenic thymocytes. In contrast, an H-2b-expressing kidney epithelial clone did not augment positive selection above background levels, implying that the effect of the thymic epithelial clone was not merely the presentation of selecting MHC molecules. Mature transgenic thymocytes generated in reaggregate cultures were able to differentiate into functionally competent cytotoxic T cells. This model provides an important in vitro system for the detailed study of the specific molecular interactions leading to positive selection of developing thymocytes.

Restricted TCR repertoire and long-term persistence of donor-derived antigen-experienced CD4+ T cells in allogeneic bone marrow transplantation recipients.

We investigated the contribution of transfer of Ag-experienced donor T cells to the immune reconstitution of allogeneic bone marrow transplantation (BMT) recipients. To this purpose, we used a combination of cell culture methods to isolate tetanus toxoid (TT)-specific T cell clones, and a sensitive and specific heteroduplex analysis to monitor the presence of a particular clonotype using TCR N region sequences. We document that patients after BMT display a small response to TT, entirely accounted for by few donor-derived clones. These patients show a strong polyclonal response to TT vaccination; however, the T cell clones transferred with the transplant can still be detected within the polyclonal T cell lines for up to at least 5 yr after BMT. We also demonstrate that vaccination of donors with TT before BMT results in a more relevant transfer of Ag-experienced T cells, allowing the recipients to mount a strong polyclonal response without need of vaccination. These findings provide a rationale for vaccinating donors to optimize adoptive transfer of protective T cell immunity into recipients, and suggest the possibility of using preventive T cell adoptive therapy in conjunction with marrow infusion.