The dendritic cell: the immune system's adjuvant--a strategy to develop a HCV vaccine?

Increased PD-L1 expression and PD-L1/CD86 ratio on dendritic cells were associated with impaired dendritic cells function in HCV infection

Impaired hepatitis C virus (HCV)-specific T cell immunity was associated with the persistence of HCV infection. Dysfunction of dentritic cells (DCs) was believed to be involved in T cell exhaustion, but the mechanisms were rarely understood. In this study, surface costimulatory marker (CD83, CD86, and CD40), coinhibitory marker (PD-L1) expression and allostimulatory capacity of plasmacytoid DCs (pDCs) and myeloid DCs (mDCs) were evaluated in HCV-infected patients. Results showed that the expression of both costimulatory and coinhibitory markers was increased in HCV-infected patients compared with healthy controls. PD-L1/CD86 ratio was increased and positively correlated with PD-L1 expression on DCs in HCV-infected patients. Allostimulatory capacity of DCs was impaired and inversely correlated with PD-L1 expression and PD-L1/CD86 ratio. These findings suggested that the effect of inhibitory marker PD-L1 overwhelmed the effect of costimulatory markers and down regulated DC-T activation in HCV-infected patients. The results will be helpful to understand the mechanism of dysfunction of DCs in HCV infection and shed light on the DC-based immunotherapeutic strategy.

Human dendritic cells pulsed with specific lipopeptides stimulate autologous antigen-specific T cells without the addition of exogenous maturation factors

Serum-free culture conditions to generate immature human monocyte-derived DC (Mo-DC) were optimized, and the parameters that influence their maturation after exposure to lipopeptides containing CD4(+) and CD8(+) T-cell epitopes were examined. The lipopeptides contained a single CD4(+) helper T-cell epitopes, one of a number of human leucocyte antigen (HLA)-A2-restricted cytotoxic T-cell epitope and the lipid Pam2Cys. To ensure complete maturation of the Mo-DC, we examined (i) the optimal lipopeptide concentration, (ii) the optimal Mo-DC density and (iii) the appropriate period of exposure of the Mo-DC to the lipopeptides. The results showed that a high dose of lipopeptide (30 microm) was no more efficient at upregulating maturation markers on Mo-DC than a low dose (6 microm). There was an inverse relationship between Mo-DC concentration and the mean fluorescence intensity of maturation markers. In addition, at the higher cell concentrations, the chemotactic capacity of the Mo-DC towards a cognate ligand, CCL21, was reduced. Thus, high cell concentrations during lipopeptide exposure were detrimental to Mo-DC maturation and function. The duration of exposure of Mo-DC to the lipopeptides had little effect on phenotype, although Mo-DC exposed to lipopeptides for 48 rather than 4 h showed an increased ability to stimulate autologous peripheral blood mononuclear cells to release interferon-gamma in the absence of exogenous maturation factors. These findings reveal conditions for generating mature antigen-loaded DC suitable for targeted immunotherapy.

Dendritic cell function during chronic hepatitis C virus and human immunodeficiency virus type 1 infection

Hepatitis C virus (HCV) infection can persist despite HCV-specific T-cell immunity and can have a more aggressive course in persons coinfected with human immunodeficiency virus type 1 (HIV-1). Defects in antigen-presenting, myeloid dendritic cells (DCs) could underlie this T-cell dysfunction. Here we show that monocyte-derived DCs from persons with chronic HCV infection, with or without HIV-1 coinfection, being treated with combination antiretroviral therapy produced lower levels of interleukin 12 (IL-12) p70 in response to CD40 ligand (CD40L), whereas the expression of DC surface activation and costimulatory molecules was unimpaired. The deficiency in IL-12 production could be overcome by addition of gamma interferon (IFN-gamma) with CD40L, resulting in very high, comparable levels of IL-12 production by DCs from HCV- and HIV-1-infected subjects. Smaller amounts of IL-12 p70 were produced by DCs treated with the immune modulators tumor necrosis factor alpha and IL-1beta, with or without IFN-gamma, and the amounts did not differ among the uninfected and infected subjects. Blocking of IL-10 with an anti-IL-10 monoclonal antibody in the CD40L-stimulated DC cultures from HCV-infected persons increased the level of IL-12 p70 production. The ability of DCs from HCV-infected persons to stimulate allogeneic CD4+ T cells or induce IL-2, IL-5, or IL-10 in a mixed lymphocyte reaction was not impaired. Thus, myeloid DCs derived from persons with chronic HCV infection or with both HCV and HIV-1 infections have defects in IL-12 p70 production related to IL-10 activity that can be overcome by treatment of the DCs with CD40L and IFN-gamma. DCs from these infected subjects have a normal capacity to stimulate CD4+ T cells. The functional effectiveness of DCs derived from HCV-infected individuals provides a rationale for the DC-based immunotherapy of chronic HCV infection.

Gastrointestinal motility and prokinetics in the critically ill

PURPOSE OF REVIEW

Enteral nutrition is frequently unsuccessful in the critically ill due to gastrointestinal dysfunction. Current treatment strategies are often disappointing. In this article upper gastrointestinal function in health together with abnormalities seen during critical illness are reviewed, and potential therapeutic options summarized.

RECENT FINDINGS

Reflux oesophagitis occurs frequently due to reduced or absent lower oesophageal sphincter tone. In the stomach a number of motor patterns contribute to slow gastric emptying. The fundus has reduced compliance, there are less frequent contractions in both the proximal and distal stomach, isolated pyloric activity is increased and the organization of duodenal motor activity is abnormal. In response to nutrients, enterogastric feedback is enhanced, fundic relaxation and subsequent recovery is delayed, antral motility is further reduced and localized pyloric contractions stimulated. Elevated concentrations of hormones such as cholecystokinin and peptide YY are potential mediators for these phenomena. Rapid tachyphylaxis occurs with the commonly used prokinetics, metoclopramide and erythromycin, and novel agents are under investigation. Independent of gastric emptying, nutrient absorption is reduced.

SUMMARY

There has been considerable progress in understanding the pathogenesis of mechanisms causing feed intolerance in critical illness, but this is yet to be translated into therapeutic benefit.

Immunity and protection by adoptive transfer of dendritic cells transfected with hepatitis C NS3/4A mRNA

In this study, we tested the hypothesis that adoptive transfer of dendritic cells (DCs) transfected ex vivo with mRNA encoding hepatitis C virus (HCV) NS3/4A would initiate potent HCV-specific protective immune responses in vivo. Murine DCs were transfected with NS3/4A mRNA or eGFP mRNA using either electroporation or Transmessenger Transfection Reagent and then used for adoptive transfer. Electroporation resulted in higher transfection efficiency but lower levels of eGFP and NS3/4A expression when compared to transfection with Transmessenger. The murine NS3/4A mRNA-transfected DCs were functional in T cell activation in vitro. Adoptive transfer of NS3/4A mRNA-transfected DCs resulted in migration to regional lymph nodes, strong cellular immune responses and protection from challenge with vaccinia virus expressing NS3/NS4/NS5 in mice. Furthermore, although Transmessenger mediated transfection was less efficient than electroporation in terms of number of transfected cells, the DCs transfected with NS3/4A mRNA and Transmessenger expressed higher levels of protein and induced stronger immune responses and protection than DCs transfected with NS3/4A mRNA by electroporation. Since no study has explored the in vivo efficacy of mRNA-transfected DC-mediated vaccination against viral diseases, including hepatitis C, our study provided a novel vaccination strategy against hepatitis C as well as other pathogens.