Induction of Bordetella pertussis-specific immune memory by DTPa vaccines

Several vaccines are available against pertussis, differing by the number of Bordetella pertussis antigens that they contain as well as their formulation. The GlaxoSmithKline Biologicals (GSK Bio) tricomponent DTPa vaccine (DTPa3, Infanrix™), and the Sanofi-Pasteur (SP) five-component formulation (DTPa5, Pediacel™) were shown to have comparable short-term efficacy in clinical trials. However, potential differences in long-term protection were recently suggested, which might reflect the elicitation of different specific immune memory by the two vaccines. Therefore, the purpose of the present study was to investigate in mice the immune responses against B. pertussis, and particularly the establishment of specific B cell memory after immunization with DTPa3 and DTPa5 vaccines. Whereas intranasal challenge experiments showed similar protection with both vaccines, DTPa3 induced higher antibody levels to FHA and PRN than DTPa5. Further, the frequency of memory B cells was investigated by B cell ELISPOT. Higher frequencies of PT- and PRN-specific memory B cells were evidenced after vaccination with DTPa3, compared with DTPa5. Although the origin of such difference is unclear, the use of two different adjuvants (aluminum phosphate versus hydroxide) is proposed as a possible explanation. In conclusion, this study proposes that the induction of higher levels of B. pertussis antigen-specific memory B cells with DTPa3 participate to the suggested longer persistence of protection observed with this vaccine, as compared with DTPa5.

Characterization of a subset of antigen-specific human central memory CD4+ T lymphocytes producing effector cytokines

CCR7(+ )central memory (T(CM)) CD4(+) T cells play a central role in long-term immunological memory. Recent reports indicate that a proportion of CD4(+) T(CM) is able to produce effector cytokines. The phenotype and the role of this subset remain unknown. We characterized cytokine-producing human CD4(+) T(CM) specific for cleared protein and persistent viral Ag. Our results demonstrate that the type of Ag stimulation is a major determinant of CD4(+) T(CM) differentiation. CMV-specific T(CM) were significantly more differentiated than protein Ag-specific T(CM) and included higher proportions of IFN-gamma-producing cells. The expression of killer cell lectin-like receptor G1 (KLRG1) by protein Ag- and CMV-specific T(CM) was associated with increased production of effector cytokines. KLRG1(+) T(CM) expressed high levels of CD127, suggesting that they can survive long term under the influence of IL-7. The induction of KLRG1(+) T(CM) may therefore represent an important target of vaccination against pathogens controlled by cellular immune responses.

Antigen-specific central memory CD4+ T lymphocytes produce multiple cytokines and proliferate in vivo in humans

The function of Ag-specific central (T(CM)) and effector (T(EM)) memory CD4+ T lymphocytes remains poorly characterized in vivo in humans. Using CD154 as a marker of Ag-specific CD4+T cells, we studied the differentiation of memory subsets following anti-hepatitis B immunization. Hepatitis B surface Ag (HBs)-specific memory CD4+T cells were heterogeneous and included T(CM) (CCR7+CD27+) and T(EM) (CCR7(-)CD27(+/-)). HBs-specific T(CM) and T(EM) shared the capacity to produce multiple cytokines, including IL-2 and IFN-gamma. Several years postimmunization, approximately 10% of HBs-specific memory CD4+ T cells were in cycle (Ki67+) and the proliferating cells were CCR7+. These results suggest that the model of functional specialization of T(CM) and T(EM) cannot be applied to protein vaccine Ags and support the concept that T(CM) are capable of self-renewal and contribute to maintain the pool of memory cells.

Distinct mechanisms are involved in tumoristatic and tumoricidal activities of monocyte-derived dendritic cells

Monocyte-derived dendritic cells (DC) were found to inhibit proliferation of different tumor cell lines. LPS-induced maturation of DC strongly increased their capacity to inhibit tumor cell growth. We observed that tumoristatic activity of LPS-activated DC was independent of their cytotoxic potential. Indeed, LPS-activated DC were able to inhibit growth of caspase-8-deficient or Bcl-2-overexpressing Jurkat cells whereas they were not cytotoxic towards the same targets. On the other hand, we found that supernatant derived from LPS-activated DC exerted a significant anti-proliferative activity against Jurkat cells while it did not induce any cytotoxic effect. Tumor necrosis factor (TNF) was shown to critically contribute to tumor growth inhibition in this system.

[Anti-tumor immunotherapy based on dendritic cells]

In cancer immunotherapy, the use of dendritic cells (DC) loaded with tumor-associated antigens (TAA) emerged as a promising strategy. We initiated 3 pilot clinical trials with immunological endpoints using TAA loaded autologous DC. These trials showed that this approach was safe and associated with the induction of potent TAA specific IFN-gamma responses, which were transient despite the providing a further help through KLH presentation. Subcutaneous (s.c.) IL-2 administration was associated with long-lasting TAA specific IL-5 production. Clinical responses were observed in about 1/3 of the patients. Further improvements will take advantage of the use of a new type of DC cells (IL-3/IFN-beta DC) and of tumor cell-DC hybrids.

Tumoricidal activity of monocyte-derived dendritic cells: evidence for a caspase-8-dependent, Fas-associated death domain-independent mechanism

Monocyte-derived dendritic cells (DC) were found to be cytotoxic for several tumor cell lines including Jurkat cells, which were killed through a calcium-independent pathway. K562 cells were resistant, excluding a NK cell-like activity. DC-mediated apoptosis did not involve classical death receptors because it was not reversed by blocking TNF/TNFR, CD95/CD95 ligand, or TNF-related apoptosis-inducing ligand/TNF-related apoptosis-inducing ligand receptor interactions. Fas-associated death domain-deficient, but not caspase-8 deficient, Jurkat cells were killed by DC. Indeed, caspase-8 cleavage was demonstrated in Jurkat cells cocultured with DC, and the use of specific caspase inhibitors confirmed that apoptosis triggered by DC was caspase-8 dependent. Furthermore, the involvement of Bcl-2 family members in the control of DC-mediated apoptosis was demonstrated by Bid cleavage in Jurkat cells cocultured with DC and resistance of Jurkat cells overexpressing Bcl-2 to DC-mediated cytotoxicity. Overall, these data indicate that monocyte-derived DC exert a caspase-8-dependent, Fas associated death domain-independent tumoricidal activity, a finding that could be relevant to their therapeutic use in cancer.

Expression of c-FLIP(L) and resistance to CD95-mediated apoptosis of monocyte-derived dendritic cells: inhibition by bisindolylmaleimide

To gain insight into the mechanisms controlling apoptosis of dendritic cells (DC), human monocyte-derived DC were analyzed for their expression of CD95 (Fas/Apo-1) and their response to CD95 ligation. Although DC expressed the CD95 molecule on their membrane, they did not undergo apoptosis on CD95 ligation unless sensitized by cycloheximide. In parallel, DC synthesized c-FLIP(L), an inhibitor of the CD95-mediated death-signaling cascade. We also demonstrated that bisindolylmaleimide down-regulates c-FLIP(L) expression in DC and, in parallel, allows CD95-mediated apoptosis in these cells. In contrast, Bcl-2, Bcl-x(L), and Bax levels were not affected by bisindolylmaleimide. We conclude that DC resist CD95- mediated apoptosis in association with c-FLIP(L) expression and that the immunosuppressive potential of bisindolylmaleimide previously observed at the T-cell level also involves facilitation of CD95-mediated DC apoptosis.

Trypanosoma cruzi infects human dendritic cells and prevents their maturation: inhibition of cytokines, HLA-DR, and costimulatory molecules

Trypanosoma cruzi, a parasitic protozoan, is the etiological agent of Chagas' disease. Despite the many immune system disorders recognized in this infection and the crucial role played by dendritic cells (DC) in acquired immune responses, it was not known whether these cells could be infected by T. cruzi trypomastigotes and the consequences of such an infection on their immune functions. We now provide evidence that human monocyte-derived DC can be infected by T. cruzi and can support its intracellular multiplication. Interestingly, this infection has functional consequences on immature DC and on their maturation induced by lipopolysaccharide (LPS). First, after T. cruzi infection, the basal synthesis of interleukin-12 (IL-12) and tumor necrosis factor alpha (TNF-alpha) was impaired. Furthermore, the process of maturation of DC induced by LPS was drastically affected by T. cruzi infection. Indeed, secretion of cytokines such as IL-12, TNF-alpha, and IL-6, which are released normally at high levels by LPS-activated DC, as well as the up-regulation of HLA-DR and CD40 molecules, was significantly reduced after this infection. The same effects could be induced by T. cruzi-conditioned medium, indicating that at least these inhibitory effects were mediated by soluble factors released by T. cruzi. Taken together, these results provide new insights into a novel efficient mechanism, directly involving the alteration of DC function, which might be used by T. cruzi to escape the host immune responses in Chagas' disease and thus might favor persistent infection.

Inhibition of human dendritic cell functions by methylprednisolone

BACKGROUND

The aim of this study was to better define how glucocorticoids influence primary human T cell responses. Dendritic cells (DC*) are the most effective antigen presenting cells able to activate naive T cells. Previous studies have shown that dexamethasone impaired the function of murine DC. Here, we analyzed how methylprednisolone (MP) might affect the function and maturation of human DC.

METHODS

Human DC were generated from peripheral blood mononuclear cells cultured in granulocyte macrophage-colony stimulating factor and interleukin (IL)4. DC maturation was induced either by lipopolysaccharide (LPS) or by fibroblast transfected with the CD40-ligand gene (3T6-CD40L). DC phenotype was characterized by flow cytometric analysis, their cytokine production by ELISA. The ability of DC to activate naive T cells was evaluated in mixed leukocyte reactivity.

RESULTS

Although MP did not affect viability of DC, it enhanced their antigen uptake and down-regulated their basal expression of CD86. The expression of CD80 and CD54 by DC was slightly decreased and HLA-DR expression was not modified. MP prevented LPS-induced DC maturation as assessed by the inhibition of CD86, CD80 and CD54 up-regulation, CD83 induction and production of TNF-alpha, IL-6, and IL-12. In contrast, when DC were stimulated by 3T6-CD40L, MP prevented only the synthesis of IL-12. Moreover, MP-treated DC were deficient in their ability to elicit proliferative responses of CD4+CD45RA+ allogeneic T cells as well as their synthesis of interferon (IFN)-gamma, IL-5, and IL-13. CONCLUSION. Glucocorticoids exert potent suppressive effects on human DC and thereby inhibit the induction of primary T cell responses.

N-Acetyl-l-Cysteine Inhibits Primary Human T Cell Responses at the Dendritic Cell Level: Association with NF-κB Inhibition

N-acetyl-l-cysteine (NAC) is an antioxidant molecule endowed with immunomodulatory properties. To investigate the effect of NAC on the induction phase of T cell responses, we analyzed its action on human dendritic cells (DC) derived from adherent PBMC cultured with IL-4 and granulocyte-macrophage CSF. We first found that NAC inhibited the constitutive as well as the LPS-induced activity of the transcription factor NF-κB. In parallel, NAC was shown to down-regulate the production of cytokines by DC as well as their surface expression of HLA-DR, CD86 (B7-2), and CD40 molecules both at the basal state and upon LPS activation. NAC also inhibited DC responses induced by CD40 engagement. The inhibitory effects of NAC were not due to nonspecific toxicity as neither the viability of DC nor their mannose receptor-mediated endocytosis were modified by NAC. Finally, we found that the addition of NAC to MLR between naive T cells and allogeneic DC resulted in a profound inhibition of alloreactive responses, which could be attributed to a defect of DC as APC-independent T cell responses were not inhibited by NAC. Altogether, our results suggest that NAC might impair the generation of primary immune responses in humans through its inhibitory action on DC.

N-acetyl-L-cysteine inhibits primary human T cell responses at the dendritic cell level: association with NF-kappaB inhibition

N-acetyl-L-cysteine (NAC) is an antioxidant molecule endowed with immunomodulatory properties. To investigate the effect of NAC on the induction phase of T cell responses, we analyzed its action on human dendritic cells (DC) derived from adherent PBMC cultured with IL-4 and granulocyte-macrophage CSF. We first found that NAC inhibited the constitutive as well as the LPS-induced activity of the transcription factor NF-kappaB. In parallel, NAC was shown to down-regulate the production of cytokines by DC as well as their surface expression of HLA-DR, CD86 (B7-2), and CD40 molecules both at the basal state and upon LPS activation. NAC also inhibited DC responses induced by CD40 engagement. The inhibitory effects of NAC were not due to nonspecific toxicity as neither the viability of DC nor their mannose receptor-mediated endocytosis were modified by NAC. Finally, we found that the addition of NAC to MLR between naive T cells and allogeneic DC resulted in a profound inhibition of alloreactive responses, which could be attributed to a defect of DC as APC-independent T cell responses were not inhibited by NAC. Altogether, our results suggest that NAC might impair the generation of primary immune responses in humans through its inhibitory action on DC.