Complete protection against P. berghei malaria upon heterologous prime/boost immunization against circumsporozoite protein employing Salmonella type III secretion system and Bordetella adenylate cyclase toxoid

Sterile immunity against malaria can be achieved by the induction of IFNgamma-producing CD8(+) T cells that target infected hepatocytes presenting epitopes of the circumsporozoite protein (CSP). In the present study we evaluate the protective efficacy of a heterologous prime/boost immunization protocol based on the delivery of the CD8(+) epitope of Plasmodium berghei CSP into the MHC class I presentation pathway, by either a type III secretion system of live recombinant Salmonella and/or by direct translocation of a recombinant Bordetella adenylate cyclase toxoid fusion (ACT-CSP) into the cytosol of professional antigen-presenting cells (APCs). A single intraperitoneal application of the recombinant ACT-CSP toxoid, as well as a single oral immunization with the Salmonella vaccine, induced a specific CD8(+) T cell response, which however conferred only a partial protection on mice against a subsequent sporozoite challenge. In contrast, a heterologous prime/boost vaccination with the live Salmonella followed by ACT-CSP led to a significant enhancement of the CSP-specific T cell response and induced complete protection in all vaccinated mice.

CD4(+)CD25(+) T cells expressing FoxP3 in Icelandic horses affected with insect bite hypersensitivity

Insect bite hypersensitivity (IBH) is an IgE-mediated dermatitis caused by bites of midges from the genus Culicoides. We have shown previously that peripheral blood mononuclear cells (PBMC) from IBH-affected horses produce higher levels of IL-4 and lower levels of IL-10 and TGF-beta1 than those from healthy horses, suggesting that IBH is associated with a reduced regulatory immune response. FoxP3 is a crucial marker of regulatory T cells (Tregs). Here we have determined the proportion of CD4(+)CD25(+)FoxP3(+) T cells by flow cytometry in PBMC directly after isolation or after stimulation with Culicoides extract or a control antigen (Tetanus Toxoid). There were no differences between healthy and IBH horses either in the proportion of FoxP3(+)CD4(+)CD25(+) cells in freshly isolated PBMC or in the following stimulation with Tetanus Toxoid. However, upon stimulation of PBMC with the allergen, expression of FoxP3 by CD4(+)CD25(+high) and CD4(+)CD25(+dim) cells was significantly higher in healthy than in IBH horses. Addition of recombinant IL-4 to PBMC from healthy horses stimulated with the allergen significantly decreased the proportion of FoxP3 expressing cells within CD4(+)CD25(+high). These results suggest that IBH is associated with a decreased number of allergen-induced Tregs. This could be a consequence of the increased IL-4 production by PBMC of IBH-affected horses.

Long-lasting reactivity and high frequency of drug-specific T cells after severe systemic drug hypersensitivity reactions

BACKGROUND: Drug-reactive T cells are involved in most drug-induced hypersensitivity reactions. The frequency of such cells in peripheral blood of patients with drug allergy after remission is unclear. OBJECTIVE: We determined the frequency of drug-reactive T cells in the peripheral blood of patients 4 months to 12 years after severe delayed-type drug hypersensitivity reactions, and whether the frequency of these cell differs from the frequency of tetanus toxoid-reactive T cells. METHODS: We analyzed 5 patients with delayed-type drug hypersensitivity reactions, applying 2 methods: quantification of cytokine-secreting T cells by enzyme-linked immunospot (ELISpot), and fluorescent dye 5,6-carboxylfluorescein diacetate succinimidyl ester (CFSE) intensity distribution analysis of drug-reactive T cells. RESULTS: Frequencies found were between 0.02% and 0.4% of CD4(+) T cells reacting to the respective drugs measured by CFSE analysis, and between 0.01% and 0.08% of T cells as determined by ELISpot. Reactivity was seen neither to drugs to which the patients were not sensitized nor in healthy individuals after stimulation with any of the drugs used. CONCLUSION: About 1:250 to 1:10,000 of T cells of patients with drug allergy are reactive to the relevant drugs. This frequency of drug-reactive T cells is higher than the frequency of T cells able to recognize recall antigens like tetanus toxoid in the same subjects. A substantial frequency could be observed as long as 12 years later in 1 patient even after strict drug avoidance. Patients with severe delayed drug hypersensitivity reactions are therefore potentially prone to react again to the incriminated drug even years after strict drug avoidance.

Alternative vaccination against equine botulism (BoNT/C)

REASON FOR PERFORMING STUDY: In Europe the incidence of botulism in horses has increased in the last decade due to the growing popularity of haylage feeding. Recombinant vaccines are safer and less expensive to produce and are generally better tolerated than toxoids. OBJECTIVES: To investigate whether the recombinant C-terminal half of the heavy chain of the botulinum neurotoxin C (Hc BoNT/C) in combination with an immunstimulatory adjuvant is an appropriate vaccine candidate for horses by testing its efficacy to induce neutralising antibodies and by comparing its immunogenic properties and adverse reactions to a commercial toxoid vaccine. Formation of oedema and local pain reactions were assessed. ELISA and Western blot assay against Hc BoNT/C and testing of neutralising antibody induction in a mouse protection assay were used to evaluate the immune response. RESULTS: With the recombinant vaccine, only minor local swelling with full recovery after 5 days was noted after brisket injections. The toxoid vaccine produced local, painful reactions with longer recovery periods of up to 2 weeks. Horses vaccinated with either vaccine induced neutralising antibodies after the second booster vaccination, while seroconversion on ELISA and Western blot to Hc BoNT/C was apparent after the first recombinant vaccination, and at various time points in the vaccination schedule in horses that received commercial toxoid vaccine. CONCLUSION: The recombinant vaccine showed fewer adverse reactions compared to the only commercially available vaccine but induced similar concentrations of neutralising antibodies. There was no correlation between the serological response to Hc BoNT/C and the neutralising capacity of serum. POTENTIAL RELEVANCE: Recombinant Hc BoNT/C is an appropriate vaccine candidate to stimulate production of neutralising antibodies against botulinum neurotoxin C in horses and creates only minor local reactions at the injection site.

Immune response of horses to vaccination with the recombinant Hc domain of botulinum neurotoxin types C and D

Botulinum neurotoxins, predominantly serotypes C and D, cause equine botulism through forage poisoning. The C-terminal part of the heavy chain of botulinum neurotoxin types C and D (HcBoNT/C and D) was expressed in Escherichia coli and evaluated as a recombinant mono- and bivalent vaccine in twelve horses in comparison to a commercially available toxoid vaccine. A three-dose subcutaneous immunization of adult horses elicited robust serum antibody response in an ELISA using the immunogen as a capture antigen. Immune sera showed dose-dependent high potency in neutralizing specifically the active BoNT/C and D in the mouse protection assay. The aluminium hydroxide based mono- and bivalent recombinant HcBoNT/C and D vaccines were characterized by good compatibility and the ability to elicit protective antibody titers similar or superior to the commercially available toxoid vaccine.

Comparing Haemophilus influenzae type b conjugate vaccine schedules: a systematic review and meta-analysis of vaccine trials

BACKGROUND The optimal schedule and the need for a booster dose are unclear for Haemophilus influenzae type b (Hib) conjugate vaccines. We systematically reviewed relative effects of Hib vaccine schedules. METHODS We searched 21 databases to May 2010 or June 2012 and selected randomized controlled trials or quasi-randomized controlled trials that compared different Hib schedules (3 primary doses with no booster dose [3p+0], 3p+1 and 2p+1) or different intervals in primary schedules and between primary and booster schedules. Outcomes were clinical efficacy, nasopharyngeal carriage and immunological response. Results were combined in random-effects meta-analysis. RESULTS Twenty trials from 15 countries were included; 16 used vaccines conjugated to tetanus toxoid (polyribosylribitol phosphate conjugated to tetanus toxoid). No trials assessed clinical or carriage outcomes. Twenty trials examined immunological outcomes and found few relevant differences. Comparing polyribosylribitol phosphate conjugated to tetanus toxoid 3p+0 with 2p+0, there was no difference in seropositivity at the 1.0 μg/mL threshold by 6 months after the last primary dose (combined risk difference -0.02; 95% confidence interval: -0.10, 0.06). Only small differences were seen between schedules starting at different ages, with different intervals between primary doses, or with different intervals between primary and booster doses. Individuals receiving a booster were more likely to be seropositive than those at the same age who did not. CONCLUSIONS There is no clear evidence from trials that any 2p+1, 3p+0 or 3p+1 schedule of Hib conjugate vaccine is likely to provide better protection against Hib disease than other schedules. Until more data become available, scheduling is likely to be determined by epidemiological and programmatic considerations in individual settings.

Detection of Clostridium perfringens type C in pig herds following disease outbreak and subsequent vaccination

Immunisation of sows using Clostridium perfringens type C toxoid vaccines is recommended to prevent necrotising enteritis (NE) on pig breeding farms. Absence of disease, however, oftentimes leads to the false assumption of pathogens being eradicated. The prevalence of C perfringens type C was determined by PCR in faecal samples of piglets and sows in three Swiss pig breeding farms two to four years after implementation of a vaccination programme following disease outbreaks. C perfringens type C could still be detected several years after an outbreak despite absence of NE. In-herd prevalence of the pathogens varied significantly between the farms and was also lower compared with a farm which experienced a recent outbreak. In conclusion, C perfringens type C can be detected on once-affected farms, even in the absence of NE for several years.

In vitro induction of functional allergen-specific CD4+ CD25high Treg cells in horses affected with insect bite hypersensitivity

BACKGROUND Insect bite hypersensitivity (IBH) is a recurrent allergic dermatitis of horses with similarities to human atopic eczema, caused by bites of insects of the genus Culicoides. Previous studies suggested a dysregulated T cell tolerance to Culicoides allergen in IBH-affected horses. OBJECTIVE We have investigated whether the suppressive function of CD4(+) CD25(high) cells is impaired in IBH-affected horses and possible ways to restore it. METHODS CD4(+) CD25(-) cells sorted from peripheral blood mononuclear cells (PBMC) were stimulated with irradiated autologous PBMC pulsed with Culicoides or tetanus toxoid as control antigen, in the presence of CD4(+) CD25(high) cells. Furthermore, Culicoides-specific CD4(+) CD25(high) regulatory cells were expanded or induced from CD4(+) CD25(-) cells in vitro in the presence of a combination of rIL-2 and rTGF-β1 (rIL-2/rTGF-β1) or of retinoic acid and rapamycin (RetA/Rapa). Proliferation was determined by [(3) H] thymidine incorporation and cytokine production measured by flow cytometry. RESULTS The ability of Culicoides- but not tetanus-stimulated CD4(+) CD25(high) cells to suppress proliferation of CD4(+) CD25(-) cells was significantly lower in IBH-affected horses (28%) than in healthy controls (86%). The decreased suppression in IBH-affected horses was associated with a significantly higher proportion of IL-4(+) cells and a lower percentage of FoxP3(+) IL-10(+) compared to controls. Addition of rIL-2/rTGF-β1 or of RetA/Rapa to Culicoides-stimulated CD4(+) CD25(high) cells from IBH-affected horses significantly increased the proportion of FoxP3(+) IL-10(+) cells. We also found that RetA/Rapa induced a more significant decrease in the frequency of IL-4(+) cells than rIL-2/rTGF-β1. Moreover, the suppressive activity of Culicoides-stimulated CD4(+) CD25(high) cells was significantly restored by both rIL-2/rTGF-β1and RetA/Rapa, albeit in an antigen-unspecific manner. In contrast, in vitro induced Culicoides-specific CD4(+) CD25(high) cells suppressed proliferation of CD4(+) CD25(-) cells in an antigen-specific manner. CONCLUSION AND CLINICAL RELEVANCE The in vitro induction of functional allergen-specific Treg cells in IBH-affected horses suggests a potential therapeutic use of these cells in allergy.

Depletion of regulatory T cells augments a vaccine-induced T effector cell response against the liver-stage of malaria but fails to increase memory

Regulatory T cells (T(reg)) have been shown to restrict vaccine-induced T cell responses in different experimental models. In these studies CD4(+)CD25(+) T(reg) were depleted using monoclonal antibodies against CD25, which might also interfere with CD25 on non-regulatory T cell populations and would have no effect on Foxp3(+)CD25(-) T(reg). To obtain more insights in the specific function of T(reg) during vaccination we used mice that are transgenic for a bacterial artificial chromosome expressing a diphtheria toxin (DT) receptor-eGFP fusion protein under the control of the foxp3 gene locus (depletion of regulatory T cell mice; DEREG). As an experimental vaccine-carrier recombinant Bordetella adenylate cyclase toxoid fused with a MHC-class I-restricted epitope of the circumsporozoite protein (ACT-CSP) of Plasmodium berghei (Pb) was used. ACT-CSP was shown by us previously to introduce the CD8+ epitope of Pb-CSP into the MHC class I presentation pathway of professional antigen-presenting cells (APC). Using this system we demonstrate here that the number of CSP-specific T cells increases when T(reg) are depleted during prime but also during boost immunization. Importantly, despite this increase of T effector cells no difference in the number of antigen-specific memory cells was observed.

Immunization with a circumsporozoite epitope fused to Bordetella pertussis adenylate cyclase in conjunction with cytotoxic T-lymphocyte-associated antigen 4 blockade confers protection against Plasmodium berghei liver-stage malaria

The adenylate cyclase toxoid (ACT) of Bordetella pertussis is capable of delivering its N-terminal catalytic domain into the cytosol of CD11b-expressing professional antigen-presenting cells such as myeloid dendritic cells. This allows delivery of CD8+ T-cell epitopes to the major histocompatibility complex (MHC) class I presentation pathway. Recombinant detoxified ACT containing an epitope of the Plasmodium berghei circumsporozoite protein (CSP), indeed, induced a specific CD8+ T-cell response in immunized mice after a single application, as detected by MHC multimer staining and gamma interferon (IFN-gamma) ELISPOT assay. This CSP-specific response could be significantly enhanced by prime-boost immunization with recombinant ACT in combination with anti-CTLA-4 during the boost immunization. This increased response was accompanied by complete protection in a number of mice after a challenge with P. berghei sporozoites. Transient blockade of CTLA-4 may overcome negative regulation and hence provide a strategy to enhance the efficacy of a vaccine by amplifying the number of responding T cells.