Fusion of Na-ASP-2 with human immunoglobulin Fcγ abrogates histamine release from basophils sensitized with anti-Na-ASP-2 IgE.

Na-ASP-2 is a major protein secreted by infective third-stage larvae (L3) of the human hookworm Necator americanus upon host entry. It was chosen as a lead vaccine candidate for its ability to elicit protective immune responses. However, clinical development of this antigen as a recombinant vaccine was halted because it caused allergic reactions among some of human volunteers previously infected with N. americanus. To prevent IgE-mediated allergic reactions induced by Na-ASP-2 but keep its immunogenicity as a vaccine antigen, we designed and tested a genetically engineered fusion protein, Fcγ/Na-ASP-2, composed of full-length Na-ASP-2 and truncated human IgG Fcγ1 that targets the negative signalling receptor FcγRIIb expressed on pro-allergic cells. The chimeric recombinant Fcγ/Na-ASP-2 protein was expressed in Pichia pastoris and shared the similar antigenicity as native Na-ASP-2. Compared to Na-ASP-2, the chimeric fusion protein efficiently reduced the release of histamine in human basophils sensitized with anti-Na-ASP-2 IgE obtained from individuals living in a hookworm-endemic area. In dogs infected with canine hookworm, Fcγ/Na-ASP-2 resulted in significantly reduced immediate-type skin reactivity when injected intradermally compared with Na-ASP-2. Hamsters vaccinated with Fcγ/Na-ASP-2 formulated with Alhydrogel(®) produced specific IgG that recognized Na-ASP-2 and elicited similar protection level against N. americanus L3 challenge as native Na-ASP-2.

[Immunity in human schistosomiasis: hope for a vaccine]. / L'immunité dans les schistosomoses humaines: perspectives vaccinales.

Schistosomiasis remains a major worldwide public health problem in several endemic areas despite implementation of control measures. Vaccination would be an effective, long-term treatment option for future control of schistosomiasis. Although several parasite antigens have been identified as schistosomiasis vaccine candidates, major hurdles must still be overcome to develop a vaccine suitable for clinical trials in the field. Better understanding of immune responses to Schistosoma infection in both animal models and humans suggests that development of a vaccine is possible. The purpose of this review is to summarize the mechanisms of protective immunity against Schistosoma infection and to provide perspective on the development of a vaccine.

A phase 1 study of the safety, reactogenicity, and immunogenicity of a Schistosoma mansoni vaccine with or without glucopyranosyl lipid A aqueous formulation (GLA-AF) in healthy adults from a non-endemic area.

BACKGROUND: Schistosomiasis caused by Schistosoma mansoni (Sm) is a chronic, debilitating and potentially deadly neglected tropical disease. The licensure of a vaccine to prevent schistosomiasis would represent a major breakthrough in public health. METHODS: The safety and immunogenicity of a candidate Sm vaccine were assessed in this phase I, double-blind, dose-escalation trial. Seventy-two healthy Sm-naïve 18-50 year olds were randomized to receive 3 doses ∼ 8 weeks apart of saline placebo, or 10 µg, 30 µg, or 100 µg of recombinant Sm-Tetraspanin-2 vaccine formulated on aluminum hydroxide adjuvant (Sm-TSP-2/Al) with or without 5 µg of glucopyranosyl lipid A aqueous formulation (GLA-AF). Clinical and serologic responses were assessed for 1 year after dose 3. RESULTS: Vaccines were safe and well-tolerated. The most common reactions were injection site tenderness and pain, and headache and fatigue. Tenderness and pain were more frequent in groups receiving vaccine with GLA-AF than placebo (p = 0.0036 and p = 0.0014, respectively). Injection site reactions among those given Sm-TSP-2/Al with GLA-AF lasted 1.22 and 1.33 days longer than those receiving Sm-TSP-2/Al without GLA-AF or placebo (p < 0.001 for both). Dose- and adjuvant-related increases in serum IgG against Sm-TSP-2 were observed. Peak IgG levels occurred 14 days after dose 3. Seroresponse frequencies were low among recipients of Sm-TSP-2/Al without GLA-AF, but higher among subjects receiving 30 µg or 100 µg of Sm-TSP-2/Al with GLA-AF. More seroresponses were observed among those given 30 µg or 100 µg of Sm-TSP-2/Al with GLA-AF compared to placebo (p = 0.023 and p < 0.001, respectively). Seroresponse frequencies were 0%, 30%, 50%, and 89%, respectively, among those given placebo, or 10 µg, 30 µg or 100 µg of Sm-TSP-2/Al with GLA-AF, suggesting a dose-response relationship for Sm-TSP-2/Al with GLA-AF (p = 0.0001). CONCLUSIONS: Sm-TSP-2/Al with or without GLA-AF was safe and well tolerated in a Sm-naïve population. A vaccine like the one under development may represent our best hope to eliminating this neglected tropical disease.

Stage-specific immune responses in human Necator americanus infection.

We describe how hookworms interact with their human hosts by comparing lymphocyte phenotyping, proliferative responses, and cytokine and chemokine secretion patterns in adults who are either mono-infected with Necator americanus or egg-negative controls resident in an area of high transmission in Brazil. Cellular immune responses against crude hookworm antigen extracts from different developmental stages were evaluated simultaneously. Principal component analysis (PCA) was used to reduce the standardized immune responses. Random effects multivariate regression was then used to investigate whether principal components (PC) differ between the two groups once potential confounders and effect modifiers have been accounted for. Although hookworm patients had reduced percentages of T and B cells, they had higher levels of activated CD4(+) T and CD19(+) B cells. This state of 'immune activation' coincided with lower proliferative responses, especially to third-stage larval antigen. Cytokine levels in mono-infected adults were also lower and characterized by a mixed Th1/Th2-type profile. Excretory/secretory antigen from adult worms was a potent modulator of the immune response, resulting in diminished TNF-alpha and IL-10 secretion in peripheral blood mononuclear cells (PBMC) from hookworm infected patients. We propose that the longevity of hookworms in their human hosts results from a stage-specific, down-modulation of the immune response.

Sputum isolation of Wangiella dermatitidis in patients with cystic fibrosis.

We report a case of invasive fungal pulmonary infection in a cystic fibrosis patient. Clinical deterioration coincided with isolation of Wangiella dermatitidis from her sputum, and treatment with amphotericin B followed by voriconazole resulted in clinical improvement and sterilization of the sputum. This case suggests that W. dermatitidis may be an etiologic agent of invasive pulmonary disease in the cystic fibrosis population.