Micro Array-Assisted Analysis of Anti-Schistosome Glycan Antibodies Elicited by Protective Vaccination With Irradiated Cercariae

Serum antibody screening using glycan arrays

Humans and other animals produce a diverse collection of antibodies, many of which bind to carbohydrate chains, referred to as glycans. These anti-glycan antibodies are a critical part of our immune systems' defenses. Whether induced by vaccination or natural exposure to a pathogen, anti-glycan antibodies can provide protection against infections and cancers. Alternatively, when an immune response goes awry, antibodies that recognize self-glycans can mediate autoimmune diseases. In any case, serum anti-glycan antibodies provide a rich source of information about a patient's overall health, vaccination history, and disease status. Glycan microarrays provide a high-throughput platform to rapidly interrogate serum anti-glycan antibodies and identify new biomarkers for a variety of conditions. In addition, glycan microarrays enable detailed analysis of the immune system's response to vaccines and other treatments. Herein we review applications of glycan microarray technology for serum anti-glycan antibody profiling.

Antigenic epitope targets of rhesus macaques self-curing from Schistosoma mansoni infection

The self-cure of rhesus macaques from a schistosome infection and their subsequent strong immunity to a cercarial challenge should provide novel insights into the way these parasites can be eliminated by immunological attack. High-density arrays comprising overlapping 15-mer peptides from target proteins printed on glass slides can be used to screen sera from host species to determine antibody reactivity at the single epitope level. Careful selection of proteins, based on compositional studies, is crucial to encompass only those exposed on or secreted from the intra-mammalian stages and is intended to focus the analysis solely on targets mediating protection. We report the results of this approach using two pools of sera from hi- and lo-responder macaques undergoing self-cure, to screen arrays comprising tegument, esophageal gland, and gastrodermis proteins. We show that, overall, the target epitopes are the same in both groups, but the intensity of response is twice as strong in the high responders. In addition, apart from Sm25, tegument proteins elicit much weaker responses than those originating in the alimentary tract, as was apparent in IFNγR KO mice. We also highlight the most reactive epitopes in key proteins. Armed with this knowledge, we intend to use multi-epitope constructs in vaccination experiments, which seek to emulate the self-cure process in experimental animals and potentially in humans.

Safety and infectivity of female cercariae in Schistosoma-naïve, healthy participants: a controlled human Schistosoma mansoni infection study

BACKGROUND

A controlled human infection model for schistosomiasis (CHI-S) can speed up vaccine development and provides insight into early immune responses following schistosome exposure. Recently, we established CHI-S model using single-sex male-only Schistosoma mansoni (Sm) cercariae in Schistosoma-naïve individuals. Given important differences in antigenic profile and human immune responses to schistosomes of different sex, we pioneered a single-sex female-only CHI-S model for future use in vaccine development.

METHODS

We exposed 13 healthy, Schistosoma-naïve adult participants to 10 (n = 3) or 20 (n = 10) female cercariae and followed for 20 weeks, receiving treatment with praziquantel (PZQ) 60 mg/kg at week 8 and 12 after exposure.

FINDINGS

The majority (11/13) participants reported rash and/or itch at the site of exposure, 5/13 had transient symptoms of acute schistosomiasis. Exposure to 20 cercariae led to detectable infection, defined as serum circulating anodic antigen levels >1.0 pg/mL, in 6/10 participants. Despite two rounds of PZQ treatment, 4/13 participants showed signs of persistent infection. Additional one- or three-day PZQ treatment (1 × 60 mg/kg and 3 × 60 mg/kg) or artemether did not result in cure, but over time three participants self-cured. Antibody, cellular, and cytokine responses peaked at week 4 post infection, with a mixed Th1, Th2, and regulatory profile. Cellular responses were (most) discriminative for symptoms.

INTERPRETATION

Female-only infections exhibit similar clinical and immunological profiles as male-only infections but are more resistant to PZQ treatment. This limits future use of this model and may have important implications for disease control programs.

FUNDING

European Union's Horizon 2020 (grant no. 81564).

Models of Protective Immunity against Schistosomes: Implications for Vaccine Development

After many decades of research, a schistosome vaccine still looks to be a distant prospect. These helminths can live in the human bloodstream for years, even decades, surrounded by and feeding on the components of the immune response they provoke. The original idea of a vaccine based on the killing of invading cercariae in the skin has proven to be illusory. There has also been a realisation that even if humans develop some protection against infection over a protracted period, it very likely involves IgE-mediated responses that cannot provide the basis for a vaccine. However, it has also become clear that both invasive migrating larvae and adult worms must expose proteins and release secretions into the host environment as part of their normal biological activities. The application of modern 'omics approaches means that we now have a much better idea of the identity of these potential immune targets. This review looks at three animal models in which acquired immunity has been demonstrated and asks whether the mechanisms might inform our vaccine strategies to achieve protection in model hosts and humans. Eliciting responses, either humoral or cellular, that can persist for many months is a challenge. Arming of the lungs with effector T cells, as occurs in mice exposed to the radiation-attenuated cercarial vaccine, is one avenue. Generating IgG antibody titres that reach levels at which they can exert sustained immune pressure to cause worm elimination, as occurs in rhesus macaques, is another. The induction of memory cell populations that can detect trickle invasions of larval stages remains to be explored. One promising approach is the analysis of protective antibodies using high-density peptide arrays of target proteins to identify reactive regions. These can be combined in multi-epitope constructs to immunise a host against many targets simultaneously and cheaply.

Glycosphingolipids in human parasites

Glycosphingolipids (GSLs) are comprised of glycans (oligosaccharides) linked to a lipid containing a sphingosine moiety. They are major membrane components in cells of most animals, and importantly, they also occur in parasitic protozoans and worms that infect people. While the endogenous functions of the GSLs in most parasites are elusive, many of these GSLs are recognized by antibodies in infected human and animal hosts, and thus, their structures, biosynthesis, and functions are of great interest. Such knowledge of GSLs could lead to new drugs and diagnostics for treating infections, as well as novel vaccine strategies. The diversity of GSLs recently identified in such infectious organisms and aspects of their immune recognition are major topics of this review. It is not intended to be exhaustive but to highlight aspects of GSL glycans in human parasites.

Helminth Glycans at the Host-Parasite Interface and Their Potential for Developing Novel Therapeutics

Helminths are parasitic worms that have successfully co-evolved with their host immune system to sustain long-term infections. Their successful parasitism is mainly facilitated by modulation of the host immune system via the release of excretory-secretory (ES) products covered with glycan motifs such as Lewis X, fucosylated LDN, phosphorylcholine and tyvelose. Evidence is accumulating that these glycans play key roles in different aspects of helminth infection including interactions with immune cells for recognition and evasion of host defences. Moreover, antigenic properties of glycans can be exploited for improving the efficacy of anti-helminthic vaccines. Here, we illustrate that glycans have the potential to open new avenues for the development of novel biopharmaceuticals and effective vaccines based on helminth glycoproteins.

Glycan Array Evaluation of Synthetic Epitopes between the Capsular Polysaccharides from Streptococcus pneumoniae 19F and 19A

Vaccination represents the most effective way to prevent invasive pneumococcal diseases. The glycoconjugate vaccines licensed so far are obtained from capsular polysaccharides (CPSs) of the most virulent serotypes. Protection is largely limited to the specific vaccine serotypes, and the continuous need for broader coverage to control the outbreak of emerging serotypes is pushing the development of new vaccine candidates. Indeed, the development of efficacious vaccine formulation is complicated by the high number of bacterial serotypes with different CPSs. In this context, to simplify vaccine composition, we propose the design of new saccharide fragments containing chemical structures shared by different serotypes as cross-reactive and potentially cross-protective common antigens. In particular, we focused on Streptococcus pneumoniae (Sp) 19A and 19F. The CPS repeating units of Sp 19F and 19A are very similar and share a common structure, the disaccharide ManNAc-β-(1→4)-Glc (A-B). Herein, we describe the synthesis of a small library of compounds containing different combinations of the common 19F/19A disaccharide. The six new compounds were tested with a glycan array to evaluate their recognition by antibodies in reference group 19 antisera and factor reference antisera (reacting against 19F or 19A). The disaccharide A-B, phosphorylated at the upstream end, emerged as a hit from the glycan array screening because it is strongly recognized by the group 19 antisera and by the 19F and 19A factor antisera, with similar intensity compared with the CPSs used as controls. Our data give a strong indication that the phosphorylated disaccharide A-B can be considered a common epitope among different Sp 19 serotypes.

Context-Specific Procedures for the Diagnosis of Human Schistosomiasis – A Mini Review

Schistosomiasis is a parasitic disease caused by trematode blood flukes of the genus Schistosoma, affecting over 250 million people mainly in the tropics. Clinically, the disease can present itself with acute symptoms, a stage which is relatively more common in naive travellers originating from non-endemic regions. It can also develop into chronic disease, with the outcome depending on the Schistosoma species involved, the duration and intensity of infection and several host-related factors. A range of diagnostic tests is available to determine Schistosoma infection, including microscopy, antibody detection, antigen detection using the Point-Of-Care Circulating Cathodic Antigen (POC-CCA) test and the Up-Converting Particle Lateral Flow Circulating Anodic Antigen (UCP-LF CAA) test, as well as Nucleic Acid Amplification Tests (NAATs) such as real-time PCR. In this mini review, we discuss these different diagnostic procedures and explore their most appropriate use in context-specific settings. With regard to endemic settings, diagnostic approaches are described based on their suitability for individual diagnosis, monitoring control programs, determining elimination as a public health problem and eventual interruption of transmission. For non-endemic settings, we summarize the most suitable diagnostic approaches for imported cases, either acute or chronic. Additionally, diagnostic options for disease-specific clinical presentations such as genital schistosomiasis and neuro-schistosomiasis are included. Finally, the specific role of diagnostic tests within research settings is described, including a controlled human schistosomiasis infection model and several clinical studies. In conclusion, context-specific settings have different requirements for a diagnostic test, stressing the importance of a well-considered decision of the most suitable diagnostic procedure.

Schistosomiasis then and now: what has changed in the last 100 years?

Only with the completion of the life cycles of Fasciola hepatica in 1883 and 30 years later those of Schistosoma japonicum (1913), Schistosoma haematobium and Schistosoma mansoni (1915) did research on schistosomiasis really get underway. One of the first papers by Cawston in 1918, describing attempts to establish the means of transmission of S. haematobium in Natal, South Africa, forms the historical perspective against which to judge where we are now. Molecular biology techniques have produced a much better definition of the complexity of the schistosome species and their snail hosts, but also revealed the extent of hybridization between human and animal schistosomes that may impact on parasite adaptability. While diagnostics have greatly improved, the ability to detect single worm pair infections routinely, still falls short of its goal. The introduction of praziquantel ~1982 has revolutionized the treatment of infected individuals and led directly to the mass drug administration programmes. In turn, the severe pathological consequences of high worm burdens have been minimized, and for S. haematobium infections the incidence of associated squamous cell carcinoma has been reduced. In comparison, the development of effective vaccines has yet to come to fruition. The elimination of schistosomiasis japonica from Japan shows what is possible, using multiple lines of approach, but the clear and present danger is that the whole edifice of schistosome control is balanced on the monotherapy of praziquantel, and the development of drug resistance could topple that.