Antibodies fused to innate immune molecules reduce initiation of Cryptosporidium parvum infection in mice

Identification of the glycopeptide epitope recognized by a protective Cryptosporidium monoclonal antibody

Cryptosporidium species are a leading cause of pediatric diarrheal disease and death in low- and middle-income countries and pose a particular threat to immunocompromised individuals. As a zoonotic pathogen, Cryptosporidium can have devastating effects on the health of neonatal calves. Despite its impact on human and animal health, consistently effective drug treatments for cryptosporidiosis are lacking and no vaccine is available. We previously showed that C. parvum mucin-like glycoproteins, gp40, and gp900 express an epitope identified by a monoclonal antibody 4E9. 4E9 neutralized C. parvum infection in vitro as did glycan-binding proteins specific for the Tn antigen (GalNAc-α1-S/T). Here, we show that 4E9 ameliorates disease in vivo in a calf challenge model. The 4E9 epitope is present on C. hominis in addition to C. parvum gp40 and gp900 and localizes to the plasma membrane and dense granules of invasive and intracellular stages. To characterize the epitope recognized by 4E9, we probed a glycan array containing over 500 defined glycans together with a custom-made glycopeptide microarray containing glycopeptides from native mucins or C. parvum gp40 and gp15. 4E9 exhibited no binding to the glycan array but bound strongly to glycopeptides from native mucins or gp40 on the glycopeptide array, suggesting that the antibody epitope contains both peptide and glycan moieties. 4E9 only recognized glycopeptides with adjacent S or T residues in the motif S*/T*-X-S*/T* where X = 0 or 1. These data define the 4E9 epitope and have implications for the inclusion of the epitope in the development of vaccines or other immune-based therapies.

Genomics and molecular epidemiology of Cryptosporidium species

Cryptosporidium is one of the most widespread protozoan parasites that infects domestic and wild animals and is considered the second major cause of diarrhea and death in children after rotavirus. So far, around 20 distinct species are known to cause severe to moderate infections in humans, of which Cryptosporidium hominis and Cryptosporidium parvum are the major causative agents. Currently, ssurRNA and gp60 are used as the optimal markers for differentiating species and subtypes respectively. Over the last decade, diagnostic tools to detect and differentiate Cryptosporidium species at the genotype and subtype level have improved, but our understanding of the zoonotic and anthroponotic transmission potential of each species is less clear, largely because of the paucity of high resolution whole genome sequencing data for the different species. Defining which species possess an anthroponotic vs. zoonotic transmission cycle is critical if we are to limit the spread of disease between animals and humans. Likewise, it is unclear to what extent genetic hybridization impacts disease potential or the emergence of outbreak strains. The development of high resolution genetic markers and whole genome sequencing of different species should provide new insights into these knowledge gaps. The aim of this review is to outline currently available molecular epidemiology and genomics data for different species of Cryptosporidium.

The in vitro and ex vivo effect of Auranta 3001 in preventing Cryptosporidium hominis and Cryptosporidium parvum infection

Background

Cryptosporidium is a major cause of diarrhea worldwide in both humans and farm animals with no completely effective treatment available at present. In this study, we assessed the inhibitory effect of different concentrations of Auranta 3001 (0.1, 0.5 and 1%), a novel natural feed supplement, on C. hominis and C. parvum invasion of human ileocecal adenocarcinoma (HCT-8), bovine primary cells and C. parvum invasion of HCT-8, bovine primary cells and bovine intestinal biopsies. The effect of the feed supplement on the production of pro-inflammatory cytokines IL-8 and INF-γ, the anti-inflammatory cytokine IL-10, the expression of CpSUB1 protease gene during infection was also assessed by quantitative PCR (q-PCR). Transepithelial electrical resistance (TEER) was employed to measure the integrity of tight junction dynamics of the culture models.

Results

Pre-treatment of intestinal cells or oocysts with the Auranta 3001 significantly reduced the invasiveness of C. hominis and C. parvum against HCT-8 and bovine primary cells in a dose dependent manner. The most pronounced reduction in the invasiveness of both parasites was observed when Auranta 3001 was present during infection. Levels of IL-8 were significantly reduced in both HCT-8 and bovine primary cells, while the levels of INF-γ and IL-10 showed opposite trends in the two cell lines during infection in the presence of Auranta 3001. CpSUB1 gene protease expression, which mediates infection, was significantly reduced suggesting that this enzyme is a possible target of Auranta 3001.

Conclusions

Although, C. hominis and C. parvum use different invasion mechanisms to infect cells, the novel feed additive can significantly attenuate the entry of Cryptosporidium in HCT-8 cells, primary bovine cells and bovine intestinal biopsies and thus provide an alternative method to control cryptosporidiosis.

5-Aminopyrazole-4-Carboxamide-Based Compounds Prevent the Growth of Cryptosporidium parvum

Cryptosporidium parvum calcium-dependent protein kinase 1 (CpCDPK1) is a promising target for drug development against cryptosporidiosis. We report a series of low-nanomolar CpCDPK1 5-aminopyrazole-4-carboxamide (AC) scaffold inhibitors that also potently inhibit C. parvum growth in vitro Correlation between anti-CpCDPK1 and C. parvum growth inhibition, as previously reported for pyrazolopyrimidines, was not apparent. Nonetheless, lead AC compounds exhibited a substantial reduction of parasite burden in the neonatal mouse cryptosporidiosis model when dosed at 25 mg/kg.

Novel Bumped Kinase Inhibitors Are Safe and Effective Therapeutics in the Calf Clinical Model for Cryptosporidiosis

Cryptosporidiosis, caused by the apicomplexan parasite Cryptosporidium parvum, is a diarrheal disease that has produced a large global burden in mortality and morbidity in humans and livestock. There are currently no consistently effective parasite-specific pharmaceuticals available for this disease. Bumped kinase inhibitors (BKIs) specific for parasite calcium-dependent protein kinases (CDPKs) have been shown to reduce infection in several parasites having medical and veterinary importance, including Toxoplasma gondii, Plasmodium falciparum, and C. parvum In the present study, BKIs were screened for efficacy against C. parvum infection in the neonatal mouse model. Three BKIs were then selected for safety and clinical efficacy evaluation in the calf model for cryptosporidiosis. Significant BKI treatment effects were observed for virtually all clinical and parasitological scoring parameters, including diarrhea severity, oocyst shedding, and overall health. These results provide proof of concept for BKIs as therapeutic drug leads in an animal model for human cryptosporidiosis.

CCL20 Displays Antimicrobial Activity Against Cryptosporidium parvum, but Its Expression Is Reduced During Infection in the Intestine of Neonatal Mice

CCL20 is a chemokine with antimicrobial activity. We investigated its expression and role during neonatal cryptosporidiosis, a worldwide protozoan enteric disease leading to severe diarrhea. Surprisingly, during infection by Cryptosporidium parvum, CCL20 production by the intestine of neonatal mice is reduced by a mechanism independent both of the enteric flora and of interferon γ, a key cytokine for the resolution of this infection. However, oral administration of recombinant CCL20 to neonatal mice significantly reduced the parasite load by a mechanism that was independent of immune cell recruitment and occurred instead by direct cytolytic activity on free stages of the parasite. MiR21 functionally targets CCL20 and is upregulated during the infection, thus contributing to the downregulation of the chemokine. Our findings demonstrate for the first time the direct antiparasitic activity of CCL20 against an enteric protozoan and its downregulation during C. parvum infection, which is detrimental to parasite clearance.

Biochemical and functional characterization of CpMuc4, a Cryptosporidium surface antigen that binds to host epithelial cells

Cryptosporidium spp. are intracellular apicomplexan parasites that cause outbreaks of waterborne diarrheal disease worldwide. Previous studies had identified a Cryptosporidium parvum sporozoite antigen, CpMuc4, that appeared to be involved in attachment and invasion of the parasite into intestinal epithelial cells. CpMuc4 is predicted to be O- and N-glycosylated and the antigen exhibits an apparent molecular weight 10kDa larger than the antigen expressed in Escherichia coli, indicative of post-translational modifications. However, lectin blotting and enzymatic and chemical deglycosylation did not identify any glycans on the native antigen. Expression of CpMuc4 in Toxoplasma gondii produced a recombinant protein of a similar molecular weight to the native antigen. Both purified native CpMuc4 and T. gondii recombinant CpMuc4, but not CpMuc4 expressed in E. coli, bind to fixed Caco-2A cells in a dose dependent and saturable manner, suggesting that this antigen bears epitopes that bind to a host cell receptor, and that the T. gondii recombinant CpMuc4 functionally mimics the native antigen. Binding of native CpMuc4 to Caco2A cells could not be inhibited with excess CpMuc4 peptide, or an excess of E. coli recombinant CpMuc4. These data suggest that CpMuc4 interacts directly with a host cell receptor and that post-translational modifications are necessary for the antigen to bind to the host cell receptor. T. gondii recombinant CpMuc4 may mimic the native antigen well enough to serve as a useful tool for identifying the host cell receptor and determining the role of native CpMuc4 in host cell invasion.

Prospects for immunotherapy and vaccines against Cryptosporidium

Cryptosporidium spp is a ubiquitous parasite that has long been recognized as a frequent cause of protozoal diarrhea in humans. While infections in immunocompetent hosts are usually self-limiting, immunocompromised individuals can develop severe, chronic, and life-threatening illness. Vaccine development or immunotherapy that prevents disease or reduces the severity of infection is a relevant option since efficacious drug treatments are lacking. In particular, children in developing countries might benefit the most from a vaccine since cryptosporidiosis in early childhood has been reported to be associated with subsequent impairment in growth, physical fitness, and intellectual capacity. In this review, immunotherapies that have been used clinically are described as well as experimental vaccines and their evaluation in vivo.

Antibody fusions reduce onset of experimental Cryptosporidium parvum infection in calves

Cryptosporidium parvum is one of the main causes of diarrhea in neonatal calves resulting in significant morbidity and economic losses for producers worldwide. We have previously demonstrated efficacy of a new class of antimicrobial antibody fusions in a neonatal mouse model for C. parvum infection. Here, we extend efficacy testing of these products to experimental infection in calves, the principal target species. Neonatal calves were challenged with C. parvum oocysts and concomitantly treated with antibody–biocide fusion 4H9-G1-LL37 over the course of four days. This resulted in reduced severity of the disease when compared to control animals. Overall clinical health parameters showed significant improvement in treated animals. Oocyst shedding was reduced in treated when compared to control animals. Control of oocyst shedding is a prerequisite for breaking the cycle of re-infection on dairy farms. Antibody–biocide fusion products thus have the potential to reduce the impact of the infection in both individual animals and in the herd.

Cryptosporidiosis-an overview

Apicomplexan protozoan parasites of the genus Cryptosporidium infect the gastrointestinal tract and lungs of a wide variety of animals, including humans. The majority of human infections are due to either Cryptosporidium hominis (C. hominis) and/or Cryptosporidium parvum (C. parvum). The parasite has a complex life cycle that includes both asexual and sexual stages. While there are invasive free living stages, proliferation and differentiation take place within a unique parasitrophorous vacuole under the host cell brush border but outside the host cell cytoplasm. Infection is spread by environmentally resistant spores that primarily contaminate drinking water and occasionally food sources, which may cause significant outbreaks of diarrhea that generally lasts less than 2 w in immunocompetent individuals. In immunodeficient or immunosuppressed individuals, diarrhea may be copious and can result in significant morbidity and mortality, particularly in AIDS patients. Although diagnosis is relatively simple, effective drug treatment, particulary for infections in immunodeficient patients, has not been uniformly successful. This overview summarizes the species known to infect humans, aspects of the parasite life cycle, sources of infection, the pathophysiology of cryptosporidiosis, the immune response to infection, diagnosis, treatment and some aspects of cryptosporidiosis in China.

Phospholipases and cationic peptides inhibit Cryptosporidium parvum sporozoite infectivity by parasiticidal and non-parasiticidal mechanisms

The apicomplexan parasite Cryptosporidium parvum is an important cause of diarrhea in humans and cattle, and it can persistently infect immunocompromised hosts. No consistently effective parasite-specific pharmaceuticals or immunotherapies for control of cryptosporidiosis are presently available. The innate immune system represents the first line of host defense against a range of infectious agents, including parasitic protozoa. Several types of antimicrobial peptides and proteins, collectively referred to herein as biocides, constitute a major effector component of this system. In the present study, we evaluated lactoferrin, lactoferrin hydrolysate, 5 cationic peptides (lactoferricin B, cathelicidin LL37, indolicidin, β-defensin 1, β-defensin 2), lysozyme, and 2 phospholipases (phospholipase A2, and phosphatidylinositol-specific phospholipase C) for anti-cryptosporidial activity. The biocides were evaluated either alone or in combination with 3E2, a monoclonal antibody (MAb) against C. parvum that inhibits sporozoite attachment and invasion. Sporozoite viability and infectivity were used as indices of anti-cryptosporidial activity in vitro. All biocides except lactoferrin had a significant effect on sporozoite viability and infectivity. Lactoferrin hydrolysate and each of the 5 cationic peptides were highly parasiticidal and strongly reduced sporozoite infectivity. While each phospholipase also had parasiticidal activity, it was significantly less than that of lactoferrin hydrolysate and each of the cationic peptides. However, each phospholipase reduced sporozoite infectivity comparably to that observed with lactoferrin hydrolysate and the cationic peptides. Moreover, when 3 of the cationic peptides (cathelicidin LL37, β-defensin 1, and β-defensin 2) were individually combined with MAb 3E2, a significantly greater reduction of sporozoite infectivity was observed over that by 3E2 alone. In contrast, reduction of sporozoite infectivity by a combination of either phospholipase with MAb 3E2 was no greater than that by 3E2 alone. These collective observations suggest that cationic peptides and phospholipases neutralize C. parvum by mechanisms that are predominantly either parasiticidal or non-parasiticidal, respectively.