Delayed Time to Cryptosporidiosis in Bangladeshi Children is Associated with Greater Fecal IgA against Two Sporozoite-Expressed Antigens

Specific Cryptosporidium antigens associate with reinfection immunity and protection from cryptosporidiosis

There is no vaccine to protect from cryptosporidiosis, a leading cause of diarrhea in infants in low- and middle-income countries. Here, we comprehensively identified parasite antigens associated with protection from reinfection. A Cryptosporidium protein microarray was constructed by in vitro transcription and translation of 1,761 C. parvum, C. hominis, or C. meleagridis antigens, including proteins with a signal peptide and/or a transmembrane domain. Plasma IgG and/or IgA from Bangladeshi children longitudinally followed for cryptosporidiosis from birth to 3 years of age allowed for identification of 233 seroreactive proteins. Seven of these were associated with protection from reinfection. These included Cp23, Cp17, Gp900, and 4 additional antigens - CpSMP1, CpMuc8, CpCorA and CpCCDC1. Infection in the first year of life, however, often resulted in no detectable antigen-specific antibody response, and antibody responses, when detected, were specific to the infecting parasite genotype and decayed in the months after infection. In conclusion, humoral immune responses against specific parasite antigens were associated with acquired immunity. While antibody decay over time and parasite genotype-specificity may limit natural immunity, this work serves as a foundation for antigen selection for vaccine design.

Children develop Immunity to cryptosporidiosis in a high transmission intensity area

Background

Cryptosporidium is one of the top causes of diarrhea in Bangladesh infants. Cryptosporidium infections lead to the production of antibody immune responses, which were associated with a decrease in parasite burden and decreased disease severity in subsequent infections.

Methods

We conducted a longitudinal study of cryptosporidiosis from birth to five years of age in an urban slum of Dhaka Bangladesh. We then retrospectively tested the concentration of anti-Cryptosporidium Cp17 or Cp23 IgA in surveillance stool samples collected from 54 children during their first 3 years of life by enzyme-linked immunosorbent assay (ELISA). We also assessed the concentration of both IgA and IgG antibodies specific to Cryptosporidium Cp17 and Cp23 in the concentration of anti-Cryptosporidium Cp17 or Cp23 IgA and IgG antibodies in the children's plasma (1- 5 years).

Results

The seroprevalence of both anti- Cp23 and Cp17 antibodies was high at ≤ one year of age and reflected the exposure of these children in this community to cryptosporidiosis. In Bangladesh, the prevalence of cryptosporidiosis is high during the rainy season (June to October) but decreases during the dry season. In younger infants' plasma anti-Cp17 and Cp23 IgG and anti-Cp17 IgA levels were markedly increased during the rainy season in line with the higher initial exposure to the parasite at this time. Both anti-Cp17, anti-Cp23 fecal IgA and the parasite burden declined during repeat infections.

Conclusions

We found that anti-Cryptosporidium plasma and fecal antibody levels in children could contribute to the decrease in new infections in this study population.

Conservation, abundance, glycosylation profile, and localization of the TSP protein family in Cryptosporidium parvum

Cryptosporidium parvum is a zoonotic apicomplexan parasite and a common cause of diarrheal disease worldwide. The development of vaccines to prevent or limit infection remains an important goal for tackling cryptosporidiosis. At present, the only approved vaccine against any apicomplexan parasite targets a conserved adhesin possessing a thrombospondin repeat domain. C. parvum possesses 12 orthologous thrombospondin repeat domain-containing proteins known as CpTSP1-12, though little is known about these potentially important antigens. Here, we explore the architecture and conservation of the CpTSP protein family, as well as their abundance at the protein level within the sporozoite stage of the life cycle. We examine the glycosylation states of these proteins using a combination of glycopeptide enrichment techniques to demonstrate that these proteins are modified with C-, O-, and N-linked glycans. Using expansion microscopy, and an antibody against the C-linked mannose that is unique to the CpTSP protein family within C. parvum, we show that these proteins are found both on the cell surface and in structures that resemble the secretory pathway of C. parvum sporozoites. Finally, we generated a polyclonal antibody against CpTSP1 to show that it is found at the cell surface and within micronemes, in a pattern reminiscent of other apicomplexan motility-associated adhesins, and is present both in sporozoites and meronts. This work sheds new light on an understudied family of C. parvum proteins that are likely to be important to both parasite biology and the development of vaccines against cryptosporidiosis.

Development of Two Mouse Models for Vaccine Evaluation against Cryptosporidiosis

Cryptosporidiosis was shown a decade ago to be a major contributor to morbidity and mortality of diarrheal disease in children in low-income countries. A serious obstacle to develop and evaluate immunogens and vaccines to control this disease is the lack of well-characterized immunocompetent rodent models. Here, we optimized and compared two mouse models for the evaluation of vaccines: the Cryptosporidium tyzzeri model, which is convenient for screening large numbers of potential mixtures of immunogens, and the Cryptosporidium parvum-infected mouse pretreated with interferon gamma-neutralizing monoclonal antibody.

Advances in therapeutic and vaccine targets for Cryptosporidium: Challenges and possible mitigation strategies

Cryptosporidium is known to be the second most common diarrheal pathogen in children, causing potentially fatal diarrhea and associated with long-term growth stunting and cognitive deficits. The only Food and Drug Administration-approved treatment for cryptosporidiosis is nitazoxanide, but this drug has not shown potentially effective results in susceptible hosts. Therefore, a safe and effective drug for cryptosporidiosis is urgently needed. Cryptosporidium genome sequencing analysis may help develop an effective drug, but both in vitro and in vivo approaches to drug evaluation are not fully standardized. On the other hand, the development of partial immunity after exposure suggests the possibility of a successful and effective vaccine, but protective surrogates are not precise. In this review, we present our current perspectives on novel cryptosporidiosis therapies, vaccine targets and efficacies, as well as potential mitigation plans, recommendations and perceived challenges.

Nonsterile immunity to cryptosporidiosis in infants is associated with mucosal IgA against the sporozoite and protection from malnutrition

We conducted a longitudinal study of cryptosporidiosis from birth to three years of age in an urban slum of Dhaka Bangladesh. Fecal DNA was extracted from monthly surveillance samples and diarrheal stool samples collected from 392 infants from birth to three years. A pan-Cryptosporidium qPCR assay was used to identify sub-clinical and symptomatic cryptosporidiosis. Anthropometric measurements were collected quarterly to assess child nutritional status. 31% (121/392) of children experienced a single and 57% (222/392) multiple infections with Cryptosporidium. Repeat infections had a lower burden of parasites in the stool (Cq slope = -1.85; p<0.0001) and were more likely to be sub-clinical (Chi square test for trend; p = 0.01). Repeat infections were associated with the development of growth faltering (Pearson correlation = -0.18; p = 0.0004). High levels of fecal IgA antibodies against the Cryptosporidium Cp23 sporozoite protein at one year of life were associated with a delay in reinfection and amelioration of growth faltering through three years of life (HAZ IgA high responders -1.323 ± 0.932 versus HAZ -1.731 ± 0.984 p = 0.0001). We concluded that nonsterile immunity to cryptosporidiosis in young children was associated with high levels of mucosal IgA anti-Cp23 and protection from diarrhea and growth faltering. Trial Registration: NCT02764918.