Intranasal vaccination in mice with an attenuated Salmonella enterica Serovar 908htr A expressing Cp15 of Cryptosporidium: Impact of malnutrition with preservation of cytokine secretion

Cryptosporidium is a protozoan parasite associated with acute and persistent diarrhea that, even in asymptomatic persons, can impair normal growth and potentially cognitive and physical development in young children. The recent availability of the complete gene sequence for Cryptosporidium hominis antigen Cp15 allows examination of innovative vaccine regimens involving intra-nasal antigen priming with live bacterial vectors applicable to human populations. We used a recently described weaned mouse model of cryptosporidiosis, where nourished and malnourished vaccinated mice receive the Cp15 antigen recombinant with cytolysinA on a Salmonella serovar Typhi CVD 908-htr A vector, followed by parenteral exposure to antigen with adjuvant. After challenge with Cryptosporidium oocysts via gavage, parameters of infection and disease (stool shedding of parasites, growth rates) were quantified, and serum/lymphoid tissue harvested to elucidate the Cp15-specific adaptive immune response. In vaccinated nourished mice, the regimen was highly immunogenic, with strong antigen-specific IL-6 and IFN-γ secretion and robust Cp15-specific immunoglobulin titers. In vaccinated malnourished mice, secretion of cytokines, particularly IFN-γ, and antigen-specific humoral immunity were generally undiminished despite protein deprivation and stunted growth. In contrast, after natural (oral) challenge with an identical inoculum of Cryptosporidium oocysts, cytokine and humoral responses to Cp15 were less than one-fourth those in vaccinated mice. Nevertheless, vaccination resulted in only transient reduction in stool shedding of parasites and was not otherwise protective against disease. Overall, immunogenicity for a C. hominis antigen was documented in mice, even in the setting of prolonged malnutrition, using an innovative vaccine regimen involving intra-nasal antigen priming with a live enteric bacterial vector, that has potential applicability to vulnerable human populations irrespective of nutritional status.