Date Published: August 28, 2018
Publisher: Public Library of Science
Author(s): Neima Briggs, Junfei Wei, Leroy Versteeg, Bin Zhan, Brian Keegan, Ashish Damania, Jeroen Pollet, Kelly S. Hayes, Coreen Beaumier, Christopher A. Seid, Jamie Leong, Richard K. Grencis, Maria Elena Bottazzi, K. Jagannadha Sastry, Peter J. Hotez, Edward Mitre.
Human whipworm (Trichuris trichiura) infects approximately 1 in 15 people worldwide, representing the leading infectious cause of colitis and subsequent, inflammatory bowel disease (IBD). Current control measures focused on mass deworming have had limited success due to low drug efficacies. Vaccination would be an ideal, cost-effective strategy to induce protective immunity, leading to control of infection and transmission. Here we report the identification of whey acidic protein, a whipworm secretory protein, as a strong immunogen for inducing protective efficacy in a surrogate mouse T. muris infection model. The recombinant WAP protein (rTm-WAP49), as well as a single, highly conserved repeat within WAP (fragment 8) expressed as an Na-GST-1 fusion protein (rTm-WAP-F8+Na-GST-1), generate a strong T helper type 2 (Th2) immune response when delivered as subcutaneous vaccines formulated with Montanide ISA 720. Oral challenge with T. muris infective eggs following vaccination led to a significant reduction in worm burden of 48% by rTm-WAP49 and 33% by rTm-WAP-F8+Na-GST-1. The cellular immune correlates of protection included significant antigen-specific production of Th2 cytokines IL-4, IL-9, and IL-13 by cells isolated from the vaccine-draining inguinal lymph nodes, parasite-draining mesenteric lymph nodes, and spleen in mice vaccinated with either rTm-WAP49 or rTm-WAP-F8+Na-GST-1. The humoral immune correlates included a high antigen-specific ratio of IgG1 to IgG2a, without eliciting an IgE-mediated allergic response. Immunofluorescent staining of adult T. muris with WAP antisera identified the worm’s pathogenic stichosome organ as the site of secretion of native Tm-WAP protein into the colonic mucosa. Given the high sequence conservation for the WAP proteins from T. muris and T. trichiura, the results presented here support the WAP protein to be further evaluated as a potential human whipworm vaccine candidate.
It is estimated that 465 million people are living with whipworms (Trichuris trichiura) in their colon, predominately in the developing nations of the Americas, Asia, and Africa. In children, T. trichiura infections cause chronic colitis, resulting in nutritional deficiencies, growth stunting, and cognitive impairment . In adults, Trichuris-induced colitis is being studied as a possible major environmental driver of inflammatory bowel disease . The current approach to human trichuriasis control relies on mass deworming campaigns with yearly, single dose albendazole or mebendazole . However, this approach has shown limited benefit against trichuriasis due to low efficacy, high rates of post-treatment reinfection, and failure to co-implement adequate sanitation and hygiene practices [4,5]. It is therefore important to design better or alternative strategies to helminth prevention, including the development of a trichuriasis vaccine . While there is no direct evidence that humans develop protective immunity to trichuriasis, epidemiological studies suggest that there is an age-related reduction in worm burden and adult worm longevity in humans beginning in adolescence that may be due to acquired immunity [7,8].
With nearly a half-billion people afflicted, trichuriasis is one the most prevalent infectious diseases in the world, and yet there are limited prophylactic and therapeutic options. Using the T. muris infection of AKR mouse as a surrogate model of T. trichiura infection in humans, here we describe the identification of a whey acidic protein (WAP) as a highly expressed secretory protein from the stichosome of the worm that is effective in inducing a strong Th2 immunity and significant protection against oral challenge with T. muris eggs. The recombinant WAP protein (rTm-WAP49) as well as the highly conserved fragment 8 of WAP expressed as a fusion protein with Na-GST-1 tag (rTm-WAP-F8+Na-GST-1) were equally effective in inducing protective Th2 immunity.