Ryan Laboratory: Edward T. Ryan, MD

Overview

Our research focuses on host-bacterial pathogen interactions and immune responses, with a particular focus on enteric infections and the development of vaccines protective against enteric infections, and development of diagnostic assays. Specific focus areas include Vibrio cholerae, the cause of cholera; Salmonella enterica, the causes of typhoid and paratyphoid fever; and Shigella spp, the cause of bacillary dysentery-shigellosis. We work in collaborative efforts with researchers at the International Centre for Diarrhoeal Disease Research in Dhaka Bangladesh (ICDDR,B).

Research Projects

Immune responses during cholera

In a collaborative effort with researchers at the International Centre for Diarrhoeal Disease Research in Dhaka, Bangladesh (ICDDR,B), we are evaluating immune responses in humans infected with Vibrio cholerae, the cause of cholera. V. cholerae is endemic in over 50 countries, infects approximately 3-5 million individuals globally, and results in the death of tens of thousands of individuals each year. Individuals most affected by cholera are those most impoverished, especially those lacking safe water and sanitary facilities, as well as individuals displaced by war, famine, disasters, and conflict. Cholera can be explosively epidemic, and the global burden of cholera may well increase with severe weather events and increasing informal urbanization. V. cholerae is a human-restricted infection, and current cholera vaccines provide relatively short-term protection against disease, especially in young children. The mediators of protective immunity against cholera are poorly understood. To address this, we are applying a number of high throughput and platform technologies to assess innate and adaptive immune responses in humans with cholera and their household contacts, stratifying responses in the latter by subsequent protection from disease, and comparing responses in the former to those that occur in recipients of current cholera vaccines. A goal of these studies is to identify the mediators of protection against cholera, in order to advance improved prevention strategies, as well as to advance vaccine development and deployment.

Pertinent to this and most importantly, we have recently identified a central mechanism of protection against cholera in humans: antibodies that target the polysaccharide that surrounds the Vibrio cholerae bacteria (O-specific polysaccharide; OSP) bind to V. cholerae in the intestinal lumen of infected humans, thereby activating a phage/membrane stress response system in the bacteria involving cyclic di-GMP bacterial signaling. Anti-OSP antibodies essentially physiologically shift V. cholerae from a virulent, toxin-expressing, motile phenotype to a hypovirulent, hypometabolic, sessile organism expressing an extracellular matrix component of V. cholerae biofilm with significantly decreased cholera toxin expression. This profound impact results in a complete disruption of the sequence of bacterial pathogenic events that would otherwise occur in the intestinal lumen and that are required to result in the watery diarrhea characteristic of cholera. Our findings strongly suggest that next generation cholera vaccines should target inducing high level and durable anti-OSP responses, especially in young children who bear a large burden of cholera and in whom current cholera vaccines have only low and short duration efficacy.

Host-pathogen interactions during typhoid fever

In a collaborative effort with researchers at the International Centre for Diarrhoeal Disease Research in Dhaka, Bangladesh (ICDDR,B), we are evaluating host-pathogen interactions and immune responses in humans infected with Salmonella enterica serotype Typhi (the cause of typhoid fever) and S. Paratyphi (the cause of paratyphoid fever). Together, S. Typhi and S. Paratyphi cause approximately 20 million cases of enteric fever world-wide, resulting in approximately 200,000 deaths each year. Most of these deaths occur in impoverished children and young adults. Although usually caused by S. Typhi, one in four cases of enteric fever is caused by S. Paratyphi in many areas of the world. S. Typhi and S. Paratyphi are particularly common among urban residents in informal settlements and slums, although any individual lacking safe water and sanitary facilities is at risk of infection. Vaccines against S. Typhi provide only 50-60% protection against disease for 2-5 years, and, at present, there is no commercially available vaccine against S. Paratyphi. There is also no good point-of-care test to diagnose individuals with enteric fever, and S. Typhi and S. Paratyphi are becoming increasingly resistant to antimicrobial agents.To address this, we are evaluating host-pathogen interactions directly in humans infected with S. Typhi and S. Paratyphi. We are applying a number of technologies to evaluate innate and adaptive immune responses directly in humans infected with S. Typhi and S. Paratyphi in Bangladesh, and we are evaluating bacterial responses in humans during these human-restricted infections. The goal of these studies is to develop improved diagnostic assays, antimicrobial agents, and preventative strategies against these infections.

Host-pathogen interactions during shigellosis

Shigellosis is another leading cause of death of children under 5 years of age in LMIC settings and among displaced populations and refugees. Building upon our cholera-related work, we initiated analysis of immune responses and host-pathogen interactions during shigellosis, including in young children in Bangladesh. This work includes assessing the relationship between functional antibody activity and protection from shigellosis, and we are working with colleagues at the Ragon Institute and the icddr,b in Bangladesh. We are particularly interested in assessing functional antibody attributes that mediate protection against shigellosis, including those that target the polysaccharide that surrounds the bacteria (O-specific polysaccharide; OSP). We have already identified that functional (not total) OSP-specific IgA responses that activate polymorphonuclear cells (PMNs) mediated protection against shigella infection in an endemic area, and that Fc-dependent OSP-specific IgG responses activate monocytes and that such activation can attract PMNs. In brief, we are beginning to tease apart the actual mechanism of protection against shigellosis in low-resource settings (as we previously did for cholera).

Immunization approaches for enteric infection

A fundamental challenge facing many enteric and mucosal vaccines is their inability to induce long-term protective immunity. Many of these vaccines may not be prominent inducers of memory cells, which play critical roles in mediating long-term protection against disease. Using our analysis of memory B and T cell induction during wild-type human enteric infection in Bangladesh, we are evaluating the ability of a number of vaccination approaches and strategies to induce long-term memory responses protective against mucosal and enteric infections, including development of enteric conjugate vaccines, and analysis of oral-parenteral prime-boosting approaches. We are performing components of this work with colleagues at the International Vaccine Institute (IVI), Seoul, Korea.

Global TravEpiNet (GTEN)

To extend our analysis of infections associated with living in, traveling through, or immigrating from resource-limited areas, we also work with the U.S. Centers for Disease Control and Prevention through the GTEN (Global TravEpiNet; Global Travelers’ Epidemiology Network) Program. GTEN’s mission is to advance the health of American residents who travel internationally, as well as to lessen the likelihood of disease importation into home communities. GTEN-related resources are available at Heading Home Healthy.