Sm-p80-Based Schistosomiasis Vaccine: Preparation for Human Clinical Trials

Abstract

Mass antiparasitic drug administration programs and other control strategies have made important contributions in reducing the global prevalence of helminths. Schistosomiasis, however, continues to spread to new geographic areas. The advent of a viable vaccine and its deployment, coupled with existing control efforts, is expected to make significant headway towards sustained schistosomiasis control. In 2016, Science ranked the schistosomiasis vaccine as one of the top 10 vaccines that needs to be urgently developed. A vaccine that is effective against geographically distinct forms of intestinal/hepatic and urinary disease is essential to make a meaningful impact in global reduction of the disease burden. In this opinion article, we focus on salient features of schistosomiasis vaccines in different phases of the clinical development pipeline and highlight the Sm-p80-based vaccine which is now being prepared for human clinical trials.

Keywords: Schistosoma haematobium; Schistosoma japonicum; Schistosoma mansoni; neglected tropical disease (NTD); protective immunity; schistosomiasis; vaccine.

Figure 1

Worldwide distribution of schistosomiasis. Reproduced from http://wwwnc.cdc.gov/travel/yellowbook/2016/infectious-diseases-related-to-travel/schistosomiasis.

Figure 2

Sm-p80 Vaccine Efficacy at Different Levels of Infection, Disease, and Transmission. The Sm-p80 vaccine can lead to a reduction in transmission, by decreasing expulsion of eggs into the environment (1). The vaccine also has detrimental effects on eggs and inhibits the hatching of eggs into miracidia (2). The Sm-p80 vaccine has robust prophylactic efficacy due to its effectiveness against schistosomular development into adult worms (5). This vaccine is the only vaccine which has been shown to eliminate already established adult worms thus exhibiting a therapeutic efficacy (6). The vaccine’s effectiveness is also pronounced in reducing the egg retention in tissues (anti-pathology efficacy) (7).

Figure 3

Development Roadmap for a Schistosomiasis Vaccine. Development of a vaccine entails many different aspects including identification of appropriate vaccine target; evaluation of the vaccine candidate in efficacy and disease animal models; and vaccine process development for clinical development. This long and arduous process can take decades and appreciable amount of funding is needed to develop a vaccine from bench to bedside. Abbreviations: GLP, good laboratory practices; GMP, good manufacturing practices.