Plasmodium falciparum multi-epitope string of pre-erythrocytic antigens (ME)

The Plasmodium falciparum multi-epitope (ME) string of pre-erythrocytic antigens is a synthetic recombinant construct designed to elicit a broad and potent cellular immune response against the liver stage of malaria (NIH, 2020). It typically comprises approximately 20 epitopes—including B-cell, CD4+ T-cell, and CD8+ T-cell epitopes—derived from several key pre-erythrocytic proteins such as the circumsporozoite protein (CSP), liver-stage antigen 1 (LSA-1), LSA-3, and exported antigen 1 (EXP-1) (Journal of Infectious Diseases, 2015). This string is most frequently utilized as a fusion protein with the thrombospondin-related adhesion protein (TRAP), creating the ME-TRAP vaccine candidate (Nature Communications, 2013). Delivered through viral vectors like Chimpanzee Adenovirus 63 (ChAd63) and Modified Vaccinia virus Ankara (MVA), the ME string aims to prime and boost the host's immune system to recognize and destroy infected hepatocytes before the parasite can transition to the symptomatic blood stage (PLoS One, 2013). The construct is specifically engineered to provide broad population coverage by including epitopes that bind to a wide array of Human Leukocyte Antigen (HLA) alleles (NIH, 2020). While clinical trials have demonstrated high immunogenicity and some degree of sterile protection in malaria-naive individuals, achieving high and durable efficacy in endemic populations remains a significant challenge (PLoS One, 2016). The vaccine's mechanism of action relies on the induction of unnatural immunity, where the magnitude of the T-cell response exceeds that seen in natural infections (NIH, 2014). Safety profiles for vaccines incorporating this string generally show acceptable reactogenicity, with common side effects being transient and localized (NIH, 2020).

Other names

Multi-epitope stringMEMultiple epitope stringME-TRAP (fusion component)

Induction of potent CD8+ and CD4+ T-cell responses against liver-stage Plasmodium falciparum parasites to prevent progression to the blood stage.