The expression of PF3D7_1146100; a novel, essential Plasmodium falciparum antigen, and its evaluation as a target of protective immunity to clinical malaria.

Abstract

The use of reverse vaccinology in vaccine candidate antigen discovery has led to identification of many Plasmodium falciparum novel antigens. Some of these antigens are essential for parasite survival and could be evaluated as targets of protective immunity to clinical malaria that is acquired naturally. Targeting essential antigens identified through functional genomic studies involving loss-of-function, could aid in the development of an effective next generation sub-unit vaccine. For these studies to be successful, the antigens must be expressed in their correctly folded structure in a heterologous expression system. This study aimed at expressing PF3D7_1146100, one of the novel, essential P. falciparum antigens, and assess the protective role of antibodies against it in clinical malaria using sera from a prospective cohort of children (N=343) from Junju, Kilifi, Kenya. PF3D7_1146100 was sub-cloned into pTT28, an expression vector, and transfected into Expi 293F cells for recombinant protein expression. The antigen was purified and characterized using SDS PAGE and Western blotting. Immunogenicity of the recombinant protein and the correlation between its immune responses and protection against clinical malaria was determined using indirect ELISA. In a univariate logistic regression analysis, anti-PF3D7_1146100 antibodies were correlated with protection against clinical malaria at an odds ratio of 0.63(0.42-0.95) at 95% C.I and p value=0.027. After adjusting for age and exposure, the odds ratio was 0.73(0.44-1.16) at 95% C.I with a p-value=0.176. The essentiality and immunogenicity of this antigen indicates that it is a potential vaccine candidate targeting the blood stage of the parasite. The successful expression of PF3D7_1146100 and its analysis as a target of the immune system, provides a basis for studying other novel essential and conserved antigens. This also provides an opportunity to study its function, a knowledge which could contribute to vaccine and drug development not only against P. falciparum but also other Apicomplexa organisms.