Differential T‐cell responses to a chimeric Plasmodium falciparum antigen; UB05‐09, correlates with acquired immunity to malaria

Abstract

The development of a sterilizing and cost-effective vaccine against malaria remains a major problem despite recent advances. In this study, it is demonstrated that two antigens of P. falciparum UB05, UB09 and their chimera UB05-09 can serve as protective immunity markers by eliciting higher T-cell responses in malaria semi-immune subjects (SIS) than in frequently sick subjects (FSS) and could be used to distinguish these two groups. UB05, UB09 and UB05-09 were cloned, expressed in E. coli, purified and used to stimulate PBMCs isolated from 63 subjects in a malaria endemic area, for IFN-γ production, which was measured by the ELISpot assay. The polymorphism of UB09 gene in the malaria infected population was also studied by PCR/sequencing of the gene in P. falciparum field isolates. All three antigens were preferentially recognized by PBMCs from SIS. IFN-γ production induced by these antigens correlated with the absence of fever and parasitaemia. UB09 was shown to be relatively well-conserved in nature. It is concluded that UB05, UB09 and the chimera UB05-09 posses T-cell epitopes that are associated with protection against malaria and could thus be used to distinguish SIS from FSS eventhough acute infection with malaria has been shown to reduce cytokine production in some studies. Further investigations of these antigens as potential diagnostic and/or vaccine candidates for malaria are indicated.

Preclinical efficacy and immunogenicity assessment to show that a chimeric Plasmodium falciparum UB05‐09 antigen could be a malaria vaccine candidate

“…It has been shown that protective immunity provoked by whole organism immunization indicates the accumulation of small responses to a large number of antigens; likewise, a single antigen with one or more epitopes could be enough to illicit a protective immune response when presented to the immune system in an appropriate manner . UB05‐09 is composed of 2 antigen fragments with multiple B‐ and T‐cell epitopes as shown in previous bioinformatics analyses . It is therefore capable of stimulating both arms of the immune system to provide protection against P. yoelii infection.…”

“…Hence, values obtained for test antigens were specific. The protein purity and homogeneity was checked by SDS‐PAGE to be approaching homogeneity as earlier published …”

“…Briefly, the study genes were amplified from a P. falciparum 3D7 cDNA library and cloned into pET32a+ expression vector. The antigens were overexpressed and purified from Escherichia coli BL21 strain …”

“…, PDB PF10_0372) that was proposed as a marker of protective immunity. Another antigen, UB09, was also identified alongside UB05 and later characterized . UB09 is a fragment of circumsporozoite protein‐related antigen (CRA) (GenBank accession no.…”

“…Differential immune screening is an unbiased systems biology approach that allows for the identification of potential vaccine candidates using antibodies from semi-immune vs susceptible subjects in endemic areas. 17,18 This approach led to the identification of UB05 (GenBank accession no. DQ235690.1, PDB PF10_0372) that was proposed as a marker of protective immunity.…”