Induction of Specific T-Cell Responses, Opsonizing Antibodies, and Protection againstPlasmodium chabaudi adamiInfection in Mice Vaccinated with Genomic Expression Libraries Expressed in Targeted and Secretory DNA Vectors

Abstract

It has been proposed that a multivalent malaria vaccine is necessary to mimic the naturally acquired resistance to this disease observed in humans. A major experimental challenge is to identify the optimal components to be used in such a multivalent vaccine. Expression library immunization (ELI) is a method for screening genomes of a pathogen to identify novel combinations of vaccine sequences. Here we describe immune responses associated with, and the protective efficacy of, genomic Plasmodium chabaudi adami DS expression libraries constructed in VR1020 (secretory), monocyte chemotactic protein-3 (chemoattractant), and cytotoxic T lymphocyte antigen 4 (lymph node-targeting) DNA vaccine vectors. With splenocytes from vaccinated mice, specific T-cell responses, as well as gamma interferon and interleukin-4 production, were observed after stimulation with P. chabaudi adami-infected erythrocytes, demonstrating the specificity of genomic library vaccination for two of the three libraries constructed. Sera obtained from mice vaccinated with genomic libraries promoted the opsonization of P. chabaudi adami-infected erythrocytes by murine macrophages in vitro, further demonstrating the induction of malaria-specific immune responses following ELI. Over three vaccine trials using biolistic delivery of the three libraries, protection after lethal challenge with P. chabaudi adami DS ranged from 33 to 50%. These results show that protective epitopes or antigens are expressed within the libraries and that ELI induces responses specific to P. chabaudi adami malaria. This study further demonstrates that ELI is a suitable approach for screening the malaria genome to identify the components of multivalent vaccines.

A Bicistronic DNA Vaccine Containing Apical Membrane Antigen 1 and Merozoite Surface Protein 4/5 Can Prime Humoral and Cellular Immune Responses and Partially Protect Mice against VirulentPlasmodium chabaudi adamiDS Malaria

“…with BC construct 1. Opsonization of IRBC and subsequent internalization and destruction by macrophages have been shown to be a major factor contributing to a reduction in parasitemia during crisis in P. chabaudi mouse models (24)(25)(26). The opsonizing capacity of prechallenge sera taken from mice vaccinated i.m.…”

Induction of Strain-Transcending Immunity againstPlasmodium chabaudi adamiMalaria with a Multiepitope DNA Vaccine

“…In the present study, we have used expression library immunization (ELI) as an approach to identify new combinations of crossprotective antigens within the malaria genome, using P. c. adami in mice as a model test system. ELI has been shown to be protective against Mycoplasma (2), Leishmania (43), and Plasmodium, where we showed that mice were significantly protected against virulent P. c. adami DS infection by vaccination with a homologous genomic expression library (46,58). We hypothesized that our library contains multiple antigen sequences, many of which could be novel hypothetical sequences known to exist in the genome (18), and that this multivalent antigen cocktail may elicit good cross-protection due to sequence conservation between strains.…”

“…A genomic library from P. chabaudi adami DS was produced in the DNA vaccine vector VR1020 as described previously (46,58). A total of 10 pools (termed 3KA-3KJ), each comprising approximately 3,000 individual clones, were constructed and stored at Ϫ80°C as glycerol stocks.…”

“…Preparation of plasmid DNA from the 30K library or from the V9ϩ and V50ϩ pools was performed as described previously (46,58). DNA purified under endotoxinfree conditions was precipitated onto gold microcarriers at a ratio of 100 g DNA/50 mg carriers, such that each projectile used for vaccination contains about 1 g DNA, as described previously (46,58).…”

“…Segregation of the P. c. adami DS VR1020 genomic expression library and evaluation of vaccine efficacy. The original library construction and evaluation of the ability of the library to induce survival after homologous challenge with virulent P. c. adami DS are described down to the level of the 3KA subpools (46,58). Subpool 3KA-4 induced the highest protection (63% survival).…”