Immunization with a Combination of Merozoite Surface Proteins 4/5 and 1 Enhances Protection against Lethal Challenge withPlasmodium yoelii

Abstract

It is widely believed that subunit vaccines composed of multiple components will offer greater protection against challenge by malaria, and yet there is little experimental evidence to support this view. We set out to test this proposition in the Plasmodium yoelii challenge system in rodents by comparing the degree of protection conferred by immunization with a mixture of merozoite surface proteins to that conferred by single proteins. We therefore examined a defined protein mixture made of the epidermal growth factor-like domains of P. yoelli merozoite surface protein 1 (MSP1) and MSP4/5, the homologue of P. falciparum MSP4 and MSP5. In the present study we demonstrate that this combination of recombinant proteins dramatically enhances protection against lethal malaria challenge compared to either protein administered alone. Many mice immunized with the MSP4/5 plus MSP1 19 combination did not develop detectable parasitemia after challenge. Combined immunization with MSP1 19 and yMSP4/5, a product characterized by lower protective efficacy, also greatly enhanced protection by reducing peak parasitemias and increasing the numbers of survivors. In some combination trials, levels of antibodies to MSP1 19 were elevated compared to the MSP1 19 alone group; however, improved protection occurred regardless of whether boosting of the anti-MSP1 19 response was observed. Boosting of anti-MSP1 19 did not appear to be due to contaminating endotoxin in the EcMSP4/5 material since enhanced protection was observed in C3H/HeJ mice, which are endotoxin insensitive. Collectively, these experiments show that multiantigen combinations offer enhanced levels of protection against asexual stage infection and suggest that combinations of MSP1, MSP4, and MSP5 should be evaluated further for use in humans.

Oral Immunization with a Combination ofPlasmodium yoeliiMerozoite Surface Proteins 1 and 4/5 Enhances Protection against Lethal Malaria Challenge

“…Importantly, we have demonstrated that oral immunization with recombinant PyMSP4/5 plus PyMSP1 19 induces antibodies to both antigens and also provides enhanced protection against parasite infection. These data are consistent with those achieved by parenteral immunization (8) and provide a rationale for developing multicomponent oral vaccines.…”

Multi-antigenic DNA immunization using herpes simplex virus type 2 genomic fragments

“…When SGV-H2 was evaluated in an infectious challenge model it was much more effective than the single-gene plasmids confirming the previously demonstrated advantage of multi-antigenic vaccines. 4,5 The SGV-H2 in this experiment also produced better protection than the plasmid mixture although the reason is unclear and may require further experimentation to determine if the difference is significant. Nevertheless, from the infectious challenge studies, the SGV-H2 shows good potency based on its multi-antigenic nature.…”

“…3 Evidence suggests that a broad immune response composed of multiple antigens is more protective than a narrow focused response. 4,5 Since a single protective antigen has not been identified for many diseases, a strategy of delivering multiple antigens would, therefore, have an enhanced likelihood of success by increasing the number of potential antigens. For commercial purposes, the cost, formulation and manufacturing issues could limit the feasibility of delivering a mixture of single-gene DNA vaccines.…”

Growth-Inhibitory Antibodies Are Not Necessary for Protective Immunity to Malaria Infection

“…(GST-PyMSP1 19 ) or as a hexahistidine-tagged fusion in Saccharomyces cerevisiae (yPyMSP1 19 ) (20,38). To generate PyMSP1 19 -specific antibodies, two female New Zealand White rabbits were injected subcutaneously with 100 g of GSTPyMSP1 19 or 50 g of yPyMSP1 19 , emulsified in complete Freund's adjuvant.…”

“…Immunization of mice with recombinant PyMSP1 19 and the subsequent challenge infection were performed as previously described (20,39). Briefly, BALB/c mice (females, 6 to 8 weeks old) were immunized intraperitoneally with 25 g or 10 g of purified recombinant PyMSP1 19 emulsified in complete Freund's adjuvant.…”