Immunization with SPf66 and subsequent infection with homologous and heterologous Plasmodium falciparum parasites.

Abstract

Abstract. In an area of intense transmission, a malaria vaccine could reduce infection due to the parasite types represented in the vaccine, but have no detectable effect on the overall frequency of infection if it did not protect against infection with heterologous parasites. These studies were performed to determine whether immunization with SPf66 decreased infection with homologous parasites containing the 11 amino acid peptide from merozoite surface protein-1 (MSP-1) in SPf66, or increased infection due to heterologous parasites containing heterologous (alternative) MSP-1 sequences. Based on this 11 amino acid peptide (YSLFQKEKMVL), three forward primers (S,Q,V) were designed to amplify the MSP-1 sequence present in SPf66, and 3 additional forward primers (G,H,I) to amplify the alternative MSP-1 sequence (YGLFHKEKMIL). This strategy was validated by polymerase chain reaction (PCR) amplification and dideoxy sequencing with 14 cloned laboratory isolates, which demonstrated that each primer amplified one MSP-1 sequence or the other, but not both. The technique was then used to examine filter paper blots from an SPf66 vaccine study of 69 subjects in Saradidi, Kenya. In that study, the prevalence of infection with YSLFQKEKMVL or YGLFHKEKMIL type parasites was unaffected by immunization with SPf66 (based on PCR amplification with the S, Q, V, G, H and I primers, respectively). These results suggest that immunization with SPf66 does not produce a selective effect in vivo. They demonstrate a molecular method to test for selection in vivo as an indirect measure of vaccine efficacy.Between one and two million deaths result from falciparum malaria each year, 90% of which occur among children less than five years of age in sub-Saharan Africa.1 In addition, the recent worldwide increase in the morbidity and mortality of malaria caused by drug-resistant Plasmodium falciparum has strengthened the argument for development of a malaria vaccine.2,3 SPf66 is a synthetic peptide vaccine candidate with the following sequence: 4,5

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

“…However, there is little experimental evidence to suggest that this would work for malaria. Trials with antigen combinations such as Spf66 and NYVAC-7 have given inconsistent or poor results (3,23,24,35,39), and in none of these experiments is there evidence that the combination performs better than single antigens. Shi et al (34) demonstrated the ability to raise growth-inhibitory sera in rabbits by immunization with multiple blood-stage epitopes but did not demonstrate that this approach was more effective than a particular epitope given singly.…”

Molecular incidence and clearance of Plasmodium falciparum infection

“…Filter paper blots were extracted as described previously [ 12 – 14 ]. After extraction and storage at 4 °C, parasite DNA was amplified using the polymerase chain reaction (PCR) with Taq polymerase and allotype-specific primers for the Block 2 region of msp1 [ 12 – 14 ].…”

The molecular epidemiology of malaria

“…The malaria vaccine SPf66 contains a 11‐mer peptide corresponding to part of the block 1 region of the polymorphic antigen MSP1. Study of parasites obtained from subjects immunized with this vaccine in The Gambia or in Kenya and from controls did not show any evidence for selection against parasites with the MSP1 block allele similar to that in the vaccine (Masinde et al . 1998; Haywood et al .…”