Genetic diversity of transmission-blocking vaccine candidates Pvs25 and Pvs28 in Plasmodium vivax isolates from Yunnan Province, China

Background: Transmission-blocking vaccines (TBVs) have been considered an important strategy for disrupting the malaria transmission cycle, especially for Plasmodium vivax malaria, which undergoes gametocytogenesis earlier during infection. Pvs25 and Pvs28 are transmission-blocking vaccine candidates for P. vivax malaria. Assessment of genetic diversity of the vaccine candidates will provide necessary information for predicting the performance of vaccines, which will guide us during the development of malaria vaccines. Results: We sequenced the coding regions of pvs25 and pvs28 from 30 P. vivax isolates from Yunnan Province, identifying five amino acid haplotypes of Pvs25 and seven amino acid haplotypes of Pvs28. Among a total of four mutant residues, the predominant haplotype of Pvs25 only had the I130T substitution. For Pvs28, a total of eight amino acid substitutions were identified. The predominant haplotype of Pvs28 had two substitution at positions 52 (M52L) and 140 (T140S) with 5-6 GSGGE/D tandem repeats at the end of fourth EGF-like domain. Most amino acid substitutions were common with previous reports from South Asian isolates. Although the nucleotide diversity of pvs28 (π = 0.0034 ± 0.0012) was significantly higher than pvs25 (π = 0.0013 ± 0.0009), it was still conserved when compared with the blood stage vaccine candidates. Conclusions: Genetic analysis revealed limited genetic diversity of pvs25 and pvs28, suggesting antigenic diversity may not be a particular problem for Sal I based TBVs in most P. vivax-endemic areas of China.