Molecular Evolution And Antigenic Drift Of Type 3 Immunodeficiency Vaccine-Derived Polioviruses Excreted From A Patient With Immunodeficiency In Ningxia, China

So far, the Global Polio Eradication Initiative (GPEI) has made great achievements, and has entered the endgame stage. One of the most important links of GPEI at present is the replacement of the oral polio vaccine (OPV) with the use of the inactivated polio vaccine (DPV) in a global scope. In mainland of China, IPV will be gradually introduced into national immunization program and OPV will be withdrawn step by step in the near future. Therefore, immunodeficiency vaccine-derived polioviruses (iVDPVs) excreted from long-term shedders with immunodeficiency will become increasingly important, because these VDPVs will be the only source of live polioviruses distributed in nature when wild polioviruses were eradicated and OPV were completely withdrawn.Here, we reported a case of a 2.5 year-old child patient with acute flaccid paralysis who was diagnosed as primary immunodeficiency (PID) in Ningxia in 2011. Twelve consecutive stool specimens was collected from the patient and twelve iVDPVs strains (named as CHN15017-1 to CHN15017-12, one strain per stool sample) were isolated from the patient during the period from onset to death. Nucleotide sequencing analysis of the plaque-purified iVDPVs showed that they differed from the parental Sabin 3 strain by 2-3.5% in VP1 region and were genetically related, which revealed closely evolutionary relationships among these iVDPVs isolates. Further full-length genome sequencing analysis indicated that all twelve iVDPVs had high homologies and were all Sabin 3/Sabin 1 recombinants sharing a common crossover site in 2C region, and the two key determinants of attenuation and temperature sensitivity phenotype of Sabin 3 (U in the 5’untranslated region and T in the VP1 region) had reverted. Temperature sensitive experiments showed two of twelve iVDPVs strains (the first two strains CHN 15017-1 and CHN15017-2) still retained partial temperature sensitivity phenotype of Sabin 3 strain, that is, they can only replicate at 36℃ (optimal temperature for virus propagation) and can’t replicate at 39.5℃ (supraoptimal temperature for virus propagation). While the other ten iVDPVs strains (CHN15017-3 to CHN15017-12) had distinctly lost temperature sensitive phenotype. Nineteen amino acid substitutions were found among all twelve iVDPVs compared with parental Sabin 3 strain, of which only one (K1419R) was found on the subsequent ten iVDPVs isolates, suggesting that this site may be a potential determination site involved in temperature sensitivity phenotype among these iVDPVs isolates. A Bayesian Monte Carlo Markov Chain (MCMC) phylogenetic analysis based on the VP1 coding region showed an average evolution rate of 2.79x10"2 total substitutions/site/year of these iVDPVs, and the initiating OPV dose was estimated to be given around 4 October 2009.This study indicate that the iVDPVs patient persistently excreted high titer iVDPVs to the environment, which have some properties resembled circulating VDPVs, such as unusually high genetic divergence, reversion of key attenuated determinants, change of temperature-sensitive phenotypes, and so on, and these iVDPVs posed a potential risk to the polio eradication program. Based on these findings, we provide valuable information on the genetic structure, temperature sensitivity, and antigenic drift properties of iVDPVs that long-term evolved in a single PID patient, and expand our very limited knowledge about the dynamic change and evolution pathway of iVDPV populations in PID patient during long-term evolution. Our study will also provide the necessary valuable information for maintaining the free-polio status in China and for developing the polio vaccine immunization strategy in the post global polio eradication era.