Engineering the Live-Attenuated Polio Vaccine to Prevent Reversion to Virulence

Abstract

Summary The live-attenuated oral poliovirus vaccine (OPV or Sabin vaccine) replicates in gut-associated tissues, eliciting mucosa and systemic immunity. OPV protects from disease and limits poliovirus spread. Accordingly, vaccination with OPV is the primary strategy used to end the circulation of all polioviruses. However, the ability of OPV to regain replication fitness and establish new epidemics represents a significant risk of polio re-emergence should immunization cease. Here, we report the development of a poliovirus type 2 vaccine strain (nOPV2) that is genetically more stable and less likely to regain virulence than the original Sabin2 strain. We introduced modifications within at the 5′ untranslated region of the Sabin2 genome to stabilize attenuation determinants, 2C coding region to prevent recombination, and 3D polymerase to limit viral adaptability. Prior work established that nOPV2 is immunogenic in preclinical and clinical studies, and thus may enable complete poliovirus eradication.

Development of a new oral poliovirus vaccine for the eradication end game using codon deoptimization

“…The results from this preclinical evaluation of nOPV-CD informed the decision to initiate the first in-human clinical trial of new polio vaccines since the 1950s. A manuscript describing the results of the initial Phase I testing of our nOPV-CD candidate as well as an additional candidate was recently published 38,39 . In that study, 15 adults with routine IPV immunization backgrounds received 10 6 50% cell culture infectious dose units (CCID 50 ) of nOPV2-CD by oral administration.…”

“…Saturation of the CpG incorporation was spread evenly over the capsid cassette. The S15 domain V 5′ UTR modification has been described elsewhere 38,46 . Standard cloning methods were used to insert the modified 5′ UTR S15 domain V and capsid constructs (synthesized by GenScript) 20 .…”

“…To further improve genetic stability, our codon-deoptimized nOPV2 strain (nOPV2-CD) also features a modified 5′ UTR. This modification stabilizes a known attenuation determinant in Sabin OPV2, preventing reversion at the site which is associated with many cVDPV2 4,17,[33][34][35][36][37][38] .…”

Engineering a fidelity-variant live-attenuated vaccine for chikungunya virus

“…Complicating matters, RNA-dependent RNA polymerases lack proofreading capabilities and incorporate erroneous nucleotides in progeny genomes at relatively higher rates than DNA-genomic counterparts 24,25 , resulting in a higher rate of genetic drift, which is undesirable in an attenuated pathogen for commercial propagation as a vaccine. Two ways to circumvent this challenge are to either incorporate attenuating elements in a LAV that cannot be easily reverted through point mutation or recombination, similar to approaches currently in use for a novel poliovirus LAV 34 or to reduce the error rate of the attenuated pathogen, thus reducing the reversion potential. In this study, we explored both approaches with an emphasis on designing a high-fidelity-variant of a CHIKV LAV known to be genetically unstable during human clinical testing.…”

“…Fidelity-altering mutations have previously been demonstrated to have a negative impact on viral fitness, with increased replication fidelity associated with RNA virus attenuation 26,28,31 . The attenuating nature of these mutations, coupled with the potential reduction in LAV replication errors, have made fidelity variants a promising approach for rational vaccine design [32][33][34] . Herein we report on the incorporation of the previously described fidelity-altering mutations nsP2 G641D /nsP4 C483Y in the liveattenuated vaccine, CHIKV-181/25, as a method for modulating replication errors.…”