Cold-Adapted Viral Attenuation (CAVA): Highly Temperature Sensitive Polioviruses as Novel Vaccine Strains for a Next Generation Inactivated Poliovirus Vaccine

Abstract

The poliovirus vaccine field is moving towards novel vaccination strategies. Withdrawal of the Oral Poliovirus Vaccine and implementation of the conventional Inactivated Poliovirus Vaccine (cIPV) is imminent. Moreover, replacement of the virulent poliovirus strains currently used for cIPV with attenuated strains is preferred. We generated Cold-Adapted Viral Attenuation (CAVA) poliovirus strains by serial passage at low temperature and subsequent genetic engineering, which contain the capsid sequences of cIPV strains combined with a set of mutations identified during cold-adaptation. These viruses displayed a highly temperature sensitive phenotype with no signs of productive infection at 37°C as visualized by electron microscopy. Furthermore, decreases in infectious titers, viral RNA, and protein levels were measured during infection at 37°C, suggesting a block in the viral replication cycle at RNA replication, protein translation, or earlier. However, at 30°C, they could be propagated to high titers (9.4–9.9 Log10TCID50/ml) on the PER.C6 cell culture platform. We identified 14 mutations in the IRES and non-structural regions, which in combination induced the temperature sensitive phenotype, also when transferred to the genomes of other wild-type and attenuated polioviruses. The temperature sensitivity translated to complete absence of neurovirulence in CD155 transgenic mice. Attenuation was also confirmed after extended in vitro passage at small scale using conditions (MOI, cell density, temperature) anticipated for vaccine production. The inability of CAVA strains to replicate at 37°C makes reversion to a neurovirulent phenotype in vivo highly unlikely, therefore, these strains can be considered safe for the manufacture of IPV. The CAVA strains were immunogenic in the Wistar rat potency model for cIPV, inducing high neutralizing antibody titers in a dose-dependent manner in response to D-antigen doses used for cIPV. In combination with the highly productive PER.C6 cell culture platform, the stably attenuated CAVA strains may serve as an attractive low-cost and (bio)safe option for the production of a novel next generation IPV.

Economic impact of thermostable vaccines

“… * Source: Benin CMYP[13] † Source: WHO Vaccine Volume Calculator; WHO Prequalified Vaccines Database[14] ‡ Source: cMYP Costing Tool 3.6; UNICEF Product Menu[15] § Source: Personal communications with INCLEN ** Source: Niger cMYP[16] …”

Continued use of poliovirus after eradication: hyper‐attenuated strains as a safe alternative for release testing of human immunoglobulins

“…While only destruction of the virus would eliminate any risk of accidental release, a switch to alternative, hyper‐attenuated PV strains that are unable to infect humans may equally minimize the risks of transmission and disease in the event of facility‐associated dissemination into the environment, a strategy that was already proposed by the WHO and FDA more than a decade ago . Replication incompetent pseudoviruses or hyper‐attenuated PV strains have been developed and their use in vaccine production, immunogenicity studies, immunotherapy, monitoring of the environment, or neutralizing antibody titers has been proposed. The feasibility to use such hyper‐attenuated strains for vaccine production has been shown and was confirmed for the monitoring of PV neutralizing antibody titers in the QC of immunoglobulin, another essential medicinal, in this work.…”

Poliovirus Studies during the Endgame of the Polio Eradication Program

“…Type 2 Sabin strain cannot be handled in BSL-2 laboratories since the implementation of GAP III. PV pseudoviruses and hyper-attenuated strains might serve the alternatives to live PV, including the type 2 Sabin strain, in the biological tests that currently require live PV (e.g., neutralization test) (46,58,59,65).…”