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Characterization of a live-attenuated HCMV-based vaccine platform.

ABSTRACT: Vaccines based on cytomegalovirus (CMV) demonstrate protection in animal models of infectious disease and cancer. Vaccine efficacy is associated with the ability of CMV to elicit and indefinitely maintain high frequencies of circulating effector memory T cells (TEM) providing continuous, life-long anti-pathogen immune activity. To allow for the clinical testing of human CMV (HCMV)-based vaccines we constructed and characterized as a vector backbone the recombinant molecular clone TR3 representing a wildtype genome. We demonstrate that TR3 can be stably propagated in vitro and that, despite species incompatibility, recombinant TR3 vectors elicit high frequencies of TEM to inserted antigens in rhesus macaques (RM). Live-attenuated versions of TR3 were generated by deleting viral genes required to counteract intrinsic and innate immune responses. In addition, we eliminated subunits of a viral pentameric glycoprotein complex thus limiting cell tropism. We show in a humanized mouse model that such modified vectors were able to establish persistent infection but lost their ability to reactivate from latency. Nevertheless, attenuated TR3 vectors preserved the ability to elicit and maintain TEM to inserted antigens in RM. We further demonstrate that attenuated TR3 can be grown in approved cell lines upon elimination of an anti-viral host factor using small interfering RNA, thus obviating the need for a complementing cell line. In sum, we have established a versatile platform for the clinical development of live attenuated HCMV-vectored vaccines and immunotherapies.

SUBMITTER: Caposio P

PROVIDER: S-EPMC6917771 | biostudies-literature | 2019 Dec

REPOSITORIES: biostudies-literature

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Project description:Avian influenza A (H7N9) virus has emerged recently and continues to cause severe disease with a high mortality rate in humans prompting the development of candidate vaccine viruses. Live attenuated influenza vaccines (LAIV) are 6:2 reassortant viruses containing the HA and NA gene segments from wild type influenza viruses to induce protective immune responses and the six internal genes from Master Donor Viruses (MDV) to provide temperature sensitive, cold-adapted and attenuated phenotypes.LAIV candidate A/Anhui/1/2013(H7N9)-CDC-LV7A (abbreviated as CDC-LV7A), based on the Russian MDV, A/Leningrad/134/17/57 (H2N2), was generated by classical reassortment in eggs and retained MDV temperature-sensitive and cold-adapted phenotypes. CDC-LV7A had two amino acid substitutions N123D and N149D (H7 numbering) in HA and one substitution T10I in NA. To evaluate the role of these mutations on the replication capacity of the reassortants in eggs, the recombinant viruses A(H7N9)RG-LV1 and A(H7N9)RG-LV2 were generated by reverse genetics. These changes did not alter virus antigenicity as ferret antiserum to CDC-LV7A vaccine candidate inhibited hemagglutination by homologous A(H7N9) virus efficiently. Safety studies in ferrets confirmed that CDC-LV7A was attenuated compared to wild-type A/Anhui/1/2013. In addition, the genetic stability of this vaccine candidate was examined in eggs and ferrets by monitoring sequence changes acquired during virus replication in the two host models. No changes in the viral genome were detected after five passages in eggs. However, after ten passages additional mutations were detected in the HA gene. The vaccine candidate was shown to be stable in the ferret model; post-vaccination sequence data analysis showed no changes in viruses collected in nasal washes present at day 5 or day 7.Our data indicate that the A/Anhui/1/2013(H7N9)-CDC-LV7A reassortant virus is a safe and genetically stable candidate vaccine virus that is now available for distribution by WHO to vaccine manufacturers.

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Characterization of a live-attenuated HCMV-based vaccine platform.

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