title: Accumulation of defective interfering viral particles in only a few passages in Vero cells attenuates mumps virus neurovirulence.
abstract: Immunization programs have implemented live attenuated mumps vaccines which reduced mumps incidence ≥97%. Some of the vaccine strains were abandoned due to unwanted side effects and the genetic marker of attenuation has not been identified so far. Our hypothesis was that non-infectious viral particles, in particular defective interfering particles (DIPs), contribute to neuroattenuation. We showed that non-infectious particles of the mumps vaccine L-Zagreb attenuated neurovirulence of wild type mumps virus 9218/Zg98. Then, we attenuated recent wild type mumps virus MuVi/Zagreb.HRV/28.12 in Vero cells through 16 passages but already the fifth passage (p5) showed accumulation of DIPs and attenuated neurovirulence in a newborn rat model when compared to the second passage (p2). Sequence analysis of the p2 and p5 revealed a single mutation in the 5' untranslated region of the HN gene. Analysis of the expression level of the HN protein showed that this mutation does not affect the expression of the protein. We conclude that the passages of MuVi/Zagreb.HRV/28.12 in Vero cells for only three passages accumulated DIPs which attenuate neurovirulence. These findings reveal DIPs as a very promising and general neuroattenuating factor which should be considered in the rational design of the new mumps vaccine.
authors.affiliation: Centre for Research and Knowledge Transfer in Biotechnology, University of Zagreb, Rockefellerova 10, 10 000 Zagreb, Croatia. Electronic address: msantak@unizg.hr.
authors.forename: Maja
authors.initials: M
authors.lastname: Šantak
authors.affiliation: Centre for Research and Knowledge Transfer in Biotechnology, University of Zagreb, Rockefellerova 10, 10 000 Zagreb, Croatia.
authors.forename: Maja
authors.initials: M
authors.lastname: Markušić
authors.affiliation: Quality Control Department, Institute of Immunology, Svetonedeljska Cesta 14, 10 431 Sveta Nedelja, Croatia.
authors.forename: Maja Lang
authors.initials: ML
authors.lastname: Balija
authors.affiliation: Quality Control Department, Institute of Immunology, Svetonedeljska Cesta 14, 10 431 Sveta Nedelja, Croatia.
authors.forename: Sandra Keć
authors.initials: SK
authors.lastname: Kopač
authors.affiliation: Centre for Research and Knowledge Transfer in Biotechnology, University of Zagreb, Rockefellerova 10, 10 000 Zagreb, Croatia.
authors.forename: Renata
authors.initials: R
authors.lastname: Jug
authors.affiliation: Department of Laboratory Medicine, Karolinska University Hospital Huddinge, 14 186 Stockholm, Sweden.
authors.forename: Claes
authors.initials: C
authors.lastname: Örvell
authors.affiliation: Department of Histology and Embryology, School of Medicine, Braće Branchetta 20, 51000 Rijeka, Croatia.
authors.forename: Jelena
authors.initials: J
authors.lastname: Tomac
authors.affiliation: Centre for Research and Knowledge Transfer in Biotechnology, University of Zagreb, Rockefellerova 10, 10 000 Zagreb, Croatia.
authors.forename: Dubravko
authors.initials: D
authors.lastname: Forčić
mesh_terms: D000818:Animals; D001483:Base Sequence; D045744:Cell Line, Tumor; D002522:Chlorocebus aethiops; D003673:Defective Viruses / Q000276:immunology*; D006801:Humans; D008969:Molecular Sequence Data; D009109:Mumps virus / Q000235:genetics / Q000276:immunology*; D051381:Rats; D014613:Vaccines, Attenuated / Q000235:genetics; D014709:Vero Cells / Q000276:immunology / Q000821:virology; D014771:Virion; D014774:Virulence / Q000235:genetics
chemical_list: D014613:Vaccines, Attenuated
keywords: Attenuation; Defective interfering particles; Infectious virus; Mumps virus; Neurovirulence