title: Attenuation of Chikungunya virus vaccine strain 181/clone 25 is determined by two amino acid substitutions in the E2 envelope glycoprotein.
abstract: Chikungunya virus (CHIKV) is the mosquito-borne alphavirus that is the etiologic agent of massive outbreaks of arthralgic febrile illness that recently affected millions of people in Africa and Asia. The only CHIKV vaccine that has been tested in humans, strain 181/clone 25, is a live-attenuated derivative of Southeast Asian human isolate strain AF15561. The vaccine was immunogenic in phase I and II clinical trials; however, it induced transient arthralgia in 8% of the vaccinees. There are five amino acid differences between the vaccine and its parent, as well as five synonymous mutations, none of which involves cis-acting genome regions known to be responsible for replication or packaging. To identify the determinants of attenuation, we therefore tested the five nonsynonymous mutations by cloning them individually or in different combinations into infectious clones derived from two wild-type (WT) CHIKV strains, La Reunion and AF15561. Levels of virulence were compared with those of the WT strains and the vaccine strain in two different murine models: infant CD1 and adult A129 mice. An attenuated phenotype indistinguishable from that of the 181/clone 25 vaccine strain was obtained by the simultaneous expression of two E2 glycoprotein substitutions, with intermediate levels of attenuation obtained with the single E2 mutations. The other three amino acid mutations, in nsP1, 6K, and E1, did not have a detectable effect on CHIKV virulence. These results indicate that the attenuation of strain 181/clone 25 is mediated by two point mutations, explaining the phenotypic instability observed in human vaccinees and also in our studies.
authors.affiliation: Institute for Human Infections and Immunity, Sealy Center for Vaccine Development, and Department of Pathology, University of Texas Medical Branch, Galveston, Texas, USA.
authors.forename: Rodion
authors.initials: R
authors.lastname: Gorchakov
authors.forename: Eryu
authors.initials: E
authors.lastname: Wang
authors.forename: Grace
authors.initials: G
authors.lastname: Leal
authors.forename: Naomi L
authors.initials: NL
authors.lastname: Forrester
authors.forename: Kenneth
authors.initials: K
authors.lastname: Plante
authors.forename: Shannan L
authors.initials: SL
authors.lastname: Rossi
authors.forename: Charalambos D
authors.initials: CD
authors.lastname: Partidos
authors.forename: A Paige
authors.initials: AP
authors.lastname: Adams
authors.forename: Robert L
authors.initials: RL
authors.lastname: Seymour
authors.forename: James
authors.initials: J
authors.lastname: Weger
authors.forename: Erin M
authors.initials: EM
authors.lastname: Borland
authors.forename: Michael B
authors.initials: MB
authors.lastname: Sherman
authors.forename: Ann M
authors.initials: AM
authors.lastname: Powers
authors.forename: Jorge E
authors.initials: JE
authors.lastname: Osorio
authors.forename: Scott C
authors.initials: SC
authors.lastname: Weaver
mesh_terms: D018354:Alphavirus Infections / Q000473:pathology / Q000821:virology; D019943:Amino Acid Substitution; D000818:Animals; D065632:Chikungunya Fever; D002646:Chikungunya virus / Q000276:immunology* / Q000472:pathogenicity*; D004195:Disease Models, Animal; D005260:Female; D006023:Glycoproteins / Q000235:genetics / Q000276:immunology; D051379:Mice; D011247:Pregnancy; D014613:Vaccines, Attenuated / Q000009:adverse effects / Q000235:genetics / Q000276:immunology; D014759:Viral Envelope Proteins / Q000235:genetics* / Q000276:immunology; D014765:Viral Vaccines / Q000009:adverse effects / Q000235:genetics* / Q000276:immunology*; D014774:Virulence
chemical_list: D006023:Glycoproteins; D014613:Vaccines, Attenuated; D014759:Viral Envelope Proteins; D014765:Viral Vaccines