Rapid Communication Use of chimeric adenoviral vectors to assess capsid neutralization determinants

AbstractIn order to elucidate the relative importance of neutralizing determinants on each of the three major adenoviral capsid components, wehave generated chimeric vectors where the hexon protein, or the fiber protein, or both hexon and fiber proteins of one serotype (SimianAdenovirus 24/Pan 7) have been replaced by those of another (Simian Adenovirus 23/Pan 6). The effect of each replacement was evaluatedby neutralization assays and by attempted vector re-administration into mice. Both hexon and fiber were found to harbor neutralizationepitopes although in vivo transduction was more severely affected by anti-hexon antibodies.D 2005 Elsevier Inc. All rights reserved. Keywords: Adenovirus; Adenovirus neutralization; Hexon; Penton; Fiber IntroductionHumoral immunity to adenoviruses has emerged as oneof the most important hurdles for gene therapy usingadenoviral vectors. The use of adenoviral gene therapyvectors based on different non-cross reacting serotypes isbeing investigated by several groups as a means toadminister adenoviral vectors, either in a re-administrationsetting, or in subjects with circulating antibodies against thecommon serotypes such as human adenovirus serotype 5(Ad5). Early studies designed to determine the adenoviralcapsid components against which neutralizing antibodieswere directed concluded that both group-specific (located onthe hexon protein) and type-specific (located on the fiberprotein) components were responsible for the elicitation ofneutralizing antibodies in rabbits (Wilcox and Ginsberg,1963), guinea pigs (Kjellen and Pereira, 1968) and humans(Banks et al., 1966; Kasel et al., 1964). Although therelative importance of the components varied betweendifferent experimental systems, in most studies, the hexonwas found to be the principal target for neutralizingantibodies (Gelderblom et al., 1968; Kjellen and Pereira,1968; Norrby, 1969; Wilcox and Ginsberg, 1963). Severalgroups have reported that purified fiber does not cause theelicitation of neutralizing antibodies (Kjellen and Pereira,1968; Pettersson et al., 1968; Wadell, 1972). Also, Mautnerand Willcox (1974) noted that the amount of purified fiberor hexon immunogen that is required for mice to produceneutralizing antibodies is considerably higher than thatrequired when the intact adenovirus is used, indicating thatthe trimeric forms of the hexon and fiber present neutraliza-tion domains that may be difficult to reconstitute usingpurified capsid proteins and may not accurately reflect theresponse to an infection with the intact virus. The minorcapsid components such as pIX, IIIa, pVI, and pVIII havenot been shown to elicit the production of neutralizingantibodies.Because gene therapy protocols frequently require re-administration, and because serotype-specific anti-adenovi-ral antibodies have been shown to preclude efficacious