Human cytomegalovirus (CMV) is a viral pathogen that infects both genders, who remain asymptomatic unless they receive immunosuppressive drugs or acquire infections that cause reactivation of latent virus. CMV infection also causes serious birth defects following primary maternal infection during gestation. A safe and effective vaccine to limit disease in this population continues to be elusive. A well-studied antigen is glycoprotein B (gB), which is the principal target of neutralizing antibodies (NAb) towards CMV in humans and has been implicated as the viral partner in the receptor-mediated infection by CMV in a variety of cell types. Antibody-mediated virus neutralization has been proposed as a mechanism by which host immunity could modify primary infection. Towards this goal, an attenuated poxvirus, modified vaccinia virus Ankara (MVA), has been constructed to express soluble CMV gB (gB680-MVA) to induce CMV NAb. Very high levels of gB-specific CMV NAb were produced after two doses of the viral vaccine. NAb were durable within a twofold range for up to 6 months. Neutralization titers developed in immunized mice are equivalent to titers found clinically after natural infection. This viral vaccine, expressing gB derived from CMV strain AD169, induced antibodies that neutralized CMV strains of three different genotypes. Remarkably, preexisting MVA and vaccinia virus (poxvirus) immunity did not interfere with subsequent immunizations of gB680-MVA. The safety characteristics of MVA, combined with the robust immune response to CMV gB, suggest that this approach could be rapidly translated into the clinic.Human cytomegalovirus (HCMV) is a member of the herpesvirus family. It is a major cause of congenital disease, resulting in an estimated 4,000 cases of symptomatic congenital cytomegalovirus (CMV) infection per year in the United States (58). An effective CMV vaccine that can prevent or reduce CMV-associated disease is highly desirable. Early studies have indicated that HCMV gB is the major target of NAb that are induced by naturally acquired CMV infection (16,39). It is the most highly conserved envelope glycoprotein of human herpesviruses (38). Thus, CMV gB has been an attractive candidate for CMV vaccine development. CMV gB vaccines using recombinant gB protein expressed from plasmid DNA and gB expressed in several different viral vectors (ALVAC, adenovirus, and vaccinia virus [VV]) have been investigated with animal models (9,13,23,26,31,40,54). Safety and moderate immunogenicity have been demonstrated with these vaccines, but no licensed CMV vaccine is available. A live attenuated Towne strain of CMV, either alone or with a gB subunit vaccine as a prime-boost, have also been evaluated in human subjects (1, 2, 48).Full-length CMV gB is synthesized as a 907-amino acid (aa) precursor in CMV-infected cells with a predicted molecular mass of 105 kDa, but it can be glycosylated to form a 170-kDa modified protein (17). To enable pharmaceutical development, truncated and secretable forms of gB were derived. These in...

No abstract

IntroductionInvestigators have focused on developing transgenic (Tg) mice containing human leukocyte antigen (HLA) alleles such as A*0201 (A2.1) in the class I system or DR1 in the class II system to address the problem of selection of epitopes that bind to major histocompatibility complex (MHC) molecules in an experimental model system. 1,2 Cellular immune responses to vaccines can then be studied in an easily manipulated vertebrate system with immunologic similarities to humans. We and others have characterized a repertoire of cytotoxic T-lymphocyte (CTL) epitopes specific for the immunodominant protein, cytomegalovirus (CMV)-pp65. 3,4 The choice of using CTL epitopes derived from CMV was based upon the absence of a Food and Drug Administration-approved vaccine modality against this significant opportunistic infection of solid organ and hematopoietic cell transplantation (HCT) recipients or its congenital manifestations. [5][6][7] The utility of using HLArestricted CTL epitopes is derived from the fact that HCT recipients are HLA typed and can be selected to be potential responders to the epitope-based vaccine. Reactivation of CMV and viremia are closely monitored during the first several months after HCT, representing a unique opportunity to investigate the properties of a therapeutic vaccine. [8][9][10] CMV-infected cells express pp65 both early and late after infection, making it an appropriate vaccine target. 11,12 Vaccines incorporating them would provide a strategy to immunize against CMV infection in the clinical setting. Since CMV-pp65 contains an HLA A2.1-specific epitope that is recognized by T cells from humans and from mice of the H-2 b background containing an HLA A2.1 or chimeric (human/mouse) A2.1/K b transgene, it has been chosen as a model class I epitope for these studies. 3,13,14 To circumvent allele specificity for the required T-helper (T H ) epitope, a series of T H sequences that promiscuously bind to either human or murine class II MHC alleles have been evaluated in combination with the CMV-pp65 HLA A*0201-restricted epitope. 13,15 In the last decade, investigators have studied the optimal means of delivering peptides corresponding to either CTL or T H epitopes as experimental vaccines. Peptides have been emulsified in adjuvants, complexed to alum, or suspended in liposomes, to name a few of the delivery strategies. [16][17][18] Successful epitope vaccine strategies against viruses, bacteria, and tumor antigens have been developed in mice using these delivery vehicles. 19,20 In addition, The publication costs of this article were defrayed in part by page charge payment. Therefore, and solely to indicate this fact, this article is hereby marked ''advertisement'' in accordance with 18 U.S.C. section 1734. modification of the primary structure of peptides by incorporating lipids also has been extensively studied in both experimental animals and in man. 21,22 Lipopeptides (lipidated peptides) specific for hepatitis B (HBV), HIV, and tumor antigens have been studied clinically in phase 1 and...