Preclinical development of an adjuvant-free peptide vaccine with activity against CMV pp65 in HLA transgenic mice

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...

The Immunodominant CD8 T Cell Response to the Human Cytomegalovirus Tegument Phosphoprotein pp65495–503 Epitope Critically Depends on CD4 T Cell Help in Vaccinated HLA-A*0201 Transgenic Mice

“…Injection of a mixture of two cationic tat/e6+n4 and tat/C128 peptides (complexed with ODN) into A2-HHD-II mice efficiently induced e6-specific CD8 T cells (Fig. 4C, group 2), confirming previous reports (32,35). In contrast, e6-specific CD8 T cell responses were not induced when the respective tat/e6+n4 and tat/ C128 vaccines were injected into different sites (i.e., into the right and left tibialis anterior muscles) of A2-HHD-II mice (Fig.…”

“…Monospecific, peptide-based vaccines delivering the e6 epitope of pp65 and MHC class II-binding, heterologous pan DR epitopeor tetanus toxin-derived CD4 T cell helper epitopes have been shown to efficiently induce CD8 T cell responses in HLA-A*0201 tg mice (32,35). The sequence N terminal to and comprising the FIGURE 3.…”

“…5B, group 4). C128-specific, I-A peptide vaccines is critical to induce e6-specific CD8 T cell responses in A2-DR1 mice, we fused a universal DR-binding tetanus toxin-derived TT 830-843 (TT830) helper peptide (35,57) to the e6 peptide. This generated the tat/e6/TT830 vaccine (tat-QGIKANSKFIGITE-NLVPMVATV).…”

“…CD4 T cell help is required for the induction and maintenance of functional CD8 T cell responses (20)(21)(22)(23)(24)(25)(26)(27), but immunodominance hierarchies also operate in Ag-specific CD4 T cell responses (24,28). The immunogenicity of monospecific, peptide-based vaccines has been shown to be significantly enhanced by codelivering heterologous or homologous helper CD4 T cell epitopes (29)(30)(31)(32)(33)(34)(35). CD4 T cell help depends on the copresentation of helper and CD8 T cell epitopes by the same APC (36).…”

Nasal Peptide Vaccination Elicits CD8 Responses and Reduces Viral Burden after Challenge with Virulent Murine Cytomegalovirus

“…CD4 cells provide important help in the generation of CD8 responses after peptide vaccination (24). The inclusion of CD4 epitopes in a peptide vaccine may enhance responses to CD8 epitopes, or even overcome the need for an adjuvant (15).…”