CMV infection remains an important problem for transplantation. No successful vaccine has been developed that prevents new infections or even controls existing ones. Pharmacologic treatments have limitations regarding their side effects and the development of resistant strain Asymptomatic CMV-seropositive individuals of survivors of CMV infection after BMT, have an ongoing cytotoxic T lymphocyte (CTL) response to CMV, which can be measured after in vitro stimulation (IVS), either using HLA tetrameter binding or chromium release assay (CRA). The CTL response has multiple targets, however, the response to the tegument protein pp65 predominates in most individuals examined. Although many CTL epitopes have already been mapped from two immunodominant CMV proteins (pp65 and pp150), a significant number have yet been determined, and their elucidation will lead to a broad-based vaccine strategy for all major ethic groups in the United States. Immunodominance of CTL responses to CMV proteins will be determined utilizing IVS strategies together with known CTL epitopes. In contrast, little is known of the predominance of CTL targets from CMV in BMT recipients. The frequency of CMV-specific CTL will be enumerated using flow cytometry with HLA tetramers, and the frequency of those CTL will be compared to viral load measurements using plasma PCR methods. As a means to enhance the immunogenicity of previous defined CTL epitopes, a combinatorial peptide chemistry approach will be used with the known CTL epitopes from pp65 and pp150, which have affinities that are in the micromolar to approach will be used with the known CTL epitopes from pp65 and pp150, which have affinities that are in the micromolar to nanomolar range. Analogue peptides will be defined that will be evaluated initially using HLA A*0201 restricted and pp65- specific T cell clones, to develop a more immunogenic CTL epitope which may lead to a more effective CMV vaccine. The functionality of these analogue peptides will be shown utilizing in vivo immunization of HLA-transgenic mice and IVS studies stimulating a memory response in human PBMC specific for killing of CMV infected fibroblasts in vitro. Two Phase II trials will evaluate modalities including CMV lipopeptide immunization in combination with standard tetanus toxin immunization of BMT recipients. Augmentation of the memory response to tetanus- specific CD4+ T cells will be evaluated by in vitro methods, and the duration of infection-free survival of BMT recipients will be measured using standard clinical parameters. Finally, the utility of targeting a single CMV protein utilizing a CTL epitope vaccine strategy versus targeting two or more CMV proteins will be evaluated using CMV lipopeptide immunization of BMT recipients. Since the endpoint of the trial is a reduction in the incidence of CMV-associated disease, the comparison must be done utilizing a patient population likely to have measurable CMV viral load. Taken together, these strategies of defining CTL epitopes, augmenting their immunogenicity, and defining efficacious ways to delay them to CMT recipients will aid in the development of an effective CMV vaccine both as therapeutic and prophylactic agent.
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