Memory T cells specific for murine cytomegalovirus re-emerge after multiple challenges and recapitulate immunity in various adoptive transfer scenarios.

Reconstitution of CMV-specific immunity after transplant remains a primary clinical objective to prevent CMV disease, and adoptive immunotherapy of CMV-specific T cells can be an effective therapeutic approach. Because of viral persistence, most CMV-specific CD8(+) T cells become terminally differentiated effector phenotype CD8(+) T cells (TEFF). A minor subset retains a memory-like phenotype (memory phenotype CD8(+) T cells [TM]), but it is unknown whether these cells retain memory function or persist over time. Interestingly, recent studies suggest that CMV-specific CD8(+) T cells with different phenotypes have different abilities to reconstitute sustained immunity after transfer. The immunology of human CMV infections is reflected in the murine CMV (MCMV) model. We found that human CMV- and MCMV-specific T cells displayed shared genetic programs, validating the MCMV model for studies of CMV-specific T cells in vivo. The MCMV-specific TM population was stable over time and retained a proliferative capacity that was vastly superior to TEFF. Strikingly, after transfer, TM established sustained and diverse T cell populations even after multiple challenges. Although both TEFF and TM could protect Rag(-/-) mice, only TM persisted after transfer into immune replete, latently infected recipients and responded if recipient immunity was lost. Interestingly, transferred TM did not expand until recipient immunity was lost, supporting that competition limits the Ag stimulation of TM. Ultimately, these data show that CMV-specific TM retain memory function during MCMV infection and can re-establish CMV immunity when necessary. Thus, TM may be a critical component for consistent, long-term adoptive immunotherapy success.

Protective immunization against murine cytomegalovirus infection using adenoviruses and poxviruses expressing hepatitis B virus chimeras.

Recombinant adenoviruses, poxviruses, and plasmid DNA vaccines encoding different hepatitis B virus (HBV)/murine cytomegalovirus (MCMV) protein chimeras were used to immunize mice. Processing of the chimeras resulted in presentation of a protective Ld/CD8+ T-cell epitope of the immediate early 1 protein pp89 (IE1 pp89) of MCMV to the immune system. Different levels of immunogenicity were observed depending on: (i) the type of viral vector used, (ii) whether the antigens were included in the cellular secretion pathway, and (iii) the location of the protective epitope within the chimeric protein. An adenovirus expressing a secretory HBV core protein with the MCMV epitope in its C-terminus induced the highest immune response. When the most immunogenic adenovirus and vaccinia virus were used in a heterologous prime-boost immunization protocol, even higher levels of epitope-specific T cells were obtained. Furthermore, responses were protective against a challenge with MCMV, inducing up to a 96% reduction of viral load in immunized animals, as determined by a sensitive real-time PCR assay. Together, these results confirmed previous observations of the efficient use of adenoviral and poxviral vectors in prime-boost protocols for immunization against diseases whose resolution depends on cellular immunity, as well as the aptness of correctly designed chimeric carrier proteins to facilitate this goal.