CMV epitope selection and its use in T cell reconstitution in patients undergoing haematopoietic stem cell transplantation
Infection due to cytomegalovirus (CMV) can cause morbidity and mortality in the post HSCT setting in those who acquire or reactivate CMV. Approximately 60-70% of patients undergoing HSCT will reactivate CMV and without prompt antiviral therapy 20-30% will go on to develop CMV end organ disease. The cell mediated immune response notably that mediated through cytotoxic T lymphocytes (CTL) is essential in the maintenance of viral latency and the resolution of primary infections. Peptide mixes were utilised that cover the CMV antigens pp65 and IE1 to study the functionality of CD4+ and CD8+ T cells in patients post HSCT. CMV lysate was also used as it contains all potential antigens that could stimulate a T cell response. There was no detectable CD4+ T cell response to CMV lysate in patients that had detectable CMV replication, additionally the CD8+ T cell responses against pp65 and IE1 was not adequate to prevent CMV replication in the absence of a CD4+ T cell response. The data presented here demonstrates the importance of a CD4+ T cell response to CMV in the HSCT setting and also highlights the benefit of both a CD8+ T cell responses to both IE1 and pp65. By using overlapping 15mer peptides both the IE1 and pp65 antigens were mapped and new epitopes are described that could be used in the construction of peptide vaccines. New peptides were identified from both pp65 and IE1 that are presented in association with HLA- B*2705andB*5801. We also examined the CMV specific T cell responses in individuals with Common Variable immunodeficiency syndrome (CVID). Three CVID patients developed CMV disease and were then treated with antiviral therapy. The data presented here shows that these patients have a high number of T cells that respond to the CMV antigens IE1 and pp65, indicating that these patients do experience CMV reactivations resulting in persistent antigenic stimulation. We also investigated the influence of different HLA alleles on peptide presentation. Our studies revealed that a HLA allele hierarchy exists which is dependent on the alleles present in an individual, notably those who are HLA-B*0702 presented CMV peptides in association with B*0702 regardless of other HLA molecules that are present. This is relevant when considering what peptides should be included in a vaccine.