Designing CD8 T-cell mRNA vaccines targeting the viral large T antigen to prevent BK polyomavirus disease after kidney transplantation.
BK polyomavirus (BKPyV) continues to threaten kidney transplantation outcomes by directly or indirectly causing premature allograft failure. Insufficient BKPyV-specific immunity underlies the onset and duration of BKPyV-DNAemia and nephropathy. BKPyV-specific T-cells have been correlated with protection and include cytotoxic CD8 T-cells targeting immunodominant 9mer-epitopes encoded in the viral large tumor-antigen (LTag). To develop vaccines increasing LTag-specific T-cells, we reduced the 695 amino acid-long LTag to 143 residues or less, comprising four clusters of immunodominant 9mers presented by 54 HLA-alleles. Prediction algorithms allowed to improve global coverage, AAY-linker placement, proteasomal processing, and solubility. Using a human cell culture vaccination model, transfection of adherent monocytes with LTAG1-mRNA and LTAG2-mRNA demonstrated the expected 13.9kD and 15.2kD immunogens, respectively. LTAG2-mRNA induced higher CD8 T-cell responses than LTAG1-mRNA, with an interferon-γ-positive CD62L-CD45RA-effector memory phenotype and cytotoxicity for BKPyV-replicating primary human renal tubular epithelial cells. We tested three additional candidates (LTAG3-mRNA, LTAG4-mRNA, LTAG5-mRNA) by changing AAY-linkers and extending immunogenic regions. The encoded immunogens were expressed and increased upon proteasome inhibitor treatment. LTag5-expanded T-cells showed BKPyV-specific interferon-γ expression and cytotoxicity. Our results demonstrate novel approaches to design modular mRNA-based vaccine candidates for clinical development of non-secreted antigens using BKPyV as a paradigm of non-enveloped DNA viruses.