A phase I trial of recombinant modified vaccinia ankara (MVA) vaccine encoding Epstein-Barr virus (EBV) antigens

Background: EBV+ve nasopharyngeal carcinoma (NPC) selectively expresses the EBV-coded nuclear antigen EBNA1 and latent membrane protein LMP2. A recombinant vaccinia virus MVA-EL, encodes an EBNA1/LMP2 fusion, is designed to boost T cell immunity to these tumour-associated antigens. It was tested in Hong Kong, an area endemic for NPC, in a phase I dose escalation trial to determine a safe and immunogenic dose for phase II. Methods: MHC I/II-typed NPC patients (pts), all >12 weeks after primary therapy, received three intra-dermal vaccinations of MVA-EL at 3-weekly intervals, with dose escalations of 5x107, 1x108, 2x108, 3.3x108 and 5x108 pfu providing dose limiting toxicity (DLT) had not been observed on the previous cohort. Blood samples were taken during pre-screening, immediately before and 1 week after each cycle of vaccination, and at 11, 14, 26 and 52 weeks post-vaccination. Cryo-preserved peripheral blood mononuclear cells (PBMC) were later tested for spot-forming cells (sfc) in interferon-gamma ELIspot assays against complete EBNA1 and LMP2 15-mer peptide mixes and against defined epitope peptides selected according to MHC-type. Results: Eighteen pts were treated, three per dose level 1-4 and six at the highest dose. No DLT occurred. Pre-existing immunity to EBNA1 and/or LMP2 was observed in 16/18 pts with mean frequencies of 181 (EBNA1) and 81 (LMP2) sfc/106 PBMC. Immunity to one or both antigens was significantly increased in 15/18 pts, with mean sfc/106 PBMC among responders reaching 411 and 237 after the second, and 353 and 213 after the third vaccination, while immunity to control antigens (a non-vaccine EBV antigen and influenza) showed no such change. Furthermore, the size of EBNA1/LMP2 responses strongly suggested a linear relationship with vaccine dose. Screening on defined peptides identified individuals mounting both MHC I and II-restricted responses to known epitopes in one or both target antigens. Conclusions: MVA-EL is safe and immunogenic at all doses tested. The recommended dose for phase II is 5x108pfu because this dose induced the strongest responses.