Immunodominance of lytic cycle antigens in Epstein-Barr virus-specific CD4+ T cell preparations for therapy.

Epstein-Barr virus (EBV) is associated with a number of human
malignancies. EBV-positive post-transplant lymphoproliferative
disease in solid organ and hematopoietic stem cell transplant
recipients has been successfully treated by the adoptive transfer
of polyclonal EBV-specific T cell lines containing CD4+ and CD8+ T
cell components. Although patients receiving T cell preparations
with a higher CD4+ T cell proportion show better clinical
responses, the specificity of the infused CD4+ component has
remained completely unknown. We generated LCL-stimulated T cell
lines from 21 donors according to clinical protocols, and analyzed
the antigen specificity of the CD4+ component in EBV-specific T
cell preparations using a genetically engineered EBV mutant that is
unable to enter the lytic cycle, and recombinantly expressed and
purified EBV proteins. Surprisingly, CD4+ T cell lines from acutely
and persistently EBV-infected donors consistently responded against
EBV lytic cycle antigens and autoantigens, but barely against
latent cycle antigens of EBV hitherto considered principal
immunotherapeutic targets. Lytic cycle antigens were predominantly
derived from structural proteins of the virus presented on MHC II
via receptor-mediated uptake of released viral particles, but also
included abundant infected cell proteins whose presentation
involved intercellular protein transfer. Importantly, presentation
of virion antigens was severely impaired by acyclovir treatment of
stimulator cells, as currently performed in most clinical
protocols. These results indicate that structural antigens of EBV
are the immunodominant targets of CD4+ T cells in LCL-stimulated T
cell preparations. These findings add to our understanding of the
immune response against this human tumor-virus and have important
implications for the improvement of immunotherapeutic strategies
against EBV.