Whole Yeast Delivering Recombinant Virus-Like Particles Stimulates Antigen-Specific Memory CD4+ and CD8+ T Cells

Yeast cells represent unique vehicles for antigen delivery approaches and have been demonstrated to elicit robust innate and adaptive immune responses. A clinically relevant antigen, the matrix protein pp65 of human cytomegalovirus (CMV), was recombinantly expressed in S. cerevisiae as full-length protein alone or N-terminally fused to the Gag protein from the L-A yeast virus. Electron microscopy confirmed that the Gag/pp65 fusion protein was able to self assemble into virus-like particles (VLP). The ability of both pp65 variants to stimulate human pp65-specific memory T lymphocytes of CMV-seropositive donors was analyzed using an ex vivo whole blood assay in which whole recombinant S. cerevisiae served as antigen delivery system. Pp65-VLP were able to specifically activate a higher number of CD4+ and CD8+ memory T lymphocytes than pp65 alone. Furthermore, heat-treatment of yeasts increased the frequency of activated T cells. Our results suggest the usage of recombinant VLP within intact yeast cells as a promising approach for antigen delivery.