Specific activation of CMV-primed human T lymphocytes by cytomegalovirus pp65 expressed in fission yeast

Abstract

Threatening virus infections constantly illustrate the growing need for novel vaccines that specifically induce efficient T cell-mediated immune responses. In this study, we used a human whole blood assay to determine the activation of antigen-specific human T lymphocytes by a viral antigen of human cytomegalovirus (HCMV). The major HCMV tegument protein pp65, recombinantly expressed in fission yeast (Schizosaccharomyces pombe), specifically activated antigen-specific CD4- and CD8-positive memory T cells in blood of HCMV seropositive donors. Moreover, the immune response against recombinant pp65, in particular that of CD8 class I major histocompatibility complex-restricted cytotoxic T cells, was similar to the response against the intact HCMV. Since fission yeast cells per se did not activate a significant number of human T lymphocytes ex vivo, the system described here might represent a novel approach in vaccine development as well as in the identification of vaccine candidates directly from human whole blood.

Delivery of functional DNA and messenger RNA to mammalian phagocytic cells by recombinant yeast

“…Yeast-based DNA/mRNA delivery B Walch et al Importantly, transfer of the respective nucleic acid from phagolysosomes to the cytosol of APC takes place even without the need of additional and potential toxic components such as pore-forming toxins like listeriolysin O, adding further evidence to the fact that yeast cells fulfill the preconditions of a highly efficient delivery vehicle for nucleic acids. In line with this, APCs are neither killed nor significantly impaired in growth or function after yeast cell uptake (this work and Breinig et al 32 ), whereas attenuated bacterial carriers like Listeria monocytogenes have been repeatedly shown to be toxic to infected APCs and other cell types. 5,[38][39][40] So far, the mechanism of DNA/mRNA transfer from phagolysosomes to the cytosol is completely unknown.…”

“…Noteworthy and in strong contrast to many known bacterial or viral systems, yeast cells do neither interfere with cell growth nor cell function of mammalian APCs. 32,33 Using CMV pp65 as a model antigen, we could also demonstrate an effective specific T cell activation in a human system after antigen processing and presentation. We preselected CMV-positive individuals with a significant frequency of CMV-specific CD8+ T cells.…”

“…A simple rupture of the phagolysosomes seems unlikely as such an event would release lysosomal activity, which, as a consequence, would presumably affect the viability of the APCs. However, there are several reports in which proteins delivered by recombinant yeast are capable of entering in particular the MHC I pathway via crosspresentation, 11,12,18,20,32 a mechanism whose molecular basis is currently controversially discussed. One explanation for this phenomenon could be the observation that phagosomes containing exogenous proteins merge with the endoplasmic reticulum (ER) in professional APCs, such as macrophages and DCs.…”

Surface-modified yeast cells: A novel eukaryotic carrier for oral application

“…In the last years, we and other groups described the successful usage of intact, recombinant yeast cells for the delivery of both proteins [17][18][19][20][21][22] and functional nucleic acids [23][24][25][26][27][28] …”

Schizosaccharomyces pombe: A novel transport vehicle of functional DNA and mRNA into mammalian antigen-presenting cells

“…Besides S. cerevisiae, we found that antigen-expressing nonconventional yeasts like Sz. pombe are capable of stimulating antigen-specific T-cells in human blood [8,9]. Furthermore, Sz.…”