Coupling presentation of MHC class I peptides to constitutive activation of antigen-presenting cells through the product of a single gene

Priming of naive CD8 T cells by dendritic cells (DCs) entails both effective antigen presentation on MHC class I products and co-stimulatory signaling. Their optimal coupling is a major goal in the development of CTL-inducing vaccines. We recently reported that a membranal derivative of the invariant MHC-I light chain, β₂-microglobulin (β₂m), markedly stabilizes MHC-I molecules and can serve as a universal platform for exceptional presentation of genetically linked peptides. To test whether it is possible to equip the resulting MHC-I complexes with an inherent ability to activate antigen-presenting cells, we engrafted the intracellular Toll/IL-1 receptor domain of mouse Toll-like receptor (TLR) 4 or TLR2 onto the peptide-β₂m scaffold. We evaluated the level of peptide presentation and status of cell activation conferred by such constructs in stably transfected mouse RAW264.7 macrophages and mRNA-transfected mouse DC2.4 DCs. We show that the encoded peptide-β₂m-TLR polypeptides are expressed at the cell surface, pair with endogenous heavy chains, stabilize MHC-I products, prompt efficient peptide-specific T-cell recognition and confer a constitutively activated phenotype on the transfected cells, as judged by the up-regulation of pro-inflammatory genes and surface co-stimulatory molecules. Our results provide evidence that the product of a single recombinant gene can couple MHC peptide presentation to TLR-mediated signaling and offer a safe, economical and highly versatile modality for a novel category of genetic CTL-inducing vaccines.