TARGETED DELIVERY OF PEPTIDE EPITOPES TO CLASS-I MAJOR HISTOCOMPATIBILITY MOLECULES BY A MODIFIED PSEUDOMONAS EXOTOXIN

Cytotoxic T lymphocytes (CTLs) expressing the CD8 surface marker recog nize peptides in association with major histocompatibility complex (MH C) class I molecules. Although most peptides expressed on MHC class I molecules are derived from self- or virally encoded proteins, delivery of exogenous proteins to the cytosol can result in their being proces sed for presentation to CTLs on MHC class I molecules. We describe two fusion proteins (PEMa and PENP), consisting of the binding and transl ocating domains of Pseudomonas exotoxin A (PE), fused to peptide epito pes from influenza A matrix protein and nucleoprotein, respectively. T hese fusion proteins were internalized and processed by MHC class I-po sitive target cells, resulting in sensitization of target cells for ly sis by peptide-specific CTLs. A point mutation known to interfere with intoxication by wild-type PE also reduced the ability of PEMa to sens itize target cells. Fusion of peptide or polypeptide epitopes with PE provides a potential means of eliciting CTLs without the use of self-r eplicating agents, as well as a useful probe for studying MHC class I- restricted antigen processing.