Thomas Graddis

Enhanced major histocompatibility complex class I-dependent presentation of antigens modified with cationic and fusogenic peptides.

Soluble extracellular protein antigens are notoriously poor stimulators of CD8+ cytotoxic T-lymphocyte (CTL) responses, largely because these antigens have inefficient access to an endogenous cytosolic pathway of the major histocompatibility complex (MHC) class I–dependent antigen presentation. Here, we present a strategy that facilitates antigen penetration into the cytosol of antigen-presenting cells (APC) by addition to the antigen of charge-modifying peptide sequences. As a result of this intervention, the charge modification enhances antigen uptake into APC by counteracting the repulsive cell surface charge, and then endosomal membranes are disrupted with a subsequent release of antigen into the cytosol. This technology significantly improves MHC class I–dependent antigen presentation to CTL, enabling a more efficient generation of specific CTL immunity in vivo. The strategy described here has potential for use in developing efficient vaccines for antigen-specific immunotherapy of human malignancies.

Antitumor vaccination with HER-2-derived recombinant antigens

Certain types of malignant tumors overexpress HER‐2, a transmembrane glycoprotein of the class I receptor tyrosine kinase erbB family. To develop an effective HER‐2 vaccine for the selective immunotherapy of these malignancies, we have genetically engineered fusion proteins containing portions of extra‐ and intracellular HER‐2 domains. Activated dendritic cells (DC) cocultured with these novel antigens (Ag) could induce potent responses of Ag‐specific T‐cell lines in vitro and a protection against HER‐2‐expressing tumor in vivo. The protective capabilities of HER‐2‐derived fusion proteins correlated with the efficiency of their presentation to Ag‐specific T‐cell hybridomas. The most effective Ag contained GM‐CSF, the presence of which facilitated their internalization by antigen‐presenting cells (APC) in a receptor‐mediated manner.

Specific stimulation of MHC-transgenic mouse T-cell hybridomas with xenogeneic APC.

From the recombinant human leukocyte antigen (HLA)-DR1/H2-E(k) major histocompatibility complex (MHC) class II-transgenic mice, we have generated two CD4(+) T-cell hybridomas specific for peptides which were derived from human prostatic acid phosphatase (PAP) complexed to the human class II molecule HLA-DR1. Both hybridomas strongly react to PAP-pulsed antigen-presenting cells (APC) from transgenic mice. Interestingly, these hybridomas also responded to PAP antigen presented by HLA-DR1-positive human APC. The species-mismatched T-cell stimulation occurs despite the biologic discordance in participating accessory molecules, which are required for the optimal T-cell-APC interaction. Our results demonstrate various degrees of functional interaction between coreceptors, costimulatory molecules, and integrins, which are expressed on the surface of T-cell hybridomas and heterologous APC.

Major Histocompatibility Complex Class I-Restricted Presentation of Protein Antigens without Prior Intracellular Processing

Proteins in their native form are incapable of stimulating antigen (Ag)‐specific T cells, which can only recognize major histocompatibility complex (MHC)‐bound peptides that have been generated by intracellular processing within antigen‐presenting cells (APCs). Here, we show that APCs can trigger MHC class I‐restricted T‐cell responses after presenting proteins without conventional intracellular processing, provided the immunostimulatory MHC class I‐binding peptide sequence is incorporated at the carboxy‐terminal position. Such MHC‐bound proteins do not stimulate T cells directly, because the contact between MHC/peptide complex and its cognate ligand is sterically hindered by the amino‐terminal bulk of the protein. Removal of the latter via an extracellular Ag proteolysis by the T‐cell‐ and/or APC‐derived enzymes is required for effective T‐cell stimulation. Our data challenge the established concept that only small peptides can bind to the MHC class I molecules.