Engineering and characterization of a murine MHC class II-immunoglobulin chimera expressing an immunodominant CD4 T viral epitope

T cells recognize peptides derived from the processing of proteins by antigen presenting cells (APCs) in association with the major histocompatibility complex (MHC) moleules. We have engineered a murine MHC class II antigen presenting molecule consisting of the extracellular domains of I-E(d)α and I-E(d)β chains to which the CD4 T cell immunodominant epitope HA110-120 of the hemagglutinin (HA) of the A/PR/8/34 influenza virus was covalently linked at the N-terminus of the I-E(d)β chain. The HA110-120-I-E(d)αβ complex was dimerized by the Fc portion of an IgG2a linked at the C-terminus of the I-E(d)β chain. SF9 insect cells infected with baculovirus carrying both I-E(d)α and HA110-120-I-E(dβ)-Fcγ2a genes, secreted a disulfide-stabilized dimer of the HA110-120-I-E(d)αβ-Fcγ2a molecule, designated as DEF. The chimeric molecule preserved the structural integrity of both MHC-peptide complex and Fc portion of IgG2a, and was able to: (i) bind specifically to the cognate T cell receptors (TCRs) and to the immunoglobulin FcγRII receptor (FcR), (ii) induce complement-mediated cell cytotoxicity, and (iii) trigger early production of IL-2 in cognate T cells. Chimeric antigen presenting molecules with these characteristics may represent a novel platform for the development of immunomodulatory agents of therapeutic use.