A RECOMBINANT SINGLE-CHAIN HLA-A2.1 MOLECULE, WITH A CIS ACTIVE BETA-2-MICROGLOBULIN DOMAIN, IS BIOLOGICALLY-ACTIVE IN PEPTIDE BINDING AND ANTIGEN PRESENTATION

We have constructed a recombinant single-chain human HLA-A2.1 molecule (from A0201) with a covalently attached beta(2)m. This molecule (MSC beta A2.1) can be detected on the surface of transfected beta(2)m(-) human cells by conformational antibodies W6/32 and BB7.2 and by anti-h uman beta(2)m mAb BM-63. The covalent beta(2)m, now a domain of the MS C beta A2.1 molecule, does not rescue endogenous Class I surface expre ssion. Instead, it works in cis to achieve correct folding of the sing le-chain molecule. Immunoprecipitation shows that MSC beta A2.1 is a 6 0-kDa molecule with no dissociable beta(2)m The half-life of the MSC b eta A2.1 molecule on transfected cell surfaces was as long as that of two-chain HLA-A2.1 molecules. The MSC beta A2.1 molecule was active in presentation of HTLV-I Tax 11-19 peptide and an endogenous peptide to specific CTL, MSC beta A2.1 molecules and wild-type HLA-A2.1 molecule s on live cells can bind the HBV core peptide 18-27 with comparable af finities. These results show that MSC beta A2.1 molecules retain the f unctional ability to present both pulsed and endogenous antigens co th e appropriate T cells, and thus may be useful components of antiviral vaccines.