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 A*0201) with a covalently attached beta 2m. This molecule (MSC beta A2.1) can be detected on the surface of transfected beta 2m- human cells by conformational antibodies W6/32 and BB7.2 and by anti-human beta 2m mAb BM-63. The covalent beta 2m, now a domain of the MSC beta A2.1 molecule, does not rescue endogenous Class I surface expression. Instead, it works in cis to achieve correct folding of the single-chain molecule. Immunoprecipitation shows that MSC beta A2.1 is a 60-kDa molecule with no dissociable beta 2m. The half-life of the MSC beta 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 molecules on live cells can bind the HBV core peptide 18-27 with comparable affinities. These results show that MSC beta A2.1 molecules retain the functional ability to present both pulsed and endogenous antigens to the appropriate T cells, and thus may be useful components of antiviral vaccines.