Secretion of genetically engineered human/mouse class I antigens

Two soluble, secreted forms of HLA-B7 were engineered by the creation of hybrid human/mouse molecules containing the polymorphic 5′ region of the HLA-B7 gene and the secretory 3′ region of the mouse Q10 d gene. The hybrid, designated F1, is the first construct with only human extracytoplasmic domains, consisting of exons for the leader peptide and the three extracellular domains (α1, α2, α3) of B7 spliced to the exons for the Q10 d truncated transmembrane and 3′ untranslated (3′UT) sequences. The second construct, designated C2, is similar but has the human α3 replaced by the Q10 α3 domain. Protein product from each construct was best demonstrated after gene transfection into the J27.2 cell line. In particular, secretion of the F1 product proves that the Q10 α3 domain is not necessary for secretion of class I/Q10 hybrids. Moreover, the two soluble B7 forms, which differ only in their α3 domain, are similarly recognized by monoclonal antibodies W6/32 (anti-HLA-ABC), BBM.1 (anti-human ß 2 microglobulin), and allo-B7-antibody, but differentially recognized by monoclonal antibody Q1/28 (anti-HLA class I heavy chain). Production of such soluble hybrid class I molecules in large amounts should allow critical structural and functional studies of these proteins.