Purified truncated recombinant HLA-B7 molecules abrogate cell function in alloreactive cytotoxic T lymphocytes by apoptosis induction

Background. Soluble MHC class I molecules are ubiquitous in human body flui ds, including serum, urine, sweat, and cerebrospinal fluid. However, their biological function has remained unresolved. Membrane-derived human soluble MHC molecules (soluble human leukocyte antigen; sHLA) have been shown to i nduce apoptosis in alloreactive cytotoxic T lymphocytes (CTL), Here we repo rt the efficacy of recombinant soluble HLA-B7 (rsHLA-B7) to modulate T-cell function. Methods. Primers of HLA-B7 were designed to allow amplification of a cDNA l acking the transmembrane and cytoplasmic domains yielding a truncated gene. rsHLA-B7 molecules were expressed in the human myeloma cell line 721.221 a nd purified by affinity chromatography using the BB7.7 mouse monoclonal ant ibody. CTL were generated from peripheral blood lymphocytes derived from he althy blood donors by stimulation with irradiated Epstein Parr virus-transf ormed HLA-B7-positive B cells. CTL were preincubated with rsHLA-B7, and cyt otoxicity and apoptosis were tested according to standard procedure. Results. A total of 2 x 10(6) cells/ml secreted 10 mu g/ml rsHLA-B7 as dete rmined by a conformation-dependent ELISA, suggesting that rsHLA-B7 do not r equire the transmembrane and cytoplasmic regions for proper folding. After purification by affinity chromatography, rsHLA-B7 induced apoptosis in anti -HLA-B7 CTL, but not in anti-HLA-A2-specific, CTL. As a consequence, allore cognition of target cells by the CTL was significantly blocked. Conclusion. Recombinant sHLA are sufficient binding cues for T cells, which efficiently induce apoptosis and block allorecognition of target cells by CTL. Thus, recombinant sHLA molecules may become a valuable new modality fo r specific immunological therapeutic intervention.