Class-, gene-, and group-specific HLA silencing by lentiviral shRNA delivery.

HLA incompatibility is the most relevant immunologic barrier to cell-based therapies. Improvement of histocompatibility is essential to achieving better survival of allogeneic cells in the foreign organism. RNA interference technology can be used to selectively and stably reduce cellular HLA class I expression. In the present study, we designed small interfering RNA (siRNA) molecules that target either beta2-microglobulin (beta2m) or HLA-A heavy chain transcripts and identified sensitive sites on the target RNAs using an in vitro transcription/translation (IVTT) system. Transfection of siRNA into B-lymphocyte cell lines (B-LCLs) resulted in specific reduction of HLA class I or HLA-A antigen expression by 79% at the mRNA and protein levels. An allele-specific HLA silencing rate of 65% was achieved in a B-LCL heterozygous for HLA-A*24,*68 allospecificities using HLA-A*68-specific siRNA. Lentiviral delivery of short hairpin RNA into HeLa and B-LCL cells resulted in selective and permanent silencing of HLA class I or HLA-A by up to 90% even under inflammatory conditions. In cytotoxicity and proliferation assays, it was demonstrated that HLA class I knockdown was effective in preventing antibody-mediated cell lysis and CD8+ T cell response, while the residual HLA expression in HLA-silenced cells was protective against NK-cell-mediated lysis. The present data strongly suggest that silencing of HLA expression in a class-, gene-, and group-specific manner is an effective approach that may provide a new basis for developing new immunotherapies in the field of regenerative medicine.