Identification and characterization of human minor histocompatibility antigens.

摘要

Human minor histocompatibility antigens (mHag) present significant barriers to successful bone marrow transplantation in that they represent the targets of donor-derived CTL that mediate GVHD. The structure of, and genes encoding, human mHag are still largely unknown, yet knowledge of these factors is necessary to better understand the immune responses against them. To address this issue, we first describe the use of novel mass spectrometry instrumentation to identify a male-specific mHag restricted by HLA-A*0101 (A1-HY). This antigen has the sequence IVDC*LTEMY, where C* represents a cysteine disulfide bonded to a second cysteine residue. The core peptide sequence is encoded by DFFRY, a Y chromosome gene not previously identified as the source of an HY antigen. The female form of the peptide differs from the male form by the substitution of serine for the C* residue. Both peptides are expressed on the cell surface at 30 or fewer copies per cell. However, A1-HY specific CTL recognize the DFFRY-derived peptide at a 1500-fold lower dose than the female homolog. Second, we report the identification of the gene encoding the previously identified HA-2 mHag. In doing so, we developed a technique we have termed homology mapping to predict 1.9 kb of the HA-2 message. Using RT-PCR, we not only confirmed the existence of this message in HA-2+ cells, but also determined that HA-2 (YIGEVLVSV) differs from its nonantigenic allelic counterpart (YIGEVLVSM) by a single amino acid change at position 9 of the epitope. This amino acid change results in failure of the latter peptide to be presented at the cell surface. Our genetic data has also allowed us to develop an RFLP-based genotyping technique for determining HA-2 allelism, and to confirm that the gene is expressed only in cells of hematopoetic origin. Lastly, we have classified this novel gene as a human class I unconventional myosin named MYO1G. These studies have thus identified one new minor H peptide and two new mHag-encoding genes, and thereby provide additional information about both the genetic origins of human mHag as well as the influence of posttranslational modifications of Class I associated peptides on T cell recognition.