ATP Dependent Interferon Responsive (ADIR) Gene Encodes an Activation Induced Minor Histocompatibility Antigen Recognized on Multiple Myeloma by CD8+ T Cells.

Minor histocompatibility antigens (mHag) play an important role in beneficial graft versus tumor (GVT) reactivities but mHag reactive T cells may also cause graft versus host disease (GVHD). A female patient with relapsed multiple myeloma (MM) after allogeneic HLA identical stem cell transplantation (SCT) responded 7 weeks after donor lymphocyte infusion (DLI) by developing transient acute GVHD grade II and complete clearance of the malignant cells resulting in a long lasting complete remission. From blood and bone marrow samples that were taken at the time of the clinical response, a dominant HLA-A2 restricted CD8+ CTL designated RDR2, was isolated that recognized the patients MM cells, PHA-blasts and EBV-LCL, but not resting T cells. To identify the peptide recognized by CTL RDR2, HLA-A2 was isolated from EBV-LCL that were recognized by CTL RDR2, and peptides were separated and fractionated by HPLC techniques applying several different separation conditions. Various HPLC fractions were analyzed by mass spectrometry (MS) and tested for recognition by CTL RDR2 in ⁵¹Chromium release assays. Based on the correlation between the presence of specific masses in the MS analyses and the reactivity of the fractions, candidate masses were selected, sequence analysis was performed, and synthetic peptides were generated. An 11-mer peptide was recognized by CTL RDR2 and was found to be identical to amino acid 13–23 of an alternatively translated protein of the ATP dependent interferon responsive (ADIR) gene. ADIR gene constructs forcing translation into the alternative frame displayed higher recognition as compared to constructs resulting in normal translation. Patient but not donor cells contained a known genomic polymorphism in the ADIR gene resulting in an amino acid change from serine (S) to phenylalanine (F) in the alternative frame. When ADIR gene transcripts from a panel of 76 unrelated HLA-A2 positive individuals were sequenced, a 100% correlation was found between the presence of the ADIR polymorphism and lysis of PHA-blasts by CTL RDR2. The polymorphism was present in 43 out of 76 individuals tested. We designated the mHag LB-ADIR-1F. Tetramer staining of patient samples taken after DLI showed at the peak of the response 2.6% LB-ADIR-1F specific CD8+ T cells. Despite the high number of circulating cytotoxic CTL, GVHD was mild, and rapidly disappeared after treatment. Since ADIR gene expression is not restricted to hematopoiesis, we compared recognition of LB-ADIR-1F expressing hematopoietic cell types with recognition of LB-ADIR-1F expressing mesenchymal stem cells and biliary epithelial cells. In both IFNg production assays and in cytotoxicity assays responses to MM cells, other hematological malignancies and activated T and B cells were strong, whereas resting T cells and non hematopoietic cells displayed only minor stimulatory capacity and were poorly lysed by LB-ADIR-1F specific T cells. In conclusion, the ADIR gene encodes a new frequently occurring mHag, and recognition of the antigen by LB-ADIR-1F reactive cells seems to depend on the activation state of the target cells. We therefore hypothesize that administration of LB-ADIR-1F reactive T cells may result in GVT responses, and that concurrent GVHD development may depend on the activation state of GVHD target tissues.