Detailed Analysis of CD8+ T Cell Immunity and Identification of a Novel Minor Histocompatibility Antigen Contributing to Graft-Versus- Leukemia Reactivity.

Donor lymphocyte infusion (DLI) can be an effective cellular immunotherapy for patients with hematological malignancies after HLA-matched allogeneic stem cell transplantation (alloSCT). The effect of DLI is mediated by donor derived T cells recognizing minor histocompatibility antigens (mHags) on malignant cells of the recipient. These donor originated T cells may also induce Graft-versus-Host Disease (GvHD) when directed against mHags with broad expression on non-malignant tissues of the patient. In this study, we performed a detailed analysis and characterization of mHags recognized by CD8+ T cells contributing to Graft-versus-Leukemia (GvL) reactivity in a patient treated with DLI for relapsed chronic myeloid leukemia (CML) more than one year after HLA-matched alloSCT. The GvL effect in this patient was accompanied with only mild GvHD of the skin.

To investigate the specificity of the CD8+ T cell response induced in this patient, activated (HLA-DR+) CD8+ T cells were single cell sorted from a bone marrow sample obtained five weeks after DLI by flowcytometry. A number of isolated CD8+ T cell clones were shown to be specific for mHags, as determined by differential recognition of patient and donor EBV-transformed B cells (EBV-LCL) in IFN-g ELISA and 51Crrelease assays. By screening a panel of third party EBV-LCL sharing one or more HLA class I restriction molecules with the patient, CD8+ T cell clones directed against 7 different mHags were identified, including the known hematopoiesis restricted mHags HA-1 and HA-2, which are presented in HLA-A*0201. Of the 5 remaining specificities, 4 mHags were presented in HLA-B*4001 (B60) and one mHag in HLA-B*0801. To determine the tissue distribution patterns in more detail, we tested recognition of selected non-malignant hematopoietic cells (monocytes, B cells, T cells), malignant CD34+ CML precursor cells, and skin-derived fibroblasts. One HLA-B*4001-restricted T cell clone (clone ZRZ16) failed to recognize all primary hematopoietic cells and skin fibroblasts. The four remaining T cell clones were all capable of recognizing and lysing (specific subsets of) non-malignant hematopoietic cells and malignant CD34+ CML precursor cells. Fibroblast recognition could be demonstrated for two of these four T cell clones. Since clone ZRZ16 failed to recognize all hematopoietic and non-hematopoietic cells, except for EBV-LCL, we tested whether this clone selectively recognizes antigen presenting cells (APC), which are known to be required for efficient induction of immune responses in vivo. Clone ZRZ16 showed indeed strong recognition of monocyte-derived dendritic cells as well as in vitro differentiated CD34+ CML cells with APC phenotype. To identify the mHag recognized by the CD8+ T cell clone, we screened a cDNA expression library constructed from EBV-LCL from the patient. One single cDNA was isolated as the target for B*4001 restricted CD8+ T cell clone ZRZ16. The epitope recognized by this clone was derived from the 3’ untranslated region (UTR) of a cDNA encoding thyroid hormone receptor interactor 10 (TRIP10). The peptide epitope was translated in a reading frame different from the TRIP10 protein and comprises three single nucleotide polymorphisms, which were all different between patient and donor. Two of the three SNPs were shown to be important for recognition by clone ZRZ16. Despite ubiquitous tissue expression of the TRIP10 gene as determined by public microarray analysis, CD8+ T cells specific for the newly-identified LB-TRIP10-1EPC mHag selectively recognized APC and failed to recognize CD34+ CML precursor cells, suggesting a predominant role in the initiation, but not effector, phase of the anti-tumor response. In conclusion, our data show a detailed analysis of mHag specific CD8+ T cell immunity induced in a patient successfully treated with DLI for relapsed CML and provide evidence for differential involvement of HLA class I restricted mHags in the onset and execution of GvL reactivity.