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The alloreactive human T cell clone MBM15 was found to exhibit dual specificity recognizing both an antigen in the context of the HLA class I A2 molecule and an antigen in the context of the HLA class II DR1. We demonstrated that the dual reactivity that was mediated via a single clonal T cell population depended on specific peptide binding. For complete recognition of the HLA-A2-restricted specificity the interaction of CD8 with HLA class I is essential. Interestingly, interaction of the CD8 molecule with HLA class I contributed to the HLA-DR1-restricted specificity. T cell clone MBM15 expressed two in-frame T cell receptor (TCR) V[Alpha] transcripts (V[Alpha]1 and V[Alpha]2) and one TCR V[Beta] transcript (V[Beta]13). To elucidate whether two TCR complexes were responsible for the dual recognition or one complex, cytotoxic T cells were transduced with retroviral vectors encoding the different TCR chains. Only T cells transduced with the TCR V[Alpha]1V[Beta]13 combination specifically recognized both the HLA-[A2.sup.+] and HLA-[DR1.sup.+] target cells, whereas the V[Alpha]2V[Beta]13 combination did not result in a TCR on the cell surface. Thus a single TCR[Alpha][Beta] complex can have dual specificity, recognizing both a peptide in the context of HLA class I as well as a peptide in the context of HLA class II. Transactivation of T cells by an unrelated antigen in the context of HLA class II may evoke an HLA class I-specific T cell response. We propose that this finding may have major implications for immunotherapeutic interventions and insight into the development of autoimmune diseases.

Background: Patients with hematologic malignancies can be successfully treated with donor lymphocyte infusion after HLA-matched allogeneic hematopoietic stem cell transplantation. The effect of donor lymphocyte infusion is mediated by donor T cells recognizing minor histocompatibility antigens. T cells recognizing hematopoietic restricted minor histocompatibility antigens may induce selective graft-versus-leukemia reactivity, whereas broadly-expressed antigens may be targeted in graft-versus-host disease., Design and Methods: We analyzed in detail CD8(+) T-cell immunity in a patient with relapsed chronic myelogenous leukemia who responded to donor lymphocyte infusion with minimal graft-versus-host disease of the skin. CD8(+) T-cell clones specific for 4 HLA-B*40:01 restricted minor histocompatibility antigens were isolated which were identified by screening a plasmid cDNA library and whole genome association scanning. Detailed T-cell reactivity and monitoring experiments were performed to estimate the clinical and therapeutic relevance of the novel antigens., Results: Three antigens were demonstrated to be expressed on primary leukemic cells of various origins as well as subtypes of non-malignant hematopoietic cells, whereas one antigen was selectively recognized on malignant hematopoietic cells with antigen presenting cell phenotype. Skin derived fibroblasts were only recognized after pre-treatment with IFN-γ by two T-cell clones., Conclusions: Our data show evidence for different roles of the HLA-B*40:01 restricted minor histocompatibility antigens in the onset and execution of the anti-tumor response. All antigens may have contributed to a graft-versus-leukemia effect, and one minor histocompatibility antigen (LB-SWAP70-1Q) has specific therapeutic value based on its in vivo immunodominance and strong presentation on leukemic cells of various origins, but absence of expression on cytokine-treated fibroblasts.

Background and Objectives: Cytotoxic T-lymphocytes (CTL) have been generated in vitro against chronic myeloid leukemia (CML)-associated BCR/ABL-specific peptides. We analyzed the existence of high-avidity T cells recognizing endogenously processed BCR/ABL-specific proteins., Design and Methods: We performed binding studies of BCR/ABL-specific peptides, proteosomal digestion of BCR/ABL breakpoint overlapping protein, mass spectrometry of eluates from HLA-*0301-transduced K562 cells, and tried to isolate peptide-specific T-cells using tetramers., Results: We confirmed the binding of the BCR/ABL-specific peptides KQSSKALQR to HLA-A*0301 and GFKQSSKAL to HLA-B*0801. Proteasomal digestion showed cleavage sites leading to KQSSKALQR but not to GFKQSSKAL. Using mass spectrometry KQSSKALQR could not be detected in the eluates from HLA-A*0301-transduced K562 cells. We attempted to induce BCR/ABL-specific CTL lines from 4 healthy donors using dendritic cells pulsed with KQSSKALQR and performed single cell sorting to isolate tetramer-positive T cells. None of 31 generated clones showed BCR/ABL-specific cytotoxicity. Isolation of tetramer-positive cells from peripheral blood of relapsed CML patients after allogeneic transplantation treated with donor lymphocyte infusion resulted in 38 T-cell clones which did not show peptide-specific cytotoxicity., Interpretation and Conclusions: We provide evidence that BCR/ABL protein processing can lead to KQSSKALQR peptide binding to HLA-A*0301. However, KQSSKALQR could not be detected in HLA-A*0301-transduced K562 cells, and KQSSKALQR could not be demonstrated to induce high-avidity BCR/ABL-specific CTL.