SPECIFIC T CELL RESPONSES TO BCR-ABL CHIMERIC PROTEIN

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The hallmark of chronic myelogenous leukemia (CML) is the transposition of the c-abl oncogene from chromosome 9 to the specific breakpoint cluster region (bcr) of the bcr gene on chromosome 22. The transposition results in the formation of a new fusion bcr-abl gene which encodes a 210 kD chimeric protein with abnormal tyrosine kinase activity. The c- abl and bcr genes are expressed by normal cells and thus the encoded proteins are presumably non-immunogenic. However, the joining region segment of the p210 chimeric protein is composed of unique sequences of c-abl amino acids joined to bcr amino acids joined to bcr amino acids which are expressed only by malignant cells. Preliminary studies have shown that the joining region of bcr-abl protein is immunogenic to T cells. Bcr-abl proteins are appealing candidate targets for immunotherapy for several reasons including: (a) bcr-abl protein is an antigen shared by many individuals with malignancy-being detected in greater than 95% of patients with CML and 13% of patients with acute lymphocytic leukemia; (b) bcr-abl protein is intimately associated with malignant transformation as well as maintenance of the malignant phenotype. Thus, antigen-negative variants are not likely; (c) T cells can recognize and respond to the joining region segment of bcr/abl protein which is expressed only by malignant cells. Thus therapy would be selective with minimal potential for toxicity; (d) normal bone marrow precursors commonly co-exist with the malignant clone in the bone marrow of CML patients, so that selective destruction of the malignant clone would leave normal hematopoiesis intact; (e) T cell therapy of CML in the form of allogeneic bone marrow transplantation (BMT) has already been shown to be effective. Patients with CML who develop graft-vs-host disease (GVHD) following HLA-identical BMT rarely relapse, implying that donor T cells recognizing minor histocompatibility antigens are capable of eradicating CML cells. T cells immune to bcr-abl might function as T cells immune to minor histocompatibility antigens but without the toxicity of GVHD; (f) the potential problems of T cell tolerance and anergy to proteins expressed by malignant cells can be easily circumvented by using an HLA-identical bone marrow donor as a source of immune T cells for specific adoptive therapy- a procedure already shown to be effective for transferring virus-specific immunity. The specific aims of the current proposal are: (1) tp develop methods to use bcr-abl specific CD4+ T cells for tumor therapy in murine models; (2) to develop methods for generating and utilizing bcr-abl specific class I MHC-restricted CD8+ T cells in murine models; (3) to determine whether patients with CML have existent CD4+ T cells primed to p210 bcr- abl protein; (4) to determine whether patients with CML have existent CD8+ T cells primed to p210 bcr-abl; (5) to determine whether T cells with reactivity to p210 bcr-abl protein can be detected and procured from normal individuals, particularly HLA-identical siblings who might serve as a source of immune T cells to be used as part of a bone marrow transplantation procedure; (6) to determine whether patients with CML develop specific humoral responses to p210 bcr-abl protein; (7) to develop and evaluate bcr-abl vaccines in mice that are appropriate for eventual use in humans.