|Ph.D Thesis||Department of Biology|
|Supervisor:||Prof. Reiter Yoram|
Several studies revealed that tumor progression is often associated with the development of mechanisms that enable tumor escape from the host's immune system. One mechanism is down regulation of peptide presentation via class I MHC on tumor cells surface. Moreover, tumor antigens presented by class I MHC not always stimulate the adaptive immune response. We describe herein a new cancer immunotherapy strategy that combines the advantage of well-established tumor targeting high affinity recombinant fragments of antibodies with the known specific, efficient and potent killing ability of CD8 T lymphocytes.
We constructed a recombinant molecule in which scHLA-A2 was genetically fused to the variable domains of the anti mesothelin antibody SS1 which targets ovarian carcinomas and mesotheliomas. The construct, termed HLA-A2/ ss1(scFv), was expressed in E. coli and functional molecules were produced by in vitro refolding of inclusion bodies in the presence of an HLA-A2-restricted EBV antigenic peptide. FACS assays showed that HLA-A2-negative mesothelin-positive cells were coated with the HLA-A2/ ss1(scFv) molecule in a manner that was entirely dependent upon the specificity of the targeting Ab fragment. Moreover, when targeted to tumor cells expressing mesothelin, the molecule induced very efficient cell lysis as indicated by cytotoxic assays. Most importantly, these molecules exhibited potent anti tumor activity in vivo in nude mice bearing pre-established human tumor xenografts. When injected intravenously into tumor bearing nude mice, followed by adoptive transfer of EBV specific human CTLs, the tumors xenografts showed marked regression.
We showed the ability of the HLA-A2/ ss1(scFv) molecule to mediate efficient killing of tumor cells in vitro and in vivo by recruiting human T lymphocytes specific for viral antigen. These experiments demonstrate two major advantages of the new concept. The ability to direct CTLs to specific population of tumor cells based on tumor specific antibodies, and the ability to recruit specific population of CTLs dictated by the peptide bound to the HLA-A2 /scFv. Our results suggest that recombinant MHC-scFv fusion molecules could represent a new approach to immunotherapy, bridging the antibody and T lymphocyte attack on cancer cells.