Ph.D Thesis Department of Biology

Ravit Oren


Redirecting T Cell with Chimeric Receptors Composed of T
Cell Receptor-like Antibodies toward the Tumor
Derived Antigen WT1 Presented on MHC
Complex

Supervisor: Prof. Reiter Yoram
Full thesis text - English Version   Full Thesis text


Abstract

Adoptive transfer of antigen-specific T lymphocytes is an attractive form of immunotherapy for haematological malignancies and solid cancers. However, acquiring sufficient numbers of host derived tumor-specific T lymphocytes by selection and expansion is challenging, as these cells may be rare or anergic, and they often have a low affinity to tumor-specific antigens.   To overcome this difficulty, the strategy of using engineered T cells has been developed. By cell engineering, tumor-targeting of T cells can be achieved using chimeric receptors, which are based on two common formats composed from different antigen-recognition elements. The first is based on αβTCR genes, drived from T-cell clones that are transferred into the patient's T cells. The second format is based on antibody Fv fragments fused with a cytotoxic T-cell-signaling molecule.

 In the past decade, our laboratory isolated antibodies that recognize MHC-peptide complexes. Such TCR-like antibodies exhibit both the binding properties and kinetics of antibodies (e.g., high affinity), and mimic the specificity of TCRs. In the study presented here, we isolated TCR-like antibodies, termed F2 and F3, which recognize HLA-A2-WT1Db126 complexes with an affinity of 400 nM and 30 nM, respectively. Using these TCR-like antibodies, we generated chimeric receptors by fusing the scFv form of the antibody with a cytotoxic T-cell-signaling molecule. By transduction of these chimeric receptors into primary T cells, we were able to generate T cells that recognize HLA-A2-WTDb126 complexes with different affinities. A retroviral vector containing αβTCR genes directed against HLA-A2-WTDb126 complexes (Hans Stauss et al.) was used as a comparison for low-affinity T cells, which represents the T cells' physiological binding affinity.

 The study revealed that increased T-cell receptor binding affinity affected the receptor's ability to maintain its specificity and resulted in a leakage in the receptor's discrimination ability, i.e., cross reactivity to HLA-A2 complexes presenting irrelevant peptides.