The invention relates to the field of immunology and immunotherapy, in particular, to adoptive T cell therapy of cancer utilizing T cell receptor (TCR)-engineered T cells. The invention provides novel methods and tools for identification and cloning of TCR, which are also applicable for identification of other receptors such as B cell receptors or antibodies. The invention provides immortalized cell lines able to induce subset specific (e.g. CD4 + or CD8 + specific) hybridization during co-culture, e.g., with primary lymphocytes of mice or men. The immortalized cells are engineered to express two mutated glycoproteins derived from the paramyxovirus family, namely hemagglutinin (H) and fusion (F) or a derivative thereof. H is a chimeric protein not able to bind to its natural ligands, fused to a targeting ligand capable of specifically binding to a specific cell surface antigen such as a lymphocytic subset-marking ligand (e.g. CD4 or CD8); fusion (F) mediates the fusion of cellular membranes of the immortalized cell line and cells, e.g., primary lymphocytes, H has bound to. The methods of the invention comprise preparing a hybridoma cell expressing a receptor, comprising steps of co-culturing a cell expressing a specific cell surface antigen and said receptor with the specific immortalized cells of the invention. The invention also relates to the hybridoma cells obtainable by said method.