The invention concerns an isolated animal cell comprising at least a transgene including at least a nucleotide sequence coding for at least a human polypeptide involved in the recognition and/or antigenic activation by T cells. The invention is characterised in that said cell, or a progeny of said cell, expresses at least all or part of the or said human polypeptide(s), and the homologous endogenous animal gene coding for an animal polypeptide homologous with said human peptide is invalid. The invention also concerns the corresponding transgenic animal. The cell and the transgenic animal of the invention can be used in a method for screening compounds which modulate an immune response in humans. The invention further concerns the use of the inventive cell as cell rendered autologous or tolerated by the immune system.