The invention relates to a method of producing a multichimeric mouse comprising a functional xenogenic (human) immune system restricted to the MHC class I and/or class II molecules (HLA molecules) of the xenogenic species solely, and a functional tissue. The invention relates also th the use of the multichimeric mouse obtainable by said method, to study the immunopathogenesis of tissue-specific diseases (infectious, tumoral or auto-immune pathologies) and to their applications to design and test vaccines or immunotherapeutic agents against these pathologies.