Novel system for the evaluation of the activity and/or specificity of a viral component

A method for the evaluation of at least one property selected from the group consisting of activity and specificity of a surface protein comprising the steps of:

• a) using a transgenic non-human animal comprising in its genome one or more viral sequence, but being deficient in one or more surface protein sequence required for generation of infectious virus;
• b) introducing into said transgenic non-human animal the one or more surface protein sequence under control of a ubiquitous regulatory element, thereby allowing reconstitution of viral particle generation within cells of the transgenic non-human animal for which the surface protein is functional;
• c) maintaining the transgenic animal under suitable conditions allowing the production and release of infectious viral particles in cells of said transgenic non-human animal for which the surface protein is functional;
• and
• d) detecting at least one site selected from the group consisting of cells and tissues in which viral particles are produced,
• wherein the production of viral particles by a cell or tissue indicates that the surface protein is functional in the cell or tissue.

A method for the evaluation of the distribution of a cellular receptor for a ligand in an animal comprising the steps of:

• a) introducing into a cell of a transgenic non-human animal comprising in its genome one or more viral sequence, but being deficient in one or more viral sequence comprising a gene which encodes a viral surface protein required for the generation of the virus, a viral vector comprising the viral sequence comprising the gene which encodes the viral surface protein, thereby allowing reconstitution of the viral particle generation in the cell of the transgenic animal, wherein the viral sequence encoding the viral surface protein contains the coding sequence of the ligand so that upon expression of this sequence a modified viral surface protein is produced that contains the sequence of the ligand in the part of the protein that is accessible for interaction with the cellular receptor;
• b) maintaining the transgenic animal under suitable conditions allowing the production of viral particles in cells of the transgenic animal;
• and
• c) detecting the cells in which viral particles are produced, wherein the production of virus by a cell indicates that the cell contains the cellular receptor.