Cells transfected with DNA sequences encoding for a PreImplantation Factor (PIF) or a PIF and one or more fusion tag(s) are disclosed. Also disclosed are DNA sequences encoding for synthetic PIFs, a PIF fusion peptide made of a PIF and one or more fusion tags, methods of treatment using the transfected cells that express a PIF, an R-I-K-P peptide, compositions containing the R-I-K-P peptide, and methods of identifying a compound that binds to an active site of an WX
