1234567Cells 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 WXWXXXREWFXXXW receptor wherein each X can be any amino acid.