Abstract: Homologous recombination is employed to inactivate genes, particularly genes associated with MHC antigens. Particularly, the .beta..sub.2 -microglobulin gene is inactivated for reducing or eliminating Class I MHC antigens. The resulting cells may be used as universal donors. In addition, embryonic stem cells may be modified by homologous recombination for use in producing chimeric or transgenic mammalian hosts, which may be used as source of universal donor organs.

Abstract: Homologous recombination is employed to inactivate genes, particularly genes associated with MHC antigens. Particularly, the .beta..sub.2 -microglobulin gene is inactivated for reducing or eliminating Class I MHC antigens. The resulting cells may be used as universal donors. In addition, embryonic stem cells may be modified by homologous recombination for use in producing chimeric or transgenic mammalian hosts, which may be used as source of universal donor organs, or as models for drug and transplantation therapies.

Abstract: Compounds are provided which can be used in the preparation of reagents useful for quantitatively determining the presence of .beta.-adrenergic blocking agents. These compounds contain a derivative of the blocking agent which is linked to an antigen or enzyme, the antigen conjugates being useful for preparing antibodies, and the enzyme conjugates being useful as detectors in an immunoassay as well. Additionally carboxylic acids, esters and aldehydes which are derivatives of the blocking agents are provided which are useful in preparing the above conjugates.