Xenograft rejection suppression.

A biological tissue comprising endothelial cells which may be induced to generate a compound that downregulates expression of a cell adhesion molecule by the cells, the compound being either (a) a polynucleotide complementary in sequence to a part of the gene or mRNA encodes the cell adhesion molecule, (b) a polynucleotide comprising a ribozyme sequence that specifically targets a gene or mRNA encoding the cell adhesion molecule, or (c) a peptide having specific binding affinity for the molecule cell adhesion.