EPO and anemia (phenotype): This may be due to several factors, including 1) a possible lower physiological trigger for EPO production in porcine kidney due to lower normal hemoglobin concentration, 2) reduced binding affinity of porcine EPO for human EPO receptor, 3) myelosuppression due to immunosuppressive medications, and 4) anemia of chronic disease due to chronic low-grade inflammation associated with a renal xenograft.