Most people dont have an identical twin who can or will give them a kidney. But the closer the genetic match between the donor and recipient then the better the results of transplantation. The main match is the blood group ABO system. To ensure that the recipients antibodies do not attack the donor kidney the donor and recipient should be matched. A recipient who is blood group A will have antibodies present against B and so cannot receive a kidney from someone who is B or AB. A recipient who is blood group B will have antibodies against A and so cannot receive a kidney from someone who is A or AB.