For renal transplants - not sure if there’s an upper limit, although each subsequent transplant becomes a more difficult match (as antibodies build up) and eventually may have to remove previous transplants. Generally renal transplants go in the right or left groin with native kidneys left in place. If one transplant fails, a transplant to the opposite side may be attempted, or a different location (such as intra-abdominal). Otherwise, will need to explant the first transplant