Kidney exchange solves incompatibility matching

Because a kidney must be physiologically compatible, a healthy person who loves someone needing a kidney often cannot donate to them—sometimes due to antibodies developed through childbirth against the partner's leukocyte antigens; kidney exchange solves this by having incompatible donor-patient pairs swap, so each donor gives to a compatible stranger and their loved one receives from another donor, with chains begun by non-directed donors multiplying the effect.