Two patients were switched from CNI or mammalian target of rapamycin inhibitors to belatacept, one due to tacrolimus-induced thrombotic microangiopathy (confirmed by graft biopsy showing severe signs of CNI arteriolar toxicity and no deposition of immunoglobulin or C3) and the other because of mammalian target of rapamycin-associated side effects. Here, C3 is linked to Genetic thrombotic microangiopathy.