The genetic composition of a donor impacts long-term allograft survival after kidney transplantation. Effects of the recipient's genetic make-up, particularly variation in immune response pathway genes, are less certain. Bay et al. reveal improved graft survival in transplant recipients with lower copy numbers of the complement 4 gene (C4) after receipt of deceased-donor kidneys. Genomics breakthroughs in nephrology and immunology will likely revolutionize the field of transplant medicine.