Kidney Transplant: Immunosuppression & Complications
Balancing rejection against drug toxicity for life
Candidacy, Timing, and the Maintenance Regimen
Why transplant. For most patients with kidney failure, a transplant gives longer survival and better quality of life than any form of dialysis. Refer for evaluation once eGFR falls below 30 mL/min/1.73 m² (ideally 6–12 months before dialysis is expected); waitlisting, and accrual of deceased-donor waiting time, can begin once eGFR is 20 or less. The best result is a preemptive living-donor transplant done before dialysis starts: living-donor kidneys last longer, and time on dialysis worsens later graft and patient survival.
Pretransplant preparation. Candidates need ABO and HLA typing, a crossmatch (recipient serum against donor lymphocytes) for preformed donor-specific antibodies, cardiovascular evaluation, and cancer screening. Pregnancy, transfusion, or a prior transplant sensitizes patients (high panel-reactive antibody). Live vaccines such as MMR and varicella must be given at least 4 weeks before surgery; afterward only inactivated vaccines (yearly injectable influenza, pneumococcal, hepatitis B, recombinant zoster) are used.
Induction and maintenance. Induction at surgery uses basiliximab (anti-CD25, the IL-2 receptor α chain) or depleting antithymocyte globulin. Maintenance is usually lifelong triple therapy: tacrolimus dosed to trough levels, mycophenolate, and low-dose prednisone. Tacrolimus (via FKBP12) and cyclosporine (via cyclophilin) inhibit calcineurin, blocking NFAT-driven IL-2 transcription. Belatacept, a CTLA-4–Ig costimulation blocker, is a CNI-free option reserved for EBV-seropositive recipients because of PTLD risk.
Immunosuppressant Toxicities and Interactions
Calcineurin inhibitors (CNIs). Acute nephrotoxicity is dose-dependent afferent arteriolar vasoconstriction that reverses when the dose is lowered; chronic exposure leaves irreversible arteriolar hyalinosis and striped interstitial fibrosis. CNIs also cause hyperkalemia (type 4 RTA pattern), hypomagnesemia from renal wasting, hyperuricemia and gout, hypertension, dyslipidemia, neurotoxicity (tremor, headache, seizures, PRES), new-onset diabetes after transplant, and thrombotic microangiopathy. Tacrolimus is more diabetogenic and neurotoxic; cyclosporine causes more hypertension, hyperlipidemia, and hyperuricemia, plus gingival hyperplasia (shared with phenytoin and calcium channel blockers) and hirsutism.
| Drug | Mechanism | Hallmark toxicities | Pearls |
|---|---|---|---|
| Tacrolimus, cyclosporine | Calcineurin inhibition → ↓ IL-2 | Nephrotoxicity, ↑ K, ↓ Mg, hypertension, tremor, diabetes, TMA | Trough-guided dosing; CYP3A4 substrates |
| Mycophenolate | IMP dehydrogenase inhibition → ↓ de novo guanine synthesis, which lymphocytes rely on | Diarrhea, leukopenia, anemia | Teratogenic → azathioprine ≥6 weeks before conception |
| Azathioprine | Prodrug of 6-mercaptopurine | Myelosuppression, hepatotoxicity, pancreatitis, skin cancer | Xanthine oxidase inhibitors or TPMT deficiency → pancytopenia |
| Sirolimus, everolimus | Bind FKBP12, inhibit mTOR → block IL-2 signaling | Poor wound healing, lymphocele, hyperlipidemia, pneumonitis, mouth ulcers, proteinuria, cytopenias | No vasoconstriction; fewer new skin SCCs; avoided in pregnancy |
| Prednisone | ↓ Cytokine gene transcription | Hyperglycemia, osteoporosis, avascular necrosis, cataracts | High-dose pulses treat acute rejection |
CYP3A4 interactions. CNIs and mTOR inhibitors are CYP3A4 and P-glycoprotein substrates. Inhibitors (azole antifungals, clarithromycin, erythromycin, diltiazem, verapamil, grapefruit juice, ritonavir) raise levels and cause toxicity; inducers (rifampin, carbamazepine, phenytoin, phenobarbital, St John's wort) lower levels and precipitate rejection. Adjust doses and recheck troughs whenever these start or stop, or choose alternatives such as azithromycin. NSAIDs and aminoglycosides add nephrotoxicity; ACE inhibitors, ARBs, and trimethoprim add hyperkalemia.
Antimetabolites and mTOR inhibitors. Mycophenolate is teratogenic (first-trimester loss; ear, facial, and cleft malformations), so women need contraception and a switch to azathioprine before conception. Azathioprine becomes 6-mercaptopurine, which xanthine oxidase inactivates; allopurinol or febuxostat therefore causes thiopurine accumulation and severe pancytopenia, so switch to mycophenolate or cut azathioprine to one-quarter to one-third of the dose. Sirolimus and everolimus promote wound dehiscence and lymphoceles, so they are avoided right after surgery.
Gout is common after transplant: avoid NSAIDs, treat flares with glucocorticoids, lower colchicine doses with cyclosporine, and never pair a xanthine oxidase inhibitor with full-dose azathioprine.
Rejection
| Type | Timing | Mechanism and biopsy | Management |
|---|---|---|---|
| Hyperacute | Minutes to hours | Preformed anti-ABO or anti-HLA antibodies fix complement → graft thrombosis (type II hypersensitivity) | Remove graft; prevented by ABO matching and a negative crossmatch |
| Acute T-cell–mediated | Days to months | Interstitial lymphocytes with tubulitis ± endarteritis | Pulse IV methylprednisolone; antithymocyte globulin if steroid-resistant |
| Acute antibody-mediated | Days to months, or later with new antibodies | Donor-specific antibodies, glomerulitis, peritubular capillaritis, C4d deposition | Plasmapheresis + IVIG ± rituximab, plus steroids |
| Chronic | Months to years | Interstitial fibrosis and tubular atrophy (IF/TA), transplant glomerulopathy (duplicated GBM) | Irreversible; ensure adherence, control BP and proteinuria |
Clinical picture. Acute rejection, most often T-cell–mediated, is usually an asymptomatic creatinine rise, occasionally with fever, graft tenderness, or oliguria. Nonadherence and low CNI levels are the main modifiable triggers and also provoke new donor-specific antibodies. Chronic rejection causes slowly rising creatinine, proteinuria, and hypertension.
Approach to a Rising Creatinine
The causes are treated in opposite ways (steroids treat rejection but worsen BK nephropathy), so evaluate in steps:
- Volume and drugsPrerenal states, NSAIDs, ACE inhibitors or ARBs, diuretics, trimethoprim.
- Tacrolimus troughHigh suggests CNI toxicity; low raises concern for rejection.
- Urinalysis and graft ultrasound with DopplerHydronephrosis, urine leak, lymphocele, renal artery stenosis, or vascular thrombosis.
- Plasma BK PCR and donor-specific antibodiesPolyomavirus versus antibody-mediated injury.
- Graft biopsyThe only way to confirm rejection and separate it from CNI toxicity, BK nephropathy, or recurrent disease.
Timing clues. The first week brings delayed graft function (ischemic ATN, mostly deceased donors), vascular thrombosis (sudden anuria), and urine leaks; lymphoceles, ureteral stenosis, and acute rejection follow over weeks to months. Transplant renal artery stenosis causes resistant hypertension, a graft bruit, or a creatinine jump on an ACE inhibitor and is treated with angioplasty and stenting. Primary FSGS can recur within days as heavy proteinuria.
BK polyomavirus nephropathy. Reactivation, mostly in the first year, causes tubulointerstitial nephritis and ureteral stenosis that mimic rejection. Plasma BK PCR screens; biopsy shows SV40-staining nuclear inclusions, and urine may contain "decoy cells." Treatment is reducing immunosuppression, usually the antimetabolite first; no reliable antiviral exists.
Infection Prevention, Malignancy, and Cardiovascular Risk
Prophylaxis. For the first months, TMP-SMX prevents Pneumocystis (and covers toxoplasma, Nocardia, many urinary pathogens) and valganciclovir prevents CMV, highest risk in a seronegative recipient of a seropositive donor (D+/R−). Valganciclovir causes leukopenia; trimethoprim raises potassium and blocks creatinine secretion. Opportunistic infections are covered with the immunocompromised host.
Skin cancer. The most common post-transplant malignancy; squamous cell carcinoma outnumbers basal cell carcinoma (reversed ratio) and behaves aggressively. Recipients need yearly skin examinations and sun protection; for recurrent SCC, converting a CNI to sirolimus reduces new tumors, whereas azathioprine increases UV-related risk.
PTLD. EBV-driven B-cell proliferation, most frequent in the first year and in EBV-seronegative recipients of seropositive grafts, especially after T-cell–depleting induction. It causes fever, lymphadenopathy, or masses in the graft, gut, or CNS. First reduce immunosuppression; add rituximab for CD20-positive disease, with chemotherapy when needed.
Cardiovascular disease. The leading cause of death after kidney transplant; most recipients who die have a functioning graft. Hypertension, post-transplant diabetes (tacrolimus, steroids), and dyslipidemia compound pre-existing CKD vascular disease, so control all three aggressively, using lower statin doses with cyclosporine, which raises statin levels.
Other noninfectious late problems: post-transplant erythrocytosis (treated with an ACE inhibitor or ARB), persistent tertiary hyperparathyroidism with hypercalcemia, and steroid-induced osteoporosis.