Kidney Transplantation: Comprehensive Study Notes

Overview and significance

  • Kidney transplantation is the treatment of choice for end-stage kidney disease (ESKD).
    • Worldwide, tens of thousands of transplants performed; >$220{,}000$ patients living with a functioning kidney transplant in the U.S. today.
    • First successful kidney transplant in 1954 (Boston) between identical twins.
    • Immunosuppression advances in the 1960s (e.g., azathioprine and prednisone) enabled allograft across non-identical individuals; calcineurin inhibitors in the 1970s–1980s improved 1-year survival notably.
  • Survival and long-term outcomes
    • 1-year survival in the U.S.: living-donor ≈ 98 ext{%}, deceased-donor ≈ 93 ext{%}.
    • Long-term survival: living-donor allografts ≈ 19extyears19 ext{ years}; deceased-donor ≈ 12extyears12 ext{ years}.
    • Age-related perioperative mortality (first year): 2 ext{%} (18–34), 3 ext{%} (35–49), 6.8 ext{%} (≥50–60).
    • Transplantation provides improved life expectancy and quality of life compared with remaining on dialysis, with benefits evident days to months after transplant.
  • Pathophysiology and outcomes
    • Acute rejection now rare; most grafts fail due to chronic processes: interstitial fibrosis/tubular atrophy, vasculopathy, glomerulopathy.
    • Chronic injury results from a combination of alloimmune response, drug toxicity, and other insults.

Recent activity and current state (U.S.)

  • Transplant volume (2022): >19,00019{,}000 deceased-donor and ~6,0006{,}000 living-donor kidney transplants.
  • Waitlist dynamics
    • Increasing number of ESKD patients leads to more waitlist candidates; donor shortage remains a critical challenge.
    • 2022 data: ≈ 139,000139{,}000 adult candidates on the waiting list; ~25,00025{,}000 transplants per year.
  • Allocation changes to expand donor pool and equity
    • 2014 allocation reform: KDPI implemented to estimate graft failure risk using 10 donor factors; KDPI ranges 0–100%.
      -KDPI interpretation:
    • Lower KDPI values → higher expected posttransplant survival.
    • Kidneys with KDPI < 20% are allocated to the 20% of recipients with the best expected posttransplant survival.
    • KDPI > 85% (formerly Expanded Criteria Donor, ECD) directed to patients who would fare poorly on dialysis but benefit from earlier transplantation despite lower quality.
    • 2021 distance-based allocation policy: kidneys offered first to candidates within 250 nautical miles of donor hospitals; intended to reduce geographic disparities but associated with more complex sharing, higher discard rates, and longer cold ischemia time.
  • Donor pool expansion strategies
    • DCD kidneys now commonly used; ~30 ext{%} of total deceased donor transplants.
    • HCV-positive donor organs used since 2017 for HCV-positive or even some HCV-negative recipients to expand the pool; now about 9 ext{%} of deceased kidney transplants.
    • HOPE Act: allowed organ donation from HIV-positive candidates; >100100 transplants performed.
    • Blood type considerations: B wait times longer; eligible B candidates with low anti-A titer can receive A-type donor kidneys to reduce disparities (notably in African-American ESKD population).
    • Xenotransplantation: advances with kidneys from genetically engineered pigs; three experimental kidney transplants into brain-dead recipients in 2022; ongoing issues include xenoimmunity, zoonosis transmission, and ethical challenges, but potential for unlimited organs.
  • Definitions and data references
    • Table 325-1: Definition of a Non-Heart-Beating Donor (Donation After Cardiac Death, DCD): I) brought in dead; II) unsuccessful resuscitation; III) awaiting cardiac arrest; IV) cardiac arrest after brainstem death; V) cardiac arrest in a hospital patient.
    • Table 325-2: Graft and patient survival for kidneys transplanted in the U.S. 1999–2018:
    • 1-year follow-up: Deceased donor graft 94 ext{%}, patient 95 ext{%}; Living donor graft 98 ext{%}, patient 99 ext{%}.
    • 5-year follow-up: Deceased donor graft 76 ext{%}, patient 77 ext{%}; Living donor graft 87 ext{%}, patient 87 ext{%}.
    • 10-year follow-up: Deceased donor graft 54 ext{%}, patient 67 ext{%}; Living donor graft 70 ext{%}, patient 83 ext{%}.
  • Contextual takeaway
    • Despite excellent 1-year outcomes, longer-term survival benefits vary; ongoing improvements in immunosuppression, organ allocation equity, and donor pool expansion remain central to the field.

Recipient evaluation and contraindications

  • Broad benefit: virtually all ESKD patients benefit from transplantation with longer life expectancy and better quality of life.
  • Absolute contraindications to kidney transplantation
    • Chronic illness predicting <2 years of survival.
    • Active malignancy.
    • Active infection.
    • Psychosocial issues preventing adherence to care.
    • Active substance abuse.
  • Cardiovascular risk assessment
    • High cardiovascular mortality risk in ESKD; thorough preoperative and postoperative cardiovascular evaluation for coronary artery disease, valvular disease, and heart failure.
  • Age and functional assessment
    • No official age limit at many centers; >20 ext{%} of waitlisted candidates are >65 years.
    • Must assess physical and cognitive function comprehensively.
  • Cancer considerations
    • History of malignancy is not an absolute contraindication; cancer-free wait times of 2−52{-}5 years depending on malignancy type/stage are recommended to reduce recurrence risk.
  • Infections and antiviral considerations
    • Latent indolent infections (HIV, hepatitis B or C, TB) should be routine in workup.
    • Historically AIDS and active hepatitis were absolute contraindications; potent antiviral regimens now allow transplantation in selected cases.
  • Immunologic contraindications and desensitization
    • Preformed antibodies against donor kidney (ABO antigens or HLA class I/II) threaten hyperacute rejection.
    • Screen with ABO compatibility and cross-matching; desensitization strategies (plasmapheresis, IVIG) used to reduce antibody levels.
    • Non-HLA minor antigens can elicit alloimmune responses; less strong initially and more suppressible with standard immunosuppression.
    • HLA mismatch burden correlates with graft survival; more mismatches → higher rejection risk, though HLA-identical transplants can still fail due to non-HLA antigens or prior sensitization.
    • Emerging data: LIMS-1 non-HLA polymorphisms may contribute to acute rejection risk; more non-HLA antigens likely to be discovered.

HLA matching, tissue typing, and donor evaluation

  • HLA matching principles
    • Major histocompatibility complex (HLA) antigens are highly polymorphic; matching improves graft survival.
    • Tissue typing historically used serology; now molecular HLA typing by genomic sequencing is standard.
    • Number of mismatches at HLA-A, B, and DR loci correlates with graft survival; more mismatches → higher rejection risk.
    • Even HLA-identical transplants can be rejected, possibly due to sensitization to non-HLA antigens.
  • Non-HLA and minor antigens
    • Some non-HLA antigens restricted to endothelium/monocytes described; clinical relevance variable.
    • Minor histocompatibility antigens do not elicit antibodies; sensitization detectable mainly by cytotoxic T cells (rarely practical for routine use).
  • Eplets and antigen recognition
    • Eplets: short sequences of polymorphic amino acids on HLA antigens; recognized by antibodies; eplet mismatches, especially at HLA-DQ loci, are linked to acute rejection risk.
  • Desensitization approaches
    • Desensitization can reduce anti-donor antibodies via plasmapheresis and IVIG and lowers hyperacute rejection risk.
  • Donor pairing strategies
    • Kidney paired donation programs increasingly used to enable compatible transplants when a donor is incompatible.

Donor evaluation

  • Living donors
    • Principle: first, do no harm; exclude conditions that would cause donor morbidity after donation (e.g., hypertension, diabetes, proteinuria).
    • Long-term risk of ESKD after donation is small but present: approximately 0.3{-}0.4 ext{%} baseline risk, with an absolute increase of 0.2{-}0.3 ext{%} versus healthy non-donors.
    • Special considerations:
    • In relatives of type 1 diabetics, screen for anti-insulin/islet antibodies; perform glucose tolerance testing.
    • African-American donors have higher risk for ESKD; consider APOL1 risk allele screening (Chap. 326).
    • Predonation genetic testing is increasingly used to stratify donor risk.
    • Surgical evaluation: selective renal arteriography to assess anatomy and laterality, size mismatch; most nephrectomies are performed laparoscopically to minimize recovery.
    • Ethical, legal, financial considerations: conflicts of interest prohibited; ongoing efforts to reduce barriers to living donation.
  • Deceased donors
    • Donors should be free of malignant neoplasms, hepatitis, and HIV to minimize transmission; under certain circumstances, HCV- and HIV-positive organs can be used.
    • Higher risk of graft failure with elderly donors, donors with AKI, or kidneys with prolonged ischemia.
    • Regulatory framework: Organ Procurement and Transplant Network (OPTN) governs allocation and outcomes analysis.
    • Preservation and ischemia
    • Cold pulsatile perfusion can maintain kidneys up to ~48exth48 ext{ h}; normothermic perfusion studied but not standard.
    • Ischemic time ideally <24exth24 ext{ h} to allow typing, crossmatching, and transport logistics.

Presensitization and crossmatching

  • Sensitization sources
    • Blood transfusion, prior transplant, and pregnancy are common sensitizing events.
    • Vaccination or infection less common sources.
  • Crossmatching approaches
    • Donor T lymphocytes (class I only) used as surrogate target to detect circulating anti-HLA class I antibodies; positive cytotoxic crossmatch predicts hyperacute rejection and is an absolute contraindication.
    • Flow cytometric crossmatch is more sensitive; detects anti-HLA IgG antibodies not always detected by cytotoxic crossmatch; not always a contraindication.
  • Preformed antibodies against donor antigens
    • Anti-class II (HLA-DR and DQ) antibodies carry higher risk of graft loss, especially after prior early loss of a kidney transplant.
  • Non-HLA antibodies and eplets
    • Some non-HLA antibodies described; clinical relevance uncertain.
    • Eplet matching highlights additional antigenic differences contributing to rejection risk.
  • Desensitization and donation strategies
    • Plasmapheresis + IVIG used to reduce donor-specific antibodies prior to transplantation.
    • Kidney paired donation programs help presensitized candidates receive compatible organs.

Immunology of rejection

  • Rejection mechanisms
    • T cell–mediated rejection (TCMR): recipient T cells react to donor HLA in the graft.
    • CD4+ T cells respond to class II (HLA-DR) incompatibility; secrete proinflammatory cytokines -> amplify immune response.
    • CD8+ cytotoxic T cells respond to class I (HLA-A, B) antigens -> cytotoxic lysis of donor cells.
    • Antibody-mediated rejection (ABMR): circulating donor-targeting antibodies against donor antigens.
    • Follicular helper T cells (Tfh) promote B cell differentiation into plasma cells; plasma cells secrete donor-specific antibodies against HLA and non-HLA antigens.
    • Endothelial injury and capillary deposition of antibodies leading to injury via complement-dependent and independent mechanisms.
  • Pathways of T cell activation
    • Full activation requires TCR engagement with alloantigens presented by MHC (direct pathway) and costimulation (CD28–CD80/CD86) on APCs.
    • Indirect pathway involves recipient self-APCs presenting donor-derived peptides; both pathways contribute to rejection, with the indirect pathway being a normal physiologic process in recognizing foreign antigens.
  • Diagnostic footprint and biomarkers
    • C4d deposition in peritubular capillaries and glomerular basement membrane is a diagnostic marker for ABMR when accompanied by circulating donor-specific antibodies.
    • Noninvasive biomarkers are being explored (see later section): donor-derived cell-free DNA, urine chemokines (e.g., CXCL9), urine exosomes.

Immunosuppressive therapy: induction and maintenance

  • Drug classes and general approach
    • Immunosuppression is life-long (except identical twins or some bone marrow–kidney transplants); current therapies suppress broad immune responses with variable memory-sparing effects.
    • Therapies are divided into two phases: induction (perioperative) and maintenance (long-term).
  • Induction therapy
    • Depleting agents: Antithymocyte globulin (ATG) is lymphocyte-depleting (polyclonal antibodies from animals) that can require months–years for immune reconstitution.
    • Monoclonal depletors: Alemtuzumab targets CD52 (B cells, T cells, NK cells, macrophages, etc.).
    • Nondepleting agents: Target the activated T cell IL-2 receptor (CD25, the 55-kDa chain) to prevent early rejection while preserving broader immune defense.
    • Induction intent: reduce early acute rejection and may spare calcineurin inhibitors (CNIs) early post-transplant.
  • Maintenance therapy
    • Most common backbone: a calcineurin inhibitor (CNI) such as tacrolimus or cyclosporine plus an antimetabolite (usually mycophenolate) with or without early steroid withdrawal.
    • Belatacept: a costimulatory blocker (CTLA-4–Ig) used as an alternative to long-term CNI therapy; approved for kidney transplant recipients.
    • mTOR inhibitors: sirolimus (rapamycin) and everolimus; used as alternatives or adjuncts to CNIs in some cases.
    • Antimetabolites
    • Azathioprine: prodrug requiring activation; TPMT inactivation determines risk; has declined in use due to efficacy of newer agents; avoid concurrent allopurinol or monitor carefully due to drug interactions.
    • Mycophenolate mofetil/sodium: metabolized to mycophenolic acid; inhibits inosine monophosphate dehydrogenase; GI intolerance with relatively less marrow suppression than azathioprine.
    • Steroids
    • Glucocorticoids are important adjuncts for induction and maintenance; typical perioperative methylprednisolone dose 250−500extmg250{-}500 ext{ mg}, tapered to 20extmg20 ext{ mg} within a week; long-term maintenance often 5−10extmg/day5{-}10 ext{ mg/day}.
    • Main adverse effects: impaired wound healing and infection risk; efforts aim to minimize long-term steroid exposure.
    • Calcineurin inhibitors (CNIs)
    • Cyclosporine: inhibits calcineurin, reducing IL-2 transcription; nephrotoxicity, hypertension, dyslipidemia, hirsutism, gingival hyperplasia, diabetes.
    • Tacrolimus: similar mechanism; less hirsutism/gingival hyperplasia; higher risk of posttransplant diabetes; managed with therapeutic drug monitoring due to nephrotoxicity and narrow therapeutic window; interactions with macrolide antibiotics, azoles, and non-dihydropyridine calcium channel blockers raise CNI levels; inducers like phenytoin/carbamazepine lower levels.
  • Sirolimus/everolimus (mTOR inhibitors)
    • Inhibit T-cell growth factor signaling, blocking IL-2 signaling to prevent proliferation.
    • Can be used with CNIs or mycophenolic acid to reduce CNI exposure;
    • Side effects: GI upset, stomatitis/mucositis, pneumonitis, hyperlipidemia, thrombocytopenia; poor wound healing limits perioperative use.
  • Belatacept
    • CTLA-4–Ig fusion protein; blocks CD80/CD86, preventing CD28 costimulation; reduces T-cell activation and promotes anergy/apoptosis.
    • FDA-approved for kidney transplantation; BENEFIT trial (7-year follow-up) showed improved patient and graft survival with belatacept vs cyclosporine but higher early acute rejection risk.
  • Other notes
    • TPMT genotyping/phenotyping is recommended before starting azathioprine due to risk of severe myelosuppression in TPMT-deficient patients.
    • Drug interactions and therapeutic drug monitoring are essential due to narrow therapeutic windows for CNIs and interactions with antibiotics/antifungals and certain antihypertensives.

Clinical course and perioperative management

  • Preoperative considerations
    • Adequate hemodialysis within 48exth48 ext{ h} prior to surgery if needed to prevent perioperative potassium disturbances.
  • Surgical technique and early function
    • Graft placement: recipient iliac fossa via retroperitoneal approach.
    • Anastomoses: donor renal artery to recipient external iliac artery; donor renal vein to recipient external iliac vein.
    • Ureteronephric anastomosis: donor ureter to bladder mucosa.
    • Native kidney nephrectomy is rare unless enlarged polycystic kidney or chronic infection; immediate urine production from the graft is common.
    • Acute tubular injury from ischemia may cause postoperative diuresis and electrolyte losses (Na, K, water).
    • Serum creatinine should fall as the allograft begins functioning; typical recovery within 2extweeks2 ext{ weeks}, but up to 6extweeks6 ext{ weeks} has been reported.
  • Early posttransplant management
    • Induction and maintenance immunosuppression start on surgery day; CNIs can be delayed a few days if lymphocyte-depleting induction is used.
    • Monitoring and adjustment guided by clinically high- or low-risk status (see Fig. 325-2 algorithm).
    • PRA (panel reactive antibodies) quantifies anti-donor antibodies against a donor pool; used to guide risk stratification.
  • Risk stratification and management algorithm
    • Low-risk patients: standard immunosuppression; less potent induction (e.g., basiliximab).
    • High-risk patients: more aggressive immunosuppression (e.g., ATG) or CNI-sparing strategies in the immediate posttransplant period.
  • Diagnostic and imaging follow-up for dysfunction
    • If early graft dysfunction occurs, first exclude prerenal causes, obstruction, and vascular issues with ultrasonography.
    • Ultrasound/doppler to assess graft vasculature and blood flow; check for urinoma, hematoma, or lymphocele.
    • Allograft biopsy is the gold standard for diagnosing acute TCMR and ABMR.

Rejection: recognition, diagnosis, and management

  • Clinical recognition
    • Rejection often presents with a rise in serum creatinine; fever, swelling, or tenderness over the graft may be absent.
    • Rule out other causes: ATN, CNI toxicity, BK nephropathy, recurrent glomerular disease.
  • Diagnostics
    • Doppler ultrasound for vascular and urinary issues.
    • Allograft biopsy with Banff classification for TCMR (cell-mediated) and ABMR (antibody-mediated).
    • Endpoints for ABMR include C4d deposition in peritubular capillaries and circulating donor-specific antibodies.
  • Treatment of rejection
    • TCMR: high-dose steroids (e.g., methylprednisolone) at 500−1000extmg/day500{-}1000 ext{ mg/day} for 3extdays3 ext{ days}; nonresponse prompts ATG therapy.
    • ABMR: aggressive therapy due to endothelial injury and antibodies; plasmapheresis, IVIG, anti-CD20 (rituximab), and bortezomib for plasma cells; management of complement-mediated injury is a consideration.
  • Emerging biomarkers and future tools
    • Noninvasive biomarkers in development include donor-derived cell-free DNA, urine chemokines (e.g., CXCL9), and urine exosomes to aid in rejection diagnosis, prognosis, and personalized immunosuppression.

Chronic complications and long-term management

  • Major causes of death after kidney transplantation
    • Cardiovascular events: ≈ 29 ext{%}.
    • Infection: ≈ 18 ext{%}.
    • Malignancy: ≈ 17 ext{%}.
  • Opportunistic infections by time course (Table 325-4 summary)
    • Peritransplant (<1 month): wound infections, Aspergillus, oral candidiasis, BK virus.
    • Early (1–6 months): Hepatitis B and C, CMV, Pneumocystis jirovecii, Legionella, Listeria.
    • Late (>6 months): ongoing risk for CMV, Pneumocystis, Hepatitis B/C, Herpesviruses, and other opportunistic pathogens.
  • Prevention and management of infections
    • Prophylaxis against Pneumocystis jirovecii with daily low-dose TMP-SMX for 6extmonths6 ext{ months}.
    • Local therapy for oral candidiasis (nystatin).
    • Systemic fungal infections require antifungals; treat CMV disease with valganciclovir (prevention and treatment).
    • BK virus risk managed by regular BK viral load monitoring and reduction of maintenance immunosuppression when positive.
  • BK virus biology and management
    • BK virus remains latent in kidney/urothelium; reactivation under immunosuppression leads to nephropathy and graft loss if untreated.
    • Biopsy can show interstitial nephritis, tubular cytopathic changes, and viral antigens.
    • Treatment: primarily reduction of maintenance immunosuppression; alternative therapies (leflunomide, cidofovir, quinolones, IVIG) have mixed results.
  • Chronic lesions and graft dysfunction
    • Chronic rejection: chronic active ABMR and recurrent disease; hypertension and CNI nephrotoxicity contribute to decline.
    • Hypertension control is crucial; calcium channel blockers can favorably influence long-term outcomes; target blood pressure ≈ 120−130/70−80extmmHg120{-}130/70{-}80 ext{ mmHg}.
    • Hypercalcemia may indicate persistent hyperparathyroid activity; partial parathyroidectomy considered in refractory cases.
    • Anemia post-transplant often reflects marrow suppression from immunosuppressants (e.g., azathioprine, mycophenolate, mTOR inhibitors); EPO may be needed.
  • Malignancy risk
    • Post-transplant cancer risk elevated (≈5{-}6 ext{%}); skin cancers and lip cancers most common.
    • PTLD (often EBV-associated) occurs with higher frequency in transplant recipients; prognosis generally poor.
    • Cancer treatment often requires immunosuppression reduction, surgery, chemotherapy, and radiotherapy; cancer immunotherapy carries high allograft rejection risk.
  • Hepatitis and antiviral considerations
    • Chronic hepatitis B and C can complicate immunosuppression; direct-acting antivirals have dramatically reduced HBV/HCV-related risk in modern practice.
  • Future directions and equity
    • Ongoing advances in immunologic/genetic understanding of alloimmunity; noninvasive biomarkers for rejection monitoring; personalized immunosuppression strategies.
    • Efforts needed to improve equity and access to kidney transplantation and to optimize individualized care for recipients.

Practical takeaways and clinical notes

  • KDPI and allocation are central to contemporary organ distribution and recipient selection: lower KDPI kidneys tend to yield better posttransplant survival; high KDPI kidneys are used when earlier transplantation offers overall benefit.
  • Xenotransplantation and broader donor pools (DCD, HCV/HIV donor utilization) are expanding options but require careful ethical and medical considerations.
  • Immunologic risk assessment (sensitization, crossmatching, HLA matching, epitope eplets) informs both donor selection and desensitization strategies.
  • Early posttransplant management relies on balancing graft protection with minimizing infection and drug toxicity; induction therapy is tailored to risk, and maintenance therapy typically combines CNIs, antimetabolites, and steroids with evolving options like belatacept.
  • Rejection management hinges on prompt diagnosis (biopsy as gold standard) and targeted therapy for TCMR and ABMR, with a trend toward noninvasive biomarkers to guide decisions.
  • Long-term care focuses on cardiovascular risk reduction, infection prevention, cancer surveillance, and management of metabolic complications (hypertension, diabetes, dyslipidemia, anemia).
  • Throughout, personalized medicine, ethical considerations (donor risks, consent, and equity), and advancements in antiviral therapies and diagnostic tools will continue to shape practice.

Key terms and concepts to memorize

  • KDPI: Kidney Donor Profile Index, ranges from 00 to 100 ext{%}; lower values favor higher posttransplant survival.
  • DCD: Donation after Cardiac Death; ~30 ext{%} of deceased donor kidneys.
  • HCV/HIV donor utilization: expands donor pool; HOPE Act enables HIV-positive donors in select contexts.
  • ABMR vs TCMR: antibody-mediated vs T-cell–mediated rejection; diagnostic markers include C4d and donor-specific antibodies.
  • Eplets: small surface amino acid sequences on HLA antigens; mismatches can influence rejection risk.
  • Immunosuppressive drug families: CNIs (tacrolimus, cyclosporine), antimetabolites (mycophenolate, azathioprine), steroids, mTOR inhibitors (sirolimus, everolimus), co-stimulation blocker (belatacept), induction antibodies (ATG, alemtuzumab, basiliximab).
  • Common posttransplant complications: infections (CMV, BK virus, Pneumocystis, fungal pathogens), cardiovascular disease, malignancy (PTLD and skin cancers).