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RENAL TRANSPLANTATION IN CHILDHOOD. Lynne P. Yao, M.D. INOVA Fairfax Hospital for Children Fairfax, VA. Overview. Review basic transplantation immunology Review immunosuppressive agents used in children Review clinical renal transplantation outcomes in children

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Renal transplantation in childhood l.jpg

RENAL TRANSPLANTATION IN CHILDHOOD

Lynne P. Yao, M.D.

INOVA Fairfax Hospital for Children

Fairfax, VA


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Overview

  • Review basic transplantation immunology

  • Review immunosuppressive agents used in children

  • Review clinical renal transplantation outcomes in children

  • Review specific complications of renal transplantation in children

  • Review the role of the general pediatrician in the care of a child with a renal transplant

  • Review future directions in renal transplantation


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Historical perspectives

  • 1902: First experimental kidney transplantation by Emerich Ullmann

  • 1933: First human kidney transplant by Voronoy

  • 1950-53: First functioning human kidney transplant (2 centers)

  • 1961: Azathioprine first used successfully

  • 1962: First use of tissue matching to select a donor

  • 1963: Prednisolone and Azathioprine combination produced longer graft survival

  • 1972: Successful transplantation into a 9 month-old girl

  • 1978: First clinical use of cyclosporine A


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Transplant immunology

  • ABO group matching

    • Blood group mismatches result in hyperacute rejection in most cases

    • ABO incompatible donor protocols underway in children

  • Human Leukocyte Antigen (HLA) matching

  • Panel Reactive Antibodies (PRA) and Crossmatching

  • Rejection

    • an immune response raised by the recipient against foreign (donor) alloantigens

    • allograft rejection is a coordinated event


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HLA (Human Leukocyte Antigen) matching

  • HLA system is divided into 2 classes

  • Class I: HLA-A, HLA-B, HLA-C

    • Expressed on most cell surfaces

  • Class II: HLA-DR, HLA-DP, HLA-DQ

    • Expressed predominantly on antigen presenting cells

  • HLA-A, HLA-B, HLA-DR most important in clinical transplantation

  • HLA genes located on short arm of chromosome 6

  • HLA antigens are inherited in a Mendelian fashion as codominant alleles


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Example of HLA matching

HLA locus

A B DR

Mother 3/29 13/44 5/7

Father 2/1 8/42 4/3

Patient 3/18/445/3

  • Result: Patient is a 3/6 antigen match with each parent (haplotype match)

  • Haplotype matching improves graft survival because minor (unidentified) HLA loci are also matched


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Crossmatching

  • Used to detect presence of preformed HLA antibodies against donor tissues

  • Lymphocytes from donor are incubated with recipient serum, complement added, and cell lysis is detected

  • Positive crossmatch is associated with high risk for hyperacute rejection

  • Prevents development of hyperacute rejection


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Panel reactive antibodies (PRA)

  • PRA

    • Used to assess likelihood of positive crossmatch

    • Lymphocytes from a “representative” panel of donors are incubated with serum from patient

    • Expressed as a percentage of panel cells showing activity

    • High PRA levels are associated with greater likelihood of positive crossmatch

    • Major risk factors for high PRA are prior blood transfusion, pregnancy, and prior transplant


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T lymphocyte activation

from Arakelov, Lakkis, Semin. Nephrol., 20:2, 2000


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CD4 and CD8 interactions

CD4 and B cell interactions

Other CD4 interactions

Interactions mediated by CD40 costimulatory pathway

(from Arakelov, Lakkis, Semin. Nephrol., 20:2, 2000)



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The “paradigms” of transplant immunosuppression

  • The Proliferation Paradigm

    • drugs that prevent immune cell proliferation prevent rejection

    • Prednisone, Azathioprine, Mycophenolate Mofetil

  • The Depletion Paradigm

    • drugs that decrease immune cell numbers prevent rejection

    • polyclonal and monoclonal antibodies

  • The Cytokine Paradigm

    • drugs that modify cytokine production prevent rejection

    • Calcineurin inhibitors, Prednisone, IL-2R monoclonal antibodies




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Pediatric Renal Transplantation

  • NAPRTCS (North American Pediatric Renal Transplant Cooperative Study)

    • Voluntary, collaborative effort

    • 150 participating centers in US, Canada, Mexico, and Costa Rica

    • Registry for pediatric renal transplants since 1987

    • Registry for ESRD since 1992

    • Registry for chronic renal insufficiency since 1995


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Characteristics of Pediatric Dialysis Patients

Number Percent

From Neu, Pediatr. Nephrol., 17:2002



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Age at transplantation

Age Number Percent


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Cadaveric donor Living related donor

Patient survival by age at primary transplantation



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Cadaveric donor Living related donor

Primary graft survival by age at time of transplantation



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Risk factors for chronic rejection

Relative risk increase p-value


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% Rejection

Time to first rejection episode


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Risk factors for acute rejection

Characteristics Living donor Cadaver donor

RR p-value RR p-value

From McDonald, Amer. J. Transplan., 1:2001


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Time in years

Cadaveric donor Living related donor

Primary graft survival by race


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Significant complications

  • Growth failure

  • Infection

  • Posttransplant lymphoproliferative disorder (PTLD)

  • Diabetes mellitus


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Growth failure

  • Growth fails to improve after renal transplantation in several studies

    • Improvement in growth occurs only in the younger age groups (age 0-5 years)

    • Long term steroid therapy is implicated

    • Change to alternate day dosing of prednisone has shown to improve growth

    • Growth hormone improves growth

    • Growth hormone not associated with increased risk of rejection or significant graft

    • Theoretical risk of malignancy


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Infectious complications

  • Bacterial

    • Generally more likely in early posttransplant period

  • Viral

    • CMV and other Herpes viruses

    • CMV infections relative common and symptoms may be severe

    • CMV infection may increase risk of chronic rejection

  • EBV

    • Infection can produce spectrum of disease

  • Varicella

    • Risk significantly decreased with immunization pretransplant


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PTLD

  • Malignancy associated with polyclonal expansion of B cells associated with rise in EBV titers

  • Incidence of PTLD in pediatric renal transplants is 1.2% overall

  • Incidence has increased slightly

  • Increased incidence with use of tacrolimus, white race, and cadaver donor

  • Treatment generally involves reduction in immunosuppression dose and antiviral agents


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Posttransplant diabetes mellitus (PTDM)

  • Occurs in small number (2.6%) of pediatric renal transplant patients

  • Higher risk groups

    • African American race

    • Use of tacrolimus

  • No differences based on overweight, presence of specific HLA antigens, family history, or prednisone dose

  • Increased incidence of acute rejection in PTDM group


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Role of general pediatrician

  • Growth and development

  • Surveillance for infection

  • Immunizations

    • Live virus vaccines can be given if prednisone dose is low

    • Influenza vaccine and pneumococcal vaccine are recommended

  • Awareness of potential drug interactions

    • drugs that increase activity of CYP450 will increase metabolism of calcineurin inhibitors

    • Tegretol, Dilantin, INH, Phenobarbital, Rifampin

    • drugs that compete for metabolism by CYP450 will decrease the metabolism of calcineurin inhibitors

    • Cimetidine, ketoconazole, erythromycin, diltiazem


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Future directions

  • Steroid withdrawal or steroid avoidance protocols

  • Designer immunosuppression

  • Tolerance

  • Xenotransplantation


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Transplant tolerance

  • A state where the immune system does not respond to a specific antigen: A Way to Peace

  • Strategies to induce tolerance

    • CD28 and CD40L blockade

    • CTLA4 and FasL blockade

  • Studies in nonhuman primates are promising

  • No data on long term effects, or long term graft function



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Xenotransplantation

  • The need: 12,000 renal transplants were performed, but 42,000 patients remained on waiting lists

  • The solution: xenotransplantation

    • Major obstacles: hyperacute rejection, delayed xenograft function, and “xenoses”

    • Search for the suitable species



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Kidney allocation and distribution

  • 1984: US Congress passes National Organ Transplant Act (NOTA)

  • NOTA provides for the establishment and operation of an Organ Procurement and Transplantation Network (OPTN)

  • 1986: United Network of Organ Sharing (UNOS) was awarded the contract to develop OPTN

  • US is divided into regions each with a separate Organ Procurement Organization (OPO)

  • Washington Regional Transplant Consortium (WRTC) is the Washington metropolitan area OPO


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Allocation of cadaveric kidneys

UNOS scoring system


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% Graft survival

Time in years

Cadaveric donor Living related donor

Primary graft survival by use of induction antibody


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Time in years

Cadaveric donor Living related donor

Primary graft survival by number of transfusions


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Prednisone

  • First immunosuppressive agent used

  • Several immunosuppressive effects

    • inhibit gene transcription of several cytokines ( IL-1, IL-2, IL-6, IF-g, TNF-a) by binding to 5’ glucocorticoid response areas of DNA

    • produces lympholysis by direct effects on lymphocyte membrane

    • causes sequestration of circulating T cells

    • antagonizes neutrophil and monocyte chemotaxis


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Prednisone

  • Side effects

    • Cardiovascular: hypertension

    • ID: infection and delayed wound healing

    • GI: peptic ulcer disease, pancreatitis

    • Endocrine: hyperglycemia, growth failure, obesity, hyperlipidemia

    • Ortho: osteoporosis, aseptic necrosis

    • Ophtho: cataracts

    • Derm: acne, hypertrichosis

    • Psych: psychosis, pseudotumor cerebri


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Azathioprine

  • History

    • Derivative of 6-MP but can be given orally

    • First drug widely used for maintenance immunosuppression

  • Immunosuppressive effects

    • metabolized to 6-thioinosinic acid and is incorporated into strands of DNA and RNA and causes chromosome breaks

    • 6-thioinosinic inhibits purine (adenine and guanine) synthesis from inosine

  • Side effects

    • Hematologic: bone marrow suppression, megaloblastic anemia

    • Derm: alopecia

    • GI: hepatic dysfunction


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Mycophenolate Mofetil

  • History

    • semi-synthetic derivative of mycophenolic acid produced by fungus Penicillium

    • approved by the FDA in 1995 for use in rejection prophylaxis in renal transplantation

  • Immunosuppressive effects

    • irreversible inhibitor of inosine monophosphate dehydrogenase (IMPDH) that converts IMP to GMP

    • prevents de novo synthesis of GMP from IMP. GMP is essential nucleoside for purine synthesis

    • lymophcytes use de novo synthesis of purines exclusively

  • Side effects

    • GI: diarrhea, GI discomfort, GI bleeding (12%)

    • Cardiovascular: hypertension

    • Hematologic: leukopenia, thrombocytopenia

    • ID: increased risk of CMV infection (10%)

    • none developed PTLD


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Polyclonal antibodies

  • ATGAM

    • Equine antilymphocyte antibody

  • Thymoglobulin

    • Rabbit antilymphocyte antibody

    • used for induction and treatment of acute rejection

  • Side effects

    • anaphylaxis: hypotension, fever, pulmonary edema, bronchospasm, diarrhea

    • PTLD


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Monoclonal antibodies

  • OKT3 (targets CD3 receptor on T cells)

  • Anti-IL-2 receptor (IL-2R) Ab

  • Anti ICAM-1 Ab

  • Anti CD40 Ab


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Cyclosporine A

  • History

    • isolated from 2 strains of fungi imperfecti

    • 1200 kD, 11 amino acid hydrophobic protein

  • Immunosuppressive effects

    • forms heterodimeric complex with a cytoplasmic receptor protein (cyclophilin)

    • This complex binds calcineurin and inhibits its phosphatase activity

    • also enhances TGF-b expression which inhibits IL-2

  • Side effects

    • Renal: nephrotoxicity due to renal vasoconstriction, interstitial fibrosis, de-novo thrombotic microangiopathy, hypomagnesemia, type IV RTA (hyperkalemia), hyperuricemia

    • Cardiovascular: hypertension

    • GI: hepatotoxicity, cholestasis

    • Neuro: seizures, coma, cortical blindness, tremor, dysesthesia

    • Derm: hypertrichosis, gingival hyperplasia, acne


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Tacrolimus

  • History

    • a macrolide antibiotic derived from the fungus Streptomyces tsukubaensis

    • first used on liver transplant recipients in 1989

  • Immunosuppressive effects

    • mechanism of action similar to cyclosporine A

    • forms heterodimeric complex with a cytoplasmic receptor protein (FK-binding protein)

    • This complex binds calcineurin and inhibits its phosphatase activity

  • Side effects

    • Renal: similar nephrotoxicity profile as cyclosporine A

    • Endo: hyperglycemia, overt diabetes (10%)

    • GI: anorexia, diarrhea, nausea

    • Neuro: similar to cyclosporine A

    • Oncologic: post-transplantation lymphoproliferative disease (PTLD) (5-10%)

    • ID: increased incidence of CMV infection (13%)


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Sirolimus

  • History

    • structure very similar to tacrolimus, also a macrolide antibiotic derived from the fungus Streptomyces hydroscopicus

    • also known as rapamycin, named after a fungus found on the island of Rapa Nui (Easter Island)

  • Immunosuppressive effects

    • binds to FK-binding protein

    • inhibits co-stimulatory path (CD28) translocation of transcription factor

    • may be synergistic with cyclosporine A and tacrolimus

    • no nephrotoxicity or hyperglycemia

  • Side Effects

    • Heme:

    • Endocrine:

    • NO NEPHROTOXICITY