8. Transplantation Basic Concepts: Brain Death, Indications, Immunosuppression

I. Basic Concepts of Transplantation

Transplantation: Transfer of cells, tissues or organs from donor to recipient to restore missing/damaged function
Used mainly in end-stage organ failure when conservative/surgical alternatives are insufficient
Can be life-saving → Heart, liver, lung
Can be life-improving and survival-improving → Kidney, pancreas, intestine, hematopoietic stem cell transplantation
Main surgical principle → Remove, preserve, transport and implant organ with the shortest safe ischemic time

Types by Donor-Recipient Relationship

Type	Meaning	Example / note
Autograft	Same individual	Skin graft, vein graft, bone graft
Isograft	Between genetically identical individuals	Monozygotic twins; minimal rejection risk
Allograft	Between genetically non-identical individuals of the same species	Most organ transplantation
Xenograft	Between different species	Experimental/limited; strong immunological barrier

Types by Anatomical Position

Orthotopic transplantation → Graft placed in the normal anatomical position
Examples → Heart, liver, lung
Heterotopic transplantation → Graft placed in a different anatomical position
Examples → Kidney transplant to iliac fossa, pancreas transplant to iliac fossa

Commonly Transplanted Organs / Tissues

Kidney → Most frequent solid organ transplant
Liver
Heart
Lung
Pancreas
Small intestine / multivisceral transplant
Hematopoietic stem cells / bone marrow
Tissues → Cornea, skin, bone, vessels, heart valves

Donor Types

1. Living Donor

Can be genetically related or non-genetically related
Non-related donor may be emotionally related, e.g. spouse/partner/close friend
Living donation must protect donor safety and requires free informed consent
Possible donations → Kidney, liver segment, hematopoietic stem cells/bone marrow, rarely lung lobe or pancreas segment in selected centers

Usual donor criteria → Healthy, good organ function, acceptable age/BMI, no active infection, no active malignancy, no severe psychiatric/substance problem
Lung donor specific → Non-smoker or very low smoking history, excellent lung function
Advantages → Elective timing, shorter ischemic time, better planning, often better long-term graft outcomes, lower delayed graft function in kidney transplantation

2. Deceased Donor

Donation after brain death (DBD) → Brain death confirmed, circulation maintained by ICU support until retrieval
Donation after circulatory death (DCD) → Death declared by irreversible circulatory/respiratory arrest before retrieval
Donor management aims to preserve organs → Oxygenation, circulation, temperature, electrolytes, urine output, infection control

Compatibility and Allocation Principles

ABO blood group compatibility is essential for most organ transplants
HLA matching especially important in kidney and hematopoietic stem cell transplantation
Important HLA loci → HLA-A, HLA-B, HLA-DR
Crossmatch → Tests whether recipient has antibodies against donor antigens
Negative crossmatch reduces hyperacute rejection risk
Organ size matching important → Heart, lung, liver
Other allocation factors → Urgency, waiting time, pediatric priority, sensitization, logistics, cold ischemic time, Eurotransplant/national rules

II. Brain Death and Consent

Brain death: Complete, permanent and irreversible cessation of all brain function, including brainstem function
Legally and medically death in jurisdictions that recognize neurological death criteria
Important because organs may remain perfused by mechanical ventilation and circulatory support
Diagnosis must be independent from transplant interest

Causes

Primary brain injury → Direct intracranial pathology

Examples → Traumatic brain injury, intracranial hemorrhage, ischemic stroke with edema, brain tumor, raised intracranial pressure

Secondary brain injury → Global cerebral hypoxia/ischemia

Examples → Cardiorespiratory arrest, severe hypoxia, shock

Prerequisites Before Testing

Known sufficient cause of coma
Irreversibility established
No confounding factors

Exclude → Sedatives/intoxication, hypothermia, severe metabolic/endocrine disturbance, neuromuscular blockade, shock
Imaging may support diagnosis and cause → CT/MRI/angiography according to local protocol

Clinical Criteria

Irreversible coma → No consciousness, no response compatible with brain activity
Absence of brainstem reflexes
Apnea → No spontaneous breathing during apnea test despite adequate CO2 stimulus

Brainstem reflexes checked → Pupillary light reflex, corneal reflex, oculocephalic/oculovestibular reflexes, gag/cough reflex, motor response to cranial stimulation
Spinal reflexes may persist and do not exclude brain death
Ancillary tests if needed/local protocol → EEG, cerebral angiography, CT angiography, transcranial Doppler, perfusion studies

Consent Models

Explicit consent / opt-in → Donation allowed only if donor gave consent during life or family/legal representative authorizes according to law
Presumed consent / opt-out → Donation allowed unless the person objected during life according to legal rules
Hungarian practice → Presumed consent for deceased donation; written objection during life prevents organ removal
Living donation → Always requires free, informed, specific consent and donor protection

III. Indications for Organ Transplantation

General indication → End-stage irreversible organ failure or selected malignant/metabolic disease where transplantation gives survival/QOL benefit
Patient must be fit enough to survive operation and lifelong follow-up/immunosuppression
Contraindications vary by organ and center

Common Indications by Organ

Organ	Main indications
Kidney	End-stage renal disease, usually GFR < 15 ml/min/1.73 m2 or dialysis-dependent kidney failure Causes → Diabetes mellitus, hypertension, glomerulonephritis, polycystic kidney disease
Liver	End-stage liver disease/cirrhosis, acute liver failure, selected hepatocellular carcinoma within criteria, metabolic/genetic disease Causes → HBV, HCV, alcohol-associated liver disease, NASH/MASLD, autoimmune liver disease, Wilson disease
Heart	End-stage heart failure refractory to maximal therapy, usually NYHA IV or severe functional limitation Causes → Ischemic cardiomyopathy, dilated cardiomyopathy, congenital/valvular disease in selected cases
Lung	End-stage pulmonary disease refractory to treatment Causes → COPD/emphysema, pulmonary fibrosis, cystic fibrosis/bronchiectasis, pulmonary arterial hypertension
Pancreas	Type 1 diabetes with severe complications, e.g. hypoglycemia unawareness or labile diabetes; often simultaneous pancreas-kidney transplant
Small intestine	Intestinal failure/short bowel syndrome with life-threatening complications of parenteral nutrition or loss of venous access
Hematopoietic stem cells	Leukemia, lymphoma, aplastic anemia, immunodeficiency and selected genetic/metabolic hematological diseases

General Contraindications / Problems

Active uncontrolled infection
Active extra-organ malignancy or insufficient tumor-free interval, depending on tumor type
Severe irreversible comorbidity with unacceptable operative risk
Active substance abuse or inability to adhere to treatment/follow-up
Severe uncontrolled psychiatric/social problem affecting compliance
Advanced age alone is not absolute → Biological fitness matters

IV. Immunosuppression and Graft Rejection

Allografts are recognized as foreign by recipient immune system
Purpose of immunosuppression: Prevent rejection while minimizing infection, malignancy and drug toxicity
Usually lifelong after solid organ transplantation
Combination therapy → Lower dose of each drug, different mechanisms, less toxicity than maximal single-drug therapy

Immunosuppressive Regimens

1. Induction Therapy

Strong immunosuppression around transplantation/perioperative period
Goal → Reduce early acute rejection risk
Agents → High-dose corticosteroids, anti-thymocyte globulin (ATG), basiliximab
Rituximab may be used in selected antibody-mediated/desensitization protocols, not routine induction for all patients

2. Maintenance Therapy

Long-term lower-dose immunosuppression
Calcineurin inhibitors → Tacrolimus, cyclosporine A
Antimetabolites / antiproliferative agents → Mycophenolate mofetil, azathioprine
mTOR inhibitors → Sirolimus, everolimus
Corticosteroids → Prednisolone/methylprednisolone
Typical regimen → Tacrolimus + mycophenolate + steroid, modified according to organ, risk and toxicity

Types of Graft Rejection

Type	Timing / mechanism	Features / treatment
Hyperacute rejection	Minutes-hours Preformed recipient antibodies against donor ABO/HLA antigens	Immediate graft thrombosis/failure; rare due to ABO testing and crossmatch Treatment usually graft removal/supportive; prevention is essential
Acute rejection	Days-weeks/months Mainly T-cell mediated; can be antibody-mediated	Graft dysfunction; signs depend on organ Treatment → Increase immunosuppression, high-dose steroids, ATG or antibody-directed therapy depending on type
Chronic rejection	Months-years Chronic immune injury + fibrosis/vasculopathy	Progressive graft dysfunction and loss Often irreversible; optimize immunosuppression and treat risk factors

Clinical Signs of Rejection: Examples

Kidney → Rising creatinine/BUN, oliguria, hypertension, proteinuria, graft tenderness sometimes
Liver → Rising bilirubin/transaminases/ALP/GGT, fever, malaise
Heart → Heart failure, arrhythmia, reduced ejection fraction; often biopsy surveillance
Lung → Dyspnea, falling spirometry, hypoxia, infiltrates
General → Fever and graft tenderness can occur but are not specific

Side Effects of Immunosuppression

Infections → Bacterial, viral, fungal, opportunistic
Important opportunistic infections → CMV, Pneumocystis jirovecii, fungal infections, BK virus in kidney transplant
Malignancy → Skin cancer, post-transplant lymphoproliferative disorder (PTLD), virus-related cancers
Nephrotoxicity → Especially calcineurin inhibitors
Metabolic complications → Diabetes, hyperlipidemia, hypertension, weight gain
Bone marrow suppression → Leukopenia, anemia, thrombocytopenia with antimetabolites
Wound-healing problems → Especially mTOR inhibitors and steroids
Steroid effects → Osteoporosis, Cushingoid features, hyperglycemia, infection risk

Exam focus: Define transplantation types, distinguish living/deceased donors, know brain death criteria and consent models, list main organ indications, explain induction vs maintenance immunosuppression, and classify rejection into hyperacute, acute and chronic.