organ and tissue transplants

What are the four types of transplantation based on donor-recipient relation

• Autograft – Self-transplant (e.g., skin graft).

• Syngeneic transplant – Identical twin donor.

• Allograft – Same species, genetically different.

• Xenograft – Different species (e.g., pig heart valve)

what is the Major Histocompatibility Complex (MHC)?

• Found on chromosome 6.

• Encodes HLA proteins that differentiate self from non-self.

What are the two types of MHC molecules?

• MHC-I – Found on all nucleated cells, presents to CD8+ T cells.

• MHC-II – Found on APCs, presents to CD4+ T cells.

How are HLA genes inherited?

Co-dominantly expressed

What is hyperacute rejection, and how is it prevented?

Very rapid form of transplant rejection, occurs within minutes to hours after

• Cause: Pre-existing anti-HLA or ABO antibodies.

• Prevention: Cross-matching to detect antibodies.

What is acute rejection, and how is it treated?

Transplant rejection that occurs within days to months post-transplant.

• Cause: T-cell-mediated response.

• Treatment: Immunosuppressive drugs

What is chronic rejection

Transplantation rejection that occurs after 6 months to years.

• Cause: Progressive immune damage → fibrosis and graft dysfunction.

• Outcome: Irreversible; may require re-transplantation

What is Graft vs Host Disease (GvHD), and when does it occur?

Donor T cells attack recipient tissues, common in stem cell transplantation

What are symptoms of GvHD?

Rash, liver dysfunction, diarrhoea, bone marrow failure

How is GvHD prevented?

Irradiation of donor cells, immunosuppressive drugs.

Why is ABO matching important?

Prevents hyperacute rejection

Which HLA gene is most important in solid organ transplantation?

HLA-DR.

What is the purpose of cross-matching?

• Tests recipient serum against donor lymphocytes.

• If lysis occurs = Incompatible (higher rejection risk).

What are two key HLA typing methods?

• Lymphocytotoxicity Test (LCT) – Uses antisera to detect HLA antigens.

• PCR-based Typing – Uses DNA sequencing for high-resolution HLA typing

Why is lifelong immunosuppression required?

Prevents immune rejection of the graft

What are the three phases of immunosuppressive therapy?

• Induction – High-dose drugs post-transplant.

• Maintenance – Long-term lower-dose therapy.

• Rejection treatment – High-dose therapy during rejection episodes

What are major classes of immunosuppressive drugs?

• Corticosteroids – Anti-inflammatory.

• Calcineurin inhibitors – Block IL-2 to suppress T cells.

• mTOR inhibitors – Inhibit T-cell proliferation.

• Monoclonal antibodies – Block specific immune molecules.

What are common side effects of immunosuppressants?

Infections, cancer risk

What factors influence kidney transplant allocation?

• ABO & HLA matching.

• HLA-DR matching is crucial.

• Waiting time & recipient age

Why is HLA matching not required for liver and cornea transplants?

• Liver: Tolerates mismatched HLA due to its immune-regulatory functions.

• Cornea: Immune-privileged site

What is the primary requirement for heart/lung transplants

Size compatibility & short ischemia time (<4 hours)

Why does stem cell transplantation require strict HLA matching?

Prevents GvHD and ensures engraftment.