1. TISSUE TRANSPLANTATION REQUIREMENTS
GOAL: Replacement of diseased, damaged or worn-out tissues
Can be life-saving
At the same time may provoke powerful immune responses
REQUIREMENTS
Introduce transplants to allow normal functions
Maintain the health of both the recipient and the transplant
The immune system of the recipient must be prevented from mounting an adaptive immune respone against the graft to avoid rejection
 inactivation of the immune system

2. TRANSPLANTATION IMMUNOLOGY
THE ALLO-REACTIVE IMMUNE RESPONSE IS DIRECTED AGAINST TRANSPLANTATION ANTIGENS
Major transplantation antigens are encoded by classical MHC genes
Minor transplantation antigens are encoded by any polymorphic gene and are recognized as peptides in the context of MHC
Blood group antigens are considered as tissue-specific transplantation antigens
T CELLS ARE EDUCATED IN THE PRESENCE OF SELF MHC ALLOTYPES
OTHER MHC ALLOTYPES ARE RECOGNIZED AS FOREIGN BY T LYMPHOCYTES
REJECTION OF INCOMPATIBLE TISSUE IS MEDIATED PRIMARILY BY T LYMPHOCYTES
NK CELLS AND ANTIBODY MEDIATED EFFECTOR FUNCTIONS ARE ALSO INVOLVED

3. ORGAN, TISSUE OR CELL TRANSPLANT
AUTOLOGOUS
syngraft
SYNGENIC
ALLOGENEIC
Kidney, cornea, liver, heart, lung
bone marrow-derived haematopoietic cells (HSC)
allograft
autograft
Skin, muscle, stem cell, dendritic cell, cartilage
BLOOD TRANSFUSION
Bone marrow-derived haematopoietic cells (HSC)

4. GRAFT REJECTION IS THE RESULT OF SPECIFIC IMMUNE RESPONSE
Primary rejection
mouse strain
10 days
Lymphocyte transfer
from immunized mouse
6 months
Secondary rejection
mouse strain
3 days - MEMORY
Naive mouse
Primary rejection
mouse strain
10 days
Rapid rejection of the transplant is mediated by a memory immune response

5. Hyperacute rejection is caused by pre-existing antibodies binding to the graft.

6. MECHANISMS OF TISSUE REJECTION
HYPERACUTE REJECTION
Xenograft or AB0 incompatible graft
Natural IgM antibodies against carbohydrates
Galα1-3Gal on xenograft endothelial cells
Antibodies generated upon previous blood transfusion, pregnancy or transplantation – MHC-specific antibodies bind to endothelial cells
Mismatch of recipient serum with donors B and T cells
Complement and clotting system
NK cell – mediated IgG-dependent ADCC
Necrotic tissue demage
EARLY ACUTE REACTION – 2 – 5 days
Previous sensitization of cytotoxic T cells
IgG-dependent ADCC
LATE ACUTE and CHRONIC REACTION – 7 – 21 days
Th1 – mediated cellular immune response
Delayed Type Hypersensitivity
Fibrosis
Proliferation of smooth muscle cells
Atherosclerosis
Activation of cytotoxic T lymphocytes

7. THE TRANSFUSION REACTION IS MEDIATED BY ANTIBODIES
BLOOD GROUP AND HLA-SPECIFIC ANTIBODIES INDUCE HYPERACUTE REJECTION THROUGH COMPLEMENT ACTIVATION
THE TRANSFUSION REACTION IS MEDIATED BY ANTIBODIES
Red blood cells do not express MHC class I or class II molecules
A, B, 0 ANTIGENS are expressed by endothelial cells of blood vessels (solid vascularized organs)
ANTIBODIES to blood group antigens bind to blood vessels, activate complement
Type II hypersensitivity
Hyperacute rejection – cannot be reversed, should be avoided
Anti – HLA ANTIBODIES
Arise from pregnancy, blood transfusion, previous transplant
Cross match: test recipient’s serum to donor lymphocytes
Panel reactive antibody (PRA) – % of positive reactions
Complement activation
Flow cytometry – more sensitive
Separated T and B cells to detect MHC class I and MHC class II specific antibodies
Anti – MHC I react with both B and T lymphocytes
Anti – MHC II react with B lymphocytes only

8. ORGAN, TISSUE OR CELL TRANSPLANTATION
ALLOGENEIC
Late Acute rejection: Both patients and the organ has tissue damage that releases danger signals – INFLAMMATION – ENHANCE MHC expression
The immune response is mediated by CD4 and CD8 T-cells Effector mechanisms are identical to that of Type IV hypersensitivity
Patients are prepared by administration of immunosuppressive
drugs or T-cell specific antibodies prior to transplantation
Transplant rejection
Host versus graft
HVG

9. Acute rejection of a kidney graft through the direct pathway of allo-recognition.
Donor dendritic cells in the graft (in this case a kidney) carry complexes of donor HLA molecules and donor peptides on their surfaces. The dendritic cells are carried to a draining secondary lymphoid organ (the spleen is illustrated here), where they move to the T-cell areas. Here, they activate the recipient's T lymphocytes whose receptors can bind specifically to the complexes of allogeneic donor HLA (both class I and class II) in combination with donor peptides. After activation, the effector T cells travel in the blood to the grafted organ, where they attack cells that display the peptide:HLA-molecule complexes for which the T cells are specific.
Acute rejection takes days to develop
The rejected graft is swollen and has deep-red areas of hemorrhage and gray areas of necrotic tissue.

10. Alloreactive T-cells of the recipient or of the donor
Can be detected by Mixed Lymphocyte Reaction
(MLR)
Peripheral blood mononuclear cells, which include lymphocytes and monocytes, are isolated from the two individuals to be tested. The cells from the person who serves as the stimulator (yellow) are first irradiated to prevent their proliferation. Then they are mixed with the cells from the other person who serves as the responder (blue) and cultured for five days (top panel). In the culture, responder lymphocytes are stimulated by allogeneic HLA class I and II molecules expressed by the stimulator's monocytes and the dendritic cells that differentiate from the monocytes. The stimulated lymphocytes proliferate and differentiate into effector cells. Five days after mixing, the culture is assessed for T-cell proliferation (bottom left panel), which is due to CD4 T cells recognizing HLA class II differences, and for cytotoxic T cells (bottom right panel) produced in response to HLA class I differences. The mixed lymphocyte reaction was instrumental in distinguishing MHC class II from MHC class I.

11. PRESENTATION OF GRAFT - DERIVED PEPTIDES TO RECIPIENT’S T CELLS
DonorGraft APC
Recipient T
Donor peptide
Recipient peptide
DIRECT PRESENTATION
Recipient
Host
APC T
Donor peptide
INDIRECT PRESENTATION
Demaged, apoptotic/necrotic tissue cells and soluble proteins (MHC)
Host Versus Graft reaction HVG
High percentage of T cells are activated
DEPLETION OF GRAFT – DERIVED PROFESSIONAL APC REDUCES REJECTION

12. Indirect presentationDC B
The processing and presentation of allogeneic HLA class I by a dendritic cell (DC) of the recipient is shown. The dendritic cell activates helper CD4 T cells, which in turn activate B cells that have bound and internalized allogeneic donor HLA molecules. Shown here is a cognate interaction that leads to the production of an anti-HLA class I antibody. Anti-HLA class II antibodies can be produced similarly. Because activated endothelium expresses both HLA class I and II molecules, antibodies against both classes of HLA molecule can contribute to chronic rejection.

13. MOLECULAR BASIS OF THE ALLO-RESPONSE
ANTIGENS PRESENTED
BY ALLO- AND SELF APC
RECIPIENT T CELLS
Allo-MHC + allo-peptide
Allo-MHC + self-peptide
Allo-MHC + self peptide
Allo-MHC + any-peptide
Self-MHC + allo-peptide
Self-MHC + any-peptide
HIGH PERCENTAGE OF RECIPIENT’S T CELLS ARE RESPONDING

14. ACUTE REJECTION T CELLS Plasma cells
KIDNEY TRANSPLANTATION
HEART TRANSPLANTATION
T CELLS
Plasma cells
T lymphocytes in the myocardium. Labeled with anti-CD3 antibody
Lymphocytes and plasma cells around renal tubules. Occurs after terminating immune suppression (CSA)
REJECTION IS PRIMARILY MEDIATED BY MHC-SPECIFIC T LYMPHOCYTES BUT PLASMA CELLS ARE ALSO PRESENT

15. Chronic rejection – may take months
Targeted against the vasculature of the transplant
Results in the thickening of the vessel wall and narrowing of the lumina
Left-hand panel: chronic rejection is initiated by the interaction of anti-HLA class I alloantibodies with blood vessels of the transplanted organ. Antibodies bound to endothelial cells (E) recruit Fc receptor-bearing monocytes and neutrophils. EL, internal elastic lamina; SMC, smooth muscle cells. Right-hand panel: accumulating damage leads to EL thickening and to infiltration of the underlying intimas with SMCs, macrophages (M), granulocytes (G), alloreactive T cells (T), and antibodies. The net effect is to narrow the lumen of the blood vessel and create a chronic inflammation that intensifies tissue remodeling. Eventually the vessel becomes obstructed, ischemic, and fibrotic.
E: endothel M: macrophage
G: granulocyte EL: elastic lamina
T: alloreactive T SMC: smooth muscle

16. Chronic rejection
Interstitial fibrosis and chronic inflammation. Renal arteries are fibrous and thickened. No treatment, can occur months or years after transplantation.
Interstitial fibrosis after chronic rejection in transplanted kidney.

17. SHORTAGE OF TRANSPLANTABLE ORGANS
Animal organs – Xenogeneic transplantation
Xenograft
PRIMATES – danger of viral transmission
PIG – equivalant organs size – hyperacute rejection
„natural” anti-pig antibodies in human blood
recognize carbohydrates on pig endothelial cells
galactosyl α-1,3-galactosyl β-1,4-N acetylglucosaminyl (Gal)
Activate complement – cell damage
Human decay acceleration factor (DAF) transgenic pig – several days
KO - α-1,3-galactosyl transferase – 6 months survival

18. BONE MARROW TRANSPLANTATION IS A SPECIAL CASE OF ORGAN TRANSPLANTATION
Transplantation of the donor’s hematopoietic and immune systems to the recipient
Receipient’s immune response is inhibited
γ-irradiation, drugs
No rejection of the transplant
No host versus graft rejection
Donor bone marrow-derived mature T lymphocytes recognize recipient’s tissues
Graft versus host reaction - against all tissues
Acute autoimmun reaction, can be fatal
Elimination of mature T cells prevents GVH
Methotrexate and cyclosporin A inhibit GVHD
Elimination of mature T cells inhibits engraftment and anti-leukemia effect – may cause rejection

19. DEFECTS OF HEMOTPOIETIC CELLS CAN BE CORRECTED BY BONE MARROW TRANSPLANTATION
Degree of HLA matching of the healthy donor and the patient determines the success of transplantation
Reduces alloreactions against the graft HVG 
Reduces graft versus host reaction GVH 
Ensures efficient presentation of graft antigens by graft APC in the thymus
Positive selection of graft T lymphocytes on host thymic epithelial cells will produce graft-derived T cells – shared MHC
The host’s immune system will be reconstituted by donor-derived lymphocytes

20. ORGAN, TISSUE OR CELL TRANSPLANTATION Cardiovascular diseases
Pre-treatment
ALLOGENEIC
Bone marrow
Treat tumor
Correct deficiency
Cardiovascular diseases
Graft versus Host
GVH
GVHD
Transplant rejection
Host versus graft
HVG

21. Blocked by CSA and FK506 CYCLOSPORIN (CSA) AND TACROLIMUS (FK506)
INAKTIV
ACTIVE
Dephosphorylation
NF-AT translocation to the nucleus
Blocked by CSA and FK506
Gene activation, expression of cytokines and activation molecules

22. Some more ways to block the rejectionof transplants
FTY720: Synthetic analogue of a fungal toxin called Myriocin.
Sphingoson-like structure
Agonist of the S1P receptor, alters T-cell recirculation, traps them in LNs
Peripheral T-cell number is decreased, but no major T-cell defect!

23. BONE MARROW TRANSPLANTATION Special case of tissue transplantation
Graft versus host reaction GVH
Graft versus host disease – GVHD
chronic and systemic
Mature T cells transplanted with the bone marrow react with recipient cells
Elimination of donor T cells can prevent GVHD
Elimination of donor T cells decreases graft versus leukemia effect
Bone marrow transplantation is used for correcting SCID
Graft-donor T
Recipient peptide
Recipient APC
survive
Graft-donor T
Recipientpeptide
Graft Versus Host Reaction

24. Figure 11.1 The rash characteristic of GVHD often starts on the face.
Also involves palms and soles
Panel a: early GVHD in the skin. Lymphocytes are emerging from blood vessels (lower arrow) and adhering to the basal layer of the epidermis (upper arrow). Panel b: the basal cells of the epidermis begin to swell and vacuolate. Their nuclei become condensed (dark staining) as these cells die (arrow). Panel c: advanced destruction of the skin by GVHD, with sloughing of the epidermis (arrow). Photographs kindly provided by Robert Sackstein.
Panel a: early GVHD in the skin. Lymphocytes are emerging from blood vessels (lower arrow) and
adhering to the basal layer of the epidermis (upper arrow). Panel b: the basal cells of the epidermis begin
to swell and vacuolate. ...

25. GVHD in the colon
Inflammatory cells have invaded the crypts of the intestine and destroyed the normal architecture (arrow). Photograph kindly provided by Mark Shlomchik.