TRANSPLANTATION IMMUNOLOGY ALLOGRAFT GRAFT DONOR CLINICAL TRANSPLANTATION IMMUNOSUPPRESSIVE THEORY

1. TRANSPLANTATION
IMMUNOLOGY
SUGANDH CHAUHAN
MSC. BIOTECHNOLOGY
CENTRAL UNIVERSITY OF
HARYANA

2. TOPICS
• Introduction
• Immunologic basis of graft rejection
• Allograft rejection displays specificity and memory
• T cells role in allograft rejection
• Graft donors and recipients are typed for RBC and MHC antigens
• Graft rejection occurs in two stages
• Graft rejection reactions
• General immunosuppressive therapy
• Specific immunosuppressive therapy
• Clinical transplantation
• Summary

3. INTRODUCTION
• Transplantation refers to the act of transferring cells , tissues or
organs from one site to another.
• Diseases can be cured by implantation of a healthy organ , tissue or
cells (a graft )from one individual to another.
• Alexis Carrel reported the first systematic study of transplantation in
1908 ;he interchanged both kidneys in a series of nine cats.
• The first successful human kidney transplant which was between
identical twins was accomplished in Boston in 1954.

4. CONT….

5. IMMUNOLOGIC BASIS OF GRAFT REJECTION
• The degree of immune response to a graft varies with type of graft.
• AUTOGRAFT is self tissue transferred from one body site to another
in the same individual . Examples are -
• Transferring healthy skin to a burned area in burn patients
• Use of healthy blood vessels to replace blocked coronary arteries

6. CONT…..
• ISOGRAFT is tissue transferred between genetically identical
individuals.
• In inbred strains of mice , an isograft can be performed from one
mouse to another syngeneic mouse.
• In humans , an isograft can be performed between genetically
identical (monozygotic) twins.

7. CONT…..
• ALLOGRAFT is tissue transferred between genetically different
members of the same species . In mice, an allograft is performed by
transferring tissue or an organ from one strain to another.
• In humans, organ grafts from one individual to another are allografts
unless the donor and recipient are identical twins.

8. CONT….
• XENOGRAFT is tissue transferred between different species (e.g., the
graft of a baboon heart into a human).
• Autografts and isografts are usually accepted due to the genetic
identity between graft and host.
• Because an allograft is genetically dissimilar to the host, it is often
recognized as foreign by the immune system and is rejected.

9. ALLOGRAFT REJECTION DISPLAYS
SPECIFICITY AND MEMORY
• The rate of allograft rejection varies according to the tissue involved.
Skin grafts are rejected faster than other tissues such as kidney or
heart.
• If an inbred mouse of strain A is grafted with skin from strain B,
primary graft rejection, known as first-set rejection occurs .The skin
first becomes revascularized between days 3 and 7.
• The vascularized transplant becomes infiltrated with lymphocytes,
monocytes, neutrophils , and other inflammatory cells.
• There is decreased vascularization of the transplanted tissue by 7–10
days, visible necrosis by 10 days , and complete rejection by 12–14
days.

11. CONT…..
• Immunologic memory is demonstrated when a second strain - B graft
is transferred to a previously grafted strain-A mouse.
• In this case, complete rejection occur within 5–6 days; this
secondary response is called second-set rejection.

12. T CELLS ROLE IN ALLOGRAFT REJECTION
• T cells play a key role in allograft rejection. For ex- Nude mice , which
lack a thymus and functional T cells were incapable of allograft
rejection and these mice even accept xenografts.
• When T cells derived from an allograft primed mouse are transferred
to an unprimed syngeneic mouse , the recipient shows a second set
rejection to an initial allograft.
• Analysis of T cell subpopulation involved in allograft rejection has
implicated both CD8+ and CD4+ populations.

14. CONT…..
• Mice were injected with monoclonal Ab to deplete T cells and rate of
graft rejection was measured.
• Removal of CD8+ had no effect on graft survival and graft was
rejected at the same rate (15 days )
• Removal of CD4+ prolonged graft survival from 15 – 30 days.
• Removal of both CD8+ and CD4+ T cells resulted in long term survival
of allograft (60 days )
• This indicate that both CD8+ and CD4+ T cells participate in rejection.

15. SIMILAR ANTIGENIC PROFILES FOSTER
ALLOGRAFT ACCEPTANCE
• Tissues that are antigenically similar are called histocompatible and
do not induce immune response that leads to tissue rejection.
• Antigens that determine histocompatibility are encoded by more than
40 different loci , but the loci responsible for allograft rejection are
located within MHC.
• When mice from two different inbred strains , with haplotypes b and
k are mated then all F1 progeny inherit one haplotype from each
parent.

16. CONT…..
-F1 offspring have the MHC type b/k and can accept graft from either
parent .Neither of parental strains can accept grafts from F1 offspring
because each parent lacks one of the F1 haplotypes.
-For purposes of organ or bone marrow grafts there is 25% chance of
identity within the MHC between siblings.

19. GRAFT DONORS AND RECIPIENTS ARE TYPED FOR
RBC AND MHC ANTIGENS
• Differences in blood group and MH antigens are responsible for graft
rejection reactions ; various tissue typing procedures to identify these
antigens have been developed.
• Initially , donor and recipient are screened for ABO blood group
compatability .The blood gp antigens are expressed on RBCs ,
epithelial cells and endothelial cells.
• Antibodies produced in recipient to these antigens induce Ab
mediated complement lysis of incompatible donor cells .
• HLA typing of potential donors and recipient can be accomplished
with a microcytotoxicity test.

20. CONT…..
• In this test WBCs from donors and recipient are distributed into a
series of wells on a microtiter plate and then Abs specific for class I
and class II MHC allele are added to different wells.
• After incubation complement is added to wells , and cytotoxicity is
assessed by uptake of various dyes (eg. Trypan blue ) by the cells.
• If WBCs express MHC allele then the cells will be lysed upon addition
of complement and these dead cells take up dye.
• It thus indicate the presence or absence of various MHC alleles.

22. CONT…..
• Mixed lymphocyte reaction (MLR) used to quantify the degree of class
II MHC compatability between potential donors and recipient.
• Lymphocytes from donor are irradiated or treated with mitomycin C
to prevent cell division and then added to cells from recipient.
• If the class II antigens on two cell population are different the
recipient cells will divide rapidly and take up large quantities of
radioactive thymidine into cell DNA.

24. GRAFT REJECTION OCCURS IN TWO STAGES
• Graft rejection is caused by a cell mediated immune response to
alloantigens (MHC molecules ) expressed on cells of graft .The process of
graft rejection is divided into two stages :-
• SENSITIZATION STAGE –
• CD4+ and CD8+ T cells recognize alloantigens expressed on cells of foreign
graft and induces T cell proliferation in the host.
• EFFECTOR STAGE –
• Immune destruction of graft takes place.
• A variety of effector mechanism participate in allograft rejection .The most
common are cell mediated reactions involving DTH and CTL mediated
cytotoxicity.

25. CONT….
• Recognition of foreign class I alloantigens on the graft by host CD8+
cells can lead to CTL mediated killing.
• Cytokines secreted by T helper cells play central role.
• IL-2, IFN-ʏ and TNF-β are important mediators of graft rejection.
• IL-2 promotes T-cell proliferation and generally is necessary for the
generation of effector CTLs .

27. GRAFT REJECTION REACTIONS
• Graft rejection reactions have various time courses depending upon
the type of tissue grafted and the immune response involved.
• HYPERACUTE REJECTION REACTIONS
• These reactions occur within first 24 hours of transplantation.
• Caused by preexisting host serum antibodies specific for antigens of
graft.

29. CONT…..
• ACUTE REJECTION REACTIONS
• Begin in about 10 days after transplantation.
• It is mediated by T cell responses.
• CHRONIC REJECTION REACTIONS
• Occurs from months to years after transplantation.
• Include both humoral and cell mediated responses by the recipient.

30. GENERAL IMMUNOSUPRESSIVE THERAPY
• Transplantation requires some degree of immunosuppression if the
transplant is to survive.
• Azathioprine a potent mitotic inhibitor is given just before and after
transplantation to diminish T cell proliferation.
• Corticosteroids are anti inflammatory agents that exert their effects
on immune response.
• Cyclosporin A , FK506 and rapamycin are fungal metabolites with
immunosuppressive properties.
• X irradiation eliminates lymphocytes in the transplant recipient just
before grafting.

31. SPECIFIC IMMUNOSUPPRESSIVE THERAPY
• Experimental approaches using monoclonal antibodies suppress graft
rejection responses . These antibodies may act by:-
• Deleting populations of reactive cells
• Blocking co-stimulatory signals can induce anergy
• T-helper cell activation requires a co-stimulatory signal in addition to
signal mediated by the T cell receptor.
• The interaction between B7 molecule on membrane of APCs and
CD28 on T cells provides one such signal.
• Lacking a co-stimulatory signal , antigen activated T cells become
anergic. T cell activation require CD40 present on APC and CD40
ligand present on T cell.

33. CLINICAL TRANSPLANTATION
• For a no. of illness transplantation is the only means of therapy . The
frequency with which a given organ is transplanted depends on
following factors –
• Clinical situation in which transplantation is implanted
• Availability of organs
• Difficulty in performing transplantation

35. CONT…..
• Most commonly transplanted organ is the kidney.
• Matching of blood and histocompatibility groups is advantageous in
kidney transplantation because the organ is heavily vascularized.
• Bone marrow transplants are used for leukemia , anemia and
immunodeficiency diseases especially SCID.
• The recipient of a bone marrow transplant is suppressed before
grafting.
• Because the donor bone marrow contains immunocompetent cells ,
the graft may reject host , causing graft – versus- host disease (GVHD)

36. CONT…..
• Various treatments are used to prevent GVHD in bone marrow
transplantation.
• The transplant recipient is placed on a regimen of
immunosuppressive drugs to inhibit the immune response of the
donor cells.
• Another approach is to treat the donor bone marrow with anti-T cell
antisera or monoclonal antibodies specific for T cells before
transplantation thereby depleting the T cells.

37. CONT…..
• Heart transplant is a challenging operation.
• The first heart transplant was carried out in South Africa by Dr.
Christian Barnard in 1964.
• Lung transplantation either by itself or in conjunction with heart
transplantation used to treat diseases like cystic fibrosis and
emphysema.
• Liver transplants treat congenital defects and damage from viral or
chemical agents.

38. CONT…..
• Pancreas transplantation provide the regulated levels of insulin
necessary to make the diabetic individual normal thereby offers a
cure for diabetes mellitus.
• Skin grafts are used to treat burn victims.
• The critical shortage of organs available for transplantation may be
solved in the future by using organs from nonhuman species
(xenotransplants )
• A major problem with xenotransplants is that it has the potential of
spreading pathogens from donor to recipient ; these pathogens cause
diseases like xenozoonoses that are fatal for humans.

39. SUMMARY
• Graft rejection is an immunologic response displaying the attributes
of specificity , memory , and self / nonself recognition . There major
types of rejection reactions :-
• Hyperacute rejection mediated by preexisting host antibodies to
graft antigens.
• Acute graft rejection in which T helper cells mediate tissue damage
• Chronic rejection involve both cellular and humoral immune
components.

40. CONT…..
• The immune response to tissue antigens encoded within MHC is the
strongest force in rejection.
• The match between a recipient and potential graft donor is assessed by
typing MHC class I and class II antigens.
• The process of graft rejection occurs in two stages –sensitization and
effector stage.
• Certain sites in the body including cornea of eye , brain , testes ,and uterus
do not reject transplants despite genetic mismatch between donor and
recipient.
• Specific tolerance to alloantigens is induced by exposure to them in utero
or by injection of neonates.

41. THANK YOU