Basic concepts of Graft Rejection and immunology of tumor and Immunotherapy for Cancer for UG and PG Medical students.

1. Transplant and Cancer Immunology
Dr. Suprakash Das
Assist.Prof.

2. Introduction
 Organ transplantation and cancer are 2 situations where host immune system plays
a deciding role in survival of such transplants or tumors inside the host.
 In organ transplantation, immune response against the graft is a barrier to
successful transplantation, and suppression of the immune system is the key for
the transplant survival.
 In cancer, the situation is opposite suppressing immunity gives opportunity for
many types of cancer to grow and hence, enhancing immunity against the cancer
cells, is the principal used for treatment od cancers.
 Transplant, also called graft or organ transplant, in medicine, a section
of tissue or a complete organ that is removed from its original natural site and
transferred to a new position in the same person or in a separate individual.

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5. Transplant Immunology
Classification Of Transplants.
 Transplantation refers to transfer of a Graft or Transplant (Cells, Tissues, or
Organs) from one site to another.
 The individual from whom the transplant is taken is referred as the Doner
and the individual to whom it is transplanted is called Recipient.
Transplants are classified in various ways
Based on Organ/ Tissue transplanted- Kidney/ Heart/ Skin Grafts.
Based on anatomical site of the organ:
Orthotopic Grafts- When tissue or organ grafts are transplanted to their
anatomically normal sites in the recipient, then such grafts are known as
orthotropic grafts. e.g. Skin grafts.
Heterotopic grafts- They are placed in anatomically abnormal sites, e.g.
Thyroid tissue transplanted in a subcutaneous pocket.

6. Heterotopic Heart Transplant

7. Orthotopic
Ovarian
Transplant

8. Transplant Immunology
Classification Of Transplants.
Vital and Static Transplants:-
 Vital Grafts are live grafts, such as Kidney or heart, are expected to survive and function
physiologically in the recipient.
 Static grafts are non-living structures, like bone or artery which merely provide a scaffolding on
which a new tissue is laid by the recipient.
Based on genetic relationship:-
Autograft- It is a self tissue transplanted from one part of body site to another in the same
individual. Example- Transferring healthy skin to a burned area in burn patients and use of healthy
vessels of the same person to replace blocked coronary artery.
Isograft or Synthetic Graft- It is a tissue transferred between genetically identical individuals
(Monozygotic Twins)
Allografts- It is a tissue transferred between non-identical members of the same species. (e.g,
Kidney/ Heart Transplant)
Xenograft- Tissue transferred between different species. (Graft of baboon heart into man).

10. Histocompatibility Antigens
Introduction
 Histocompatibility means a state of mutual tolerance that allows some tissues to be
grafted effectively to others.
 Histocompatibility between the graft and the recipient would decide whether the graft is
going to be accepted or rejected.
 If a graft and recipient tissue are histocompatible to each other (i.e. Antigenically
similar), then the graft is accepted. Usually, autografts and isografts are histocompatible.
 Histoincompatible (i.e. antigenically dissimilar) grafts are generally rejected by the
recipient. Allografts and xenografts are usually histoincompatible.
Transplantation antigens
 These are antigens of the allografts against which the recipient would mount an immune
response.
 MHC molecules (Major Histocompatibility Complex) are the most important
transplantation antigens.

11. Histocompatibility Antigens
Introduction
 Apart from that, ABO and Rh blood group systems also play a role in determining
the histocompatibility.
Minor Histocompatibility Antigens (MHA)-
 They are peptides derived from normal cellular proteins from donated organ.
Immune response against these molecules is weaker , hence they pose less risk for
graft rejection than MHC molecules.
 One of the exception is when a graft is transferred from a male donor to a female
recipient.
 The graft tissue of male donor (XY) would have male specific minor
histocompatibility (H-Y) antigens determined by the Y chromosome which will be
absent in the female recipient (XX).
 Hence, rejection of graft is more in Male to Female compare to Female to male.
 This unilateral sex linked incompatibility is known as Eichwald-Silmser Effect.

19. Types of Graft Rejection
• Graft Rejection
Hyper Acute-
Mins to Hours
Acute-
Weeks to Months
Chronic-
Months to Years
Preformed Antibodies
Tc & Ab Mediated
DTH & Ab
Mediated

20. Types of Graft Rejection
Hyperacute Rejection-
 This occurs within minutes to hours of transplantation and is characterized
by Thrombosis of the Graft vessels and Ischemic Necrosis of the graft.
 It is mediated by circulating antibodies that are specific for antigens on the
graft epithelial cells and that are present before transplantation.
 In an individual, exposure to foreign HLA antigens can occur as a
consequence of –
Previous blood transfusion
Pregnancy
Organ Transplantation
 Following which, the individual develops antibodies against these antigens
which may be anti-ABO/ anti-HLA specific for allogenic MHC molecules.

21. Types of Graft Rejection
 If an individual with these pre-existing antibodies receives a graft containing the same foreign
HLA antigen, then the graft will be rejected earlier or more vigorously.
 Hyperacute rejections can be prevented by matching the donor and recipient  Blood Group
Antigens (ABO Matching) and HLA antigens (HLA Typing)
 Acute Graft Rejection
 It is due to an active immune response of the host stimulated by the allo-antigens in the graft.
 Its mediated by TC cells, occasionally TH cells and antibodies specific for allo-antigens in the graft.
 TC cells Directly kills graft cells
 TH cells Cytokines Inflammation in Graft
 Antibody Complement activation by classical pathway Damage of Graft vasculature.
 Current Immunosuppressive therapy is designed mainly to prevent/reduce Acute Rejection by

25. ACUTE REJECTION
OF GRAFT

26. Types of Graft Rejection
 Chronic graft rejection is an indolent form of graft damage that occurs over
months to years, leading to progressive loss of graft function.
 Chronic rejection may be manifested as fibrosis of the graft and by gradual
narrowing of the graft vessels Graft Arteriosclerosis.
 T cells that reacts against graft allo-antigens secrete cytokines, which
stimulate the proliferation and activities of fibroblasts and vascular smooth
muscle cells in the graft.
 The smooth cell proliferation in the vascular intima represent a specialized
form of chronic DTH reaction.
 Alloantibodies also contribute to chronic rejection.
 Chronic rejection is refractory to most of the therapeutic options and
becoming a leading cause of graft rejection/failure.

29. Factors Influencing Allograft Rejection-
The rate of allograft rejection varies according to the 
 Tissue involved: Skin> Kidney/Heart
 Genetic distance between donor and recipient: More the genetic
distance, faster the rejection. Autografts and Isografts are well
accepted.
 Immunological Memory: Rejection is faster when another graft is
placed to a recipient from the same donor. This happens bcz memory
cells produced against the first graft would differentiate quickly into
effector cells, and that in turn reject the second graft faster.

30. Graft Acceptance and Rejection
Autograft acceptance-
 When an skin graft is transplanted to the same individual at a different site,
 revascularization takes place by 3-7 days followed by healing ,7-10 days resolution
and acceptance of the graft, 12-14 days.
First set rejection
 When an allograft is placed for the first time from a donor to a recipient, the type of
primary graft rejection that develops is known as primary graft rejection.
 The skin becomes re-vascularized between days, 3-7; as the rejection develops, the
vascularized transplant becomes infiltrated with lymphocytes, monocytes, neutrophils and
other inflammatory cells.
 There is a decrease vascularization of the transplanted tissue by 7-10 days,
 Visible necrosis by 10 days, and
 Complete rejection by 12-14 days.

31. Graft Acceptance and Rejection
Second set rejection
 If an recipient who rejected a graft by the first set response, another
graft from the same donor is transplanted , will be rejected by an
accelerated fashion.
 Although vascularization starts but inflammation starts soon and graft
is rejected by the 6th day.

36. Mechanism of Graft Rejection
 Graft rejection is primarily caused by a T-cell mediated immune response to allo-
antigens expressed on the graft cells, primarily the MHC molecules.
 T-cells response to MHC antigens involves recognition of the both donor MHC
molecules and the peptide ligand present on the cleft of the MHC molecules.
The peptides present on the groove of the allogenic class 1 MHC molecules are
derived from protein synthesized within the allogenic cells.
The peptides present in the groove of the allogenic (donor) class 2 MHC
molecules are generally proteins taken up and processed by allogenic APCs.
The process of graft rejection can be divided into 2 stages:
1. A Sensitization Phase- Which involves alloantigen (mainly MHC graft
molecules) presentation to recipient T cells
2. Effector Stage- In which immune destruction of graft takes place due to
activation of recipient’s T cells.

37. Mechanism of Graft Rejection
Sensitization Phase
 T cells in the recipient may recognize donor alloantigens in the graft in 2 different ways
1. Direct pathway
2. Indirect pathway, depending on what cells in the graft are displaying their alloantigens to
the recipient T cells.
1. Direct pathway of Alloantigenic presentation
 Many graft tissues contain APCs (e.g. dendritic cells & macrophages) and when the tissue
is transplanted, the APCs are also carried along with graft to the recipient.
 The allogenic MHC molecules on the graft APCs are directly presented to the recipient
helper T-cells.
 This pathway is responsible for most acute rejections mediated by cytotoxic T cells.

38. Mechanism of Graft Rejection
2. Indirect pathway for Allogenic Presentation
 This is similar to that for recognition of any foreign antigen by the
host APCs.
 The graft cells are ingested by the recipient’s APCs-> donor
alloantigens processed and presented by the MHC molecules on
recipient’s APCs to recipient’s helper T cells.
 This pathway is responsible for most of the chronic rejection mediated
by helper T cells (specialized DTH reaction)

39. Mechanism of Graft Rejection
Effector Phase
 A variety of effector mechanism participate in the allograft rejection. The most common
are cell-mediated rejections involving delayed type hypersensitivity T cells and cytotoxic
T cells.
 Delayed type hypersensitivity- Activated T-cells differentiated into TDTH cells. Cytokines
from TDTH cells (INF-𝛾) activate macrophages which destroy the target cells by
producing lytic enzymes.
 Cytotoxic T cells: CD8+ Tc kills graft cells recognizing the allogenic MHC 1 molecules.
 Antibody mediated mechanisms: Cytokines produced by helper T cells to produce
antibodies. Antibodies are also important in mounting immune response against the graft
mainly in hyperacute graft rejection.
 Mechanisms involved are
Complement mediated lysis
ADCC

44. Prevention of Graft Rejection
Laboratory Test for Histocompatibility
ABO Blood Grouping compatibility testing by blood grouping and cross matching.
HLA typing
 In this test donor’s antigens expressed on the surface of the leucocytes (HLA) or their gene to that
of the recipient is matched.
Phenotypic Methods:
Serology- Microcytotoxicity
Tissue typing- Mixed Lymphocyte Reaction
Genotypic Methods:
PCR detecting HLA genes.
PCR-RFLP (Restriction Fragment Length Polymorphism)
PCR-SSOP (Sequence Specific Oligonucleotide Probing) Most reliable Methods.
PCR-SSP (Sequence Specific Primer)
PCR-DNA Sequencing

45. Prevention of Graft Rejection
Immunosuppressive Therapy
 Immunosuppressive agents can be categorized as induction therapy and maintenance treatment.
 The treatment goal is prevention of graft rejection and tolerance induction. Induction allows one
to withhold high doses of conventional immunosuppression, consisting of parenteral drugs.
 Maintenance immunosuppression is usually given orally as a lifelong treatment.
 Early immunosuppressive regimens included high-dose corticosteroids and azathioprine.
 Further improvements were achieved in the 1980s by the addition of calcineurin inhibitors to
these regiments, improving graft survival dramatically.
 In the modern era, individualization of immunosuppressive regimes is possible by introduction of
new agents, e.g., proliferation signal inhibitors and co-stimulation blockade.
 The adaptive immune response against the donor graft starts with the recognition of an
alloantigen by a naive T cell.
 The T cell subsequently proliferates and differentiates. This primary event requires the interaction
of the T cell receptor (TCR) with antigen presented as a peptide by the antigen-presenting cell
(APC) and a co-stimulatory receptor/ligand interaction on the T cell/ APC cell surface.

46. Prevention of Graft Rejection
Immunosuppressive Therapy
 Activation of T cells and proliferation is described by the three-signal model.
 Signal 1 is when an APC binds to the TCR and triggers the T cell.
 Signal 2 is when co-stimulator molecules and ligands bind. The activation of both
signals 1 and 2 is needed to result in the expression of cytokines, e.g., interleukin-
2 (IL-2).
 Signal 3 is when stimulation of the IL-2 receptor on the T cell surface triggers T
cell proliferation.
 Immunosuppressive agents may affect
(1) the cytokine release/production of activated T cells,
(2) the T cell proliferation,
(3) downregulate/inhibit TCR, or
(4) cause T cell depletion.

49. Graft-versus-Host Reaction
 Graft-versus-host reaction is a condition, where the graft mounts an immune
response against the host (i.e. recipient) and rejects the host.
 In contrary to the usual situation of graft rejections, in which the recipient mounts
an immune response against the graft antigens.
The GVH occurs when the following conditions are present
The graft must contain immunocompetent T cells (stem cells/ Bone marrow/
Thymus transplant)
The recipient should possess transplantation antigens that are abscent in the graft.
The recipient may be immunologically suppressed, therefore can’t mount immune
response against the graft.
Types:GVH occurs in 2 forms
Acute/ Fulminant GVH: Occurs within the first 100 days of post-
transplantation. It is a major challenge in BM transplantation.

50. Graft-versus-Host Reaction
Chronic GVH disease: It is a less severe form that occurs after 100
days of post-transplantation.
Clinical Manifestation
Selective damage to liver (Hepatomegaly)
Skin rashes
diarrhea
In chronic disease there is a damage to connective tissues and
exocrine glands.
Treatment- I.V Glucocorticoids.

52. CANCER IMMUNOLOGY
 Tumor immunology involves the study of antigens on the tumor cells and the
immune response to these antigens.
Tumor Antigens: 2 types of antigens have been found:
Tumor Specific Transplantation Antigen (TSTAs)
Tumor Associated Transplantation Antigen (TATAs)
Tumor Specific Transplantation antigen:
 They are present on the tumor cells and are absent on the normal cells of the body.
 They may result from mutations in tumor cells that generate altered cellular
proteins, cytosolic processing of these proteins would give rise to noble peptides
that are presented with Class 1 MHC molecules, inducing a cell mediated immune
response by tumor specific TC cells.
 TSTAs can be induced by Chemical/ Physical or Viral Carcinogens.

53. CANCER IMMUNOLOGY
 In chemically/physically induced tumor, TSTAs are tumor specific.
Different tumor contain different TSTAs even induced by same
carcinogen. Example: Methylcholanthrene/ UV Rays.
 In contrast, TSTAs of virus induced tumor is virus specific, all tumors
induced by the same virus would have the same antigen.
 Tumor Associated Transplantation Antigens
 They are not unique to tumor cells and may also expressed by normal
cells but at a very low level. Their levels gets exponentially high in
tumor cells. Some of the examples are given below

55. Immune Response Against Tumor Cells
 Both humoral and cell-mediated immune responses are induced by tumor
antigens that results in the destruction of the tumor cells.
 In general, the cell mediated response appear to play a major role, especially
Tc Cells and NK cells.
 Specific TC cells Recognize tumor antigens presented by Class-1 MHCs
on surface of tumor cells.
 However, as the expression of class 1 MHCs are decreased in a number of
tumors, thereby, limiting the role of specific TC cells in their destruction.
 NK cells Decreased MHC expression Withdrawal of Inhibitory
receptor induced NK cells suppression Activation receptors (Fc) can bind
to antibody coated tumor cells ADCC

57. Cancer Immunotherapy
 Cancer immunotherapy is the use of immune system to treat cancer.
3 main groups of immunotherapy are used to treat cancers:
Cell based therapies
Antibody therapies
Cytokine therapies.
 They all provoke the immune system to attack the tumor cells by using these cancer antigens as
targets.
 Cell based therapy-
 Also known as Cancer Vaccines, usually involve removal of immune cells from patients with
cancer, either from Blood or a tumor immune cells specific for the tumor will be activated,
grown and returned to the person with cancer where these immune cells provoke an immune
response against the cancer.
 Cells that can be used in cancer vaccine NK Cells, TC cells, Dendritic cells.
 The only cell based therapy currently approved- Dendritic cells (Provenge) Prostate cancer.

63. Cancer Immunotherapy
Cytokine therapy
• Administration of cytokine can regulate and and coordinate the behavior of immune
system.
INF-𝛂 It is used to treat 
Hairy cell leukemia
Kaposi’s sarcoma
Follicular lymphoma
CML
Malignant myeloma
IL-2
Malignant melanoma
Renal cell carcinoma

65. THIS CAN BE ONLY DONE BY MOVIE SUPERHEROS…..
DOCTORS HAVE TO OBEY THE RULES OF TRANSPLANT IMMUNOLLOGY