Transplant and Cancer Immunology

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. 

3. I M M U N E T O L E R A N C E

4. 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.

5. Heterotopic Heart Transplant

6. Orthotopic Ovarian Transplant

7. 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).

8. 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.

9. 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 .

10. Types of Graft Rejection Graft Rejection Preformed Antibodies Tc & Ab Mediated DTH & Ab Mediated

11. 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.

12. 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 T C cells, occasionally TH cells and antibodies specific for allo -antigens in the graft. T C cells  Directly kills graft cells T H 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

13. ACUTE REJECTION OF GRAFT

14. 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.

15. 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.

16. 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.

17. 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 6 th day.

18. 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:  A Sensitization Phase- Which involves alloantigen (mainly MHC graft molecules) presentation to recipient T cells Effector Stage- In which immune destruction of graft takes place due to activation of recipient’s T cells.

19. Mechanism of Graft Rejection Sensitization Phase  T cells in the recipient may recognize donor alloantigens in the graft in 2 different ways Direct pathway 2. Indirect pathway, depending on what cells in the graft are displaying their alloantigens to the recipient T cells. 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.

20. 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)

21. 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 T DTH 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

22. 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

23. 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.

24. 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.

25. 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.

26. 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.

27. 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 T C cells. TSTAs can be induced by Chemical/ Physical or Viral Carcinogens.

28. 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

29. 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 T C 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 T C 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

30. 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.

31. 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

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