IMMUNOLOGY OF TRANSPLANTATION Prof.Mohammed Al-homrany.

IMMUNOLOGY OF IMMUNOLOGY OF TRANSPLANTATIONTRANSPLANTATION

Prof.Mohammed Al-homranyProf.Mohammed Al-homrany

MAJOR CONCEPTS IN MAJOR CONCEPTS IN TRANSPLANT IMMUNOLOGYTRANSPLANT IMMUNOLOGY

How does the immune system deal with a How does the immune system deal with a transplant, i.e. What are the mechanisms of transplant, i.e. What are the mechanisms of rejection?rejection?

What are the current clinical strategies to block What are the current clinical strategies to block rejection?rejection?

What are the new and future strategies to promote What are the new and future strategies to promote specific immune tolerance?specific immune tolerance?

What is the role of xenotransplantation?What is the role of xenotransplantation?

What is graft versus host disease?What is graft versus host disease?

Basics of ImmunosuppressionBasics of Immunosuppression

Immune system distinguishes self from non-selfImmune system distinguishes self from non-self

Antigen: anything that can trigger an immune Antigen: anything that can trigger an immune responseresponse

B-cell (lymphocyte) – secretes antibodies, B-cell (lymphocyte) – secretes antibodies, presents antigen to T-cellpresents antigen to T-cell

T-cell (lymphocyte), secretes cytokines (ex. IL-T-cell (lymphocyte), secretes cytokines (ex. IL-2), directs and regulates immune responses, 2), directs and regulates immune responses, also attacks infected, cancerous or foreign cellsalso attacks infected, cancerous or foreign cells

Basics of ImmunosuppressionBasics of Immunosuppression

Immune system distinguishes self from non-selfImmune system distinguishes self from non-self

Antigen: anything that can trigger an immune Antigen: anything that can trigger an immune responseresponse

B-cell (lymphocyte) – secretes antibodies, B-cell (lymphocyte) – secretes antibodies, presents antigen to T-cellpresents antigen to T-cell

T-cell (lymphocyte), secretes cytokines (ex. IL-T-cell (lymphocyte), secretes cytokines (ex. IL-2), directs and regulates immune responses, 2), directs and regulates immune responses, also attacks infected, cancerous or foreign cellsalso attacks infected, cancerous or foreign cells

Basics of ImmunosuppressionBasics of Immunosuppression

Cytokines are chemical messengers – bind to Cytokines are chemical messengers – bind to target cells, encourage cell growth, trigger cell target cells, encourage cell growth, trigger cell activity, direct cell traffic, destroy target cells, activity, direct cell traffic, destroy target cells, and activate phagocytes (“cell eaters”)and activate phagocytes (“cell eaters”)

IL-2 activates T-cells and causes proliferation IL-2 activates T-cells and causes proliferation

T-cell surface markers (CD3, CD25, CD52 and T-cell surface markers (CD3, CD25, CD52 and T-cell receptor) CD=cluster of differentiation of T-cell receptor) CD=cluster of differentiation of T-cellsT-cells

MAJOR HISTOCOMPATIBILITY COMPLEX MAJOR HISTOCOMPATIBILITY COMPLEX (MHC(MHC))

Is located on short arm of chromosome 6Is located on short arm of chromosome 6 It includes 3 regionsIt includes 3 regions: class Ia: class Ia (loci A, B, C) (loci A, B, C)

class Ibclass Ib (loci E, F, G, H), (loci E, F, G, H), class IIclass II (loci DR, DQ, (loci DR, DQ, DP) and DP) and class IIIclass III

Genes of class Ia and class II are highly Genes of class Ia and class II are highly polymorphic, while those of class Ib and class polymorphic, while those of class Ib and class III are notIII are not

Polymorphism means occurence of several Polymorphism means occurence of several allelles ie.genes allelles ie.genes enencoding various MHC coding various MHC antigens located at the same locusantigens located at the same locus

MAJOR HISTOCOMPATIBILITY ANTIGENSMAJOR HISTOCOMPATIBILITY ANTIGENS

Histocompatibility antigens are cell surface Histocompatibility antigens are cell surface

expressed on all cells (class I) and on APC, expressed on all cells (class I) and on APC,

B cells, monocytes/macrophages (class II)B cells, monocytes/macrophages (class II)

They are targets for rejectionThey are targets for rejection

They are inherited from both parents as MHC They are inherited from both parents as MHC

haplotypes and are co-dominantly expressedhaplotypes and are co-dominantly expressed

MINOR HISTOCOMPATIBILITY ANTIGENSMINOR HISTOCOMPATIBILITY ANTIGENS

They also participate in rejection but to lesser They also participate in rejection but to lesser degreedegree

Disparity of several minor antigens may result Disparity of several minor antigens may result in rejection, even when MHC antigens are in rejection, even when MHC antigens are concordant between donor and recipientconcordant between donor and recipient

They include blood group antigens, tissue They include blood group antigens, tissue and organ antigens, normal cellular and organ antigens, normal cellular constituentsconstituents

They are peptides derived from polymorphic They are peptides derived from polymorphic cellular proteins bound to MHC class I moleculescellular proteins bound to MHC class I molecules

What is Tolerance?What is Tolerance?

Immunologic unresponsiveness by the Immunologic unresponsiveness by the recipient to the graft in the absence of recipient to the graft in the absence of maintenance immunosuppression.maintenance immunosuppression.

Self-nonself discriminationSelf-nonself discrimination

Self

No response Strong response

Non-selfor foreign

ToleranceTolerance

Tolerance--->specific Tolerance--->specific unresponsiveness triggered by unresponsiveness triggered by previous exposure to Ag.previous exposure to Ag.

Natural Tolerance (self tolerance)Natural Tolerance (self tolerance): : Unresponsiveness to self Ags.Unresponsiveness to self Ags.

Acquired toleranceAcquired tolerance::

Unresponsiveness to foreign Ags.Unresponsiveness to foreign Ags.

ToleranceToleranceToleranceTolerance

Why is it important to study tolerance?Why is it important to study tolerance?

AutoimmunityAutoimmunityCancerCancerTransplantationTransplantation InfectionsInfectionsVaccinesVaccines

TYPES OF GRAFTSTYPES OF GRAFTS

Autologous graft (autograft)Autologous graft (autograft) – in the same – in the same individual: from one site to another oneindividual: from one site to another one

Isogenic (isograft)Isogenic (isograft) – between genetically – between genetically identical individualsidentical individuals

Allogeneic (allograft or homograftAllogeneic (allograft or homograft)) – between – between different members of the same speciesdifferent members of the same species

Xenogeneic (xenograft)Xenogeneic (xenograft) – between mmbers of – between mmbers of different speciesdifferent species

MECHANISMS OF MECHANISMS OF REJECTIONREJECTION

MECHANISMS OF REJECTIONMECHANISMS OF REJECTION

Depend on disparity of genetic background Depend on disparity of genetic background between donor and recipientbetween donor and recipientT cells are critical in graft rejectionT cells are critical in graft rejectionRejection responses in molecular terms, are due Rejection responses in molecular terms, are due to TCR-MHC interactionto TCR-MHC interactionGraft and host MHC molecules present different Graft and host MHC molecules present different peptidespeptidesDifferent MHC molecules have different peptide-Different MHC molecules have different peptide-binding groovesbinding groovesT lymphocytes can directly recognize and T lymphocytes can directly recognize and respond to foreign MHC moleculesrespond to foreign MHC molecules

ALLOREACTIVE CELLS ARE SO ALLOREACTIVE CELLS ARE SO COMMON, BECAUSE:COMMON, BECAUSE:

Foreign MHC molecules differ from self MHC at Foreign MHC molecules differ from self MHC at

multiple different aminoacid residues, each of multiple different aminoacid residues, each of

which may produce determinant recognized by which may produce determinant recognized by

a different cross-reactive T cell clonea different cross-reactive T cell clone

Thus, each foreign MHC molecule is recognized Thus, each foreign MHC molecule is recognized

by multiple clones of T cellsby multiple clones of T cells

2% of host T cells are capable recognizing and 2% of host T cells are capable recognizing and

responding to a single MHC foreign moleculeresponding to a single MHC foreign molecule

Types OF REJECTIONTypes OF REJECTION

Hyperacute rejectionHyperacute rejection antibodies to HLA and ABO blood group system antibodies to HLA and ABO blood group system (hours or first days)(hours or first days)

Acute rejectionAcute rejection T cells (days or weeks)T cells (days or weeks)

Chronic rejectionChronic rejection various mechanisms: cell-mediated, deposition various mechanisms: cell-mediated, deposition of antibodies or antigen antibody complexes with of antibodies or antigen antibody complexes with subsequent obliteration of blood vessels and subsequent obliteration of blood vessels and interstitial fibrosis (months or years)interstitial fibrosis (months or years)

PATHOGENESIS OF CHRONIC REJECTIONPATHOGENESIS OF CHRONIC REJECTION

Is the result of organ damage by Is the result of organ damage by immunologic and non-immunologic factorsimmunologic and non-immunologic factors

Initially – the minor damage and activation Initially – the minor damage and activation of endothelium by cytotoxic T cells and of endothelium by cytotoxic T cells and antibodiesantibodies

PATHOGENESIS OF CHRONIC REJECTIONPATHOGENESIS OF CHRONIC REJECTION -2 -2

Production by endothelial cells biologically active Production by endothelial cells biologically active mediators (PDGF, PAF, TNF, thromboxans etc.)mediators (PDGF, PAF, TNF, thromboxans etc.)

Secretion of cytokines by infiltrating lymphocytesSecretion of cytokines by infiltrating lymphocytes

Mitogenic effect on myocytes and fibroblasts Mitogenic effect on myocytes and fibroblasts results in cell proliferation and fibrosisresults in cell proliferation and fibrosis

Histology of graft rejectionHistology of graft rejection

VARIABLES DETERMINING TRANSPLANT OUTCOMEVARIABLES DETERMINING TRANSPLANT OUTCOME

Donor-host antigenic disparityDonor-host antigenic disparity

Strength of host anti donor responseStrength of host anti donor response

Immunosuppressive regimenImmunosuppressive regimen

The condition of the allograftThe condition of the allograft

Primary disease of the hostPrimary disease of the host

CHRONIC REJECTION IS MORE FREQUENT WHEN:CHRONIC REJECTION IS MORE FREQUENT WHEN:

Were previous epiWere previous epissodes of acute rejectionodes of acute rejection

There is a low number of compatible HLA There is a low number of compatible HLA antigens with recipientantigens with recipient

PatientPatient on on inadequate immunosuppression inadequate immunosuppression

CHRONIC REJECTION IS MORE FREQUENT WHEN:CHRONIC REJECTION IS MORE FREQUENT WHEN:

In the case of cytomegaly virus infectionIn the case of cytomegaly virus infection

The period of organ storage was too longThe period of organ storage was too long

Patient is heavy smoker and/or is Patient is heavy smoker and/or is

hyperlipidemichyperlipidemic

Organ mass is unproportionally small as Organ mass is unproportionally small as

compared to body masscompared to body mass

Immunosuppressive Immunosuppressive AgentsAgents

Management of a Transplant RecipientManagement of a Transplant Recipient

Induction TherapyInduction Therapy: administer medications that : administer medications that provide marked suppression prior to and during provide marked suppression prior to and during the first week post transplantation, some agents the first week post transplantation, some agents can also block B-cell mediated rejectioncan also block B-cell mediated rejection

Maintenance TherapyMaintenance Therapy: administer : administer immunosuppressive agents continuously to immunosuppressive agents continuously to prevent acute rejectionprevent acute rejection

Administer medications to induce Tolerance?Administer medications to induce Tolerance?

History of Kidney TransplantationHistory of Kidney Transplantation

1950’s1950’sFirst successful kidney transplant First successful kidney transplant Total body irradiation for immunosuppressionTotal body irradiation for immunosuppressionSteroidsSteroids

1960’s1960’sAzathioprineAzathioprine

1970’s1970’sPolyclonal anitbodies – anti-lymphocyte globulin (now Polyclonal anitbodies – anti-lymphocyte globulin (now AtgamAtgam, Thymoglobulin, Thymoglobulin))

1980’s1980’sCyclosporine (Sandimmune Cyclosporine (Sandimmune ), “triple drug therapy”), “triple drug therapy”Monoclonal antibody, OKT3 (Orthoclone Monoclonal antibody, OKT3 (Orthoclone ) in 1985) in 1985

IImmunosuppressant Discoveries 1990-2000mmunosuppressant Discoveries 1990-2000

Tacrolimus (PrografTacrolimus (Prograf))

Mycophenolate Mofetil (Cellcept Mycophenolate Mofetil (Cellcept ) )

Basiliximab (Simulect Basiliximab (Simulect ) )

Cyclosporine Microemulsion (Neoral Cyclosporine Microemulsion (Neoral ))

Daclizumab (Zenapax Daclizumab (Zenapax ))

Rabbit Antithymocyte globulin (Thymoglobulin Rabbit Antithymocyte globulin (Thymoglobulin ))Sirolimus (Rapamune Sirolimus (Rapamune ))

MODERN IMMUNOSUPPRESSIVE THERAPYMODERN IMMUNOSUPPRESSIVE THERAPY

CCyyclosporinclosporin (CsA), (CsA), TacrolimusTacrolimus (FK-506) – inhibit IL-2 (FK-506) – inhibit IL-2 production by T cellsproduction by T cells calcineurin antagonistcalcineurin antagonist

Sirolimus (rapamycinSirolimus (rapamycin) – inhibits ) – inhibits signals transmitted by signals transmitted by IL-2 binding to IL-2RIL-2 binding to IL-2R (antiproliferating effect) (antiproliferating effect)

AzathioprineAzathioprine – reduces numbers and function both, T – reduces numbers and function both, T and B cells, by inhibition of purine metabolismand B cells, by inhibition of purine metabolism

MODERN IMMUNOSUPPRESSIVE THERAPYMODERN IMMUNOSUPPRESSIVE THERAPY -2 -2

Mycophenolate mofetilMycophenolate mofetil (MMF) – inhibits DNA (MMF) – inhibits DNA synthesis and protein glycosylationsynthesis and protein glycosylation

Anti-IL-Anti-IL-2 monoclonal antibodies2 monoclonal antibodies

FTY 720FTY 720 – dramatic effect on lymphocyte – dramatic effect on lymphocyte migrationmigration

GRAFT VERSUS HOST GRAFT VERSUS HOST DISEASE (GVHDISEASE (GVH))

GRAFT VERSUS HOST DISEASE (GVHGRAFT VERSUS HOST DISEASE (GVH))

Is common complication in recipients of Is common complication in recipients of bone marrow transplantsbone marrow transplants

Is due to the presence of alloreactive T Is due to the presence of alloreactive T cells in the graftcells in the graft

It results in severe tissue damage, It results in severe tissue damage, particularly to the skin and intestineparticularly to the skin and intestine

GRAFT VERSUS HOST DISEASE (GVH)GRAFT VERSUS HOST DISEASE (GVH)

It may be avoided by careful typing, It may be avoided by careful typing, removal of mature T cells from the graft removal of mature T cells from the graft and by immunosuppressive drugsand by immunosuppressive drugs

It is manifested by marked rise of several It is manifested by marked rise of several cytokines in patient’s serum (IFN-cytokines in patient’s serum (IFN-, TNF, , TNF, IL-1, IL-2, IL-4)IL-1, IL-2, IL-4)

RISK FACTORS IN FORMATION OF GVHRISK FACTORS IN FORMATION OF GVH

Acute GVHAcute GVHPrevious pregnancies in Previous pregnancies in female donorfemale donor

High T cell number in High T cell number in marrowmarrow

HLA disparityHLA disparity

Transplant from female to Transplant from female to malemale

Low immunosuppressionLow immunosuppression

Herpes virus infectionHerpes virus infection

Chronic GVHChronic GVHAging of donor and Aging of donor and recipientrecipient

Donor’s leukocyte Donor’s leukocyte transfusiontransfusion

Previous acute GVHPrevious acute GVH

High dosage radiationHigh dosage radiation

Transplant from female to Transplant from female to manman

HLA disparity HLA disparity

Xenogeneic Xenogeneic transplantationtransplantation

PERSPECTIVES OF XENOGENEIC GRAFTSPERSPECTIVES OF XENOGENEIC GRAFTS

Potential advantage due to larger Potential advantage due to larger accessibility of animal organsaccessibility of animal organs

Monkeys are apparently the most suitable Monkeys are apparently the most suitable donors, but dangerous because of donors, but dangerous because of potential risk of retrovirus transfer within potential risk of retrovirus transfer within graftgraft

PERSPECTIVES OF XENOGENEIC GRAFTSPERSPECTIVES OF XENOGENEIC GRAFTS

Pigs are now considered because of Pigs are now considered because of similar sizes of organs and erythrocytes to similar sizes of organs and erythrocytes to human oneshuman ones

The major obstacle – presence in man The major obstacle – presence in man (1%) of natural antibodies vs.(1%) of natural antibodies vs. Gal Gal (galactose-(galactose--1,3-galactose) causing -1,3-galactose) causing hyperacute rejectionhyperacute rejection

Xenogenic TransplantationXenogenic Transplantation

>50,000 people that need organs die while waiting for a >50,000 people that need organs die while waiting for a donordonor

Studies are underway involving nonhuman organs Studies are underway involving nonhuman organs

Attention has been focused on the pig but the problem is the Attention has been focused on the pig but the problem is the existence of natural or preformed antibodies to carbohydrate existence of natural or preformed antibodies to carbohydrate moieties expressed in the grafts endothelial cellsmoieties expressed in the grafts endothelial cells

As a consequence activation of the compliment cascade As a consequence activation of the compliment cascade occurs rapidly and hyperacute rejection ensuesoccurs rapidly and hyperacute rejection ensues

Concern has given to debate about the safe use of Concern has given to debate about the safe use of xenografts and animal tissues that the tissues might harbor xenografts and animal tissues that the tissues might harbor germsgerms

stem cells for stem cells for TransplantsTransplants

Source of stem cells for Source of stem cells for Transplants Transplants

Bone Marrow graftBone Marrow graft

Peripheral Blood Stem Cells Peripheral Blood Stem Cells (PBSCT)(PBSCT)

Umbilical cordUmbilical cord

Peripheral Blood Stem Cells (PBSCT)Peripheral Blood Stem Cells (PBSCT)Stem cells collected peripherally using apheresis (cell Stem cells collected peripherally using apheresis (cell separator machine)separator machine)

Less invasive; less discomfort; less morbidity than BMLess invasive; less discomfort; less morbidity than BM

Outpatient procedureOutpatient procedurePBSCT results in more rapid hematopoietic recovery PBSCT results in more rapid hematopoietic recovery than BMthan BMNo difference in treatment outcomeNo difference in treatment outcomeQuickly replacing traditional BMQuickly replacing traditional BM

Using cytokine stimulation (G-CSF injections)Using cytokine stimulation (G-CSF injections) BM releases large number CD34 stem cells into circulationBM releases large number CD34 stem cells into circulation Stem cells harvested via peripheral lineStem cells harvested via peripheral line

Source of stem cells for Source of stem cells for Transplants Transplants

Goals of Transplant ResearchGoals of Transplant Research

Prevent rejection and graft lossPrevent rejection and graft loss

Reduce the amount of immunosuppressionReduce the amount of immunosuppression Decrease side effectsDecrease side effects Decrease toxicity and long term effectsDecrease toxicity and long term effects

Enhance long term patient and graft survivalEnhance long term patient and graft survival

Provide reasonable cost effective therapyProvide reasonable cost effective therapy

Improve patient adherence and quality of lifeImprove patient adherence and quality of life

Induce Tolerance (no long term medications, reduces Induce Tolerance (no long term medications, reduces adverse effects, improves quality of life)adverse effects, improves quality of life)