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Embed code for: Transplantation and GvHD
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What is graft-versus-host disease and how can we make this complication a little more bearable for the recipient?
JOURNAL CLUB PRESENTATION
● solid organ transplantation(kidney,liver,lung,skin grafts)
bone marrow transplantation(BMT)/hematopoietic stem cells transplantation(HSCT)
● Xenografts, which are grafts between members of different species
Autografts, which are grafts from one part of the body to another (eg, skin grafts), are not foreign tissue and, therefore, do not elicit rejection.
Isografts, which are grafts between genetically identical individuals (eg, monozygotic twins), also undergo no rejection.
Allografts are grafts between members of the same species that differ genetically. This is the most common form of transplantation. The degree to which allografts undergo rejection depends partly on the degree of similarity or histocompatibility between the donor and the recipient.
WHO IS MAINLY RESPONSIBLE FOR THE LACK OF SUCCES IN TRANSPLANTATION??
●It is the antigenic differences in the MHC molecules themselves that result in strong responses that are principally responsible for transplant rejection.
● The main function of MHC molecules is to bind to peptide fragments derived from pathogens and display them on the cell surface for recognition by the appropriate T-cells(endogenous antingens-MHC I-Th; exogenous antigen-MHC II-Tcyt).
●MHC molecules express on their surface not only foreign peptides,but also they constantly expose self peptides-> in this way they allow our T lymphocytes to watch the integrity of our genome,which is threatened during viral infection/neoplastic transformation
● In the case of infection the viral genome rapidly inhibits the expression of cell peptides whose position in the cleft is taken over by viral peptides=>T cytotoxic response
● Why do we normally not develop immune responses against MHC-self peptides complexes??
THE MOLECULAR BASIS OF ALLORECOGNITION
●Diffrences in MHC molecules are the main responsible for transplant rejection.
● So what happens when we make for example a HLA-incompatible solid organ allogeneic transplantation to a patient??
The patient’s immune system will respond to the antigenic HLA molecules.
● The term allorecognition refers to immune responses to MHC encoded differences (allo-MHC).
So how does the immune system of the recipient respond to allo-MHC?
●For B cells:Donor allo-MHC molecules often have a slightly different conformation than recipient MHC molecules so that the recipient’s B cells recognize them as foreign.
● In contrast, the physiological role of a T cell is to recognize foreign antigen in the context of self-MHC. It may therefore be initially more difficult to see why T cells should be stimulated so vigorously by the presence of allo-MHC molecules in an incoming graft.
Still,there have been reported cases in which a transplant between HLA-identical siblings have been rejected..why??
●When a transplant between HLA-identical siblings is rejected, it is due to differences in MiHAs(MINOR HISTOCOMPATIBILITY AGENTS)
● Minor histocompatibility antigens are genetically different proteins that can be presented by MHC molecules to the T-cells, which see these antigens as foreign and so mount an immune response.
● for example- The best characterised minor antigen is the Y chromosome derived HY peptide that bound to female MHC can induce an immune response.
HEMATOPOIETIC STEM CELL TRANSPLANTATION
●diseases involving hematopoietic cells, a primary immunodeficiency or a blood cell cancer, that calls for the replacement of the patient’s hematopoietic system.
● Bone marrow
the classic sourse.For more than 40 years doctors performed bone marrow transplants by anesthetizing the donor,puncturing a bone-typically the hip bone-and drawing out the bone marrow cells using a seringe
● Umbilical cord blood
Used as a HSC sourse since 1980-1990
● Periphereal blood
● It has been known for decades that a small number of stem and progenitor cells circulate in the blood stream.
● So a few days before stem cell harvesting,the donor is injected in the fatty tissue with a cytokine,a granulocyte colony stimulating factor- Filgrastim(Neupogen-trade name),Pegfilgrastim(Neulasta-trade name),Plerixafor(Mozobil-trade name)-the bone marrow is stimulated to produce stem cells and since there is not enough room in the marrow stem cells are pushed out.
● Of the cells collected only 5 to 20 precent will be true HSC.Thus,when medical researchers commonly refer to periphereal harvested stem cells,this is something of a minsomer.
● As is true for bone marrow ,the periphereal blood harvest is a mixture of stem cells,progenitors and white blood cells of various degrees of maturity,in some cases the harvest can be even contaminated with tumour cells.
● Hematopoietic stem cell transplantation (HSCT) involves the intravenous (IV) infusion of harvested stem cells to reestablish hematopoietic function .
Manipulation of stem cells grafts-Tcell depletion
●Lower incidence of acute/chronic Gvhd
● Reduced or no requirement for posttransplantation immune suppression
as GVHD prophylaxis
● Delayed immune recostitution,longer time to engraftement
● Loss of GVL effect
● Increased risk for posttransplantation inffections
● Overall survival not improved
Preparative or conditioning regimens
Myeloablation=severe or complete depletion of bone marrow cells;consists in administration of high doses of chemotherapy/radiation prior to HSCT
Nonmyeloablative regimens –
These are immunosuppressive but not myeloablative and rely on the graft-versus-tumor effect to kill tumor cells with donor T cells.
GRAFT VERSUS HOST DISEASE
●arises when the donor lymphocytes(especially mature Tcells) from the HSCT mounts an immunological attack against the host’s tissues.
● graft-versus-host disease can occur even when HLA-identical siblings are the donors.,especially due to minor histocompatibility antigens.
● GvHD can be classified as acute or chronic based on the timing of onset and clinical features.
Skin:macular papular rash
Ocular manifestations burning, irritation, photophobia
Oral and GI manifestations include dryness, dysphagia
Obstructive lung disease, with wheezing, dyspnea, and chronic cough
Antilymphocyte Globulin for Prevention of Chronic Graft-versus-Host Disease
Purpose of the study
●In this article are reported the results of a trial that was designed to study wheter including ATG in the myeloablative conditioning regimen would reduce the risk of chronic GvHD among patients in complete remission for acute leukemia who received periphereal-blood stem cells from an HLA identical sibling.
-in this study,patients were randomly assigned to receive ATG or not receive ATG as a part of myeloablative conditioning regimen
The conditioning regimen
●Total-body irradiation(12 Gy) plus cyclophosphamide(120 mg/kg/body weigh)
●Busulfan(16 mg/kg orally/12,8 mg I.V) plus cyclophosphamide(120mg/kg)
●Total-body irradiation plus etoposide(30 to 60 mg per kg)
+for those randomly assigned to the ATG group the conditioning regimen included ATG (10 mg/kg) on the days 3,2,1 before the alogeneic HSCT from an HLA identical donor
PATIENT ELIGIBILITY CRITERIA FOR STUDY
●Had acute myeloid or lymphoblastic leukemia that was in its first or subsequent complete remission
●Had indication for allogeneic HSCT
●Had adequate function of major organ systems –hepatic,renal (creatinine cleareance>30ml/min),pulmonary,cardiac(left ejection fraction at least 30%)
->based on this criteria from a total of 168 patients that were taken in consideration,7 were excluded before randomization because they did not match the criteria
From 161 randomized patients
6 were excluded because the donor withdrew
4 developed progressive disease
=>155 patients remained in the trial
●the study included pacients from different medical centers
● an independent ethics committee at each site of study approved the protocol(available on NEJM.org)
● all pacients provided written consent
Graft failure and Engraftment
Acute and Chronic GvHD
Non ATG Group
GVHD GRADE 2,3,4
GVHD GRADE 3,4
32,2% ATG/68,7% non ATG
59,4%ATG/64,6% non ATG 74,1%ATG/77,9%non ATG
●Chronic GVHD is leading cause of late illness and death after allogeneic hematopoietic stem cell transplantation
●One of the risk factors for the development of GVHD after alogeneic HSCT is the use of periphereal blood stem cells as a graft source since T cell levels in the grafts are higher than those in the marrow
●In the study the incidence of GVHD at 2 years was 36.5 percentage points lower when ATG was added to the conditiong regimen than when it was not added.
●The major source of concern associated with any T cell depletion is the higher risk of relapse that results from the loss of graft versus leukemia effects,a result that has been observed in several studies.
●However,after a follow up of 2 years,there was not observed a significant higher rate of relapse in the ATG group than in the non ATG group,the rates of relapse-free and overall survival were similar in the two groups.
●Within 1 year after transplantation 91% of patients in the ATG group had discontinued immunosuppressive medication with cyclosporine.
●The ATG preparation used in the study is a polyclonal antihuman T lymphocyte immune globulin derived from rabbits after immunization with the Jurkat human T cell line.The highly purified immune globulin consists of antibodies exhibiting a direct effect on T cell through opsonization and lysis after complement activation.
● Because antigens such as CD19 and CD 138 are also targeted by ATG,antitumour effects have been observed in B cell cancers.
● Also the effect of ATG on B cells may have contributed to the significant reduction in chronic GVHD.
CONCLUSION OF THE STUDY
● This study shows that incorporation of ATG in the myeloablative conditioning regimen before transplantation of periphereal blood stem cells from HLA identical siblings resulted in a significantly lower rate of chronic GVHD than the rate without ATG.
● The rates of relapse free and overall survival were similar in the two groups.
STUDY END POINTS
● Chronic GVHD is one leading cause of death among patients who survive for 2 years after transplantation
● Extending the follow up period for these patients would confirm its effect on long term survival .
● Unfortunately this study was terminated at 2 years and long term follow up data for the patients who participated in the study are not available.
TAKE HOME MESSAGES!
●Hematopoietic stem cell transplantation (HSCT) involves the intravenous (IV) infusion of harvested stem cells to reestablish hematopoietic function .
● The periphereal blood harvest is a mixture of stem cells,progenitors and white blood cells of various degrees of maturity(including mature Tcells).
● T cell depletion of the graft can be made in vivo by using ATG(polyclonal anti T lymphocyte immunoglobulin).Altough there are also disadvantages of this procedure ,many studies show that it results in a lower incidence of both acute and chronic GVHD.
1. The history and future of T-cell depletion as graft-versus-host disease prophylaxis
for allogeneic hematopoietic stem cell transplantation
Vincent T. Ho and Robert J. Soiffer
2. Factors affecting thymic function after allogeneic hematopoietic
stem cell transplantation
Kenneth Weinberg, Bruce R. Blazar, John E. Wagner, Edward Agura, Brenna J. Hill, Monika Smogorzewska,
Richard A. Koup, Michael R. Betts, Robert H. Collins, and Daniel C. Douek
3. Specificity of T‑cell alloreactivity
Nathan J. Felix and Paul M. Allen
4. The Immune Response
Basic and Clinical Principles
Tak W. Mak and Mary E. Saunders
5. Thomas' Hematopoietic Cell Transplantation: Stem Cell Transplantation, Fourth Edition Editor(s): Frederick R. Appelbaum, Stephen J. Forman, Robert S. Negrin, Karl G. Blume
X-, have the most disparity and elicit the maximal immune response, undergoing rapid rejection.
MHC I-all cells except those who lack nucleus
MHC II-B lymp,dendritic cells,macrophages+other cells in inflammation
MHC is highly polimorphic-advantage-each MHC allele binds some peptides better than others.
T cells that could be activated by the MHC-self peptide complex are eliminated.
An allele or allel, is one of a number of alternative forms of the same gene or same genetic locus
● HLA class I molecules-encoded by three clusters of loci that belong to MHC genes termed HLA-A,HLA-B,HLA-C.HLA class II molecules- encoded by three clusters of loci that belong to MHC genes termed HLA-DR,HLA-DQ,HLA-DP. These genes encoding for HLA class I,II are inherited in family as haplotypes(=group of genes or alleles which are usually inherited as a unit,with low recombination frequencies).
Theoretically,T cells should not be able to start an immune response against any peptide bound to allo-MHC because it should not be able to recognise the MHC and as I previously said in order to activate a T cell,the lymphocyte should make contact with both epitope and MHC.
● There are two mechanisms that account for these T cell responses: direct allorecognition and indirect allorecognition.
●The process cand be repetead daily,1-5 days until enough CD34+cells are collected.There is estimated that there are needed more than 2 million CD34+ cells/kg of body weigh.
How do they get to bone marrow?
Mature T cells-assure a grade of defense+they are responsible for the graft versus tumour effect.They can attack remining tumour cells in the body.
In vitro-monoclonal antibodies
Before we perform the complete transplantation we must first destroy the host’s bone marrow,to make space for the new one+destroy the remaining cancerous cells.There cannot be two different immune systems in the same host.
the graft-HSC,progenitor cells but also mature T donor cells.We can use the donor T cells to attack tumour cells(graft versus tumour effect).
Cyclophosphamide-used in chimiotherapy An alkylating agent adds an alkyl group to DNA-it interfers with DNA replication
Etoposide-cytotoxic anticancer drug which belongs to the topoisomerase inhibitor drug class.
32,2 ATG group
68,7 non ATGis one leading cause of death among patients who survive for 2 years after transplantation
5. Thomas' Hematopoietic Cell Transplantation: Stem Cell Transplantation, Fourth Edition Editor(s): Frederick R. Appelbaum, Stephen J. Forman,