tissue transplantation

Question 1

what are the most common tissues donated?

Answer 1

amniotic tissue, bone, cornea, heart valves, sclera, skin and tendons, heart, lungs, liver, kidney, pancreas, pancreas islet cells, small bowel and stomach.

Question 2

define autograft/autologous graft

Answer 2

tissues (i.e skin grafts) that are transplanted from one area on an individual to another area on the same individual

Question 3

define isograft

Answer 3

graft involves donors and recipients that are genetically identical such as maternal twins. In the research realm, we have mice and rats that are genetically identical or syngeneic and thus, can easily accept tissue grafts. Given that they are genetically identical, their MHC molecules are seen as “self” and thus are viewed as being
histocompatible with the recipient.

Question 4

define allograft

Answer 4

graft involves donors and recipients from the same species. Although you may think that this graft would be compatible, there is sufficient genetic diversity among the MHC molecules (histoincompatible) to induce a robust host immune response commonly leading to rejection.

Question 5

define xenograft

Answer 5

graft involves donors and recipients that are from different species. this type of graft would be histoincompatible and also rejected

Question 6

what is the most common type of graft?

Answer 6

allograft

Question 7

hyperacute rejection

Answer 7

occurs relatively quickly from minutes to several hours and is mediated by preformed antibodies

Question 8

example of hyperacute rejection

Answer 8

blood transfusion reaction in which blood type A is transferred to a blood type B recipient

Question 9

acute rejection

Answer 9

1. antibody-mediated acute rejection: involving antibodies and complement activation, which
   usually manifests within 7 days to several months.
2. acute cellular rejection: denoted by mononuclear cell infiltration (i.e. lymphocytes and macrophages). This type of rejection is commonly seen within weeks to several years, often when physicians try to taper the potent immunosuppressive drugs that patients are receiving

Question 10

chronic rejection

Answer 10

rejection involves months to years and
involved both the antibody-mediated and cell-mediated immunity. It is believed that the
recipient’s immune system slowly damages the donor organ over time

Question 11

alloantigens/ transplantation antigens /histocompatibility antigens

Answer 11

the antigens the recipient host
immune system must recognize foreign antigens on the graft and mount a response to it

Question 12

MHC

Answer 12

• found on human chromosome 6.
• code for the human leukocyte antigens (HLA), which are polymorphic molecules responsible for eliciting the strongest of responses to allogeneic tissues
• The genes in this region code for class I (HLA-A, -B, -C) and class II (HLA-DR, -DP, -DQ) molecules

Question 13

minor histocompatibility antigens

Answer 13

unique proteins unique to one individual, but not another individual. So, although T cells may play a major role in organ rejection, the innate and both arms of the adaptive immune systems are involved in rejection

Question 14

direct pathway of allorecognition

Answer 14

recipient’s own T cells are able to directly recognize and respond to foreign self-proteins presented by intact MHC molecules on the surface of donor cells . This also activates the donor APCs that can in turn activate the recipient’s T cells.
- results in a more potent immune response against the graft

Question 15

indirect pathway of allorecognition

Answer 15

alloantigen proteins are processed by recipient self APCs and presented to the recipient’s T cells
- results in a more gradual and less intense immune response again the graft

Question 16

inflammatory response immune system type and T helper cell type

Answer 16

innate
Th1

Question 17

Th1 cytokines produced

Answer 17

FNα, IFNβ, IFNγ, TNFα, TNFβ, IL-12p70 and IL-2

Question 18

Th2 mediated cytokines promote rejection via eosinophils

Answer 18

IL-4, IL-2 and IL-5

Question 19

Th17 cytokine promote rejection via neutrophils

Answer 19

IL-6, IL-23 and TGF β

Question 20

what alone has been reported to upregulate Tregs promoting graft acceptance?

Answer 20

TGF β

Question 21

4 different types of differentiation pathways that naïve CD4+ T cells can take

Answer 21

The classic proinflammatory pathway mediated by IL-12p70 and IL-2 promotes Th1 differentiated IFNγ-producing cells that activate Macs to reject the allograft, an example of a delayed type hypersensitivity (DTH) response. Activated naïve CD4+ T cells in the presence of IL-4 and IL-2 can differentiate into a Th2 T cell producing IL-5 which can drive eosinophil-mediated graft rejection. Further, activated naïve CD4+ T cells in the presence of IL-6,
IL-23 and TGFβ leads Th17 cells producing IL-17 that mediates neutrophil rejection of the graft.
The message here is that allograft rejection is mediated by different subsets of T cells. The last pathways for naïve CD4+ T cell differentiation involves TGFβ alone, which appears to drive Treg differentiation leading to allograft acceptance. Note: In the above illustration, IL-2 blocks Th17 differentiation.

Question 22

determining tissue or organ compatibility

Answer 22

tissue typing, blood typing, cross-matching

Question 23

blood typing

Answer 23

performed by mixing a whole blood sample with commercial antibodies against Type A or Type B looking for agglutination or hemolysis. Serum cross-matching is performed with the
recipient’s serum and the donor’s leukocytes to rule out if the recipient had previously been
exposed to the donor’s HLA via other medical procedures (i.e. blood transfusion etc)

Question 24

tissue typing

Answer 24

procedure in which the donor and recipient’s human leukocyte antigens (HLA) are screened for level of similarity or compatibility. This focus is primarily on the HLA Class I genes (A, B and C) and Class II genes (DRB1, DRB4, DRB5, DQA1, DQB1, DPA1 and DPB1) or proteins.

Question 25

Serology (Commercial Antibody Test)

Answer 25

The original method involved collecting peripheral blood from the donor and enriching the lymphocytes for HLA typing using commercial anti-HLA antibodies in the presence of complement (i.e. rabbit) looking for lysis. This test was simple, quick and cost effective. It was limited by the available commercial antibodies employed. Given the HLA phenotypes were highly diverse, the assay missed other epitopes and thus, was not always accurate.

Question 26

PCR-based sequence-specific primers (SSP) or sequence-specific oligonucleotide probes
(SSOP)

Answer 26

These molecular tests have largely replaced serology as they are more accurate
and sensitive. Both of these tests, take time and have to be evaluated in light of result
turn-around time. RT-PCR is also an accurate and fast test, but as with the other
molecular tests relatively expensive. Still, is there really a need to put a cost value on a
test to help decide whether a graft is going to take or be rejected

Question 27

Reference strand-mediated conformational analysis (RSCA)

Answer 27

molecular test used for HLA typing. The test takes the donor’s sample is mixed with a commercial reference HLA allele and run on a gel electrophoresis. Similar to the serology test, there is only a limited number of reference HLA alleles available making it a less attractive
test

Question 28

Direct DNA sequencing

Answer 28

determining the nucleotide sequence or order of nucleotides within a DNA segment. This currently is the most accurate method for HLA
typing. There are 2 approaches: Sanger sequencing or next generation (Next-Gen)
sequencing. The Sanger sequencing employs selective chain-terminating dideoxynucleotides via DNA polymerase during DNA replication, in vitro. Next-Gen sequencing is the new gold standard that has revolutionized genomic research.

Question 29

Mixed Leukocyte Reaction (MLR)

Answer 29

enriched peripheral blood leukocytes (specifically lymphocytes) from both the donor and recipient are co-cultured together to determine if they will mount a response against
each other. If you look at Table 19.2, you can see the various ways in which the assay
can be setup. From the stand point of assessing for tissue rejection, the best procedure
would be to chemically inactivate (I.e. using Mitomycin C) the donor lymphocytes and
determine if the recipient lymphocytes (i.e. cytotoxic T cell) would react and kill the
donor lymphocytes. I use to run these assays. They are labor intensive and time consuming. The assay I use to run also included a radioactive probe which involved a lot
more regulations and expensive equipment. With the advent of the DNA tests, it is
highly likely that this assay is not used on a routine basis

Question 30

Stem Cell Transplantation

Answer 30

Hematopoietic stem cell (HCT) transplantation is the procedure in which donor stem cells are transplanted to the recipient bone marrow in order to re-establish normal, healthy hematopoietic stem cell lineage that will yield normal and healthy blood cells.
This type of transplantation occurs when the recipient’s own HCT is defective (I.e. SCIDs) or
diseased (i.e. leukemia). In both situations, the recipient is usually irradiated or administered
chemotherapy at high enough doses to destroy the existing bone marrow. As with all grafts,
tissue typing is extremely critical here as incorrect or sloppy HLA typing can lead to a condition known as Graft-Versus-Host Disease

Question 31

Graft-Versus-Host Disease (GVHD)

Answer 31

GVHD is a unique disease in which the donated bone marrow or stem cells upon differentiation and maturation into mature immune cells (i.e.
lymphocytes) recognize the recipient’s cells in the body as foreign and mount a response
against them. There are 2 forms of GVHD: acute GVHD and chronic GVHD. The clinical signs and severity can vary by patient, but skin inflammation and jaundice are common clinical signs. The acute form usually occurs within the first 100 days of the transplant. The acute form is usually associated with skin rash, liver involvement (i.e. jaundice), nausea and diarrhea. The chronic form appears later and typically involves multiple organ systems

Question 32

Xenogeneic Transplantation

Answer 32

As organ transplantation has become a more common treatment for a large number of diseases, the demand for these organs has outpaced the supply. As a result, tens of thousands of people on the transplant list die each year, that roughly 20-25% of the patients on the organ transplant list. This has pushed transplantation medicine to focus on other organ sources, such as xenogeneic transplants or animal to human transplants. To be honest, it is an ethical dilemma not to mention a medical dilemma. It is an ethical dilemma, because select animal species are raised for the purpose of harvesting their organs. This logically doesn’t sit well with animal rights groups, in particular species that are closely related to man or that are companion animals. Food animals, such as the bovine (cow) or porcine (pig) don’t seem to generate the same level of opposition. Presently, pigs are the most animals used in xenogeneic transplants. Similar to allografts, xenografts are immunogenic and will mobilize the recipient’s immune system to reject the graft. What scientists are now focusing on is using genetic engineering to manipulate the pig donor organ’s immunogenicity. The only other medical concern regarding xenogeneic organ transplants is the potential risk of the transplant carrying infectious agents (i.e. porcine viruses) to the recipient. Currently, there is no data that shows porcine viruses pose a risk to humans who have received pig organ transplants

Question 33

The Fetus: A Natural Allograft

Answer 33

developing fetus evade the maternal immune system: the maternal immune system cannot detect the developing fetus. The placenta serves as a major barrier to the maternal immune system. The fetal cells that make up the outer trophoblast of the placenta lack discernible MHC Class I and Class II molecules, which prevents T cell recognition. They do possess a special class Ib MHC, HLA-G, which can function as a ligand for the killer inhibitory receptor on NK cells and block their activation. In addition, the uterine environment, under in part by maternal hormones, secretes a number of different proteins and cytokines that suppress immune response