Question

Indicate whether each of the following statements (a-e) is TRUE or FALSE.  If you think a statement is FALSE, explain why. (10 pts)

a.  TRUE / FALSE  Graft rejection is mediated by pre-existing host T cell effectors and antibodies specific for antigens on the grafted tissue.

b.  TRUE / FALSE  Allogeneic grafts between individuals with identical HLA genes will be accepted.

c.  TRUE / FALSE    Your parents are generally going to be your best source of tissues if you need a transplant.

d.  TRUE / FALSE    Graft rejection only occurs when alloantigens from the grafted tissue are picked-up by recipient APCs and presented to recipient T cells.

e. TRUE / FALSE   In Graft Versus Host Disease (GVHD) innate cells from the grafted tissue recognize host alloantigens and begin attacking host tissues.

Answer 1

•Graft rejection

•Graft rejection reflects the presence of immunocompetent cells in the host that specifically recognize and react to donor-derived stem cells. Several factors influence the likelihood of graft rejection, in particular: a) the degree of immunocompetence of the host; b) the degree of HLA disparity between donor and recipient; c) the number and source of stem cells infused; d) the type of conditioning regimen used; e) the possible pre-sensitization of the host to donor histocompatibility antigens; and f) the presence and source of donor T cells in the graft.

Answer a:- true

-The immune response that results in graft rejection is a complex phenomenon, with respect both to the manner in which the graft antigens are presented to, and recognized by, the host leukocytes, and in the effector phase of the response that generally results in graft damage. The immune response to a transplanted organ consists of both cellular (lymphocyte mediated) and humoral (antibody mediated) mechanisms. Although other cell types are also involved, the T cells are central in the rejection of grafts. The rejection reaction consists of the sensitization stage and the effector stage.

Answer b:- TRUE

- In an allogeneic transplant, stem cells are collected from a matching donor and transplanted into the patient to suppress the disease and restore the patient's immune system. An allogeneic stem cell transplant is different from an autologous stem cell transplant, which uses stem cells from the patient's own body. Tissue typing uses proteins called human leukocyte antigens (HLA), which are found on white blood cells and tissues, to determine whether a donor’s stem cells are the right match. Through an HLA test, pathologists compare the patient’s blood and tissue type against a donor’s blood samples.

•Donors may include:

•HLA-matched relative (most often a sibling)

•HLA-matched unrelated donor

•HLA miss-matched family member

•Unrelated umbilical cord blood

Answer c:- true

- In an allogeneic transplant, the patient receives stem cells from a family member (parent or sibling) or unrelated donor who shares the same group of proteins expressed on the surface of white blood cells called human leukocyte antigen (HLA). These stem cells are collected from the donor's bloodstream or bone marrow.

Answer d :- true.

Answer e:- true

- Graft-versus-host disease (GVHD) is an immune condition that occurs after transplant procedures when immune cells from the donor (known as the graft or graft cells) attack the recipient patient host's tissues; the disease is a side effect that is common after an allogeneic bone marrow transplant (stem cell transplant).