> See also: > - Reference # Transplants & Transfusions Three major problems: 1. The transplanted organ/tissue must retain its - Allogeneic: - Xenogeneic: Transplants between sufficiently genetically identical individuals within a species are known as *allografts* Those between different species are *xenografts*, such as pig heart transplants. If transplanted tissues *do not stimulate* an immune response it can be referred to as an *immunologically privileged site*. ## Types of Transplants ### Hematopoietic Stem Cell Transplants (HSCT) #### Grafts vs Leukemia (GvL) **GvL:** When donor immune cells recognize and attack residual leukemia or cancer cells in the recipient. One crucial consideration during transplantation is to ensure a balance is made between the beneficial grafts-vs-leukemia (GvL) effect and harmful autoimmune reactions - Both targets are human cells, even if one (leukemia) is cancerous they would still share many similarities ## Transplant Complications why can’t we just take this organ and move it over there without causing a whole ruckus… **Host-Versus-Graft Disease (HvGD):** attacking new cells/tissue - aaa **Graft-Versus-Host Disease (GvHD):** Primarily associated with *HSCT*, When immune cells from a donor (graft) recognize the recipient’s tissues as foreign and mount an immune response - Affected by the degree of [[human leukocyte antigen (HLA)]] matching between donor and recipient - Involves “pro-inflammatory [[cytokines|cytokine storm]]” in mechanism - Dendritic cells are most impactful phagocytic cell due to their superior antigen uptake, T-Cell co-stimulatory molecules, and the production o ### Alloreactivity Alloreactivity Allogenic activat **allograft rejection** occurs when transplanted tissue (graft) or cells from a genetically different donor to the graft - The term “*alloreactivity*” is generally associated with T-Cells, but many other components of the immune system can also participate in this phenomenon TODO: - [ ] How do expressed HLAs vary between parents of offspring? How does this impact the suitability of close relatives donating organs/stem cells - [ ] Not exactly an autoimmune disorder but shares many similarities (explain why?) ### Factors Impacting Success #### Pre-existing Autoimmune Disorders If a patient has a pre-existing [[Autoimmunity|autoimmune disease]], their native white blood cells could already be causing inflammatory responses. At the end of the day, the white blood cells of the donor (graft) and those of the host use the same underlying mechanisms. This means that even if the donor cells did not display any risk of autoimmunity, they could still contribute to the signaling cascade as they only interact with the signaling molecules ([[cytokines]]) and not the autoreactive host cells themselves.