Thymus transplantation

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Thymus transplantation
ICD-9-CM 07.94

Thymus transplantation is a form of organ transplantation where the thymus is moved from one body to another. It is used in certain immunodeficiencies, such as DiGeorge Syndrome. [1]



Thymus transplantation is used to treat infants with DiGeorge syndrome, which results in an absent or hypoplastic thymus, in turn causing problems with the immune system's T-cell mediated response. It is used in people with complete DiGeorge anomaly, which are entirely athymic. This subgroup represents less than 1% of DiGeorge syndrome patients. [2]

Nezelof syndrome is another thymus-related disease where it can be used. [3]

Thymus transplantation can also be used in pediatric patients with a Foxn1 deficiency. [4]

Co-transplantation with other organs

In the 2000s, promising animal experiments into transplanting thymic tissue and another organ at the same time were carried out, in order to improve the recipient's tolerance of the transplanted organ, and to reduce the need for immunosuppressing drugs like tacrolimus. Such trials have been performed with kidney and heart transplants, drastically extending the time the animals were surviving without immunosuppressing drugs. [5] The first human heart-and-thymus co-transplantation was performed on Easton Sinnamon in 2022, a newborn who suffered from both a lack of T cells, and a serious heart defect. Depending on the development, it is planned to wean him off immunosuppressant drugs, but it remains to be seen whether the same technique is viable in adults, as the thymus shrinks with age, with the bone marrow taking over T cell production. [6]

Effects and prognosis

A study of 54 DiGeorge syndrome infants resulted in all tested subjects having developed polyclonal T-cell repertoires and proliferative responses to mitogens. The procedure was well tolerated and resulted in stable immunoreconstitution in these infants. It had a survival rate of 75%, having a follow-up as long as 13 years. [2]

Complications include an increased susceptibility to infections while the T cells have not yet developed, rashes and erythema. [2]

Graft-versus-host disease

Theoretically, thymus transplantation could cause two types of graft-versus-host disease (GVHD): First, it could cause a donor T cell-related GVHD, because of T cells from the donor that are present in the transplanted thymus that recognizes the recipient as foreign. Donor T cells can be detected in the recipient after transplantation, but there is no evidence of any donor T cell-related graft-versus-host disease. [2] [7]

Second, a thymus transplantation can cause a non-donor T cell-related GVHD because the recipients thymocytes would use the donor thymus cells as models when going through the negative selection to recognize self-antigens, and could therefore still mistake own structures in the rest of the body for being non-self. This is a rather indirect GVHD because it is not directly cells in the graft itself that causes it, but cells in the graft that make the recipient's T cells act like donor T cells. It would also be of relatively late-onset because it requires the formation of new T cells. It can be seen as a multiple-organ autoimmunity in xenotransplantation experiments of the thymus between different species. [8] Autoimmune disease is a frequent complication after human allogeneic thymus transplantation, found in 42% of subjects over 1 year post transplantation. [9] However, this is partially explained by that the indication itself, that is, complete DiGeorge syndrome, increases the risk of autoimmune disease. [2]

Related Research Articles

<span class="mw-page-title-main">Transplant rejection</span> Rejection of transplanted tissue by the recipients immune system

Transplant rejection occurs when transplanted tissue is rejected by the recipient's immune system, which destroys the transplanted tissue. Transplant rejection can be lessened by determining the molecular similitude between donor and recipient and by use of immunosuppressant drugs after transplant.

Post-transplant lymphoproliferative disorder (PTLD) is the name given to a B cell proliferation due to therapeutic immunosuppression after organ transplantation. These patients may develop infectious mononucleosis-like lesions or polyclonal polymorphic B-cell hyperplasia. Some of these B cells may undergo mutations which will render them malignant, giving rise to a lymphoma.

<span class="mw-page-title-main">Hematopoietic stem cell transplantation</span> Medical procedure to replace blood or immune stem cells

Hematopoietic stem-cell transplantation (HSCT) is the transplantation of multipotent hematopoietic stem cells, usually derived from bone marrow, peripheral blood, or umbilical cord blood in order to replicate inside of a patient and to produce additional normal blood cells. It may be autologous, allogeneic or syngeneic.

<span class="mw-page-title-main">Graft-versus-host disease</span> Medical condition

Graft-versus-host disease (GvHD) is a syndrome, characterized by inflammation in different organs. GvHD is commonly associated with bone marrow transplants and stem cell transplants.

Allotransplant is the transplantation of cells, tissues, or organs to a recipient from a genetically non-identical donor of the same species. The transplant is called an allograft, allogeneic transplant, or homograft. Most human tissue and organ transplants are allografts.

<span class="mw-page-title-main">Cell therapy</span> Therapy in which cellular material is injected into a patient

Cell therapy is a therapy in which viable cells are injected, grafted or implanted into a patient in order to effectuate a medicinal effect, for example, by transplanting T-cells capable of fighting cancer cells via cell-mediated immunity in the course of immunotherapy, or grafting stem cells to regenerate diseased tissues.

<span class="mw-page-title-main">Omenn syndrome</span> Medical condition

Omenn syndrome is an autosomal recessive severe combined immunodeficiency. It is associated with hypomorphic missense mutations in immunologically relevant genes of T-cells such as recombination activating genes, Interleukin-7 receptor-α (IL7Rα), DCLRE1C-Artemis, RMRP-CHH, DNA-Ligase IV, common gamma chain, WHN-FOXN1, ZAP-70 and complete DiGeorge syndrome. It is fatal without treatment.

<span class="mw-page-title-main">BK virus</span> Member of the polyomavirus family

The BK virus, also known as Human polyomavirus 1, is a member of the polyomavirus family. Past infection with the BK virus is widespread, but significant consequences of infection are uncommon, with the exception of the immunocompromised and the immunosuppressed. BK virus is an abbreviation of the name of the first patient, from whom the virus was isolated in 1971.

<span class="mw-page-title-main">Nezelof syndrome</span> Medical condition

Nezelof syndrome is an autosomal recessive congenital immunodeficiency condition due to underdevelopment of the thymus. The defect is a type of purine nucleoside phosphorylase deficiency with inactive phosphorylase, this results in an accumulation of deoxy-GTP which inhibits ribonucleotide reductase. Ribonucleotide reductase catalyzes the formation of deoxyribonucleotides from ribonucleotides, thus, DNA replication is inhibited.

A thymocyte is an immune cell present in the thymus, before it undergoes transformation into a T cell. Thymocytes are produced as stem cells in the bone marrow and reach the thymus via the blood.

<span class="mw-page-title-main">Minor histocompatibility antigen</span>

Minor histocompatibility antigen are peptides presented on the cellular surface of donated organs that are known to give an immunological response in some organ transplants. They cause problems of rejection less frequently than those of the major histocompatibility complex (MHC). Minor histocompatibility antigens (MiHAs) are diverse, short segments of proteins and are referred to as peptides. These peptides are normally around 9-12 amino acids in length and are bound to both the major histocompatibility complex (MHC) class I and class II proteins. Peptide sequences can differ among individuals and these differences arise from SNPs in the coding region of genes, gene deletions, frameshift mutations, or insertions. About a third of the characterized MiHAs come from the Y chromosome. Prior to becoming a short peptide sequence, the proteins expressed by these polymorphic or diverse genes need to be digested in the proteasome into shorter peptides. These endogenous or self peptides are then transported into the endoplasmic reticulum with a peptide transporter pump called TAP where they encounter and bind to the MHC class I molecule. This contrasts with MHC class II molecules's antigens which are peptides derived from phagocytosis/endocytosis and molecular degradation of non-self entities' proteins, usually by antigen-presenting cells. MiHA antigens are either ubiquitously expressed in most tissue like skin and intestines or restrictively expressed in the immune cells.

Transplantable organs and tissues may refer to both organs and tissues that are relatively often transplanted, as well as organs and tissues which are relatively seldom transplanted. In addition to this it may also refer to possible-transplants which are still in the experimental stage.

Graft-versus-tumor effect (GvT) appears after allogeneic hematopoietic stem cell transplantation (HSCT). The graft contains donor T cells that can be beneficial for the recipient by eliminating residual malignant cells. GvT might develop after recognizing tumor-specific or recipient-specific alloantigens. It could lead to remission or immune control of hematologic malignancies. This effect applies in myeloma and lymphoid leukemias, lymphoma, multiple myeloma and possibly breast cancer. It is closely linked with graft-versus-host disease (GvHD), as the underlying principle of alloimmunity is the same. CD4+CD25+ regulatory T cells (Treg) can be used to suppress GvHD without loss of beneficial GvT effect. The biology of GvT response is still not fully understood but it is probable that the reaction with polymorphic minor histocompatibility antigens expressed either specifically on hematopoietic cells or more widely on a number of tissue cells or tumor-associated antigens is involved. This response is mediated largely by cytotoxic T lymphocytes (CTL) but it can be employed by natural killers as separate effectors, particularly in T-cell-depleted HLA-haploidentical HSCT.

Microtransplantation (MST) is an advanced technology to treat malignant hematological diseases and tumors by infusing patients with granulocyte colony-stimulating factor (G-CSF) mobilized human leukocyte antigen (HLA)-mismatched allogeneic peripheral blood stem cells following a reduced-intensity chemotherapy or targeted therapy. The term "microtransplantation" comes from its mechanism of reaching donor cell microchimerism.

Guo Mei is a hematologist and associate director of 307th Hospital of Chinese People’s Liberation Army and deputy director of Radiation Research Institute.

T-cell depletion (TCD) is the process of T cell removal or reduction, which alters the immune system and its responses. Depletion can occur naturally or be induced for treatment purposes. TCD can reduce the risk of graft-versus-host disease (GVHD), which is a common issue in transplants. The idea that TCD of the allograft can eliminate GVHD was first introduced in 1958. In humans the first TCD was performed in severe combined immunodeficiency patients.

In the immune system, veto cells are white blood cells that have a selective immunomodulation properties. Veto cells were first described in 1979 as cells that “can prevent generation of cytotoxic lymphocytes by normal spleen cells against self-antigens”. Hence, veto cells delete T cells that recognize the veto cells.

<span class="mw-page-title-main">Shimon Slavin</span> Israeli professor of medicine

Shimon Slavin is an Israeli professor of medicine. Slavin pioneered the use of immunotherapy mediated by allogeneic donor lymphocytes and innovative methods for stem cell transplantation for the cure of hematological malignancies and solid tumors, and using hematopoietic stem cells for induction of transplantation tolerance to bone marrow and donor allografts.

Allogeneic processed thymus tissue, sold under the brand name Rethymic, is a thymus tissue medical therapy used for the treatment of children with congenital athymia. It takes six months or longer to reconstitute the immune function in treated people.

<span class="mw-page-title-main">Congenital athymia</span> Rare immune disorder where the thymus is missing at birth

Congenital athymia is an extremely rare disorder marked by the absence of the thymus at birth. T cell maturation and selection depend on the thymus, and newborns born without a thymus experience severe immunodeficiency. A significant T cell deficiency, recurrent infections, susceptibility to opportunistic infections, and a tendency to develop autologous graft-versus-host disease (GVHD) or, in the case of complete DiGeorge syndrome, a "atypical" phenotype are characteristics of congenital athymia.


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