The treatment of choice for these children is bone marrow or stem cell transplantation. The ideal donor is a tissue matched relative. Matching is determined by testing the blood cells for surface proteins HLA-A, HLA-B, and HLA-D, with HLA-D being the most important match to insure significant survival. Prior to transplantation, the patient may undergo irradiation (form of radiation therapy) or immunosuppressive chemotherapy (a group of chemicals that reduce the chances of rejection) to insure survival of the donated bone marrow or stem cell.
This measure is taken to prevent graft-versus-host disease (a reaction of the engrafted tissue against the recipient) and to insure that all new B- and T-cells arise from the donor's normal bone marrow stem cells. In the absence of a tissue matched sibling, patients can be given a T-cell depleted bone marrow transplant from a relative or other partially matched donor. However, graft-versus-host disease (reaction of the engrafted tissue against the recipient) or incomplete reconstitution can occur if no identical normal donor is available. Other sources of donor stem cells can come from the blood of the donor, if procedures are used to boost the number of stem cells that are present. An additional source of stem cells which can be used in the reconstitution of an infant with SCID is the cord blood of unrelated normal infants. In several research studies, it has been shown that saving cord blood samples from normal infants can provide additional resource; as for bone marrow or other stem cell transplants, one attempts to match the donated stem cells to the infant.
Restoration of normal cellular immunity occurs three to six months following a successful transplantation, while normal antibody production may take one to three years. During this period, gammaglobulin therapy may be used to provide protection against recurrent pyogenic (pus producing) infections.
When successful, this treatment corrects the patient's immune system defect. Recent success rates for this procedure approach 80% for tissue matched bone marrow or stem cell donors.
Other approaches to overcoming the patient's immune defect have been reported, but with varying success. One method, for infants or children with adenosine deaminase deficiency, has been to infuse normal red cells which are a source of this enzyme, or treat with a drug called PEG-ADA.
Pending correction of the immune defect, children with this serious chronic disease should be isolated from children outside the family, and even their own brothers and sisters if the latter are exposed to a virus (especially chicken pox), bacteria, or fungi. School officials should be asked to notify the family if chicken pox occurs in a sibling's school. If a sibling has had a close contact with chicken pox, the affected child should move to another house during the incubation period.
Accidental exposure to chicken pox should be followed with varicella immune globulin within 72 hours. Acyclovir should be used if lesions appear. Siblings should be vaccinated with only killed virus because they might excrete live virus, which could be dangerous to the immune compromised patient. These patients should never receive live virus vaccinations.
Prior to transplantation, infants with Severe Combined Immunodeficiency should generally not be taken to such public places as day care nurseries, church nurseries, shopping centers, or other places where they may be exposed to infection. Their contact with relatives, especially small children, should be limited.
Other precautions include hand washing, good nutrition (which may include intravenous feeding), and prophylactic doses of trimethoprim/sulfamethoxazole (brand name: Bactrim/Septra) to prevent infection with Pneumocystis carinii pneumonia.
Although it does not replace B-cell (antibody producing cells) deficiency, gammaglobulin therapy should be instituted to restore antibody levels in the blood until the B-cell system is restored by transplantation.
Finally, these infants need a great deal of family support because of repeated hospitalizations and painful procedures associated with hospitalization. In some geographical areas, support groups and other resources are available for these families to assist parents in dealing with the affected child, in maintaining spousal relationship and in providing love and support to other children in the family.
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