Corrective treatment of SCID

Haematopoietic stem cell transplantation (HSCT)

Brief information is provided about HSCT here, but much more detailed information can be provided by the bone marrow transplant (BMT) unit and on our website.

In most cases, HSCT offers the only long-term cure for SCID. HSCT aims to replace the faulty immune system with an immune system from a healthy donor. Stem cells, from which all the cells of the immune system develop, can be obtained from healthy bone marrow (bone marrow transplantation; BMT), or in some cases, from umbilical cord blood or donor blood. Bone marrow, blood or umbilical cord blood can be taken from a suitable, healthy donor and given by transfusion into a vein to a child with SCID.

An HSCT is not an operation like a heart or kidney transplant. Stem cells contained in the donor bone marrow are able to find their way from the bloodstream to your child’s bone marrow, where they start to produce healthy blood cells. An HSCT does involve a number of risks, and complications can arise afterwards – some of which are temporary, others of which can be life threatening. You will have the opportunity to discuss this in detail with an immunologist and transplant consultant on several occasions.

Soon after the diagnosis of SCID is confirmed, blood samples will be collected from members of the family to determine the tissue type of each member. If a family member is found to have an identical tissue type to the affected baby, they will be selected to be the donor. There is a 1 in 4 (25 per cent) chance that full siblings will have identical tissue types. If there is no suitable family donor an un-related donor will be sought from the worldwide donor registries.

Donating bone marrow involves having a general anaesthetic but it is a relatively
minor procedure. Donating stem cells obtained from blood involves taking some preparatory medication (which is given by injection) and undergoing a procedure known as ‘apheresis’. Both types of donation involve minimal risk to the donor.

Once a donor has been identified, the family will meet members of the transplant
team, who will ensure that the family has ample opportunity to see the transplant
unit, discuss worries and ask questions. In most cases, chemotherapy drugs are needed to prepare the body to receive a new immune system, reducing the chance of rejection of the new bone marrow by the child’s own immune cells. If a perfectly matched bone marrow donor has been found within the immediate family, then chemotherapy is not always necessary. Not all children will receive exactly the same drug combinations.

Gene therapy

Gene therapy aims to correct the underlying genetic abnormality by replacing the faulty gene in immune cells with a normal copy. It is currently undergoing clinical trials in selected patients who have certain specific conditions. It has been successful in correcting the immune deficiency in a small number of children affected by X-linked SCID and the ADA-deficient form of SCID. It may also be available soon for some other genetic forms of SCID. For the child, gene therapy is a relatively straightforward procedure and if successful offers a cure.

Gene therapy involves taking stem cells from an affected child’s blood or bone
marrow. These are then manipulated in the laboratory, inserting a normal copy of the defective genes using complex technology. Once corrected, the cells are returned a few days later by transfusion into the child. As in a stem cell transplant, these new stem cells find their way to the bone marrow, where they start to produce healthy immune cells. This is known as somatic gene therapy – altered genetic material is only present in cells derived from the infused stem cells and cannot be passed on to future generations.

People worry about the idea of gene therapy because of the possibilities of eugenics (generating an improved population through selection of its best characteristics for breeding). Manipulating genes that can be passed on to offspring is known as germ line gene therapy and is not permitted by law.

Further information about gene therapy can be found here and will also be provided by the gene therapy team as needed.

Reviewed April 2017