HSCT is the standard treatment for SCID. It is also a high-risk treatment and can have complications stemming from the introduction of the donor cells, as well as the effects of conditioning, which can require chemotherapy. Though medical problems can arise, it’s important to remember that HSCT is a necessary lifesaving treatment for a child with SCID.

Listed below are possible complications and side effects that could occur when a child has an HSCT.

Infection
A major concern when a child undergoes a HSCT is infection. The child might have an infection going into the transplant, or develop one post-transplant. Conditioning the child with chemotherapy or other drugs will weaken the child’s immune system further, making the child more prone to infection.

Infection can result in the child being very ill with any type of virus, bacteria, or fungi. The child is particularly vulnerable to infection in the weeks and months after the transplant, as the new immune system is forming.

Doctors will treat the child with preventative antibiotics before, during, and after the transplant. It can take the child several weeks to produce enough white blood cells to fight infection, so sometimes doctors give the child injections to jumpstart white blood cell production. Immunoglobulin, or Ig, antibody replacement therapy is also given during the transplant process to help prevent infection.

Graft Versus Host Disease
After the transplant, the child may develop graft versus host disease, or GVHD. GVHD occurs when the immune system cells from the donor, or “the graft,” attack the child, or “host.” The reason for this is because the new immune system cells, specifically the T cells, from the donor see the existing organs and tissues in the child as “foreign.” The attacks occur on the skin, the gastrointestinal tract, the mucous membranes, and certain organs like the liver and lungs. This condition is treated with steroids and other drugs.

Failure to Engraft
After the transplant, doctors check the child’s blood on a regular basis to see if the donated immune system cells are growing and dividing. Sometimes, the new cells do not survive in the child and this complication is called failure to engraft. Doctors typically will repeat the transplant, sometimes administering conditioning to the child beforehand to improve the possibility of a successful transplant on the second attempt.

Conditioning Side Effects
Before the child undergoes the HSCT, in some cases, the child will receive medications, including chemotherapy, in a process known as conditioning. Sometimes the child will develop complications from the conditioning with chemotherapy. Some of these complications are short-term, while others may be long-term.

In the short-term, the chemotherapy drugs can affect tissues, including those in the mouth, throat, and intestines. A child may experience sores in those areas, which leads to pain, drooling, nausea, vomiting, and diarrhea.

Because the chemotherapy can cause severe blistering in the mouth, the baby may refuse to eat. If a child doesn’t feed through a bottle, then the child will need a feeding tube in the nasal passage or receive IV nutrition temporarily. The tube will go in the child’s nose and the formula will be given to the child through the tube.

The chemotherapy drugs also can deplete all the cells in the bone marrow, making the child susceptible to infections. The child can become anemic and suffer from bleeding problems.

Possible long-term complications from chemotherapy drugs include harm to the vital organs such as the brain, lungs, kidney, and liver. Some of the time, the complications are reversible with medication.

Other long-term complications include reduced fertility and increased risk of cancer.

Despite the risks, there are reasons to consider conditioning with chemotherapy. These include:

• Greater chance of the donated stem cells growing and making healthy cells for an immune system, and lower risk of the donated cells failing to grow
• Increased chance of a stronger recovery, with potentially higher counts of all types of white cells
• Improves the chance of normal B cell function. B cells are the cells that make antibodies. Therefore, the child may have a better chance of producing functioning antibodies, preventing the need for lifelong infusions of immunoglobulin and allowing the child to receive vaccinations.
• Increased likelihood that the HSCT will be effective for a longer time in the child's life