Severe Combined Immunodeficiency (SCID)

What is severe combined immunodeficiency (SCID)?

Patients with severe combined immunodeficiency (SCID) are born without a functioning immune system and therefore are at increased risk of infections and death before the age of 2. A variety of genetic defects can produce SCID.

What are the symptoms of SCID, and how is it diagnosed?

Symptoms include diarrhea, fungal infections, and failure to thrive. In the past, patients were diagnosed based upon their clinical presentation or family history. Now, many patients are diagnosed based upon a newborn screening before they develop any infections. Patients with SCID are categorized by their primary genetic defect, but common to all forms of SCID is an absence of protective T and B cell immunity to environmental pathogens including bacteria, viruses and fungi. The diagnosis of SCID is confirmed by genetic testing and the assessment of the patient’s T and B cell numbers and function.

How is SCID treated at Stanford Children’s Health?

The only curative therapy for SCID is stem cell transplantation from a healthy individual or with the patient’s own genetically modified cells, also known as gene therapy.

The therapy of choice for most patients with SCID is stem cell transplantation from a healthy matched donor, usually a sibling. If a healthy matched sibling donor is not available, then stem cell transplantation from a half-matched, or haploidentical, family donor, usually the mother, is the next-best option. In the past, using a mismatched donor could increase the chances of developing graft-versus-host disease (GVHD). Stanford doctors can now deplete T cells that cause graft-versus-host disease from the stem cell graft before transplantation, reducing the risk of GVHD and enabling every patient to find a donor. If no family member is a suitable donor, a matched unrelated donor can be used.

Because the purpose of the stem cell transplantation is to permanently correct the patient’s immune system, patients receive chemotherapy before stem cell transplantation to eradicate the patient’s dysfunctional immune system, which allows the donor stem cells to engraft, leading to permanent correction. It usually takes four to six weeks after transplantation for patients to have developed adequate immune function to protect them from infections so that they can be discharged from the hospital.

Why choose Stanford Children’s Health for SCID treatment?

At Stanford Children’s Health, we are working to make stem cell transplants safer and accessible to every patient with SCID. Stanford’s Alice Bertaina, MD, PhD, is an internationally renowned expert in depleting T cells from a mismatched stem cell graft to reduce GVHD. This rare technique has been shown to significantly reduce the risk of GVHD to the level seen in fully matched donors, while also reducing other post-transplant complications. This means that every patient with SCID can now find a suitable stem cell donor. Dr. Bertaina has performed more than 400 transplants using this approach.

We are also working to make stem cell transplantation safer for patients with SCID. Stanford’s Judith Shizuru, MD, is making stem cell transplantation safer by eliminating the need for chemotherapy before transplant. Patients receive an antibody before their stem cell transplant to make space for the normal stem cells to grow, without the need for chemotherapy. Patients are currently being treated with the antibody on a clinical trial for SCID patients.