Survival of the SCID Patient

WRITTEN BY: Nicholas Breehl

A recent study highlights the effectiveness of treatments provided to patients of severe combined immunodeficiency (SCID). The study reveals a relationship between the genotype of the patients SCID and the efficacy of a stem cell transplant in regards to immune system reconstitution and survival rates. The study’s lead researcher is a pediatric immunologist at CHU Sainte-Justine and professor at Université de Montréal, Dr. Elie Haddad.

Severe combined immunodeficiency or SCID is an inherited immune system disorder characterized by abnormalities with responses of both T cells and B cells – the white blood cells needed for immune system function). Common signs and symptoms include increased susceptibility to infections including ear infections; pneumonia or bronchitis; oral thrush; and diarrhea.

SCID may be caused by mutations in any of several genes and can be inherited in an X-linked recessive (most commonly) or autosomal recessive manner. The most common type of SCID is the X-linked severe combined immunodeficiency (XSCID).

The study was international and included the medical history of more than 600 patients ranging from 1982-2012 in over 30 different centers. The study published in Blood incorporated those SCID individuals that received a hematopoietic stem cell transplant as their therapy.

"Immune diseases are among the top priorities at CHU Sainte-Justine in terms of care, teaching, and research," Haddad said. "There are only one or two cases of SCID per year in Quebec. Having access to such a cohort of patients with this rare disease and over such a long period has provided us with significant and unique data to advance our knowledge in this area."

After reviewing the data, the results describe survival rates of patients who receive stem cell transplants from related donors are most successful. While around 86 percent of patients who undergo stem cell transplants are from non-related donors and the success of their therapy is strongly impacted by the genotype of the patient.

Interestingly, the data show the lower the age of the patient and the absence of infection during therapy increased the success of the transplant and the longevity of the patient thereafter.

"We need to develop patient-specific treatment strategies," Haddad said. "There is a critical need for neonatal screening to establish appropriate isolation, implement infection-prevention measures, particularly before transplantation, and ensure rapid referral for bone-marrow transplant or gene therapy after diagnosis."

"In our future research, our objective will be to analyze the late effects of conditioning and the quality of long-term immune-system reconstitution after hematopoietic cell transplant for this deficiency," said Haddad. Finally, the scientists remark, “Our data emphasize the need for patient-tailored treatment strategies depending upon the underlying SCID genotype.”