Gut microbiome variations during hematopoietic stem cell transplant in severe combined immunodeficiency.

The composition of the gut microbiome is unstable in infancy,1
with many environmental factors determining its development including mode of delivery, method of feeding, antibiotic exposure, and neonatal hospitalisation.2
Severe combined immunodeficiency (SCID), a primary T-lymphocyte immunodeficiency causing severe viral infections, Pneumocystis jiroveci pneumonitis, chronic diarrhea, and failure to thrive, is fatal in infancy without hematopoietic stem cell transplantation (HSCT). Once diagnosed, children with SCID receive prolonged courses of antibiotics and breast-feeding frequently ceases during this critical time for gut microbiome development.3
Chemotherapeutic conditioning often precedes HSCT and can cause mucositis and severe immunosuppression, increasing the risk of bacteremia. HSCT can be complicated by graft-versus-host-disease (GvHD) causing severe gut inflammation. In HSCT in adults, overgrowth by a dominant gut microbiome species and the subsequent reduced diversity have been associated with gut GvHD4
, 5
and bacteremia.6
However, the gut microbiome in HSCT in infancy, specifically in SCID, has not been explored.