Lentiviral Gene Transfer for Treatment of Children Older Than Two Years of Age With X-Linked Severe Combined Immunodeficiency (XSCID)

Transduced cell product administered intravenously over approximately 30 minutes by authorized licensed personnel consistent with NIH Clinical Center Department of Transfusion Medicine's standard operating procedures for cellular products.

3mg/kg per day with drug levels obtained on Day -3. Busulfan dose on day -2 will be adjusted (if busulfan AUC result is available) to achieve targeted busulfan AUC 4500 min\*umol/L/day. If the result is not available in time to adjust, then proceed to give the standard 3mg/kg on the second day

Mucositis prophylaxis commenced- Infusion of keratinocyte growth factor (palifermin) at 60 mcg/kg/day before (Days -6 to Day -4) administration of busulfan and (Days +1 to +3) post-busulfan administration