To investigate the effect of umbilical cord blood stem cell transplantation (UCBT) on children with severe recombination activating genes (RAG) mutation combined with immunodeficiency disease (SCID) .

A retrospective analysis was conducted. Eight children with severe RAG mutation combined with immunodeficiency disease (SCID) , received umbilical cord blood stem cell transplantation (UCBT) at Children's Hospital of Fudan University from January 2015 to June 2019, including 6 males and 2 females. All patients received busulfan (BU) / cyclophosphamide (CY) pre- treatment programs to reduce toxicity, and used tacrolimus monotherapy to prevent graft-versus- host disease (GVHD) . Clinical and laboratory data were collected before and after cord blood stem cell transplantation to evaluate the treatment afterwards. Continuous variable data that do not conform to normal distribution were represented by median (minimum to maximum) and categorical data by case (relative ratio) .

The results of eight patients who received umbilical cord blood stem cell transplantation (UCBT) showed that the median of total nucleated cells infusion amount was 14.73 (5.06 - 27.27) ×10⁷/ kg and median of CD34⁺ cells amount was 4.14 (1.75 -13.30) ×10⁵/ kg. Of the eight patients, seven were successfully implanted with a median time of neutrophil implantation time 25 (15 - 45) days and a median time of platelet implantation 34 (33 - 43) days. As of the last follow-up, the follow-up time was 9.2 (0.3 - 31.3) months. Three patients died early after transplantation, five survived disease-free and achieved immune reconstitution, the median time to terminate intravenous IV globulin (IVIG) infusion was 84 (63 - 100) days.

Umbilical cord blood transplantation (UCBT) has achieved certain efficacy in the treatment of severe combined immunodeficiency disease (SCID) caused by RAG gene mutation.