Predicting Optimal Timing of Halting IVIG Therapy after HSCT for SCID

Rationale: Significant practice variation suggests the optimal approach to halting antibody replacement after hematopoietic stem cell transplantation (HSCT) for severe combined immunodeficiency (SCID) is currently undefined. 

Methods: We retrospectively studied all patients undergoing HSCT for SCID at our center between 1995 and 2014 with thorough B cell flow cytometric analyses. B cell subsets, humoral immunity and engraftment were compared between patients who successfully discontinued IVIG on first attempt and those who failed. 

Results: Of 21 eligible patients, 20 remain alive (follow up range 0.7 to 32 years). Ten patients stopped IVIG successfully on first attempt, while 6 failed (3 were subsequently successful). 5 patients never trialed off IVIG. The 10 successful transitioners on initial halt had higher IgM than the six who failed in the 9 months prior to halting IVIG or 3 months after halting, without higher switched-memory B cells (SwBm) or IgA levels.  Patients able to remain off IVIG trended towards higher SwBm and IgM at 18 months (both p = 0.07), with significantly higher SwBm, IgM, and B cell engraftment 5+ years post transplant (n = 13, p = 0.006, 0.007 and 0.04 respectively).  Nine patients currently receive IVIG: 4 with X-SCID, one each with Artemis and JAK3. 

Conclusions: Studying failed attempts to transition off IVIG may improve our decision-making post-HCST for SCID. IgM may be the best indicator in the early post-transplant period, and higher SwBm, IgM and B cell engraftment may be better predictors of IVIG-independence 5+ years after transplant.