Outcomes of Hematopoietic Stem Cell Transplantation in 5 Patients with Autosomal Recessive RIPK1-Deficiency.

Receptor Interacting Serine/Threonine Kinase 1 (RIPK1) is widely expressed and integral to inflammatory and cell death responses. Autosomal recessive RIPK1-deficiency, due to biallelic loss of function mutations in RIPK1, is a rare inborn error of immunity (IEI) resulting in uncontrolled necroptosis, apoptosis and inflammation. Although hematopoietic stem cell transplantation (HSCT) has been suggested as a potential curative therapy, the extent to which disease may be driven by extra-hematopoietic effects of RIPK1-deficiency, which are non-amenable to HSCT, is not clear. We present a multi-centre, international review of an additional 5 RIPK1-deficient children who underwent HSCT. All patients presented with very early onset inflammatory bowel disease, 2 also suffered from inflammatory arthritis. Median age at transplant was 3 years (range 1-5 years); 1 received matched sibling marrow, 1 matched unrelated peripheral blood stem cells (PBSC), 2 TCRαβ/CD19-depleted PBSC from maternal-haploidentical donors, and 1 had TCRαβ/CD19-depleted PBSC from a mismatched unrelated donor. All received reduced-toxicity conditioning, based on treosulfan (n = 4) or busulfan (n = 1); 1 patient underwent a successful second transplant following autologous reconstitution. Four of five patients (80%) survived; 1 child died due to multi-drug resistant pseudomonas infection and multi-organ failure. With a median duration of 14 months follow-up, 2 survivors were disease-free, and 2 had substantially improving enteropathy. These findings demonstrated that HSCT is a potential curative therapy for RIPK1-deficiency.