1. ¹Department of Pediatrics, Division of Hematology/Oncology, Stem Cell Transplantation Program, Penn State Children's Hospital, Hershey, PA, USA
2. ²Department of Surgical Pathology, Penn State Children's Hospital, Hershey, PA, USA
3. ³Division of Allergy, Immunology and Rheumatology, Penn State Children's Hospital, Hershey, PA, USA

Correspondence: KG Lucas, E-mail: klucas@psu.edu

IPEX syndrome (immune dysfunction, polyendocrinopathy, enteropathy, X-linked) is a disorder of regulatory T-cell function, which can be associated with a fatal outcome early in life. Allogeneic stem cell transplant (SCT) can be curative for this disorder, but pre-transplant disease-related complications may preclude a full myeloablative conditioning regimen. We report a 7-year-old boy with an immune deficiency consistent with IPEX, who successfully underwent a submyeloablative conditioning regimen consisting of fludarabine, busulfan and anti-thymocyte globulin.

This patient was a full-term male child born to parents from Puerto Rico, who experienced no immediate postnatal complications. During the first year of life, he developed iron deficiency anemia, three episodes of pneumonia (one caused by Pneumocystis carinii, the others presumed bacterial) and dermatitis. His IgG level was 139 mg/dl and IgM was 32 mg/dl, and he began to receive monthly intravenous immunoglobulin replacement. B-, T- and NK-cell numbers were within the normal range, but mitogen proliferation assays were consistently 20–30% of control values. His severe dermatitis was later diagnosed as Norwegian scabies, and he was successfully treated with topical permethrin. Before transplant, he experienced multiple episodes of abdominal pain, diarrhea, reactive airway disease and pneumonia. During this time, he developed stridor and was diagnosed with recurrent laryngeal papillomatosis, which on pathologic evaluation revealed inflammatory nodules with granulation tissue, and no evidence of human papilloma virus by polymerase chain reaction (PCR) analysis. He had multiple hospital admissions for CO₂ laser treatment of his laryngeal papillomas, as well as for management of his chronic malnutrition and lower gastrointestinal tract hemorrhage. A colonoscopy revealed diffuse mucosal ulcerations and inflammation. Considering his clinical course, plans were made for allogeneic stem cell transplantation, potentially using umbilical cord blood from his future sibling as a source of stem cells. His infant brother was only haploidentical and was not used as a donor. At 3 months of age, our patient's sibling developed failure to thrive, enteritis and thrombocytopenia, and was diagnosed with IPEX syndrome based on sequencing data showing a mutation in exon 10 of the FOXP3 gene (Dr Troy Torgerson, Fred Hutchinson Cancer Research Center). We have been unable to detect this or other mutations in FOXP3 by sequencing analysis of pre-transplant blood cells from our patient.

In February 2005, at 6 years of age, our patient received an HLA 5/6-matched, unrelated donor umbilical cord blood transplant providing 1.1 10⁸ total nucleated cells/kg and 3 10⁵ CD34+ cells/kg. He received a conditioning regimen consisting of fludarabine 30 mg/m²/day i.v. for 6 days, busulfan 0.8 mg/kg/dose i.v. every 6 h for 2 days and rabbit anti-thymocyte globulin (Genzyme, Cambridge, MA, USA) 3 mg/kg/day for 4 days. Graft-versus-host disease (GVHD) prophylaxis consisted of cyclosporine A and mycophenylate mofetil. The patient achieved myeloid engraftment on day 14, and was platelet and red cell transfusion independent by days 29 and 56, respectively. PCR-single tandem repeat analysis revealed 81, 91 and 98% donor chimerism at 1, 2 and 8 months post-transplant, respectively. Of note is the fact that his stridor resolved 3 weeks following his chemotherapy. At 7 months post-transplant, the patient developed GVHD of the colon, which resolved with a course of oral corticosteroids. At 14 months post-transplant, the patient developed EBV reactivation, and was successfully treated with 4 weekly doses (375 mg/m²) of anti-CD20 monoclonal antibody. Although the patient has no current evidence of GVHD, infection or airway issues, he continues to have poor linear growth, and is receiving growth hormone injections.

The defective gene in IPEX, FOXP3, is considered a 'master switch' for regulatory T-cell (Treg) development and encodes the forkhead box P3 transcription factor. Treg dysfunction leads to T-cell activation and autoimmunity, with the resulting clinical findings in these patients.¹ This transcription repressor is specifically expressed in CD4+CD25+ T cells in the periphery and in the thymus.² Mutations in the FOXP3 gene in the Xp11.23–Xq13.3 coding region have been shown to result in impaired Treg function in several IPEX families; however, some patients with IPEX may not have a demonstrable mutation in the coding region of FOXP3.³ IPEX syndrome is the human equivalent of the scurfy defect in mice, and allogeneic bone marrow transplantation has been shown to be curative of this defect in the mouse model. In preclinical studies, 50% of scurfy mice given allogeneic bone marrow transplants, following sublethal total body irradiation survived long-term, with donor chimerism ranging from 1.7 to 50%.⁴ Transfer of T-cell enriched splenocytes has also resulted in improvement or resolution of autoimmune disease in these animals and facilitated long-term survival.

Most IPEX patients develop symptoms related to autoimmunity during the first 3 months of their life. The most common presenting features are enteropathy, diabetes mellitus and failure to thrive, and many patients also have eczema, hemolytic anemia, thrombocytopenia (from autoantibodies), autoimmune hypothyroidism, splenomegaly and lymphadenopathy.⁵ The most common causes of death in untreated patients include hemorrhage, sepsis and complications related to diabetes mellitus. This diagnosis may be difficult to establish, as lymphocyte numbers are normal in many patients, and mitogen stimulation assays can be low to normal.^{6, 7, 8} Histologically, biopsies of the small and large intestine may reveal flattening of the villi and chronic inflammation.

The long-term prognosis for patients with IPEX syndrome is poor. A recent review of previously reported IPEX patients (n=52) indicated that only six of these patients have survived long term.⁵ Immune suppression has been tried in these patients, and most respond at least temporarily. T cells from scurfy mice are resistant to cyclosporine A suppression,⁸ which is consistent with the limited success of cyclosporine and tacrolimus in humans. Bindl et al.⁹ reported on the use of sirolimus in three patients with IPEX syndrome. One patient who was refractory to conventional immunosuppressive medications maintained remission for over 5 years on combination therapy with sirolimus and methotrexate. The two other subjects had resolution of their enteropathy, although both had persistent infiltrates in the lamina propria on intestinal biopsies, and one patient continued to have allergic skin manifestations and infections (albeit much less frequently). There is insufficient data to indicate how long these individuals need to remain on immunosuppressive therapy.

Allogeneic SCT can be curative for this disorder, but mixed results have been seen.^{5, 10, 11} Wildin and group reported two patients who underwent allogeneic SCTs for IPEX, and both had resolution of enteropathy, rash and other autoimmune manifestations, but unfortunately died from infectious complications. Baud et al.¹⁰ reported a patient with IPEX transplanted with HLA identical bone marrow following a myeloablative conditioning regimen. This patient engrafted but died of hemophagocytic syndrome, with 3–30% donor chimerism post-transplant. Another patient receiving a matched sibling bone marrow transplant achieved mixed chimerism and experienced resolution of clinical symptoms.¹¹ Considering the comorbidities encountered in our patient pre-transplant, we chose a submyeloablative approach. As seen in other IPEX patients undergoing SCT, our patient had improvement in clinical symptoms within weeks of receiving the conditioning regimen. Although our patient tolerated the conditioning regimen very well and had a short period of aplasia, he did develop infections post transplant. For those children who do not respond or have only partial improvement following immunosuppressive therapy, allogeneic SCT using a submyeloablative approach could be considered. Considering the fact that some IPEX patients may have experienced significant organ toxicity before transplant that could complicate the use of high-dose chemotherapy, a reduced intensity preparative regimen may be preferable to minimize toxicity.