Genes and Immunity (2001) 2, 422–432 2001 Nature Publishing Group All rights reserved 1466-4879/01 $15.00 www.nature.com/gene Unexpected and variable phenotypes in a family with JAK3 deficiency DM Frucht1, M Gadina1, GJ Jagadeesh2, I Aksentijevich1, K Takada1, JJH Bleesing3, J Nelson1, LM Muul2, G Perham4, G Morgan5,7, EJA Gerritsen5,8, RF Schumacher6, P Mella6, PA Veys5, TA Fleisher3, ER Kaminski4, LD Notarangelo6, JJ O’Shea1 and F Candotti2 1Arthritis and Rheumatism Branch, National Institute of Arthritis, Musculoskeletal and Skin Diseases, Bethesda, MD, USA; 2Genetics and Molecular Biology Branch, National Human Genome Research Institute, Bethesda, MD, USA; 3Department of Laboratory Medicine, Clinical Center, National Institutes of Health, Bethesda, MD, USA; 4Derriford Hospital, Plymouth, UK; 5Great Ormond Street Hospital, London, UK; 6Department of Pediatrics, University of Brescia, Italy Mutations of the Janus kinase 3 (JAK3) have been previously described to cause an autosomal recessive variant of severe combined immunodeficiency (SCID) usually characterized by the near absence of T and NK cells, but preserved numbers of B lymphocytes (T-B+SCID). We now report a family whose JAK3 mutations are associated with the persistence of circulating T cells, resulting in previously undescribed clinical presentations, ranging from a nearly unaffected 18-year-old subject to an 8-year-old sibling with a severe lymphoproliferative disorder. Both siblings were found to be compound heterozygotes for the same deleterious JAK3 mutations: an A96G initiation start site mutation, resulting in a dysfunctional, truncated protein product and a G2775(+3)C mutation in the splice donor site sequence of intron 18, resulting in a splicing defect and a predicted premature stop. These mutations were compatible with minimal amounts of functional JAK3 expression, leading to defective cytokine-dependent signaling. Activated T cells in these patients failed to express Fas ligand (FasL) in response to IL-2, which may explain the accumulation of T cells with an activated phenotype and a skewed T cell receptor (TcR) V␤ family distribution. We speculate that residual JAK3 activity accounted for the maturation of thymocytes, but was insufficient to sustain IL-2-mediated homeostasis of peripheral T cells via Fas/FasL interactions. These data demonstrate that the clinical spectrum of JAK3 deficiency is quite broad and includes immunodeficient patients with accumulation of activated T cells, and indicate an essential role for JAK3 in the homeostasis of peripheral T cells in humans. Genes and Immunity (2001) 2, 422–432. Keywords: JAK3; SCID; IL-2; Fas ligand; lymphoproliferation Introduction largely accounts for the lack of thymocyte development in mice and humans lacking JAK3.9–11 Additionally, The Janus kinase 3 (JAK3) member of Janus kinases JAK3-deficient humans and mice present with impaired ␥ ␥ associates with the common chain ( c) of the IL-2, 4, 7, NK cell development that is most likely due to defective 9, and 15 receptors and is necessary for normal down- IL-15 signaling, as IL-15 knockout mice have a nearly stream signaling by members of the signal transducer complete absence of peripheral NK cells.12 1,2 and activators of transcription (STAT) family. The cen- We hypothesized that the phenotype of patients with tral role of JAK3 in T cell development is highlighted by partial JAK3 deficiency might be quite different from that patients with JAK3-deficiency and severe combined of patients reported thus far with classical T-B+ SCID. immunodeficiency (SCID) due to the lack of circulating T Partial signaling through the IL-7 receptor in this case + 3–5 cells and presence of dysfunctional B cells (T-B SCID). might be sufficient to sustain thymic development of T Targeted disruption of the Jak3 gene in mice also leads lymphocytes and to allow their appearance in the periph- to profound immunodeficiency, but with defects in both eral circulation where they could manifest consequences 6–8 T and B cell development. The T cell defect of JAK3- of defective signaling in other JAK3-dependent path- deficient humans and mice resembles that of IL-7 and IL- ways. In this regard it is worth noting that mice with ␣ ␣ ␣ 7 receptor chain (IL7R ) null mice and IL-7R deficient targeted disruptions of IL-2 or its receptor ␣ or ␤ chains SCID patients, suggesting that defective IL-7 signaling are characterized by autoimmunity and/or lymphoprolif- eration, despite the well-established role of IL-2 in cellu- lar proliferation.13–15 This is thought to be a consequence Correspondence: DM Frucht, MD, Cell Biology Laboratory, Building 29B, of the lack of IL-2-mediated apoptotic signals for acti- Room 3NN22 Bethesda, MD 20892, USA. E-mail: fruchtȰcber.fda.gov 7 vated T lymphocytes. Depending on the context, there- Current address: Medical Research Council Laboratories, PO Box fore, IL-2 can have seemingly opposing effects. Although 273, Banjul, The Gambia, West Africa. 8Current address: Department of Pediatrics, Medical Center poorly defined, a role for JAK3 in mediating IL-2-depen- Rijnmond-South, Rotterdam, The Netherlands. dent apoptosis signals is suggested by the presence of Received 19 June 2001; revised and accepted 9 August 2001 activated/memory and auto-reactive T cells in JAK3- Unexpected phenotypes in JAK3 deficiency DM Frucht et al 423 deficient mice16,17 and the development of activated T tration of the gut, bone marrow (Figure 2a), and liver lymphocytes in one patient with JAK3 deficiency.18 These (Figure 2b) was demonstrated which was characterized T cells also are characterized by a limited T cell receptor by a predominance of oligoclonal CD8+ T cells (data not repertoire, consistent with oligoclonal peripheral expan- shown). Attempts to treat the patient’s condition with sion of the few thymocytes that escape the developmen- azathioprine and steroids were unsatisfactory, ultimately tal blockade.17,18 leading to treatment with allogeneic bone marrow trans- We have been screening patients whose immunodefi- plantation (BMT) from his HLA-identical sister (II,3) at ciency status could be due to partial JAK3 deficiency and, age 9. Although engraftment was demonstrated, the in this report, we describe a family carrying mutations patient died from multi-organ failure complicating a sep- leading to severely reduced levels of functional JAK3, but sis episode 5 weeks after BMT. Pre-treatment DNA and allowing residual cytokine signaling and the develop- EBV-B cells were available for analysis. ment of peripheral T cells. Two siblings in this family had variable clinical presentations ranging from overt to Immunological findings very mild immunodeficiency, despite carrying identical The immunological phenotype of patient II,2 on admit- JAK3 mutated alleles. These patients had elevated num- tance to the Clinical Center, NIH is reported in Table 1 bers of activated peripheral lymphocytes, and severe and together with that of her brother (II,4) at 6 months, 4 and progressive multi-organ lymphocytic infiltration was 7 years of age. Both patients II,2 and II,4 demonstrated T observed in one case. Studies of FasL expression in lym- cell lymphopenia primarily due to a reduced number of phocytes from one of these patients showed defective up- CD4+ T cells. In patient II,2, both CD4+ and CD8+ T sub- regulation in response to IL-2 that could help explain sets showed a large reduction in the number of na¨ıve these findings. cells, identified by dual expression of CD45RA and CD62L, a finding consistent with reduced thymic output. In addition, patient II,2 had a high proportion of ␥␦ T Results cells in her peripheral blood, all of which were of the V␦2 subset. This finding was consistent with peripheral Clinical history of patients expansion of these cells, which can develop via extra- Four children resulted from the non-consanguineous thymic pathways.19 Such an expansion was not apparent union of two northern European parents. No biological in patient II,4. One characteristic of T cells in both samples were available from the first male child (Figure patients was the high percentage of T cells that expressed 1, subject II,1) who died at 10 months of age from Pneum- HLA-DR, indicating increased activation compared to ocystis carinii pneumonia (PCP). normal controls. In addition, the NK cell counts in both The medical history of subject II,2 included an unde- patients were extremely low, whereas both B cell num- fined lung infection at age 1, a severe varicella infection bers were within the normal range or elevated (Table 1). and occasional ear and urinary tract infections until age 7. The level of serum immunoglobulin (Ig) in patient II,4 at During laboratory evaluations as potential bone marrow the time of his first hospitalization for PCP indicated a donor for her brother (II,4) she was found to have reduced production of IgG levels (IgG: 290 mg/dl, IgA: reduced T cell counts and was subsequently maintained 27 mg/dl, IgM: 147 mg/dl) for which he was started on on antibiotic prophylaxis. At age 9, she developed recur- monthly infusions of intravenous immunoglobulin rent cutaneous warts that spontaneously disappeared by (IVIG). Serum Ig levels in patient II,2 were consistently age 14. At the time of this study she was 18 years of age normal. No other relatives in the family were known to and in good health. have immunological problems. The second male/fourth child (II,4) had delayed Since proliferation studies performed in 1988 on umbilicus healing and developed PCP at the age of 6 samples from patient II,4 revealed defective T cell pro- months. At age 2 he developed giardiasis and, at age 3, liferation in response to PHA (Stimulation Index = 7.7, presented with pneumococcal pneumonia and a second not shown), we proceeded to determine whether this was PCP. At age 5, he developed severe varicella and, at age the case for the patient II,2 as well.