Expanding the mutation spectrum in ICF syndrome: Evidence for a gender bias in ICF2.

BACKGROUND: Immunodeficiency, centromeric instability, and facial anomalies (ICF) syndrome is a rare, genetically heterogeneous, autosomal recessive disorder. Patients suffer from recurrent infections caused by reduced levels or absence of serum immunoglobulins. Genetically, 4 subtypes of ICF syndrome have been identified to date: ICF1 (DNMT3B mutations), ICF2 (ZBTB24 mutations), ICF3 (CDCA7 mutations), and ICF4 (HELLS mutations). AIM: To study the mutation spectrum in ICF syndrome. MATERIALS AND METHODS: Genetic studies were performed in peripheral blood lymphocyte DNA from suspected ICF patients and family members. RESULTS: We describe 7 ICF1 patients and 6 novel missense mutations in DNMT3B, affecting highly conserved residues in the catalytic domain. We also describe 5 new ICF2 patients, one of them carrying a homozygous deletion of the complete ZBTB24 locus. In a meta-analysis of all published ICF cases, we observed a gender bias in ICF2 with 79% male patients. DISCUSSION: The biallelic deletion of ZBTB24 provides strong support for the hypothesis that most ICF2 patients suffer from a ZBTB24 loss of function mechanism and confirms that complete absence of ZBTB24 is compatible with human life. This is in contrast to the observed early embryonic lethality in mice lacking functional Zbtb24. The observed gender bias seems to be restricted to ICF2 as it is not observed in the ICF1 cohort. CONCLUSION: Our study expands the mutation spectrum in ICF syndrome and supports that DNMT3B and ZBTB24 are the most common disease genes.

Reconstitution of lymphocyte subpopulations after paediatric bone marrow transplantation.

We prospectively studied the reconstitution of lymphocyte subpopulations in a group of 22 children, who survived disease-free at least 6 months after allogeneic BMT for a haematological malignancy. Absolute counts of total lymphocytes, B lymphocytes, T lymphocytes, and CD4+ helper T lymphocytes reached the 5th percentile (p5) of age-matched reference values within 6 months after BMT in 15, 17, 7 and 2 patients, respectively. In particular, CD4+ helper T lymphocyte reconstitution was very slow. Unexpectedly, CMV reactivation had a profound positive influence upon the number of CD4+ helper T lymphocytes in the children. In five patients, absolute B lymphocyte counts above the 95th percentile were reached from 6 months after BMT onwards, mimicking normal ontogeny. Unlike normal ontogeny, the percentages of helper T lymphocytes expressing the 'naive' CD45RA isoform were low and those expressing the 'memory' CD45RO isoform were high in the first 3 months after BMT, as described before. Thereafter, the CD45RA:CD45RO ratio slowly normalised. Also, CD7 expression was absent on up to 90% of T lymphocytes in the first months after BMT, and on a steadily decreasing percentage thereafter, as recently described in adults. However, the absolute counts of CD45RO+/CD4+ and CD7-/CD4+ helper T lymphocytes did not change significantly. So, we found no evidence of peripheral expansion of previously primed donor-derived 'memory' T lymphocytes during the follow-up period which spanned 1-18 months after BMT. The absolute counts of 'naive' CD45RA+ helper T lymphocytes did not show a faster increase after BMT than in adults, despite the presumed presence of a non-involuted thymus in children. Bone Marrow Transplantation (2000) 25, 267-275.

Resetting the adaptive immune system after autologous stem cell transplantation: lessons from responses to vaccines.

Autologous stem cell transplantation (ASCT) to treat autoimmune diseases (AID) is thought to reset immunological memory directed against autoantigens. This hypothesis can only be studied indirectly because the exact nature of the pathogenetic autoantigens is unknown in most AID. Therefore, 19 children with juvenile idiopathic arthritis (JIA) or systemic lupus erythematodes (SLE) and 10 adults with multiple sclerosis (MS) were vaccinated with the T-cell-dependent neoantigen rabies and the recall antigen tetanus toxoid after, respectively before, bone marrow harvest. Both vaccinations were repeated after ASCT. All except two of the responders mounted a primary antibody response to rabies after revaccination, and 44% of the responders mounted a primary antibody response to tetanus boost after ASCT. These data show that immunological memory to a neoantigen is lost in most patients with AID after immunoablative pretreatment; however, memory to a recall antigen boosted before bone marrow harvest is only lost in part of the patients. Disease progression was arrested in all patients with JIA/SLE except one, but only in a minority of MS patients. Clinical outcome on a per case basis was not associated with the profile of the immune response toward the vaccination antigens after ASCT.

Vaccination with rabies to study the humoral and cellular immune response to a T-cell dependent neoantigen in man.

We investigated the humoral (antigen-specific immunoglobulin isotypes, IgG subclasses, and avidity maturation) and cellular (antigen-specific in vitro proliferation) immune response in 18 healthy adult volunteers, following a primary and a single booster vaccination with the T-cell dependent neoantigen rabies administered at a 3-months interval. The IgG antibody titer showed a mean 31-fold increase (range 3-154) 4 weeks after the first vaccination and a memory response was observed after booster vaccination, i.e. high IgG titers, switch from IgM to IgG and IgA and increased antibody avidity. All healthy adults showed a rabies-induced proliferative response with a mean stimulation index of 45 (range 3.5-200) after in vitro stimulation of PBMC obtained at 4 weeks after booster vaccination. The results obtained in this study provide a frame of reference for the interpretation of specific immune responses to the T-cell dependent neoantigen rabies in patients suspected of a primary or secondary immunodeficiency. Humoral and cellular immune responses to the rabies neoantigen provide complementary information on the condition of the immune system of an individual. Five patients diagnosed with a combined immunodeficiency were vaccinated using the same protocol and showed a number of abnormalities, either in the humoral or the cellular immune response to the rabies neoantigen.