The functional interaction of BAFF and APRIL with TNF receptor superfamily members BAFFR, TACI and BCMA is crucial for development and maintenance of humoral immunity in mice and humans. Using a candidate gene approach, we identified homozygous and heterozygous mutations in TNFRSF13B, encoding TACI, in 13 individuals with common variable immunodeficiency. Homozygosity with respect to mutations causing the amino acid substitutions S144X and C104R abrogated APRIL binding and resulted in loss of TACI function, as evidenced by impaired proliferative response to IgM-APRIL costimulation and defective class switch recombination induced by IL-10 and APRIL or BAFF. Family members heterozygous with respect to the C104R mutation and individuals with sporadic common variable immunodeficiency who were heterozygous with respect to the amino acid substitutions A181E, S194X and R202H had humoral immunodeficiency. Although signs of autoimmunity and lymphoproliferation are evident, the human phenotype differs from that of the Tnfrsf13b-/- mouse model.

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A prospective, open-label, multicenter, single-arm, Phase III study evaluated the efficacy and safety of Hizentra(®), a 20% human IgG for subcutaneous administration, in 51 primary immunodeficiency patients over 40 weeks. Patients previously on intravenous or subcutaneous IgG were switched to weekly subcutaneous infusions of Hizentra(®) at doses equivalent to their previous treatment. IgG levels achieved with Hizentra(®) were similar to pre-study levels with subcutaneous, and higher by 17.7% than pre-study levels with intravenous IgG. No serious bacterial infections were reported in the efficacy period. The rate of all infections was 5.18/year/patient, the rates of days missed from work/school, and days spent in hospital were 8.00/year/patient and 3.48/year/patient, respectively. Local reactions (rate 0.060/infusion) were mostly mild (87.3%). No serious, Hizentra(®)-related adverse events were reported. Individual median infusion durations ranged between 1.14 and 1.27 h. Hizentra(®) maintained or improved serum IgG levels without dose increases and effectively protected patients against infections.

Peripheral blood lymphocytes (PBL) and alloreactive T cell lines of two male infants born to consanguinous parents and presenting with severe combined immunodeficiency (SCID) showed a pronounced deficiency in T cell activation. Although phenotypically normal, the proliferative response of the childrens' T cells was strongly reduced but could be improved by the addition of interleukin-2 (IL-2). Furthermore both childrens' T cells were unable to produce the cytokines IL-2, interferon-gamma (IFN-gamma), IL-4 and tumor necrosis factor-alpha (TNF-alpha). This multiple cytokine production deficiency could not be restored by IL-2 or co-stimulatory signals provided by antigen-presenting cells (APC). Moreover, mRNA for IL-2 and IFN-gamma could not be detected. In contrast, expression of the activation-dependent cell surface markers CD25 and CD69 was within normal limits. To determine whether the functional defect of the patients' T cells was due to the absence or abnormal binding of transcription factors involved in cytokine gene expression, electrophoretic mobility shift assays were used to examine the DNA binding of AP-1, Oct, CREB, SP1, NF-kappa B and the nuclear factor of activated T cells (NF-AT) to their respective response elements in the promoter of the IL-2 gene. Whereas AP-1, NF-kappa B, Oct, CREB and SP1 displayed normal binding activities in nuclear extracts, the binding of NF-AT to its IL-2 promoter response element was barely detectable both before and after T cell stimulation. Our results strongly suggest that this NF-AT/DNA binding defect is responsible for the multiple cytokine deficiency and the SCID phenotype observed in the two infant brothers.

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