Targeting Notch Signaling as a Safe and Effective Treatment for Autoimmune and Lymphoproliferative Diseases.

Patients and mice with both the autoimmune lymphoproliferative syndrome (ALPS) and systemic lupus erythematosis (SLE) have T cell dysregulation and produce both abnormal, activated T lymphocytes and an unusual T cell population, Double Negative T cells (DNTs, cell phenotype: CD3+, CD4-, CD8-, TCR αβ+). The Notch signaling pathway is important in T cell lineage development, including development of DNTs, and in T cell activation. Inhibitors of this pathway are in clinical development, because inhibiting Notch signaling may be effective in treating Alzheimer’s disease and T cell leukemia. We hypothesized that inhibiting Notch signaling would be effective in reducing symptoms and treating the disease in patients with ALPS and SLE by both reducing the production of abnormal DNTs and by blocking aberrant T cell activation. We tested this hypothesis using two murine models of defective lymphocyte apoptosis, CBA-lpr^cg and MRL-lpr. CBA-lpr^cg has a phenotype similar to human ALPS, as these mice develop massive lymphadenopathy and splenomegaly with DNT infiltration of these organs. In the MRL-lpr background, the apoptotic defect manifests itself in a phenotype similar to human SLE, as these mice develop autoantibodies, glomerulonephritis, and a vasculitic dermatitis. Mice were randomized to treatment with a low dose (5mg/kg/day) of the α-secretase inhibitor, DAPT, for 5 days a week by gavage versus vehicle. Treatment response was followed with assessment of DNTs in peripheral blood and lymphoid tissue by flow cytometry, by monitoring of lymph node and spleen size with small animal ultrasound, and ELISA to quantify antibody titer for anti-dsDNA IgG specific antibodies. We found a profound and statistically significant decrease in antibody titer (p = 0.02), lymphadenopathy (p = 0.006), and splenomegaly (p = 0.008) after only 4 weeks, comparing mice treated with DAPT to control animals (Table). Treated mice also had decreased absolute DNTs in their spleens (p = 0.02) and lymph nodes (p = 0.04) compared to control. Treated mice had a trend toward decreased absolute DNTs in peripheral blood; however, more animals are being enrolled on this study to reach 80% power to detect a statistically significant difference. Finally, treated MRL-lpr mice showed stabilization or improvement in their characteristic vasculitic skin disease, whereas control animals showed progression. We found the response to DAPT was durable, having treated mice for over 12 weeks. Also, with this dosing schema, mice experienced no toxicity. They did not manifest any gastrointestinal symptoms, as have been reported with other γ-secretase inhibitors. In summary, inhibiting the Notch signaling pathway appears to be a safe and well-tolerated means of treating autoimmune and lymphoproliferative diseases. This is the first report to use γ-secretase inhibitors to treat non-malignant, T-lymphocyte mediated disease.