Abstract

Autoimmune Lymphoproliferative Syndrome (ALPS) is a disorder of abnormal lymphocyte survival caused by defective Fas-mediated apoptosis. Patients with ALPS develop lymphadenopathy, hepatosplenomegaly, and an increased number of an unusual T cell population, characterized as T cells that are CD3+ CD4− CD8− and referred to as double negative T cells (DNTs). Although ALPS is a rare disorder, we have shown it may be more common than previously appreciated. Treatment options for patients with ALPS are limited. Rapamycin, an mTOR inhibitor, has been shown to induce apoptosis in nonmalignant B and T lymphocytes and we have demonstrated its potential efficacy in models of lymphoid leukemia. Because ALPS is caused by defective lymphocyte apoptosis, we hypothesized rapamycin would be effective in ALPS by inducing apoptosis in these abnormal cells, controlling the lymphoproliferation that is the hallmark of the disease. We confirmed this hypothesis by using a murine model of ALPS, CBA-lprcg, treating animals that had developed significant lymphadenopathy and splenomegaly with rapamycin. We followed response to treatment with serial assessment of DNTs in peripheral blood and lymphoid tissue by flow cytometric determination and by serial monitoring of lymph node and spleen size with small animal ultrasound. This is the first report to use this novel and powerful tool to measure murine lymphoproliferation and we found 3-dimensional ultrasound measurements in the mice correlated to actual tissue measurements at sacrifice (r = 0.9648, p = 0.0001). We found a dramatic and statistically significant decrease in DNTs (p = 0.02), lymphadenopathy (p = 0.003), and splenomegaly (p = 0.03) after only 4 weeks when comparing mice treated with rapamycin to control animals (Table). We found no toxicities and no evidence of myelosuppression in treated animals. We performed immunoblots to evaluate a major mTOR signaling pathway intermediate (phospho-S6) on lymph node biopsies obtained from mice before and after treatment with rapamycin and found a correlation between clinical response and biochemical response (downregulation of phospho-S6). In summary, rapamycin, a safe and well tolerated medicine, is effective in murine ALPS and its use should be explored in patients with the disease.

Rapamycin Effective in ALPS

Disease Parameter (1) Rapamycin Treated(2) Vehicle Control(2) p value 
(1) Average number of DNTs, volume of lymph nodes, and area of spleens were the same between groups at initiation of treatment. (2) Average (range) after 4 weeks of treatment 
DNTs of blood by FACS (mm3) 2440 (1343 – 3756) 9957 (4426 – 20384) 0.02 
Lymph node volume by ultrasound (mm3) 52 (3 – 193) 760 (366 – 1043) 0.003 
Splenic area by ultrasound (mm2) 54 (20 – 103) 179 (95 – 336) 0.03 
Disease Parameter (1) Rapamycin Treated(2) Vehicle Control(2) p value 
(1) Average number of DNTs, volume of lymph nodes, and area of spleens were the same between groups at initiation of treatment. (2) Average (range) after 4 weeks of treatment 
DNTs of blood by FACS (mm3) 2440 (1343 – 3756) 9957 (4426 – 20384) 0.02 
Lymph node volume by ultrasound (mm3) 52 (3 – 193) 760 (366 – 1043) 0.003 
Splenic area by ultrasound (mm2) 54 (20 – 103) 179 (95 – 336) 0.03 

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