ONO-4641 is a second-generation sphingosine 1-phosphate (S1P) receptor modulator that exhibits selectivity for S1P receptors 1 and 5. Treatment with ONO-4641 leads to a reduction in magnetic resonance imaging disease measures in patients with relapsing-remitting multiple sclerosis. The objective of this study was to explore the potential impact of ONO-4641 treatment based on its immunomodulatory effects. Severe aplastic anemia is a bone marrow (BM) failure disease typically caused by aberrant immune destruction of blood progenitors. Although the T helper type 1-mediated pathology is well described for aplastic anemia, the molecular mechanisms driving disease progression remain undefined. We evaluated the efficacy of ONO-4641 in a mouse model of aplastic anemia. ONO-4641 reduced the severity of BM failure in a dose-dependent manner, resulting in higher blood and BM cell counts. By evaluating the mode of action, we found that ONO-4641 inhibited the infiltration of donor-derived T lymphocytes to the BM. ONO-4641 also induced the accumulation of hematopoietic stem cells in the BM of model mice. These observations indicate, for the first time, that S1P receptor modulators demonstrate efficacy in the mouse model of aplastic anemia and suggest that treatment with ONO-4641 might delay the progression of aplastic anemia. SIGNIFICANCE STATEMENT: ONO-4641 is a second-generation sphingosine 1-phosphate (S1P) receptor modulator selective for S1P receptors 1 and 5. In this study, we demonstrated that ONO-4641 regulates the trafficking of T lymphocytes along with hematopoietic stem and progenitor cells, leading to alleviation of pancytopenia and destruction of bone marrow in a bone marrow failure-induced mouse model mimicking human aplastic anemia.
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