Except allogenic bone marrow transplantation with either myeloablative or reduced intensity conditioning, there is no effective treatment for PMF. Age-related morbility and mortality factors limit this application. Anti-Jak2 treatment relieves splenomegaly but does not improve cytopenia. IMiDs on the other hand can improve anemia in up-to 20% of transfusion dependent anemic patients with PMF. In order to asses the underlying mechanism and to predict treatment responsiveness, in vitro suppression of Treg cells by lenalidomide correlated to clinical treatment response was performed. Seven patients with transfusion dependent and ESD (erythropoietin stimulating drugs) resistant PMF were studied. Mononuclear cells from blood in patients with PMF were cultured in the culture medium with FCS and Il-2 (100 IU/ml) in the presence of lenalidomide or DMSO for 6 days, the cells were then stained for Treg cells (CD4+, CD 25 +,and FoxP3+,) and analyzed by flow cytometry using Treg Detection Kit from Miltenyi Biotec Inc (Auburn, CA). Treg cells were enumerated as percentage of selected CD4 + cells. The results showed that in the 4 patients who responded to lenalidomide treatment, Treg cells were suppressed by the in vitro testing by lenalidomide, while in the three patients who were clinically refractory to lenalidomide treatment, their Treg cells were not suppressed by in vitro lenalidomide treatment. These results suggest that in transfusion dependent PMF, Treg cells may play a role in the pathogenesis of anemia and that effectiveness of lenalidomide treatment may be partly related to its suppression of Treg cells. Further studies to recruit more patients and to explore the role of Treg cells in modulating erythroipoiesis in PMF using the erythroid methylcellulose culture systems are currently in progress.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5632.