IL-27 ERADICATES PEDIATRIC B-ALL CELLS IN VIVO BY TARGETING TUMOR INITIATING CELLS

Background. B-acute lymphoblastic leucemia (B-ALL) is the most common pediatric hematologic cancer which derives from aberrant expansion of early B lymphocytes in the bone marrow (BM). B-ALL is organized as a cellular hierarchy sustained by tumor initiating cells (TIC) at the apex which are the only cells with self-renewal ability, which generate both rapidly proliferating clonogenic progenitors and leukemic blasts, and maintain the bulk population of cancer cells. TIC are quiescent, slowly dividing cells and are refractory to chemotherapeutic agents that kills highly proliferating cells within the tumor. Therefore, complete eradication of this tumor may depend on the efficacy of therapies that target also TIC cells. IL-27 is a pro-inflammatory cytokine and shows anti-tumor activity in different murine solid tumors through indirect mechanisms such as immune stimulation and/or inhibition of angiogenesis. Aims. Objective of this study was to investigate the role of IL-27 as potential anti-tumor agent against primary B-ALL cells in vivo by targeting blasts and/or TIC populations. No information is available on the role of IL-27 in these cells. Methods. Blasts and TIC from BM of B-ALL patients after informed consent were tested for the expression of both chains of IL-27 receptor (R) (i.e. gp130 and WSX-1), by flow cytometry. The in vivo experiments were performed using primary B-ALL cell samples injected into SCID/NODIl2rg-/- (NOG) mice that were treated with PBS (controls) or human recomibinant (hr) IL-27. The IL-27 anti-tumor activity was evaluated in terms of tumor mass formation and spreading. Leukemic cells were searched at the primary site of tumor cell inoculation (subcutaneously and in the peripheral blood ) as well as in the lymphoid organs (spleen, BM, lymph nodes) by flow cytometry and immuohistochemical analysis. In order to demonstrate unambiguously that IL-27 functions directly on B-ALL cells we cultured primary B-ALL cells in the presence or absence of hrIL-27 and tested them for apoptosis and proliferation (flow cytometry) and angiogenesis by chorioallantoic membrane (CAM) assay. Results. Both blast and TIC popultions expressed complete IL-27R. In the in vivo experiments, B-ALL cells were found in the PB, BM and spleens from controls, whereas the same cells were present in the BM only from IL-27 treated animals. The TIC population was also reduced in the BM from treated mice as compared to BM of controls. The in vitro experiments showed that IL-27 inhibited proliferation and angiogenesis, and induced apoptosis of B-ALL cells, demonstrating that IL-27 targets directly neoplastic B-ALL cells. Conclusions. Taken together, our results show for the first time that IL-27 inhibits B-ALL spreading in vivo and may act against both leukemic blasts and TIC. This study may open new perspectives for playing therapeutic protocols based on such double anti-tumor effect by IL-27, and aimed to obtained a complete eradication of B-ALL in pediatric patients at diagnosis and/or relapse.