Abstract 1094: Role of the CRLF2 ligand TSLP in normal human B-cell development

Abstract

Abstract B cell acute lymphoblastic leukemia (B-ALL) is the most common childhood malignancy. Defects that result in overexpression of CRLF2, a cytokine receptor component, have recently been linked with poor outcome in both high-risk and non-high-risk B-ALL. CRLF2, together with the IL-7R alpha chain, forms the signaling receptor for the cytokine TSLP (Thymic Stromal-derived LymphoPoietin). TSLP-induced CRLF2 signaling results in proliferation of murine B cell progenitors, however, the role of TSLP in murine B cell development remains controversial and little is known of its role in human B lymphopoiesis. Human TSLP and CRLF2, in contrast to other cytokine/receptor pairs that act on B cell progenitors, show low homology to their murine counterparts (<40%), lack species cross reactivity, and activate differing intracellular pathways than in mice. Thus, human model systems are essential for understanding the role of CRLF2 function in normal and malignant B lymphopoiesis. We have developed a novel human-only in vitro culture model that allows the study of human B cell development under highly selective cytokine stimulation. This model is based on co-culturing CD34+ hematopoietic stem cells (HSCs) with primary human bone marrow stroma supplemented with selective exogenous cytokines and/or specific cytokine neutralizing antibodies. We have previously used this model to show that IL-7 increases B cell progenitors by over 60 fold and that IL-7 is essential for normal human B cell production (J. Immunol. 2009 82:4255). Here we use our human-only in vitro model to examine the role of TSLP-induced signals in normal human B cell development. Our data show that TSLP induces an expansion of human B cell progenitor populations generated from HSCs in cord blood that is similar in magnitude to that observed for IL-7. A comparison of TSLP and IL-7 effects shows that TSLP targets early B cell progenitors (CD34+) inducing expansion of this population with limited differentiation. In contrast, IL-7 induces rapid differentiation to the CD34- stage followed by proliferation. RT-PCR and ELISA analysis show that normal human bone marrow stoma express both TSLP and IL-7, thus establishing an endogenous source of these cytokines at the site of normal and malignant hematopoiesis. Our data provide evidence that TSLP and IL-7 exert differential and stage specific effects on proliferation and differentiation of B cell progenitors and suggest that deregulation of the complex interplay between these signals in normal differentiation could set the stage for malignant transformation to B-ALL in the presence of cooperative defects in JAK2 and/or Ikaros. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1094. doi:10.1158/1538-7445.AM2011-1094