A novel xenograft model to study the role of TSLP-induced CRLF2 signals in normal and malignant human B lymphopoiesis

Abstract

T hymic stromal lymphopoietin (TSLP) stimulates in vitro proliferation of human fetal B-cell precursors. However, its in vivo role during normal human B lymphopoiesis is unknown. Genetic alterations that cause overexpression of its receptor component, cytokine receptor-like factor 2 (CRLF2), lead to high-risk B-cell acute lymphoblastic leukemia implicating this signaling pathway in leukemogenesis. We show that mouse thymic stromal lymphopoietin does not stimulate the downstream pathways (JAK/STAT5 and PI3K/AKT/mTOR) activated by the human cytokine in primary high-risk leukemia with overexpression of the receptor component. Thus, the utility of classic patient-derived xenografts for in vivo studies of this pathway is limited. We engineered xenograft mice to produce human thymic stromal lymphopoietin (+T mice) by injection with stromal cells transduced to express the cytokine. Control (-T) mice were produced using stroma transduced with control vector. Normal levels of human thymic stromal lymphopoietin were achieved in sera of +T mice, but were undetectable in -T mice. Patient-derived xenografts generated from +T as compared to -T mice showed a 3-6-fold increase in normal human B-cell precursors that was maintained through later stages of B-cell development. Gene expression profiles in high-risk B-cell acute lymphoblastic leukemia expanded in +T mice indicate increased mTOR pathway activation and are more similar to the original patient sample than those from -T mice. +T/-T xenografts provide a novel pre-clinical model for understanding this pathway in B lymphopoiesis and identifying treatments for high-risk B-cell acute lymphoblastic leukemia with overexpression of cytokine-like factor receptor 2.

Suppressors and activators of JAK-STAT signaling at diagnosis and relapse of acute lymphoblastic leukemia in Down syndrome

“…Similarly, we speculate that leukemic cells carrying CRLF2 rearrangements-and, hence, expressing the TSLP receptor-may survive chemotherapy during complete remission by interacting with TSLP-producing cells in the bonemarrow niche. The experimental examination of this hypothesis is challenging, because mouse TSLP is not reactive with the human TSLP receptor (67). The hypothesis suggests that targeting TSLP [for example, by the novel anti-TSLP antibodies (68)] or the TSLP receptor [by for example, CRLF2 antibodies or CAR-T cells (69,70)] may be a useful additional therapy-better than JAK inhibition-to prevent relapse in patients with DS and sporadic CRLF2 pos ALL.…”

Fine-Tuning Patient-Derived Xenograft Models for Precision Medicine Approaches in Leukemia

“…Binding of TSLP induces downstream activation of the JAK2-STAT5 (Janus Kinase 2-Signal Transducer and Activator of Transcription 5) (figure 2) and PI3K/AKT/mTOR (Phosphoinositide3-kinase/protein kinase B/mechanistic target of rapomycin) pathways in CRLF2 B-ALL cells. 2324 Activation of these pathways induces changes in gene expression and cellular functions that are associated with survival and proliferation of leukemia cells. 25–27 CRLF2-mediated signals are therefore likely to contribute to leukemogenesis, disease progression and chemoresistance.…”

On mice and humans: the role of thymic stromal lymphopoietin in human B-cell development and leukemia

“…For this reason, the in vivo models currently used are not optimized enough to recapitulate the correct environment for every type of human hematopoietic or leukemic cell. This problem has been recently addressed by the development of several models of humanized mice expressing human cytokines, as described in detail by the recent excellent review in Haematologica by Theocarides et al 1 In this issue of Haematologica, Francis et al 2 created a chimeric mouse able to produce human thymic stromal lymphopoietin (TSLP) to study the effect of human TSLP on human B-cell development and human B-cell precursor acute lymphoblastic leukemias (BCP-ALLs) with abnormal expression of the TSLP receptor (TSLPR) (Figure 1). The generation of this mouse was required since the homology between mouse and human TSLP is only 43% and 35% for the TSLPR, with no cross reactivity between the species.…”

“…Regardless of these limitations, the findings of Francis et al clearly demonstrate that, despite the almost absent expression of the receptor, TSLP can support human B-cell lymphopoiesis. 2 Unlike the uncertainty of its importance in normal B-cell development, a clear role has emerged for the TSLP pathway in BCP-ALL. Up to two-thirds of BCP-ALL in children with Down syndrome and 5%-10% of BCP-ALL children and adults without Down syndrome have acquired genomic aberrations leading to a markedly increased expression of CRLF2, and hence the receptor to TSLP, in the malignant blast cells.…”

“…10 The model created by Francis et al allowed the first in vivo examination of the role of human TSLP in B-cell development ( Figure 1). 2 Human bone marrow stroma cell line (HS27) transduced to secrete human TSLP were given by intra-peritoneal injection to NSG mice and survived in the peritoneal cavity (they were not detectable either in the spleen or bone marrow (BM) of the mice) reaching serum levels of TSLP similar to those of human blood. The advantage of this model consists in the ability to modulate the serum levels of hTSLP based on the timing and number of stromal cells injected.…”