Abstract 1528: Molecular mechanisms of TSLP as a therapy for CRLF2 B-Cell acute lymphoblastic leukemia

Abstract B-cell acute lymphoblastic leukemia (B-ALL) is the most common type of leukemia in children. B-ALL characterized by cytokine receptor-like factor 2 (CRLF2) overexpression (CRLF2 B-ALL) has a survival rate of <30% and is the highest risk sub-group of B-ALL in both adults and children. CRLF2 is a receptor component for the cytokine thymic stromal lymphopoietin (TSLP). TSLP plays a role in the survival and proliferation of B-cell precursors, thus explaining the oncogenic role of increased CRLF2 signaling in CRLF2 B-ALL. To our surprise, we found that high-levels of TSLP eliminated leukemia cells in patient-derived xenograft (PDX) models of CRLF2 B-ALL. CRLF2 and IL-7 receptor-alpha (IL-7Ra) form the heterodimer type-I cytokine receptor for TSLP cytokine. Binding of TSLP to its CRLF2 receptor complex induces JAK-STAT5 and PI3K-AKT pathway signals. TSLP shares the IL-7Ra with Interleukin 7 (IL-7) which has a heterodimer receptor consisting of IL-7Ra and the common gamma chain. High-levels of IL-7 (50 ng/ml) have been shown to induce IL-7Ra internalization and degradation in T-cells. We hypothesize that high-level TSLP induces internalization and degradation of IL-7Ra leading to CRLF2 signal inhibition, death of CRLF2 B-ALL cells and the anti-leukemia effects that we have observed in PDX mice. To test this hypothesis, we treated CRLF2 B-ALL cell lines with different TSLP concentrations to observe the effect of TSLP on its receptor and CRLF2 signaling. Flow cytometry data showed that continuous or a pulse of high-dose TSLP induced a loss of surface IL-7Ra expression for up to 24 hours. Phosphorylation assays showed that cells cultured with high-dose TSLP were unresponsive to subsequent TSLP-induced phosphorylation events (pSTAT5 and pRPS6), indicating CRLF2 signal inhibition. In conclusion, high-dose TSLP induces loss of (IL-7Ra) and inhibition of CRLF2 signaling. These results suggest that TSLP exerts its anti-leukemia effects by shutting down CRLF2-mediated signals possibly via the loss of the IL-7Ra receptor component. Citation Format: Hossam Alkashgari, Cornelia Stoian, Caleb Ruiz-Jimenez, Jacqueline Coats, Carlos A. Casiano, Sinisa Dovat, Kimberly J. Payne. Molecular mechanisms of TSLP as a therapy for CRLF2 B-Cell acute lymphoblastic leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1528.