Unraveling Stat Signaling In Npm/Alk-Induced Lymphoma: Stat3 But Not Stat5 Is Required For Lymphomagenesis In A Bone Marrow Transplantation Model Using Conditional Knockout Mice

Abstract Abstract 1969 Poster Board I-992 Introduction: NPM/ALK is a constitutively activated, oncogenic kinase leading to the development of anaplastic large cell lymphoma in humans. Multiple pathways have been implicated in NPM/ALK-dependent signaling including STAT3 and STAT5. In a transgenic mouse model it could be demonstrated that STAT3 is critical for NPM/ALK-driven lymphomagenesis. However, deletion of STAT3 did not lead to prolonged survival of the mice. In addition, the role of STAT5 in NPM/ALK-positive lymphoma in vivo is largely unclear. Methods: We used the established murine bone marrow (BM) transplantation model using BM derived from STAT3 and STAT5 conditional knock-out (fl/fl) mice. Precisely, we harvested BM from STAT3fl/fl and STAT5fl/fl mice and expressed NPM/ALK-Cre/EGFP in the BM cells by using retroviral gene transfer. BM cells were transplanted in lethally irradiated wild-type mice. Expression of NPM/ALK and deletion of STAT3 and STAT5 was determined in BM cells. Results: BM from STAT3fl/fl and STAT5fl/fl mice was successfully harvested, retrovirally infected, and transplanted in recipient mice. Analysis of BM cells revealed expression of NPM/ALK and deletion of STAT3 or STAT5 in NPM/ALK-Cre/EGFP-infected STAT3fl/fl and STAT5fl/fl BM respectively. Within the STAT3 group, control mice transplanted with NPM/ALK-EGFP-infected STAT3fl/fl BM died after 2-3 weeks from a NPM/ALK-positive lymphoma. An additional control group transplanted with NPM/ALK-Cre/EGFP-transduced wild-type BM also died from a NPM/ALK lymphoma but with an increased latency. Notably, mice transplanted with NPM/ALK-Cre/EGFP-infected STAT3fl/fl (STAT3-deleted) BM showed a significantly prolonged survival compared to either control groups including 5 mice that survived at least 300 days after transplantation. Interestingly, only about 60% of these mice died from an NPM/ALK-positive high-grade lymphoma or myeloma-like disease, whereas the remaining animals died from other (irradiation-induced) diseases. In contrast, 150 days post transplantation STAT5 deletion in NPM/ALK expressing BM cells did not increase survival of the transplanted mice compared to the control group with wild-type BM using NPM/ALK-Cre/EGFP retrovirus. Conclusion: Specific deletion of STAT3 but not STAT5 in NPM/ALK-expressing cells markedly attenuates disease progression. The described transplantation model using BM from conditional knock-out mice and an Cre-containing expression vector is extremely helpful to specifically study signaling in oncogene-driven hematological malignancies. Disclosures: No relevant conflicts of interest to declare.