The Role Of 4-1BBL Reverse Signaling On The Biofunctions Of M5 Leukemia Cells And The Underlying Mechanisms

4-1BBL is also named CD137L, its receptor is 4-1BB(CD137), 4-1BBL/4-1BB is an important member of TNF/TNFR superfamily. 4-1BBL/4-1BB reverse signaling can activate monocytes and promotes proliferation of monocytes. and 4-lBBL is also expressed on some types of malignancies, such as a fraction of leukemia cells. Constitutive 4-1BBL coexpression on both human T and B leukemia cell lines. Surprisingly, in spite of the low expression level, tumor 4-1 BBL molecule signaled in T and B leukemia cells inducing proliferation and prolonging survival, but the role of leukemia CD137/CD137L system in vivo is unknown. It is important to find more effective clinical treatment strategy by studying the biology mechanisms of leukemia, that can killed the tumor cells more specially. Now, we studied the effects and mechanisms of 4-1 BBL reverse signaling to the monocytic leukemia cell line SHI-1.Part I. The expression and function of 4-lBBL on SHI-1 cell line in vitroThe expression of 4-1 BBL on monocytic leukemia cell line SHI-1 was analyzed by FCM. Our result indicated that SHI-1 cells high express 4-1 BBL. SHI-1 cells stimulated by agonistic mAb against 4-lBBL(lF1) . SHI-1 cells of 1F1 containing 5μg/ml or 10μg/ml mAb, proliferated more rapidly than the control groups. There were no morphological changes of SHI-1 between the control groups and other groups. That indicated 4-1 BBL reverse signaling might confer an advantage to the survival of SHI-1 cells. Part II. Establishment of human acute monocytic leukemia - SCID mice modelSHI-1 cells were transplanted i.p. into mice with severe combinedimmunodeficient(SCID). Engraftment of human leukemia in mice was monifored by serial tail vein sampling at regular intervals followed by flow cytometory (FCM) on surfacemarks as well as CD14,CD137L expression levels. All dying mice were dissectted and internal organs were examined to trace signs of leukemic infiltration. The liver, spleen, kidney and BM were examined using FCM and immunostochemistry , for detecting the appearance and distribution of the SHI-1 cells. We found that varying dose of SHI-1 cells could be xengrafted in SCID mice and the time of engraftment related to the dose that injected in the mice. Leukemic cells of 5 x 106> 1 x 107 dose disseminate to murine tissues. That indicated the SHI-1/SCID mice may be very useful for investigating the biologicalcharacteristics of acute monocytic leukemia(AML).Partlll. The role of anti-4-lBBL mAb on monocytic leukemia cells and their mechanismWe chose l*106 cells as the appropriate dose to establish the SHI-1/SCID mice model. 50ug/mouse or lOOug/mouse 1F1 MAb was injected regularly into the mice after 3 days of the transplantation.In conclusion, we approved 4-1BBL high expressed on SHI-1 cells, and 4-1BBL reverse signaling could promote proliferation of the cells in vitro; and Established a new human acute monocytic leukemia - SCID mice model, found the reverse signaling had the same effect to SHI-1 cells in vivo. The SHI-1/SCID mice may be very useful for studying the biology and treatment of leukemia.