M.Sc Thesis

M.Sc StudentKabha Mona
SubjectCharacterization of Molecules Inducing Regulatory Features
of Chronic Lymphocytic Leukemia Cells
DepartmentDepartment of Medicine
Supervisors DR. Netanel Horowitz
DR. Shimrit Ringlshtein
DR. Tamar Katz


Chronic lymphocytic leukemia (CLL) is the most common leukemia among adults in Western Countries. Despite recent advances in CLL treatment, it remains incurable. A hallmark of CLL is severe immune deficiency resulting in increased susceptibility to infections and failure to generate an antitumor immune response promoting tumor progression. CLL cells induce changes in the tumor microenvironment characterized by alterations within the T cell repertoire such as increased frequency of regulatory T cells(Tregs), impaired ability to form immunological synapse and increased expression of exhaustion markers. The unique CLL phenotype characterized by IL-10 competence, and the expression of CD5, CD38 and CD27 imply that CLL cells share features with the recently described IL- 10 producing regulatory B cells. However, the mechanisms utilized by CLL cells to impose their inhibitory functions are not fully understood. Previous studies conducted in our lab have demonstrated that TLR-9- activated CLL cells generate and secrete IL10, inhibit autologous CD4 T-cell proliferation and induce regulatory T-cells (Tregs) from autologous CD4 T-cells. We hypothesized that CLL cells secrete molecules of inhibitory potential capable of modulating the immune system. The first molecule examined was IL10 and results demonstrated that knocking down IL-10 expression in TLR-9 activated CLL cells result in attenuation of their inhibitory effect on CD4 T-cell proliferation, demonstrating the involvement of IL-10 in mediating the inhibitory effect of the malignant cells. The second molecule addressed was TPO, since recent evidence obtained in ITP indicated that TPO may possess immune modulating activity, leading to enhanced regulatory activity. High TPO serum levels have been described in CLL, thus we hypothesized that TPO may itself be a mediator of the inhibitory features in CLL. Our results showed that CLL cells express TPO, further increased following TLR-9 activation. Moreover, TPO was found to inhibit CD4 T-cell proliferation and induce Tregs, while no effect was found on their healthy counterpart. This can be largely attributed to the increased TPO receptor expression detected on patients' T cells compared to T cells from healthy donors. Importantly, TPO activity could not be attributed to increased IL10 generation by the CLL B-cells. Finally, our results demonstrated that BCR signaling is also involved in promoting the inhibitory phenotype of CLL cells through IL-10 expression, these findings support our hypothesis that TLR-9 and BCR pathway signaling lead to the generation of molecules involved in immune suppressive activity in CLL.