Transdifferentiation of human lymphoma cells and a potential therapeutic application
In another line of research we asked whether human lymphoma B cells could be reprogrammed into macrophages by C/EBPa.
In Burkitt’s lymphoma, proliferation of mature B cells is induced by the activation of Myc expression following translocation of the oncogene to the IgH enhancer. We found that the majority of 23 lymphoma and leukemia cell lines tested responded with a complete or partial change in the expression of the B cell marker CD19 and the macrophage marker Mac-1. Two lines in whch high levels of C/EBPa expression could be maintained, the Burkit lymphoma line Seraphina and the B cell precursor acute leukemia RCV-ACH, could be stably transdifferentiated into functional, quiescent macrophages. Remarkably, the conversion efficiency was nearly 100%, far higher than the frequency of the recently described conversion of human fibroblasts into neurons.
We next asked whether transdifferentiation inhibits the formation of tumors after transplantation into immunodeficient mice. We found (in collaboration with J. A. Martinez Climent, U. de Navarra) using both the Burkitt’s lymphoma cells line and the immature B cell leukemia line stably expressing C/EBPaER that tumor formation could be inhibited by inducing their transdifferentiation into macrophages. Moreover, tumor formation could be delayed even when administering the inducer in vivo, 10 days after inoculation of untreated, inducible tumor cells.
The results described suggest that it might be possible to find drugs that can induce transdifferentiation as a potentially new therapeutic avenue to treat leukemias and lymphomas.
As part of the BLUEPRINT project of the EU we therefore developed a reporter system consisting of the tamoxifen inducible C/EBPaER containing cell line BLaER1 line consisting in the lysozyme promoter driving the expression of tdTomato. These cells turn red when they are induced to transdifferentiate into macrophages. Using these cells, we screened at the screening facility more than 2,000 compounds, consisting of pharmacologically active compounds, a phytochemical libray as well as drugs targeting known signaling pathways. We are currently validating candidate compounds. A similar screen is ongoing in collaboration with Sanofi Aventis in Toulouse.
Reference publication: Rapino et al., C/EBPa Induces Highly Efficient Macrophage Transdifferentiation of B Lymphoma and Leukemia Cell Lines and Impairs Their Tumorigenicity, Cell Reports (2013), http://dx.doi.org/10.1016/j.celrep.2013.03.003
The left image shows tumorigenic human B cells (Burkitt's lymphoma). The right image shows the same cells after activating C/EBPa for 5 days, when they acquire a macrophage morphology.