Transdifferentiation of Malignant B-Cells into Macrophages in a Murine Model of Burkitt´s Lymphoma

B-cell lymphomas, such as Burkitt's lymphoma, are malignant diseases of the hematopoietic system. They arise from transformed B-cells originating from diverse primary and secondary lymphatic tissues. Like in other cancers, the stroma of lymphomas is typically infiltrated by so-called tumor-associated macrophages (TAMs), which execute manifold tumor-specific functions. Interestingly it was shown, that mature B-cells could be efficiently re-programmed into macrophages by the overexpression of myeloid-specific transcription factors. Moreover, other studies observed in vitro that this lymphoid/myeloid plasticity might be also caused by oncogenes in cultured B-cells of murine lymphoma models. Therefore we consider, if lymphoma B-cells themselves might be a source of TAMs, besides the well-known infiltration of monocytic cells into the tumor environment. Based on the system of CD45.1/2 allotypes, a murine model of lymphoma was thus developed, which allows tracking of the conversion of lymphoma B-cells into TAMs.

It could be shown, that some lymphoma B-cells of the established model in fact spontaneously switched into a macrophage-like phenotype. Accordingly, they start to express typical macrophage markers, but seem to perform a transition into a myeloid-like expression profile on the level of transcription as well. Furthermore, analysis of the recombined immunoglobulin heavy chain confirmed the clonal identity of lymphoma b-cells and TAMs. Although these cells do not exhibit an overt immunological phenotype, they show elementary functional properties of macrophages, such as phagocytosis as well as a post-mitotic character. Moreover, transdifferentiated B-cells cells were resistant to chemotherapy and persist after treatment, while lymphoma B-cells were eradicated.

Which consequences the lymphoid/myeloid plasticity of lymphoma B-cells has for tumor development, progression, as well as for the outcome of therapy, and if these observations could be transferred to human tumors, will be object of future investigations.