A tumor-related lymphoid progenitor population supports hierarchical tumor organization in canine B-cell lymphoma

Background: Tumors have heterogeneous properties, which could be explained by the existence of hierarchically and biologically distinct tumor cells such as tumor-initiating cells (TICs). This model is clinically important, as TICs are promising targets for cancer therapies. However, TICs in spontaneous B-cell lymphoma have not been conclusively identified. Hypothesis/Objectives: Tumor cells with a progenitor phenotype exist in B-cell lymphoma, reflecting a hierarchical organization. Animals: Twenty-eight client-owned dogs with previously untreated B-cell lymphoma and 6 healthy dogs. Methods: This was a prospective study. Flow cytometry was used to identify lymphoid progenitor cells (LPCs) that coexpressed hematopoietic progenitor antigens CD34, CD117, and CD133, with lymphoid differentiation markers CD21 and/or CD22 in B-cell lymphoma. The polymerase chain reaction for antigen receptor rearrangements was used to analyze clonality and relatedness of tumor populations. A xenograft model with NOD/SCID/IL-2Rγ ^-/- mice was adapted to expand and serially transplant primary canine B-cell lymphoma. Results: LPCs were expanded in lymph nodes from 28 dogs with B-cell lymphoma compared with 6 healthy dogs (P= .0022). LPCs contained a clonal antigen receptor gene rearrangement identical to that of the bulk of tumor cells. Canine B-cell lymphoma xenografts in recipient mice that maintained LPCs in the tumors were recurrently observed. Conclusions and Clinical Importance: These results suggest the presence of a hierarchy of tumor cells in B-cell lymphoma as has been demonstrated in other cancers. These findings have the potential to impact not only the understanding of lymphoma pathogenesis but also the development of lymphoma therapies by providing novel targets for therapy.