Patient-Derived Xenografts (PDX) of B Cell Lymphoma in NSG Mice: A Mouse Avatar for Developing Personalized Medicine

Introduction: In the United States, over 90% of non-Hodgkin's lymphomas (NHL) are derived from mature B lymphocytes. More than 500,000 individuals in the U.S. are living with non-Hodgkin's lymphoma, yet despite an improving 5-year survival rate estimated at 69% for 2014, almost 20,000 deaths were predicted for the year. Personalized medicine for NHL, while still in its infancy, has the potential to improve patient survival and quality of life during treatment. The promise of personalized medicine depends on the ability to guide patient treatment and develop targeted therapies that are specifically tailored to each person's cancer. A key component of this goal is a method to test drug regimens on individual patient samples. To this end, we have developed a new experimental paradigm: mouse Avatars of lymphoma progression using NOD.Cg-PrkdcscidIl2rgtm1Wjl/SzJ (NSG) mice. Defects in both adaptive and innate immunity in NSG mice provide murine hosts receptive for human primary tumors.

Results: Here we describe three examples of B cell lymphoma derived from patient samples that were successfully engrafted into NSG mice (the first two specimens were from lymph node biopsies, and the third from bone marrow). Case 1 was derived from follicular lymphoma (FL) Grade 3A with a t(14;18)(q32q21) BCL2-IGH rearrangement. When small tumor specimens were implanted intra-peritoneally (i.p.), discrete tumors formed in recipient mice and dissemination of tumor cells was also observed in spleen and bone marrow. Lymphomas from these mice were subsequently adoptively transferred to 6 secondary recipient NSG host mice to generate widely disseminated tumors, including one mouse with intestinal and pancreatic tumors. Case 2 was diagnosed as diffuse large B cell lymphoma (DLBCL) transformed from pre-existing FL with a t(14;18)(q32q21) BCL2-IGH rearrangement. Fragments of involved lymph node implanted i.p. in NSG mice grew as 0.8-1.4 cm tumors in the abdomen, and tumor cells were also detected in spleen and bone marrow of the mice. Case 3 was a high grade B cell lymphoma (BL) transformed from follicular lymphoma with bone marrow and central nervous system (CNS) involvement. The lymphoma was described as B-cell lymphoma unclassified, with features intermediate between DLBCL and Burkitt's lymphoma. The tumor exhibited a t(8;14) c-myc translocation and a high level of MYC protein expression. A single cell suspension of patient bone marrow was injected intravenously into NSG mice and after 3 months, 6 of 8 recipient mice developed CNS disease with pathology resembling human CNS lymphoma with perivascular and parenchymal invasion. The bone marrow from these mice had nearly 90% lymphoma cells, and high levels of infiltration were also observed in spleen and peritoneal cavity. Transfer of lymphoma cells isolated from CNS of primary recipient mice to secondary mice resulted in lymphoma cells in peripheral blood, spleen, bone marrow, and brain.

Conclusions: Altogether, we have successfully developed a new experimental paradigm utilizing mouse Avatars from primary patient B-cell lymphomas. These cases include a spectrum of B-cell lymphoma subtypes including FL, transformed DLBCL, and high grade BL (with MYC translocation). This experimental approach provides a powerful platform for evaluating response to standard and novel therapeutic approaches. This model will also permit investigation of the basis for bone marrow and CNS dissemination of tumor cells in the NSG mouse model, given the clinical importance of B cell lymphoma invasion of these sites. To the best of our knowledge, this is the first demonstration of CNS disease in a B cell lymphoma PDX system. Continued examination of primary, secondary and tertiary grafts and establishment of additional NSG PDX models are ongoing.