Leukemogenic Fusion Gene (p190 BCR-ABL) Transduction Into Hematopoietic Stem/Progenitor Cells In the Common Marmoset

Patients with Philadelphia chromosome (p190 BCR-ABL fusion gene)-positive acute lymphoblastic leukemia have a poor prognosis despite intensive therapeutic intervention. Although a rodent model of this leukemia was previously established, the genetic and physiological differences between humans and rodents make it difficult to extrapolate the results from these models and apply these findings to human cases. Primates are more genetically related to humans than rodents. In this study, we attempted to develop a leukemia non-human primate model that mimics various human systems.

(1) A third-generation VSV.G pseudotyped lentiviral vector expressing the p190 BCR-ABL fusion gene driven by CMV or PGK promoter was produced (HIV-CMV/PGK-BCR-ABL). Ba/F3 cells, a mIL-3-dependent murine hematopoietic cell line, were transfected with this vector and cultured without mIL-3. These cells rapidly expanded after 12 days, indicating that p190 BCR-ABL gene expression allowed the Ba/F3 cells to grow autonomously. Next, using a biotin-labeled anti-marmoset CD34 monoclonal antibody (clone MA24) which was produced in our laboratory, MACS-sorted bone marrow CD34⁺ cells were transduced with the lentiviral vector (HIV-CMV/PGK-BCR-ABL) and subjected to the colony formation assay. In the majority of examined colonies, p190 BCR-ABL gene was detected regardless of the promoter. Taken together, the above findings indicate that p190 BCR-ABL gene was efficiently transduced into marmoset hematopoietic stem/progenitor cells. (2) Peripheral blood mononuclear cells (PBMNCs) were collected from individual marmosets after mobilizing the hematopoietic stem/progenitor cells with G-CSF. These cells were stimulated with cytokines (hIL3, hSCF and hTPO), followed by the transduction with the lentiviral vector. These cells were transplanted into marmosets preconditioned with busulfan. In this ex vivo transduction method, p190 BCR-ABL gene expression which was detected in PBMNCs by nested RT-PCR disappeared after day 56 and 100 in two marmosets. (3) Concentrated lentiviral vector was directly injected into the bone marrow cavity of individual marmosets pretreated with 5-fluorouracil and prednisolone. In this in vivo direct injection method, p190 BCR-ABL gene expression was maintained for more than one year and a half. Transduction of p190 BCR-ABL gene into hematopoietic stem/progenitor cells was confirmed by colony forming assay. In this model, one marmoset unexpectedly developed myelofibrosis-like disease. However, none of the marmosets have developed leukemia to date.

We successfully achieved sustained p190 BCR-ABL gene expression in vivo. This novel in vivo approach will help to develop a marmoset leukemia model in the future. Because a multiple-hit model of oncogenesis has been proposed for various human cancers, a genetic mutation in addition to p190 BCR-ABL may be required for the malignant transformation of hematopoietic stem/progenitor cells in the common marmoset.

No relevant conflicts of interest to declare.