Engraftment of chronic myeloid leukemia in SCID mice

Chronic myeloid leukemia (CML) is a clonal disorder of primitive hematopoietic stem cells characterized by a reciprocal translocation between chromosomes 9 and 22. Animal models of CML would be useful to study the biology and potential therapies in this disease. Mice with severe combined immunodeficiency (SCID) which will accept human xenografts have been useful in the study of a variety of human malignancies. CML has been difficult to establish in SCID mice possibly due to the lack of a functioning human stroma and relevant cytokines. To facilitate engraftment we injected cells in matrigel which is a soluble extract of basement membranes; is liquid below 22 degrees C and gels at 37 degrees C. CD34+ myeloid blast crisis cells (2 x 10(6)) were mixed in matrigel and injected subcutaneously into 10 SCID mice. All mice developed large tumours which spread to the mouse BM and spleen. However the percentage of human cells in the mouse BM and spleen was variable and ranged from 1 to 50 per cent. In contrast chronic phase (CP) CML cells mixed in matrigel did not form subcutaneous tumours and spread to the BM and spleen was detectable by PCR and not macroscopically. Groups of mice were injected with matrigel containing 1-20 x 10(7) MNC (2-20 x 10(5) CD34+ cells) from five patients with CP CMP. Bcr-abl sequences were detected by RT-PCR in the peripheral blood (PB) of 38/84 (45 per cent) mice at 3-10 weeks following injection of the CML cells but rarely at later time points. In addition, 33/75 (44 per cent) of mice sacrificed between 7 and 35 weeks following injection of CML cells were bcr/abl positive in the bone marrow and 17/70 (24 per cent) were positive in the spleen. Bcr-abl positive human CFU-GM colonies were also cultured from the murine bone marrow of several mice indicating that hematopoietic progenitor cells were able to migrate from the matrigel and engraft in murine hematopoietic organs. Engraftment of CP-CML was more successful in mice given higher numbers of CD34+ cells. Histological examination revealed that myeloid cells grow locally in the matrigel for several weeks, during which time the matrigel is infiltrated by blood vessels which may allow for the migration of CML progenitors to the murine bone marrow. This model system may be useful for studying the role of immunotherapy after allogeneic and autologous bone marrow transplantation.