[Analysis of in vivo cell proliferation of ATL using SCID mice]

We made a model of in vivo cell proliferation of leukemic cells from adult T cell leukemia (ATL) patients using severe combined immunodeficient (SCID) mice. SCID mice injected with ATL cells from 6 of 8 ATL patients were found to have the tumor. DNA analysis revealed that the clone of the cells proliferating in mice was the same as that of the original leukemic cells. Histologic examination showed that the pattern of the infiltration of ATL cells in mice was similar to that of an ATL patient. Next, we examined the tumorigenicity of HTLV-I infected cell lines using SCID mice. Seven HTLV-I infected cell lines were injected into SCID mice and it was found that 4 of them were capable of proliferating in SCID mice. HTLV-I infected cell lines of non-leukemic cell origin could not engraft in SCID mice, indicating that these cells seemed not to have the enough genetic changes to acquire the tumorigenic potential. Analysis of gene expression suggested that neither IL-2 nor HTLV-I viral product was directly involved in the neoplastic cell growth of ATL. Furthermore, T cells immortalized by introduction of Tax could not engraft in SCID mice, indicating that the expression of tax gene seemed not to be sufficient for the neoplastic cell growth in vivo.