Establishment of Novel Disease Models for Human Acute Type ATL and HTLV-I Carrier Using NOD-scid/IL2rg^null Mouse.

[Purpose] Adult T cell leukemia (ATL) is developed by clonal proliferation of human T cell leukemia virus-type 1 (HTLV-I) infected CD4⁺ human T cells, and is one of the most intractable leukemia in adults. Excellent animal model has been desired to fully investigate the pathophysiology of HTLV-I infected cells in vivo. However, acute type primary ATL has been previously reported to engraft poorly in NOD-scid recipients and it was difficult to study human T cells physiologically developed from hematopoietic stem cells (HSCs) in vivo. We aimed to develop novel disease models for acute type ATL and HTLV-I carrier using newborn NOD-scid/IL2rg^null mice.

[Method and Result] First, to analyze the engraftment levels of acute type ATL cells, 2.5–10 million peripheral blood (PB)-derived CD4⁺ cells from acute type ATL patients were intravenously transplanted into newborn NOD-scid/IL2rg^null recipients following sublethal irradiation. At 6 weeks after transplantation, the engraftment of hCD45⁺hCD3^dimhCD4⁺hCD25⁺ cells were detected in recipients’ PB and the engraftment levels increased over time. The phenotypical characterization of hCD3^dimhCD4⁺hCD25⁺ was similar to that of primary patient sample. Until 16 weeks post-transplantation, recipient exhibited ruffled fur and lethargy and was sacrificed to analyze the engraftment and infiltration of ATL cells. All the engrafted human CD45⁺ cells expressed CD4 and CD25, and the engraftment levels of human ATL cells were higher than 90% in the PB and the spleen of recipients. Lymphadenopathy and splenomegaly were seen, which were not seen in untransplanted mice or in the mice transplanted with cord blood-derived CD34⁺CD38⁻ cells. Abnormal multi-lobulated flower-like cells were present in the PB and the spleen of recipients as evidenced by May-Grunwald-Giemsa staining. Infiltration of human CD4⁺ ATL cells into the spleen, lymph nodes (LNs), and liver of recipients was demonstrated. Nested polymerase chain reaction (PCR) confirmed the presence of HTLV-I genome in the recipient spleen. These results suggest that, after transplantation of primary acute type ATL cells, NOD-scid/IL2rg^null mice properly mimicked the clinical features of ATL, showing efficient infiltration of tumor cells. Next, to understand leukemogenic process of normal CD4⁺ T cells through transmission of HTLV-I, we infused mitomycin-C (MMC)-treated HTLV-I cell lines (MT-2) into the humanized NOD-scid/IL2rg^null mice which possess human hematopoiesis derived from cord blood HSCs. At 7 to 12 weeks after infusion of MT-2 cells, atypical lymphocytes were found in the PB and LNs cells of recipients. Nested PCR of pX region demonstrated the presence of the HTLV-I genome in the recipient bone marrow cells. These results suggest that the transmission of HTLV-I from MMC-treated MT-2 cells to normal CD4⁺ T lymphocytes occurred in vivo in the humanized NOD-scid/IL2rg^null recipients. This model may be useful as a model for the carrier state for HTLV-I.

[Conclusion] These new disease model mice may recapitulate the pathology of human acute type ATL and HTLV-I carrier state. These models can be useful tool to investigate the pathogenesis of ATL and to develop the curative treatment for ATL.