| 研究実績の概要 |
First, in order to determine the identity of immune cells responsible for the eradication of HOXA9-Sytl1 cells in vivo, we inoculated these cells into RAG2-/- mice and found HOXA9-Sytl1 cells being able to survive and expand up to leukemia onset. This result demonstrates that T and/or B lymphocytes are involved in the immune reaction leading to the elimination of HOXA9-Sytl1 cells, which suggests the implementation of an adaptative immune response.
Which of T or B cells are the critical cells involved in this immune response is under investigation, by inoculation of HOXA9-Sytl1 cells into CD3-/- and μMT-/- mice. However, HOXA9-Sytl1 cells inoculation into wt B6 mice did not lead to serum IgG production, suggesting that B cells are probably not employed in this process.
Interestingly, co-incubation of HOXA9-Sytl1 cells with splenic cells in vitro did not lead to immune reaction. Indeed, T and B cells activation markers did not increase in the presence of leukemic cells, and lymphocyte proliferation did not occur. This suggests that, in vivo, a sophisticated multi-step process (and multi-cell) is likely to occur.
Unexpectedly, we found that long term co-incubation of HOXA9-Sytl1 cells with splenic cells in vitro led to the appearance of fibroblast-like cells that, on a phenotypic screening, seem to be telocytes. Co-incubation of HOXA9-MEIS1 cells showed the same result, therefore this phenomenon is not under the MEIS1 control. However, interplay might be different between telocytes, splenic cells and HOXA9-Sytl1 or HOXA9-MEIS1, giving rise to an adaptive immune response or not.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
2: おおむね順調に進展している
理由
The exact type of immune reaction generated by inoculation of HOXA9-Sytl1 cells and the protective mechanisms conferred by MEIS1-overexpression are far from being elucidated and turned out to be more complex than initially predicted.
The complex nature of this immune reaction has slowed down the progress for solving this issue. However, overall progress is going rather smoothly thanks to unexpected discoveries that were not initially planned, for example the involvement of telocytes in the process, which opens new concepts for the working hypothesis. Several still unraveled muti-step immune mechanisms are expected to be found involved in leukemic cell detection, and maybe in tumor cell detection as a general mechanism.
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| 今後の研究の推進方策 |
We are planning to shed clarity onto the precise role of telocytes into the immune detection of HOXA9-Sytl1 cells, since telocytes have been shown to be involved in immune surveillance. We suspect telocytes to be the prime cells responsible for the very early detection of leukemic cells, giving rise to warning signals for the immune system that lead to its activation.
In this hypothesis, HOXA9-MEIS1 cells would be either not detected, or would control telocytes for either not sending warning signals, or inducing a switch of this warning signals to desired signals. One of this desired signal could be the recruitment and control of stem cells (since telocytes have also been shown to be involved in this process), particularly mesenchymal-stem cells, which are known to be immunosuppressive cells.
Indeed, since we found that leukemic cells induce the proliferation of splenic telocytes in vitro, whether leukemic cells express MEIS1 or not, HOXA9-MEIS1 cells might take advantage of telocytes by forcing them to recruit mesenchymal stem cells in vivo, while HOXA9-Sytl1 cells would be unable to do so. In this regard, we are currently generating conditional mesenchymal stem cells depleted mice (diphteria toxin A transgenic mice x Nestin-Cre mice). We expect HOXA9-MEIS1 cells to be unable to survive into this mice, due to the lost ability to immunosuppress the immune system.
The critical MEIS1-target genes responsible for this process will be screened through microarray analysis. Potentially, inoculation of leukemic cells into mice deleted for these genes will be investigated.
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