Immune evasion of AML cells from FceRI+ cells through MEIS1 activity

2019 Fiscal Year Research-status Report

• Project/Area Number: 19K07678
• Research Institution: Japanese Foundation for Cancer Research
• Principal Investigator: アーノ クズィネ 公益財団法人がん研究会, がん研究所 発がん研究部, 研究員 (70725621)
• Project Period (FY): 2019-04-01 – 2022-03-31
• Keywords: Acute Myeloid Leukemia / Meis1 / Immune evasion

Outline of Annual Research Achievements

In vivo inoculation of HOXA9-MEIS1 cells into C57Bl/6 mice leads to leukemia onset while HOXA9-SYK cells are unable to do so.
We inoculated HOXA9-SYK cells into Mcpt8-DTR+ transgenic mice treated with Diphtheria Toxin (basophil-depletion) and found that HOXA9-SYK cells can expand in these mice, leading to leukemia onset. This result demonstrated that basophils are responsible for the elimination of HOXA9-SYK cells in C57Bl/6 mice.
In vitro, proliferation of HOXA9-SYK cells was inhibited when co-incubated with splenic cells, while HOXA9-MEIS1 expansion was poorly affected. Importantly, depletion of FceRI+ cells (basophils and mast cells) from splenocytes abrogated the proliferation inhibiting capacity of splenocytes on HOXA9-SYK cells, demonstrating that FceRI+ cells are responsible for this inhibiting process, while poorly affecting HOXA9-MEIS1 cells.
These results demonstrated that MEIS1 confers immune evasion capacity to leukemic cells by escaping from basophil-mediated inhibition.
We found that the proliferation inhibiting capacity of FceRI+ cells was mediated through secreted factors since supernatant was sufficient to suppress proliferation of HOXA9-SYK cells. Proteome LC-MS/MS analysis of splenic supernatant led to the identification of a significant number of proteins such as chemokines (CCL6 and CCL9) and proteases such as cathepsin D, L1, macrophage metalloelastase, prosaposin…

Current Status of Research Progress

3: Progress in research has been slightly delayed.

Reason

In January 2020, I changed institute from JFCR to National Cancer Center East Hospital (Kashiwa), starting a new project on cancer immunotherapy. I am still a visiting scientist at JFCR and I pursue experiments related to the above project, but at a lower pace since these projects have to be achieved in different institutes.

Strategy for Future Research Activity

We are planning to shed clarity onto the identification of the molecules present in splenic supernatant that are responsible for the inhibition of HOXA9-SYK cells and how MEIS1 protects from these molecules.
Experiments based on molecular weight separation through centrifugation of supernatant (Amicon Ultra Centrifugal Filters) showed that molecules less than 3kDa are responsible for inhibition of HOXA9-SYK cells, suggesting that protein fragments rather than full proteins are responsible for this effect. We will focus our investigation on CCL6 and CCL9 fragments.
Second, we would like to emphasize the role of basophils in the elimination of leukemic cells by transferring basophils into C57Bl/6 mice followed by inoculation of HOXA9-MEIS1 cells. A high number of in vivo basophils may protect even against HOXA9-MEIS1 cells-mediated leukemia onset, which may lead to a potential cell-based therapy.
We also would like to verify whether splenic supernatant can be used as a medical treatment to prevent leukemic cells expansion, by injecting this supernatant intravenously into HOXA9-MEIS1 cells-inoculated mice. We expect in vivo expansion of HOXA9-MEIS1 cells to be negatively affected by splenic supernatant.
Finally, we will attempt to understand how MEIS1 expression confers protection from basophil-secreted factors by scrutinizing MEIS1-target genes involved in negatively affecting the identified factor(s).