Credit: St Jude Children’s
Research Hospital
Researchers say they’ve gained new insight into the production of natural killer (NK) cells.
And their findings may help them generate greater numbers of the cells in culture, which could have implications for the treatment of leukemia and other malignancies.
A previous study conducted by the same team revealed that the gene E4bp4 must be switched on to allow the immune system to produce NK cells.
Their new work suggests that E4bp4 expression is required for progenitor cells to commit to the NK lineage. And the gene promotes NK-cell development by regulating expression of the transcription factors Eomes and Id2.
The researchers described these discoveries in the Journal of Experimental Medicine.
“We are excited to find that E4bp4 has such a crucial role in determining the decisive point where blood progenitor cells become NK cells,” said study author Hugh Brady, of Imperial College London in the UK.
“We are now starting to apply this to human blood stem cells to work out how switching on E4bp4 can allow us to make lots of robust human NK cells in culture. We are hoping to make human NK cells that will have improved survival and be very toxic to cancer cells when transfused into patients. Hopefully, this will allow a big reduction in the number of NK cells needed to treat an individual patient.”
To gain insight into NK-cell production, Dr Brady and his colleagues evaluated 2 types of mice with NK-cell deficiencies. The Il15ra knockout mouse model cannot mediate IL-15 signaling, which is critical for NK-cell production. And the T-bet (Tbx21) knockout model lacks a transcription factor that’s crucial for NK-cell development.
Analysis of the Il15ra model revealed that the absence of E4bp4 perturbs NK-cell development earlier than the absence of IL-15 signaling. This suggests E4bp4 acts before IL-15, which was previously considered the definitive factor required for NK-cell production.
The researchers also found that E4bp4 is required for the production of NK progenitors, but T-bet is not. And this suggests E4bp4 acts before T-bet in NK-cell development.
To investigate these findings further, the team took cells at various stages of NK-cell differentiation from wild-type bone marrow and measured their expression of transcription factor mRNAs.
They detected E4bp4 transcript in both lymphoid-primed multipotent progenitors (LMPPs) and common lymphoid progenitors (CLPs), and E4bp4 expression increased at later stages of NK-cell development.
Based on these results, the researchers speculated that E4bp4 might be a lineage commitment factor controlling the development of NK progenitors from CLPs. To test that theory, they restored E4bp4 expression in purified E4bp4-/- CLPs to see if this could re-establish NK-cell development.
The team sorted CLPs from E4bp4-/- bone marrow, cultured them in lymphocyte-inducing conditions, transduced them with E4bp4 or empty vector, and moved on to NK-cell-inducing conditions. But neither cell type produced NK cells.
So the researchers decided to initiate the culture at an earlier developmental stage, using LMPPs. They cultured LMPPs, which exhibited a CLP phenotype at the time of transduction. And CLPs transduced with E4bp4 gave rise to NK cells, but CLPs transduced with empty vector did not.
As these results suggest that E4bp4 acts at the earliest possible point in NK-cell development, the team wanted to characterize E4bp4’s relationship with transcription factors that are likely to act downstream.
They tested several transcription factors known to play a part in NK-cell production and function. But only Eomes and Id2 proved essential for E4bp4 to direct the production of fully functional, mature NK cells.
