Preliminary data generated by the Sarantopoulos laboratory indicated that the AIM2 and DNase1L3 genes were upregulated in B cells in cGVHD patients in comparison with patients without cGVHD.
AIM2 is a protein that detects DNA in the cytosol and the nucleus. In presence of DNA, AIM2 recruits the inflammasome platform components, which ends up in a form of cell death called pyroptosis. It is well known that B cell death is a pivotal immune tolerance mechanism to delete auto-reactive and abnormal B cells. It is also known that AIM2 is mainly expressed after antigen encounter and then B cell activation. However, it is currently not known whether AIM2 induced death is a tolerance mechanism in activated B cells.
Therefore, our first aim was to determine whether DNA-sensing by AIM2 in activated B cells was responsible for B cell pyroptosis. It was not the case and this could be due to the fact that AIM2 is mainly located in the nucleus of B cells, which we discovered using microscopy.
Our second aim was then to determine what is the actual function of AIM2 in B cells. Comparing normal mice to mice deficient in AIM2 after immunization with a protein, we observed that AIM2 could regulate activated B cells and could promote Ab-production of AIM2-expressing B cells. Importantly, similar data were recently published by another group of scientists. How precisely AIM2 regulates B cell biology is under active investigation.
Our third aim was to determine whether an aberrant AIM2 pathway supports pathological B cells in cGVHD. Indeed, data obtained in aims 1 and 2 suggested that the function of AIM2 in B cells could be highly relevant in cGVHD. Using a mouse model of allo-HCT, we showed that AIM2 was overexpressed by B cells during cGVHD, thus confirming human data. We are now investigating how a selective deficiency of AIM2 in B cells from the donors impacts the development of activated and pathological B cells during cGVHD.
DNase1L3 is a critical enzyme that is mainly produced by immune cells other than B cells. DNase1L3 regulates DNA ligands availability for immune DNA sensors and then B cell tolerance. However, it is currently not known what is the function of DNase1L3 expressed by B cells. Using a mouse model of allo-HCT, we showed that DNase1L3 was overexpressed by B cells during cGVHD, thus confirming human data. A selective deficiency of DNase1L3 in mouse B cells did not modified B cells populations at baseline or after immunization against an exogenous antigen. A first mouse allo-HCT experiments showed that a selective deficiency of Dnase1L3 in B cells from the donors increased the development of cGVHD eye symptoms. We are now repeating the experiment to confirm these results as well as pursuying experiments with human B cells.
