A fluorescent reporter model to study the role of T-DC during infection and cancer

Abstract TDC are hematopoietic cells that combine dendritic cell (DC) and conventional T cell markers and functional properties. They were identified in secondary lymphoid organs (SLO) of naïve mice as cells expressing CD11c, MHC-II, and TCRβ chain. TDC expand in response to TCR-mediated stimulation, but they also express the DC lineage marker Zbtb46. Moreover, TDC are characterized by a cytotoxic gene signature, including high expression of IFNγ and granzymes. Unfortunately, using CD11c as a marker for TDC has the caveat of its upregulation on different cells (including T cells) upon activation. Therefore, a more specific marker could be useful to further investigate TDC functions in peripheral organs or during inflammation. We exploited the unique genetic profile of TDC to obtain a reporter mouse model in which TDC are marked with two different fluorescent proteins (Zbtb46-GFP and Gzmb-Tomato). This model allowed us to use Zbtb46 instead of CD11c as a marker for TDC, in order to investigate the frequency and localization of TDC in peripheral tissues such as liver, small intestine, and lung. RNA sequencing analysis confirmed that TDC identified with this reporter model have an overlapping gene signature with the one already reported for TDC. In addition, frequency and total numbers of Zbtb46+ TDC in the SLO recapitulated those previously found using CD11c, thus confirming the validity of our model. Interestingly, we found that TDC numbers in the SLO increased upon LCMV infection, indicating that TDC might play a role during viral infections. Further studies aimed at identifying the localization of TDC in peripheral organs, and their role in several pathological settings are ongoing. M.K. is supported by the Italian Ministry of Education, University and Research grants SIR-RBSI14BAO5 and PRIN-2017ZXT5WR