# Divergent CD27 expression marks the Treg induction trajectory

## TL;DR

The study shows that CD27 expression identifies a specific type of regulatory T cells that may help treat autoimmune diseases.

## Contribution

CD27 is identified as a marker for induced Tregs with superior regulatory function during immune tolerance induction.

## Key findings

- CD27 is upregulated in memory-like Tregs during in vitro induction by tolerogenic dendritic cells.
- CD27 and TIGIT co-expression correlates with stronger regulatory capacity in induced Tregs.
- Higher CD27+ Treg ratios in T1D patients correlate with improved immune regulation ex vivo.

## Abstract

The induction of antigen-specific Tregs is explored as strategy to restore immune tolerance and halt progression of autoimmune diseases. However, the phenotypic changes in development of induced antigen specific Tregs in vivo have not been defined extensively. CD27 expression marks superior suppressive naturally occurring Tregs (nTregs) while in cancer, this showed to be a prognostic marker for tumor progression. Tumors indeed can promote the immunosuppressive effects of the CD27-CD70 co-stimulatory axis, and CD27 has been a target for immune checkpoint blockade in cancer. In this study, we explored changes in CD27 expression along with a panel of markers associated with immune regulation.

For this, we induced Tregs in vitro from naive CD4 T cells by tolerogenic dendritic cells (tolDCs) and compared their phenotypes to effector T cells induced in parallel cultures by pro-inflammatory mDCs in time following priming.

Clustering analysis revealed three clustering groups distinguishing induced Treg cultures from effector T cells, all marked by high CD27 expression, of which two clusters had a memory-like phenotype and expressed regulatory markers TIGIT, PD-1 and CD38. The kinetics of CD27 expression showed that naive T cells increase CD27 expression during their differentiation into memory-like Tregs, whereas CD27 is lost during differentiation into proinflammatory effector T cells. Furthermore, the presence of CD27 and TIGIT expressing memory-like Tregs positively correlated with the inhibition capacity of the induced Treg lines in vitro. Increased ratios of these Tregs over effector T cells in vivo following vaccination of T1D patients with tolerogenic DCs pulsed with islet autoantigen correlated with increased islet-specific immune regulation ex vivo.

Our results define a population of induced Tregs in vitro and in vivo that is marked by elevated CD27 expression. Hence, CD27 expression may be useful to monitor therapeutic efficacy of Treg induction in vivo in clinical trials.