O002 Targeting IL-10 producing B cells in rheumatoid arthritis and primary sjÖgren syndrome is promising to increase regulatory T cells but not to decrease pro-inflammatory T cells
Authors: J Mielle, R Audo, A Nutz, M Hahne, L Macia, B Combe, P Guilpain, J Morel, C Daien
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Introduction</h3> The role of regulatory B cells in tolerance has been established in both preclinical and clinical studies. There is no specific marker for human regulatory B cells. They have been mainly ascribed to CD24<sup>hi</sup>CD38<sup>hi</sup> and C24<sup>hi</sup>CD27<sup>+</sup> B cells which can increase regulatory T cells and decrease pro-inflammatory Th1 and TNFα-producing T cells. However, in patients with auto-immune diseases, such as Rheumatoid Arthritis (RA) or Sjögren Syndrome (pSS), CD24<sup>hi</sup>CD38<sup>hi</sup> and C24<sup>hi</sup>CD27<sup>+</sup> B cells lose their regulatory functions. It is thus needed to find a better marker of Breg cells that correlate with regulatory functions in both healthy controls and patients. As Breg cell functions are mainly mediated by IL-10, some authors use IL-10 production to define Breg cells, which are then called B10<sup>+</sup> cells. We previously showed that B10<sup>+</sup> cells are decreased in RA and negatively correlated with the disease activity, suggesting a key role of regulatory B10<sup>+</sup> cells in autoimmune diseases. Before using B10<sup>+</sup> cells as a therapeutic strategy it is necessary to precisely determine their functions. However, it remains unknown if any B cell secreting IL-10 has regulatory functions and which ones. <h3>Objectives</h3> To assess the functions of B10<sup>+</sup> cells, compared to non-IL-10 producing B cells (B10<sup>neg</sup> cells) on T cell differentiation in healthy controls (HC) and in patients with auto immune diseases, namely RA and pSS. <h3>Methods</h3> B10<sup>+</sup> cells were induced by a 24 hour stimulation with CpG and sorted using isolation kits and flow cytometry. We evaluated their effect on naïve T cell differentiation into Th1, TNFα- producing T cells, Treg cells and IL-10 producing T cells (Tr1). We characterised the interaction between B10<sup>+</sup> cells and T cells, using blocking antibodies against IL-10, CD80, CD86, PD1 and transwell experiments. <h3>Results</h3> B10<sup>+</sup> cells of HC converted more naïve T cells into Treg cells and Tr1 than B10<sup>neg</sup> cells (p=0.03 and p=0.02). Blocking either IL-10 secretion or cellular contacts between B10<sup>+</sup> cells and T cells abolished the induction of Treg cells. Surprisingly, conversely to CD24<sup>hi</sup>CD27<sup>+</sup> B cells, B10<sup>+</sup> cells failed to decrease Th1 and TNFα-producing T cell conversion, compared to B10<sup>neg</sup> cells. This might be due to a different expression of PDL1 and PDL2 between B10<sup>+</sup> cells and CD24<sup>hi</sup>CD27<sup>+</sup> B cells. Similarly to HC, B10<sup>+</sup> cells from RA and pSS patients induced more Treg cells compared to B10<sup>neg</sup> cells (p=0.02 in RA; p=0.03 in pSS). However, conversely to HC and pSS-B10<sup>+</sup> cells, RA-B10<sup>+</sup> increased the conversion of naïve T cells into Th1, compared to B10<sup>neg</sup> cells (p=0.033). We also observed an increased expression of PDL2 on RA-B10<sup>+</sup> cells compared to HC-B10<sup>+</sup> cells that could explain this effect on Th1 differentiation. <h3>Conclusions</h3> IL-10 secretion can be an interesting marker to define Breg subsets acting on regulatory T cell differentiation. Thus, increasing the number of B10<sup>+</sup> cells, seems a promising therapeutic strategy especially in patients who lack the most of Treg cells. Additional markers are needed to define which subset of Breg cells can control inflammatory response. The role of PD1/PDL2 in B10<sup>+</sup> cell function might also open new insights. <h3>Disclosure of interest</h3> None declared