TIGIT-positive circulating follicular helper T cells display robust B-cell help functions: potential role in sickle cell alloimmunization

Abstract

© F e r r a t a S t o r t i F o u n d a t i o nphoid T FH , cT FH cells can express significant levels of surface programmed cell death-1 (PD-1), 31 although the function of PD-1 on T FH cells remains controversial since it is associated with both promotion 16,17 and inhibition of B-cell responses. 18,[32][33][34] Taken together, these reports underscore the need for better characterization of markers for cT FH cells displaying defined functions not only in steady state but also in diseases. Remarkably, PD-1 has been described as a member of the growing family of inhibitory receptors also referred to as immune checkpoints, responsible for aborting T-cell responses. 35 Interestingly, another member of the immune checkpoint family, TIGIT (T-cell immunoreceptor with Ig and immunoreceptor tyrosinebased inhibitory domains), was reported to be overexpressed on both tonsillar and cT FH cells, 17 and was shown to be involved in interactions between T cells and follicular dendritic cells to regulate B-cell responses. 36,37 However, the functional activity of TIGIT on T FH cells, including cT FH cells, has not been studied to date.In this study, we took the approach of using TIGIT and PD-1 to characterize the phenotype and function of circulating T FH subsets and to investigate whether expression of these molecules on cT FH cells modulated their functions in healthy volunteer donors and in a group of chronically transfused SCD patients with or without alloantibodies. Methods Human samplesAll studies were approved by the Institutional Review Boards of the New York Blood Center (NYBC). De-identified fresh leukopaks were obtained from healthy donors at the NYBC. For SCD patients' samples, blood was obtained solely from discard apheresis waste bags obtained during erythrocytapheresis procedures at the Children's Hospital of Philadelphia (see Online Supplementary Material for details). T-cell studiesFreshly-sorted CD4 + T-cell subsets and autologous naïve or memory B cells were used (see Online Supplementary Material for details). Blocking antibodies for TIGIT 38 and PD-1 34,39 were preincubated with sorted T cells before being co-cultured with autologous B cells. Results PD- Expression of ICOS, CD40L and IL-21 by TIGIT + cT FH cellsWe next tested whether TIGIT + cT FH cells were functionally different from cT FH + cT FH populations from a small number of healthy donors (n=3 or 4) were sorted and their ability to express T FH -associated co-stimulatory markers and cytokines following stimulation was compared to those of sorted autologous PD-1 -/TIGIT -subsets (gating strategy shown in Online Supplementary Figure S1). As a control, sort-purified autologous CXCR5 -non-cT FH cells expressing TIGIT E. Godefroy et al. 1416haematologica | 2015; 100(11) A B C© F e r r a t a S t o r t i F o u n d a t i o n ("TIGIT+") or not ("TIGIT-") were also tested. We first monitored expression of co-stimulatory molecules CD40L and ICOS, both specialized in providing Bcell help, on T-cell subsets before or after stimulation by immunos...

TIGIT-positive circulating follicular helper T cells and sickle cell alloimmunization

“…The recent discovery of regulatory follicular T cells (T FR ) expressing high levels of PD-1 17 may help to reconcile these divergent findings. Although TIGIT expression on T cells has been studied previously, [24][25][26][27][28][29] the function of TIGIT on T FH cells is being addressed for the first time in the study by Godefroy et al 20 The authors show that TIGIT-expressing cells represent almost half of the cT FH population, while PD-1 + cells, all coexpressing TIGIT, are significantly less frequent, accounting for about 9% of the cT FH cells. 20 Several subsets of cT FH have previously been characterized.…”

“…Although TIGIT expression on T cells has been studied previously, [24][25][26][27][28][29] the function of TIGIT on T FH cells is being addressed for the first time in the study by Godefroy et al 20 The authors show that TIGIT-expressing cells represent almost half of the cT FH population, while PD-1 + cells, all coexpressing TIGIT, are significantly less frequent, accounting for about 9% of the cT FH cells. 20 Several subsets of cT FH have previously been characterized. Three main subsets, named T FH 1, T FH 2 and T FH 17, can be identified not only by their ability to produce type 1, 2 and 17 cytokines or express their respective transcription factors (T-bet, GATA3, RORc), but also by their expression of chemokine receptors CXCR3 and CCR6.…”

“…13 Based on chemokine receptor expression, the authors show that TIGIT + cT FH represent a subset phenotypically different from any of the three populations previously described. 20 Interestingly, TIGIT + cT FH can produce IL-4 and to some extent interferon-gamma. Accordingly, both T FH 1 and T FH 2 can be found in TIGIT + cT FH independently of the cells' PD-1 expression.…”

“…issue of the journal, 20 Godefroy et al examine the role of two immune checkpoints 21 expressed by CD4 + /CD45RA -/CXCR5 + circulating follicular helper T (cT FH ) cells: the programmed cell death-1 (PD-1) and the T-cell immunoreceptor with Ig and immunoreceptor tyrosine-based inhibitory domains (TIGIT) surface molecules. The function of PD-1 on T FH cells remains controversial and has been described as both promoting 15,16 and reducing 17,22,23 humoral responses in different models.…”

“…Accordingly, both T FH 1 and T FH 2 can be found in TIGIT + cT FH independently of the cells' PD-1 expression. 20 IL-17 secretion was not tested. Nonetheless, these findings establish that TIGIT + cells, whether or not they express PD-1, represent a novel subset of cT FH .…”