Construction of self-recognizing regulatory T cells from conventional T cells by controlling CTLA-4 and IL-2 expression

Abstract

Thymus-produced CD4+ regulatory T (Treg) cells, which specifically express the transcription factor forkhead box p3, are potently immunosuppressive and characteristically possess a self-reactive T-cell receptor (TCR) repertoire. To determine the molecular basis of Treg suppressive activity and their self-skewed TCR repertoire formation, we attempted to reconstruct these Treg-specific properties in conventional T (Tconv) cells by genetic manipulation. We show that Tconv cells rendered IL-2 deficient and constitutively expressing transgenic cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) were potently suppressive in vitro when they were preactivated by antigenic stimulation. They also suppressed in vivo inflammatory bowel disease and systemic autoimmunity/ inflammation produced by Treg deficiency. In addition, in the thymus, transgenic CTLA-4 expression in developing Tconv cells skewed their TCR repertoire toward higher self-reactivity, whereas CTLA-4 deficiency specifically in developing thymic Treg cells cancelled their physiological TCR self-skewing. The extracellular portion of CTLA-4 was sufficient for the suppression and repertoire shifting. It interfered with CD28 signaling to responder Tconv cells via outcompeting CD28 for binding to CD80 and CD86, or modulating CD80/CD86 expression on antigen-presenting cells. Thus, a triad of IL-2 repression, CTLA-4 expression, and antigenic stimulation is a minimalistic requirement for conferring Treg-like suppressive activity on Tconv cells, in accordance with the function of forkhead box p3 to strongly repress IL-2 and maintain CTLA-4 expression in natural Treg cells. Moreover, CTLA-4 expression is a key element for the formation of a self-reactive TCR repertoire in natural Treg cells. These findings can be exploited to control immune responses by targeting IL-2 and CTLA-4 in Treg and Tconv cells.immune tolerance | CD25 | thymic selection

Differential roles of epigenetic changes and Foxp3 expression in regulatory T cell-specific transcriptional regulation

“…7). This model explains the finding that Foxp3 + Treg cells can produce certain proinflammatory cytokines (such as IFN-γ) until they receive strong TCR stimulation, which shuts off the cytokine production and evokes potent suppressive activity through upregulating suppression-associated molecules (39). The model can also be exploited to control a variety of physiological or pathological immune responses through peripheral generation of functionally stable Treg cells from conventional T cells and targeting the generation and functional stability of natural Treg cells.…”

CTLA-4 controls follicular helper T-cell differentiation by regulating the strength of CD28 engagement

“…A major portion of CTLA-4 function can be attributed to its role in Treg (9, 42) and CTLA-4 expression, along with IL-2 repression, is the minimal requirement to confer Treg-like suppressive activity (43). One mechanism of action of CTLA-4 is the down-regulation of costimulatory ligands on APCs (7-10), which can occur via a process of transendocytosis (11).…”

Regulatory T cells in cancer immunotherapy

“…As CTLA-4 has much higher affinity than CD28 for their common ligands CD80 and CD86, CTLA-4 expressed by Treg cells may physically outcompete CD28 on Tconv [23,24]. Furthermore, CTLA-4 on Treg cells down-modulates expression of CD80 and CD86 on DCs, thereby hindering the activation of Tconv cells at this level [20,25,26]. Thus, Treg expression of CTLA-4 is essential for Treg-mediated immune suppression.…”

“…Indeed, adapting this triad is able to convert Tconv cells into Treg-like suppressive T cells effective in vivo and in vitro, indicating these three events are minimally required for constructing Treg-suppressive activity [26]. These molecular processes are also good targets to control Treg function and development in the context of tumor immunity.…”