Tumor necrosis factor receptor family costimulation increases regulatory T-cell activation and function via NF-κB

Targeting co-stimulatory molecules in autoimmune disease

Therapeutic targeting of immune checkpoints has garnered significant attention in the area of cancer immunotherapy, in which efforts have focused in particular on cytotoxic T lymphocyte antigen 4 (CTLA4) and PD1, both of which are members of the CD28 family. In autoimmunity, these same pathways can be targeted to opposite effect: to curb the over-exuberant immune response. The CTLA4 checkpoint serves as an exemplar, whereby CTLA4 activity is blocked by antibodies in cancer immunotherapy and augmented by the provision of soluble CTLA4 in autoimmunity. Here, we review the targeting of co-stimulatory molecules in autoimmune diseases, focusing in particular on agents directed at members of the CD28 or tumour necrosis factor receptor families. We present the state of the art in co-stimulatory blockade approaches, including rational combinations of immune inhibitory agents, and discuss the future opportunities and challenges in this field.

TNFα/TNFR2 signaling pathway: an active immune checkpoint for mesenchymal stem cell immunoregulatory function

BACKGROUND

In addition to their multilineage potential, mesenchymal stem cells (MSCs) have a broad range of functions from tissue regeneration to immunomodulation. MSCs have the ability to modulate the immune response and change the progression of different inflammatory and autoimmune disorders. However, there are still many challenges to overcome before their widespread clinical administration including the mechanisms behind their immunoregulatory function. MSCs inhibit effector T cells and other immune cells, while inducing regulatory T cells (T regs), thus, reducing directly and indirectly the production of pro-inflammatory cytokines. TNF/TNFR signaling plays a dual role: while the interaction of TNFα with TNFR1 mediates pro-inflammatory effects and cell death, its interaction with TNFR2 mediates anti-inflammatory effects and cell survival. Many immunosuppressive cells like T regs, regulatory B cells (B regs), endothelial progenitor cells (EPCs), and myeloid-derived suppressor cells (MDSCs) express TNFR2, and this is directly related to their immunosuppression efficiency. In this article, we investigated the role of the TNFα/TNFR2 immune checkpoint signaling pathway in the immunomodulatory capacities of MSCs.

METHODS

Co-cultures of MSCs from wild-type (WT) and TNFR2 knocked-out (TNFR2 KO) mice with T cells (WT and TNFα KO) were performed under various experimental conditions.

RESULTS

We demonstrate that TNFR2 is a key regulatory molecule which is strongly involved in the immunomodulatory properties of MSCs. This includes their ability to suppress T cell proliferation, activation, and pro-inflammatory cytokine production, in addition to their capacity to induce active T regs.

CONCLUSIONS

Our results reveal for the first time the importance of the TNFα/TNFR2 axis as an active immune checkpoint regulating MSC immunological functions.

Exemplifying complexity of immune suppression by a "canonical" speech: A glimpse into TNFRSF-activated signaling pathways in Treg cells

Regulatory T (Treg) cells are crucial mediators of immune tolerance suppressing self-reactive T cells and preventing autoimmune diseases. Besides activation of the T cell receptor (TCR), empowerment of Treg cell functions requires co-accessory signals, such as those released by the TNF receptor superfamily (TNFRSF) that, however, can also promote immunostimulatory responses when engaged by effector T cells. In this issue of European Journal of Immunology, Lubrano di Ricco et al. [Eur. J. Immunol. 2020. 50: 972-985] have taken a closer look at the important question of the functional meaning of TNFRSF-activated signaling pathways in Treg cells. They have demonstrated that costimulation by TNFR2, 4-1BB, GITR, DR3, but not OX40 in mouse Foxp3⁺ Treg cells activates the same and unique signaling pathway, i.e., canonical NF-κB, which in turn leads to Foxp3 gene upregulation, cell expansion in vitro and in vivo, and suppressive activity in an experimental model of colitis. Moreover, induction of markers of T helper 2 (Th2) and Th17 as well as of genes encoding proteins involved in noncanonical NF-κΒ was also observed. We here discussed how these findings further highlight the emerging concept of Treg cell plasticity in immune tolerance.