Targeting CD28, CTLA-4 and PD-L1 Costimulation Differentially Controls Immune Synapses and Function of Human Regulatory and Conventional T-Cells

Abstract

CD28, CTLA-4 and PD-L1, the three identified ligands for CD80/86, are pivotal positive and negative costimulatory molecules that, among other functions, control T cell motility and formation of immune synapse between T cells and antigen-presenting cells (APCs). What remains incompletely understood is how CD28 leads to the activation of effector T cells (Teff) but inhibition of suppression by regulatory T cells (Tregs), while CTLA-4 and PD-L1 inhibit Teff function but are crucial for the suppressive function of Tregs. Using alloreactive human T cells and blocking antibodies, we show here by live cell dynamic microscopy that CD28, CTLA-4, and PD-L1 differentially control velocity, motility and immune synapse formation in activated Teff versus Tregs. Selectively antagonizing CD28 costimulation increased Treg dwell time with APCs and induced calcium mobilization which translated in increased Treg suppressive activity, in contrast with the dampening effect on Teff responses. The increase in Treg suppressive activity after CD28 blockade was also confirmed with polyclonal Tregs. Whereas CTLA-4 played a critical role in Teff by reversing TCR-induced STOP signals, it failed to affect motility in Tregs but was essential for formation of the Treg immune synapse. Furthermore, we identified a novel role for PD-L1-CD80 interactions in suppressing motility specifically in Tregs. Thus, our findings reveal that the three identified ligands of CD80/86, CD28, CTLA-4 and PD-L1, differentially control immune synapse formation and function of the human Teff and Treg cells analyzed here. Individually targeting CD28, CTLA-4 and PD-L1 might therefore represent a valuable therapeutic strategy to treat immune disorders where effector and regulatory T cell functions need to be differentially targeted.

Selective CD28 Antagonist Blunts Memory Immune Responses and Promotes Long-Term Control of Skin Inflammation in Nonhuman Primates

“…However, CD28 blockade has so far been experimentally achieved using antagonists of CD80/86, the molecular ligands of CD28, that in addition to inhibiting CD28-mediated costimulation also prevent interaction of CD80 with crucial checkpoints such as CTLA-4 and PD-L1 (11). We have previously reported that selective blockade of CD28 differentially controls in vitro human effector and regulatory memory CD4 + T lymphocyte activation in comparison with CD80/86 antagonist (19). CTLA-4-and PD-L1-dependent mechanisms were shown to play a key role in the stability of the immune synapse and on the velocity and motility of memory T lymphocytes.…”

“…Selective CD28 blockade was described to induce immune tolerance and regulatory cells in transplant experimental models (14)(15)(16)(17)(18). We previously described that selective monovalent CD28 versus CD80/86 antagonists differentially control human effector and regulatory memory T cell activation in vitro at the immune synapse level (19). In the present study, we evaluated a novel selective antagonist of CD28 (FR104, a humanized pegylated anti-CD28 Fab9 Ab fragment), devoid of agonist activity (20,21), in Ag-specific memory responses in vitro and in nonhuman primate models.…”

Selective blockade of CD28 on human T cells facilitates regulation of alloimmune responses

“…However, in clinical trials, an increase in the incidence of acute rejection with CTLA4-Ig treatment compared with cyclosporine standard immunosuppression has been observed (4). In addition, direct CD80/86 blocking strategies inhibit CTLA4 signaling, which is crucial to the function of Tregs, thus impacting the potential development of immunological unresponsiveness (5)(6)(7). With the progression of cellular therapies to the clinic, there is a concern regarding the effect CTLA4-Ig would have on Treg therapy for the treatment of immune pathologies, including transplant rejection.…”

Selective CD28 antagonist prevents Aldara‐induced skin inflammation in non‐human primates

“…We previously described that this novel drug candidate promoted immune tolerance and induced long-term allograft survival in non-human primates (2,3). It also efficiently prevented brain inflammation in an experimental autoimmune encephalomyelitis (EAE) non-human primates model (4) and, as opposed to CD80/ 86 antagonists, differentially controlled human effector and regulatory memory T-cell activation in vitro at the immune synapse level (5). Here, we evaluated the therapeutic potential of this novel selective CD28 antagonist to control skin inflammation.…”