Background Protein Kinase C theta (PKC-θ), a member of the PKC family of serine/threonine kinases, is essential in T cell receptor (TCR) signaling and T cell activation . Inhibition of PKC-θ activity may provide new therapeutic options for autoimmune diseases with a T effector cell dependent pathology. CC-90005 is a highly selective small molecule inhibitor of PKC-θ.
Objectives Evaluate the impact of specific PKC-θ inhibition on T-cell activation and anergy using the highly selective inhibitor CC-90005.
Methods Human peripheral blood mononuclear cell (PBMC) or isolated T cell cultures were pre-treated with CC-90005 (0.1–10 μM) and stimulated for various times up to 24 h with anti-CD3 and anti-CD28 activation of the TCR, followed by a washout incubation period (1 h-24 h). Cells were then re-stimulated in the presence or absence of CC-90005 and cultured a further 24–96 h. T cell activation was assessed by CD25 and CD69 cell surface expression, thymidine incorporation, and cytokine production.
Results Upon TCR stimulation, CC-90005 significantly inhibited CD25 and CD69 expression and T cell proliferation in PBMC and isolated T cells. Similarly, CC-90005 inhibited the production of Th1, Th2, Th17 and other pro-inflammatory cytokines. Furthermore, the inhibitory effects of CC-90005 on T cell activation persisted after washout in stimulated T cells, indicating an induction of an anergic cell state. CC-90005 anergy induction was shown to require only short initial exposures of as little as 2 h and to maintain anergy for as long as 48–96 h post CC-90005 washout. However, T cells pre-treated with the inhibitor in the absence of concomitant TCR stimulation were able to respond to stimulus after as little as 1 h washout, indicating a rapid recovery of PKC-θ activity and T-cell function. CC-90005 upregulated an anergy-related E3 ubiquitin ligase, Gene related to anergy in lymphocytes (GRAIL) in T cells. Elevated expression level of GRAIL was maintained in unresponsive T cells after washout, suggesting that GRAIL was a possible downstream mediator of CC-90005 effect on T cell anergy.
Conclusions CC-90005, a specific inhibitor of PKC-θ, significantly inhibits TCR-mediated T cell activation, proliferation, and cytokine production. Moreover, inhibition of these T-cell functions persists after drug withdrawal and restimulus of T-cells, but only if the primary T cell activation event occurrs in the presence of CC-90005. Thus, CC-90005 induces a functional unresponsiveness anergic state in T cells if present during TCR activation, which may have long-term therapeutic benefit in the treatment of T-cell mediated autoimmune and allergic inflammatory conditions.
Zhang EY, Kong K-F, Altman A. The yin and yang of protein kinase C-theta (PKCθ): a novel drug target for selective immunosuppression. Elsevier Inc. 2013. doi:10.1016/B978–0-12–404717–4.00006–8.
Disclosure of Interest None declared