Background RhuDex, under development as an orally available immunomodulating agent, inhibits the CD80-CD28 costimulatory pathway, thus preventing the interaction between T lymphocyte and APC receptors necessary for T cell activation and proliferation.
Objectives We have investigated the effect of RhuDex in vitro on the activation, proliferation and T helper subclass differentiation of naïve, memory and activated T cells.
Methods Monocyte-derived dendritic cells, maturated in vitro and expressing CD80, were co-cultured with allogeneic naïve and memory T cells in the presence of a monoclonal antibody to CD3. Preactivated T cells, additionally stimulated by an anti-CD28 antibody and thus independent of further co-stimulatory signals, were used as control. RhuDex and the comparator drug abatacept, also interfering with costimulation, were added at the start of the culture. T cell proliferation was measured using a CFSE assay, while T cell activation was assessed by CD25 surface expression using flow cytometry, and release of cytokines IFNγ, IL-4, IL-17A and TNFα was measured by ELISA.
Results RhuDex blocked the activation of naïve T cells with a half-maximal inhibitory concentration (IC50) of 8-10μg/mL, while higher concentrations (up to 30μg/ml) were needed to inhibit memory T cell activation. Similarly high concentrations of RhuDex did not show any reversive effect on the activation status of preactivated T cells. Proliferation of naïve and memory T cells was inhibited by RhuDex with an IC50 of ∼3μg/ml, while the effect on activated T cells was much less pronounced, with concentrations as high as 30μg/ml resulting in only a weak (35%) reduction of proliferation.
IFNγ-release, a Th1 response indicator, from naïve and memory T cells was inhibited in the presence of RhuDex with an IC50 of 2-4μg/ml, but this was not observed for activated T cells. A similar pattern of effect was also observed for IL-17A release from these types of T cells. In contrast, RhuDex exposure increased IL-4 release, an indicator for Th2-activation, in naïve T cells up to 4-fold. Importantly, this latter effect was not observed with the comparator drug abatacept. However, RhuDex also showed no or only weak effects on IL-4 secretion from memory- and activated T cells.
Finally, RhuDex was also found to inhibit TNFα release from naïve, memory and activated T cells, with an IC50 of ∼2μg/ml, and >10μg/ml, respectively.
Conclusions These results support blockade of T cell activation resulting in reduced proliferation and cytokine secretion as the primary mode of action of RhuDex. In line with current knowledge, this blockade appears to be more effective in resting T cell populations that are, in contrast to already activated T cells, more dependent on co-stimulatory signals for activation and proliferation. Furthermore, RhuDex inhibited cytokine release from naïve and memory T cells, with a pronounced inhibitory effect on Th1- and Th17 cytokines. Taken together, the observed inhibitory effect on T cell activation, proliferation and cytokine-release suggests RhuDex as a promising candidate for the treatment of rheumatoid arthritis.
Disclosure of Interest F. Wartha Employee of: MediGene AG, P. Hofmann-Goebel Employee of: MediGene AG, A. Skapenko: None Declared, H. Schulze-Koops Consultant for: MediGene AG