Session Title: T cell Biology in Rheumatoid Arthritis and Other Arthritis
Session Type: Abstract Submissions (ACR)
Regulatory T cells (Tregs) are essential for maintaining normal immune homeostasis. We have previously reported that tregalizumab is a humanized, non-depleting, CD4 agonistic antibody that selectively activates Tregs. The specific functionality of tregalizumab may originate from the recognition of a unique epitope on domain 2 of CD4 that is not recognized by other anti-CD4 monoclonal antibodies. Tregalizumab is in clinical development for the treatment of rheumatoid arthritis (RA). Currently, a Phase IIb trial –TREAT 2b– is in progress to further evaluate the efficacy and safety of tregalizumab and define the optimal dose in combination with methotrexate (MTX) in adults with RA and an inadequate response to MTX.
Recent data have shown that pro-inflammatory cytokines may have a profound negative effect on the suppressive properties of Tregs or on the responsiveness of effector cells to suppression. Serum cytokine levels for RA patients have been reported in the range of: IL 1β: 0‑0.269 ng/mL; IL-6: 0-1.078 ng/mL; TNFα: 0.001-2.952 ng/mL (Meyer et al., 2010). Therefore, we performed in vitro studies to investigate the effects of pro-inflammatory cytokines on the ability of tregalizumab to activate Treg suppressive activity.
Allogenic effector T cells (Teffs) isolated from healthy volunteers were co-cultured with freshly isolated Tregs and APCs from a different blood donor (mixed lymphocyte reaction, MLR) in the presence of different concentrations of cytokines as previously described by Trinschek et al.(2013). Cell proliferation was measured by incorporation of radioactive thymidine. Suppression was derived by the ratio of the radioactive count obtained in the co-culture in presence of Treg versus no Treg. At least 3 independent experiments were performed at different days using cells isolated from different blood donors.
In the absence of cytokine, activation of Tregs with tregalizumab resulted in strong suppression of Teff proliferation, on average at least 50% reduction of cell proliferation was measured with tregalizumab at 1 µg/mL. In presence of pro-inflammatory cytokines, little effects were observed. At the concentrations tested, corresponding to levels rarely measured in plasma from RA patients (up to 2000 ng/mL of IL-1ß and 500 ng/mL of IL-6), neither IL-1ß nor IL-6 inhibited tregalizumab-induced suppression of Teff proliferation. In case of TNFα, only the highest concentrations tested (50 and 100 ng/mL) had a marginal effect on tregalizumab-induced suppression.
In this in vitro study, activation of Tregs by tregalizumab and the suppression of Teffs was not notably inhibited by pro-inflammatory cytokines, only moderately by TNFα at very high concentration. This result gives further insights into the potential of tregalizumab to activate Tregs in the presence of systemic levels of pro-inflammatory cytokines that are elevated in autoimmune diseases such as RA. Further in vitro investigations are in progress to determine if the observed moderate effect of TNFα is the result of a reduction of Treg suppressive activity or an increased Teff-resistance to Treg suppression. In similar experimental conditions, effects of MTX or prednisolone will also be assessed.
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-effect-of-a-pro-inflammatory-milieu-on-tregalizumab-bt-061-induced-regulatory-t-cell-activity/