Abstract 990: CD40L Antibody Stabilizes Platelet Aggregates Formed in Response to Physiological Stimuli
An unexpected high incidence of thromboembolic complications has been described in patients with systemic autoimmune diseases treated with anti-CD40L immunotherapy. We aimed to investigate the effect of CD40L mAb on platelet aggregation in response to physiological stimuli.
Methods: PRP was isolated from systemic venous blood (0.38% citrate) of anesthetized open-chest pigs. Optical aggregometry was performed in a four-channel Chrono-log 570 SV aggregometer at 1000 rpm and 37°C. The CD40L blocking mAb clone 5c8 used in clinical trials for autoimmune diseases, which reacts with swine CD40L, was used.
Results: In untreated swine PRP samples, ADP-induced aggregation was partially reversible with time even for ADP concentrations provoking maximal effect. CD40L mAb 5c8 did not induce platelet aggregation per se at any concentration tested (1–100 μg/ml), neither did significantly affect maximal aggregation or slope values of aggregation curves obtained with different ADP concentrations. However, it inhibited spontaneous deaggregation observed in controls. This effect was significant for 100 μg/ml 5c8 mAb and 20 μM ADP, with the same tendency for 10 μg/ml 5c8 and for lower ADP concentrations. If 5c8 mAb was added after induction of maximal aggregation by ADP, the stabilizing effect on platelet aggregates was also observed with a latency of 2 min. These effects were not observed with an irrelevant isotype-matched immunoglobulin.
Conclusions: CD40L mAb 5c8 does not significantly affect initial ADP-induced platelet aggregation in swine, but produces stabilization of platelet aggregates. CD40L expression levels achieved with physiological or pathophysiological platelet activation can sustain the stabilizing effect of CD40L mAb 5c8 on deaggregation, and this effect could help to explain the mechanism of CD40L mAb-induced thromboembolic complications.