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P554. A prospective assessment of antidrug antibody response over time by a new ELISA in patients with IBD treated with infliximab

V. Ussia, L. Ceccarelli, S. Maltinti, G. Di Fluri, M.G. Mumolo, V. Bolognesi, A. Ricchiuti, M. Bellini, S. Marchi, F. Costa, Pisa University, Gastroenterology, Pisa, Italy

Background

The clinical efficacy of Infliximab (IFX) in IBD patients well correlates with serum trough levels (TL). The development of anti-IFX antibodies (ATI) is considered the main cause of loss of response (LOR) to drug. Few data are reported on concomitant presence of ATI and IFX mainly because commercially available ELISA are unable to detect ATI in the presence of IFX, moreover, the clinical impact of this coexistence is completely unknown as prospective studies investigating this issue are lacking.

Aim: To assess prospectively the evolution of anti-IFX response over time and to investigate the clinical significance of coexistence of ATI and IFX in IBD patients on IFX therapy.

Methods

We evaluated 80 sera from 15 IBD patients (8 CD and 7 UC) on scheduled IFX treatment between September 2012 and November 2013.

Blood was drawn immediately before each infusion, after the induction phase, to assess TL of IFX and ATI by a new ELISA test (Immunodiagnostik AG, Bensheim, Germany) able to measure free and bound antibodies against IFX. LOR was defined on the basis of international accepted criteria.

Results

LOR was observed in 5/15 (33%) patients (3 UC, 2 CD). Positive ATI (>10 UA/ml) values were inversely correlated with TL (r = −0.364, p = 0.0009). Sixty percent of patients developed ATI (5 UC, 4 CD) and 46.7% (5 UC, 2 CD) had low drug levels (<1.44 mcg/ml). Four patients were ATI positive in the presence of detectable TL (>1.44 mcg/ml), 2 of them (1 CD, 1 UC) were in clinical remission, in the other 2 (both CD) with LOR, response was restored by shortening the interval between infusions.

It is noteworthy, that in 3 ATI positive patients with LOR (2 CD, 1 UC), a progressive decrease of ATI values was observed after IFX dose adjustment. We also observed that a TL below 3 mcg/ml was predictive of ATI development in 90% of patients (5 UC, 4 CD); furthermore, most patients (7 out of 9) developed ATI within the first 6 months from the induction phase.

Conclusion

In our prospective study the use of a new ELISA test, allowing to measure free and bound antibodies, confirmed the inverse correlation between ATI and IFX TL.

Identification of ATI when the drug is still detectable could be helpful to select those patients at higher risk to develop LOR who mostly benefit from an early adjustment of IFX treatment.