Testing of anti-activated protein C antibodies in four drotrecogin alfa (activated) severe sepsis studies

Introduction

This study evaluated anti-activated protein C (anti-APC) antibody (Ab) development in drotrecogin alfa (activated) (DAA) (recombinant human APC)-treated adult patients with severe sepsis.

Methods

Serum and plasma samples were collected for anti-APC Ab testing from patients in the PROWESS, EVBF (ENHANCE substudy), ADDRESS and XPRESS trials at baseline (BL) and on days 14, 28 and 60 (except PROWESS). PROWESS and ADDRESS were placebo-controlled studies. All patients in EVBF and XPRESS were DAA-treated. An ELISA detecting anti-APC IgA/IgG/IgM Abs (sensitivity: 0.26 μg/ml) was used to screen all serum samples from patients who had a BL sample and at least one post-BL sample. Confirmed positive samples (binding inhibited ≥ 50% with 50 μg/ml exogenous DAA) were titered by twofold serial dilutions. IgG isolated from plasma of positive samples was tested for neutralizing activity against DAA-induced prolongation of aPTT. Positive anti-APC Ab was analyzed on an 'as treated' basis.

Results

The proportions of patients who tested negative for BL and positive for post-BL anti-APC Abs in all studies are presented in Figure 1, and were similar in the DAA and placebo cohorts at each sampling time. Twenty-five DAA patients and 24 placebo patients had a negative BL but positive post-BL anti-APC Abs; all were alive at day 28 and all but two in each group were alive at hospital discharge, including all eight with positive neutralizing Abs. No thrombotic events were reported. No relationship between the titer of anti-APC Abs and neutralizing Abs was observed. In PROWESS, no difference in markers of coagulopathy between Ab-positive and Ab-negative patients was observed.

Figure 1

Patients with negative BL and positive post-BL anti-APC Abs. *DAA not given.

Conclusion

The proportion of patients with anti-APC or neutralizing Ab was low and was similar between the 1,855 DAA patients and 1,493 placebo patients tested. No relationship between anti-APC Ab development and adverse reactions was observed. There was no evidence that the anti-APC Abs detected represented a specific immune response to DAA therapy.