Infliximab for Crohn’s disease

SIRS, The treatment of steroid-refractory/dependent Crohn's disease has greatly improved with the development of humanized monoclonal antibodies to the pro-in ̄ammatory cytokine tumour necrosis factor-a (TNF-a). Recently, Nikolaus et al. and Cornillie et al. have assessed the clinical and immunological mechanisms of response and failure of treatment with the humanized anti-TNF-a antibody in ̄iximab. Nikolaus et al. followed 24 steroid-refractory active Crohn's disease patients for 16 weeks after a single infusion of in ̄iximab. The antibody was found to downregulate the lipopolysaccharide-induced secretion of TNF-a by peripheral blood cells, and to decrease the nuclear concentration of NFjB transcription factor p65 in mucosal biopsies. Relapsers were characterized by an early rise in TNF-a production, before reactivation of the clinical symptoms. The authors ascribed these ®ndings to the antibody-induced death of TNF-a-producing cells, and an early reactivation of the immune response was expected to be caused by the different genetic make-up of the non-responding patients. Cornillie et al. studied the pharmacokinetics of in ̄iximab and its effects on the systemic and local immune functions in a large number of Crohn's disease patients. They found no differences in the serum levels of in ̄iximab between responders and non-responders, but showed that the antibody decreased the T-helper-1 cytokine production of lamina propria cells. They speculated that the latter observation was due to increased in situ lysis and reduced homing of these cells by in ̄iximab. The execution of the study by Nikolaus et al. has one major shortcoming, i.e. the use of a whole-blood assay to determine the TNF-a-producing capacity of cells, which has major consequences for the interpretation of their results. The enzyme-linked immunoabsorbent assay (ELISA) they used (R & D Systems, Minneapolis, USA) shows a major interference by in ̄iximab, as established using similar culture and assay conditions, i.e. 5% CO2, 37 °C and 0.1 lg lipopolysaccharide/mL blood for 24 h, on blood samples from seven Crohn's disease patients and two healthy controls. The pre-infusion whole-blood median TNF-a secretion level of these Crohn's disease patients was 381 pg/mL (range, 205±5056 pg/mL), and blood samples taken 2 h after the end of the in ̄iximab infusion (5 mg/kg body weight) showed hardly any detectable TNF-a secretion: 10 pg/mL (range, 0±31 pg/mL). The addition of 75 lg/mL in ̄iximab to four whole-blood samples of two controls, followed by 24 h lipopolysaccharide stimulation, was also found to almost completely inhibit TNF-a levels: median 0 pg/mL (0±28 pg/mL) compared to 3223 pg/mL (394±5945 pg/mL) without in ̄iximab. The addition of autologous in ̄iximab plasma to the prein ̄iximab plasma, both after lipopolysaccharide stimulation, of the four individuals with the highest TNF-a level resulted in a 97.3% (96.3±98.6%) reduction from 3868 pg/mL (1537±5945 pg/mL) to 111 pg/mL (22± 221 pg/mL). In addition, incubating plasma samples of the pre-in ̄iximab lipopolysaccharide-stimulated whole blood of the patients and controls and a 750 pg/mL TNF-a ELISA standard with a similar in ̄iximab concentration for 2 h in vitro resulted in undetectable TNFa levels of all samples, except for the highest patient and control plasma, which decreased from 5056 to 31 pg/mL and 5945 to 70 pg/mL, respectively. Finally, we assessed whether in ̄iximab had lysed the TNF-a-producing cells by adding pre-infusion plasma to the whole-blood cell pellet of thoroughly washed (four times) blood obtained 2 h after the end of the in ̄iximab infusion of the same patient, followed by 24 h lipopolysaccharide stimulation, in three patients. The addition of pre-infusion plasma to the in ̄iximab-exposed cell pellet increased the TNF-a levels from 11 pg/mL (11± 15 pg/mL), with in ̄iximab, to a median of 245 pg/mL (174±280 pg/mL), which turned out to be 97.6% (56.7±127.9%) of the level (287 pg/mL; 136±432 pg/ mL) obtained with washed pre-infusion whole-blood samples. Aliment Pharmacol Ther 2001; 15: 2041±2042.