Development and validation of immunoassays to quantify the half-antibody exchange of an IgG4 antibody, natalizumab (Tysabri®) with endogenous IgG4

Natalizumab is a humanized IgG4 monoclonal antibody which binds human α4 integrin and is approved for treatment of multiple sclerosis and Crohn's disease. Assessment of the in vivo disposition of natalizumab presents a unique assay development challenge due to the ability of human IgG4 antibodies to undergo half-antibody exchange in vivo. Such exchange generates IgG4 molecules of mixed specificity comprising a natalizumab heavy-light chain pair coupled to an IgG4 heavy-light chain pair of unknown specificity. Since exchanged and non-exchanged species cannot be quantified independently using a single enzyme linked immunosorbent assay (ELISA), a novel quantitation strategy was developed employing two ELISAs: one measuring total natalizumab including both intact and exchanged molecules, and the second measuring only intact natalizumab. The presence and amount of exchanged natalizumab in serum is calculated by the difference in values obtained in the two assays. To evaluate assay performance, a control reagent was created from natalizumab and an irrelevant humanized monoclonal IgG4 antibody. Subsequent validation demonstrated that both assays are specific, accurate, and precise within the working ranges of the assays (1.5-10μg/mL for total and 0.5-12μg/mL for intact natalizumab assays). The mean accuracy, intra- and inter-assay precision for both assays were 82-113%, ≤9% and ≤20%, respectively. Additionally, the limits of detection of intact and exchanged natalizumab were established using statistical methods. The utility of the two-assay strategy was confirmed by analyzing samples from a pharmacokinetic study in rats using different variants of natalizumab administered along with another human IgG4 antibody as an exchange partner.     

The Noble plication: new indication for a historical procedure

Complications following ileal pouch-anal anastomosis (IPAA) have been well-described in the literature. While rare, small bowel volvulus following IPAA has been described. We describe the successful use of the modified Noble plication in such a patient with small bowel volvulus about an elongated mesentery. This largely ‘historical’ technique is well-suited to manage small bowel volvulus, especially when non-resectional management is preferred.     

Where does the Occluded Artery Trial leave the late open artery hypothesis?

As of April 2007 the early open artery hypothesis is alive and well, but the late open artery hypothesis is adrift. For the foreseeable future, stable patients with persistent occlusion of the infarct artery late after myocardial infarction, and without severe ischaemia or uncontrollable angina, should be managed initially with optimal medical treatment alone, and not with percutaneous coronary intervention. Efforts should focus on establishing reperfusion earlier, including reducing the time to patient presentation.     

Hemodynamic parameters are prognostically important in cardiogenic shock but similar following early revascularization or initial medical stabilization: a report from the SHOCK Trial

BACKGROUND: In cardiogenic shock (CS), conclusive data on serial hemodynamic measurements for treatment guidance and prognosis are lacking. METHODS: The SHOCK (Should We Emergently Revascularize Occluded Coronaries for Cardiogenic Shock?) Trial tested early revascularization (ERV) vs initial medical stabilization (IMS) in CS complicating acute myocardial infarction and serially assessed hemodynamics by pulmonary artery catheter. RESULTS: Data were available in 278 patients (95%) surviving to the first measurement with predominant left ventricular failure at baseline and in 174 patients (70%) at follow-up. Baseline and follow-up hemodynamic data were similar in the treatment groups. The median time from CS to baseline measurements was 3.3 h in both treatment groups, whereas follow-up measurements were obtained earlier in the IMS group (median time, 10.6 h) than in the ERV group (median time, 12.5 h; p = 0.043). At baseline, stroke volume index (SVI) was an independent predictor of 30-day mortality after adjustment for age (odds ratio, 0.69 per 5 mL/m2 increase; 95% confidence interval, 0.55 to 0.87; p = 0.002). At follow-up, both stroke work index (SWI) [odds ratio, 0.54 per 5 g/m/m2 increase; 95% confidence interval, 0.39 to 0.76; p < 0.001] and SVI (odds ratio, 0.59 per 5 mL/m2 increase; 95% confidence interval, 0.45 to 0.77; p < 0.001) were similarly powerful predictors of 30-day mortality after adjustment for age. CONCLUSIONS: SVI and SWI are the most powerful hemodynamic predictors of 30-day mortality in CS patients. Hemodynamic parameters are similar for surviving patients following ERV and IMS. Thus, early hemodynamic stability after IMS should not delay revascularization since long-term outcomes are superior with ERV.     

Microbiological profile of septic complication in patients with cardiogenic shock following acute myocardial infarction (from the SHOCK study)

We sought to assess the microbiologic profile of patients with suspected sepsis who participated in the SHould we emergently revascularize Occluded Coronaries in cardiogenic shocK? (SHOCK) trial, a randomized controlled trial of early coronary revascularization in patients with cardiogenic shock complicating acute myocardial infarction. A protocol-mandated SEPSIS form was completed prospectively for 54 patients (18%) with fever or leukocytosis suggestive of sepsis. These patients were divided further into those with positive (n = 40) or negative (n = 14) culture results. The predominant pathogen isolated in patients with positive culture results was Staphylococcus aureus (32%), followed by Klebsiella pneumoniae and Pseudomonas aeruginosa. Patients with both positive and negative culture results had longer median durations of mechanical ventilation (p <0.001 and p = 0.02), intra-aortic balloon pump (IABP) support (p = 0.074 and p = 0.021), and hospital stay (p <0.001 and p = 0.048) than controls. Sepsis was predicted by both duration of IABP support (p = 0.007) and use of multiple central catheters (p = 0.026). In conclusion, clinical sepsis is common after cardiogenic shock complicating acute myocardial infarction, particularly in patients who received prolonged IABP support or had multiple central catheters.     

Impact of female sex on death and bleeding after fibrinolytic treatment of myocardial infarction in GUSTO V

BACKGROUND: Women with acute myocardial infarction are more likely than men to experience reinfarction, bleeding, or death. This difference has been hypothesized to be due to older age, treatment delay, and comorbidities in women. Use of diagnostic and therapeutic modalities may also differ. There is controversy regarding whether female sex is an independent risk factor for death and/or bleeding. METHODS: The GUSTO (Global Use of Strategies to Open Occluded Arteries in Acute Coronary Syndromes) V Investigators studied standard-dose reteplase vs standard-dose abciximab plus half-dose reteplase in patients with myocardial infarction. RESULTS: Women were older and more often had diabetes mellitus and hypertension. Angiography and percutaneous coronary intervention were less frequent in women. Death (9.8% vs 4.4% at 30 days; odds ratio [OR], 2.00; 95% confidence interval, 1.59-2.53; P < .001) and bleeding (6.4% vs 2.5%; OR, 1.31; 95% confidence interval, 1.18-1.45; P < .01) were more common in women. There was no association between treatment assignment and death in either sex; bleeding was more common in both sexes receiving combination therapy. Female sex was independently associated with mortality. After Killip class greater than 1 (OR, 4.7), female sex (OR, 2.0) was the strongest correlate of death. Female sex was independently associated with bleeding for both treatments. CONCLUSIONS: Female sex is independently associated with death and bleeding complications among fibrinolytic-treated patients with myocardial infarction. There remains a sex differential in the use of angiography and, therefore, percutaneous coronary intervention after fibrinolysis. Further research will determine what mediates excess risk in women.