Validation and life-cycle management of a quantitative ligand-binding assay for the measurement of Nulojix(®), a CTLA-4-Fc fusion protein, in renal and liver transplant patients.

BACKGROUND: Nulojix(®) is a fusion protein composed of the Fc portion of a human IgG1 linked to the extracellular modified domain of CTLA-4. Nulojix differs from another Bristol Myers Squibb product, Orencia(®) by two amino acids and was approved by the FDA on 15 June 2011 for the prophylaxis of organ rejection in adult patients receiving kidney transplant. RESULTS: A sandwich ELISA utilizing two monoclonal antibodies against CTLA-4 was employed for Nulojix quantification and pharmacokinetic analysis. At least 17 analysts have qualified on the assay and contributed to reportable results over the last 7 years. In-study accuracy and precision demonstrate suitable performance: %bias within -4 to 4%, %CV ≤13% and total error within 6-15%. Incurred sample reanalysis was completed in applicable disease-state populations. The assay was automated and validated in additional clinical matrices (ascites and urine) and Nulojix quantification was validated in the presence of clinically relevant co-administered compounds. In 2011, the biotinylation procedure was modified meriting a regression change (quadratic to 4-parameter logistic) and associated partial validation. CONCLUSION: This long-term pharmacokinetic program provides a good example of the dynamic clinical environment and adaptation requirements of ligand-binding assays.