Optimization of the membrane purification of a polysaccharide-protein conjugate vaccine using backpulsing

The optimization of a membrane purification step to remove unreacted polysa ccharide from a protein-polysaccharide conjugate is described. A key compon ent in this work was the introduction of membrane backpulsing to reduce mem brane fouling. The backpulsing parameters of pulse duration, frequency and pressure were optimized to minimize cycle time and buffer usage and to maxi mize process capacity, while still achieving the required 50-fold purificat ion and greater than 90% step yield. It was determined that optimal perform ance requires frequent pulses (approximately 1 min(-1)) and short durations (less than 1 s). After implementing the optimal backpulsing conditions, th e gradual deterioration in membrane performance which had been observed pre viously was eliminated and acceptable polysaccharide sieving was maintained throughout the diafiltration. Depending on the polysaccharide serotype, a 3.5-10-fold reduction in buffer usage and a 3-8-fold reduction in cycle tim e were accomplished. Interestingly, with the introduction of membrane backp ulsing, it was observed that decreasing the shear rate at the membrane sign ificantly increased polysaccharide sieving for backpulsed diafiltrations. ( C) 1999 Elsevier Science B.V. All rights reserved.