Haemophilus influenzae type b conjugate vaccine stability: catalytic depolymerization of PRP in the presence of aluminum hydroxide

The structural stability of the Haemophilus influenzae type b (Hib) capsula r polysaccharide, polyribosylribitolphosphate (PRP) in an aluminum hydroxid e adsorbed, polysaccharide-protein conjugate vaccine was monitored using mo difications of an HPLC assay developed by Tsai et al. [Tsai C-M, Gu X-X, By rd RA. Quantification of polysaccharide in Haemophilus influenzae type b co njugate and polysaccharide vaccines by high-performance anion-exchange chro matography with pulsed amperometric detection. Vaccine 1993;12:700-706.]. A s applied to products containing PRP conjugated to the outer membrane prote in complex (OMPC) from Neisseria meningitidis, this assay allows direct mea surement of the total PRP content in very complex samples including commerc ial vaccine products. In addition, with the use of a high-speed centrifugat ion step, the assay can be used to directly quantify any PRP that is not co njugated to the OMPC carrier protein. These results provide evidence of wha t appears to be a catalytic reaction taking place between the phosphodieste r bond of PRP and the aluminum hydroxide adjuvant that results in hydrolysi s of the PRP polymer into smaller chain lengths and liberation of PRP oligo mers from the conjugate particle. The reaction approaches an asymptotic lim it after approximately two years at 2-8 degrees C. Clinical studies which s pan this time period confirm that the modest decrease in conjugated PRP con tent over time does not impact the overall clinical effectiveness of PRP-OM PC-containing vaccines. (C) 1999 Elsevier Science Ltd. All rights reserved.