PHYSICOCHEMICAL AND ANTIGENIC PROPERTIES OF TETANUS AND DIPHTHERIA TOXOIDS AND STEPS TOWARDS IMPROVED STABILITY

Physico-chemical, antigenic and immunogenic properties may be altered during microencapsulation of antigens and their release from poly(lact ic acid) and poly(lactic-co-glycolic acid) microspheres. Here, the phy sico-chemical, conformational and antigenic stability of tetanus and d iphtheria toxoids was studied in aqueous solutions stressed by elevate d temperature and the presence of lactic and glycolic acids. Further, the stabilising effect of albumin was investigated. The analytical too ls used were fluorimetry, circular dichroism spectroscopy, turbidimetr y, electrophoresis and ELISA. Elevated temperatures altered the physic o-chemical and antigenic properties of the toxoids to a greater extent than the acids (50 mM) did. Substantial unfolding and chemical change s of tryptophan were observed upon 1-4 weeks of incubation at 60 degre es C. At 4 degrees C, only minor conformational changes were observed, even in the presence of the acids. Furthermore, 40% of the tetanus to roid antigenicity was lost after 7 days at 37 degrees C. This loss inc reased in the presence of the acids. At 60 degrees C, the antigenicity had completely vanished. Very importantly, 0.5% albumin preserved the tetanus antigenicity over 6 weeks' incubation at 37 degrees C, regard less of the presence of glycolic acid. This qualifies albumin as poten tial stabilising additive for toroid loaded poly(lactic acid) and poly (lactic-co-glycolic acid) microspheres. (C) 1998 Elsevier Science B.V. All rights reserved.