FRACTION-1 CAPSULAR ANTIGEN (F1) PURIFICATION FROM YERSINIA-PESTIS-CO92 AND FROM AN ESCHERICHIA-COLI RECOMBINANT STRAIN AND EFFICACY AGAINST LETHAL PLAGUE CHALLENGE

As a first step in formulating an improved plague vaccine, we develope d a simple purification strategy that produced high yields of pure cel l-associated and culture supernatant-derived fraction 1 capsular antig en (F1) from both avirulent Yersinia pestis CO92 (Pgm(-) Lcr(-)) and a n Escherichia coli F1-producing recombinant strain. Cell-associated F1 was partially purified by sequential ammonium sulfate precipitations of a sodium chloride extract of acetone-dried bacteria harvested from broth cultures. Cell-free F1 was precipitated directly from culture su pernatants with a single application of 30% ammonium sulfate. F1 explo iting the aggregative property of F1, large quantities of purified hig h-molecular-weight F1 species from both cell extracts and supernatants were isolated in the void volume of a preparative gel filtration colu mn. Highly purified, endotoxin-free FI, combined with two different ad juvants, induced very high F1 titers in mice and protected them agains t either subcutaneous (70 to 100% survival) or aerosol (65 to 84% surv ival) challenge with virulent organisms. This protection was independe nt of the source of the antigen and the adjuvant used. F1-induced prot ection against both subcutaneous and aerosol challenge was also signif icantly better than that conferred by immunization with the licensed k illed whole-cell vaccine. Our results indicate that F1 antigen represe nts a major protective component of previously studied crude capsule p reparations, and immunity to F1 antigen provides a primary means for t he host to overcome plague infection by either the subcutaneous or res piratory route.