Generation of protective immune responses to plague by mucosal administration of microsphere coencapsulated recombinant subunits

We have investigated noninvasive immunization to plague. Recombinant subuni t antigens, Fl and V from Yersinia pestis, were coencapsulated in biodegrad able poly(L-lactide) microspheres and intranasally administered to mice ove r a range of dose levels. Proteins retained antigenicity during, and postmi croencapsulation as evidenced by immunoblotting and capture enzyme-linked i mmunosorbent assay protocols. Supporting the rationale that a subunit antig en based vaccine for plague should contain both the Fl and V antigens, we o bserved that systemic antibody titres to V were improved by concomitant nas al immunization with Fl. Conversely, serum titres to Fl were unaffected by the presence of V in the nasal inoculum. Interestingly, intramuscular injec tion of Fl augmented humoral immunity to nasally applied V antigen, suggest ing that Fl adjuvantizes nasally instilled V even when introduced at a spat ially distinct location. Although the magnitude of the specific serum respo nse to nasally applied microspheres and equivalent doses of soluble subunit s was not always directly proportional to administered dose and frequency o f dosing, generally coencapsulated antigens evoked higher titred serum anti body responses. Also, when T-cell recall indices were measured they were fo und to be maximum in microsphere vaccinees. As few as two appropriately tim ed nasal inoculations of coencapsulated Fl and V afforded complete protecti on from >100 LD50's inhalational challenge with virulent Y. pestis. These d ata expand on previous findings from our laboratories, providing further in sight into the mechanics of safeguarding mice from plague through nasal imm unization. Further, these results demonstrate that in a murine model, solid protection from pneumonic plague can be engendered by two intranasal admin istrations of appropriately formulated recombinant proteins. (C) 2000 Elsev ier Science B.V. All rights reserved.