Microencapsulation of a synthetic peptide epitope for HTLV-1 in biodegradable poly(D,L-lactide-co-glycolide) microspheres using a novel encapsulationtechnique

A novel procedure has been developed for the encapsulation of peptide antig ens in poly(lactide-co-glycolide) (PLGA) microspheres, which employs triflu oroacetic acid (TFA) as a carrier solvent for both the polymer and antigen. The antigen/polymer solution is emulsified in mineral oil containing sorbi tan trioleate (Span 85) as an emulsifier and a low level of cottonseed oil to extract the TFA. Fluoresceinisothiocyanate-labelled bovine serum albumin (FITC-BSA) was used as a model antigen to characterize the microencapsulat ion. Microspheres were of the desired size (< 10 mm) for targeting to antig en-presenting cells, and released the model antigen slowly after an initial burst release (11%) in PBS/0.02% Tween 80 at 37<degrees>C. Subsequently, a potential peptide vaccine, designated MVFMF2, for the human T-lymphotropic virus type 1 (HTLV-1) was encapsulated at 4.7% loading using the novel oil -in-oil method. In vivo immune responses were examined in rabbits immunized with (i) encapsulated MVFMF2 together with encapsulated adjuvant (N-acetyl -glucosamine-3yl-acetyl-L-alanyl-D-isoglutamine, nor-MDP, (ii) encapsulated MVFMF2 without adjuvant, and (iii) free peptide with adjuvant. Inoculation of the encapsulated peptide produced an antibody response similar to that of the free peptide emulsified in adjuvant. Moreover, the elevated immune r esponse elicited by the encapsulated peptide was observed without multiple booster immunizations and irrespective of whether an adjuvant was used. Add itionally, the antibodies raised against both free and encapsulated MVFMF2 had similar affinities, as judged by competitive enzyme-linked immunosorban t assay (ELISA), indicating that the encapsulated peptide retained a signif icant fraction of its epitopes. Hence, these results demonstrate that pepti de vaccines can be encapsulated in PLGA microspheres using a common carrier solvent for both the peptide and polymer, which produces a desirable immun e response in the absence of an adjuvant.