Abstract: This invention relates to an immunostimulating composition comprising encapsulating microspheres, which may contain a pharmaceutically-acceptable adjuvant, wherein said microspheres having a diameter between 1 nanometer (nm) to 10 microns (um) are comprised of (a) a biodegradable-biocompatible poly(DL-lactide-co-glycolide) as the bulk matrix, wherein the relative ratio between the amount of lactide and glycolide components are within the range of 40:60 to 0:100 and wherein said poly (DL-lactide-co-glycolide) is present in an uncapped form and an end-capped form wherin a ratio of uncapped to end-capped forms is 99/1 to 1/99, and (b) an immunogenic substance comprising Colony Factor Antigen (CFA/II), hepatitis B surface antigen (HbsAg), or a physiologically similar antigen that serves to elicit the producton of antibodies in animal subjects. The preparation of its composition and its use as a vaccine is also disclosed.