- AbstractTwo strategies for increasing liposome stability in vivo are described in this review. The first strategy involves the encapsulation of liposomes within polymeric microcapsules of alginate-poly(L-lysine) that retained the liposomes inside but allowed the outward diffusion of proteins of 100 kDa or less, once they were released from the encapsulated liposomes. In vivo studies revealed that the microencapsulated liposome systems (MELs) extended the delivery of a model antigen, bovine serum albumin (BSA), for more that 80 days, resulting in the prolonged production of high levels of antigen-specific antibodies. The antibody levels were higher that those obtained with rats injected with BSA in complete Freund's adjuvant, or in liposomes. The unique construction of MELs enabled also the enzymatically-triggered pulsatile delivery of proteins from encapsulated liposomes, which was not possible before with liposomes.