Liposomal adjuvants for human vaccines

ABSTRACT

Introduction: Liposomes are well-known as drug carriers, and are now critical components of two of six types of adjuvants present in licensed vaccines. The liposomal vaccine adjuvant field has long been dynamic and innovative, and research in this area is further examined as new commercial products appear in parallel with new vaccines. In an arena where successful products exist the potential for new types of vaccines with liposomal adjuvants, and alternative liposomal adjuvants that could emerge for new types of vaccines, are discussed.

Areas covered: Major areas include: virosomes, constructed from phospholipids and proteins from influenza virus particles; liposomes containing natural and synthetic neutral or anionic phospholipids, cholesterol, natural or synthetic monophosphoryl lipid A, and QS21 saponin; non-phospholipid cationic liposomes; and combinations and mixtures of liposomes and immunostimulating ingredients as adjuvants for experimental vaccines.

Expert opinion: Liposomes containing monophosphoryl lipid A and QS21 have considerable momentum that will result soon in emergence of prophylactic vaccines to malaria and shingles, and possible novel cancer vaccines. The licensed virosome vaccines to influenza and hepatitis A will be replaced with virosome vaccines to other infectious diseases. Alternative liposomal formulations are likely to emerge for difficult diseases such as tuberculosis or HIV-1 infection.

KEYWORDS:

• Adjuvant
• immunostimulation
• liposomes
• vaccine

Article highlights.

• The development and introduction of liposomes as vaccine adjuvants in the greater context of the adjuvant field are described.

• Virosomes were the original marketed liposomal human pharmaceutical product, licensed for vaccines to hepatitis A (1994) and influenza (1999), and they are still potentially useful for new types of vaccines.

• Liposomes containing MPLA and QS21 saponin have achieved success as adjuvants for vaccines that are about to be licensed for malaria and shingles vaccines.

• Unique mechanisms account for adjuvant activities of formulations of liposomes containing immunostimulating molecules.

• New generations of liposomes containing MPLA, with or without QS21, and cationic nonphospholipid liposomes, are being actively developed as adjuvants for novel vaccines to tuberculosis, HIV-1 infection, malaria, heroin addiction, and Alzheimer’s disease.

This box summarizes key points contained in the article.

Declaration of interest

This work was supported through a Cooperative Agreement Award (no.W81XWH-07-2-067) between the Henry M. Jackson Foundation for the Advancement of Military Medicine and the U.S. Army Medical Research and Materiel Command (MRMC). The views expressed in this article are those of the authors and do not necessarily reflect the official policy of the Department of the Army, Department of Defense, or the U.S. Government. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed