Liposomal vaccine formulations as prophylactic agents: design considerations for modern vaccines

Viral infections and liposomes-based vaccines
Viruses are ethiologic agents of different diseases in ani-
mals [
74
] (including humans [
75
, 
76
]), plants [
77
], para-
sites [
78
, 
79
] and bacteria [
80
, 
81
]. The basic definition of 
a virus is a non-living infectious agent that requires living 
cells for its replication and survival, which allows spread-
ing of the disease. This cell lysis leads to inflammation 
and tissue damage which are detrimental for the host, 
enhancing the state of the disease. Additionally, some 
viruses, like HIV, destroy immune cells hindering effec-
tive immune responses when other infections (secondary 
infections in seropositive patients) occur. Viral infections 
can be treated by either antiviral therapeutic [
82
] or by 
prophylactic vaccine [
83
] approaches. Here, we will pre-
sent several examples of vaccine applications based on 
liposomes for the prophylactic treatment of certain viral 
infections.
Hepatitis
One of the most significant viruses that affect human 
health are hepatitis viruses. Hepatitis is an inflamma-
tion of the liver tissue caused by the five types of hepatitis 
viruses (A, B, C, D and E). Hepatitis A and E are spread 
through contaminated food or water sources. Hepati-
tis B (HBV) is sexually transmitted or during pregnancy 
and birth. Both HBV and hepatitis C can be transmit-
ted through blood (needle exchange by IV users) and 
hepatitis D can only infect people infected with HBV. 
Two seminal reports investigated novel approaches for 
the prophylactic treatment of HBV utilizing cationic 
lipids. Brunel et al. reported the effectiveness of recom-
binant hepatitis B surface antigen (HBsAg) presenta-
tion based on DC-Cholesterol liposomes or aluminum 
hydroxide (alum) adjuvants in a subcutaneous vaccine 
model [
84
]. The DC-Chol-based vaccine elicited anti-
body (IgG1 and IgG2a) titers in three mice lines (BALB/c, 
OF1 and B10.M). Compared to the alum-based vaccine, 
which demonstrated weak immunogenicity, DC-Chol 
liposomes induced controlled T
H
1 and T
H
2 immune 
responses characterized by normal, but significant lev-
els of cytokines IL-2 and IFN-γ and IL-5, respectively. 
Controlled immune responses are important to avoid 
inflammation that could result in tissue damage. The 
researchers concluded that cationic lipids like DC-Chol 
could be used as adjuvants, enhancing the immuno-
genicity of previously non-immunogenic vaccines, spe-
cifically in the development of prophylactic vaccines 
against hepatitis B virus. Another group investigated 
the use of a transcutaneous vaccine for the treatment of 
HBV infections [
85
]. In that report, the vaccine presents 
some differences from the Brunel et al. article based on 
the antigen and carrier types. First, cationic transfer-
somes, a type of liposome, were prepared from DOTMA 
(1,2-di-O-octadecenyl-3-trimethylammonium propane) 
phospholipid and sodium deoxycholate (SDC) at differ-
ent DOTMA weight ratios (75–95% w/w). Second, plas-
mid DNA encoding the HBsAg gene was loaded to the 
transfersomes instead of the antigen. The transfersomes 
were not cytotoxic to HepG2 cells and were stable at dif-
ferent temperatures (4 and 28 °C). Immunization stud-
ies included HBsAg DNA-loaded tranfersomes (topical), 
naked HBsAg DNA (topical and intramuscular) and pure 
HBsAg (intramuscular) administered to BALB/c mice. 
Significant levels of anti-HBsAg antibodies and cytokines 
(IL-2 and IFN-γ) were elicited in topical DNA-loaded 
transfersomes as compared to intramuscular naked 
DNA delivery. This antibody and cytokine profile con-
firmed the induction of T
H
1 and T
H
2 immune responses 
as observed in Brunel et al. Both studies represent great 
advances in the treatment of HBV infections with novel 
approaches and administration routes that could applied 
in the future as preventive vaccines.