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

Respiratory syncytial virus
Another respiratory viral pathogen of interest is the 
respiratory syncytial virus (RSV). RSV causes respira-
tory tract infections, specifically lower respiratory tract 
infections in children and it presents high hospitaliza-
tion incidence [
87
]. An i. n. study was developed by 
Klinguer et al. in which cationic DDA liposomes were 
mixed with the recombinant fragment of the RSV G pro-
tein (BBG2Na) and administered to BALB/c mice [
88
]. 
The DDA + BBG2Na liposomal formulation presented 
significant antibody (IgG and IgA) titers at systemic 
(serum) and local (nasal) levels. Cytokine production was 
higher for IL-2 and IFN-γ in cationic liposomes carrying 
the RSV recombinant antigen, confirming the protection 
after a viral challenge and the induction of T
H
1 immune 
response. These three reports on respiratory viruses 
and their prophylactic vaccine development confirms 
the importance of mucosal immunization as it elicits 
local and systemic B- and T-cell responses [
89
]. It is also 
clear that cationic phospholipids like DDA, DC-Chol or 
DOTAP play a leading role (Table 
3
) in the immunostim-
ulation of subunit vaccines and more approaches should 
be investigated. Different administration routes were 
investigated in the studies for viral infections. However, 
we cannot verify and compared these administration 
routes to determine the best alternative due to experi-
mental differences in the studies (liposomal composition 
and targeted virus). Future experiments should focus 
their efforts in comparing different administration routes 
with the same liposomal composition and prophylactic 
treatment of a particular virus.
Bacterial infections and liposomal vaccines
Bacteria can be beneficial for humans, but also detrimen-
tal to our health when they harbor pathogenicity traits. 
Bacteria are divided in Gram positive (+) or negative (−) 
based on Gram staining, that surveys the peptidoglycan 
content in the cell wall. Gram (+) bacteria have a posi-
tive result in the Gram Stain method, which determines 
in a qualitative way the presence of the cell wall compo-
nent: a thick peptidoglycan layer. In contrast, Gram (−) 
bacteria present a negative result in the stain, indicat-
ing a thin peptidoglycan layer, sandwiched between two 
cell membranes (plasma and outer membranes). Gram