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

particles in this study induced a T
H
2 immune response 
due to increase of IL-5 and IgG1 levels. IL-1β triggers a 
T
H
17 immune response, whereas IFN-γ induces a T
H
1 
immune response. Therefore, liposome size affects the 
differentiation of cellular immune responses, rendering 
this physical parameter a key role in liposomal formula-
tion function.
Vesicle size could be affected by the storage period 
that the vaccine undergoes and by other environmental 
parameters. It is well recommended to perform stability 
studies in different environmental conditions to ensure 
that liposomal vaccine vesicles do not change over time 
[
32
]. Applying several methods during the formulation 
design and development (like spray drying, steriliza-
tion, cryoprotection and PEGylation) will lead to lipo-
somal vesicle stabilization [
33
–
35
]. These methods or 
approaches mentioned earlier avoid unwanted changes 
in vesicle morphology that could subsequently affect the 
immune responses of the vaccine. Furthermore, vesicle 
size stability can be affected by the vesicle lipid composi-
tion [
36
]. An effect observed with unstable lipid vesicles 
is coalescence, but real-time methods have been devel-
oped to study the phenomenon and control stability [
37
]. 
Additional work has discussed vesicle stability extensively 
and we recommend the reader to review the appropriate 
literature [
38
–
40
].
Lamellarity nature of the liposome
The lamellar nature of the liposomal vesicle could also 
affect the immune system causing differential responses. 
Beck et al. studied the adjuvanted immune responses to 
a recombinant HIV protein, CN54 gp140, in small uni-
lamellar (SUV) and large multilamellar vesicles (MLV) 
[
41
]. The liposomes were composed of different com-
binations of monophosphoryl lipid A (MPLA) and 
lipids (1,2-dimyristoyl-sn-glycero-3-phosphocholine, 
DMPC; 1,2-dimyristoyl-sn-glycero-3-phospho-(1ʹ-rac-
glycerol), DMPG; and cholesterol, Chol), with or with-
out the addition of the saponin QS21. SUVs without 
QS21 could induce immune responses (characteristic of 
a T
H
2 cell-mediated response) to CN54 gp140 protein 
due to high antibody production, contrasting to MLVs. 
Adding the saponin QS21 restored immune responses 
in MLVs (higher IgG1 > IgG2a and IFN-γ titers), stimu-
lating both T
H
1 and T
H
2 responses. The saponin did 
not influence SUVs immune response profile. Shek et al. 
presented one of the first experiments that compared