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

Vaccine interaction with neutrophils, monocytes and APCs
Several studies presented results on how liposome-
based vaccines interact with neutrophils and monocytes, 
key players in inflammation and immune responses. 
First, Karathanasis et al. used previously character-
ized and purified peptides to target liposomal nano-
carriers to some types of leukocyte cells [
65
]. Peptides 
Vaccinaon
Adjuvant
Angen
Immature APC
PRRs
Angen 
Uptake
Liposomal Vaccine
Endosomal Angen Processing
Processed 
Angen
Mature APC
Angen 
Presentaon
Cosmulatory
Molecules
MHC II
Upregulaon 
of MHC II & 
Cosmulatory 
Molecules
Fig. 2 Co-delivery of antigen and adjuvant to APCs in subunit vaccines. Interaction of the adjuvant with the PRR results in upregulation of co-
stimulatory molecules necessary for appropriate T cell stimulation

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De Serrano and Burkhart  J Nanobiotechnol (2017) 15:83 
were covalently attached through the carboxyl group of 
DSPE-PEG by utilizing the crosslinker N,N-dicyclohexyl-
carbodimide (DCC). Researchers found that targeted 
liposomes interacted better with monocytes and neu-
trophils, contrasting with results obtained by non-tar-
geted liposomes. Moreover, the surface density of the 
peptide directly correlated with liposomes-cell interac-
tions, making this parameter a new way to measure the 
effectiveness of the interactions and the potential induc-
tion of immune responses valuable in subunit vaccine 
development. Then, Johansen et al. investigated the tar-
geting of monocytes and the delivery of a TLR agonist 
(TMX-202) using a cationic liposomes-based formula-
tions (mainly POPC (1-palmitoyl-2-oleoyl-sn-glycero-
3-phosphocholine):DOTAP composition) [
66
]. After an 
hour incubation, the subset of monocytes targeted by the 
liposomes were lymphocytes and granulocytes (75–95%). 
A strong IL-6 and IL-12p40 induction was observed, 
accompanied by monocyte differentiation to CD14
+
/DC-
SIGN
+
DCs. Mainly found in the lymph nodes, lympho-
cytes include natural killer (NK), T and B cells, which are 
involved in innate immune responses, cell- and humoral-
mediated immunities, respectively. Granulocytes, or pol-
ymorphonuclear (PMNs) leukocytes include basophils, 
neutrophils, mast cells and eosinophils that participate 
in allergic and inflammatory reactions. The information 
gathered by the researchers is important because it can 
determine future treatments and vaccine developments 
to focus on selected immune responses, depending on 
the cell or cell types that are being targeted, reducing 
or avoiding unwanted adverse reactions (e.g. allergies or 
chronic inflammation).
After interaction with the antigen, cytokines and/
or interaction with their milieu, monocytes could dif-
ferentiate into macrophages or dendritic cells. Both cell 
types will then migrate to lymph nodes to elicit the cor-
responding adaptive immune responses. Macrophages 
and dendritic cells are specialized APCs that reside in 
the blood stream and help in antigen uptake and antigen 
presentation to T and B cells, inducing cell-mediated and 
humoral immune responses, respectively. It is known 
that antigen-containing liposomes are internalized by 
pinocytosis in macrophages and then cross presented 
to CD8
+
T cells (specialized T cells that attack and kill 
tumors), inducing antigen-specific cytotoxic T lympho-
cytes [
67
]. This cross-presentation occurs when exog-
enous antigen is up taken and presented via the class I 
major histocompatibility complex (MHC I), which clas-
sically only happens with endogenous antigens such as 
those from viruses. To cross-present and elicit a CD8
+
T lymphocyte response, the antigen must be delivered 
to the cytosol APCs. This was studied by Owais et al. in 
which yeast-derived lipids liposomes and egg PC:Chol 
liposomes were tested against J774 A1 macrophages and 
the interactions measured [
68
]. The fusion rate for yeast 
lipid liposomes to macrophages was at 40–70%, com-
pared to 1–8% for egg PC:Chol liposomes. Liposome 
contents were successfully delivered to the cytosol of 
macrophages. Ovalbumin was used as the model anti-
gen for yeast-derived lipid liposomes and it was found 
that it elicited a strong CD8
+
T cell response. Another 
group of researchers investigated the uptake mecha-
nisms of liposomes in rat peritoneal macrophages (PM) 
[
69
]. Researchers determined that two uptake systems 
exist because of cholesterol content and size differences 
of liposomes. For high- (44% molar) and medium-cho-
lesterol (33% molar) content liposomes, the complement 
receptor-mediated phagocytosis occurs. A complement-
independent uptake pathway was suggested for low-
cholesterol content liposomes since no inhibition of their 
internalization rate was observed by the anti-C3 anti-
body. Therefore, once again, lipid composition is a main 
player in liposome-cell interactions, potentially affecting 
the way immune responses develop.