This study was funded by Key Program of Chongqing Natural Science Foundation (No. cstc2020jcyj-zdxmX0027) and Chinese National Natural Science Foundation Project (No. 32270988).

The animal experiments were performed in accordance with the Guide to the Use and Care of Laboratory Animals and approved by the Laboratory Animal Welfare and Ethics Committee of the Third Military Medical University.
1. Preparation of nanoemulsions (NEs)
<ol>
	<li>For aqueous phase preparation, dissolve 0.15 g of polysorbate 80 in 28.2 mL of phosphate buffered saline (PBS) while stirring at 40 &#176;C.</li>
	<li>For oil phase preparation, use the oil phase formulation of th...

Evaluating Immunogenicity of Nanoemulsion&#45;Encapsulated Retinoic Acid in Mice

<ol>
	<li>Pulendran, B., Arunachalam, P. S., O'Hagan, D. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Emerging+concepts+in+the+science+of+vaccine+adjuvants.">Emerging concepts in the science of vaccine adjuvants.</a> Nat Rev Drug Discov. 20 (6), 454-475 (2021).</li><li>Pandey, P., Gulati, N., Makhija, M., Purohit, D., Dureja, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanoemulsion:+A+novel+drug+delivery+approach+for+enhancement+of+bioavailability.">Nanoemulsion: A novel drug delivery approach for enhancement of bioavailability.</a> Recent Pat Nanotech. 14 (4), 276-293 (2020).</li><li>Chen, W. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Disintegration+and+cancer+immunotherapy+efficacy+of+a+squalane-in-water+delivery+system+emulsified+by+bioresorbable+poly(ethylene+glycol)-block-polylactide.">Disintegration and cancer immunotherapy efficacy of a squalane-in-water delivery system emulsified by bioresorbable poly(ethylene glycol)-block-polylactide.</a> Biomaterials. 35 (5), 1686-1695 (2014).</li><li>Iwasaki, A., Omer, S. 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M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cationic+liposomes+formulated+with+synthetic+mycobacterial+cordfactor+(CAF01):+A+versatile+ddjuvant+for+vaccines+with+different+immunological+requirements.">Cationic liposomes formulated with synthetic mycobacterial cordfactor (CAF01): A versatile ddjuvant for vaccines with different immunological requirements.</a> Plos One. 3 (9), e3116 (2008).</li><li>Slutter, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nasal+vaccination+with+N-trimethyl+chitosan+and+PLGA+based+nanoparticles:+Nanoparticle+characteristics+determine+quality+and+strength+of+the+antibody+response+in+mice+against+the+encapsulated+antigen.">Nasal vaccination with N-trimethyl chitosan and PLGA based nanoparticles: Nanoparticle characteristics determine quality and strength of the antibody response in mice against the encapsulated antigen.</a> Vaccine. 28 (38), 6282-6291 (2010).</li><li>Nochi, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanogel+antigenic+protein-delivery+system+for+adjuvant-free+intranasal+vaccines.">Nanogel antigenic protein-delivery system for adjuvant-free intranasal vaccines.</a> Nat Mater. 9 (8), 685-685 (2010).</li><li>Henriksen-Lacey, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Liposomal+cationic+charge+and+antigen+adsorption+are+important+properties+for+the+efficient+deposition+of+antigen+at+the+injection+site+and+ability+of+the+vaccine+to+induce+a+CMI+response.">Liposomal cationic charge and antigen adsorption are important properties for the efficient deposition of antigen at the injection site and ability of the vaccine to induce a CMI response.</a> J Control Release. 145 (2), 102-108 (2010).</li><li>Zhong, X. F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanovaccines+mediated+subcutis-to-intestine+cascade+for+improved+protection+against+intestinal+infections.">Nanovaccines mediated subcutis-to-intestine cascade for improved protection against intestinal infections.</a> Small. 18 (1), e2105530 (2022).</li><li>Mora, J. 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In this protocol, we developed a cationic nanoemulsion-encapsulated retinoic acid to be used as an adjuvant to promote antigen-specific systemic and mucosal responses. Compared to traditional NE adjuvants, it has the following two advantages. First, in general, the surface of O/W NEs has a high negative charge, which makes it difficult to directly load antigens. Cationic NEs can effectively adsorb peptide or protein antigens and enhance the specific immunogenicity. Secondly, experience in traditional vaccine research has...

Adjuvants are often used to enhance the efficacy of a vaccine by stimulating the immune system to respond more strongly to the vaccine, thereby increasing immunity to a particular pathogen1. Nanoemulsion (NE) adjuvant refers to a colloidal dispersion system with thermodynamic stability by emulsifying a certain proportion of oil phase and aqueous phase to produce an emulsion in the form of water-in-oil (W/O) or oil-in-water (O/W)2. O/W nanoemulsion adjuvant can produce cytokines and chemokines at the injection site, induce the rapid aggregation and proliferation of important immune cells such as monocytes, neutrophils, and eosinophils, and enhance the immune response, and improve the immunogenicity of antigens3. Currently, three nanoemulsion adjuvants (MF59, AS03, and AF03) have been licensed for use in vaccines and have shown good safety and efficacy4.
However, mucosal immunity has been poorly addressed by the currently licensed adjuvant formulations in conventional parenteral vaccination5. Retinoic acid (RA) has been reported to induce intestinal homing of immune cells, but its low polarity, poor solubility in water, and poor light and thermal stability limit its use for robust enteric vaccination. Nanoemulsions offer opportunities to increase the bioavailability of highly lipophilic drugs, and the oil core of O/W emulsion adjuvants is suitable for dissolving non-polar substances such as RA6. Therefore, nanoemulsions can be used as carriers for RA in order to achieve the dual response effect of systemic immunity and mucosal immunity.
Compared to neutral or anionic delivery systems, cationic delivery systems have relatively efficient antigen encapsulation and delivery capabilities, which can enhance the immunogenicity of antigens7,8,9. The cationic surface charge of a variety of adjuvant systems is important for their adjuvant effects10,11,12. The cationic charge is an important factor in prolonging vaccine retention at the injection site, increasing antigen presentation and prolonging the stimulation of cellular immunity in the body12.
Based on the above considerations, we developed a cationic nanoemulsion to effectively co-deliver RA and antigens. The particle size and zeta potential of the nanoemulsion were determined using dynamic light scattering (DLS), and the systemic and mucosal immune responses of the nanoemulsion combined with OVA were evaluated by intramuscular injection13.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>1640 medium</td>
			<td>GIBCO, USA</td>
			<td>C11875500BT</td>
			<td></td>
		</tr>
		<tr>
			<td>450 nm Stop Solution for TMB Substrate</td>
			<td>Abcam</td>
			<td>ab171529-1000 mL</td>
			<td></td>
		</tr>
		<tr>
			<td>Automated Cell Counter</td>
			<td>Countstar, China</td>
			<td>IC1000</td>
			<td></td>
		</tr>
		<tr>
			<td>BSA</td>
			<td>Sigma-Aldrich, USA</td>
			<td>B2064-100G</td>
			<td></td>
		</tr>
		<tr>
			<td>Centrifuge 5810 R</td>
			<td>Eppendorf, Germany</td>
			<td>5811000398</td>
			<td></td>
		</tr>
		<tr>
			<td>Danamic Light Scattering</td>
			<td>Malvern</td>
			<td>Zetasizer Nano S90</td>
			<td></td>
		</tr>
		<tr>
			<td>DOTAP</td>
			<td>CordenPharma, Switzerland</td>
			<td>O02002</td>
			<td></td>
		</tr>
		<tr>
			<td>ELISpot Plus: Mouse IFN-gamma (ALP)</td>
			<td>mabtech</td>
			<td>ab205719</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal Bovine Serum</td>
			<td>GIBCO, USA</td>
			<td>10099141C</td>
			<td></td>
		</tr>
		<tr>
			<td>Full-function Microplate Reader</td>
			<td>Thermo Fisher Scientific, USA</td>
			<td>VL0000D2</td>
			<td></td>
		</tr>
		<tr>
			<td>Goat Anti-Mouse IgG1(HRP)</td>
			<td>Abcam</td>
			<td>ab97240-1mg</td>
			<td></td>
		</tr>
		<tr>
			<td>Goat Anti-Mouse IgA alpha chain (HRP)</td>
			<td>Abcam</td>
			<td>ab97235-1mg</td>
			<td></td>
		</tr>
		<tr>
			<td>Goat Anti-Mouse IgG H&#38;L (HRP)</td>
			<td>Abcam</td>
			<td>Ab205720-500ug</td>
			<td></td>
		</tr>
		<tr>
			<td>Goat&#160;Anti-Mouse IgG2a heavy chain (HRP)</td>
			<td>Abcam</td>
			<td>ab97245-1mg</td>
			<td></td>
		</tr>
		<tr>
			<td>High pressure homogenizer</td>
			<td>ATS</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>MONTANE 85 PPI</td>
			<td>SEPPIC, France</td>
			<td>L12910</td>
			<td></td>
		</tr>
		<tr>
			<td>MONTANOX 80 PPI</td>
			<td>SEPPIC, France</td>
			<td>36372K</td>
			<td></td>
		</tr>
		<tr>
			<td>OVA257&#8211;264</td>
			<td>Shanghai Botai Biotechnology Co., Ltd.</td>
			<td>NA</td>
			<td></td>
		</tr>
		<tr>
			<td>OVA323-339</td>
			<td>Shanghai Botai Biotechnology Co., Ltd.</td>
			<td>NA</td>
			<td></td>
		</tr>
		<tr>
			<td>Phosphate buffer saline</td>
			<td>ZSGB-bio</td>
			<td>ZLI-9061</td>
			<td></td>
		</tr>
		<tr>
			<td>Red Blood Cell Lysis Buffer</td>
			<td>Solarbio, China</td>
			<td>R1010</td>
			<td></td>
		</tr>
		<tr>
			<td>retinoic acid</td>
			<td>TCI, Japan</td>
			<td>TCI-R0064-5G</td>
			<td></td>
		</tr>
		<tr>
			<td>Squalene</td>
			<td>Sigma, USA</td>
			<td>S3626</td>
			<td></td>
		</tr>
		<tr>
			<td>T10 basic Ultra-Turrax</td>
			<td>IKA, Germany</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>TMB ELISA Substrate</td>
			<td>Abcam</td>
			<td>ab171523-1000ml</td>
			<td></td>
		</tr>
		<tr>
			<td>trypsin inhibitor</td>
			<td>Diamond</td>
			<td>A003570-0100</td>
			<td></td>
		</tr>
		<tr>
			<td>Tween-20</td>
			<td>Macklin, China</td>
			<td>9005-64-5</td>
			<td></td>
		</tr>
		<tr>
			<td>Ultraviolet spectrophotometer</td>
			<td>Hitachi</td>
			<td>U-3900</td>
			<td></td>
		</tr>
	</tbody>
</table>

cationic nanoemulsion-encapsulated retinoic acid as an adjuvant to promote ova&#45;specific systemic and mucosal responses

Cationic nanostructures have emerged as an adjuvant and antigen delivery system that enhances dendritic cell maturation, ROS generation, and antigen uptake and then promotes antigen-specific immune responses. In recent years, retinoic acid (RA) has received increasing attention due to its effect in activating the mucosal immune response; however, in order to use RA as a mucosal adjuvant, it is necessary to solve the problem of its dissolution, loading, and delivery. Here, we describe a cationic nanoemulsion-encapsulated retinoic acid (CNE-RA) delivery system composed of the cationic lipid 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOTAP), retinoic acid, squalene as the oil phase, polysorbate 80 as surfactant, and sorbitan trioleate 85 as co-surfactant. Its physical and chemical properties were characterized using dynamic light scattering and a spectrophotometer. Immunization of mice with the mixture of antigen (ovalbumin, OVA) and CNE-RA significantly elevated the levels of anti-OVA secretory immunoglobulin A (sIgA) in vaginal lavage fluid and the small intestinal lavage fluid of mice compared with OVA alone. This protocol describes a detailed method for the preparation, characterization, and evaluation of the adjuvant effect of CNE-RA.

Author Spotlight: Development and Evaluation of a Cationic Nanoemulsion&#45;Encapsulated Retinoic Acid System for Mucosal Vaccination

Cationic Nanoemulsion-Encapsulated Retinoic Acid as an Adjuvant to Promote OVA&#45;Specific Systemic and Mucosal Responses

We are working on a mucosal vaccine that produces an immune response as the set of infection, which has the potential to prevent infection and interrupt transmission. We have developed a catatonic nanoemulsion-encapsulated retinoic acid delivery system immunization with ovalbumin by intramuscular injection, which triggers both systemic and mucosal immune responses. In future studies, animal models of intestinal-related diseases can be used to further evaluate the effect and the mechanism of a cationic nanoemulsion-encapsulated retinoic acid in enhancing vaccine protection.

In total, four nanoemulsion formulations were prepared and characterized by their particle size (Figure 1), their zeta potential and their encapsulation efficiency as presented in Table 2. The particle size was concentrated around 160-190nm and the addition of DOTAP reversed the Zeta potential of nanoemulsion. OVA-specific serum IgG and its subgroup antibody level in serum were detected 2 weeks post third immunization. The nanoemulsion adjuvant vaccine significantly increase...

Watch this Scientific Journal Video about Author Spotlight: Development and Evaluation of a Cationic Nanoemulsion-Encapsulated Retinoic Acid System for Mucosal Vaccination at JoVE.com

In this protocol, we developed a cationic nanoemulsion-encapsulated retinoic acid (RA) to be used as an adjuvant to promote antigen-specific systemic and mucosal responses. By adding the FDA-approved RA to the nanoemulsion, antigen-specific sIgA was promoted in the vagina and small intestine after intramuscular injection of the nanoemulsion.

Cationic nanostructures have emerged as an adjuvant and antigen delivery system that enhances dendritic cell maturation, ROS generation, and antigen ...