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Vaccines are highly effective in preventing the spread of communicable diseases and are critical to overall public health. As immune stimulants vaccine adjuvants augment the level and longevity of these protective responses. Seeking novel adjuvants using parallel high throughput screens and subsequent systematic structure-activity relationship studies we identified an analogue of a hit compound, , that in screening assays retained induction of calcium (Ca ) influx, tetraspanin CD63 EV reporter activity and cell viability. Here, we further our analyses of the biological activity of related its potential use as a vaccine adjuvant. was tested for activation of murine bone marrow-derived dendritic cells (mBMDC) by flow cytometry for Ca entry, levels of CD80 and CD86 expression, and stimulation of antigen-specific T cell proliferation. Cytokines and IgG responses from BALB/c mice injected with as a single agent or as an adjuvant with ovalbumen were measured by ELISA. triggered store-operated Ca entry in mBMDC as well as increases in CD80 and CD86 surface expression. In co-culture experiments, this compound amplified the stimulation of cognate T cell proliferation. Intramuscular injection of elicited minimal systemic cytokine and chemokine release. When used as an adjuvant with ovalbumen, generated a significant antigen-specific IgG1 response with a higher splenocyte T helper 2 (Th2) cytokine response. activated mBMDCs associated with EV release and a store-operated calcium entry response. Enhanced cognate T cell proliferation was mediated either through direct engagement with compound-stimulated mBMDCs or indirectly via immunostimulatory extracellular vesicles released by -activated mBMDCs. elicited minimal systemic cytokine and chemokine release, demonstrating a promising safety profile. When used as an adjuvant in a murine vaccination model, enhanced the IgG1 response with an associated T helper 2 cytokine profile. Hence this compound shows promise as an adjuvant if a Th2 response is beneficial or in combination with other agents to provide a balanced immune response in vaccines.

Vaccine adjuvants play a crucial role in the efficacy of vaccines, particularly in immunocompromised populations. Newer agents and combination strategies are needed for adequate defense against emerging pathogens and their evolving variants. Here we report the benefit of a synergistic combination of two adjuvants: a Toll-like receptor 7 agonist, 1V270, and a calcium influx inducer, 2G272, that elicit Th1 and Th2 biased immune responses, respectively. In vitro,2G272 significantly enhanced cytokine production induced by 1V270 in human and mouse primary cells, compared to a low activity analog, 2E281, identified from structure-activity relationship studies. Using A/California/07/2009 (H1N1) inactivated influenza A virus (IIAV) as the antigen, the combination adjuvant (2G272 + 1V270) magnified IgG1 and IgG2a responses against hemagglutinin (HA) accompanied by greater hemagglutinin inhibition titers and increased germinal center formation in the draining lymph nodes of immunized BALB/c mice at comparable levels to FDA-approved comparators, MF59 and AS01B. The combination adjuvant also enhanced H1 HA-specific T cell responses, augmenting antigen-specific IFNγ secretion. Importantly, the 2G272 + 1V270 combined adjuvant promoted cross-reactive antibody and cellular immune responses against other HAs in phylogenic Group 1: H5, H11, and in Group 2: H3. C57BL/6 aged mice immunized with H1N1 IIAV and 2G272 + 1V270 generated significant anti-H1 IgG1 responses and IFNγ splenic T cell responses to H1 which were cross-reactive with H5 and H3. Collectively, our findings suggest that 2G272 + 1V270 may be a versatile vaccine co-adjuvant system for promoting a larger breadth of cross reactive Th1/Th2 immune responses and robust GC B cell formation, including in the elderly population.

Despite the clinical efficacy of current intramuscular influenza vaccines in reducing the severity of seasonal infection, they exhibit limited induction of mucosal immunity, which is essential for preventing viral transmission. In addition, intranasal vaccination can induce superior mucosal immunity, enhancing clinical efficacy and reducing transmission, and its self-boosting potential may improve coverage in older adults and those with mobility limitations. We developed Lipo-1V270, a liposomal nanoparticle formulation of the synthetic TLR7 agonist 1V270 using 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and cholesterol for mucosal vaccine delivery. In vitro immune stimulation and in vivo immunogenicity were evaluated using intramuscular and intranasal routes in mouse models, including a heterologous prime-boost regimen with inactivated influenza A virus [IIAV, A/California/04/2009 (H1N1)pdm09] adjuvanted monophosphoryl lipid A (MPLA) priming. In vitro analysis showed that Lipo-1V270 exhibited attenuated innate immune potency compared to unformulated 1V270. However, in vivo co-administration of Lipo-1V270 with IIAV significantly enhanced antigen-specific IgG1 and IgG2a responses. Subsequently, intranasal boosting with Lipo-1V270, following intramuscular priming with IIAV adjuvanted with MPLA - a component included in FDA-approved vaccines - elicited robust influenza-hemagglutinin (HA)-specific mucosal IgA and IgG responses in nasal wash. This heterologous prime-boost regimen also induced strong splenic T-cell responses and HA-specific IgG and IgA antibodies in nasal wash without causing significant weight loss for 7 days post-boost in immunized mice. Intranasal administration of Lipo-1V270 in a heterologous prime-boost vaccination regimen effectively enhances mucosal immunity against influenza virus infection, with an acceptable innate immune-mediated adverse effects profile. This strategy may be applicable to vaccines against other respiratory infectious diseases. •Vaccination with inactivated Influenza A virus (IIAV) adjuvanted with liposomal formulation of small molecule TLR7 ligand induced both Th1 and Th2 biased responses.•A heterologous immunization with MPLA prime and intranasal Lipo-1 V270 with IIAV boost strategy improved mucosal anti-influenza immune response.•Vaccination with Lipo-1V270 adjuvanted vaccine did not show immune mediated systemic adverse effects.