Subunit microparticulate vaccine delivery using microneedles trigger significant SARS-spike-specific humoral and cellular responses in a preclinical murine model

The objective of this “proof-of-concept” study was to evaluate the synergistic effect of a subunit microparticulate vaccine and microneedles (MN) assisted vaccine delivery system against a human coronavirus. Here, we formulated PLGA polymeric microparticles (MPs) encapsulating spike glycoprotein (GP) of SARS-CoV as the model antigen. Similarly, we formulated adjuvant MPs encapsulating Alhydrogel® and AddaVax™. The antigen/adjuvant MPs were characterized and tested in vitro for immunogenicity. We found that the antigen/adjuvant MPs were non-cytotoxic in vitro. The spike GP MPs + Alhydrogel® MPs + AddaVax™ MPs showed enhanced immunogenicity in vitro as confirmed through the release of nitrite, autophagy, and antigen presenting molecules with their co-stimulatory molecules. Next, we tested the in vivo efficacy of the spike GP MP vaccine with and without adjuvant MPs in mice vaccinated using MN. The spike GP MPs + Alhydrogel® MPs + AddaVax™ MPs induced heightened spike GP-specific IgG, IgG1 and IgG2a antibodies in mice. Also, spike GP MPs + Alhydrogel® MPs + AddaVax™ MPs enhanced expression of CD4+ and CD8+ T cells in secondary lymphoid organ like spleen. These results indicated spike GP-specific humoral immunity and cellular immunity in vivo. Thus, we employed the benefits of both the subunit vaccine MPs and dissolving MN to form a non-invasive and effective vaccination strategy against human coronaviruses.