IN VITRO EMULATING THE INTRAMUSCULAR ADMINISTRATION OF THE ANTI-COVID-19 BNT612B2 VACCINE TO ASSESS THE CONTRIBUTION OF STROMAL AND TISSUE-SPECIFIC CELLS IN FINE-TUNING EARLY IMMUNE SIGNATURE

Immune response to vaccines results from the coordinated action of immune cells in multiple locations across the body. An integrated picture of vaccine-driven molecular networks comes from system vaccinology studies that identified relevant signatures, belonging to innate immunity and induced early after vaccination, that correlate with and predict later adaptive vaccine-specific responses. These blood modules, found in subjects that get vaccinated with different vaccines, include pro-inflammatory cytokines, interferon (IFN)-stimulated genes and transcripts associated with metabolic alteration critical for antiviral responses, antigen presentation and B cell activation. Here, by means of human cell-based immune-relevant in vitro models, we simulated the BNT162b2 mRNA vaccine intramuscular administration in a heterologous system composed of vaccine-injected 3D muscle-like tissue (3D-MT) and peripheral blood mononuclear cells (PBMC), representing the immune compartment. To dissect stroma contribution in shaping early immune response to BNT162b2 vaccine, an in vitro system consisting of vaccine exposed human primary fibroblasts and PBMC was also used. Vaccine-injection in the 3D-MT stimulates the recruitment and phenotypical modulation of major antigen presenting cells, particularly monocytes and macrophages while factors from stromal compartment mainly account for dendritic cell expansion and activation. These phenotypical changes are in line with the capacity acquired by PBMC, in the two heterologous systems, to express an early innate immune module including the cytokines IL-15, IL-6, TNF-α, IFN-γ, the chemokines IP-10 and MCP-1 and the IFN-inducible genes MX1 and IRF1, that we previously found to be correlated with vaccine-specific humoral protective responses in subjects that get vaccinated with BNT162b2 vaccine. In particular, tissue resident muscle cells prompt PBMC to generate an immunostimulatory soluble milieu, while stromal compartment equipes PBMC to express innate immune mediators belonging to IFN signature. These findings suggest that in vitro systems composed of PBMC, stromal and tissue specific cells can be further exploited as alternative methods to animals for vaccine immunogenicity assessment, thus adhering to 3Rs principle.