Investigating the In Vitro Immunomodulatory Potential of Microparticulate β-L-Adenosine in Particulate Vaccine Candidates

Background: Immunomodulatory compounds can modify or regulate the immune responses. Given that vaccine-induced immune responses can vary in magnitude and durability depending on antigen properties and adjuvant selection. Immunomodulators that enhance antigen-specific immune responses with low toxicity may complement existing adjuvant systems. Recent studies indicate that adenosine receptor–mediated signaling can modulate dendritic cell (DC) function through mechanisms distinct from classical pathogen-associated molecular pattern (PAMP)-driven Toll-like receptor pathways. Methods: In this context, the present study comparatively evaluates poly-(lactic-co-glycolic acid) (PLGA) microparticle–encapsulated β-L-adenosine (BLA MPs) alongside established FDA-approved adjuvants to assess their immunomodulatory potential under limited-antigen conditions. FDA-approved PLGA was used to encapsulate BLA in combination with multiple viral antigens, including H1N1 influenza, Zika virus, and canine coronavirus, to enable sustained delivery, antigen protection, and efficient uptake by antigen-presenting cells. Results: Physicochemical characterization demonstrated uniform particle size distribution, a low polydispersity index, and a stable negative surface charge. Release studies showed more than 50% payload release within 12 h, with release kinetics best described by the Korsmeyer–Peppas model. Cytotoxicity evaluation using DC2.4 cells confirmed that BLA MPs were non-cytotoxic at concentrations up to 250 μg/mL. Comparative in vitro immunological assessments revealed that BLA MPs induced dendritic cell activation, including upregulation of antigen-presenting and co-stimulatory molecules, at levels largely comparable to those observed with Alum- and MF59-based formulations across multiple antigen groups. Nitric oxide production remained within comparable ranges, indicating balanced immunostimulatory activity without excessive inflammatory signaling. In select conditions, co-formulation of BLA MPs with MF59 further enhanced DC activation, supporting its role as a complementary immunomodulatory component. Conclusion: These findings align with previously reported adenosine-dependent pathways involved in DC maturation and antigen presentation. Overall, this comparative study demonstrates that PLGA-encapsulated β-L-adenosine functions as an effective immunomodulatory agent, with performance comparable to that of established FDA-approved adjuvants across diverse vaccine antigens. Further in vivo studies are warranted to evaluate dose dependency, cytokine profiles, and antibody responses to define its role within combinatorial vaccine adjuvant strategies.