Investigation of a Biodegradable Magnetic Microsphere for Subunit Vaccine Delivery and Enhanced Immunotherapy

Abstract

This investigation presented a novel approach by utilizing biodegradable magnetically driven microspheres (denoted as OMGMs) to deliver subunit vaccines and efficiently enhanced immunotherapy.

First, ovalbumin@magnetic nanoparticles (OVA@MNPs) loaded with the model protein ovalbumin (OVA) were successfully formulated, exhibiting a diameter below 100 nm. Focus-flowing microfluidic droplet generation technology produced large numbers of OMGMs at a production rate that reached over 1000 per second. This capability is critical for the practical use and commercial advancement of microstructures in biomedical applications. Subsequently, comprehensive characterization and verification of the prepared subunit vaccines and OMGMs were conducted through scanning electron microscopy, transmission electron microscopy, X-ray diffraction, zeta size and potential, and dynamic light scattering techniques. Furthermore, to assess the biocompatibility and biodegradability of the synthesized OVA@MNPs and fabricated OMGMs, a series of in vitro and in vivo experiments was performed, employing cells and mice, respectively. Results from these experiments demonstrated the favorable biocompatibility and biodegradability of OVA@MNPs and OMGMs, establishing their suitability for biomedical applications. Notably, OMGMs played a crucial role in facilitating the controlled release of the encapsulated vaccine through a gradual enzymatic degradation mechanism, significantly augmenting the therapeutic potential of subunit vaccines. OMGMs demonstrated potential for mass production and served as a promising platform for efficiently delivering subunit antigens.

Thereafter, OMGMs exhibited remarkable motion properties under magnetic force and torque actuation, enhancing the delivery of subunit vaccines to the lymphatic system. The distinct advantages of OMGMs in subunit vaccine delivery include the utilization of OVA@MNPs with nanometer-scale dimensions, facilitating subunit vaccine through the lymphatic intercellular space, and subsequent drainage to lymph nodes (LNs) rich in antigen-presenting cells (APCs). In addition, the magnetic aggregation of OVA@MNPs and the magnetic driving capabilities of OMGMs increased accumulation of vaccines in LN locations with abundant APCs. Moreover, the biodegradation of OMGMs enabled the sustained release of subunit vaccines, further enhancing antigen presentation efficiency and immune response. These combined advantages contributed to the superior drainage and targeting effects of OMGMs on subunit vaccines. For example, in vitro experiments revealed that OMGMs significantly enhanced cross-presentation levels by more than twofold compared with free OVA. Meanwhile, the secretion levels of immune response factors, such as tumor necrosis factor-α, interleukin 6, and interferon gamma, were increased by approximately 1.7, 1.2, and 1.3 times, respectively. In vivo experiments demonstrated that the total radiation efficiency of popliteal and inguinal LNs in the OMGM experimental group was increased by approximately 1.5 times compared with OVA alone. Meanwhile, efficiency at the sciatic LN and popliteal LN locations in the OMGM group was 2.3 times and 1.5 times higher than that in the OVA group, respectively, after 36 h.

Then, immunization experiments revealed that the proposed subunit vaccine delivery strategy achieved good anti-OVA antibody levels, indicating that OMGMs with a single booster immunization achieved antibody levels comparable with those in the case of two booster injections, demonstrating the possibility of using sustained-release degradation-delivered subunit vaccines to improve immunity levels. In addition, after melanoma tumor cells were inoculated into immune mice, T-cell responses were enhanced, successfully inhibiting the growth of OVA melanoma tumors. These results validated the potential of the proposed vaccine delivery strategy in enhancing subunit antigen delivery efficiency and tumor immunotherapy.

In conclusion, these findings highlighted the potential of OMGMs as a practical subunit vaccination approach, addressing the limitations associated with antigen delivery efficiency and paving the way for advanced immunotherapeutic strategies.

Date of Award	14 Jan 2025
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Gang Gary FENG (Supervisor) & Dong SUN (Supervisor)