A micro-electroporation/electrophoresis-based vaccine screening system reveals the impact of vaccination orders on cross-protective immunity.

The constant emergence of mutated pathogens poses great challenges to the existing vaccine system. A screening system is needed to screen for antigen designs and vaccination strategies capable of inducing cross-protective immunity. Herein, we report a screening system based on DNA vaccines and a micro-electroporation/electrophoresis system (MEES), which greatly improved the efficacy of DNA vaccines, elevating humoral and cellular immune responses by over 400- and 35-fold respectively. Eighteen vaccination strategies were screened simultaneously by sequential immunization with vaccines derived from wildtype (WT) SARS-CoV-2, Delta, or Omicron BA.1 variant. Sequential vaccination of BA.1-WT-Delta vaccines with MEES induced potent neutralizing antibodies against all three viral strains and BA.5 variant, demonstrating that cross-protective immunity against future mutants can be successfully induced by existing strain-derived vaccines when a proper combination and order of sequential vaccination are used. Our screening system could be used for fast-seeking vaccination strategies for emerging pathogens in the future.

Nanochannel Electro-Injection as a Versatile Platform for Efficient RNA/DNA Programming on Dendritic Cells.

The utilization of dendritic cell (DC) vaccines is a promising approach in cancer immunotherapy, and the modification of DCs for the expression of tumor-associated antigens is critical for successful cancer immunotherapy. A safe and efficient method for delivering DNA/RNA into DCs without inducing maturation is beneficial to achieve successful DC transformation for cell vaccine applications, yet remains challenging. This work presents a nanochannel electro-injection (NEI) system for the safe and efficient delivery of a variety of nucleic acid molecules into DCs. The device is based on track-etched nanochannel membrane as key components, where the nano-sized channels localize the electric field on the cell membrane, enabling lower voltage (<30 V) for cell electroporation. The pulse conditions of NEI are examined so that the transfection efficiency (>70%) and biosafety (viability >85%) on delivering fluorescent dyes, plasmid DNA, messenger RNA, and circular RNA (circRNA) into DC2.4 are optimized. Primary mouse bone marrow DC can also be transfected with circRNA with 68.3% efficiency, but without remarkably affecting cellular viability or inducing DC maturation. These results suggest that NEI can be a safe and efficient transfection platform for in vitro transformation of DCs and possesses a promising potential for developing DC vaccines against cancer.

Robust induction of B cell and T cell responses by a third dose of inactivated SARS-CoV-2 vaccine.

SARS-CoV-2 inactivated vaccines have shown remarkable efficacy in clinical trials, especially in reducing severe illness and casualty. However, the waning of humoral immunity over time has raised concern over the durability of immune memory following vaccination. Thus, we conducted a nonrandomized trial among the healthcare workers (HCWs) to investigate the long-term sustainability of SARS-CoV-2-specific B cells and T cells stimulated by inactivated vaccines and the potential need for a third booster dose. Although neutralizing antibodies elicited by the standard two-dose vaccination schedule dropped from a peak of 29.3 arbitrary units (AU)/mL to 8.8 AU/mL 5 months after the second vaccination, spike-specific memory B and T cells were still detectable, forming the basis for a quick recall response. As expected, the faded humoral immune response was vigorously elevated to 63.6 AU/mL by 7.2 folds 1 week after the third dose along with abundant spike-specific circulating follicular helper T cells in parallel. Meanwhile, spike-specific CD4+ and CD8+ T cells were also robustly elevated by 5.9 and 2.7 folds respectively. Robust expansion of memory pools by the third dose potentiated greater durability of protective immune responses. Another key finding in this trial was that HCWs with low serological response to two doses were not truly "non-responders" but fully equipped with immune memory that could be quickly recalled by a third dose even 5 months after the second vaccination. Collectively, these data provide insights into the generation of long-term immunological memory by the inactivated vaccine, which could be rapidly recalled and further boosted by a third dose.