Robust HIV-specific immune responses were induced by DNA vaccine prime followed by attenuated recombinant vaccinia virus (LC16m8 strain) boost

New vaccine production platforms used in developing SARS-CoV-2 vaccine candidates

The threat of the current coronavirus disease pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is accelerating the development of potential vaccines. Candidate vaccines have been generated using existing technologies that have been applied for developing vaccines against other infectious diseases. Two new types of platforms, mRNA- and viral vector-based vaccines, have been gaining attention owing to the rapid advancement in their methodologies. In clinical trials, setting appropriate immunological endpoints plays a key role in evaluating the efficacy and safety of candidate vaccines. Updated information about immunological features from individuals who have or have not been exposed to SARS-CoV-2 continues to guide effective vaccine development strategies. This review highlights key strategies for generating candidate SARS-CoV-2 vaccines and considerations for vaccine development and clinical trials.

The evolution of poxvirus vaccines

After Edward Jenner established human vaccination over 200 years ago, attenuated poxviruses became key players to contain the deadliest virus of its own family: Variola virus (VARV), the causative agent of smallpox. Cowpox virus (CPXV) and horsepox virus (HSPV) were extensively used to this end, passaged in cattle and humans until the appearance of vaccinia virus (VACV), which was used in the final campaigns aimed to eradicate the disease, an endeavor that was accomplished by the World Health Organization (WHO) in 1980. Ever since, naturally evolved strains used for vaccination were introduced into research laboratories where VACV and other poxviruses with improved safety profiles were generated. Recombinant DNA technology along with the DNA genome features of this virus family allowed the generation of vaccines against heterologous diseases, and the specific insertion and deletion of poxvirus genes generated an even broader spectrum of modified viruses with new properties that increase their immunogenicity and safety profile as vaccine vectors. In this review, we highlight the evolution of poxvirus vaccines, from first generation to the current status, pointing out how different vaccines have emerged and approaches that are being followed up in the development of more rational vaccines against a wide range of diseases.

Prime immunization with rotavirus VLP 2/6 followed by boosting with an adenovirus expressing VP6 induces protective immunization against rotavirus in mice

BACKGROUND

Rotavirus (RV) is the main cause of severe gastroenteritis in children. An effective vaccination regime against RV can substantially reduce morbidity and mortality. Previous studies have demonstrated the efficacy of virus-like particles formed by RV VP2 and VP6 (VLP2/6), as well as that of recombinant adenovirus expressing RV VP6 (rAd), in eliciting protective immunities against RV. However, the efficacy of such prime-boost strategy, which incorporates VLP and rAd in inducing protective immunities against RV, has not been addressed. We assessed the immune effects of different regimens in mice, including rAd prime-VLP2/6 boost (rAd+VLP), VLP2/6 prime-rAd boost (VLP+rAd), rAd alone, and VLP alone.

RESULTS

Mice immunized with the VLP+rAd regimen elicit stronger humoral, mucosal, and cellular immune responses than those immunized with other regimens. RV challenging experiments showed that the highest reduction (92.9%) in viral shedding was achieved in the VLP+rAd group when compared with rAd+VLP (25%), VLP alone (75%), or rAd alone (40%) treatment groups. The reduction in RV shedding in mice correlated with fecal IgG (r = 0.95773, P = 0.04227) and IgA (r = 0.96137, P = 0.038663).

CONCLUSIONS

A VLP2/6 prime-rAd boost regimen is effective in conferring immunoprotection against RV challenge in mice. This finding may lay the groundwork for an alternative strategy in novel RV vaccine development.

Engineered CCR5 superagonist chemokine as adjuvant in anti-tumor DNA vaccination

Chemokine receptors are promising targets for enhancing T-cell immunity and anti-cancer therapy. CCL5 is a potential adjuvant for DNA vaccination. We postulated that CCR5 superagonists could be even more effective. A CCR5 superagonist derived from natural CCL5 by directed in vitro evolution, namely 1P7, is used as a DNA vaccine adjuvant and expressed as fused chemokine-Ig (1P7-Ig). We show that OVA+1P7-Ig DNA co-inoculation induced higher frequencies of OVA-specific CD8 lymphocytes than OVA+CCL5-Ig or controls and gave an even better protection against tumor growth in a CCR5-dependant manner. Our results indicate that CCR5-superagonists may provide potent adjuvants for vaccines.

Single CX3CL1-Ig DNA administration enhances T cell priming in vivo

Upon antigenic stimulation, establishment of adaptive immune responses that determines vaccine efficacy is dependent on efficient T cell priming. Here, single CX3CL1-Ig DNA administration, a unique ligand of CX3CR1, together with viral or tumor antigens induced a strong in vivo antigen-specific T cell proliferation and effector function that was enough efficient to protect against a tumor challenge. We also showed that early expression of CX3CL1-Ig and antigens in muscle and lymphoid organs induces an increased in vivo migration of myeloid CD14+CD11c+ DC but not lymphoid CD8alpha+CD11c+ DC at these sites. Thus, by effectively directing DC toward lymphoid organs to encounter T cells, CX3CL1-Ig become a new candidate that augments T cell priming and increases efficiency of vaccination.