Platforms, advances, and technical challenges in virus-like particles-based vaccines.

Viral infectious diseases threaten human health and global stability. Several vaccine platforms, such as DNA, mRNA, recombinant viral vectors, and virus-like particle-based vaccines have been developed to counter these viral infectious diseases. Virus-like particles (VLP) are considered real, present, licensed and successful vaccines against prevalent and emergent diseases due to their non-infectious nature, structural similarity with viruses, and high immunogenicity. However, only a few VLP-based vaccines have been commercialized, and the others are either in the clinical or preclinical phases. Notably, despite success in the preclinical phase, many vaccines are still struggling with small-scale fundamental research owing to technical difficulties. Successful production of VLP-based vaccines on a commercial scale requires a suitable platform and culture mode for large-scale production, optimization of transduction-related parameters, upstream and downstream processing, and monitoring of product quality at each step. In this review article, we focus on the advantages and disadvantages of various VLP-producing platforms, recent advances and technical challenges in VLP production, and the current status of VLP-based vaccine candidates at commercial, preclinical, and clinical levels.

Corrigendum to "PRAK-03202: A triple antigen virus-like particle vaccine candidate against SARS CoV-2"[Heliyon 7 (10) (October 2021) e08124].

[This corrects the article DOI: 10.1016/j.heliyon.2021.e08124.].

PRAK-03202: A triple antigen virus-like particle vaccine candidate against SARS CoV-2.

The rapid development of safe and effective vaccines against severe acute respiratory syndrome coronavirus 2 (SARS CoV-2) is a necessary response to coronavirus outbreak. Here, we developed PRAK-03202, the world's first triple antigen virus-like particle vaccine candidate, by cloning and transforming SARS-CoV-2 gene segments into a highly characterized S. cerevisiae-based D-Crypt™ platform, which induced SARS CoV-2 specific neutralizing antibodies in BALB/c mice. Immunization using three different doses of PRAK-03202 induced an antigen-specific (spike, envelope, and membrane proteins) humoral response and neutralizing potential. Peripheral blood mononuclear cells from convalescent patients showed lymphocyte proliferation and elevated interferon levels suggestive of epitope conservation and induction of T helper 1-biased cellular immune response when exposed to PRAK-03202. These data support further clinical development and testing of PRAK-03202 for use in humans.

Mycobacterial transcript cleavage factor Gre, exhibits chaperone-like activity.

Gre factors reactivate stalled elongation complexes by enhancing the intrinsic transcript cleavage activity of RNA polymerase. Previous work by us has shown that unlike in Escherichia coli (E.coli), Mycobacterium tuberculosis Gre factor is essential for its survival. Apart from their role in transcription regulation Gre factors have been implicated in stress response. A recent study has shown the role of E.coli GreA as a cellular chaperone, which inhibits aggregation of substrate proteins under heat stress condition. Moreover it was shown that GreA enables E.coli to survive heat shock and oxidative stress. In the current work, we have characterized the moonlighting chaperone activity and its plausible mechanism in Mycobacterium smegmatis Gre (MsGre) factor. We show here that MsGre prevents heat-induced aggregation of the substrate protein and also protects enzymatic activity. Interestingly Gre factor exists as a dimer in solution and does not undergo heat induced oligomerization. From the 8-anilino-1-naphthalene sulfonate (ANS) binding studies MsGre was shown to expose hydrophobic surface upon heat stress that would allow binding to unfolded or partially folded substrate protein. From Circular Dichroism (CD) studies, we also show that MsGre has a stable secondary structure under thermal stress. We propose that the presence of C-terminal FKBP-like fold in MsGre factor that might contribute to its chaperone-like function.

MSMEG_6292, a Mycobacterium smegmatis RNA polymerase secondary channel-binding protein: purification, crystallization and X-ray diffraction analysis.

The transcriptional activity of RNA polymerase (RNAP) is controlled by a diverse set of regulatory factors. A subset of these regulators modulate the activity of RNAP through its secondary channel. Gre factors reactivate stalled elongation complexes by enhancing the intrinsic cleavage activity of RNAP. In the present study, the protein MSMEG_6292, a Gre-factor homologue from Mycobacterium smegmatis, was expressed heterologously in Escherichia coli and purified using standard chromatographic techniques. The hanging-drop vapour-diffusion crystallization method yielded diffraction-quality crystals. The crystals belonged to the trigonal space group P3121 (or its enantiomorph P3221), with unit-cell parameters a = b = 83.15, c = 107.07 Å, α = ß = 90, γ = 120°. The crystals diffracted to better than 3.0 Šresolution. Molecular-replacement attempts did not yield any phasing models; hence, platinum derivatization was carried out with K2PtCl4 and derivative data were collected to 3.4 Šresolution.