Mitigating the looming vaccine crisis: production and delivery of plasmid-based vaccines

Trust collapse caused by the Changsheng vaccine crisis in China

BACKGROUND

The public acceptance and implementation of vaccination programs is essential to prevent infectious diseases. However, vaccine adverse events may cause public panic and eventually lead to an increasing number of populations who were hesitant or refuse to participate in these vaccination programs. In 2018, the Changsheng vaccine crisis broke out in mainland China, and 252,600 unqualified DTP vaccines were reported to be used for child vaccination. In this study, we observed media and public reactions toward the vaccine crisis.

METHODS

This study conducted Internet surveillance by four mainstream indicators from July 15th to August 7th, including social media (WeChat, Sina Weibo), online news and Baidu search index. We also analyzed the emotional perceptions of people in crisis through an online questionnaire survey.

RESULTS

During the crisis, huge number of articles emerged on Internet, 125,882,894 articles (including forwarding) on WeChat friends circle, 1,877,660 Sina Weibo posts, 648,265 online news and 4,986,521 Baidu search indexes. Most of these articles were negative and expressed the public's weak confidence to the China-made vaccines. Public confidence in vaccines was undermined by the actions of the manufacturer and the government.

CONCLUSIONS

The DTP vaccine crisis led to panic about immunization and eroded trust in the immunization program and in the government. Restoring public confidence in Chinese-made vaccines will take a long time, and meticulous management in vaccine production, and strict government regulation will help to alleviate public anxiety about vaccine safety and ultimately restore confidence.

Increasing plasmid-based DNA vaccine construct (16 kb pSVK-HBVA) production in Escherichia coli XL10-Gold through optimization of media component

At present, there are production processes to produce protein by Escherichia coli (E. coli) fermentation. Research on the design and optimization of the plasmid fermentation medium, however, is less advanced. The fermentation medium that is optimized for plasmid DNA production is different from the medium that is optimized for protein production. So, establishing a scientific and rational method to optimize the fermentation medium used for plasmid production is very important. Previously, our laboratory developed a novel therapeutic DNA vaccine (named pSVK-HBVA) for hepatitis B based on the alphavirus replicon, and found that E. coli XL10-Gold was the optimal host strain for the production of plasmid pSVK-HBVA. The aim of this study was to establish a scientific and rational method to optimize the fermentation medium used for plasmid production, and investigate the effect of growth medium composition on the production of plasmid pSVK-HBVA harboured in E. coli XL10-Gold, as well as to optimize the medium composition.

The one-factor-at-a-time experiments demonstrated that Luria-Bertani (LB) was the optimal basic medium. The optimal carbon source and nitrogen source were glycerol and home-made proteose peptone, respectively. Based on the Plackett–Burman (PB) design, proteose peptone, glycerol and NH₄Cl were identified as the significant variables, which were further optimized by the steepest ascent (descent) method and central composite design. Growth medium optimization in 500-mL shake flasks by response surface methodology resulted in a maximum volumetric yield of 13.61 mg/L, which was approximately 2.5 times higher than that obtained from the basic medium (LB).

Transposon leads to contamination of clinical pDNA vaccine

We report an unexpected contamination during clinical manufacture of a Human Papilomavirus (HPV) 16 E6 encoding plasmid DNA (pDNA) vaccine, with a transposon originating from the Escherichia coli DH5 host cell genome. During processing, presence of this transposable element, insertion sequence 2 (IS2) in the plasmid vector was not noticed until quality control of the bulk pDNA vaccine when results of restriction digestion, sequencing, and CGE analysis were clearly indicative for the presence of a contaminant. Due to the very low level of contamination, only an insert-specific PCR method was capable of tracing back the presence of the transposon in the source pDNA and master cell bank (MCB). Based on the presence of an uncontrolled contamination with unknown clinical relevance, the product was rejected for clinical use. In order to prevent costly rejection of clinical material, both in-process controls and quality control methods must be sensitive enough to detect such a contamination as early as possible, i.e. preferably during plasmid DNA source generation, MCB production and ultimately during upstream processing. However, as we have shown that contamination early in the process development pipeline (source pDNA, MCB) can be present below limits of detection of generally applied analytical methods, the introduction of "engineered" or transposon-free host cells seems the only 100% effective solution to avoid contamination with movable elements and should be considered when searching for a suitable host cell-vector combination.

Chromatographic Removal of Endotoxins: A Bioprocess Engineer's Perspective

Gram-negative bacteria are widely used for the production of gene-based products such as DNA vaccines and bio-drugs, where endotoxin contamination can occur at any point within the process and its removal is of great concern. In this article, we review the structures of endotoxin and the effects that it causes in vivo. The endotoxin removal strategies are also discussed in the light of the different interaction mechanisms involved between endotoxins and bioproducts particularly plasmid DNA and proteins. For most cases, endotoxin removal is favoured at a highly ionic or acidic condition. Various removal methods particularly chromatography-based techniques are covered in this article according to the relevant applications.

Analysis of selective metal-salt-induced endotoxin precipitation in plasmid DNA purification using improved Limulus amoebocyte lysate assay and central composite design

Recent advancements in plasmid DNA (pDNA) production involve the development of innovative and cost-effective methods as well as reduced number of unit operations. This study investigates the feasibilities of using a metal salt to selectively remove endotoxins from clarified cell lysates containing plasmid DNA. Screening of endotoxin precipitation in various metal salt solutions and optimization of process conditions (pH, ion concentration, temperature, and incubation time) using central composite design experiments have been carried out successfully. Results show that selective endotoxin precipitation (<0.05 EU/μg) can economically be carried out during the alkaline cell lysis procedure (neutralization step) at a pH condition similar to that of alkaline-lysed cell lysate, a low ZnSO(4) concentration (0.5 M), a minimum incubation time (30 min), and a temperature of 15 °C. In summary, this method provides ease of subsequent plasmid DNA purification due to reduced bulk impurities and cost-effective and most importantly high endotoxin removal (>80%) and plasmid recovery (>90%).