Optimisation of Mycobacterium bovis BCG Fermentation and Storage Survival

Comparison Between Simple Batch and Fed-Batch Bioreactor Cultivation of Recombinant BCG

Background/Objectives: Tuberculosis continues to be a significant global health concern, causing 1.3 million deaths in 2022, particularly affecting children under 5 years old. The Bacillus Calmette-Guérin (BCG) vaccine, developed in 1921, remains the primary defense against tuberculosis but requires modernized production methods. The recombinant BCG-pertussis strain shows potential in providing dual protection against tuberculosis and whooping cough, especially for vulnerable newborns, and enhanced efficacy against bladder cancer. Implementing submerged cultivation techniques for rBCG-pertussis production can offer increased productivity and standardization. Methods: This study explores a fed-batch cultivation strategy with pH-stat control to feed L-glutamic acid through the acid pump into 1 L bioreactor. Three pH values were evaluated for fed-batch and a simple batch without pH control was done for comparison. The viable cell concentration was compared before and after freeze-drying samples harvested during the cultures. Results: L-glutamic acid was identified as the preferred substrate for rBCG-pertussis. While the fed-batch strategy did not enhance the maximum specific growth rate compared to simple batch cultivation, it did improve the specific growth rate after day 4 in the pH 7.4-controlled fed-batch cultures, thereby reducing the cultivation time. Fed-batch cultures controlled at three pH levels exhibited lower optical density than the simple batch, although the viable cell counts were similar. Notably, samples harvested after day 8 from the simple batch cultures showed a reduction in CFU/mL after freeze-drying, whereas all fed-batch samples exhibited high recovery of viable cell counts post lyophilization. Conclusions: The additional glutamate supplied to the fed-batch cultures may have protected the cells during the lyophilization process.

Comparison of Lowenstein Jensen Media and Ogawa Media Usage for Viability Test of BCG Vaccine Pasteur P11732 and Russian (Moscow) - 384 sub-strains

The BCG vaccines on the market have employed a Mycobacterium bovis (M. bovis) sub-strains derived from the initial strain. To date, there has been no recommendation regarding the sub-strains with the highest effectiveness when administered to humans. Because it remains the standard for Tuberculosis treatment, the quality of the BCG vaccine must be verified. The viability test is one of the parameters for BCG vaccine quality control. The culture method has become the gold standard for viability testing with various testing media. The present study aimed to evaluate the performance of Lowenstein Jensen (LJ) and Ogawa media for the viability test of Pasteur 1173P2 and Russian (Moscow) - 384 sub-strains of M. bovis in the BCG vaccine. The number of culturable particles of each sub-strain in the BCG vaccine was estimated and statistically evaluated using the t-test. The colonies of the Pasteur 1173P2 have characteristics; tended to clump on both mediums with tiny, rough, and pale yellow/cream colors. Although the colony character of the Russian (Moscow) - 384 generally has similar feature, it did not cluster and had a smooth texture. In terms of growth rate, LJ and Ogawa media performed similarly for Pasteur 1173P2 and Russian (Moscow) - 384 sub-strains. Maximum growth is reached by the fifth week. The culturable particles of Pasteur P1173P2 sub-strains did not differ between mediums. Whereas the growth of the Russian (Moscow) - 384 sub-strains was statistically better on Ogawa media. The results of this study reveal that the performance of the media used for determining the number of culturable particles is based on the sub-strains of M. bovis present in the BCG vaccine.

RNA Microarray-Based Comparison of Innate Immune Phenotypes between Human THP-1 Macrophages Stimulated with Two BCG Strains

Currently, the only available vaccine against tuberculosis is Mycobacterium bovis Bacille Calmette-Guérin (BCG). Pulmonary tuberculosis protection provided by the vaccine varies depending on the strain, the patient’s age and the evaluated population. Although the adaptive immune responses induced by different BCG strains have been widely studied, little conclusive data is available regarding innate immune responses, especially in macrophages. Here, we aimed to characterize the innate immune responses of human THP-1-derived macrophages at the transcriptional level following a challenge with either the BCG Mexico (M.BCG) or Phipps (P.BCG) strains. After a brief in vitro characterization of the bacterial strains and the innate immune responses, including nitric oxide production and cytokine profiles, we analyzed the mRNA expression patterns and performed pathway enrichment analysis using RNA microarrays. Our results showed that multiple biological processes were enriched, especially those associated with innate inflammatory and antimicrobial responses, including tumor necrosis factor (TNF)-α, type I interferon (IFN-I) and IFN-γ. However, four DEGs were identified in macrophages infected with M.BCG compared to P. BCG. These findings indicated the proinflammatory stimulation of macrophages induced by both BCG strains, at the cytokine level and in terms of gene expression, suggesting a differential expression pattern of innate immune transcripts depending on the mycobacterial strain.

After 100 Years of BCG Immunization against Tuberculosis, What Is New and Still Outstanding for This Vaccine?

In 2021, most of the world was reasonably still concerned about the COVID-19 pandemic, how cases were up and down in different countries, how the vaccination campaigns were ongoing, and most people were familiar with the speed with which vaccines against SARS-Co-V2 were developed, analyzed, and started to be applied in an attempt to curb the pandemic. Because of this, it may have somehow passed relatively inadvertently for people outside of the field that the vaccine used to control tuberculosis (TB), Mycobacterium bovis Bacille Calmette-Guérin (BCG), was first applied to humans a century ago. Over these years, BCG has been the vaccine applied to most human beings in the world, despite its known lack of efficacy to fully prevent respiratory TB. Several strategies have been employed in the last 20 years to produce a novel vaccine that would replace, or boost, immunity and protection elicited by BCG. In this work, to avoid potential redundancies with recently published reviews, I only aim to present my current thoughts about some of the latest findings and outstanding questions that I consider worth investigating to help develop a replacement or modified BCG in order to successfully fight TB, based on BCG itself.