Large-scale production of recombinant miraculin protein in transgenic carrot callus suspension cultures using air-lift bioreactors

Statistical Experimental Designs for cLTB-Syn Vaccine Production Using Daucus carota Cell Suspension Cultures

The carrot-made LTB-Syn antigen (cLTB-Syn) is a vaccine candidate against synucleinopathies based on carrot cells expressing the target antigen LTB and syn epitopes. Therefore, the development of an efficient production process is required with media culture optimization to increase the production yields as the main goal. In this study, the effect of two nitrogen sources (urea and glutamate) on callus cultures producing cLTB-Syn was studied, observing that the addition of 17 mM urea to MS medium favored the biomass yield. To optimize the MS media composition, the influence of seven medium components on biomass and cLTB-Syn production was first evaluated by a Plackett-Burman design (PBD). Then, three factors were further analyzed using a central composite design (CCD) and response surface methodology (RSM). The results showed a 1.2-fold improvement in biomass, and a 4.5-fold improvement in cLTB-Syn production was achieved at the shake-flask scale. At the bioreactor scale, there was a 1.5-fold increase in biomass and a 2.8-fold increase in cLTB-Syn yield compared with the standard MS medium. Moreover, the cLTB-Syn vaccine induced humoral responses in BALB/c mice subjected to either oral or subcutaneous immunization. Therefore, cLTB-Syn is a promising vaccine candidate that will aid in developing immunotherapeutic strategies to combat PD and other neurodegenerative diseases without the need for cold storage, making it a financially viable option for massive immunization.

Improvement of recombinant miraculin production in transgenic tomato by crossbreeding-based genetic background modification

An important optimization step in plant-based recombinant protein production systems is the selection of an appropriate cultivar after a potential host has been determined. Previously, we have shown that transgenic tomatoes of the variety 'Micro-Tom' accumulate incredibly high levels of miraculin (MIR) due to the introduction of MIR gene controlled by a CaMV35S promoter and a heat-shock protein terminator. However, 'Micro-Tom' is unsuitable for commercial production of MIR as it is a dwarf cultivar characterized by small-sized fruit and poor yield. Here, we used the crossbreeding approach to transfer the high MIR accumulation trait of transgenic 'Micro-Tom' tomatoes to 'Natsunokoma' and 'Aichi First', two commercial cultivars producing medium and large fruit sizes, respectively. Fruits of the resultant crossbred lines were larger (~ 95 times), but their miraculin accumulation levels (~ 1,062 μg/g fresh mass) were comparable to the donor cultivar, indicating that the high miraculin accumulation trait was preserved regardless of fruit size or cultivar. Further, the transferred trait resulted in a 3-4 fold increase in overall miraculin production than that of the previously reported line 5B. These findings demonstrate the effectiveness of crossbreeding in improving MIR production in tomatoes and could pave the way for a more efficient production of recombinant proteins in other plants.

Cellular engineering of plant cells for improved therapeutic protein production

In vitro cultured plant cells, in particular the tobacco BY-2 cell, have demonstrated their potential to provide a promising bioproduction platform for therapeutic proteins by integrating the merits of whole-plant cultivation systems with those of microbial and mammalian cell cultures. Over the past three decades, substantial progress has been made in improving the plant cell culture system, resulting in a few commercial success cases, such as taliglucerase alfa (Elelyso^®), the first FDA-approved recombinant pharmaceutical protein derived from plant cells. However, compared to the major expression hosts (bacteria, yeast, and mammalian cells), plant cells are still largely underutilized, mainly due to low productivity and non-human glycosylation. Modern molecular biology tools, in particular RNAi and the latest genome editing technology CRISPR/Cas9, have been used to modulate the genome of plant cells to create new cell lines that exhibit desired "traits" for producing therapeutic proteins. This review highlights the recent advances in cellular engineering of plant cells towards improved recombinant protein production, including creating cell lines with deficient protease levels or humanized glycosylation, and considers potential development in the future.