Efficient production of recombinant secretory IgA against Clostridium difficile toxins in CHO-K1 cells

Enhancing quality and yield of recombinant secretory IgA antibodies in Nicotiana benthamiana by endoplasmic reticulum engineering

The production of complex multimeric secretory immunoglobulins (SIgA) in Nicotiana benthamiana leaves is challenging, with significant reductions in complete protein assembly and consequently yield, being the most important difficulties. Expanding the physical dimensions of the ER to mimic professional antibody-secreting cells can help to increase yields and promote protein folding and assembly. Here, we expanded the ER in N. benthamiana leaves by targeting the enzyme CTP:phosphocholine cytidylyltransferase (CCT), which catalyses the rate-limiting step in the synthesis of the key membrane component phosphatidylcholine (PC). We used CRISPR/Cas to perform site-directed mutagenesis of each of the three endogenous CCT genes in N. benthamiana by introducing frame-shifting indels to remove the auto-inhibitory C-terminal domains. We generated stable homozygous lines of N. benthamiana containing different combinations of the edited genes, including plants where all three isofunctional CCT homologues were modified. Changes in ER morphology in the mutant plants were confirmed by in vivo confocal imaging and substantially increased the yields of two fully assembled SIgAs by prolonging the ER residence time and boosting chaperone accumulation. Through a combination of ER engineering with chaperone overexpression, we increased the yields of fully assembled SIgA by an order of magnitude, reaching almost 1 g/kg fresh leaf weight. This strategy removes a major roadblock to producing SIgA and will likely facilitate the production of other complex multimeric biopharmaceutical proteins in plants.

Impact of Lysine to Methionine Ratios on Antioxidant Capacity and Immune Function in the Rumen of Tibetan Sheep: An RNA-Seq Analysis

With global protein prices on the rise, lowering protein levels in animal feed, together with balancing diet composition and reducing nitrogen emissions, can both reduce the environmental impact of agriculture and save on feed costs. However, the formulation of an ideal amino acid (AA) composition is crucial for better protein utilization by livestock. This study aimed to investigate the effects of different lysine to methionine ratios on the antioxidant capacity and immune function of the rumen in Tibetan sheep. Ninety male Tibetan sheep, weaned at 2 months of age, were randomly divided into three groups (1:1, 2:1 and 3:1 lysine ratios) and subjected to a 100-day feeding trial. RNA sequencing (RNA-seq) was utilized to analyse the impact of different AA ratios on gene expression in rumen tissue, whereas the levels of antioxidant enzymes (total antioxidant capacity [T-AOC], superoxide dismutase [SOD], glutathione peroxidase [GSH-Px] and catalase [CAT]) and immunoglobulins (immunoglobulin A [IgA], immunoglobulin G [IgG] and immunoglobulin M [IgM]) were evaluated. The results indicated that the 1:1 group significantly upregulated the expression of PTGS2, PLA2G12A and PLA2G4 genes, enhancing antioxidant enzyme activity, reducing free radical production and modulating systemic immune responses. COL16A1 and KCNK5 were highly expressed in the protein digestion and absorption pathway, maintaining the structural integrity and function of the rumen epithelium. BMP4 and TGFBR2 were significantly enriched in the cytokine-cytokine receptor interaction pathway and positively correlated with CAT and T-AOC. ITGA8 was upregulated in the 1:1 group, participating in the regulation of various cellular signalling pathways. ATP2B1 was enriched in the cyclic guanosine monophosphate (cGMP)- protein kinase G (PKG) signalling and mineral absorption pathways, primarily influencing oxidative stress and immune responses by regulating intracellular calcium ion concentration. This study demonstrates that a 1:1 lysine to methionine ratio is most beneficial for enhancing the antioxidant capacity and immune function of the rumen in Tibetan sheep.

Multiplex genome editing eliminates lactate production without impacting growth rate in mammalian cells

The Warburg effect, which describes the fermentation of glucose to lactate even in the presence of oxygen, is ubiquitous in proliferative mammalian cells, including cancer cells, but poses challenges for biopharmaceutical production as lactate accumulation inhibits cell growth and protein production. Previous efforts to eliminate lactate production in cells for bioprocessing have failed as lactate dehydrogenase is essential for cell growth. Here, we effectively eliminate lactate production in Chinese hamster ovary and in the human embryonic kidney cell line HEK293 by simultaneous knockout of lactate dehydrogenases and pyruvate dehydrogenase kinases, thereby removing a negative feedback loop that typically inhibits pyruvate conversion to acetyl-CoA. These cells, which we refer to as Warburg-null cells, maintain wild-type growth rates while producing negligible lactate, show a compensatory increase in oxygen consumption, near total reliance on oxidative metabolism, and higher cell densities in fed-batch cell culture. Warburg-null cells remain amenable for production of diverse biotherapeutic proteins, reaching industrially relevant titres and maintaining product glycosylation. The ability to eliminate lactate production may be useful for biotherapeutic production and provides a tool for investigating a common metabolic phenomenon.

Multiplex genome editing eliminates the Warburg Effect without impacting growth rate in mammalian cells

The Warburg effect is ubiquitous in proliferative mammalian cells, including cancer cells, but poses challenges for biopharmaceutical production, as lactate accumulation inhibits cell growth and protein production. Previous efforts to eliminate lactate production via knockout have failed in mammalian bioprocessing since lactate dehydrogenase has proven essential. However, here we eliminated the Warburg effect in Chinese hamster ovary (CHO) and HEK293 cells by simultaneously knocking out lactate dehydrogenase and regulators involved in a negative feedback loop that typically inhibits pyruvate conversion to acetyl-CoA. In contrast to long-standing assumptions about the role of aerobic glycolysis, Warburg-null cells maintain wildtype growth rate while producing negligible lactate. Further characterization of Warburg-null CHO cells showed a compensatory increase in oxygen consumption, a near total reliance on oxidative metabolism, and higher cell densities in fed-batch cell culture. These cells remained amenable for production of diverse biotherapeutic proteins, reaching industrially relevant titers and maintaining product glycosylation. Thus, the ability to eliminate the Warburg effect is an important development for biotherapeutic production and provides a tool for investigating a near-universal metabolic phenomenon.

Stability Engineering of Recombinant Secretory IgA

Secretory IgA (SIgA) presents a promising avenue for mucosal immunotherapy yet faces challenges in expression, purification, and stability. IgA exists in two primary isotypes, IgA1 and IgA2, with IgA2 further subdivided into two common allotypes: IgA2m(1) and IgA2m(2). The major differences between IgA1 and IgA2 are located in the hinge region, with IgA1 featuring a 13-amino acid elongation that includes up to six O-glycosylation sites. Furthermore, the IgA2m(1) allotype lacks a covalent disulfide bond between heavy and light chains, which is present in IgA1 and IgA2m(2). While IgA1 demonstrates superior epitope binding and pathogen neutralization, IgA2 exhibits enhanced effector functions and stability against mucosal bacterial degradation. However, the noncovalent linkage in the IgA2m(1) allotype raises production and stability challenges. The introduction of distinct single mutations aims to facilitate an alternate disulfide bond formation to mitigate these challenges. We compare four different IgA2 versions with IgA1 to further develop secretory IgA antibodies against SARS-CoV-2 for topical delivery to mucosal surfaces. Our results indicate significantly improved expression levels and assembly efficacy of SIgA2 (P221R) in Nicotiana benthamiana. Moreover, engineered SIgA2 displays heightened thermal stability under physiological as well as acidic conditions and can be aerosolized using a mesh nebulizer. In summary, our study elucidates the benefits of stability-enhancing mutations in overcoming hurdles associated with SIgA expression and stability.

Recombinant neutralizing secretory IgA antibodies for preventing mucosal acquisition and transmission of SARS-CoV-2

Passive delivery of antibodies to mucosal sites may be a valuable adjunct to COVID-19 vaccination to prevent infection, treat viral carriage, or block transmission. Neutralizing monoclonal IgG antibodies are already approved for systemic delivery, and several clinical trials have been reported for delivery to mucosal sites where SARS-CoV-2 resides and replicates in early infection. However, secretory IgA may be preferred because the polymeric complex is adapted for the harsh, unstable external mucosal environment. Here, we investigated the feasibility of producing neutralizing monoclonal IgA antibodies against SARS-CoV-2. We engineered two class-switched mAbs that express well as monomeric and secretory IgA (SIgA) variants with high antigen-binding affinities and increased stability in mucosal secretions compared to their IgG counterparts. SIgAs had stronger virus neutralization activities than IgG mAbs and were protective against SARS-CoV-2 infection in an in vivo murine model. Furthermore, SIgA1 can be aerosolized for topical delivery using a mesh nebulizer. Our findings provide a persuasive case for developing recombinant SIgAs for mucosal application as a new tool in the fight against COVID-19.

Non-cytopathic bovine viral diarrhea virus (BVDV) inhibits innate immune responses via induction of mitophagy

Bovine viral diarrhea virus (BVDV) belongs to the genus Pestivirus within the family Flaviviridae. Mitophagy plays important roles in virus-host interactions. Here, we provide evidence that non-cytopathic (NCP) BVDV shifts the balance of mitochondrial dynamics toward fission and induces mitophagy to inhibit innate immune responses. Mechanistically, NCP BVDV triggers the translocation of dynamin-related protein (Drp1) to mitochondria and stimulates its phosphorylation at Ser616, leading to mitochondrial fission. In parallel, NCP BVDV-induced complete mitophagy via Parkin-dependent pathway contributes to eliminating damaged mitochondria to inhibit MAVS- and mtDNA-cGAS-mediated innate immunity responses, mtROS-mediated inflammatory responses and apoptosis initiation. Importantly, we demonstrate that the LIR motif of ERNS is essential for mitophagy induction. In conclusion, this study is the first to show that NCP BVDV-induced mitophagy plays a central role in promoting cell survival and inhibiting innate immune responses in vitro.

The impact of different levels of wheat diets on hepatic oxidative stress, immune response, and lipid metabolism in Tibetan sheep (Ovis aries)

BACKGROUND

Compared with corn, wheat contains higher crude protein, amino acids concentration. However, wheat contains a mass of anti-nutritional factors, resulting in increased of the digesta viscosity and impaired the intestinal function in ruminant.

OBJECTIVE

This study aimed to investigate the effects of substitution of different amounts of wheat for corn on hepatic metabolism in the Tibetan lamb.

METHODS

Ninety Tibetan lambs (Body weight = 12.37 ± 0.92 kg) were randomly assigned to three groups: 0% wheat diet (Control), 10% wheat diet (Low group), and 15% wheat diet (High group). The feeding trial lasted for 130 d, including a 10 d adaption period. Hepatic gene expression profiling was performed via RNA sequencing after the conclusion of the feeding trials.

RESULTS

Results showed that greater level of glutathione peroxidase levels in L group compared with those of the C and H groups (P < 0.05). The immune indexes, including interleukin-1β (IL-1β), immunoglobulin A (IgA), and IgM were also elevated in L group compared with the other groups (P < 0.05). Compared with H group, the hepatocytes were arranged radially, and hepatic plates anastomosed with each other to form a labyrinth-like structure in L group. Transcriptomic analysis showed 872 differentially expressed genes (DEG) between H and L group, of which 755 were down-regulated and 117 were up-regulated. Through Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, 32 pathways were significantly enriched (Q-value < 0.05), such as the cAMP signaling pathway, Th1 and Th2 cell differentiation, leukocyte transendothelial migration, platelet activation and adipocytokine signaling pathway. Additionally, the expression of comment DEGs were verified via quantitative reverse-transcription polymerase chain reaction.

CONCLUSION

In summary, our findings suggest that wheat can be supplemented up to 10% in Tibetan sheep, contributing to improve the hepatic oxidative stress, immune response and lipid metabolism through regulating the expression of related genes.

Neutralising Effects of Different Antibodies on Clostridioides difficile Toxins TcdA and TcdB in a Translational Approach

Given the high prevalence of intestinal disease in humans and animals, there is a strong need for clinically relevant models recapitulating gastrointestinal systems, ideally replacing in vivo models in accordance with the principles of the 3R. We established a canine organoid system and analysed the neutralising effects of recombinant versus natural antibodies on Clostridioides difficile toxins A and B in this in vitro system. Sulforhodamine B cytotoxicity assays in 2D and FITC-dextran barrier integrity assays on basal-out and apical-out organoids revealed that recombinant, but not natural antibodies, effectively neutralised C. difficile toxins. Our findings emphasise that canine intestinal organoids can be used to test different components and suggest that they can be further refined to also mirror complex interactions between the intestinal epithelium and other cells.

Intramuscular mRNA BNT162b2 vaccine against SARS-CoV-2 induces neutralizing salivary IgA

Intramuscularly administered vaccines stimulate robust serum neutralizing antibodies, yet they are often less competent in eliciting sustainable "sterilizing immunity" at the mucosal level. Our study uncovers a strong temporary neutralizing mucosal component of immunity, emanating from intramuscular administration of an mRNA vaccine. We show that saliva of BNT162b2 vaccinees contains temporary IgA targeting the receptor-binding domain (RBD) of severe acute respiratory syndrome coronavirus-2 spike protein and demonstrate that these IgAs mediate neutralization. RBD-targeting IgAs were found to associate with the secretory component, indicating their bona fide transcytotic origin and their polymeric multivalent nature. The mechanistic understanding of the high neutralizing activity provided by mucosal IgA, acting at the first line of defense, will advance vaccination design and surveillance principles and may point to novel treatment approaches and new routes of vaccine administration and boosting.