Conformational characterization of the mammalian-expressed SARS-CoV-2 recombinant receptor binding domain, a COVID-19 vaccine.

The COVID-19 pandemic has caused a large number of diseases worldwide. There are few vaccines to constrain this disease and the value of them is high. In this sense, the antigens of the vaccine platform Soberana, the receptor binding domain from SARS-CoV-2 Spike protein, both the monomeric (mRBD) and dimeric (dRBD) forms, have been developed. This study encompassed several analyses by different techniques like circular dichroism (CD), fluorescence spectroscopy (FS) and Gel Filtration- High Performance Liquid ChLC of mRBD and dRBD. Monomer and dimer exhibited similar far-UV CD spectral characteristics with 54% of ß-sheet content. Similar conformational features according to near-UV CD and FS studies were observed in both RBD. Stress stability studies by far-UV CD, FS, biological activity and GF-HPLC at 37 °C showed that mRBD is very stable. On the other hand, dRBD fluorescent emission showed a shift towards higher wavelengths as the incubation time increases, suggesting exposition of tryptophan residues, unlike what happens with mRBD. Biological activity outcome confirms these results. GF-HPLC profiles showed that in mRBD, the product of molecular stress are dimers and does not increase over time. However, dRBD showed dimer fragmentation as the main degradation species. This study reveals the usefulness of CD techniques for the analysis of degradation of RBD molecules as well as showed the difference in stability of both RBD molecules. Besides, our work provides useful insights into the production of a key protein used in diagnosis and therapeutics to fight COVID-19 pandemia.

Production of an anti-TNFα antibody in murine myeloma cells by perfusion culture.

Infliximab is a mouse/human chimeric IgG1 monoclonal antibody which recognizes the proinflammatory cytokine, tumor necrosis factor α (TNFα), and inhibits receptor interactions, thereby decreasing inflammation and autoimmune response in patients. This monoclonal antibody has been successfully used to treat rheumatoid arthritis, ankylosing spondylitis, and psoriatic arthritis. However, the high treatment cost limits patient access to this biotherapy. One alternative to this problem is the use of biosimilars. In this work, we describe the stable expression and physicochemical characterization of an anti-TNFα antibody. While infliximab is produced in recombinant murine SP2/0 cells, our anti-TNFα IgG antibody was expressed in recombinant murine NS0 myeloma cells. The best anti-TNFα antibody-expressing clone was selected from three clone candidates based on the stability of IgG expression levels, specific productivity as well as TNFα-binding activity compared to commercial infliximab. Our results indicate that the selected cell clone, culture medium, and fermentation mode allowed for the production of an anti-TNFα antibody with similar characteristics to the reference commercially available product. An optimization of the selected culture medium by metabolomics may increase the volumetric productivity of the process to satisfy the demand for this product. Further experiments should be performed to evaluate the biological properties of this anti-TNFα antibody. KEY POINTS: • An anti-TNFα antibody was produced in NS0 cells using perfusion culture. • A proprietary chemically defined culture medium was used to replace commercially available protein-free medium. • The purified anti-TNFα antibody was comparable to the reference marketed product.

Development of a scalable single process for producing SARS-CoV-2 RBD monomer and dimer vaccine antigens.

We have developed a single process for producing two key COVID-19 vaccine antigens: SARS-CoV-2 receptor binding domain (RBD) monomer and dimer. These antigens are featured in various COVID-19 vaccine formats, including SOBERANA 01 and the licensed SOBERANA 02, and SOBERANA Plus. Our approach involves expressing RBD (319-541)-His6 in Chinese hamster ovary (CHO)-K1 cells, generating and characterizing oligoclones, and selecting the best RBD-producing clones. Critical parameters such as copper supplementation in the culture medium and cell viability influenced the yield of RBD dimer. The purification of RBD involved standard immobilized metal ion affinity chromatography (IMAC), ion exchange chromatography, and size exclusion chromatography. Our findings suggest that copper can improve IMAC performance. Efficient RBD production was achieved using small-scale bioreactor cell culture (2 L). The two RBD forms - monomeric and dimeric RBD - were also produced on a large scale (500 L). This study represents the first large-scale application of perfusion culture for the production of RBD antigens. We conducted a thorough analysis of the purified RBD antigens, which encompassed primary structure, protein integrity, N-glycosylation, size, purity, secondary and tertiary structures, isoform composition, hydrophobicity, and long-term stability. Additionally, we investigated RBD-ACE2 interactions, in vitro ACE2 recognition of RBD, and the immunogenicity of RBD antigens in mice. We have determined that both the monomeric and dimeric RBD antigens possess the necessary quality attributes for vaccine production. By enabling the customizable production of both RBD forms, this unified manufacturing process provides the required flexibility to adapt rapidly to the ever-changing demands of emerging SARS-CoV-2 variants and different COVID-19 vaccine platforms.

Safety and immunogenicity of anti-SARS-CoV-2 heterologous scheme with SOBERANA 02 and SOBERANA Plus vaccines: Phase IIb clinical trial in adults.

BACKGROUND: SOBERANA 02 has been evaluated in phase I and IIa studies comparing homologous versus heterologous schedule (this one, including SOBERANA Plus). Here, we report results of immunogenicity, safety, and reactogenicity of SOBERANA 02 in a two- or three-dose heterologous scheme in adults. METHOD: Phase IIb was a parallel, multicenter, adaptive, double-blind, randomized, and placebo-controlled trial. Subjects (n = 810) aged 19-80 years were randomized to receive two doses of SARS-CoV-2 RBD conjugated to tetanus toxoid (SOBERANA 02) and a third dose of dimeric RBD (SOBERANA Plus) 28 days apart; two production batches of active ingredients of SOBERANA 02 were evaluated. Primary outcome was the percentage of seroconverted subjects with ≥4-fold the anti-RBD immunoglobulin G (IgG) concentration. Secondary outcomes were safety, reactogenicity, and neutralizing antibodies. FINDINGS: Seroconversion rate in vaccinees was 76.3% after two doses and 96.8% after the third dose of SOBERANA Plus (7.3% in the placebo group). Neutralizing IgG antibodies were detected against D614G and variants of concern (VOCs) Alpha, Beta, Delta, and Omicron. Specific, functional antibodies were detected 7-8 months after the third dose. The frequency of serious adverse events (AEs) associated with vaccination was very low (0.1%). Local pain was the most frequent AE. CONCLUSIONS: Two doses of SOBERANA 02 were safe and immunogenic in adults. The heterologous combination with SOBERANA Plus increased neutralizing antibodies, detectable 7-8 months after the third dose. TRIAL REGISTRY: https://rpcec.sld.cu/trials/RPCEC00000347 FUNDING: This work was supported by Finlay Vaccine Institute, BioCubaFarma, and the Fondo Nacional de Ciencia y Técnica (FONCI-CITMA-Cuba, contract 2020-20).

Safety and immunogenicity of anti-SARS CoV-2 vaccine SOBERANA 02 in homologous or heterologous scheme: Open label phase I and phase IIa clinical trials.

BACKGROUND: SOBERANA 02 is a COVID-19 vaccine based on SARS-CoV-2 recombinant RBD conjugated to tetanus toxoid (TT). SOBERANA Plus antigen is dimeric-RBD. Here we report safety and immunogenicity from phase I and IIa clinical trials using two-doses of SOBERANA 02 and three-doses (homologous) or heterologous (with SOBERANA Plus) protocols. METHOD: We performed an open-label, sequential and adaptive phase I to evaluate safety and explore the immunogenicity of SOBERANA 02 in two formulations (15 or 25 µg RBD-conjugated to 20 µg of TT) in 40 subjects, 19-59-years-old. Phase IIa was open-label including 100 volunteers 19-80-years, receiving two doses of SOBERANA 02-25 µg. In both trials, half of volunteers were selected to receive a third dose of the corresponding SOBERANA 02 and half received a heterologous dose of SOBERANA Plus. Primary outcome was safety. The secondary outcome was immunogenicity evaluated by anti-RBD IgG ELISA, molecular neutralization of RBD:hACE2 interaction, live-virus-neutralization and specific T-cells response. RESULTS: The most frequent adverse event (AE) was local pain, other AEs had frequencies ≤ 5%. No serious related-AEs were reported. Phase IIa confirmed the safety in 60 to 80-years-old subjects. In phase-I SOBERANA 02-25 µg elicited higher immune response than SOBERANA 02-15 µg and progressed to phase IIa. Phase IIa results confirmed the immunogenicity of SOBERANA 02-25 µg even in 60-80-years. Two doses of SOBERANA02-25 µg elicited an immune response similar to that of the Cuban Convalescent Serum Panel and it was higher after the homologous and heterologous third doses. The heterologous scheme showed a higher immunological response. Anti-RBD IgG neutralized the delta variant in molecular assay, with a 2.5-fold reduction compared to D614G neutralization. CONCLUSIONS: SOBERANA 02 was safe and immunogenic in persons aged 19-80 years, eliciting neutralizing antibodies and specific T-cell response. Highest immune responses were obtained in the heterologous three doses protocol. TRIAL REGISTRY: https://rpcec.sld.cu/trials/RPCEC00000340, https://rpcec.sld.cu/trials/RPCEC00000347.

Purification and Conformational Characterization of a Novel Interleukin-2 Mutein.

Toxicity of high-dose IL-2-based therapies have motivated the development of the IL-2 mutein, which has low expansion properties for regulatory T lymphocytes. The development of two variants (A and B) for the IL-2 mutein purification as well as a conformational comparative study by Circular dichroism (CD) and fluorescence spectroscopy of these products were evaluated. For the first time, in our center, were used of DTT and 2% SDS in the solubilization step to decrease the aggregates on intermediate product, which favors that disulfide bridges are correctly formed during re-folding. A molecular weight of 18 kDa to the monomeric form and of 25-37 kDa to the oligomeric species were estimated by SDS-PAGE. IL-2 mutein showed similar far-UV CD spectral characteristic typical of cytokines with 41% of α-helix content. Batches obtained by Process B showed similar conformational features according near-UV CD and FS studies. However, those obtained by Process A differed in their folding. IL-2 mutein showed that conformational features by near-UV CD were affected by 2% SDS, no variations on secondary structure were observed. Melting temperature values by far-UV CD were higher than 95 °C, indicating a high thermal stability. Finally, the drug product obtained by Process B showed similar conformational characteristics by near-UV CD and FS, and higher biological activity values (7.0 × 103 ng/mL) in the cell proliferation assay with respect to Process A. Also, the recovery was 15% higher than in the Process A and exhibited a 78.48% of purity. Indeed, Process B was selected for the purification.

Screening and selection strategy for the establishment of biosimilar to trastuzumab-expressing CHO-K1 cell lines.

The high prices of biopharmaceuticals or biologics used in the treatment of many diseases limit the access of patients to these novel therapies. One example is the monoclonal antibody trastuzumab, successfully used for breast cancer treatment. An economic alternative is the generation of biosimilars to these expensive biopharmaceuticals. Since antibody therapies may require large doses over a long period of time, robust platforms and strategies for cell line development are essential for the generation of recombinant cell lines with higher levels of expression. Here, we obtained trastuzumab-expressing CHO-K1 cells through a screening and selection strategy that combined the use of host cells pre-adapted to protein-free media and suspension culture and lentiviral vectors. The results demonstrated that the early screening strategy obtained recombinant CHO-K1 cell populations with higher enrichment of IgG-expressing cells. Moreover, the measurement of intracellular heavy chain polypeptide by flow cytometry was a useful metric to characterize the homogeneity of cell population, and our results suggest this could be used to predict the expression levels of monoclonal antibodies in early stages of cell line development. Additionally, we propose an approach using 25 cm2 T-flasks in suspension and shaking culture conditions as a screening tool to identify high producing cell lines. Finally, trastuzumab-expressing CHO-K1 clones were generated and characterized by batch culture, and preliminary results related to HER2-recognition capacity were successful. Further optimization of elements such as gene optimization, vector selection, type of amplification/selection system, cell culture media composition, in combination with this strategy will allow obtaining high producing clones.

Establecimiento del esquema de purificación de los antígenos de SOBERANA®02, SOBERANA®Plus y SOBERANA 01 / Establishment of the purification scheme for SOBERANA®02, SOBERANA®Plus and SOBERANA 01 antigens

La urgente necesidad de desarrollar y producir vacunas seguras y efectivas para garantizar la reducción de la propagación del coronavirus de tipo 2 causante del síndrome respiratorio agudo severo, hizo que el Centro de Inmunología Molecular y el Instituto Finlay de Vacunas, desarrollaran dos vacunas y un candidato vacunal contra la COVID-19, que tienen como componente la molécula del dominio de unión al receptor (aa 319-541) del virus. Para establecer el proceso productivo, se realizaron experimentos en los posibles pasos del proceso de purificación de la molécula del dominio de unión al receptor (aa 319-541), con vistas a su posterior transferencia tecnológica a escala industrial. Dicha molécula está fusionada con una etiqueta de hexahistidina en su extremo C-terminal y presenta nueve residuos de cisteína en su secuencia que forman cuatro enlaces disulfuros intramoleculares, quedando una cisteína libre que permite obtener dos moléculas: dimérica y monomérica, antígenos que forman parte de las vacunas SOBERANA®02 y SOBERANA®Plus y el candidato vacunal SOBERANA 01. Se determinaron las mejores condiciones de adsorción de las matrices cromatográficas de afinidad por quelatos metálicos, intercambio catiónico y exclusión molecular. Se evaluó el desempeño del proceso a escala piloto y se caracterizó la molécula de acuerdo a sus propiedades físico-químicas y biológicas. Los resultados obtenidos mostraron un 60,02 ± 5,15por ciento de recuperación total de la proteína de interés, con más del 98% de pureza en ambas moléculas, una eficiente remoción de contaminantes y una antigenicidad mayor del 90por ciento referido al monómero control del dominio de unión al receptor con 99 por ciento de pureza, lo que demuestra que el proceso establecido es eficiente en la obtención de un producto con la calidad requerida(AU)

The urgent need to develop and produce safe and effective vaccines to guarantee the reduction of the spread of the type 2 coronavirus that causes severe acute respiratory syndrome, led the Center for Molecular Immunology and the Finlay Vaccine Institute to develop two vaccines and one candidate vaccine to combat the 2019 coronavirus pandemic. As part of the establishment of the production process, experiments were carried out on the possible steps of the purification process of the receptor binding domain molecule (aa 319-541) with a view to its subsequent technological transfer on an industrial scale. This molecule is fused with a hexahistidine tag at its C-terminal end and has nine cysteine residues in its sequence that form four intramolecular disulfide bonds; leaving a free cysteine that allows two molecules to be obtained: dimeric and monomeric, which constitute the antigens of the SOBERANA®02 and SOBERANA®Plus vaccines and the SOBERANA 01 vaccine candidate. The best adsorption conditions of the chromatographic matrices of affinity for metal chelates, cationic exchange and molecular exclusion were determined. The performance of the process was evaluated on a pilot scale and the molecule was characterized according to its physical-chemical and biological properties. The results obtained showed a 60.02 ± 5.15percent total recovery of the protein of interest with more than 98% purity in both molecules, an efficient removal of contaminants and an antigenicity greater than 90percent referred to the control monomer of the domain receptor binding with 99% purity; which demonstrates that the established process is efficient in obtaining a product with the required quality(AU)

Conformational characterization of the mammalian-expressed SARS-CoV-2 recombinant receptor binding domain, a COVID-19 vaccine

The COVID-19 pandemic has caused a large number of diseases worldwide. There are few vaccines to constrain this disease and the value of them is high. In this sense, the antigens of the vaccine platform Soberana, the receptor binding domain from SARS-CoV-2 Spike protein, both the monomeric (mRBD) and dimeric (dRBD) forms, have been developed. This study encompassed several analyses by different techniques like circular dichroism (CD), fluorescence spectroscopy (FS) and Gel Filtration- High Performance Liquid ChLC of mRBD and dRBD. Monomer and dimer exhibited similar far-UV CD spectral characteristics with 54% of ß-sheet content. Similar conformational features according to near-UV CD and FS studies were observed in both RBD. Stress stability studies by far-UV CD, FS, biological activity and GF-HPLC at 37 °C showed that mRBD is very stable. On the other hand, dRBD fluorescent emission showed a shift towards higher wavelengths as the incubation time increases, suggesting exposition of tryptophan residues, unlike what happens with mRBD. Biological activity outcome confirms these results. GF-HPLC profiles showed that in mRBD, the product of molecular stress are dimers and does not increase over time. However, dRBD showed dimer fragmentation as the main degradation species. This study reveals the usefulness of CD techniques for the analysis of degradation of RBD molecules as well as showed the difference in stability of both RBD molecules. Besides, our work provides useful insights into the production of a key protein used in diagnosis and therapeutics to fight COVID-19 pandemia.