Transient Expression in HEK-293 Cells in Suspension Culture as a Rapid and Powerful Tool: SARS-CoV-2 N and Chimeric SARS-CoV-2N-CD154 Proteins as a Case Study

In a previous work, we proposed a vaccine chimeric antigen based on the fusion of the SARS-CoV-2 N protein to the extracellular domain of the human CD40 ligand (CD154). This vaccine antigen was named N-CD protein and its expression was carried out in HEK-293 stably transfected cells, grown in adherent conditions and serum-supplemented medium. The chimeric protein obtained in these conditions presented a consistent pattern of degradation. The immunization of mice and monkeys with this chimeric protein was able to induce a high N-specific IgG response with only two doses in pre-clinical experiments. In order to explore ways to diminish protein degradation, in the present work, the N and N-CD proteins were produced in suspension cultures and serum-free media following transient transfection of the HEK-293 clone 3F6, at different scales, including stirred-tank controlled bioreactors. The results showed negligible or no degradation of the target proteins. Further, clones stably expressing N-CD were obtained and adapted to suspension culture, obtaining similar results to those observed in the transient expression experiments in HEK-293-3F6. The evidence supports transient protein expression in suspension cultures and serum-free media as a powerful tool to produce in a short period of time high levels of complex proteins susceptible to degradation, such as the SARS-CoV-2 N protein.

Impact of in vitro HIV infection on human thymic regulatory T cell differentiation

Background

The differentiation and function of immunosuppressive regulatory T cells (Tregs) is dictated by the master transcription factor FoxP3. During HIV infection, there is an increase in Treg frequencies in the peripheral blood and lymphoid tissues. This accentuates immune dysfunction and disease progression. Expression of FoxP3 by thymic Tregs (tTregs) is partially controlled by TGF-β. This cytokine also contributes to Treg development in the peripheral blood and lymphoid tissues. Although TGF-β mediates lymphoid tissue fibrosis and peripheral Treg differentiation in HIV-infected individuals, its role in the induction and maintenance of Tregs within the thymus during HIV infection remains unclear.

Methods

Thymocytes were isolated from fresh human thymic tissues obtained from pediatric patients undergoing cardiac surgery. Infection by both R5- and X4-tropic HIV-1 strains and TGF-β treatment of human thymocytes was performed in an in vitro co-culture model with OP9-DL1 cells expressing Notch ligand delta-like 1 without T cell receptor (TCR) activation.

Results

Despite high expression of CCR5 and CXCR4 by tTregs, FoxP3 +  CD3highCD8- thymocytes were much less prone to in vitro infection with R5- and X4-tropic HIV strains compared to FoxP3-CD3highCD8- thymocytes. As expected, CD3highCD4+ thymocytes, when treated with TGF-β1, upregulated CD127 and this treatment resulted in increased FoxP3 expression and Treg differentiation, but did not affect the rate of HIV infection. FoxP3 expression and Treg frequencies remained unchanged following in vitro HIV infection alone or in combination with TGF-β1.

Conclusion

FoxP3 expression and tTreg differentiation is not affected by in vitro HIV infection alone or the combination of in vitro HIV infection and TGF-β treatment.

Membrane Chromatography-Based Downstream Processing for Cell-Culture Produced Influenza Vaccines

New influenza strains are constantly emerging, causing seasonal epidemics and raising concerns to the risk of a new global pandemic. Since vaccination is an effective method to prevent the spread of the disease and reduce its severity, the development of robust bioprocesses for producing pandemic influenza vaccines is exceptionally important. Herein, a membrane chromatography-based downstream processing platform with a demonstrated industrial application potential was established. Cell culture-derived influenza virus H1N1/A/PR/8/34 was harvested from benchtop bioreactor cultures. For the clarification of the cell culture broth, a depth filtration was selected as an alternative to centrifugation. After inactivation, an anion exchange chromatography membrane was used for viral capture and further processing. Additionally, two pandemic influenza virus strains, the H7N9 subtype of the A/Anhui/1/2013 and H3N2/A/Hong Kong/8/64, were successfully processed through similar downstream process steps establishing optimized process parameters. Overall, 41.3–62.5% viral recovery was achieved, with the removal of 86.3–96.5% host cell DNA and 95.5–99.7% of proteins. The proposed membrane chromatography purification is a scalable and generic method for the processing of different influenza strains and is a promising alternative to the current industrial purification of influenza vaccines based on ultracentrifugation methodologies.

Dynamics and epigenetic signature of regulatory T-cells following antiretroviral therapy initiation in acute HIV infection

BACKGROUND

HIV infection promotes the expansion of immunosuppressive regulatory T-cells (Tregs), contributing to immune dysfunction, tissue fibrosis and disease progression. Early antiretroviral treatment (ART) upon HIV infection improves CD4 count and decreases immune activation. However, Treg dynamics and their epigenetic regulation following early ART initiation remain understudied.

METHODS

Treg subsets were characterized by flow cytometry in 103 individuals, including untreated HIV-infected participants in acute and chronic phases, ART-treated in early infection, elite controllers (ECs), immunological controllers (ICs), and HIV-uninfected controls. The methylation status of six regulatory regions of the foxp3 gene was assessed using MiSeq technology.

FINDINGS

Total Treg frequency increased overtime during HIV infection, which was normalized in early ART recipients. Tregs in untreated individuals expressed higher levels of activation and immunosuppressive markers (CD39, and LAP(TGF-β1)), which remained unchanged following early ART. Expression of gut migration markers (CCR9, Integrin-β7) by Tregs was elevated during untreated HIV infection, while they declined with the duration of ART but not upon early ART initiation. Notably, gut-homing Tregs expressing LAP(TGF-β1) and CD39 remained higher despite early treatment. Additionally, the increase in LAP(TGF-β1)⁺ Tregs overtime were consistent with higher demethylation of conserved non-coding sequence (CNS)-1 in the foxp3 gene. Remarkably, LAP(TGF-β1)-expressing Tregs in ECs were significantly higher than in uninfected subjects, while the markers of Treg activation and gut migration were not different.

INTERPRETATION

Early ART initiation was unable to control the levels of immunosuppressive Treg subsets and their gut migration potential, which could ultimately contribute to gut tissue fibrosis and HIV disease progression.

FUNDING

This study was funded by the Canadian Institutes of Health Research (CIHR, grant MOP 142294) and in part by the AIDS and Infectious Diseases Network of the Réseau SIDA et maladies infectieuses du Fonds de recherche du Québec-Santé (FRQ-S).

Impact of extended-release niacin on immune activation in HIV-infected immunological non-responders on effective antiretroviral therapy

BACKGROUND

Background: Tryptophan (Trp) catabolism into immunosuppressive kynurenine (Kyn) is involved in immune dysregulation during HIV infection. Niacin (vitamin B3) could control the excess of tryptophan depletion and represents a potential strategy to improve immune functions and CD4 count recovery in immunological non-responder HIV-infected individuals on antiretroviral therapy (ART).

METHODS

Methods: In the CTN PT006 phase 2 pilot randomized trial, 20 adults on ART with CD4 ≤ 350 cells/µl, despite an undetectable viral load (VL) for at least 3 months, received 2000 mg of extended-release (ER)-niacin orally once daily for 24 weeks. Side effects, VL, CD4/CD8 counts, lipid profile, T-cell activation and senescence, Tregs and Th17 cell frequencies, Kyn/Trp ratio, and levels of IL-6, IP-10, sST2, I-FABP, and LBP were assessed following ER-niacin treatment.

RESULTS

Results: Thirteen participants completed the study. Treatment was interrupted in 4 patients due to loss of follow-up or personal reasons and 3 patients were discontinued due to comorbidity risks. All participants maintained a VL < 40 copies/ml, while ER-niacin did not affect CD4 and CD8 cell counts. Plasma levels of triglycerides, total, and LDL cholesterol significantly decreased, following ER-niacin treatment. ER-niacin also diminished Kyn plasma levels and slightly decreased CD4 T-cell activation. However, no improvement in CD8 subsets, Kyn/Trp ratio, Th17/Treg balance, and plasma inflammatory markers was observed.

CONCLUSIONS

Conclusions: Although ER-niacin combined with ART was well-tolerated among immune non-responders and decreased plasma lipids, it did not improve systemic inflammation, Kyn/Trp ratio, and CD4 cell recovery. Overall, ER-niacin was not effective to overcome chronic inflammation in PLWH.

Processing of Bronchoalveolar Lavage Fluid and Matched Blood for Alveolar Macrophage and CD4+ T-cell Immunophenotyping and HIV Reservoir Assessment

Bronchoscopy is a medical procedure whereby normal saline is injected into the lungs via a bronchoscope and then suction is applied, removing bronchoalveolar lavage (BAL) fluid. The BAL fluid is rich in cells and can thus provide a 'snapshot' of the pulmonary immune milieu. CD4 T cells are the best characterized HIV reservoirs, while there is strong evidence to suggest that tissue macrophages, including alveolar macrophages (AMs), also serve as viral reservoirs. However, much is still unknown about the role of AMs in the context of HIV reservoir establishment and maintenance. Therefore, developing a protocol for processing BAL fluid to obtain cells that may be used in virological and immunological assays to characterize and evaluate the cell populations and subsets within the lung is relevant for understanding the role of the lungs as HIV reservoirs. Herein, we describe such a protocol, employing standard techniques such as simple centrifugation and flow cytometry. The CD4 T cells and AMs may then be used for subsequent applications, including immunophenotyping and HIV DNA and RNA quantification.

A direct role for murine Cdx proteins in the trunk neural crest gene regulatory network

Numerous studies in chordates and arthropods currently indicate that Cdx proteins have a major ancestral role in the organization of post-head tissues. In urochordate embryos, Cdx loss-of-function has been shown to impair axial elongation, neural tube (NT) closure and pigment cell development. Intriguingly, in contrast to axial elongation and NT closure, a Cdx role in neural crest (NC)-derived melanocyte/pigment cell development has not been reported in any other chordate species. To address this, we generated a new conditional pan-Cdx functional knockdown mouse model that circumvents Cdx functional redundancy as well as the early embryonic lethality of Cdx mutants. Through directed inhibition in the neuroectoderm, we provide in vivo evidence that murine Cdx proteins impact melanocyte and enteric nervous system development by, at least in part, directly controlling the expression of the key early regulators of NC ontogenesis Pax3,Msx1 and Foxd3 Our work thus reveals a novel role for Cdx proteins at the top of the trunk NC gene regulatory network in the mouse, which appears to have been inherited from their ancestral ortholog.

Classical swine fever virus E2 glycoprotein antigen produced in adenovirally transduced PK-15 cells confers complete protection in pigs upon viral challenge

E2 is the major envelope glycoprotein present on the outer surface of the classical swine fever virus (CSFV). It is exposed as a homodimer originated by disulfide linkage and represents an important target for the induction of neutralizing immune responses against the viral infection. The E2his glycoprotein nucleotide sequence used in this work contains the CSFV E2 extracellular domain preceded by the tissue plasminogen signal peptide and a hexa-histidine tag in the 3' terminus. The recombinant antigen was produced at a range of 120-150 microg/mL in the culture media of epithelial kidney pig cells, transduced with a replication defective adenoviral vector (Ad-E2his) generated by means of cloning the E2his sequence in the vector genome. The glycoprotein was obtained from clarified culture media as a homodimer of 110 kDa with purity over 95% after a single affinity chromatography step in Ni-NTA Agarose column. The E2his characterization by lectin-specific binding assay showed the presence of N-linked oligosaccharides of both hybrid and complex types. The protective capacity of E2his was demonstrated in two immunization and challenge experiments in pigs using doses of 15 or 30 microg of the glycoprotein, emulsified in Freund's adjuvant. The intramuscular immunization followed by a unique boost three weeks later, elicited high titers of neutralizing antibodies between the second and the fourth week after the primary vaccination. The immunized animals were fully protected from the viral infection after challenge with 10(5) PLD(50) of homologous CSFV "Margarita" strain administered by intramuscular injection. Consequently, no clinical signs of the disease or viral isolation from lymphocytes were detected in the vaccinated pigs. These results suggest that the E2his antigen produced in mammalian cells may be a feasible vaccine candidate for CSF prevention.