Genetic determinants of bovine leukemia virus pathogenesis

The understanding of HTLV-induced disease is hampered by the lack of a suitable animal model allowing the study of both viral replication and leukemogenesis in vivo. Although valuable information has been obtained in different species, such as rabbits, mice, rats, and monkeys, none of these systems was able to conciliate topics as different as viral infectivity, propagation within the host, and generation of leukemic cells. An alternate strategy is based on the understanding of diseases induced by viruses closely related to HTLV-1, like bovine leukemia virus (BLV). Both viruses indeed belong to the same subfamily of retroviruses, harbor a similar genomic organization, and infect and transform cells of the hematopoietic system. The main advantage of the BLV system is that it allows direct experimentation in two different species, cattle and sheep.

Safety and immunogenicity of a respiratory syncytial virus prefusion F (RSVPreF3) candidate vaccine in older adults: phase I/II randomized clinical trial

BACKGROUND

The aim was to investigate safety and immunogenicity of vaccine formulations against respiratory syncytial virus (RSV) containing the stabilized prefusion conformation of RSV fusion protein (RSVPreF3).

METHODS

This phase I/II, randomized, controlled, observer-blind study enrolled 48 young adults (YA; 18-40 years) and 1005 older adults (OA; 60-80 years) between January and August 2019. Participants were randomized into equally sized groups to receive two doses of unadjuvanted (YA and OA) or AS01-adjuvanted (OA) vaccine or placebo two months apart. Vaccine safety and immunogenicity were assessed until one (YA) or 12 months (OA) after second vaccination.

RESULTS

The RSVPreF3 vaccines boosted humoral (RSVPreF3-specific IgG and RSV-A neutralizing antibody) responses, which increased in an antigen-concentration-dependent manner and were highest post-dose one. Compared to pre-vaccination, the geometric mean frequencies of polyfunctional CD4+ T-cells increased after each dose and were significantly higher in adjuvanted than unadjuvanted vaccinees. Post-vaccination immune responses persisted until end of follow-up. Solicited adverse events (AEs) were mostly mild-to-moderate and transient. Despite a higher observed reactogenicity of AS01-containing vaccines, no safety concerns were identified for any assessed formulation.

CONCLUSIONS

Based on safety and immunogenicity profiles, the AS01E-adjuvanted vaccine containing 120 μg of RSVPreF3 was selected for further clinical development.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03814590; URL: https://clinicaltrials.gov/ct2/show/NCT03814590.

Interaction of retroviral Tax oncoproteins with tristetraprolin and regulation of tumor necrosis factor-alpha expression

BACKGROUND

The Tax oncoproteins are transcriptional regulators of viral expression involved in pathogenesis induced by complex leukemogenic retroviruses (or delta-retroviruses, i.e., primate T-cell leukemia viruses and bovine leukemia virus). To better understand the molecular pathways leading to cell transformation, we aimed to identify cellular proteins interacting with Tax.

METHODS

We used a yeast two-hybrid system to identify interacting cellular proteins. Interactions between Tax and candidate interacting cellular proteins were confirmed by glutathione S-transferase (GST) pulldown assays, co-immunoprecipitation, and confocal microscopy. Functional interactions between Tax and one interacting protein, tristetraprolin (TTP), were assessed by analyzing the expression of tumor necrosis factor-alpha (TNF-alpha), which is regulated by TTP, in mammalian cells (HeLa, D17, HEK 293, and RAW 264.7) transiently transfected with combinations of intact and mutant Tax and TTP.

RESULTS

We obtained seven interacting cellular proteins, of which one, TTP, was further characterized. Tax and TTP were found to interact specifically through their respective carboxyl-terminal domains. The proteins colocalized in the cytoplasm in a region surrounding the nucleus of HeLa cells. Furthermore, coexpression of Tax was associated with nuclear accumulation of TTP. TTP is an immediate-early protein that inhibits expression of TNF-alpha at the post-transcriptional level. Expression of Tax reverted this inhibition, both in transient transfection experiments and in stably transfected macrophage cell lines.

CONCLUSION

Tax, through its interactions with the TTP repressor, indirectly increases TNF-alpha expression. This observation is of importance for the cell transformation process induced by leukemogenic retroviruses, because TNF-alpha overexpression plays a central role in pathogenesis.

A chimeric protein containing the N terminus of the adeno-associated virus Rep protein recognizes its target site in an in vivo assay

The Rep78 and Rep68 proteins of adeno-associated virus (AAV) type 2 are involved in DNA replication, regulation of gene expression, and targeting site-specific integration. They bind to a specific Rep recognition sequence (RRS) found in both the viral inverted terminal repeats and the AAVS1 integration locus on human chromosome 19. Previous in vitro studies implied that an N-terminal segment of Rep is involved in DNA recognition, while additional domains might stabilize binding and mediate multimerization. In order to define the minimal requirements for Rep to recognize its target site in the human genome, we developed one-hybrid assays in which DNA-protein interactions are detected in vivo. Chimeric proteins consisting of the N terminus of Rep fused to different oligomerization motifs and a transcriptional activation domain were analyzed for oligomerization, DNA binding, and activation of reporter gene expression. Expression of reporter genes was driven from RRS motifs cloned upstream of minimal promoters and examined in mammalian cells from transfected plasmids and in Saccharomyces cerevisiae from a reporter cassette integrated into the yeast genome. Our results show for the first time that chimeric proteins containing the amino-terminal 244 residues of Rep are able to target the RRS in vitro and in vivo when incorporated into artificial multimers. These studies suggest that chimeric proteins may be used to harness the unique targeting feature of AAV for gene therapy applications.

The homeobox protein MSX2 interacts with tax oncoproteins and represses their transactivation activity

Bovine leukemia virus (BLV) tax is an essential gene involved in the transcriptional activation of viral expression. Tax is also believed to be implicated in leukemogenesis because of its ability to immortalize primary cells in vitro. To gain insight into the molecular pathways mediating the activities of this important gene, we identified cellular proteins interacting with Tax. By means of a two-hybrid approach, we show that Tax specifically interacts with MSX2, a general repressor of gene expression. GST pull-down experiments and co-immunoprecipitation assays further confirmed binding specificity. Furthermore, the N-terminal residues 1-79 of MSX2 are required for binding, whereas the C-terminal residues 201-267 of MSX2 do not play a critical role. Whereas the oncogenic potential of Tax in primary cells was only slightly affected by overexpression of MSX2, the other function of Tax, namely LTR-dependent transcriptional activation, was inhibited by MSX2 in human HeLa and bovine B-lymphoblastoid (BL3) cell lines. This MSX2 repression function can be counteracted by overexpression of transcription factors CREB2 and RAP74. The Tax/MSX2 interplay thus results in repression of viral transcriptional activation possibly acting as a regulatory feedback loop. Importantly, this viral gene silencing is not strictly associated with a concomitant loss of Tax oncogenicity as measured by its ability to immortalize primary cells. And interestingly, MSX2 also interacts with and inhibits the transactivation function of the related Tax1 protein encoded by the Human T-cell leukemia virus type 1 (HTLV-1).

Immunogenicity and Safety Following 1 Dose of AS01E-Adjuvanted Respiratory Syncytial Virus Prefusion F Protein Vaccine in Older Adults: A Phase 3 Trial

BACKGROUND

The recently approved AS01E-adjuvanted respiratory syncytial virus (RSV) prefusion F protein-based vaccine for older adults (RSVPreF3 OA) demonstrated high efficacy against RSV-related disease in ≥60-year-olds.

METHODS

This ongoing phase 3 study in ≥60-year-olds evaluates immune persistence until 3 years after RSVPreF3 OA vaccination. Here, we describe interim results on humoral and cell-mediated immunogenicity, reactogenicity, and safety until 1 year post-dose 1.

RESULTS

In total, 1653 participants were vaccinated. One month post-dose 1, neutralization titers increased 10.5-fold (RSV-A) and 7.8-fold (RSV-B) vs pre-dose 1. Titers then declined to levels 4.4-fold (RSV-A) and 3.5-fold (RSV-B) above pre-dose 1 at month 6 and remained 3.1-fold (RSV-A) and 2.3-fold (RSV-B) above pre-dose 1 levels after 1 year. RSVPreF3-binding immunoglobulin G levels and CD4+ T-cell frequencies showed similar kinetics. Solicited administration-site and systemic adverse events (mostly mild to moderate and transient) were reported by 62.2% and 49.5% of participants. Serious adverse events were reported by 3.9% of participants within 6 months post-dose 1; 1 case was considered vaccine related.

CONCLUSIONS

One RSVPreF3 OA dose elicited cell-mediated and RSV-A- and RSV-B-specific humoral immune responses that declined over time but remained above pre-dose 1 levels for at least 1 year. The vaccine was well tolerated with an acceptable safety profile. Clinical Trials Registration. NCT04732871 (ClinicalTrials.gov).

96. A Candidate Respiratory Syncytial Virus (RSV) Prefusion F Protein Investigational Vaccine (RSVPreF3 OA) Is Immunogenic when Administered in Adults ≥ 60 Years of Age: Results at 6 Months after Vaccination

Background

RSV infections are frequent and can lead to respiratory complications in older adults (OA). However, there is no licensed RSV vaccine yet. Here we present immunogenicity results up to month (M) 6 after vaccination with the RSVPreF3 OA.

Methods

In this phase 3 multi-country ongoing study (NCT04732871), adults ≥ 60 years of age were randomized (3:1:1) to receive RSVPreF3 OA and to be followed up for 3 years. All participants received a dose of RSVPreF3 on day (D) 1. Humoral immune (HI) and cell-mediated immune (CMI) responses were measured in subsets of participants at pre-vaccination (D1), D31 and M6. HI outcomes included RSV-A and RSV-B neutralizing antibody (NAb) geometric mean titers (GMTs) and RSVPreF3-specific immunoglobulin G (IgG) antibody geometric mean concentrations (GMCs). The CMI response was assessed in terms of frequency of RSVPreF3-specific CD4⁺ T-cells and CD8⁺ T-cells expressing at least 2 activation markers including at least 1 cytokine among CD40L, 4-1BB, IL-2, TNF-α, IFN-γ, IL-13, IL-17 (polypositive T-cells).

Results

A total of 1653 participants received a dose of RSVPreF3 OA. Of these, 987 participants were included in the HI subset and 566 in the CMI subset at D1. The RSV-A and RSV-B GMTs and RSVPreF3-specific IgG GMCs increased between D1 and D31 followed by a decline until M6. At D31, RSV-A and RSV-B NAb GMTs were 10.5-fold and 7.8-fold higher than pre-vaccination (Figure), and RSVPreF3-specific IgG antibody GMCs was 12.2-fold higher than pre-vaccination levels. At M6, the RSV-A and RSV-B GMTs were 4.4-fold and 3.5-fold, and RSVPreF3-specific IgG antibody GMCs were 4.7-fold above pre-vaccination levels. The RSVPreF3-specific polypositive CD4⁺ T-cell median frequency (events/10⁶ cells) increased from 191 (below assay quantification limit) to 1339 at D31 and declined to 666 (above assay quantification limit) by M6. No RSVPreF3-specific CD8⁺ T-cell response was detected after RSVPreF3 OA vaccination.

Conclusion

In adults ≥ 60 years of age, 1 dose of RSVPreF3 OA was shown to be immunogenic, with both high HI and specific CMI responses at D31 post-vaccination and remained 3.5–4.7 fold above pre-vaccination levels at M6. This study will continue to monitor the immunogenicity of RSVPreF3 OA up to 3 years.

Funding

GlaxoSmithKline Biologicals SA.

Disclosures

Tino F. Schwarz, Prof. Dr. MD, Biogen, Merck-Serono, Pfizer, Alexion, Bavarian Nordic, Janssen-Cilag, AstraZeneca, Biontech, MSD: Grants|GlaxoSmithKline Biologicals SA: Honoraria John E. Ervin, MD, The Alliance for Multispecialty Research – KCM: Contractual agreement for conduct of study protocol Charles Andrews, MD, GlaxoSmithKline Biologicals SA: Institutional grant|Merck and Boehringer Ingelheim: Consulting fees outside of the submitted work Delphine Collete, PhD, GlaxoSmithKline Biologicals SA: Employee|GlaxoSmithKline Biologicals SA: Stocks/Bonds Magali de Heusch, PhD, GlaxoSmithKline Biologicals SA: Employee|GlaxoSmithKline Biologicals SA: Stocks/Bonds Nathalie De Schrevel, PhD, GlaxoSmithKline Biologicals SA: Employee|GlaxoSmithKline Biologicals SA: Ownership Interest Bruno Salaun, PhD, GlaxoSmithKline Biologicals SA: Employee|GlaxoSmithKline Biologicals SA: Stocks/Bonds Marc Lievens, MSc, GlaxoSmithKline Biologicals SA: Employee|GlaxoSmithKline Biologicals SA: Stocks/Bonds Céline Maréchal, PhD, GlaxoSmithKline Biologicals SA: Employee|GlaxoSmithKline Biologicals SA: Stocks/Bonds Phoebe Nakanwagi, Master’s in Biostatistics, GlaxoSmithKline Biologicals SA: Employee Veronica Hulstrøm, PhD MD, GlaxoSmithKline Biologicals SA: Employee.