Analysis of SARS-CoV-2 Emergent Variants Following AZD7442 (Tixagevimab/Cilgavimab) for Early Outpatient Treatment of COVID-19 (TACKLE Trial)

INTRODUCTION

AZD7442 (tixagevimab/cilgavimab) comprises neutralising monoclonal antibodies (mAbs) that bind to distinct non-overlapping epitopes on the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein. Viral evolution during mAb therapy can select for variants with reduced neutralisation susceptibility. We examined treatment-emergent SARS-CoV-2 variants during TACKLE (NCT04723394), a phase 3 study of AZD7442 for early outpatient treatment of coronavirus disease 2019 (COVID-19).

METHODS

Non-hospitalised adults with mild-to-moderate COVID-19 were randomised and dosed ≤ 7 days from symptom onset with AZD7442 (n = 452) or placebo (n = 451). Next-generation sequencing of the spike gene was performed on SARS-CoV-2 reverse-transcription polymerase chain reaction-positive nasopharyngeal swabs at baseline and study days 3, 6, and 15 post dosing. SARS-CoV-2 lineages were assigned using spike nucleotide sequences. Amino acid substitutions were analysed at allele fractions (AF; % of sequence reads represented by substitution) ≥ 25% and 3% to 25%. In vitro susceptibility to tixagevimab, cilgavimab, and AZD7442 was evaluated for all identified treatment-emergent variants using a pseudotyped microneutralisation assay.

RESULTS

Longitudinal spike sequences were available for 461 participants (AZD7442, n = 235; placebo, n = 226) and showed that treatment-emergent variants at any time were rare, with 5 (2.1%) AZD7442 participants presenting ≥ 1 substitution in tixagevimab/cilgavimab binding sites at AF ≥ 25%. At AF 3% to 25%, treatment-emergent variants were observed in 15 (6.4%) AZD7442 and 12 (5.3%) placebo participants. All treatment-emergent variants showed in vitro susceptibility to AZD7442.

CONCLUSION

These data indicate that AZD7442 creates a high genetic barrier for resistance and is a feasible option for COVID-19 treatment.

Breakthrough SARS-CoV-2 Infections in the PROVENT Prevention Trial Were Not Associated With AZD7442 (Tixagevimab/Cilgavimab) Resistant Variants

BACKGROUND

We report spike protein-based lineage and AZD7442 (tixagevimab/cilgavimab) neutralizing activity of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants identified from breakthrough infections in the PROVENT preexposure prophylaxis trial.

METHODS

Variants identified from PROVENT participants with reverse-transcription polymerase chain reaction-positive symptomatic illness were phenotypically assessed to determine neutralization susceptibility of variant-specific pseudotyped virus-like particles.

RESULTS

At completion of 6 months' follow-up, no AZD7442-resistant variants were observed in breakthrough coronavirus disease 2019 (COVID-19) cases. SARS-CoV-2 neutralizing antibody titers were similar in breakthrough and nonbreakthrough cases.

CONCLUSIONS

Symptomatic COVID-19 breakthrough cases in PROVENT were not due to resistance-associated substitutions in AZD7442 binding sites or lack of AZD7442 exposure.

CLINICAL TRIALS REGISTRATION

NCT04625725.

Molecular and phenotypic characteristics of RSV infections in infants during two nirsevimab randomized clinical trials

Nirsevimab is a monoclonal antibody that binds to the respiratory syncytial virus (RSV) fusion protein. During the Phase 2b (NCT02878330) and MELODY (NCT03979313) clinical trials, infants received one dose of nirsevimab or placebo before their first RSV season. In this pre-specified analysis, isolates from RSV infections were subtyped, sequenced and analyzed for nirsevimab binding site substitutions; subsequently, recombinant RSVs were engineered for microneutralization susceptibility testing. Here we show that the frequency of infections caused by subtypes A and B is similar across and within the two trials. In addition, RSV A had one and RSV B had 10 fusion protein substitutions occurring at >5% frequency. Notably, RSV B binding site substitutions were rare, except for the highly prevalent I206M:Q209R, which increases nirsevimab susceptibility; RSV B isolates from two participants had binding site substitutions that reduce nirsevimab susceptibility. Overall, >99% of isolates from the Phase 2b and MELODY trials retained susceptibility to nirsevimab.

Nirsevimab binding-site conservation in respiratory syncytial virus fusion glycoprotein worldwide between 1956 and 2021: an analysis of observational study sequencing data

BACKGROUND

Nirsevimab is an extended half-life monoclonal antibody to the respiratory syncytial virus (RSV) fusion protein that has been developed to protect infants for an entire RSV season. Previous studies have shown that the nirsevimab binding site is highly conserved. However, investigations of the geotemporal evolution of potential escape variants in recent (ie, 2015-2021) RSV seasons have been minimal. Here, we examine prospective RSV surveillance data to assess the geotemporal prevalence of RSV A and B, and functionally characterise the effect of the nirsevimab binding-site substitutions identified between 2015 and 2021.

METHODS

We assessed the geotemporal prevalence of RSV A and B and nirsevimab binding-site conservation between 2015 and 2021 from three prospective RSV molecular surveillance studies (the US-based OUTSMART-RSV, the global INFORM-RSV, and a pilot study in South Africa). Nirsevimab binding-site substitutions were assessed in an RSV microneutralisation susceptibility assay. We contextualised our findings by assessing fusion-protein sequence diversity from 1956 to 2021 relative to other respiratory-virus envelope glycoproteins using RSV fusion protein sequences published in NCBI GenBank.

FINDINGS

We identified 5675 RSV A and RSV B fusion protein sequences (2875 RSV A and 2800 RSV B) from the three surveillance studies (2015-2021). Nearly all (25 [100%] of 25 positions of RSV A fusion proteins and 22 [88%] of 25 positions of RSV B fusion proteins) amino acids within the nirsevimab binding site remained highly conserved between 2015 and 2021. A highly prevalent (ie, >40·0% of all sequences) nirsevimab binding-site Ile206Met:Gln209Arg RSV B polymorphism arose between 2016 and 2021. Nirsevimab neutralised a diverse set of recombinant RSV viruses, including new variants containing binding-site substitutions. RSV B variants with reduced susceptibility to nirsevimab neutralisation were detected at low frequencies (ie, prevalence <1·0%) between 2015 and 2021. We used 3626 RSV fusion-protein sequences published in NCBI GenBank between 1956 and 2021 (2024 RSV and 1602 RSV B) to show that the RSV fusion protein had lower genetic diversity than influenza haemagglutinin and SARS-CoV-2 spike proteins.

INTERPRETATION

The nirsevimab binding site was highly conserved between 1956 and 2021. Nirsevimab escape variants were rare and have not increased over time.

FUNDING

AstraZeneca and Sanofi.

Robust humoral and cellular recall responses to AZD1222 attenuate breakthrough SARS-CoV-2 infection compared to unvaccinated

Background

Breakthrough severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in coronavirus disease 2019 (COVID-19) vaccinees typically produces milder disease than infection in unvaccinated individuals.

Methods

To explore disease attenuation, we examined COVID-19 symptom burden and immuno-virologic responses to symptomatic SARS-CoV-2 infection in participants (AZD1222: n=177/17,617; placebo: n=203/8,528) from a 2:1 randomized, placebo-controlled, phase 3 study of two-dose primary series AZD1222 (ChAdOx1 nCoV-19) vaccination (NCT04516746).

Results

We observed that AZD1222 vaccinees had an overall lower incidence and shorter duration of COVID-19 symptoms compared with placebo recipients, as well as lower SARS-CoV-2 viral loads and a shorter median duration of viral shedding in saliva. Vaccinees demonstrated a robust antibody recall response versus placebo recipients with low-to-moderate inverse correlations with virologic endpoints. Vaccinees also demonstrated an enriched polyfunctional spike-specific Th-1-biased CD4+ and CD8+ T-cell response that was associated with strong inverse correlations with virologic endpoints.

Conclusion

Robust immune responses following AZD1222 vaccination attenuate COVID-19 disease severity and restrict SARS-CoV-2 transmission potential by reducing viral loads and the duration of viral shedding in saliva. Collectively, these analyses underscore the essential role of vaccination in mitigating the COVID-19 pandemic.

1160. Treatment-Emergent Viral Variants in the Phase 3 TACKLE Trial Investigating Efficacy and Safety of AZD7442 (Tixagevimab/Cilgavimab) for the Treatment of Mild to Moderate COVID-19 in Adults

Background

AZD7442 (tixagevimab/cilgavimab) is a combination of neutralizing monoclonal antibodies (mAbs) that bind to distinct epitopes on the SARS-CoV-2 spike protein, with neutralization activity against variants including Omicron. In the Phase 3 TACKLE study, AZD7442 significantly reduced severe disease progression or death and was well-tolerated through Day 29. Viral evolution during treatment has the potential for resistance selection, such as variants exhibiting reduced mAb binding. We report genotypic analysis and phenotypic characterization of variants identified over 15 days after AZD7442 treatment in TACKLE.

Methods

In TACKLE (NCT04723394), non-hospitalized adults with mild to moderate COVID19 were randomized and dosed ≤7 days from symptom onset with a single 600-mg AZD7442 dose (2 consecutive intramuscular injections, 300 mg of each antibody; n=452) or placebo (n=451). Next-generation sequencing of the spike gene was performed on SARS-CoV-2 reverse-transcription polymerase chain reaction–positive nasal swabs (at baseline and Days 3, 6, and 15). SARS-CoV-2 lineages were assigned using spike nucleotide sequences. Amino acid substitutions, insertions, and deletions were analyzed at allele fractions (AF, % of sequence reads represented by mutation) ≥25% and 3–25%.

Results

Baseline spike sequences were available from 744 participants (82.4%) (AZD7442, n=380; placebo, n=364); 87% of sequences corresponded to variants of concern/interest; these were balanced between AZD7442 and placebo groups (Table 1). Treatment-emergent (post-dosing) viral variants were rare, with 11 (4.5%) AZD7442 and 3 (1.3%) placebo participants showing the emergence of ≥1 mutation at tixagevimab/cilgavimab binding sites, with an AF ≥25% (Table 2). At AF 3–25%, treatment-emergent viral variants in the AZD7442 binding site were observed in 16 (6.6%) AZD7442 and 15 (6.5%) placebo participants.

Conclusion

Following AZD7442 treatment, low levels of SARS-CoV-2 variants bearing mutations at tixagevimab/cilgavimab binding sites were identified. These data indicate that combination of two antibodies creates a high genetic barrier for resistance, supporting the use of mAb combinations that bind to distinct epitopes for the treatment of COVID-19.

Disclosures

Gustavo H. Kijak, PharmD PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Bahar Ahani, BSC, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Douglas Arbetter, MPH, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Tyler Brady, MS, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Fernando Chuecos, BS, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Vancheswaran Gopalakrishnan, PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Tiffany L. Roe, B.S., AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Nicolette Schuko, MS, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds F.D. Richard Hobbs, FMedSci, AstraZeneca: Grant/Research Support|AstraZeneca: Principal investigator|NIHR Applied Research Collaboration, Oxford Thames Valley: Director|Oxford BRC and NIHR MedTech: Investigator|UKRI and NIHR: Grant/Research Support Francisco Padilla, MD, Amgen: Grant/Research Support|Amgen: Personal fees|AstraZeneca: Grant/Research Support|AstraZeneca: Personal fees|Boehringer Ingelheim: Grant/Research Support|Boehringer Ingelheim: Personal fees|Ferrer: Grant/Research Support|Ferrer: Personal fees|Kowa: Grant/Research Support|Kowa: Personal fees|Medix: Grant/Research Support|Medix: Personal fees|Merck Sharp and Dohme: Grant/Research Support|Merck Sharp and Dohme: Personal fees|Novartis: Grant/Research Support|Novartis: Personal fees|Pfizer: Grant/Research Support|Pfizer: Personal fees|Sanofi: Grant/Research Support|Sanofi: Personal fees|Servier: Grant/Research Support|Servier: Personal fees|Silanes: Grant/Research Support|Silanes: Personal fees Elizabeth J. Kelly, PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Hugh Montgomery, MD, AstraZeneca: Advisor/Consultant|Millfield Medical Ltd: Advisor/Consultant|UK National Institute for Health Research's Comprehensive Biomedical Research Centre at University College London Hospitals: Grant/Research Support Katie Streicher, PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds.

1953. Immune responses, viral shedding, and COVID-19 symptom burden from breakthrough SARS-CoV-2 infection in a 2:1 randomized, double-blind, placebo-controlled Phase 3 study of AZD1222 (ChAdOx1 nCoV-19) vaccination

Background

Breakthrough infections post-COVID-19 vaccination increase with waning immunity and typically produce milder disease than infections in unvaccinated individuals. We investigated immuno-virologic responses and COVID-19 symptom burden upon breakthrough infection in participants from a Phase 3 study of 2-dose primary series AZD1222 vaccination (NCT04516746) to explore disease attenuation.

Methods

Study participants who experienced protocol-defined COVID-19 symptoms initiated a series of illness visits over 28 days with collection of sera, nasopharyngeal (NP) swabs and saliva samples (SS), and documentation of symptoms (data-cut off: July 30, 2021). For baseline-seronegative participants with PCR-confirmed SARS-CoV-2 infection ≥15 days after dose 2 of AZD1222 or placebo we assessed: anti-SARS-CoV-2 spike (S), nucleocapsid (N) and neutralizing antibody (Ab) titers by multiplex immunoassay and SARS-CoV-2 pseudovirus assay in sera; viral load by quantitative RT-PCR in NP swabs; and viral shedding by qualitative and quantitative RT-PCR in SS. Data were stratified by age and SARS-CoV-2 variant, and time since primary series dose 2.

Results

Illness Day 1 (ILL-D1) S Ab GMTs in AZD1222 vaccinees were similar to peak GMTs seen 14 days after dose 2 of AZD1222 and were higher vs placebo at all timepoints. The magnitude of S Ab response differed by age: median GMTs were lower at ILL-D1 and higher at ILL-D14 in vaccinees aged ≥65 vs 18–64 years (Fig.1). ILL-D1 overall, SARS-CoV-2 ancestral, alpha, and epsilon variant viral load titers in NP swabs were lower in vaccinees vs placebo (Fig 2). Mean viral load in NP swabs and viral shedding titers in SS were lower in vaccinees vs placebo at all timepoints. Vaccinees reported fewer COVID-19 symptoms than placebo participants, and experienced shorter symptom duration, particularly for fatigue and difficulty breathing.

Figure 1. SARS-CoV-2 spike IgG antibody titers upon SARS-CoV-2 infection by participant age in AZD1222 vaccinees and placebo recipients during illness visits Figure 2. Quantification of viral load (nasopharyngeal swabs quantitative viral titer) by SARS-CoV-2 variant at Illness Visit Day 1

Conclusion

Improved S Ab responses, lower viral loads, and reduced symptom burden upon breakthrough infection in vaccinees vs placebo recipients, suggest that robust recall responses to AZD1222 vaccination may attenuate COVID-19 disease severity and duration. These findings alongside data on cellular immune responses to breakthrough infection will inform understanding of protective immunity to SARS-CoV-2 infection.

Disclosures

Magdalena E. Sobieszczyk, MD, MPH, Bill and Melinda Gates Foundation: Grant/Research Support|Gilead Sciences: Grant/Research Support|Janssen Global Services, LLC: Grant/Research Support|Merck: Grant/Research Support|National Institute of Allergy and Infectious Diseases (NIAID): Grant/Research Support|National Institutes of Health (NIH): Grant/Research Support|Sanofi Pasteur Inc.: Grant/Research Support Ann R. Falsey, MD, BioFire Diagnostics: Grant/Research Support|Janssen: Grant/Research Support|Merck, Sharp and Dohme: Grant/Research Support|Novavax: Advisor/Consultant|Pfizer: Grant/Research Support Anne F. Luetkemeyer, MD, AstraZeneca: Grant/Research Support|Gilead Sciences: Grant/Research Support Grant C. Paulsen, MD, AstraZeneca: Grant/Research Support|Moderna: Grant/Research Support|Pfizer: Grant/Research Support Sharon A. Riddler, MD, National Institute of Allergy and Infectious Diseases (NIAID): Grant/Research Support|National Institutes of Health (NIH): Grant/Research Support|Novimmune: Advisor/Consultant Merlin L. Robb, MD, Walter Reed Army Institute of Research: Advisor/Consultant Charlotte-Paige M. Rolle, MD, MPH, Gilead Sciences: Board Member|Gilead Sciences: Grant/Research Support|Gilead Sciences: Honoraria|Janssen: Board Member|ViiV Healthcare: Board Member|ViiV Healthcare: Grant/Research Support|ViiV Healthcare: Honoraria|Vindico CME: Honoraria Beverly E. Sha, MD, Gilead Sciences: Grant/Research Support|MATEC: Honoraria|University of Chicago: Grant/Research Support|US Government: Grant/Research Support Bahar Ahani, BSC, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Anastasia A. Aksyuk, PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Himanshu Bansal, MS, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Justin A. Green, MD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Brett Jepson, MS, AstraZeneca: Contractor via Cytel Jill Maaske, MD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Kathryn Shoemaker, MS, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Stephanie Sproule, MMath, AstraZeneca: Contractor via Joule/System One Ann Marie Stanley, PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Deidre Wilkins, BSC, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Tonya L. Villafana, PhD, MPH, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Elizabeth J. Kelly, PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds.

1110. AZD7442 (Tixagevimab/Cilgavimab) Demonstrates Potent In Vitro Activity Against SARS-CoV-2 Spike Variants Identified in Circulation and in Prophylaxis Clinical Studies

Background

AZD7442 is a combination of extended–half-life SARS-CoV-2–neutralizing monoclonal antibodies (tixagevimab/cilgavimab) that bind to distinct epitopes on the SARS-CoV-2 spike protein. In the PROVENT study, a single 300 mg intramuscular dose of AZD7442 demonstrated 77% efficacy for prevention of COVID-19 vs placebo at primary analysis, with 83% efficacy through 6-months follow-up, and was well-tolerated. We report conservation of AZD7442 binding sites and neutralizing activity against pseudotyped virus-like particles (VLPs) harboring spike substitutions identified in surveillance, and clinical SARS-CoV-2 isolates from the PROVENT study.

Methods

Consensus SARS-CoV-2 whole genome sequences were analyzed from open source databases to identify prevalent spike substitutions within the AZD7442 binding site. Phenotypic analyses determined neutralization susceptibility of pseudotyped VLPs with identified spike substitutions. Genotypic analyses were also performed on SARS-CoV-2 spike sequences from PROVENT study (NCT04625725) participants with RT-PCR-positive symptomatic illness.

Results

Most residues in tixagevimab (13/17) and cilgavimab (13/19) binding sites were &gt;99% conserved among global SARS-CoV-2 isolates (N=8,373,740 through Apr 19, 2022). In 2021, AZD7442 binding site polymorphisms emerged among circulating strains (prevalence: R346K, 11%; N440K, 22%; G446S, 15%; S477N, 28%; L452R, 43%; T478K, 70%; E484A, 27%; E484K, 3%; Q493R, 27%), but these did not affect AZD7442 in vitro neutralization potency. AZD7442 retained neutralization activity against variants of concern or interest tested, including Omicron BA.2, with moderate reduction observed for Omicron BA.1. By median 6-months follow-up (Aug 29, 2021, data cut-off) in the PROVENT study, there were no AZD7442-resistant substitutions observed in breakthrough SARS-CoV-2 illness visits.

Conclusion

AZD7442 retained neutralization activity against all SARS-CoV-2 variants of concern or interest evaluated. Binding site substitutions identified in circulation, and in breakthrough SARS-CoV-2 infections following a single 300 mg dose of AZD7442 in the PROVENT study, were not associated with AZD7442 escape.

Disclosures

Kevin M. Tuffy, MS, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Michael E. Abram, PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Tiffany L. Roe, B.S., AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Bahar Ahani, BSC, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Tyler Brady, MS, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Nicolette Schuko, MS, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Lori Clarke, B.S., AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Carolina Caceres, MS, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Tara Kenny, MS, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Virginia Takahashi, B.S., AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Tianhui Zhang, PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds David E. Tabor, PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Gustavo H. Kijak, PharmD PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Elizabeth J. Kelly, PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Katie Streicher, PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds.

94. Pooled analysis of nirsevimab resistance through 150 days post dose in preterm and term infants

Background

Respiratory syncytial virus (RSV) is the major cause of lower respiratory tract infection (LRTI) and hospitalization in infants. In two global pivotal placebo-controlled studies, nirsevimab, a monoclonal antibody to the RSV prefusion (F) protein with extended half-life, reduced medically attended (MA) RSV LRTI versus placebo throughout the RSV season (MELODY (Primary Cohort)/Study 3 (Proposed Dose) Pool, 79.5% efficacy). Here we summarize resistance analyses of all RT-PCR-confirmed RSV isolates from healthy term and preterm infants through 150 days post dose.

Methods

Infants were randomized 2:1 to receive one intramuscular injection of nirsevimab or placebo, prior to their first RSV season. RT-PCR-confirmed RSV isolates were reflexed for genotypic analyses of RSV F and phenotypic analyses of identified substitutions in a recombinant RSV neutralization susceptibility assay.

Results

In the pooled proposed dose analysis of Study 3 (50 mg nirsevimab if < 5 kg at dosing) and MELODY (50 or 100 mg nirsevimab if < 5 kg or ≥5 kg at dosing, respectively), no subject with MA RSV LRTI had an RSV isolate containing nirsevimab resistance-associated substitutions in either treatment group (nirsevimab, RSV A: 0/14 and RSV B: 0/5; placebo, RSV A: 0/35 and RSV B: 0/16). In Study 3 (50 mg nirsevimab if ≥5 kg at dosing), 2/18 subjects in the nirsevimab group and 0/20 subjects in the placebo group with MA RSV LRTI had an RSV isolate harbouring nirsevimab binding site substitutions I64T+K68E+I206M+Q209R (>447-fold) or N208S (>387-fold) that conferred reduced susceptibility to nirsevimab neutralization (nirsevimab, RSV A: 0/9 and RSV B: 2/9; placebo, RSV A: 0/10 and RSV B: 0/10). Subjects with RSV isolates harboring F protein sequence variations that maintained susceptibility to nirsevimab neutralization were balanced between treatment groups with no association with RSV disease severity. No subjects with non-protocol defined MA RSV LRTI cases or hospitalization due to any RSV respiratory illness had an RSV isolate conferring nirsevimab resistance.

Conclusion

Lack of nirsevimab resistance following immunization at the proposed dose supports efficacy and neutralization activity of nirsevimab against both RSV A and B strains throughout the RSV season.

Disclosures

Michael E. Abram, PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Bahar Ahani, BSC, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds David E. Tabor, PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Fiona Fernandes, PhD, AstraZeneca: Stocks/Bonds Deidre Wilkins, BSC, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Anastasia A. Aksyuk, PhD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Kevin M. Tuffy, MS, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Hong Ji, BSc, AstraZeneca: Stocks/Bonds Christine Blaze, BSc, AstraZeneca: Stocks/Bonds Tyler Brady, MS, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Pamela Griffin, MD, AstraZeneca: Stocks/Bonds Amanda Leach, MD, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Tonya L. Villafana, PhD, MPH, AstraZeneca: Employee|AstraZeneca: Stocks/Bonds Mark T. Esser, PhD, AstraZeneca: Stocks/Bonds.

RV144 vaccine imprinting constrained HIV-1 evolution following breakthrough infection

The scale of the HIV-1 epidemic underscores the need for a vaccine. The multitude of circulating HIV-1 strains together with HIV-1’s high evolvability hints that HIV-1 could adapt to a future vaccine. Here, we wanted to investigate the effect of vaccination on the evolution of the virus post-breakthrough infection. We analyzed 2,635 HIV-1 env sequences sampled up to a year post-diagnosis from 110 vaccine and placebo participants who became infected in the RV144 vaccine efficacy trial. We showed that the Env signature sites that were previously identified to distinguish vaccine and placebo participants were maintained over time. In addition, fewer sites were under diversifying selection in the vaccine group than in the placebo group. These results indicate that HIV-1 would possibly adapt to a vaccine upon its roll-out.

Factors influencing estimates of HIV-1 infection timing using BEAST

While large datasets of HIV-1 sequences are increasingly being generated, many studies rely on a single gene or fragment of the genome and few comparative studies across genes have been done. We performed genome-based and gene-specific Bayesian phylogenetic analyses to investigate how certain factors impact estimates of the infection dates in an acute HIV-1 infection cohort, RV217. In this cohort, HIV-1 diagnosis corresponded to the first RNA positive test and occurred a median of four days after the last negative test, allowing us to compare timing estimates using BEAST to a narrow window of infection. We analyzed HIV-1 sequences sampled one week, one month and six months after HIV-1 diagnosis in 39 individuals. We found that shared diversity and temporal signal was limited in acute infection, and insufficient to allow timing inferences in the shortest HIV-1 genes, thus dated phylogenies were primarily analyzed for env, gag, pol and near full-length genomes. There was no one best-fitting model across participants and genes, though relaxed molecular clocks (73% of best-fitting models) and the Bayesian skyline (49%) tended to be favored. For infections with single founders, the infection date was estimated to be around one week pre-diagnosis for env (IQR: 3–9 days) and gag (IQR: 5–9 days), whilst the genome placed it at a median of 10 days (IQR: 4–19). Multiply-founded infections proved problematic to date. Our ability to compare timing inferences to precise estimates of HIV-1 infection (within a week) highlights that molecular dating methods can be applied to within-host datasets from early infection. Nonetheless, our results also suggest caution when using uniform clock and population models or short genes with limited information content.

Molecular dating using phylogenetics allows us to estimate the date of an infection from time-stamped within-host sequences alone. There are large datasets of HIV-1 sequences, but genome and gene analyses are not often performed in parallel and rarely with the possibility to compare results against a known narrow window of infection. We showed that all but the longest genes are near-clonal in acute infection, with little information for dating purposes. For infections with single founders, we estimated the eclipse phase—the time between HIV-1 exposure and the first positive diagnostic test—to last between one and two weeks using env, gag, pol and near full-length genomes. This approach could be used to narrow the date of suspected infection in ongoing clinical trials for the prevention of HIV-1 infection.

Molecular dating and viral load growth rates suggested that the eclipse phase lasted about a week in HIV-1 infected adults in East Africa and Thailand

Most HIV-1 infected individuals do not know their infection dates. Precise infection timing is crucial information for studies that document transmission networks or drug levels at infection. To improve infection timing, we used the prospective RV217 cohort where the window when plasma viremia becomes detectable is narrow: the last negative visit occurred a median of four days before the first detectable HIV-1 viremia with an RNA test, referred below as diagnosis. We sequenced 1,280 HIV-1 genomes from 39 participants at a median of 4, 32 and 170 days post-diagnosis. HIV-1 infections were dated by using sequence-based methods and a viral load regression method. Bayesian coalescent and viral load regression estimated that infections occurred a median of 6 days prior to diagnosis (IQR: 9–3 and 11–4 days prior, respectively). Poisson-Fitter, which analyzes the distribution of hamming distances among sequences, estimated a median of 7 days prior to diagnosis (IQR: 15–4 days) based on sequences sampled 4 days post-diagnosis, but it did not yield plausible results using sequences sampled at 32 days. Fourteen participants reported a high-risk exposure event at a median of 8 days prior to diagnosis (IQR: 12 to 6 days prior). These different methods concurred that HIV-1 infection occurred about a week before detectable viremia, corresponding to 20 days (IQR: 34–15 days) before peak viral load. Together, our methods comparison helps define a framework for future dating studies in early HIV-1 infection.

HIV-1 infected individuals rarely know when they became infected but knowing when an infection occurred provides critical information regarding HIV-1 pathogenesis and epidemiology. Using a unique cohort in which infection was known to have occurred in a narrow interval, we investigated methods to estimate the timing of infections. Several methods suggested that HIV-1 infection typically occurs a median of one week before the infection can be detected by HIV-1 RNA testing. Going forward, we provide a strategy that can be used to elucidate the origin of an acute/early infection.

Platelet-rich plasma promotes the proliferation of human muscle derived progenitor cells and maintains their stemness

Human muscle-derived progenitor cells (hMDPCs) offer great promise for muscle cell-based regenerative medicine; however, prolonged ex-vivo expansion using animal sera is necessary to acquire sufficient cells for transplantation. Due to the risks associated with the use of animal sera, the development of a strategy for the ex vivo expansion of hMDPCs is required. The purpose of this study was to investigate the efficacy of using platelet-rich plasma (PRP) for the ex-vivo expansion of hMDPCs. Pre-plated MDPCs, myoendothelial cells, and pericytes are three populations of hMDPCs that we isolated by the modified pre-plate technique and Fluorescence Activated Cell Sorting (FACS), respectively. Pooled allogeneic human PRP was obtained from a local blood bank, and the effect that thrombin-activated PRP-releasate supplemented media had on the ex-vivo expansion of the hMDPCs was tested against FBS supplemented media, both in vitro and in vivo. PRP significantly enhanced short and long-term cell proliferation, with or without FBS supplementation. Antibody-neutralization of PDGF significantly blocked the mitogenic/proliferative effects that PRP had on the hMDPCs. A more stable and sustained expression of markers associated with stemness, and a decreased expression of lineage specific markers was observed in the PRP-expanded cells when compared with the FBS-expanded cells. The in vitro osteogenic, chondrogenic, and myogenic differentiation capacities of the hMDPCs were not altered when expanded in media supplemented with PRP. All populations of hMDPCs that were expanded in PRP supplemented media retained their ability to regenerate myofibers in vivo. Our data demonstrated that PRP promoted the proliferation and maintained the multi-differentiation capacities of the hMDPCs during ex-vivo expansion by maintaining the cells in an undifferentiated state. Moreover, PDGF appears to be a key contributing factor to the beneficial effect that PRP has on the proliferation of hMDPCs.

Muscle-derived stem/progenitor cell dysfunction in Zmpste24-deficient progeroid mice limits muscle regeneration

INTRODUCTION

Loss of adult stem cell function during aging contributes to impaired tissue regeneration. Here, we tested the aging-related decline in regeneration potential of adult stem cells residing in the skeletal muscle.

METHODS

We isolated muscle-derived stem/progenitor cells (MDSPCs) from progeroid Zmpste24-deficient mice (Zmpste24(-/-)) with accelerated aging phenotypes to investigate whether mutation in lamin A has an adverse effect on muscle stem/progenitor cell function.

RESULTS

Our results indicate that MDSPCs isolated from Zmpste24(-/-) mice show reduced proliferation and myogenic differentiation. In addition, Zmpste24(-/-) MDSPCs showed impaired muscle regeneration, with a limited engraftment potential when transplanted into dystrophic muscle, compared with wild-type (WT) MDSPCs. Exposure of progeroid Zmpste24(-/-) MDSPCs to WT MDSPCs rescued the myogenic differentiation defect in vitro.

CONCLUSIONS

These results demonstrate that adult stem/progenitor cell dysfunction contributes to impairment of tissue regeneration and suggest that factors secreted by functional cells are indeed important for the therapeutic effect of adult stem cells.