Natural history of preexisting AAV5 antibodies in adults with hemophilia B during the lead-in of the etranacogene dezaparvovec phase 3 study

Robert Klamroth^{1

2}, Michael Recht^{3

4}, Nigel S Key⁵, Wolfgang Miesbach⁶, Steven W Pipe⁷, Radoslaw Kaczmarek⁸, Douglass Drelich⁹, Blanca Salazar⁹, Sandra Le Quellec¹⁰, Paul E Monahan⁹, Nicholas Galante⁹, Paul van der Valk¹¹, Jacqueline Tarrant⁹

Affiliations

¹ Vivantes Klinikum, Landsberger Allee 49, 10249 Berlin, Germany.
² Institute of Experimental Hematology and Transfusion Medicine, University Hospital Bonn, Medical Faculty, University of Bonn, Sigmund-Freud-Strasse 25, 53127 Bonn, Germany.
³ Yale School of Medicine, 333 Cedar Street, New Haven, CT 06510, USA.
⁴ National Bleeding Disorders Foundation, 1230 Avenue of the Americas 16th Floor, New York, NY 10020, USA.
⁵ UNC Blood Research Center and Department of Medicine, University of North Carolina, 8008 Mary Ellen Jones Building, CB7035 Chapel Hill, NC 27514, USA.
⁶ Department of Haemostaseology and Haemophilia, University Hospital Frankfurt, Theodor-Stern-Kai 7, 60596 Frankfurt, Germany.
⁷ Departments of Pediatrics and Pathology, University of Michigan, 1500 East Medical Drive, Ann Arbor, MI 48109-5718, USA.
⁸ Department of Pediatrics, Indiana University School of Medicine, 1044 West Walnut Street, R4-116, Indianapolis, IN 46202, USA.
⁹ CSL Behring, 1020 First Avenue, King of Prussia, PA 61501, USA.
¹⁰ CSL Behring Europe, Philipp-Reis-Strasse 2, 65795 Hattersheim am Main, Germany.
¹¹ Center for Benign Haematology, Thrombosis and Haemostasis, University Medical Center Utrecht, University Utrecht, Van Creveldkliniek, Heidelberglaan 100, 3584 CX Utrecht, the Netherlands.

PMID: 40969675
PMCID: PMC12441693
DOI: 10.1016/j.omtm.2025.101568

Natural history of preexisting AAV5 antibodies in adults with hemophilia B during the lead-in of the etranacogene dezaparvovec phase 3 study

Robert Klamroth et al. Mol Ther Methods Clin Dev. 2025.

. 2025 Aug 18;33(3):101568.

doi: 10.1016/j.omtm.2025.101568. eCollection 2025 Sep 11.

Authors

Affiliations

¹ Vivantes Klinikum, Landsberger Allee 49, 10249 Berlin, Germany.
² Institute of Experimental Hematology and Transfusion Medicine, University Hospital Bonn, Medical Faculty, University of Bonn, Sigmund-Freud-Strasse 25, 53127 Bonn, Germany.
³ Yale School of Medicine, 333 Cedar Street, New Haven, CT 06510, USA.
⁴ National Bleeding Disorders Foundation, 1230 Avenue of the Americas 16th Floor, New York, NY 10020, USA.
⁵ UNC Blood Research Center and Department of Medicine, University of North Carolina, 8008 Mary Ellen Jones Building, CB7035 Chapel Hill, NC 27514, USA.
⁶ Department of Haemostaseology and Haemophilia, University Hospital Frankfurt, Theodor-Stern-Kai 7, 60596 Frankfurt, Germany.
⁷ Departments of Pediatrics and Pathology, University of Michigan, 1500 East Medical Drive, Ann Arbor, MI 48109-5718, USA.
⁸ Department of Pediatrics, Indiana University School of Medicine, 1044 West Walnut Street, R4-116, Indianapolis, IN 46202, USA.
⁹ CSL Behring, 1020 First Avenue, King of Prussia, PA 61501, USA.
¹⁰ CSL Behring Europe, Philipp-Reis-Strasse 2, 65795 Hattersheim am Main, Germany.
¹¹ Center for Benign Haematology, Thrombosis and Haemostasis, University Medical Center Utrecht, University Utrecht, Van Creveldkliniek, Heidelberglaan 100, 3584 CX Utrecht, the Netherlands.

PMID: 40969675
PMCID: PMC12441693
DOI: 10.1016/j.omtm.2025.101568

Abstract

Testing for binding or neutralizing antibodies (NAbs) to adeno-associated virus (AAV) is part of the laboratory assessment of people with hemophilia considering AAV-based gene therapy. We evaluated the natural history of NAb titers to AAV serotype 5 (AAV5) in adult males ≥18 years old with hemophilia B (factor IX ≤ 2%) during the lead-in period of a phase 3 trial prior to the infusion of etranacogene dezaparvovec to characterize NAb in addition to immunoglobulin G (IgG) and immunoglobulin M (IgM) anti-AAV5 binding antibody changes over time. At screening, 48% (32/67) of enrolled participants had detectable NAbs (NAb+) with a median titer of 58 (range: 9-3,440). Participant-specific lead-in periods differed and included discontinuers (median duration: 240 days; range: 1-360). The median intra-participant coefficient of variation of NAb titer over time was 25% (range: 2%-154%). NAb seropositivity was associated with older age (p = 0.0065). For participants with detectable anti-AAV5 NAbs and IgG, there was a high correlation of titers at each visit (median r = 0.96; range: 0.92-0.99). IgM anti-AAV5 antibodies were detectable in only 9% of participants, and seroconversion was infrequent. In conclusion, AAV5 NAb test results were consistent over 6 months, which informs the timing of NAb screening when considering gene therapy for hemophilia B.

Keywords: adeno-associated virus serotype 5; anti-AAV5; etranacogene dezaparvovec; factor IX; hemophilia B; neutralizing antibody.

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Conflict of interest statement

R. Klamroth has received grant/research support from Bayer, CSL Behring, Novo Nordisk, Octapharma, and Sobi; consultation/speaker fees from Bayer, Biomarin, Biotest, CSL Behring, Chugai, LFB, Novo Nordisk, Kedrion, Octapharma, Pfizer, Roche, Sanofi, Sobi, and Takeda/Shire. M.R. has received research support from Bayer, BioMarin, CSL Behring, Genentech, Grifols, Hema Biologics, LFB, Novo Nordisk, Octapharma, Sanofi, Spark, Takeda, and uniQure; consultancy fees from Catalyst Biosciences, CSL Behring, Genentech, Hema Biologics, Kedrion, Novo Nordisk, Pfizer, Sanofi, Takeda, and uniQure; and sits on the Board of Directors for the Foundation for Women and Girls with Blood Disorders, and Partners in Bleeding Disorders. B.S., D.D., S.L.Q., P.E.M., and N.G. are employees of CSL Behring; J.T. was an employee of CSL Behring at the time of research. R. Kaczmarek has received research funding from Bayer and consulting or lecture fees from Bayer, BioMarin, Spark, Novo Nordisk, and Pfizer. W.M. has received grant/research support from Bayer, Biotest, CSL Behring, LFB, Novo Nordisk, Octapharma, Pfizer, and Takeda/Shire; consultation/speaker fees from Bayer, BioMarin, Biotest, CSL Behring, Chugai, LFB, Novo Nordisk, Octapharma, Pfizer, Roche, Sobi, and Takeda/Shire; and consultation fees from Bayer, BioMarin, Biotest, CSL Behring, Chugai, Freeline, LFB, Novo Nordisk, Octapharma, Pfizer, Regeneron, Roche, Sanofi, Sobi, Takeda/Shire, and uniQure. S.W.P. has received consultancy fees from ApcinteX/Centessa, ASC Therapeutics, Bayer, BioMarin, CSL Behring, HEMA Biologics, Freeline, LFB, Novo Nordisk, Pfizer, Poseida Therapeutics, Regeneron/Intellia, Roche/Genentech, Sanofi, Takeda, Spark Therapeutics, and uniQure; research funding from Siemens and YewSavin; and holds a membership on a scientific advisory committee for Equilibra Bioscience and GeneVentiv. N.S.K. has received grant/research support and consultant fees from uniQure, BioMarin, and Novo Nordisk. P.v.d.V. has received consultation fees from Bayer.

Figures

**Figure 1**
NAb seroprevalence and titer per age category NAb+ status by age category in the overall population (A; N = 67) and NAb titer by age category of NAb+ participants (B; n = 32) ∗NAb titer measure considered to be an outlier. NAb, neutralizing antibody; NAb+, neutralizing antibody-positive.

**Figure 2**
Plot of NAb values for each participant who was NAb+ at screening and during the lead-in period of at least 6 months (n = 26) Please note that 6 participants were only NAb+ at screening and did not subsequently have positive NAb values during the rest of the lead-in period. AAV5, adeno-associated virus serotype 5; NAb, neutralizing antibody; NAb+, neutralizing antibody-positive.

**Figure 3**
Correlation of NAb and IgG titers at screening in the lead-in safety population (n = 20) ^aPlease note that two patients did not have quantifiable levels of IgG and were therefore omitted from this figure. AAV5, adeno-associated virus serotype 5; IgG, immunoglobulin G; NAb, neutralizing antibody.

**Figure 4**
Longitudinal NAb, IgM, and IgG measurements at visits during the lead-in phase for the participant who experienced seroconversion Please note that circles indicate a titer value

**Figure 5**
Methods used to measure antibodies to AAV5 AAV5 TI/NAb assay (A and B) and the anti-AAV5 IgG and IgM ELISA (C). AAV5, adeno-associated virus serotype 5; ELISA, enzyme-linked immunosorbent assay; HRP, horseradish peroxidase; IgG, immunoglobulin G; IgM, immunoglobulin M; Luc, luciferase; NAb, neutralizing antibody; TI, transduction inhibition. Reprinted from Liu et al. © 2023 Precision for Medicine.

See this image and copyright information in PMC

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Natural history of preexisting AAV5 antibodies in adults with hemophilia B during the lead-in of the etranacogene dezaparvovec phase 3 study

Affiliations

Natural history of preexisting AAV5 antibodies in adults with hemophilia B during the lead-in of the etranacogene dezaparvovec phase 3 study

Authors

Affiliations

Abstract

Conflict of interest statement

Figures

References

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