Antibody Response to Aerosolized Transgenic Human Alpha1-Antitrypsin
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《新英格兰医药杂志》
To the Editor: The Department of Health and Human Services has recommended the development of recombinant counterparts to blood-derived therapeutic human proteins.1 In response to this recommendation, sheep-derived transgenic human alpha1-antitrypsin (AAT) was developed for aerosolized delivery to the lungs. A flock of AAT-transgenic sheep was established by means of the nuclear transfer into sheep ova of normal human AAT complementary DNA linked to the sheep -lactoglobulin promoter.2 Human AAT was isolated from whey from the milk of transgenic sheep and purified (99.9 percent) by sequential chromatography. The major impurities in the final product were sheep AAT and sheep alpha1-antichymotrypsin (ACT), in concentrations ranging from 6.7 to 18.7 mg per liter and 60.3 to 75.8 parts per million, respectively. Purified transgenic AAT differs from normal human AAT only in the structure of three N-linked carbohydrates.
People with a deficiency of AAT are at risk for emphysema as a result of low levels of AAT in the lungs in the presence of neutrophil elastase.3 To evaluate the safety and immunogenicity of transgenic human AAT as augmentation therapy, in two sequential studies we administered 250 mg of aerosolized transgenic AAT daily for eight weeks to 41 subjects with AAT deficiency. A systemic antibody response was defined as a serum IgG antibody titer that exceeded the titer in the sample obtained at the baseline screening by a factor of 4 or more. Among the 41 subjects, antibody responses to sheep AAT occurred in 10, and antibody responses to sheep ACT occurred in 32 (Table 1). No subject had antibody to transgenic human AAT. Four subjects dropped out of the second study because of dyspnea and a decline in lung function. Antibody responses to both major impurities developed in three of these four subjects, including one in whom hypoxemia developed and pulmonary infiltrates were detected on computed tomography of the chest. One subject who participated in both studies had an antibody response to sheep AAT during the second study, with the highest rise in titer (by a factor of 12) of all subjects and a rise in the titer of antibodies to ACT by a factor of more than 16. This subject withdrew from the second study within 10 days after receiving the study drug because of exertional dyspnea and hypoxemia, both of which resolved 4 days after the study drug was discontinued.
Table 1. Adverse Events and Systemic Antibody Responses among a Total of 41 Subjects.
We observed systemic antibody responses to nonhuman protein that was present in very low concentrations in a sheep-derived transgenic human AAT formulation. Among subjects who withdrew from the study, there was a possible relationship between drug-related adverse events and a high-titer antibody response. In the absence of a control group receiving placebo, this relationship is uncertain. The clinical symptoms and secondary antibody responses that occurred in the one subject who participated in both studies suggest that reexposure could result in intolerance of nonhuman-protein impurities. These observations may represent an important obstacle to the development of transgenic human proteins for therapeutic use. Strategies to evaluate immune-mediated toxic effects of preparations of transgenic protein should be established to ensure the development of safe and effective therapies.
L. Terry Spencer, M.D.
University of Florida College of Medicine
Gainesville, FL 32610-0296
John E. Humphries, M.D.
Bayer HealthCare
Research Triangle Park, NC 27709
Mark L. Brantly, M.D.
University of Florida College of Medicine
Gainesville, FL 32610-0296
for the Transgenic Human Alpha 1-Antitrypsin Study Group
Dr. Spencer reports having served as a scientific advisor for Aventis Behring and Bayer HealthCare (which produces plasma-derived alpha1-antitrypsin and has a contractual relationship with PPL Therapeutics, the manufacturer of the transgenic alpha1-antitrypsin used in the studies in this report). Dr. Brantly reports having served as a scientific advisor for Aventis Behring, Bayer HealthCare, PPL Therapeutics, the American Red Cross, and Baxter Biologics.
References
Nightingale SD. Summary of the Advisory Committee on Blood Safety and Availability Meeting on April 27 and 28, 1998. Washington, D.C.: Department of Health and Human Services, 1998. (Accessed April 21, 2005, at http://www.hhs.gov/bloodsafety/summaries/sumapr98.html.)
Wright G, Carver A, Cottom D, et al. High level expression of active human alpha-1-antitrypsin in the milk of transgenic sheep. Biotechnology (N.Y.) 1991;9:830-4.
Blank CA, Brantly M. Clinical features and molecular characteristics of alpha 1-antitrypsin deficiency. Ann Allergy 1994;72:105-120.
People with a deficiency of AAT are at risk for emphysema as a result of low levels of AAT in the lungs in the presence of neutrophil elastase.3 To evaluate the safety and immunogenicity of transgenic human AAT as augmentation therapy, in two sequential studies we administered 250 mg of aerosolized transgenic AAT daily for eight weeks to 41 subjects with AAT deficiency. A systemic antibody response was defined as a serum IgG antibody titer that exceeded the titer in the sample obtained at the baseline screening by a factor of 4 or more. Among the 41 subjects, antibody responses to sheep AAT occurred in 10, and antibody responses to sheep ACT occurred in 32 (Table 1). No subject had antibody to transgenic human AAT. Four subjects dropped out of the second study because of dyspnea and a decline in lung function. Antibody responses to both major impurities developed in three of these four subjects, including one in whom hypoxemia developed and pulmonary infiltrates were detected on computed tomography of the chest. One subject who participated in both studies had an antibody response to sheep AAT during the second study, with the highest rise in titer (by a factor of 12) of all subjects and a rise in the titer of antibodies to ACT by a factor of more than 16. This subject withdrew from the second study within 10 days after receiving the study drug because of exertional dyspnea and hypoxemia, both of which resolved 4 days after the study drug was discontinued.
Table 1. Adverse Events and Systemic Antibody Responses among a Total of 41 Subjects.
We observed systemic antibody responses to nonhuman protein that was present in very low concentrations in a sheep-derived transgenic human AAT formulation. Among subjects who withdrew from the study, there was a possible relationship between drug-related adverse events and a high-titer antibody response. In the absence of a control group receiving placebo, this relationship is uncertain. The clinical symptoms and secondary antibody responses that occurred in the one subject who participated in both studies suggest that reexposure could result in intolerance of nonhuman-protein impurities. These observations may represent an important obstacle to the development of transgenic human proteins for therapeutic use. Strategies to evaluate immune-mediated toxic effects of preparations of transgenic protein should be established to ensure the development of safe and effective therapies.
L. Terry Spencer, M.D.
University of Florida College of Medicine
Gainesville, FL 32610-0296
John E. Humphries, M.D.
Bayer HealthCare
Research Triangle Park, NC 27709
Mark L. Brantly, M.D.
University of Florida College of Medicine
Gainesville, FL 32610-0296
for the Transgenic Human Alpha 1-Antitrypsin Study Group
Dr. Spencer reports having served as a scientific advisor for Aventis Behring and Bayer HealthCare (which produces plasma-derived alpha1-antitrypsin and has a contractual relationship with PPL Therapeutics, the manufacturer of the transgenic alpha1-antitrypsin used in the studies in this report). Dr. Brantly reports having served as a scientific advisor for Aventis Behring, Bayer HealthCare, PPL Therapeutics, the American Red Cross, and Baxter Biologics.
References
Nightingale SD. Summary of the Advisory Committee on Blood Safety and Availability Meeting on April 27 and 28, 1998. Washington, D.C.: Department of Health and Human Services, 1998. (Accessed April 21, 2005, at http://www.hhs.gov/bloodsafety/summaries/sumapr98.html.)
Wright G, Carver A, Cottom D, et al. High level expression of active human alpha-1-antitrypsin in the milk of transgenic sheep. Biotechnology (N.Y.) 1991;9:830-4.
Blank CA, Brantly M. Clinical features and molecular characteristics of alpha 1-antitrypsin deficiency. Ann Allergy 1994;72:105-120.