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Use of Yeast-Secreted In vivo Biotinylated Recombinant Antibodies (Biobodies) in Bead-Based ELISA

Authors' Affiliations: ¹ School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania; ² Molecular Diagnostics Program and ³ Cancer Prevention Program, Public Health Sciences Division, Fred Hutchinson Cancer Research Center, Seattle, Washington; and ⁴ Harvard Medical School, Department of Medical Oncology, Dana-Farber Caner Institute; and ⁵ Department of Pathology, Brigham and Womens Hospital, Harvard Medical School, Boston, Massachusetts

Requests for reprints: Nathalie Scholler, Center for Early Detection and Cure of Ovarian Cancer, School of Medicine, University of Pennsylvania, Philadelphia, PA 96104-6069. Phone: 215-898-0164; Fax: 215-573-5129; E-mail: naths{at}mail.med.upenn.edu.

Purpose: To measure circulating antigens, sandwich ELISA assays require two complementary affinity reagents. Mouse monoclonal antibodies (mAb) and polyclonal antibodies (pAb) are commonly used, but because their production is lengthy and costly, recombinant antibodies are emerging as an attractive alternative.

Experimental Design: We developed a new class of recombinant antibodies called biobodies (Bb) and compared them to mAb for use in serodiagnosis. Bbs were secreted biotinylated in vivo by diploid yeast and used as affinity reagents after Ni purification. Bead-based assays for HE4 and mesothelin were developed using Bbs in combination with pAbs (Bb/pAb assays). To assess precision, reproducibility studies were done using four runs of 16 replicates at six analyte levels for each marker. Pearson correlations and receiver-operator characteristic analyses were done in 214 patient serum samples to directly compare the Bb/pAb assays to mAb assays. Diagnostic performance of the Bb/pAb assay was further assessed in an expanded set of 336 ovarian cancer cases and controls.

Results: On average across analyte levels, Bb/pAb assays yielded within-run and between-run coefficients of variations of 11.7 and 23.8, respectively, for HE4 and 14.0 and 14.5, respectively, for mesothelin. In the subset (n = 214), Pearson correlations of 0.95 for HE4 and 0.92 for mesothelin were observed between mAb and Bb/pAb assays. The area under the curves for the mAb and Bb/pAb assays were not significantly different for HE4 (0.88 and 0.84, respectively; P = 0.20) or mesothelin (0.74 and 0.72, respectively; P = 0.38).

Conclusion: Yeast-secreted Bbs can be used reliably in cost-effective yet highly sensitive bead–based assays for use in large validation studies.