Endocytosis and Degradation of Monoclonal Antibodies Targeting Human B-Cell Malignancies

Abstract

Seven murine monoclonal antibodies (MoAbs) recognizing differentiation antigens present on B-lymphocytes were analyzed in preclinical studies for their potential use for antibody-targeted therapy of B-cell malignancies. MoAbs HD37 (anti-CD19), 1F5 (anti-CD20), HD6 (anti-CD22), MB-1 (anti-CD37), G28-5 (anti-CDw40), 7.2 (anti-class II), and DA4-4 (anti-IgM) were studied for their binding avidities, immunoreactivities, isotypes, endocytosis rates, degradation rates, and number of binding sites on Daudi cells. Lineweaver-Burke analyses of ¹²⁵I-labeled MoAbs demonstrated immunoreactivities ranging from 59 to 92%. Scatchard analyses of ¹²⁵I-MoAbs demonstrated that five of the antibodies had binding avidities in excess of 10⁹ L/M, whereas MoAbs 1F5 and HD37 had avidities of 3-4 × 10⁸ L/M. CD20, CD37, µ, and HLA Class II were found to be highly expressed (200,000–400,000 binding sites/cell) on Daudi cells whereas CD19, CD22, and CDw40 were less densely expressed (80,000–100,000 sites/cell). DA4-4 (µ), HD6 (CD22), and G28-5 (CDw40) were rapidly internalized by cells, HD37 (CD19) and MB-1 (CD37) underwent endocytosis at an intermediate rate, and 7.2 (class II) and 1F5 (CD20) were internalized slowly. Trichloroacetic acid precipitation and high-performance liquid chromatography revealed the following relative rates of ¹²⁵I-MoAb degradation: DA4-4 (µ) > HD6 (CD22) > HD37 (CD19) > G28-5 (CDw40) > MB-1 (CD37) > 1F5 (CD20) > 7.2 (class II).