title: Rituximab-mediated depletion of cynomolgus monkey B cells in vitro in different matrices: possible inhibitory effect of IgG.
abstract: The mechanism of rituximab-mediated depletion of nonmalignant CD20+B cells remains to be clarified. In this report, we examine contributions of complement- and cell-dependent killing to the rituximab-mediated depletion of cynomolgus monkey B cells in the in vitro assay. B cell depletion was assessed in whole blood, buffer, autologus plasma (plasma), heat-inactivated plasma (H/I plasma), and cobra venom factor (CVF)-treated plasma matrices in cynomolgus monkey and human samples. Rituximab-mediated B cell depletion in buffer appeared to be greater than that in whole blood or in autologus plasma. Heat inactivation of plasma resulted in the degree of B cell depletion closer to that seen in buffer, whereas CVF treatment of plasma had no effect on B cell depletion. Addition of IgG to the buffer decreased the degree of B cell depletion. The results of these studies imply that (i) plasma components (including complement) are not the mediators of the rituximab-triggered B cell depletion in the in vitro assay, suggesting that cell-mediated mechanisms are likely to be responsible for in vitro killing of normal B cells, and that (ii) some plasma components appear to inhibit rituximab-mediated B cell depletion in the in vitro assay, with IgG identified as a possible inhibitor component.
authors.affiliation: Bioanalytical Research and Development Department, Genentech, Inc., 1 DNA Way, South San Francisco, CA 94080, USA. yulia@gene.com
authors.forename: Yulia
authors.initials: Y
authors.lastname: Vugmeyster
authors.forename: Kathy
authors.initials: K
authors.lastname: Howell
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D058846:Antibodies, Monoclonal, Murine-Derived; D018951:Antigens, CD20 / Q000378:metabolism; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001402:B-Lymphocytes / Q000166:cytology / Q000187:drug effects*; D002021:Buffers; D015922:Complement C1q / Q000502:physiology; D004546:Elapid Venoms / Q000494:pharmacology; D005434:Flow Cytometry; D006801:Humans; D007074:Immunoglobulin G / Q000502:physiology*; D066298:In Vitro Techniques; D008252:Macaca fascicularis; D000069283:Rituximab
chemical_list: D000911:Antibodies, Monoclonal; D058846:Antibodies, Monoclonal, Murine-Derived; D018951:Antigens, CD20; D000970:Antineoplastic Agents; D002021:Buffers; D004546:Elapid Venoms; D007074:Immunoglobulin G; C016310:cobra venom factor; D000069283:Rituximab; D015922:Complement C1q