Neutropenia in a novel anti-mg-csf autoantibody mouse model

Abstract

Therapeutic use of cytokines in humans can result in the generation of antibodies that bind to the drug. In order to predict the potential effects of an autoantibody response to recombinant human G-CSF therapy, we developed a novel, reproducible mouse model of anti-G-CSF specific humoral immunity. Two groups of mice were immunized and boosted with mouse G-CSF (mG-CSF) chemically conjugated to either KLH or OVA on an alternating schedule. All mice immunized with the mG-CSF conjugates produced high titer, mG-CSF specific IgG responses that lasted for the length of the study (252 days). Significant neutropenia was concurrent with the rise in anti-mG-CSF IgG titers (p < 0.03). Similar to the effects reported for mG-CSF gene knockout, neutrophil counts remained at ∼ 20% of pre-immunization levels through day 252. mG-CSF immune mice had no long-term significant difference in peripheral blood hemoglobin, monocyte, lymphocyte, eosinophil, basophil, platelet, reticulocyte and RBC counts compared to control immunized mice. Similarly, bone marrow colony assays from mG-CSF immune mice demonstrated no effect of mG-CSF neutralization on the numbers or proliferative capacity of CFU-GEMM, CFU-GM and HPP-CFC progenitor cells. Thus, we conclude that generation of a high titer, anti-G-CSF IgG response in mice by immunization with mG-CSF conjugated to highly immunogenic carrier proteins does not completely eliminate neutrophil production and has little to no measurable effect on the steady state levels of other hematopoietic lineage cells. Because the concentration of the anti-G-CSF specific IgG tends to reach very high levels that are sustained in the absence of repeated exogenous antigen application, we speculate that endogenous production of mG-CSF may maintain mG-CSF specific antibody titers in this model.