Glass particles as an adjuvant: a model for adverse immunogenicity of therapeutic proteins.

Unwanted immune responses to parenterally administered therapeutic proteins pose serious safety and economic risks, but the mechanism(s) by which these responses are generated are unknown. We measured immune responses to aggregates of recombinant murine growth hormone (mGH) formed by agitation or freeze-thawing, two pharmaceutically relevant stresses, as well as to mGH adsorbed on microscopic glass or alum particles. Insoluble aggregates, even at levels below the detection limits of size-exclusion high-performance liquid chromatography analysis (<1%), induce immune responses when administered subcutaneously. Furthermore, we show that application of high hydrostatic pressures (200 MPa) reduces aggregate levels to 0.02 ng/dose and eliminates immunogenicity.