In vivo fluorescence imaging of IgG1 aggregates after subcutaneous and intravenous injection in mice.

PURPOSE: To monitor the biodistribution of IgG1 aggregates upon subcutaneous (SC) and intravenous (IV) administration in mice and measure their propensity to stimulate an early immune response.
METHODS: A human mAb (IgG1) was fluorescently labeled, aggregated by agitation stress and injected in SKH1 mice through SC and IV routes. The biodistribution of monomeric and aggregated formulations was monitored over 47 days by fluorescence imaging and the early immune response was measured by quantifying the level of relevant cytokines in serum using a Bio-plex assay.
RESULTS: The aggregates remained at the SC injection site for a longer time than monomers but after entry into the systemic circulation disappeared faster than monomers. Upon IV administration, both monomers and aggregates spread rapidly throughout the circulation, and a strong accumulation in the liver was observed for both species. Subsequent removal from the circulation was faster for aggregates than monomers. No accumulation in lymph nodes was observed after SC or IV administration. Administration of monomers and aggregates induced similar cytokine levels, but SC injection resulted in higher cytokine levels than IV administration.
CONCLUSION: These results show differences in biodistribution and residence time between IgG1 aggregates and monomers. The long residence time of aggregates at the SC injection site, in conjunction with elevated cytokine levels, may contribute to an enhanced immunogenicity risk of SC injected aggregates compared to that of monomers.