Absorbable microparticulate cation exchanger for immunotherapeutic delivery
Authors: Shalaby Waleed S. W. , Yeh Heidi , Woo Edward , Corbett Joel T. , Gray Heidi , June Carl H. , Shalaby Shalaby W. 
Published: April 2004

An absorbable microparticulate cation exchanger was synthesized as a versatile carrier for biologically active proteins. In this work, acid‐terminated polyglycolide (or polyglycolic acid) microparticulates (PG‐MP) were surface modified for either sustained release of cytokines or as a platform for immunomodulation. The intended goal was to achieve in situ recruitment/maturation of dendritic cells and activation of T cells for tumor immunotherapy. PG‐MP were prepared with a volume weighted mean diameter of 7.02 μ (range: 2.09–14.58 μ). Accessible carboxylic acid groups were determined to be 0.3 mmol/g with a corresponding zeta potential of −21.87 mV in phosphate‐buffered saline. Under low magnification, scanning electron microscopy (SEM) revealed a highly textured surface due to processing from repetitive jet milling. However, a moderately porous architecture was noted at higher magnification. Electron spectroscopy for chemical analysis was used to characterize the PG‐MP surface before and after adsorption of human granulocyte‐macrophage colony stimulating factor (GM‐CSF). Adsorption of GM‐CSF on PG‐MP (PG‐GMCSF) resulted in a modest increase in the surface atomic concentration of nitrogen (0.97%). Pretreating the surface with poly‐L‐lysine (PG/Lys‐GMCSF) prior to adding GM‐CSF produced a nearly threefold increase in the surface nitrogen concentration (4.20% compared to 1.47%). This manipulation not only increased loading content, but also prolonged the release of GM‐CSF released from 6 days to 26 days. ESCA on the post‐release PG‐MP samples (PG‐GMCSF and PG/Lys‐GMCSF) revealed a similar residual surface nitrogen concentration (2.26% vs. 2.35%). The observation was consistent with irreversibly adsorbed GM‐CSF. It is postulated that irreversibly bound GM‐CSF is released over time as a function of microparticulate degradation. Biological activity of released GM‐CSF was confirmed by the proliferation of a GM‐CSF‐dependent cell line (TF‐1) in the presence of microparticulates. PG‐MP mediated activation of T cells was achieved through irreversible adsorption of either antimouse cd3 plus antimouse cd28 monoclonal antibodies (α‐cd3/cd28‐MP) or antihuman CD3 plus antihuman CD28 monoclonal antibodies (α‐CD3/CD28‐MP) on PG‐MP. Irreversibly adsorbed antibodies were capable of activating both resting mouse and human T cells. Intracellular flow cytometry on mouse T cells revealed that nearly 50% of the activated cells produced interferon‐gamma (IFN‐γ). This was consistent with a TH‐1 or cell‐mediated response. In vivo efficacy was evaluated in a mouse flank tumor model showing a significant antitumor effect both alone and in combination. Combination therapy was most effective at preventing tumor implantation (8/8 mice) and was able induce tumor regression (4/7 mice) and/or stable disease (3/7 mice) in a regression model. In these studies, immunohistochemistry was used to confirm local recruitment of dendritic cells. In conclusion, the PG‐MP represents a novel absorbable cation exchanger that can be readily manipulated to deliver biologically active proteins for immunotherapy. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 69B: 173–182, 2004