Development of novel substrates for tumor immunotherapy.

Abstract Acid-terminated polyglycolide microparticles (PG-MP) were prepared as a versatile substrate that could be surface-modified for either immobilization of anti-cd3 and anti-cd28 mAb to activate T cells or sustained release of granulocyte-macrophage colony stimulating factor (GM-CSF) for dendritic cell (DC) recruitment and maturation. PG-MP were prepared with a volume-weighted mean diameter of 56 or 57 μm. Accessible carboxylic acid group concentration was determined by potentiometric titration to be 0.3 mmole/g and corresponded to a zeta potential of −21.87 mV. PG-MP immobilized with either anti-human CD3/CD28 or anti-mouse cd3/cd28 induced significant proliferation of T cells. Intracellular flow cytometry in activated mouse T cells was significant for IFN-γ, but not IL-4. Microparticles surface-modified for GM-CSF release were prepared from either PG-MP or PG pre-treated with poly- l -lysine (PG-Lys) to manipulate surface charge. GM-CSF released from PG-Lys-MP was observed for up to 26 days. The biologic activity of released GM-CSF was confirmed by using a h -GM-CSF-dependent cell line. The efficacy of the α-cd3/cd28-MP and GMCSF-MP was studied in a syngeneic mouse tumor prevention and regression model. Co-injection of Meth A fibrosarcoma cells with α-cd3/cd28-MP and GMCSF-MP completely prevented tumor implantation (0/24). The regression model showed complete tumor regression in four of seven animals and stable disease in three of seven. In the latter study, a dramatic level of DC infiltration was observed compared to controls.