Controlled release of interleukin-2 for tumour immunotherapy using alginate/chitosan porous microspheres

Porous microspheres were formed by the gelation of two polysaccharides, a polyanionic sodium alginate and a polycationic chitosan, followed by lyophilization which creates the porous structure. Porous microspheres were also formed by gelation of sodium alginate with CaCl2 and gelation of sodium alginate with polylysine. FITC-BSA was incorporated into the microspheres by mixing the protein with the polysaccharide solution prior to gelation. Interleukin-2 (IL-2) was incorporated into the preformed microspheres by diffusion from an external aqueous solution of IL-2. Sustained release of the proteins from porous alginate/chitosan microspheres is of longer duration than from alginate/CaCl2, or from alginate/polylysine microspheres. Activity of the released IL-2 was investigated by determining the induction of cytotoxic T lymphocytes (CTL) when incubated with tumor cells and lymphocytes. It was found that the IL-2 remained active in the alginate/chitosan microspheres since the released IL-2 triggered induction of CTL. Further, IL-2 released in a sustained manner triggered induction of CTL more efficiently than free IL-2. Tumor-killing specific activity of CTL was the same whether induced by the sustained released IL-2 or by the addition of free IL-2.