Cytokines Delivered by Biodegradable Microspheres Promote Effective Suppression of Human Tumors by Human Peripheral Blood Lymphocytes in the SCID–Winn Model

A new technology for the local and sustained delivery of immunostimulatory molecules to the tumor environment for cancer immunotherapy was evaluated. The ability of cytokines delivered by biodegradable microspheres to promote the antitumor activity of human peripheral blood lymphocytes (PBL) was tested in a human PBL, human tumor, and SCID mouse (SCID–Winn) model. Co-engraftment of human recombinant IL-12–loaded microspheres with human PBL and tumors in SCID mice promoted complete tumor suppression in as many as 100% of the mice, whereas microspheres loaded with polyethyleneglycol–interleukin-2 suppressed but did not eliminate the growth of tumor xenografts. Control microspheres (loaded with bovine serum albumin) in the presence of human PBL or cytokine-loaded microspheres in the absence of human PBL had no tumor-suppressive effect. Coincident with the enhancement of the human PBL-mediated antitumor activity in mice treated with IL-12–loaded microspheres was the production and release of human IFN-&ggr; indicating that IL-12 released from the microspheres results in the activation of the engrafted human PBL. The results establish that biodegradable microspheres represent an effective tool for the local and sustained delivery of cytokines to the tumor environment for cancer immunotherapy.