Enhancement of the antitumor properties of interleukin-2 by its targeted delivery to the tumor blood vessel extracellular matrix

Anglogenic processes depend on the precise coordination of different cell types and a complex exchange of signals, many of which derive from new specific components of the provisional, angiogenesis-related, extracellular matrix (ECM). Angiogenes is associated ECM components thus represent appealing targets for the selective delivery of therapeutic molecules to newly forming tumor vessels. Results of a previous study indicated that a high affinity recombinant antibody (L19) to ED-B, a domain contained In the anglogenesis-associated isoform of fibronectin (B-FN), selectively and efficiently targets tumor vessels. The present study shows that a fusion protein between L19 and Interleukin 2 (L19-lL-2) mediates the selective delivery and concentration of lL-2 to tumor vasculature, thereby leading to a dramatic enhancement of the therapeutic properties of the cytokine. By contrast, lL-2 fused to an irrelevant recombinant antibody used as a control fusion protein showed neither accumulation in tumors nor therapeutic efficacy. Tumors in mice treated with L19-lL-2 were significantly smaller compared to those in animals treated with saline, the control fusion protein, or lL-2 alone (P = .003, .003, and .002, respectively). Moreover, no significant differences in size were observed among the tumors from the different control groups (using the control fusion protein, a mixture of lL-2 and L19, or saline alone). Immunohistochemical analysis of tumor infiltrates demonstrated a significantly higher number of T lymphocytes, natural killer cells, and macrophages, as well as increased interferon-gamma (IFN-gamma) accumulation, in tumors from animals treated with L19-lL-2 compared to tumors from control groups. The fact that ED-B Is 100% homologous in human and mouse, thus ensuring that L19 reacts equally well with human and murine antigen, should ultimately expedite transfer of this reagent to clinical trials.