Anti-CD20-Interferon-β Fusion Protein Therapy of Murine B-Cell Lymphomas

Type I interferons (IFN alpha/beta) are cytokines with a broad spectrum of antitumor activities including antiproliferative, proapoptotic, and immunostimulatory effects, and are potentially useful in the treatment of B-cell malignancies and other cancers. To improve antitumor potency and diminish the systemic side effects of IFN, we recently developed anti-CD20-IFN alpha fusion proteins with in vitro and in vivo efficacy against both mouse and human lymphomas expressing CD20. As IFN beta binds more tightly to the IFN alpha/beta receptor (IFNAR) and has more potent antitumor activities, we have now constructed an anti-CD20 fusion protein with murine IFN beta (mIFN beta). Anti-CD20-mIFN beta was more potent than recombinant mIFN beta and anti-CD20-mIFN alpha in inhibiting the proliferation of a mouse B-cell lymphoma expressing human CD20 (38C13-huCD20). Growth inhibition was accompanied by caspase-independent apoptosis and DNA fragmentation. The efficacy of anti-CD20-mIFN beta required the physical linkage of mIFN beta to anti-CD20 antibody. Importantly, anti-CD20-mIFN beta was active against tumor cells expressing low levels of IFNAR (38C13-huCD20 IFNAR(lo)). In vivo, established 38C13-huCD20 tumors were largely insensitive to rituximab or a nontargeted mIFN beta fusion protein, yet treatment with anti-CD20-mIFN beta eradicated 83% of tumors. Anti-CD20-mIFN beta was also more potent in vivo against 38C13-huCD20 than anti-CD20-mIFN alpha, curing 75% versus 25% of tumors (P=0.001). Importantly, although anti-CD20-mIFN alpha could not eradicate 38C13-huCD20 IFNAR(lo) tumors, anti-CD20-mIFN beta treatment prolonged survival (P=0.0003), and some animals remained tumor-free. Thus, antibody fusion proteins targeting mIFN beta to tumors show promise as therapeutic agents, especially for use against tumors resistant to the effects of mIFN alpha.