Anti-CD20-interferon-β fusion protein therapy of murine B cell lymphomas

Type I interferons (IFNα/β) are cytokines with a broad spectrum of anti-tumor activities including anti-proliferative, pro-apoptotic, and immunostimulatory effects, and are potentially useful in the treatment of B cell malignancies and other cancers. To improve anti-tumor potency and diminish the systemic side effects of IFN, we recently developed anti-CD20-IFNα fusion proteins with in vitro and in vivo efficacy against both mouse and human lymphomas expressing CD20. Since IFNβ binds more tightly to the IFNα/β receptor (IFNAR) and has more potent anti-tumor activities, we have now constructed an anti-CD20 fusion protein with murine IFNβ (mIFNβ). Anti-CD20-mIFNβ was more potent than recombinant mIFNβ and anti-CD20-mIFNα 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-mIFNβ required the physical linkage of mIFNβ to anti-CD20 antibody (Ab). Importantly, anti-CD20-mIFNβ was active against tumor cells expressing low levels of IFNAR (38C13-huCD20 IFNARlo). In vivo, established 38C13-huCD20 tumors were largely insensitive to rituximab or a non-targeted mIFNβ fusion protein, yet treatment with anti-CD20-mIFNβ eradicated 83% of tumors. Anti-CD20-mIFNβ was also more potent in vivo against 38C13-huCD20 than anti-CD20-mIFNα, curing 75% versus 25% of tumors (p = 0.001). Importantly, while anti-CD20-mIFNα could not eradicate 38C13-huCD20 IFNARlo tumors, anti-CD20-mIFNβ treatment prolonged survival (p = 0.0003), and some animals remained tumor-free. Thus, Ab fusion proteins targeting mIFNβ to tumors show promise as therapeutic agents, especially for use against tumors resistant to the effects of mIFNα.