A novel Dual Signaling Protein that combines inhibition of CD47/SIRPα ‘don’t eat me’ signaling with targeted activation of 4-1BB to trigger innate and adaptive anti-cancer responses.
The mainstay of treatment for Diffuse Large B cell Lymphoma (DLBCL) is conventional chemotherapy combined with anti-CD20 monoclonal antibody rituximab (RTX). However, a subset of patients will be refractory or develop resistance to treatment and relapse with poor prognosis. Therefore, additional therapeutic options are needed. In this respect, a combination of RTX treatment with a CD47 monoclonal antibody has yielded high objective response rates in patients with relapsed/refractory DLBCL in a recent phase I trial. Here, we report on a new immunotherapeutic protein (Dual Signaling Protein – DSP107) comprised of the extracellular domains of SIRPα and 41BBL, which in addition to blocking CD47-SIRPα signaling delivers the 41BBL-41BB costimulatory signal to tumor localized T-cells. DSP107 is designed to unleash both innate and adaptive T-cell mediated immune responses targeted to the tumor site.
Uptake of fluorescently labeled cancer cells by macrophage and neutrophils was studied in phagocytosis assays with DSP107 alone and in combination with RTX. Activation of 41BB by DSP107 was studied using an HT1080.4-1BB reporter cell line with or without plate-bound CD47 or CHO wt or CHO.CD47 cells. T cell cytotoxicity was studied using SC-1.scFvCD3 with various Effector to Target (E:T) ratios. To study the activity of DSP107 in vivo, PBMCs were inoculated to NSG mice with established SUDHL6 xenografts.
Treatment with DSP107 alone or in combination with RTX augmented phagocytosis of a panel of DLBCL cell lines and primary patient-derived cells by macrophages and neutrophils. After longer-term treatment, an ~85% reduction in remaining tumor cells was detected upon combined DSP107 and RTX treatment compared to medium control. The remaining cancer cells had increased levels of apoptosis. Simultaneously, the binding of DSP107 to CD47 enabled 4-1BB costimulatory signaling in reporter cell line HT1080.4- 1BB only on CD47-coated plates or in co-cultures with CHO cells ectopically expressing human CD47. DSP107 triggered prominent T cell proliferation in mixed cultures of isolated peripheral blood T cells and augmented T cell cytotoxicity in vitro in a concentration and Effector to Target ratio-dependent manner. Finally, injection of peripheral blood mononuclear cells (PBMCs) together with DSP107 in mice with established SUDHL6 xenografts triggered a strong reduction in tumor size compared to treatment with PBMCs alone.
DSP107 clearly inhibits the CD47/SIRPα inhibitory axis and augments the phagocytic removal of cancer cells by innate immune cells. Moreover, the binding of DSP107 to CD47 enables the 4-1BBL-mediated costimulation of antitumor T cell cytotoxicity. Thus, DSP107 activates both innate and adaptive anti-cancer immunity and may be of use for the treatment of DLBCL alone or in combination with RTX.