Abstract B044: Development of a highly potent humanized antibody against CD178: A novel therapeutic target in immuno-oncology
Authors: Cerillo Georgia , Ryan Anderson J , Davis Peter D 
Published: March 2020

Abstract
CD178 (FASLG) is an emerging therapeutic target in immuno-oncology (IO) since CD178/CD95-dependent signalling plays several crucial roles in regulating the immune response to tumours including T cell persistence/survival, T cell exclusion and tumour-dependent T cell killing. Using the mouse hybridoma approach antibodies were raised against the extracellular domain (Pro134-Leu281) of recombinant human CD178. Clone 2B11 was selected for humanisation based on its excellent potency and lack of problem residues in the CDR. Following humanisation by CDR grafting and the introduction of additional mutations to improve affinity and biophysical properties, FBP002 was selected as a potential therapeutic candidate. FB-002 is an IgG4 (S228P) isotype antibody that binds CD178 with high potency in in vitro ELISA assays (IC50 161 pM; 24 ng/mL) and in Surface Plasmon Resonance (SPR) studies (KD of 97 pM). In cellular assays, FBP002 inhibits cell death induced by CD178 in both Jurkat A3 cells (IC50 2.1 ng/mL) and in unstimulated CD4+ human donor T cells (IC50 37 ng/mL). In a model of activation-induced cell death, FBP002 inhibited anti-CD3/anti-CD28 induced cytotoxicity in Jurkat A3 cells (IC50 418 ng/mL). Repeated stimulation of effector T cells can severely limit their function and blunt their anti-tumour response. To investigate the role of CD178 in sustaining T cell activation, we employed a T cell re-stimulation assay by treating human PBMCs with staphylococcal enterotoxin B (SEB) super-antigen for 5 days to activate T cells, followed by IL2 incubation for 14 days, and then a secondary treatment with SEB for 5/6 days. FBP002 significantly (p&lt;0.05) increased cell proliferation following secondary SEB treatment and was also associated with a significant increase in IFNγ production measured by ELISA (p&lt;0.05). FBP002 was more effective than either anti-PD-1 or anti-PD-L1 in this re-stimulation assay and enhanced both PD-1 and PD-L1 activity suggesting a non-overlapping role for CD178 in maintaining the function of activated T cells. To investigate in vivo effects, subcutaneous MC38 murine colon tumours were established in syngeneic immune competent female C57BL/6 mice. Once tumours reached 100 mm3, mice were treated with a surrogate anti-murine CD178 antibody (10 mg/kg i.p. twice weekly), or an isotype control. Anti-CD178 antibody treatment was well tolerated (no body weight loss) and significantly delayed MC38 tumour growth (p&lt;0.05). Immunohistchemistry and image analysis demonstrated that the anti-tumour effect was associated with an increased CD8/Treg ratio in the tumour suggesting that inhibiting CD178 signalling disproportionately protects effector T cells from apoptosis leading to a more effective immune response. In conclusion, we have developed FBP002, a highly potent humanised anti-CD178 antibody that we anticipate will have broad therapeutic potential in the immunological treatment of tumours both as a monotherapy and in combination with established IO agents due to its ability to simultaneously affect multiple aspects of tumour resistance to T cell therapies.
Citation Format: Georgia Cerillo, Anderson J Ryan, Peter D Davis. Development of a highly potent humanized antibody against CD178: A novel therapeutic target in immuno-oncology [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr B044. doi:10.1158/1535-7163.TARG-19-B044