Improving efficacy and reducing toxicity of anti-PD-L1 treatment: T-cells as delivery vehicles for anti-PD-L1 blocking nanobodies

Petit, P-F. [UCL] Zhu, Jingjing [UCL] van den Eynde, B.J. [UCL]

Background Cancer therapy has experienced a paradigm shift due to the clinical success of immune checkpoint inhibitors (ICI) such as anti-PD-L1 antibodies, yet ICI benefits remain limited to a minority of patients. On top of the resistance mechanisms limiting their efficacy, ICI are causing auto-immune side effects related to the activation of self-directed CD8 T cells. We propose a new approach using antitumoral T cells as vehicles to deliver anti-PD-L1 nanobodies specifically at the tumor site. Compared to antibodies, nanobodies offer the advantage of a good penetration ability in tissues while displaying a very short half-life in the blood stream. We evaluated whether this approach could improve efficacy and reduce toxicity compared to classical anti-PD-L1 antibody treatment. Methods Ovalbumin-specific OT-I T cells were engineered to secrete an anti-PD-L1 blocking nanobody. In MC38 Ova murine colon carcinoma model, adoptive transfer of nanobody-secreting T cells was compared with wildtype T cells alone or wildtype T cells in combination with an anti-PD-L1 antibody given by intraperitoneal injection. Treatment efficacy was assessed by measuring tumor growth over time. Flow cytometry and immuno-histochemistry (IHC) analysis on tumor, lymph nodes and spleen samples were performed to compare the distribution of the anti-PD-L1 treatment across different tissues. Results Intratumoral delivery of anti-PD-L1 nanobody improved tumor rejection compared to systemically given anti-PD-L1 antibody. According to flow cytometry and IHC analysis, anti-PD-L1 nanobody was enriched in the tumor compared to spleen and lymph nodes, while anti-PD-L1 antibody was rather enriched in spleen and lymph nodes and weakly detected in the tumor. This low systemic exposure to the nanobody could minimize the risk of developing auto-immune side effects. Conclusions Our study points out the poor penetration of anti-PD-L1 antibody in established tumors as a limitation factor for its efficacy in treating MC38 Ova tumors. Local delivery of an anti-PD-L1 nanobody could both overcome this limitation and reduce the risk of side effects as the nanobody is enriched in the tumor compared to the periphery.