Remodeling of the Tumor Microenvironment by a Chemokine/Anti-PD-L1 Nanobody Fusion Protein.

An optimal response to immune checkpoint blockade requires the presence of effector cells in the tumor microenvironment. We designed a PD-L1-targeted delivery strategy for chemokines, key molecules that drive leukocyte trafficking, to the tumor microenvironment, as a means of attracting the relevant leukocyte populations. This strategy combines a PD-L1-blocking single-domain antibody fragment (nanobody or VHH), a charge-engineered chemokine CCL21, and its subsequent characterization in a microfluidic device that resembles the tumor microenvironment. We show that the PD-L1-blocking VHH is a reliable fusion partner for the preparation of a functional chemokine fusion. Engineering the surface charge of CCL21 reduced its nonspecific binding to glycosaminoglycans, a property of chemokines that complicates their targeted delivery. Using a microfluidic assay, we show that it is possible to deliver a chemokine-VHH fusion to a PD-L1-positive environment and recruit effector cells.