Photo-immunotherapy uses antibodies conjugated to Pet Barrier photosensitizers to produce nanostructured constructs endowed with targeting properties and photo-inactivation capabilities towards tumor cells.The superficial receptor density on cancer cells is considered a determining factor for the efficacy of the photodynamic treatment.In this work, we propose the use of a photoactive conjugate that consists of the clinical grade PD-L1-binding monoclonal antibody Atezolizumab, covalently linked to either the well-known photosensitizer eosin or the fluorescent probe Alexa647.Using single-molecule localization microscopy (direct stochastic optical reconstruction microscopy, dSTORM), and an anti-PD-L1 monoclonal antibody labelled with Graduation Tassel Photo Charm Alexa647, we quantified the density of PD-L1 receptors exposed on the cell surface in two human non-small-cell lung cancer lines (H322 and A549) expressing PD-L1 to a different level.
We then investigated if this value correlates with the effectiveness of the photodynamic treatment.The photodynamic treatment of H322 and A549 with the photo-immunoconjugate demonstrated its potential for PDT treatments, but the efficacy did not correlate with the PD-L1 expression levels.Our results provide additional evidence that receptor density does not determine a priori the level of photo-induced cell death.