Cancer-selective photoimmunotherapy spares T cells and NK cells and promotes antitumor immunity in an allogeneic human 3D culture model.

Epithelial ovarian cancer (EOC) is a lethal disease typically diagnosed at a late stage. There is an urgent need for treatment modalities that eliminate microscopic metastatic deposits missed by standard therapies while simultaneously engaging antitumor immunity. Photodynamic therapy (PDT) has demonstrated immune-enhancing effects, including photodynamic priming (PDP), wherein sublethal photodynamic stress remodels the tumor microenvironment to facilitate immune activation and infiltration. Here, we investigate cancer-targeted photoimmunotherapy (PIT), a molecularly targeted form of PDT, as a strategy to build upon and potentially enhance PDP by selectively depleting cancer cells while preserving immune effectors critical to antitumor responses. Using a 3D Matrigel dome model incorporating human ovarian cancer spheroids and allogeneic immune cells, we establish a broadly accessible imaging and analysis pipeline based on fluorescent labeling and 3D confocal microscopy to quantify cancer and immune cell viability. In this system, the presence of T cells or peripheral blood mononuclear cells enhances cancer depletion following PIT, consistent with stimulation of an antitumor immune response. Importantly, PIT spares significantly more T cells and NK cells compared to untargeted PDT and cetuximab at equivalent concentrations. PIT reduces spheroid size while preserving effector immune populations within the tumor microenvironment. Together, these findings suggest that targeted PIT may extend the immune-modulatory foundations established for PDT and PDP, offering a strategy to simultaneously eradicate residual tumor deposits and promote antitumor immune priming in EOC.