In vivo imaging of cells labeled with fluorescent nanodiamonds (FNDs) is a new way of monitoring immune cells during cancer immunotherapy. FNDs are non-toxic, infinitely photostable nanomaterials that are easily conjugated with antibodies, and emit fluorescence in the near infrared spectral region. In this Phase I SBIR, we will use a murine melanoma model and outline a plan to use FNDs for imaging immunosupressive cell populations as they enter the tumor microenvironment and peripheral tissues during immunotherapy. In Objective 1, we will conjugate 50 nm FNDs with antibodies that recognize tumor-associated macrophages (TAM), myeloid-derived suppressor cells (MDSC), and regulatory T cells (T-reg). In Objective 2, we will prepare TAM, MDSC and T-reg cells and characterize them by flow cytometry using commercial fluorescent antibodies. The TAM, MDSC and T-reg will then be used to validate our antibody-FND conjugates. In Objective 3, we will prepare FND-labeled TAM, MDSC and T-reg cells ex vivo and fluorescently track these cell populations in melanoma-bearing mice receiving placebo or mouse anti-PD-L1 antibody (programmed death ligand 1) inhibitor. We will also perform parallel studies where we image antibody-FND conjugates that are directly injected through the tail-vein. Our results will provide tools for predicting the response to immunotherapy.
