Abstract

Reversing EV Induced Tumor Immune Suppression at the Sentinel Lymph Node: Role of Secretory Autophagy/Mitophagy

Lance Liotta, Co Director, George Mason University

The goal is to reverse cancer immune evasion at the level of the sentinel lymph node. Reduced expansion of CD8+Tcells and other innate immune effector cells in the cancer draining SLN is associated with progression and resistance to checkpoint inhibitors. Cancer derived extracellular vesicles (EVs) that are PD-L1 positive suppress immune recognition at the level of the SNL. Experimental goal: To remodel the SNL to overcome cancer EV-associated immune suppression and induce immune rejection of the tumor.  We developed three methodologies for this project a) Collection of draining  lymph fluid to characterize extracellular vesicles (EVs) shed by 4T1 syngeneic breast tumors growing in the mammary fat pad. b) Chromatographic separation and characterization of the repertoire of EVs shed by tumors into the tumor microenvironment interstitial space using western blotting, mass spectrometry, and electron microscopy. c) Nanoparticle delivery of purified classes of EVs to the tumor draining SNL in combination with cytokine chemoattractants for innate immune cells. Results: Murine and human breast cancer cell lines shed classic exosomes and autophagosomes. The latter are shed extracellularly by the activation of the secretory autophagy pathway. The classic exosomes(exosome marker positive) contained PD-L1. In contrast the LC3 I/II P62 positive double membrane extracellular autophagosomes contained mitochondrial components (mitophagy). SLN immune cell populations could be massively remodeled by introducing hydrogel nanoparticles that affinity release chemoattractants locally in the subcapsular sinus. Nanoparticles could also be used to deliver concentrated packages of EVs of different classes to the SLN.  Introduction of the large CD81 negative VEGF positive EV population (amphisome characteristics) to the SLN augmented tumor growth, angiogenesis, and metastasis, even when cytokine induction was used to remodel the SLN. In marked contrast, introduction of the PD-L1 positive exosomes to the SLN in combination with nanoparticle release of T-cell and dendritic cell chemoattractants, induced immune rejection of the syngeneic breast cancer, reducing tumor growth and blocking metastasis. The findings demonstrate that different classes of EVs have opposite effects on cancer immune evasion at the level of the SLN and that EV mediated immune suppression can be reversed by SLN remodeling to augment dendritic and CD8 T cells.