miRNA-5119 regulates immune checkpoints in dendritic cells to enhance breast cancer immunotherapy

The immune system recognizes and is poised to eliminate cancer but is held in check by inhibitory receptors and ligands. These immune checkpoint pathways, which normally maintain self-tolerance and limit collateral tissue damage during anti-microbial immune responses, can be co-opted by cancer to evade immune destruction. Drugs interrupting immune checkpoints, such as anti-CTLA-4, anti-PD-1, anti-PD-L1, and others in early development, can unleash anti-tumor immunity and mediate durable cancer regressions. The complex biology of immune checkpoint pathways still contains many mysteries, and the full activity spectrum of checkpoint-blocking drugs, used alone or in combination, is currently the subject of intense study. Copyright © 2015 Elsevier Inc. All rights reserved.

The immune response plays an important role in staving off cancer; however, mechanisms of immunosuppression hinder productive anti-tumor immunity. T cell dysfunction or exhaustion in tumor-bearing hosts is one such mechanism. PD-1 has been identified as a marker of exhausted T cells in chronic disease states, and blockade of PD-1–PD-1L interactions has been shown to partially restore T cell function. We have found that T cell immunoglobulin mucin (Tim) 3 is expressed on CD8+ tumor-infiltrating lymphocytes (TILs) in mice bearing solid tumors. All Tim-3+ TILs coexpress PD-1, and Tim-3+PD-1+ TILs represent the predominant fraction of T cells infiltrating tumors. Tim-3+PD-1+ TILs exhibit the most severe exhausted phenotype as defined by failure to proliferate and produce IL-2, TNF, and IFN-γ. We further find that combined targeting of the Tim-3 and PD-1 pathways is more effective in controlling tumor growth than targeting either pathway alone.