Pathogen molecular pattern receptor agonists: Treating cancer by mimicking infection

Immunotherapies such as checkpoint blockade have achieved durable benefits for patients with advanced stage cancer and have changed treatment paradigms. However, these therapies rely on a patient's own a priori primed tumor-specific T cells, limiting their efficacy to a subset of patients. Because checkpoint blockade is most effective in patients with inflamed or "hot" tumors, a priority in the field is learning how to "turn cold tumors hot." Inflammation is generally initiated by innate immune cells, which receive signals through pattern recognition receptors (PRR)–a diverse family of receptors that sense conserved molecular patterns on pathogens, alarming the immune system of an invading microbe. Their immunostimulatory properties can reprogram the immune suppressive tumor microenvironment and activate antigen-presenting cells to present tumors antigens, driving de novo tumor-specific T-cell responses. These features, among others, make PRR-targeting therapies an attractive strategy in immuno-oncology. Here, we discuss mechanisms of PRR activation, highlighting ongoing clinical trials and recent preclinical advances focused on therapeutically targeting PRRs to treat cancer.