TIGIT and cancer: The limited studies that examined the role of TIGIT on primary human NK cells were mostly performed with cells derived from patients with cancer or chronic infection and showed that patient NK cells express TIGIT, and, dependent on the conditions, TIGIT levels were found to be similar to those in healthy cells [22,23,26], downregulated in the case of some metastatic cancer patients [21] or upregulated in patients with chronic infection [27].