Expression of the immune checkpoint receptor TIGIT in seminoma

A characteristic feature of testicular seminoma is the abundance of immune cells in the tumor microenvironment, raising the possibility that immune checkpoint inhibitors may serve as a therapeutic option in these types of tumors. T cell immunoreceptor with Ig and ITIM domains (TIGIT) is an inhibitory immune checkpoint receptor in analogy to PD-1, and drugs targeting TIGIT are currently being investigated in clinical trials. Little is known about the expression of these proteins in testicular seminomas. Therefore the present study performed immunohistochemical analysis to determine the relative abundance of TIGIT and PD-1 in relation to the total CD3⁺ immune cell infiltration in a tissue microarray (TMA) constructed from 78 seminoma patients. The fraction of TIGIT⁺ and PD-1⁺ lymphocytes was highly variable in individual cancers and ranged from 2.3 to 69.4% (mean: 32.2±14.7%) for TIGIT and from 0.8 to 56.5% (mean: 21.6±13.2%) for PD-1. The same high degree of variability was also identified for the ratio of PD-1 to TIGIT positive cells, which varied from a dominance of TIGIT (PD-1: TIGIT ratio=0.02) in 74% of patients, to a predominance of PD-1 (PD-1: TIGIT ratio=12.5) in 23% of patients. In summary, the immune checkpoint receptors TIGIT and PD-1 are abundantly expressed in human seminomas. Once available, anti-TIGIT antibodies, possibly in combination with anti-PD-1 drugs, may be a reasonable therapeutic strategy for this type of cancer.