Immune checkpoint molecules: Continued interest in development of drugs Cancer cells employ various strategies such as attracting regulatory T (T reg) cells, reducing the expression of tumor antigens, triggering T cell tolerance or apoptosis, and generating immune suppressing cytokines. The immune suppressing cytokines may activate inhibitory immune checkpoints resulting in a high immunosuppressive tumor microenvironment (TME). Immune checkpoint molecules balance between pro-inflammatory and anti-inflammatory signaling, functioning as key regulators of immune responses to aid the immune system in recognition and elimination of malignant cells. They are further classified into inhibitory or stimulatory/other checkpoint molecules (Fig. ).