Programmed death-1/programmed death-ligand 1 (PD-1/PD-L1) axis and lymphoma
Immune checkpoints have become one of the most popular areas of cancer therapy. Programmed death-1/programmed death-ligand 1 (PD-1/PD-L1) axis is the most important representative of immune checkpoints until now, and three inhibitors of PD-1/PD-L1 axis have been successfully approved by Food and Drug Administration (FDA). Several clinical trials have confirmed the surprising effects and great clinical application values of PD-1/PD-L1 axis inhibitors. Lymphoma that originates in lymphocytes and differs from other solid tumors has its unique characteristics. It is not only characterized by malignant proliferation, which is similar to that of other solid tumors, but also has some characteristics of lymphocytes including T/B cells. Hence, the regulatory mechanism of PD-1/PD-L1 axis is more complex in lymphoma, making the expression and clinical value of PD-1/PD-L1 in lymphoma more elusive. In this review, we focus on illustrating the specific regulation mechanisms, expression features, clinical treatment and future challenges of PD-1/PD-L1 axis in lymphoma. 
 
 
Key words: 
Immune checkpoint; PD-1/PD-L1 axis; Lymphoma