Biomarkers in immune checkpoint inhibition therapy for cancer patients: what is the role of lymphocyte subsets and PD1/PD-L1?

Although durable clinical responses are achieved in a significant number of patients given Immune checkpoint inhibitors (ICI), like anti-CTLA-4 and anti-PD-1 inhibitors, some of the cancers have shown little or no response to ICI therapy. Even within the known responsive cancers, there is often a subset of non-responsive patients. Due to the accelerated FDA approval of these immunotherapies, the biomarker development has not been able to keep pace. Appropriate predictive, prognostic and surrogate biomarkers are needed to maximally exploit the benefits from ICI therapy for correct and timely stratification of patients to treatment, for monitoring treatment effect, and for avoiding costs and unwanted toxicities when therapy is likely to be ineffective. As the number of clinical trials exploring the utility of these treatments, both as stand-alone and as combination therapy for several cancers is escalating dramatically, the need for appropriate biomarkers is further amplified.