LAUSR

Antibody therapy targeting specific molecules has been successfully used to treat various diseases including RCC, but some patients do not respond to the therapy (Motzer et al. 2015). There is an urgent need to develop companion diagnostics to select patients that well respond to antibody therapy. PD-L1 on cancer cells suppresses immune response by binding to PD-1 on activated T cells. Antibodies targeting either PD-1 or PD-L1 block their interaction and restore immune response against cancer cells (Rijnders et al. 2017). PD-L1 expression evaluated by immunohistochemistry was used as a predictive biomarker in several studies (Gibney et al. 2016; Rijnders et al. 2017). However, its predictive role in the effect of human anti-PD-1 monoclonal antibody, Nivolumab, in RCC remains unclear (Rijnders et al. 2017). There are also few studies that have examined the predictive value of serum PD-1 levels in RCC patients (Zhu and Lang 2017). Antibody-based assays to determine the level of target molecules in serum and tissues are highly dependent on the epitope recognized by the antibody. We hypothesized that the use of therapeutic antibody, Nivolumab, rather than other PD-1 antibodies as a capture antibody in ELISA would logically give more reliable and clinically relevant results regarding the serum level of soluble form of PD-1 (Fig. 1a).