Rules-Based Medicine

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Programmed Cell Death Protein 1 (PD-1)

Ultrasensitive Immunoassay


Rules-Based Medicine has developed and manufactured an ultrasensitive immunoassay to programmed cell death protein 1 (PD-1) based on Simoa® bead technology. Being able to accurately quantitate sub-pg/mL levels of PD-1 in human serum and plasma is a valuable clinical research tool for pharmacodynamic analysis in cancer.

PD-1, also known as CD279, is the receptor for two ligands, programmed death ligand 1 (PD-L1) and programmed death ligand 2 (PD-L2). Membrane bound PD-1 is expressed mainly on T cells and B cells and is upregulated on activated T cells after induction by antigen stimulation. This upregulation is a normal mechanism to prevent unregulated T cell activation and is a major mechanism for T cell exhaustion. However, in the cancer microenvironment, high expression of PD-1 from infiltrating T cells will lead to suppression of anti-cancer immune responses. Similar immune suppression mechanism has also been found during chronic infectious diseases.

Membrane bound PD-1 have splice variants that can lead to soluble forms of PD-1 (sPD-1). Under normal circumstances and in healthy subjects, sPD-1 is not detectable. Only a handful of studies have conducted on correlating sPD-1 with cancer or infectious diseases. Circulating sPD-1 is elevated in certain types of cancer, and the level of sPD-1 can be affected by treatment. Additionally, for chronic viral infections such as HBV and HCC, sPD-1 has been correlated with viral load.

In cancer, since over expression of membrane bound PD-1 can lead to suppression of T cell activity, several anti-PD-1 biologics (pembrolizumab, nivolumab, cemiplimab) are available for cancer. Patient response to anti-PD-1 is low across the population, a biomarker to predict responses to anti-PD-1 therapy is a critical need.


Swiss-Prot Accession Number: Q15116

Alternate names for this biomarker include:

hPD-1, CD_antigen: CD279

Simoa™ Services
Biomarker LLOQ*
(Serum and Plasma)
(Undiluted Samples)
Volume Required
Serum or plasma Other fluids**
Programmed Cell Death Protein 1 (PD-1) 2.3 pg/mL 0.23 pg/mL 50 µL 150 µL

* Lower limit of quantitation (LLOQ) represents the lowest amount of an analyte that can be quantitatively determined with acceptable precision. LLOQ is determined by performing 2-fold serial dilutions of Standard to be tested in triplicate over three runs. The percent coefficient of variation (CV) is calculated for each of the dilution replicates, and the LLOQ is determined as the concentration at which the CV is 30%.

** Cerebrospinal fluid, urine, tissue culture supernatants,  bronchoalveolar lavage, synovial fluid, tissue extracts, tears, skin washings, etc.

All assay services are performed in our CLIA-certified laboratory.
Intended for Research Use Only.