Rules-Based Medicine

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Programmed Death-Ligand 1 (PD-L1)

Ultrasensitive Immunoassay


Rules-Based Medicine has developed an ultrasensitive  immunoassay to programmed death-ligand 1 (PD-L1) based on Simoa® bead technology. Being able to accurately quantitate sub-pg/mL levels of PD-L1 in human serum and plasma is a valuable clinical research tool for pharmacodynamic analysis in cancer.

PD-L1, also known as B7-H1 or CD274, is the ligand for programmed cell death 1 (PD-1). PD-L1 is expressed constitutively at low levels on resting lymphocytes, antigen-presenting cells, and specific tissue islet cells. The normal function of PD-L1 is to maintain homeostasis and to control inflammatory responses. Thus, the ligation of PD-L1/PD-1 is a major mechanism for immune tolerance, immune exhaustion, and immune evasion. Aberrant expression of membrane bound PD-L1 on cancer cells and infiltrating leukocytes in the tumor microenvironment has been correlated with poor prognosis. Additionally, pathogens that can cause chronic infections also exploit this pathway by inducing overexpression of PD-L1 on the infected host cell.

PD-L1 can also exist as a soluble protein. Th soluble PD-L1 (sPD-L1) can be released from both cancer cells and immune cells and is known to bind to membrane bound PD-1. While sPD-L1 is detectable in normal serum and the levels can increase with age, there are numerous studies examining sPD-L1 as a biomarker in cancer. Increased sPD-L1 has been associated with cancer clinical stage, poor prognosis, and increased mortality risk.

Due to the role of PD-L1 to suppress T cell activation, there are several anti-PD-L1 antibody therapy (atezolizumab, durvalumab, and avelumab) approved for cancer therapy. However, predicting patient response to biologics is a major unmet need to improving efficacy of anti-PD-L1 therapeutics.


Swiss-Prot Accession Number: Q9NZQ7

Alternate names for this biomarker include:

PDCD1 ligand 1, hPD-L1, B7 homolog 1, B7-H1, CD_antigen: CD274

Simoa™ Services
Biomarker LLOQ*
(Serum and Plasma)
(Undiluted Samples)
Volume Required
Serum or plasma Other fluids**
Programmed Death-Ligand 1 (PD-L1) 2.1 pg/mL 0.21 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.