# Matrix Type Influences the Levels of Soluble Immune Checkpoints

## TL;DR

This study shows that the type of sample (serum or plasma) affects the detection and levels of soluble immune checkpoints, which are important biomarkers in cancer and immune diseases.

## Contribution

The study reveals that matrix type influences detection frequencies and concentrations of soluble immune checkpoints.

## Key findings

- Soluble CD137, CD152, CD40, and LAG3 were detected more frequently in plasma than in serum.
- Except for CD80, most sICs showed matrix-dependent differences in detection and concentration.
- The study highlights the importance of considering sample matrix in sIC quantification for clinical studies.

## Abstract

Soluble immune checkpoints (sICs) are emerging as possible serum and plasma biomarkers in cancer and immune‐mediated diseases, but little is known about the impact of the matrix type in sIC detection. This study aimed to assess whether sIC measurements are comparable between serum and EDTA‐plasma samples.

A cohort of 38 healthy subjects was enrolled. A multiplex bead‐based assay was used to evaluate a panel of 17 sICs (CD137, 4‐1BBL, CD27, CTLA4/CD152, CD80, CD40, CD40L, GITR, GITRL, ICOSL, IDO, LAG3, PD‐1, PD‐L1, PD‐L2, TIM3, and VISTA) in paired serum and plasma‐EDTA samples. The detection frequencies, concentrations, and correlations of each sIC were analyzed by comparing the two matrices.

Soluble CD137, CD152, CD40, and LAG3 were detected more frequently in plasma, while soluble CD40L was detected predominantly in serum. The concentrations of soluble 4‐1BBL, CD27, PD‐1, VISTA were higher in plasma, while the concentrations of soluble PD‐L2 were higher in serum. The concentrations of soluble CD80, GITR, GITRL, ICOSL, IDO, and TIM3 were comparable between serum and plasma. Soluble CD27, CD80, GITRL showed a significant positive, slight correlation between plasmatic and serum concentrations.

Except for soluble CD80, the detection of the other sICs by the bead‐based assay was influenced by the matrix type. The evaluation of the best matrix for sICs should be considered before starting clinical studies.

This study aimed to assess whether the quantification of soluble immune checkpoints (sICs) is comparable between serum and EDTA‐plasma samples. We quantified 17 sICs by a multiplex bead‐based assay in paired serum and plasma‐EDTA samples collected from a cohort of 38 healthy subjects. The frequencies of detection, concentrations, and correlations of each sICs were analyzed. Except for soluble CD80, the detection of the other sICs was influenced by the matrix type, underscoring the importance of the matrix when interpreting sIC results.