Background. Diminished expression of human leukocyte antigen DR on circulating monocytes (mHLA-DR), measured by standardized flow cytometry procedure, is a reliable indicator of immunosuppression in severely injured intensive care unit patients. As such, it is used as stratification criteria in clinical trials evaluating novel immunostimulating therapies. Pre-analytical constraints relative to the short delay between blood sampling and flow cytometry staining have nevertheless limited its use in multicentric studies. The objective of the present work was to compare mHLA-DR expression between whole blood samples simultaneously drawn in EDTA or Cyto-Chex BCT tubes. Methods. In 2 university hospitals, mHLA-DR was assessed in fresh whole blood from septic patients (n = 12) and healthy donors (n = 6) simultaneously sampled on EDTA and Cyto-Chex BCT tubes. Staining was performed immediately after sampling and after blood storage at room temperature. Results. We observed the remarkable stability of mHLA-DR results when blood was collected in Cyto-Chex BCT tubes (until 48-72 h). On baseline values, despite good correlation between tubes (r = 0.98, p< 0.001), mHLA-DR expression was systematically lower with Cyto-Chex BCT. Conclusion. The present reports confirms the great potential of Cyto-Chex BCT tubes to delay mHLA-DR staining in centers without rapid access to flow cytometry facilities. However, a 30 % gap exists between results obtained with EDTA and Cyto-Chex BCT tubes. As current thresholds for clinical decisions were obtained with EDTA samples, further studies are needed to confirm clinical thresholds with Cyto-Chex BCT tubes.
Intracellular Flow Cytometry Staining Protocol v3 (protocols.io.bac7iazn)