title: Kinetics of human myeloid-derived suppressor cells after blood draw.
abstract: BACKGROUND
  Human myeloid-derived suppressor cells (MDSC) have been described as a group of immature myeloid cells which exert immunosuppressive action by inhibiting function of T lymphocytes. While there is a huge scientific interest to study these cells in multiple human diseases, the methodological approach varies substantially between published studies. This is problematic as human MDSC seem to be a sensible cell type concerning not only cryopreservation but also time point after blood draw. To date data on delayed blood processing influencing cell numbers and phenotype is missing. We therefore evaluated the kinetics of granulocytic MDSC (gMDSC) and monocytic MDSC (mMDSC) frequencies after blood draw in order to determine the best time point for analysis of this recently defined cell type.
  
  
  METHODS
  In this study, we isolated peripheral blood mononuclear cells (PBMC) of patients with HIV infection or solid tumors directly after blood draw. We then analyzed the frequencies of gMDSC and mMDSC 2, 4 and 6 h after blood draw and after an overnight rest by FACS analysis using the standard phenotypic markers. In addition, part of the cells was frozen directly after PBMC preparation and was measured after thawing.
  
  
  RESULTS
  gMDSC levels showed no significant difference using fresh PBMC over time with a limitation for the overnight sample. However they were massively diminished after freezing (p = 0.0001 for all subjects). In contrast, frequencies of fresh mMDSC varied over time with no difference between time point 2 and 4 h but a significantly reduction after 6 h and overnight rest (p = 0.0005 and p = 0.005 respectively). Freezing of PBMC decreased the yield of mMDSC reaching statistical significance (p = 0.04). For both MDSC subgroups, FACS analysis became more difficult over time due to less sharp divisions between populations.
  
  
  CONCLUSIONS
  According to our data human MDSC need to be studied on fresh PBMC. gMDSC can be studied with delay, mMDSC however should be studied no later than 4 h after blood draw. These results are crucial as an increasing number of clinical trials aim at analyzing MDSC nowadays and the logistics of blood processing implies delayed sample processing in some cases.
authors.affiliation: Sektion Klinische Infektiologie, Medizinische Klinik und Poliklinik IV, Klinikum der Universität München, Pettenkoferstr. 8a, 80336, Munich, Germany. eva.gruetzner@med.uni-muenchen.de.
authors.forename: Eva
authors.initials: E
authors.lastname: Grützner
authors.affiliation: Sektion Klinische Infektiologie, Medizinische Klinik und Poliklinik IV, Klinikum der Universität München, Pettenkoferstr. 8a, 80336, Munich, Germany. renate.stirner@med.uni-muenchen.de.
authors.forename: Renate
authors.initials: R
authors.lastname: Stirner
authors.affiliation: Sektion Klinische Infektiologie, Medizinische Klinik und Poliklinik IV, Klinikum der Universität München, Pettenkoferstr. 8a, 80336, Munich, Germany. lukas.arenz@med.uni-muenchen.de.
authors.forename: Lukas
authors.initials: L
authors.lastname: Arenz
authors.affiliation: Sektion Klinische Infektiologie, Medizinische Klinik und Poliklinik IV, Klinikum der Universität München, Pettenkoferstr. 8a, 80336, Munich, Germany. anastasia.athanasoulia@med.uni-muenchen.de.
authors.forename: Anastasia P
authors.initials: AP
authors.lastname: Athanasoulia
authors.affiliation: Medizinische Klinik und Poliklinik V, Klinikum der Universität München, Ziemssenstr. 1, 80336, Munich, Germany. kathrin.schroedl@med.uni-muenchen.de.
authors.forename: Kathrin
authors.initials: K
authors.lastname: Schrödl
authors.affiliation: Klinik und Poliklinik für Dermatologie und Allergologie, Frauenlobstraße 9-11, 80337, Munich, Germany. carola.berking@med.uni-muenchen.de.
authors.forename: Carola
authors.initials: C
authors.lastname: Berking
authors.affiliation: Sektion Klinische Infektiologie, Medizinische Klinik und Poliklinik IV, Klinikum der Universität München, Pettenkoferstr. 8a, 80336, Munich, Germany. johannes.bogner@med.uni-muenchen.de.
authors.forename: Johannes R
authors.initials: JR
authors.lastname: Bogner
authors.affiliation: Sektion Klinische Infektiologie, Medizinische Klinik und Poliklinik IV, Klinikum der Universität München, Pettenkoferstr. 8a, 80336, Munich, Germany. rika.draenert@med.uni-muenchen.de.
authors.forename: Rika
authors.initials: R
authors.lastname: Draenert
mesh_terms: D001800:Blood Specimen Collection / Q000379:methods*; D002452:Cell Count; D006801:Humans; D007700:Kinetics; D022423:Myeloid Cells / Q000166:cytology*; D010641:Phenotype; D012146:Rest