Suppression of CD3/CD28 antibody stimulated responses by human granulocytic myeloid-derived suppressor cells: fact or artefact?

T cell responses to CD3/CD28 antibodies are widely used to demonstrate the immunosuppressive activity of added human granulocytic myeloid-derived suppressor cells (G-MDSC). Granulocytic populations have the well established capability to chemically modify antibody structure and/or, phagocytose stimulatory CD3/CD28 antibody coated beads. However the possibility that the suppression observed in CD3/CD28 antibody based assays may result from the effects of the G-MDSC on the stimulatory antibodies rather than the T cells is not routinely controlled for experimentally. In the absence of controls to evaluate potential antibody associated artefacts considerable caution should be applied to the use and interpretation of this assay system as a means of defining suppressive G-MDSC populations.