Cancer patients are known to have an impaired anti-tumor immune response because of various immune escape mechanisms exerted by the tumor cells. These mechanisms involve release of soluble molecules and expression of membrane-bound proteins inhibiting different arms of the anti-tumor immune responses. The immune escape mechanisms seen in cancer patients complicate the use of immunotherapy, such as tumor vaccines and adoptive T cell transfer. The aim of our study was to investigate the presence of IL10, soluble IL2R (sIL2R; CD25) and programmed death receptor ligand 1 (PDL1) in patients with chronic myeloid leukemia (CML) and to study their role as T cell inhibitors. IL10, sIL2R and PDL1 are all known immune inhibitory molecules. IL10 is a secreted molecule that has various suppressive effects on many different immune cells. sIL2R binds IL2 efficiently and may thereby prevent the binding of IL2 to IL2R on T cells, an interaction that is necessary for proliferation and maintenance of tumor-specific T cells. PDL1-expressing tumor cells can bind programmed death receptor 1 (PD1) on T cells. This interaction can induce apoptosis in the T cells. In this study, we used cytometric bead array, ELISA and multicolor flow cytometry to screen CML patients and healthy controls for the presence of IL10, sIL2R and PDL1 in blood. Further, Alamar Blue TM assay and IFNγ detection by flow cytometry were used to investigate T cell proliferation and activation in the presence of the inhibitors. We found that the levels of IL10 and sIL2R were increased in CML patient plasma compared to the levels in healthy control subjects. The level of sIL2R in a subgroup of patients was four-fold higher than the mean level of healthy controls. Patient T cells stimulated with various strong T cell stimuli including CML-specific peptides failed to respond to stimuli as measured by flow cytometric detection of the cytotoxic T cell activation marker IFNγ, indicating that these T cells might be anergic. In vitro studies on T cells from healthy donors showed that both IL10 and sIL2R have the ability to inhibit T cell proliferation. Half of the CML patients had a PDL1 expression on the CD34 cell population raging from 1-36%. PDL1 may, hence, be involved in T cell control in CML. Taken together, our results show that T cells from CML patients fail to respond to stimuli and that these T cells may be controlled by the high levels of IL10, sIL2R and PDL1 seen in the patients. Screening for these inhibitors may aid selection of patients considered for immunotherapy.
Simonsson:Novartis: Consultancy, Honoraria, Research Funding, Sponsor; BMS: Consultancy, Honoraria, Research Funding, Sponsor; SCHERING-PLOUGH: Sponsor. Olsson-Strömberg:BMS: Honoraria.
Asterisk with author names denotes non-ASH members.