T-cell Immune Abnormality and Novel Immunotherapeutic Approach by Blocking the B7-H1-PD-1 Pathway Combined with WT1 Tumor Vaccine in Myelodysplastic Syndromes

Abstract

Myelodysplastic syndromes (MDS) are hematologic malignancies caused by the neoplastic transformation of hematopoietic stem or myeloid progenitor cells and characterized by cytopenias, excessive apoptosis of hematopoietic cells, and a high risk of progression to acute myeloid leukemia. During disease progression, clonal blasts gain a more aggressive nature, whereas nonclonal immune cells become less efficient via an unknown mechanism. Stem cell transplantation is the only curative treatment for MDS, but it is not suitable for elderly patients. B7-H1 (CD274) molecules, which are expressed on antigen-presenting cells and inhibit T-cell responses through programmed death-1 (PD-1) expressed on activated T cells, are expressed on various tumor cells, and B7-H1-expressing tumor cells evade attack by tumor-specific cytotoxic T lymphocytes (CTLs). We reported immune dysfunction associated with T cells in MDS, i.e., an increase in T-cell apoptosis, higher expression levels of PD-1 on circulating T cells, and higher levels of plasma-soluble interleukin-2 receptor. Furthermore, we demonstrated that MDS blasts overexpress Wilms tumor gene WT1 mRNA, suggesting that the anti-WT1 immune response elicited by WT1 peptide vaccine may induce tumor regression in some patients. In the current study, we investigated B7-H1 expression on MDS blasts and analyzed the characteristics and inhibitory effects on T-cell immune responses of B7-H1 blasts. Finally, to develop new strategies, we are now analyzing a novel immunotherapy involving blockade of the B7-H1-PD-1 pathway in combination with WT1 tumor vaccine and or inhibition of regulatory T cells. First, we analyzed B7-H1 expression in 3 MDS cell lines, i.e., F-36P, OIH-1, and SKM-1, and on MDS blasts from 29 MDS patients, 32 patients with acute myeloid leukemia transformed from MDS (AL-MDS), and 10 hematologically normal individuals. A high level of B7-H1 expression at the mRNA and protein levels was detected only in F-36P cells using reverse transcription-PCR and flow cytometry (FCM), respectively. B7-H1 protein was not detectable on OIH-1 and SKM-1. Blasts from patients with high-risk MDS and AL-MDS expressed B7-H1 molecules more often compared with those from low-risk MDS patients. B7-H1 molecules were expressed in fewer than 5% of blasts in normal individuals. Furthermore, we found that the cytokines interferon (IFN)-γ and tumor necrosis factor (TNF)-α, which may be associated with MDS pathophysiology, induced B7-H1 expression on SKM-1 cells or blasts from MDS patients, and that B7-H1 induction by these cytokines was mediated by nuclear factor (NF)-κB activation, whose activation was observed in MDS patients, in particular in advanced disease. Second, to investigate the characteristics of B7-H1 blasts, we analyzed proliferative advantage, i.e., cell cycle and colony formation, in B7-H1 and B7-H1 cell fractions in MDS blasts using FCM and the methylcellulose assay, respectively. B7-H1 MDS blasts had greater intrinsic proliferative capacity than B7-H1 MDS blasts when examined in both assays. Third, to investigate the immunomodulatory effects of B7-H1 MDS blasts on T-cells, T-cell apoptosis and