Expression of Functional B7-H1 Molecules on Blasts from Myelodysplastic Syndromes.

B7-H1 (CD274) is a costimulatory/coinhibitory molecule that plays a crucial role in T cell regulation in various immune responses. B7-H1 expression is detected not only on professional antigen-presenting cells but also on some tumor cells. It has been reported that B7-H1 molecules on tumor cells are associated with poor prognosis in patients with some tumors such as renal cancer and breast cancer. We reported previously that B7-H1 expression on blasts is rare in de novo acute myeloid leukemia (AML) (Clin Cancer Res, 2003). In this study, we investigated whether functional B7-H1 molecules are expressed on blasts from myelodysplastic syndromes (MDS). Using flow cytometry (FCM), we analyzed B7-H1 expression in MDS cell lines (OIH-1, SKM-1, and F36P) and on blasts in bone marrow (BM) or peripheral blood samples. These samples were obtained from 40 MDS patients and 19 patients with AML transformed from MDS (AL-MDS). Among the cell lines, F36P cells showed a high level of B7-H1 expression. In patient samples, the percentage of B7-H1⁺ blasts tended to be the highest in patients with AL-MDS, followed by refractory anemia with excess of blasts (RAEB) in transformation (RAEB-t) and RA/RAEB (P<0.1). B7-H1⁺ cases, defined as samples in which more than 5% of blasts expressed B7-H1 (5% was the highest value of B7-H1 expression in normal CD34⁺ cells in our study), were observed in 0/13, 5/15 (33.3%), and 6/12 (50%) patients in the RA, RAEB, and RAEB-t categories, respectively. B7-H1 expression in MDS cell lines and on MDS patient blasts was induced or enhanced by cultivating cells with interferon-γ (IFNγ) or tumor necrosis factor-α (TNFα), which may be involved in the pathogenesis of MDS. The positive effect of the cytokines on B7-H1 expression was also observed in normal CD34⁺ cells. The combination of IFNγ and TNFα synergistically enhanced B7-H1 expression not only in MDS cell lines and on MDS patient blasts but also in normal CD34⁺ cells. Next, to investigate the features of B7-H1⁺ MDS blasts, cell cycle was determined using FCM. The percentages of cells in G0/G1 phase were lower and those in G2/M phase were higher in B7-H1⁺ F36P cells compared with B7-H1⁻ F36P cells. The data were essentially the same for B7-H1+ and B7-H1⁻ SKM-1 cells. To investigate the immunomodulatory effect of B7-H1⁺ blasts on T cells, we examined the proliferation and apoptosis of T cells cultured with irradiated B7-H1⁺ F36P cells. The addition of blocking antibodies to B7-H1 and its receptor PD-1 in this coculture increased the proliferation and decreased the apoptosis of CD4⁺ and CD8⁺ T cells, suggesting that B7-H1 on MDS blasts induces T-cell apoptosis. Taking the results together, in MDS:

1. B7-H1 expression on blasts occurs more often in the advanced than in the early stage;

2. B7-H1 expression on blasts may be induced by cytokines derived from the BM environment;

3. B7-H1⁺ blasts cycle more actively than B7-H1⁻ blasts; and

4. B7-H1 molecules on blasts suppress T cells.

These findings indicate that B7-H1 molecules on blasts may contribute to disease progression in MDS.