Interferon-γ and Tumor Necrosis Factor-α Induce An Immunoinhibitory Molecule, B7-H1, Via NfκB Activation in Blasts of Myelodysplastic Syndromes.

Abstract Abstract 2766 Poster Board II-742 (Introduction) 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 inhibit the proliferation of tumor-specific cytotoxic T-lymphocytes and are associated with poor prognosis in patients with some tumors such as renal and breast cancers. In this study, we investigated whether functional B7-H1 molecules are expressed on blasts from myelodysplastic syndromes (MDS) and, if so, are associated with pathophysiology in specific immune evasion in MDS. (Materials and methods) (1) First, we analyzed the expression of B7-H1 mRNA and protein in MDS cell lines (OIH-1, SKM-1, and F36P) using reverse transcription-PCR and flow cytometry (FCM), respectively. Although F36P cells alone expressed B7-H1 molecules at mRNA and protein levels, interferon (IFN)-γ and more efficiently a combination of IFN-γ and tumor necrosis factor (TNF)-α enhanced or induced B7-H1 expression in all of these cell lines. Notably, the combination of IFN-γ and TNF-α induced nuclear factor (NF) γB activation of MDS cell lines, and the blocking of NFκB activation by pyrrolidine dithiocarbamate (PDTC) or NFκB inhibitor peptide turned off the B7-H1 induction. (2) To investigate whether B7-H1+ MDS blasts have a proliferative advantage, we compared the cell cycle and colony formation between B7-H1+ and B7-H1– cell fractions in F36P cells. B7-H1+ cells had fewer G0/G1-phase cells and more G2/M-phase cells compared with B7-H1– cells. Furthermore, purified B7-H1+ cells formed more colonies than B7-H1– cells in the colony-forming assay using the methylcellulose. (3) We investigated the immunomodulatory effects of B7-H1+ blasts on T cells. When normal CD3+ T cells were cultured with or without irradiated B7-H1+ F36P cells, the B7-H1+ F36P cells had markedly increased percentages of T cells showing apoptosis. The blocking antibody for B7-H1 or PD-1 inhibited the T-cell apoptosis induced by B7-H1+ cells, decreased the percentage of caspase-3+ cells in T cells, and increased T-cell proliferation. (4) We then examined B7-H1 expression on blasts from 41 MDS patients, 20 patients with acute myeloid leukemia transformed from MDS (AML-MDS), and 10 hematologically normal individuals using FCM. B7-H1+ cases, in whom more than 5% of blasts expressed B7-H1 molecules, were observed in 6 of 14 (43%) patients with refractory anemia with excess blasts (RAEB), 6 of 12 (50%) with RAEB in transformation (RAEB-t), and 4 of 20 (20%) AML-MDS patients, but in none of 15 RA patients and normal individuals. Similar to the data obtained using MDS cell lines, B7-H1 expression on blasts purified from MDS patients was induced by stimulation with IFN-γ or TNF-α, and more strikingly by their combination. PDTC inhibited the induction of B7-H1 expression. The percentages of G0/G1-phase cells were lower and those of G2/M-phase cells higher in B7-H1+ blasts than in B7-H1– blasts from patients. Furthermore, in allogeneic coculture, in which B7-H1+ blasts from an MDS patient and CD3+ T cells from healthy volunteers were cultured, T-cell proliferation was significantly augmented by blocking B7-H1 molecules. (5) Finally, we investigated the expression of PD-1, a counterreceptor of B7-H1, on circulating T cells in 34 MDS patients. PD-1 expression on CD3+, CD4+, and CD8+ T cells in MDS patients was significantly higher than that in healthy volunteers. (CONCLUSIONS) Taking the results together, in MDS: 1) B7-H1 expression on blasts occurs more often in the advanced disease stages; 2) B7-H1 expression on blasts may be induced by cytokines derived from the bone marrow environment via NFκB activation; 3) cell cycle and proliferation were more active in B7-H1+ blasts than in B7-H1– blasts; and 4) B7-H1 molecules on blasts suppress T-cell immunity. These findings indicate that B7-H1 molecules on blasts may be involved in the pathophysiology of MDS. Disclosures: No relevant conflicts of interest to declare.