CD7 Expression On Blasts Of Myelodysplastic Syndromes Is Associated With Apoptosis Resistance With Decreased Expression Of The Proapoptotic Protein Bad and An Independent Unfavorable Prognostic Factor Together With The Revised IPSS Score In Patients

CD7 is expressed on human T and NK cells and progenitors of myeloid cells as well as blasts in some patients with myelodysplastic syndromes (MDS). We showed previously that CD7 positivity of MDS blasts was associated with aggressive characteristics and poor prognosis. However, the mechanisms by which CD7-expressing MDS blasts are associated with disease progression remain unknown. In this study, we first investigated the biology of CD7-expressing MDS blasts. Second, to validate the prognostic impact of CD7 on MDS blasts, prognostic variables including the CD7 positivity of MDS blasts and a new prognostic system, the revised International Prognostic Scoring System (IPSS-R) were evaluated in Japanese MDS patients.

1) To investigate the mechanisms regulating CD7 expression, we used MDS cell lines HNT-34 and F-36P. CD7 expression on these cells was partially down-regulated by inhibition of NFκB. 2) To investigate the survival potential in CD7⁺ MDS blasts, we analyzed cell cycles and spontaneous apoptosis by flow cytometry. CD7⁺ blasts had a cell cycle advantage compared with CD7^– blasts in F-36P but not in HTN-34 cells. Compared with CD7^– HNT-34 cells, CD7⁺ HTN-34 cells were more resistant to spontaneous and serum deprivation-induced apoptosis. 3) We then compared gene and protein expression levels of apoptosis-related proteins including Bad, Bax, Bcl-2-L1, Bcl-2, caspase-3, caspase-8, caspase-9, FADD, Fas, and FasL between CD7⁺ and CD7^– blasts of these cell lines using real-time PCR and flow cytometry, respectively. CD7^– blasts had markedly higher expression levels of the Bad gene and protein compared with CD7⁺ blasts in both cell lines. The expression levels of Fas and FasL were suppressed in CD7⁺ blasts compared with CD7^– blasts in F36P cells. These results support the association of CD7 expression on MDS blasts with disease progression. 4) To reevaluate the prognostic impact of CD7 expression as well as R-IPSS, prognostic variables were analyzed in 81 MDS patients [refractory anemia (RA) 55, RA with ringed sideroblasts 7, RA with excess blasts (RAEB) 18, and RAEB in transformation 1], comprising 50 men/31 women with a median age of 67 (range 27–88) years. Immunophenotyping was performed by 3-color flow cytometry, in which blast cells were gated with a CD45-gating method, and 9 parameters including CD7 expression on MDS blasts, i.e., CD34⁺ myeloblast-related and B-progenitor-related cluster size, myeloblast CD45 expression, and aberrant expression of CD7, CD10, CD11, CD15, CD56, and B7-H1 on myeloblasts, were analyzed. Using the Cox proportional hazard regression model, we identified five prognostic variables: IPSS-R score; percentage of blasts in peripheral blood; CD7 expression; gender; and white blood cell count. The chi-square test showed that the IPSS-R score and CD7 expression were strong prognostic factors (P = 0.0114 and 0.006, respectively). Patients whose MDS blasts expressed high levels of CD7 (17% or more MDS blasts were CD7⁺) had significantly shorter survival than other patients.

Our study revealed that CD7⁺ MDS blasts had apoptosis resistance with decreased expression of apoptosis-related genes, especially Bad. Signaling via CD7 on MDS blasts might inhibit Bad expression and then confer apoptosis resistance. Further studies are in progress to clarify CD7 signaling in cell lines as well as in MDS blasts from patients. Furthermore, we demonstrated for the first time that IPSS-R as well as CD7 expression on blasts had a strong impact on MDS patient prognosis.

Kurokawa:Novartis: Consultancy, Research Funding; Bristol-Myers Squibb: Research Funding; Celgene: Consultancy, Research Funding. Shibayama:celgene: Honoraria, Research Funding; Janssen: Honoraria. Naoe:Otsuka Pharmaceutical Co., Ltd, Kyowa Hakko Kirin Co., Ltd., Wyeth, and Chugai Pharmaceutical Co., Ltd.: Research Funding.