Title: CD90 expression in mesenchymal stem cells of the malignant niche
Abstract: Hematopoietic and stromal cells interact with each other in the bone marrow. Reports suggest that the malignant transformation of the hematopoietic lineage affects the stromal counterpart, the mesenchymal stem cells (MSC). CD90 surface expression was analysed in MSC isolated from bone marrow of patients diagnosed with various hematologic malignancies. CD90 expression was lower in MSC from aged individuals (70-80 yr; 45-50%) compared to younger individuals (8-20 yrs; 95%). Bone marrow MSC of patients diagnosed with acute myeloid leukemia (AML) and aplastic anemia (AA) showed a decreased CD90 surface expression (50%+9% in AML and 38+25%). Also a ∼50% reduction in the CD90 expression was seen in patients with multiple myeloma, but no change was seen in patients diagnosed with lymphoma where there was no bone marrow involvement. Real-time PCR analysis also showed a similar trend in CD90 expression. In addition, co-culture of MSC with leukemic cell lines THP1 (acute monocytic leukemia) and K562 (chronic myeloid leukemia) resulted in decreased CD90 expression. Thus CD90 expression might mediate the leukemia and stromal stem cell interaction in the niche and we are further investigating the effect of CD90 silencing in the leukemia and bone marrow niche cell interaction.