Flow Cytometric Detection of Human Telomerase Reverse Transcriptase Expression in CD34 Positive Precursor Fraction in Myelodysplastic Syndrome Bone Marrow.

Telomerase activity has been found in most common cancers indicating that telomerase detection may be a useful marker in cancer diagnosis. For detection of telomerase activity and the expression of associated genes in cells, TRAP assay and RT-PCR are customarily used. Immunohistochemical detection of hTERT is useful to detect telomerase-positive cells in a background of non- cancerous cells. We developed a method for the detection of intra-nuclear hTERT protein, in a sub-population of hematopoietic cells, using concurrent staining cell surface antigen and multi color flow cytometry. Human leukemia and myeloma cell lines showed 100% positivity, whereas neutrophils of normal subjects showed 0% positivity, it is consistent with telomerase activity assessed by TRAP assay (r=0.71, p<0.0001) and previous observations. Then we applied this method to analyze hTERT expression in myelodysplastic syndrome (MDS). Forty MDS patients samples were obtained, 36 patients were diagnosed as low risk MDS (RA), 14 patients were diagnosed as high risk MDS (RAEB or RAEB-t) according to FAB classification. All samples were acquired after informed consent was obtained from the patients.

Expression of hTERT protein was higher in CD34-positive blast-gated cells than CD34-negative blast-gated cells. The percentage of the CD34+ cells expressing hTERT ranged from 9.66% to 90.91% in low risk MDS patients, whereas from 50.46% to 97.68% in high risk MDS. The expression level was higher in the high risk group compared to that in the low risk group in MDS (p=0.0054, p=0.0084). This observation implied that telomerase up-regulation and hTERT expression were important for disease progression and could be a marker of more advanced disease. In subsets of MDS and AML bone marrow specimens obtained from these patients, we examined the hTERT expression in CD34+/CD38 high cells and CD34+/CD38 low cells containing stem cell fraction. Of interest, some of the patients showed higher expression of hTERT in CD34+/CD38 low cells than in CD34+/CD38 high cells. This observation is inconsistent with previous reports describing normal bone marrow hematopoietic cell findings. We speculated that this phenomenon could be a marker of MDS abnormality and that telomerase up-regulation may be initiated in the more primitive precursor fraction containing hematopoietic stem cells during the disease progression. Telomerase studies may be useful for definition of the risks associated with disease severity. Multi-parameter nature of flow cytometry and its ability to identify cellular sub-populations will facilitate a fuller understanding of the mechanisms of activation of telomerase.