Background: Several studies showed the benefit of purging of acute myeloid leukemia (AML) stem cell transplants. We reported previously that purging by positive selection of CD34+ and CD133+ cells resulted in a 3-4 log tumor cell reduction (TCR) in CD34- and/or CD133- AML, but has been shown to be potentially applicable in only about 50% of cases. Similar to CD34 and CD133, CD90 marks the hematopoietic CD34 positive stem cells capable of full hematopoietic recovery after myeloablative chemotherapy, and therefore, in the present study, we explored whether a similar purging approach is possible using CD90.
Methods: CD90 expression was established by flowcytometry in diagnosis AML on the clonogenic AML CD34+ blast population by flow cytometry. Positivity was defined as >3% CD90 (CD34+) expression on blasts. For the calculation of the efficacy of TCR by positive selection, AML blasts were recognized by either prelabeling diagnosis blasts with CD45-FITC in spiking model experiments or using expression of leukemia associated marker combinations both in spiking experiments and in real transplants.
Results: In 119 patients with AML and myelodysplastic syndrome, we found coexpression of CD34 and CD90 (>3%) in 42 cases (35%). In AML patients 60 years or younger, representing the patients who are eligible for transplantation, only 23% (16/69) of the patients showed CD90 expression. Positive selection for CD90 in transplants containing CD90 negative AML resulted in a 2.8-4 log TCR in the models used.
Conclusions: Purging by positive selection using CD90 can potentially be applied effectively in the majority of AML patients 60 years or younger.
(c) 2007 Clinical Cytometry Society