Toxicity to the normal hemocytes by ALA-PDT for the ex vivo purging of hematopoietic stem cell grafts

Objective To study the toxic effects of 5-amionlevulinic acid-based photodynamic therapy (ALA-PDT) on human peripheral blood mononuclear cells (PBMCs), cord blood mononuclear cells (CBMCs) and peripheral blood stem cells (PBSCs), and furthermore, to understand the possible causes of this response. Methods We used MTT assay to detect the survival rate of PBMCs, CBMCs and PBSCs after treated by ALA-PDT under the optimum experiment conditions with U937 as control;Annexin V-FITC/PI was used to detect the pattern of cell death induced by ALA-PDT. By using flow cytometry, we detected intracellular PpIX fluorescence intensity. Results After ALA-PDT treatment the survival rate of PBMCs had no significant change;however in PBSCs and CBMCs, the survival rate reduced to 70%, and the survival rate of leukemia cell U937 was the lowest, about 30%. After incubation with ALA,except for PBMCs, intraceUuiar PplX fluorescence intensity of the other two kinds of normal haemocytes and U937 increased obviously. These results combined with the flow cytometry suggested that the main pattern of cell death here was apoptosts. Conclusion Under the optimum experiment conditions, ALA-PDT has a slight effect on normal haemocytes but excellent depletions of leukemia cells. Therefore, it can effectively purify autologons bone marrow or stem cell grafts.