Background: The increasing use of autologous hematopoietic cell support in various malignancies including leukemia and lymphoma currently bears the problem of tumor contamination of the graft with tumor cells which after re-infusion contribute to the disease relapses. It is therefore desirable to eradicate the cancer cell fraction of the graft without causing damage to the normal stem cell fraction. The purging processes based on photodynamic treatments appear to be perspective means for this purpose.
Methods and results: We investigated the effects of 5-aminolevulinic acid (ALA)--based photodynamic treatment (ALA-PDT) on the proliferation of human leukemia cell lines HL60 (promyelocytic leukemia), ML2 (myelomonocytic leukemia) and HEL (erythroleukemia) by 3H-thymidine incorporation into the cell DNA, on the viability of cell lines HL60, HEL, DAUDI (B-cell leukemia) and JURKAT (T-cell lymphoma) as well as of blast cells of acute myeloid leukemia (AML) patients by flow cytometry-propidium iodide assay, and on the clonogenic activities of normal human bone marrow cells by in vitro cloning assays. Under the conditions used (treatment with 1 mM ALA for 4 h at 37 degrees C followed by exposure to blue light dose of 18 J/cm2) the number of proliferating HL60 cells was reduced by 2.4 logs, of ML2 cells by 3.2 logs and of HEL cells by 1 log. From the mononuclear cell preparations of AML patients the blast cells were substantially reduced in eight out of ten patients. The clonogenic activities of normal bone marrow progenitor cells were largely spared: 52.5 +/- 8.9% of colony-forming units--granulocytes macrophages (CFU-GM), and 48.6 +/- 9.7% burst forming units--erythrocytes (BFU-E).
Conclusions: ALA-PDT appears to be usable principle for the depletion of residual leukemic cells from autologous transplants.