Disappearance of minimal residual lymphoblastic leukemia cells 6 months after allogeneic bone marrow transplantation without GVHD.

The recent development of the polymerase chain reaction (PCR) has enabled us to determine the hypervariable sequence of immunoglobulin heavy chain known as complementarity determining region (CDR)-III. We amplified the leukemia-specific CDR-III from common acute lymphoblastic leukemia (cALL) cells using the PCR and determined its sequence. To detect minimal residual leukemia (MRL) cells, a second round PCR was performed with clone-specific primers corresponding to 5' and 3' ends of CDR-III to detect MRL cells. A million-fold diluted leukemia cells were clearly detected. Using stepwise diluted materials, the number of residual cells was semiquantitatively estimated. In one patient with cALL, induction chemotherapy resulted in a hematologically complete remission with only a 2-log reduction of the leukemia cells. MRL cells at a level of 10(-6) were also detected within 1 month after bone marrow transplantation (BMT), but leukemia cells were not detectable 6 months after BMT.