Gr. Kitchingman, RESIDUAL DISEASE DETECTION IN MULTIPLE FOLLOW-UP SAMPLES IN CHILDREN WITH ACUTE LYMPHOBLASTIC-LEUKEMIA, Leukemia, 8(3), 1994, pp. 395-401
The polymerase chain reaction (PCR) is more sensitive than other metho
ds for detecting residual leukemic cells, and it can be used to analyz
e the dynamics of the leukemic cell population during and after chemot
herapy. Leukemia cells are identified among the normal cells through t
he use of a leukemic cell-specific signature, such as the junction for
med following rearrangement of the immunoglobulin (Ig) or T-cell recep
tor (TCR) variable (V), diversity (D), and joining (J) regions. We clo
ned the rearranged Ig or TCR genes from leukemic cells at the time of
diagnosis by regular recombinant DNA techniques, or following PCR ampl
ification, and determined the leukemic cell-specific V(D)J junctions.
Using oligonucleotides prepared to the unique junctional sequences, we
have analyzed Southern blots of PCR-amplified Ig or TCR genes from 11
patients at the time of diagnosis, and in from three to 14 follow-up
samples for periods ranging from 17 to 97 months. The level of detecti
on of residual blast cells in these patients was usually on the order
of 1 leukemic cell in 10(4) normal ones. Conditions for the hybridizat
ion and washing were individually adjusted so that the specificity of
the probes was excellent. No residual leukemic cells were found in pat
ients who remained in continuous complete remission at time points mor
e than 6 months post-diagnosis. PCR detected impending relapse in four
out of six cases, with PCR-detectable leukemic clones being present 2
, 4, 13 and 20 months prior to clinical signs of the disease. Relapse
occurred in two patients who lacked PCR evidence of leukemic blasts in
marrow samples collected 2 and 6 months before clinical recurrence, r
espectively. The leukemic cells that persisted for 3 years after a rel
apse in a patient who remained in clinical remission during this time
period eventually became undetectable by PCR.