The detection of minimal residual disease: implications for bone marrow transplantation

Sequence analysis of clonal immunoglobulin and T-cell receptor gene rearrangements in children with acute lymphoblastic leukemia at diagnosis and at relapse: implications for pathogenesis and for the clinical utility of PCR-based methods of minimal residual disease detection

Immunoglobulin (Ig) and T-cell receptor (TCR) gene rearrangements provide clonal markers useful for diagnosis and measurement of minimal residual disease (MRD) in acute lymphoblastic leukemia (ALL). We analyzed the sequences of Ig and TCR gene rearrangements obtained at presentation and relapse in 41 children with ALL to study clonal stability, which has important implications for monitoring MRD, during the course of the disease. In 42%, all original Ig and/or TCR sequences were conserved. In 24%, one original sequence was preserved but the other lost, and in 14% the original sequences were conserved with new sequences identified at relapse. In 20% only new sequences were found at relapse. Using primers designed from the novel relapse sequences, the relapse clone could be identified as subdominant clones in the diagnostic sample in 8 of 14 patients. Alteration of these clonal gene rearrangements is a common feature in childhood ALL. MRD detection should include multiple gene targets to minimize false-negative samples or include also multicolor flow cytometry. In some cases the leukemic progenitor cell might arise earlier in lineage before DHJH recombination but retain the capacity to further differentiate into cells capable of altering the pattern of Ig and/or TCR rearrangements.

Detection of t(14;18) carrying cells in bone marrow and peripheral blood from patients affected by non-lymphoid diseases

AIMS/BACKGROUND

To assess the presence of bcl-2/JH rearrangements in bone marrow and peripheral blood lymphocytes from patients affected by diseases other than malignant lymphomas. The t(14;18) (q32;q21) translocation, which juxtaposes the bcl-2 oncogene on chromosome 18 and the JH segment of the immunoglobulin heavy chain (IgH) genes on chromosome 14, is found frequently in follicular lymphomas.

METHODS

A sensitive semi-nested polymerase chain reaction (PCR) was used to detect t(14;18) translocation in bone marrow aspirates and peripheral blood lymphocytes from 48 patients. In 137 additional individuals peripheral blood lymphocytes only were tested.

RESULTS

Cells carrying bcl-2/JH rearrangements were detected in about a quarter of the bone marrow samples and half of the peripheral blood lymphocyte samples. In seven patients, t(14;18) positive cells were found in both the bone marrow and peripheral blood lymphocyte samples. The size of the PCR products and bcl-2/JH DNA sequence analysis showed that the same t(14;18) carrying clone was present in the bone marrow and the corresponding peripheral blood lymphocyte samples in three of these seven patients. Some patients had more than one bcl-2/JH rearrangement. There was no significant correlation between age and the translocation incidence. Cells carrying the t(14;18) translocation were present in peripheral blood lymphocyte samples with a similar incidence--between 47% and 52% in all age groups from 20 to 79 years. Patients older than 80 years had a lower (37%) but not significantly different incidence.

CONCLUSIONS

These findings suggest that patients affected by non-lymphoid diseases may have several t(14;18) carrying cells and some of them undergo a clonal expansion. Whether individuals with t(14;18) positive cells are at a higher risk of lymphoid malignancies remains unanswered and further epidemiological studies are required.