Autologous Bone Marrow Transplantation - Blog Science Connections

174 Detecting Residual Disease in Bone Marrow
which this is possible, the simultaneous search for a membrane marker with
one aneuploidy allows the threshold of detection to drop below 0.1 %. The flow
karyotype technique enables an analysis of many cells and, as well as being
objective, it sometimes allows the selection of abnormal chromosomes.
Cell Culture
In cell culture, a residual malignant clone emerges (3,8,9), but culture
systems do not allow absolute selectiveness in cloning tumor colony-forming
units (CFCIs) and normal CFCJs. We use cell culturing for three reasons: 1) to
study factors that control the development of leukemic or tumor CFCIs; 2) to test
the efficiency of ex vivo treatments; and 3) to detect and quantify residual
leukemic or tumor cells in a bone marrow in remission. The clonal nature of the
colonies observed by using cytogenetics (when the marker is identifiable),
immunology, and molecular biology have to be proved.
The ideal cell culture system adapted to the study of residual disease in
acute leukemia should allow the residual leukemic cells to be detected and a
selected growth phase of those cells to appear immediately recognizable. The
choice of cell culture aims at assessing the frequency of a rare occurrence but
one that is detectable through the knowledge of growth conditions. To appraise
the marrow purging methods, we believe the study of tumor CFCIs in patient
samples is a more reliable approach than the study of CFCIs in cell lines, which,
being artificial, are distinguished in terms of kinetics, phenotype, and clonality.
The tumor CFCIs, which are drowned in normal marrow cells, cannot have a
high clonal rate. In addition, with specific markers, a combination of MAbs can
be offered to separate tumor CFCIs from normal CFCIs (the elimination of a part
of normal cells is accompanied by an elimination of a concentration of
leukemic CFCIs).
Molecular Biology
The contribution of molecular biology (3,10-12) has changed traditional
techniques drastically. Rearrangements of immunoglobin genes (heavy and
light chains) in B-type clonal proliferations can be studied with the Southern blot
method. In T-cell clonal proliferations, the rearrangements of a and /3 genes
(more generally the /3 gene) of the T receptor of the antigen are studied. The
threshold of detection is low (\-5%). With the Southern blot test, 50 ug of DNA
is the minimum required (corresponding to 1-5 x 10 7
nucleated cells). This
method is therefore unsuited to the study of small cell fractions, such as one of
an isolated colony.
The oncogenes have a physiological function and serve as codes for
proteins that enter into cellular proliferation and differentiation. When their
manifestation is abnormal or disorganized, an abnormal proliferation can be
observed that might then lead to a malignant growth. Mutated oncogenes can
transcribe an abnormal protein that, when manifested at the cellular membrane
level, could lead to the production of specific MAbs of this protein. In this case, a