Autologous Bone Marrow Transplantation - Blog Science Connections

Detecting Residual Disease in Bone Marrow 173
AVAILABLE TECHNIQUES
Cytomorphology and Immunohistochemistry
Although the techniques of cytomorphology and immunohistochemistry
are not conclusive, they do, nevertheless, provide a lot of information on the
structure of tumor cells. A differential diagnosis between tumor cells and
reactive cells after chemotherapy is sometimes difficult to obtain. Cytohistology
benefits from the contribution made by immunology when the same cells in
immunophenotype or in cytology (smear or cut sections) are examined.
Immunohistochemistry can identify isolated tumor cells that traditional medullary
histology cannot detect.
Immunology
Although a panel of more than 800 monoclonal antibodies (MAbs)
grouped together in 19 clusters of differentiation exists, none of these MAbs is
actually specific to either the leukemic or tumor cell (2). MAbs supply an
immunologic phenotype of the target cell, prove its origin from a given cellular
lineage, and locate the cells that fail to acquire the properties of mature cells.
The choice of MAbs with a therapeutic aim (ex vivo treatment of the marrow)
depends on the initial phenotype. Cell cryopreservation of the initial tumor
plays a vital part that should not be omitted. These serve as references in
atypical relapses and in the choice of the ex vivo treatment.
Cytogenetics
Cytogenetics (3-5) identifies chromosomal abnormalities (translocations
in particular) of great interest in acute lymphoblastic leukemia (ALL) when a
prognosis is made. We have a very useful pure clonal marker that tracks down
residual disease and confirms the malignant origins of suspect cells. The
technical conditions in setting up the culture (dominated by the delay
separating harvest from culture—less than 60 minutes in ALL) determine the
success of the karyotype. More than 50 mitoses have to be analyzed in order to
increase the chances of finding an abnormal mitosis.
Flow Cytometry
Flow cytometry (6,7) discriminates between cells according to size;
cytoplasmic density; and fluorescent surface membrane, cytoplasmic, or
nuclear markers. With it, the threshold of sensitivity in detecting an aneuploidy
(of variable frequency according to the malignant proliferation concerned)
depends on the DNA index (which corresponds to the relationship between the
quantity of DNA in the tumor cell and the quantity of DNA in a control cell). The
threshold lies between 1 % and 5%. The specific and nonspecific fixation of some
MAbs can be distinguished when using double labeling with different fluorochromes
and phycoerythrin. The variations in antigenic density sometimes
allow a normal cell to be discriminated from a malignant cell. In instances in