Biomedical Engineering Reference
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function in a cell line model, it will equally affect all cell subsets in the blood. In
particular, different cell subsets have different rates of endocytosis, different life
spans, and different rates of differentiation. This makes it imperative to measure drug
action directly in the blood, where the drug is ultimately acting. Phospho flow is one of
the few platforms that allows this type of analysis.
15.6 PATIENT STRATIFICATION AND DIAGNOSTICS
Assuming that an effective drug has been identified, flow cytometry holds sig-
nificant promise for the growing field of personalizedmedicine. Appropriate protein
expression and signal transduction are essential in the development of healthy
immune cells and remodeling of cell communication networks drives proliferation
of diseased cells in cancer, autoimmunity, and many other human diseases. A
network-level single-cell view of signaling in healthy and diseased cells is needed to
identify shared features of malignant signaling networks and identify new therapies
that target signaling.
15.6.1 Signaling Profiles of Human Cancer
As mentioned previously, one advantage of flow cytometry is that primary samples
can be studied without the need to physically isolate the cell types of interest from
patient samples. This technique for dissecting signaling in heterogeneous cell
populations within a primary tumor was demonstrated in studies where single-cell
signaling profiles were used to map acute myeloid leukemia cell signaling and
identify patients with a high risk of not responding to chemotherapy [22]. By seeking
disease-specific signaling features and then comparing them to clinical outcome, a
profile of signaling that stratified patient riskwas obtained (Figure 15.7). As the notion
of “cancer stem cells” has moved into the mindset of molecular oncology, there are
some tantalizing hints that the signaling profile of the cell subset that appears to
contain the “killer” cells for the AML patients has stem cell-like attributes.Since the
original analysis of AML, single-cell signaling profiles have been used to determine
the effect of oncogene mutations, such as G12D in murine K-Ras and Y591
duplication in human FLT-3, on cell signaling networks and to diagnose
JMML [7, 23, 24]. The JMML study provided a flow cytometry signaling profile
that can be obtained in an afternoon (instead of the standard 3 week colony formation
assay) for JMML diagnosis. When a profile of cell signaling is closely associated with
patient outcome, it suggests that the measured signaling events might be responsible
for that outcome [4]. If so, targeting signaling events associated with poor clinical
outcomes might improve patient survival.
15.6.2 Perturbing Signaling Networks for Research and Therapy
An important aspect of the signaling profile approach is the value of evoking signaling
in the signal transduction network (Figure 15.8). By perturbing cells, through
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