MONITORING THE CELLULAR COMPONENTS OF THE IMMUNE SYSTEM DURING CLINICAL TRIALS: A TRANSLATIONAL MEDICINE APPROACH - Flow Cytometry in Drug Discovery and Development - page 192

In addition to autoimmunity, other therapeutic areas such as oncology, cardio-
vascular disease, or metabolic disease are now also known to involve aspects of the
immune system or an inflammatory component and can be elucidated using PD
biomarkers. For example, type I diabetes is now considered a T-cell-mediated
immune disease [30]. Cardiovascular disease is thought to have an important
inflammatory component. Mechanistically, atherosclerosis is primarily an inflam-
matory disease mediated by cellular components of both the innate and the adaptive
immune systems [31]. While cancer is primarily a proliferative disorder, it can be
characterized using flow cytometric assays.

9.4 CLINICAL DRUG DEVELOPMENT I: MONITORING THE
CELLULAR COMPONENTS OF THE IMMUNE SYSTEM TO ESTABLISH
THE EFFECT OF THERAPEUTIC INTERVENTION

As discussed above, abnormalities in peripheral blood leucocytes have been described
in various therapeutic areas: autoimmunity, oncology, cardiovascular, and metabolic
disease. The nature of the abnormalities—be it a change in the abundance of a given
cell type or a change in the receptor expression on a particular cell type—continues to
be dissected and appreciated. Whether these cellular biomarkers are broad signatures
of chronic, systemic inflammation or disease-specific biomarkers remains to be
determined. Monitoring these cellular abnormalities during clinical testing of
immune modulating treatments will provide a unique opportunity to validate the
cellular abnormalities with regard to their utility as biomarkers and significance in
disease pathogenesis.
For example, there are several therapeutic compounds in development targeting
CD20 þ B cells for the treatment of SLE and RA. CD20 is expressed on most B-cell
lymphomas and all normal B cells with the exception of very early progenitors and
terminally differentiated plasma cells. Anti-CD20 treatment that results in a pro-
longed but transient depletion of peripheral B cells and was first approved for
treatment of B-cell tumors in non-Hodgkin's lymphoma and chronic lymphocytic
leukemia is now emerging as a supplementary treatment for autoimmune diseases
with B-cell involvement. The hypothesis is that treatment with CD20 targeting
compounds will result in depletion of autoreactive B cells while leaving the rest of
the immune system intact.
In preliminary studies with rituximab, a cytotoxic chimeric monoclonal antibody
(mAb) directed against CD20, improvement in the clinical manifestations of SLE and
RAhas been reported [32, 33]. Data supporting a primary study objective—the degree
of B-cell depletion—were generatedwith high-sensitivity flowcytometric assays able
to measure B-cell levels in the range of 0.1 cells/ m L whole blood [33, 34]. Some
studies suggested that the degree of B-cell depletion after the primary treatment was
predictive of clinical outcome [34]. In addition to monitoring B-cell depletion, flow
cytometric assays were used tomonitor the status of the immune system bymeasuring
other cell types of both the adaptive and the innate immune systems and to assess
functionally distinct B-cell subsets (na

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ve, memory) during posttreatment B-cell