IMMUNOPHARMACOLOGIC ERADICATION OF MYELOID LEUKEMIA

Autologous bone marrow transplantation (ABMT), whereby the patient's own
marrow is used as the source of stem cell rescue, is potentially curative
in patients with acute myeloid leukemia (AML). However, the presence of
residual occult viable leukemic cells in the marrow autograft limits the
therapeutic effectiveness of ABMT in AML. To overcome this problem,
methods of ex vivo treatment ('purging') of autologous marrow must be
developed that optimally eradicate AML cells but spare normal hematopoietic
stem cells. The proposed preclinical collaborative research between the
All-Union Cancer Research Center (AUCRC), Moscow, USSR and The Johns
Hopkins Oncology Center (JHOC), Baltimore, MD, will evaluate novel ex vivo
marrow purging regimens by comparison of the effects of incubation with
graded concentrations of immunologic and/or pharmacologic agents on the
growth of normal marrow and leukemic cells, using an authentic animal model
of human AML (the LBN hybrid rat). In vitro clonogenic assays for normal
hematopoietic progenitors (colony-forming-unit, granulocyte-macrophage;
CFU-CM) and AML cells (colony-forming-unit, leukemia; CFU-Leuk), which we
have shown are predictive for hematopoietic engraftment and AML log-kill in
rats given syngeneic marrow and/or AML cells incubated ex vivo with
selected chemotherapeutic agents, will be used in these dose-response
studies. Suspensions of normal LBN marrow, AML cells maintained in sus-
pension cultures in vitro, and 10:1 mixtures of normal marrow:AML cells (to
approximate an early marrow relapse of AML) will be incubated with
complement and graded concentrations of anti-AML monoclonal antibodies
(MoAbs) AP64, RM124, and RM152, or with bruneomycin (an antineoplastic
antibiotic with potential utility as a marrow chemopurging agent), or the
alkylating agent 4-hydroperoxycyclophosphamide (4HC). After incubation,
cells will be plated for CFU-GM and CFU-Leuk assays to determine survival
of committed hematopoietic progenitors and log-kill of AML cells, and
optimal conditions for antileukemic effect with stem-cell sparing.
Variables to be examined include agent concentrations, incubation duration
and temperature, cell density, sequence of treatment, and number of cycles
of in vitro treatment. Finally, results of the above studies will be used
to examine the effects of combined immunopharmacologic incubation with
MoAbs (singly and in combination) plus bruneomycin and/ or 4HC on the
survival of CFU-GM and CFU-Leuk. These In vitro investigations of
immunopharmacologic purging in an authentic model of human leukemia are
relevant to the elucidation of basic mechanisms of normal and neoplastic
hematopoiesis and will provide the basis for subsequent collaborative
AUCRC/JHOC studies of clinical ABMT in patients with AML.