Immunoprofiling of Normal Human Donor Blood Identified Potential Pharmacodynamic Markers for JNJ-63709178 (CD123xCD3) Duobody® Antibody Treatment

Background

JNJ-63709178 (CD123xCD3) is a promising new bispecific antibody currently being investigated for the treatment for acute myeloid leukemia (AML), a disorder of early hematopoietic progenitor cells characterized by the proliferation and accumulation of immature, clonal, myeloid cells. Constitutive overexpression of the α-subunit of the interleukin-3 receptor (ie, IL-3αR/CD123) is a hallmark of the early AML progenitor cell population (ie, leukemic stem cells [LSC]), as well as leukemic blasts. CD123 is unique to the IL-3 receptor and is responsible for the high specificity and low affinity binding of IL-3. Under physiological conditions, activation of the IL-3 receptor induces proliferative, anti-apoptotic, and differentiating signals. JNJ-63709178, a humanized IgG4 bispecific DuoBody® antibody with high affinity anti-CD123 and -CD3 arms, recognizes CD123 on myeloid cells and CD3 on T cells, leading to T-cell activation, with subsequent lysis of CD123+ AML blasts. JNJ-63709178 induces potent tumor cell killing in vitro, ex vivo, and in murine AML models, and is currently being evaluated in first-in-human clinical trials. Although CD123 is distinctively expressed on leukemic cells, some populations of normal myeloid cells have been reported to express CD123. The goals of this study were to determine CD123 receptor density on various leukocyte populations in normal human peripheral blood and evaluate the effects of JNJ-63709178 on those cells to identify potential pharmacodynamic markers.

Methods

Peripheral blood samples from 6 normal human donors were analyzed ex vivo for CD123 expression on various leukocyte populations to determine receptor density. Receptor density on cells was quantified using Quantibrite PE enumeration kit. Subsequently, blood samples were treated with escalating concentrations of JNJ-63709178 (CD123xCD3) or the control compound CNTO 7008 (nullxCD3) DuoBody® antibodies and incubated at 37°C for 48 hours. After incubation, blood samples were stained and processed for analysis of T-cell activation (CD25 expression) and population persistence or depletion (frequencies within leukocytes). In the myeloid compartment, basophils, myeloid dendritic cells (mDCs), monocytes, neutrophils, and eosinophils were analyzed. In the lymphoid compartment, plasmacytoid dendritic cells (pDCs), B cells (naïve and memory), T cells (helper and cytotoxic), and natural killer (NK) cells (CD56bright and CD56dim) were analyzed.

Results

In normal human peripheral blood samples, CD123 expression was highest on pDCs and basophils (above 10,000 receptors per cell). Intermediate expression (300-3,000 receptors per cell) was observed on mDCs, monocytes, eosinophils, and naïve B cells. Low expression (10-200 receptors per cell) was observed on neutrophils, memory B cells, T cells, and NK cells. These data are in agreement with previous studies (Busfield et al. ASH 2013 abs3598). Following incubation with JNJ-63709178, potent activation of CD4+ and CD8+ T cells was observed at sub-nanomolar levels, with EC₅₀values of 0.07 nM and 0.1 nM, respectively. Higher CD123 expression and T-cell activation correlated strongly with profound depletion of basophils and pDCs, as well as partial depletion of eosinophils and monocytes. Consistent with low CD123 expression, T cells and NK cells did not show substantial dose-dependent depletion. In contrast to CD123 expression levels, B cells and neutrophils showed partial depletion, despite low CD123 expression, while mDCs did not show dose-dependent depletion, despite higher CD123 levels. The activation of T cells and cytotoxic effect on CD123-positive cells was observed only with JNJ-63709178. The control compound CNTO 7008 (nullxCD3) had no effect on T-cell activation or any of the investigated cell populations.

Conclusions

These findings highlight the potential pharmacodynamic markers of JNJ-63709178 (CD123xCD3) bispecific treatment and provide a better understanding of its mechanism of action and a rationale for receptor expression monitoring during ongoing clinical trials.