Targeting CD38 Enhances the Antileukemic Activity of Ibrutinib in Chronic Lymphocytic Leukemia

Abstract

Purpose: CD38 has emerged as a high-impact therapeutic target in multiple myeloma, with the approval of daratumumab (anti-CD38 monoclonal antibody). The clinical importance of CD38 in chronic lymphocytic leukemia (CLL) patients has been known for over two decades, though it’s relevance as a therapeutic target in CLL remains understudied. Experimental Design: We investigated the biological effects and anti-tumor mechanisms engaged by daratumumab in primary CLL cells. Besides its known immune-effector mechanisms (ADCC, CDC and ADCP), we also measured direct apoptotic effects of daratumumab alone or in combination with ibrutinib. In vivo anti-leukemic activity was assessed in a partially-humanized xenograft model. The influence of CD38 on BCR signaling was measured via immunoblotting of Lyn, Syk, BTK, PLCγ2, ERK1/2 and AKT. Results: In addition to immune-effector mechanisms; daratumumab also induced direct apoptosis of primary CLL cells, which was partially dependent on FcγR crosslinking. For the first time, we demonstrated the influence of CD38 on BCR signaling where interference of CD38 downregulated Syk, BTK, PLCγ2, ERK1/2 and AKT; effects that were further enhanced by addition of ibrutinib. In comparison to single agent treatment, the combination of ibrutinib and daratumumab resulted in significantly enhanced anti-CLL activity in vitro and significantly decreased tumor growth and prolonged survival in the in vivo CLL xenograft model. Conclusions: Overall, our data demonstrate the anti-tumor mechanisms of daratumumab in CLL; furthermore, we show how co-targeting BTK and CD38 lead to a robust anti-CLL effect, which has clinical implications.

The Many Facets of CD38 in Lymphoma: From Tumor–Microenvironment Cell Interactions to Acquired Resistance to Immunotherapy

“…Finally, it impedes adhesion to VCAM-1 by down-regulating matrix metalloproteinases, therefore inhibiting tumor infiltration and dissemination. Such findings were confirmed by Manna et al [86], who also detected apoptosis when CLL cells were exposed to Daratumumab. The same research group also detected a CD38-mediated down-regulating of BTK, and demonstrated that accordingly, Daratumumab administration enhances Ibrutinib anti-tumoral activity.…”

The Circular Life of Human CD38: From Basic Science to Clinics and Back

“…In hematology, different studies have shown that DARA may enhance macrophage-mediated phagocytosis of Burkitt’s lymphoma cells in vitro [ 60 ] and further enhance lysis by ADCC (Antibody-dependent cellular cytotoxicity) and ADCP (Antibody-dependent cellular phagocytosis) of CLL (Chronic lymphocytic leukemia) cells both in vitro and in vivo [ 61 , 62 , 63 ]. Moreover, in ex vivo peripheral blood cells from CLL patients (and in a CLL patient-derived xenograft model in vivo), DARA was noted to deplete the B-regulatory and T-regulatory cell fractions but promoted downstream activation and expansion of PD-1 low CD8 + cytotoxic T-cells.…”

Targeting CD38 is lethal to Breg-like chronic lymphocytic leukemia cells and Tregs, but restores CD8+ T-cell responses

“…CD19 1 CD5 1 CD38 hi/lo CLL cells and CD4 1 CD25 1 CD127 lo Tregs were sorted out using magnetic beads/flow-sorter (sorting and gating strategy in supplemental Materials and methods). 18 A CLL-patientderived xenograft (PDX) model was established, 22 using PBMCs isolated from a patient with CLL with CD38 1 disease, injected into NSG mice (The Jackson Laboratory). iTreg formation assays were carried out using naive Th cells prestimulated with anti-CD3 (5 mg/mL)/CD28 (5 mg/mL) antibodies followed by coculture with either autologous Breg-like (CD19 1 CD24 1 CD38 1 ) or non-Breg (CD19 1 CD24 1 CD38 2 ) CLL cells.…”

“…17 We have recently demonstrated that targeting CD38 with the anti-CD38 human monoclonal antibody (mAb) daratumumab downregulates B-cell receptor signaling and enhances the antitumor activity of ibrutinib in CLL cells and Waldenstrom macroglobulinemia tumor cells. 18,19 These investigations revealed that daratumumab induces antibodydependent cell-mediated cytotoxicity, complement-dependent cytotoxicity, antibody-dependent cellular phagocytosis, and direct apoptosis of CLL cells in vitro, and together these undergird its anti-CLL activity in vivo.…”