Tumoricidal Effects of Macrophage-Activating Immunotherapy in a Murine Model of Relapsed/Refractory Multiple Myeloma

Abstract

Myeloma remains a virtually incurable malignancy. The inevitable evolution of multi-drug resistant clones and widespread clonal heterogeneity limit the potential of traditional and novel therapies to eliminate minimal residual disease, a reliable harbinger of relapse. Here we show potent anti-myeloma activity of macrophage-activating immunotherapy (αCD40+CpG) that resulted in prolongation of progression-free and overall survival in an immunocompetent, preclinically validated, transplant-based model of multi-drug resistant, relapsed/refractory myeloma (t-Vκ*MYC). αCD40+CpG was effective in vivo in the absence of cytolytic NK, T or B cells and resulted in expansion of M1-polarized (cytolytic/tumoricidal) macrophages in the bone marrow. Moreover, we show that concurrent loss/inhibition of TPL2 (Cot, MAP3K8), a MAP3K that is recruited to activated CD40 complex and regulates macrophage activation/cytokine production, potentiated direct, ex vivo anti-myeloma tumoricidal activity of αCD40+CpG-activated macrophages, promoted production of antitumor cytokine IL12 in vitro and in vivo and synergized with αCD40+CpG to further prolong progression-free and overall survival in vivo. Our results support the combination of αCD40-based macrophage activation and TPL2 inhibition for myeloma immunotherapy. We propose that αCD40-mediated activation of innate antitumor immunity may be a promising approach to control/eradicate minimal residual disease following cytoreduction with traditional or novel anti-myeloma therapies.

Immunoregulatory roles of versican proteolysis in the myeloma microenvironment

“…Tpl2 negatively regulated Il-12p40 production in response to versikine ( Figure 1D), in a manner analogous to TLR agonists. 16 Whereas versikine induced Il-12p40 in isolation, concurrent Fcg receptor ligation through addition of ovalbumin (OVA)/anti-OVA immune complexes promoted Il-10 production and skewed macrophage polarization toward an immunoregulatory M2b phenotype (Il-12 lo -Il-10 hi ) 17 ( Figure 1E). Intact VCAN is thought to signal through TLR2.…”

Deploying myeloid cells against myeloma

“…In a recent report from our group, 9 we showed that aCD40 agonistic immunotherapy reprograms innate immune cells to exert potent anti-myeloma activity ex vivo and in vivo. aCD40-induced anti-myeloma tumoricidal effects were largely independent of cytolytic NK, T or B cells, a finding that supports the active involvement of macrophages in this process.…”

“…Therefore, TPL2 can be viewed as an "innate immune checkpoint" and rationally targeted in combination with aCD40-based immunotherapies. 9 The mechanism of action of strongly-agonistic aCD40 immunotherapy may be fundamentally different to that of weak-agonists or antagonists previously tested in myeloma with modest results (dacetuzumab, lucatumumab). 8 Whereas strong CD40 agonists may principally work through immunemediated mechanisms, weak-agonists/antagonists exert their effects primarily though antibody-dependent cell-mediated cytotoxicity (ADCC) and/or complement-mediated cytotoxicity (CMC).…”

“…aCD40-induced anti-myeloma tumoricidal effects were largely independent of cytolytic NK, T or B cells, a finding that supports the active involvement of macrophages in this process. 9 CONTACT Fotis Asimakopoulos fasimako@medicine. Moreover, we have shown that inhibition/deletion of the serine/ threonine kinase, TPL2 (Cot/MAP3K8), synergized with aCD40-based immunotherapy to enhance anti-myeloma immunity.…”

“…Third, any potential growthpromoting effects of CD40 stimulation could be mitigated by TPL2 or MEK inhibition because TPL2 controls MAPK pathway activation downstream of CD40 signaling through MEK. 9 Thus, inhibition of TPL2 signaling, acting both as an "innate immune checkpoint" in the microenvironment and as a modulator of CD40 pathway-mediated signals in tumor cells, may augment the benefits of aCD40-therapy.…”