James Torchia

Depleting tumor-specific Tregs at a single site eradicates disseminated tumors.

Activation of TLR9 by direct injection of unmethylated CpG nucleotides into a tumor can induce a therapeutic immune response; however, Tregs eventually inhibit the antitumor immune response and thereby limit the power of cancer immunotherapies. In tumor-bearing mice, we found that Tregs within the tumor preferentially express the cell surface markers CTLA-4 and OX40. We show that intratumoral coinjection of anti-CTLA-4 and anti-OX40 together with CpG depleted tumor-infiltrating Tregs. This in situ immunomodulation, which was performed with low doses of antibodies in a single tumor, generated a systemic antitumor immune response that eradicated disseminated disease in mice. Further, this treatment modality was effective against established CNS lymphoma with leptomeningeal metastases, sites that are usually considered to be tumor cell sanctuaries in the context of conventional systemic therapy. These results demonstrate that antitumor immune effectors elicited by local immunomodulation can eradicate tumor cells at distant sites. We propose that, rather than using mAbs to target cancer cells systemically, mAbs could be used to target the tumor infiltrative immune cells locally, thereby eliciting a systemic immune response.

TREM2, a DAP12-associated receptor, regulates osteoclast differentiation and function

Deficiency of the signaling adapter protein DAP12 or its associated receptor TREM2 is associated with abnormal OC development in humans. Here we examine the role of TREM2 in mouse OC development and function, including migration and resorption in vitro. These results provide new evidence that TREM2 regulates OC function independent of its effects on multinucleated OC differentiation.

TREM2- and DAP12-Dependent Activation of PI3K Requires DAP10 and Is Inhibited by SHIP1

The inositol phosphatase SHIP1 binds to a receptor-adaptor complex on osteoclasts to prevent recruitment of PI3K and inhibit receptor signaling. Keeping Osteoclasts in Check Bone resorption is mediated by cells known as osteoclasts, which develop from myeloid precursor cells. Differentiation and activation of osteoclasts depend on the signaling of receptors whose responses are mediated by the adaptor protein DAP12. One such receptor is TREM2, which drives osteoclastogenesis; deficiencies in either DAP12 or TREM2 result in similar phenotypes. TREM2- and DAP12-dependent signaling also inhibits some Toll-like receptor (TLR)–dependent responses in macrophages, another myeloid cell type. Thus, the TREM2-DAP12 signaling axis may be both stimulatory and inhibitory; however, little is known about how DAP12 functions in these different contexts. Peng et al. found that ligation of TREM2 with a cross-linking antibody triggered DAP12-dependent osteoclastogenesis that required the recruitment of phosphatidylinositol 3-kinase (PI3K) to the TREM2-DAP12 signaling complex. This signaling pathway was inhibited by the Src homology 2 (SH2) domain–dependent recruitment to TREM2-DAP12 of the inositol phosphatase SHIP1, which prevented PI3K from binding to DAP12. In addition, signaling downstream of other receptors on osteoclasts differentially recruited SHIP1 to DAP12. The authors thus propose that the stimulatory or inhibitory nature of TREM2-DAP12 signaling is regulated by SHIP1. The activation and fusion of macrophages and of osteoclasts require the adaptor molecule DNAX-activating protein of 12 kD (DAP12), which contains immunoreceptor tyrosine-based activation motifs (ITAMs). TREM2 (triggering receptor expressed on myeloid cells–2) is the main DAP12-associated receptor in osteoclasts and, similar to DAP12 deficiency, loss of TREM2 in humans leads to Nasu-Hakola disease, which is characterized by bone cysts and dementia. Furthermore, in vitro experiments have shown that deficiency in DAP12 or TREM2 leads to impaired osteoclast development and the formation of mononuclear osteoclasts. Here, we demonstrate that the ligation of TREM2 activated phosphatidylinositol 3-kinase (PI3K), extracellular signal–regulated kinase 1 (ERK1) and ERK2, and the guanine nucleotide exchange factor Vav3; induced the mobilization of intracellular calcium (Ca2+) and the reorganization of actin; and prevented apoptosis. The signaling adaptor molecule DAP10 played a key role in the TREM2- and DAP12-dependent recruitment of PI3K to the signaling complex. Src homology 2 (SH2) domain–containing inositol phosphatase-1 (SHIP1) inhibited TREM2- and DAP12-induced signaling by binding to DAP12 in an SH2 domain–dependent manner and preventing the recruitment of PI3K to DAP12. These results demonstrate a previously uncharacterized interaction of SHIP1 with DAP12 that functionally limits TREM2- and DAP12-dependent signaling and identify a mechanism through which SHIP1 regulates key ITAM-containing receptors by directly blocking the binding and activation of PI3K.

Therapeutic effect of CD137 immunomodulation in lymphoma and its enhancement by Treg depletion

Despite the success of passive immunotherapy with monoclonal antibodies (mAbs), many lymphoma patients eventually relapse. Induction of an adaptive immune response may elicit active and long-lasting antitumor immunity, thereby preventing or delaying recurrence. Immunomodulating mAbs directed against immune cell targets can be used to enhance the immune response to achieve efficient antitumor immunity. Anti-CD137 agonistic mAb has demonstrated antitumor efficacy in various tumor models and has now entered clinical trials for the treatment of solid tumors. Here, we investigate the therapeutic potential of anti-CD137 mAb in lymphoma. We found that human primary lymphoma tumors are infiltrated with CD137+ T cells. We therefore hypothesized that lymphoma would be susceptible to treatment with anti-CD137 agonistic mAb. Using a mouse model, we demonstrate that anti-CD137 therapy has potent antilymphoma activity in vivo. The antitumor effect of anti-CD137 therapy was mediated by both natural killer (NK) and CD8 T cells and induced long-lasting immunity. Moreover, the antitumor activity of anti-CD137 mAb could be further enhanced by depletion of regulatory T cell (T(regs)). These results support the evaluation of anti-CD137 therapy in clinical trials for patients with lymphoma.

Bone microenvironment specific roles of ITAM adapter signaling during bone remodeling induced by acute estrogen-deficiency.

Immunoreceptor tyrosine-based activation motif (ITAM) signaling mediated by DAP12 or Fcε receptor Iγ chain (FcRγ) have been shown to be critical for osteoclast differentiation and maturation under normal physiological conditions. Their function in pathological conditions is unknown. We studied the role of ITAM signaling during rapid bone remodeling induced by acute estrogen-deficiency in wild-type (WT), DAP12-deficient (DAP12-/-), FcRγ-deficient (FcRγ-/-) and double-deficient (DAP12-/-FcRγ-/-) mice. Six weeks after ovariectomy (OVX), DAP12-/-FcRγ-/- mice showed resistance to lumbar vertebral body (LVB) trabecular bone loss, while WT, DAP12-/- and FcRγ-/- mice had significant LVB bone loss. In contrast, all ITAM adapter-deficient mice responded to OVX with bone loss in both femur and tibia of approximately 40%, relative to basal bone volumes. Only WT mice developed significant cortical bone loss after OVX. In vitro studies showed microenvironmental changes induced by OVX are indispensable for enhanced osteoclast formation and function. Cytokine changes, including TGFβ and TNFα, were able to induce osteoclastogenesis independent of RANKL in BMMs from WT but not DAP12-/- and DAP12-/-FcRγ-/- mice. FSH stimulated RANKL-induced osteoclast differentiation from BMMs in WT, but not DAP12-/- and DAP12-/-FcRγ-/- mice. Our study demonstrates that although ITAM adapter signaling is critical for normal bone remodeling, estrogen-deficiency induces an ITAM adapter-independent bypass mechanism allowing for enhanced osteoclastogenesis and activation in specific bony microenvironments.

Targeting lymphoma with precision using semisynthetic anti-idiotype peptibodies

Significance Idiotype is a true tumor-specific surface marker on lymphoma cells, and cross-linking idiotype can directly trigger lymphoma cell death. It has not been practical, however, to target idiotype with antibodies because its sequence is unique to each patient. By chemically linking short synthetic patient-specific idiotype-binding peptides to a patient-invariant IgG Fc domain, we created a modular, antibody-like molecule that is more practical to customize. These semisynthetic peptibodies kill lymphoma cells directly, trigger tumor cell phagocytosis by macrophages, and clear human lymphoma in a mouse model of disseminated disease. This technology could add a new mechanism of action to the armament of lymphoma therapies and would not possess the toxicities and immunosuppression inherent to the current standard of care. B-cell lymphomas express a functionally active and truly tumor-specific cell-surface product, the variable region of the B-cell receptor (BCR), otherwise known as idiotype. The tumor idiotype differs, however, from patient to patient, making it a technical challenge to exploit for therapy. We have developed a method of targeting idiotype by using a semisynthetic personalized therapeutic that is more practical to produce on a patient-by-patient basis than monoclonal antibodies. In this method, a small peptide with affinity for a tumor idiotype is identified by screening a library, chemically synthesized, and then affixed to the amino terminus of a premade IgG Fc protein. We demonstrate that the resultant semisynthetic anti-idiotype peptibodies kill tumor cells in vitro with specificity, trigger tumor cell phagocytosis by macrophages, and efficiently clear human lymphoma in a murine xenograft model. This method could be used to target tumor with true precision on a personalized basis.

Abstract 648: Semi-synthetic peptibodies are a novel personalized therapeutic with activity against lymphoma in vitro and in vivo

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA The complementarity determining region, or idiotype, of the surface immunoglobulin receptor is a true tumor-specific marker on B-cell lymphomas unique to each patient. Antibodies against idiotype can induce complete regression of lymphoma in patients, but since this requires the generation of a custom monoclonal antibody for each patient, it has not been practical. We have developed a method for targeting idiotype using a novel construct that we refer to as a “semi-synthetic peptibody”. It consists of a synthetic peptide ligand for idiotype that is covalently linked to the amino terminus of a recombinant IgG Fc domain. Peptide ligands for idiotype can be identified by high throughput screens of random peptide libraries and produced inexpensively by solid-phase synthesis. Linkage of these idiotype ligands to the Fc domain enhances their pharmacokinetics and augments their anti-tumor effect by activating innate immune effectors. Since each patient-specific synthetic peptide can be chemically linked to a common IgG Fc domain, this modular design yields a custom therapeutic that may be more practical to produce than a unique biologic monoclonal antibody. We demonstrate that semi-synthetic peptibodies bind specifically to the idiotype of tumor cells and induce apoptosis by crosslinking surface immunoglobulin. Additionally, they trigger antibody dependent cellular cytotoxicity, antibody mediated phagocytosis, and complement-mediated lysis of opsonized lymphoma cells in vitro. They possess a favorable pharmacokinetic profile and are sufficient to clear tumor in SCID mice challenged intravenously with a luciferase-labeled human lymphoma cell line. Tumor clearance in vitro and in vivo mediated by peptibody was superior to that achievable with an anti-idiotype monoclonal antibody. Thus, semi-synthetic anti-idiotype peptibodies demonstrate multimodal activity against lymphoma cells in vitro and clear human lymphoma in a disseminated xenograft model. This modular, semi-synthetic design may enable a personalized and targeted therapy that is feasible to produce for patients with B-cell lymphoma. Citation Format: James Torchia, Patrick Ng, Homer Chen, Kipp Weiskopf, Ronald Levy. Semi-synthetic peptibodies are a novel personalized therapeutic with activity against lymphoma in vitro and in vivo . [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 648. doi:10.1158/1538-7445.AM2014-648

Abstract LB-139: In situ Treg immunomodulation at a single tumor site with CpG and immune checkpoint antibodies cures metastatic disease

Background: CD4+CD25+FOXP3+ regulatory T-cells (Tregs) infiltrate all tumor sites and play a central role in maintaining immune tolerance to cancers. Scientific question: Is the local immunomodulation of Tregs from a single tumor site sufficient to trigger a systemic anti-tumor immune response able to eradicate distant tumor sites ≤ Results: We found that tumor infiltrating Tregs preferentially express CTLA4 (CD152) and OX40 (CD134) compared to their counterparts in the blood and other lymphoid organs, both in mice and in human lymphomas. We show in a murine lymphoma model that OX40 and CTLA4 upregulation occurs specifically on Tregs directed against tumor antigens. Injections of low doses of anti-CTLA4 and anti-OX40 together with CpG, a TLR-9 agonist, directly into a single tumor site depletes the Tregs from the injected tumor but not from distant ones. This immunomodulation subsequently triggers an anti-tumor immune response able to cure mice with established disseminated disease. This triple combination is uniquely required as neither CpG alone nor mAbs without CpG are effective. Significance: immunomodulatory antibodies are currently under clinical development for cancer therapy. Their major toxicity is the triggering of auto-immune diseases. We show here that after injections of very little doses of these antibodies with CpG at one tumor site, their serum levels become undetectable. However, these doses are sufficient to trigger a systemic anti-tumor response able to eradicate distant sites. Impact: we recently have published positive results of intra-tumoral CpG in patients with follicular Lymphoma (Brody, Levy, et al. JCO, 2010). Anti-CTLA4 has just been approved by the FDA/EMEA in patients with metastatic melanoma. Anti-Ox40 antibodies are currently being tested in phase I/II clinical trials. Therefore, the combination described here can be tested in patients with injectable sites of lymphoma. Together, these results are in favor of a paradigm shift in cancer therapy where the immune system is targeted rather than the tumor itself. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-139. doi:1538-7445.AM2012-LB-139