Btla signaling in conventional and regulatory lymphocytes coordinately tempers humoral immunity in the intestinal mucosa.

The Btla inhibitory receptor limits innate and adaptive immune responses, both preventing the development of autoimmune disease and restraining anti-viral and anti-tumor responses. It remains unclear how the functions of Btla in diverse lymphocytes contribute to immunoregulation. Here, we show that Btla inhibits activation of genes regulating metabolism and cytokine signaling, including Il6 and Hif1a, indicating a regulatory role in humoral immunity. Within mucosal Peyer's patches, we find T-cell-expressed Btla-regulated Tfh cells, while Btla in T or B cells regulates GC B cell numbers. Treg-expressed Btla is required for cell-intrinsic Treg homeostasis that subsequently controls GC B cells. Loss of Btla in lymphocytes results in increased IgA bound to intestinal bacteria, correlating with altered microbial homeostasis and elevations in commensal and pathogenic bacteria. Together our studies provide important insights into how Btla functions as a checkpoint in diverse conventional and regulatory lymphocyte subsets to influence systemic immune responses.

Antagonizing Integrin ß3 Increases Immunosuppression in Cancer.

Integrin ß3 is critical for tumor invasion, neoangiogenesis, and inflammation, making it a promising cancer target. However, preclinical and clinical data of integrin ß3 antagonists have demonstrated no benefit or worse outcomes. We hypothesized that integrin ß3 could affect tumor immunity and evaluated tumors in mice with deletion of integrin ß3 in macrophage lineage cells (ß3KOM). ß3KOM mice had increased melanoma and breast cancer growth with increased tumor-promoting M2 macrophages and decreased CD8(+) T cells. Integrin ß3 antagonist, cilengitide, also enhanced tumor growth and increased M2 function. We uncovered a negative feedback loop in M2 myeloid cells, wherein integrin ß3 signaling favored STAT1 activation, an M1-polarizing signal, and suppressed M2-polarizing STAT6 activation. Finally, disruption of CD8(+) T cells, macrophages, or macrophage integrin ß3 signaling blocked the tumor-promoting effects of integrin ß3 antagonism. These results suggest that effects of integrin ß3 therapies on immune cells should be considered to improve outcomes. Cancer Res; 76(12); 3484-95. ©2016 AACR.

CXCR4 Protein Epitope Mimetic Antagonist POL5551 Disrupts Metastasis and Enhances Chemotherapy Effect in Triple-Negative Breast Cancer.

The SDF-1 receptor CXCR4 has been associated with early metastasis and poorer prognosis in breast cancers, especially the most aggressive triple-negative subtype. In line with previous reports, we found that tumoral CXCR4 expression in patients with locally advanced breast cancer was associated with increased metastases and rapid tumor progression. Moreover, high CXCR4 expression identified a group of bone marrow-disseminated tumor cells (DTC)-negative patients at high risk for metastasis and death. The protein epitope mimetic (PEM) POL5551, a novel CXCR4 antagonist, inhibited binding of SDF-1 to CXCR4, had no direct effects on tumor cell viability, but reduced migration of breast cancer cells in vitro. In two orthotopic models of triple-negative breast cancer, POL5551 had little inhibitory effect on primary tumor growth, but significantly reduced distant metastasis. When combined with eribulin, a chemotherapeutic microtubule inhibitor, POL5551 additively reduced metastasis and prolonged survival in mice after resection of the primary tumor compared with single-agent eribulin. Hypothesizing that POL5551 may mobilize tumor cells from their microenvironment and sensitize them to chemotherapy, we used a "chemotherapy framing" dosing strategy. When administered shortly before and after eribulin treatment, three doses of POL5551 with eribulin reduced bone and liver tumor burden more effectively than chemotherapy alone. These data suggest that sequenced administration of CXCR4 antagonists with cytotoxic chemotherapy synergize to reduce distant metastases.

Very late antigen-4 (α(4)ß(1) Integrin) targeted PET imaging of multiple myeloma.

Biomedical imaging techniques such as skeletal survey and (18)F-fluorodeoxyglucose (FDG)/Positron Emission Tomography (PET) are frequently used to diagnose and stage multiple myeloma (MM) patients. However, skeletal survey has limited sensitivity as it can detect osteolytic lesions only after 30-50% cortical bone destruction, and FDG is a marker of cell metabolism that has limited sensitivity for intramedullary lesions in MM. Targeted, and non-invasive novel probes are needed to sensitively and selectively image the unique molecular signatures and cellular processes associated with MM. Very late antigen-4 (VLA-4; also called α(4)ß(1) integrin) is over-expressed on MM cells, and is one of the key mediators of myeloma cell adhesion to the bone marrow (BM) that promotes MM cell trafficking and drug resistance. Here we describe a proof-of-principle, novel molecular imaging strategy for MM tumors using a VLA-4 targeted PET radiopharmaceutical, (64)Cu-CB-TE1A1P-LLP2A. Cell uptake studies in a VLA-4-positive murine MM cell line, 5TGM1, demonstrated receptor specific uptake (P<0.0001, block vs. non-block). Tissue biodistribution at 2 h of (64)Cu-CB-TE1A1P-LLP2A in 5TGM1 tumor bearing syngeneic KaLwRij mice demonstrated high radiotracer uptake in the tumor (12±4.5%ID/g), and in the VLA-4 rich organs, spleen (8.8±1.0%ID/g) and marrow (11.6±2.0%ID/g). Small animal PET/CT imaging with (64)Cu-CB-TE1A1P-LLP2A demonstrated high uptake in the 5TGM1 tumors (SUV 6.6±1.1). There was a 3-fold reduction in the in vivo tumor uptake in the presence of blocking agent (2.3±0.4). Additionally, (64)Cu-CB-TE1A1P-LLP2A demonstrated high binding to the human MM cell line RPMI-8226 that was significantly reduced in the presence of the cold targeting agent. These results provide pre-clinical evidence that VLA-4-targeted imaging using (64)Cu-CB-TE1A1P-LLP2A is a novel approach to imaging MM tumors.

Noncompetitive modulation of the proteasome by imidazoline scaffolds overcomes bortezomib resistance and delays MM tumor growth in vivo.

Multiple myeloma (MM) is a malignant disorder of differentiated B-cells for which standard care involves the inhibition of the proteasome. All clinically used proteasome inhibitors, including the chemotherapeutic drug bortezomib, target the catalytic active sites of the proteasome and inhibit protein proteolysis by competing with substrate binding. However, nearly all (~97%) patients become intolerant or resistant to treatments within a few years, after which the average survival time is less than 1 year. We describe herein the inhibition of the human proteasome via a noncompetitive mechanism by the imidazoline scaffold, TCH-13. Consistent with a mechanism distinct from that of competitive inhibitors, TCH-013 acts additively with and overcomes resistance to bortezomib. Importantly, TCH-013 induces apoptosis in a panel of myeloma and leukemia cell lines, but in contrast, normal lymphocytes, primary bone marrow stromal cells (hBMSC), and macrophages are resistant to its cytotoxic effects. TCH-013 was equally effective in blocking MM cell growth in co-cultures of MM cells with hBMSC isolated from CD138 negative bone marrow (BM) samples of MM patients. The cellular activity translated well in vivo where TCH-013 delayed tumor growth in an MM xenograft model to a similar extent as bortezomib.

Hedgehog-targeted therapeutics uncouple the vicious cycle of bone metastasis.

Paracrine Hedgehog (Hh) signaling, in which tumor-derived Hh ligands activate stromal cells, has been implicated in the development and progression of many cancers. Recent data suggest that Hh-targeted therapeutics exert direct effects on host cells, thus interrupting a "vicious cycle" to bone metastasis that involves osteoblasts, osteoclasts, and tumor cells.

The ADP receptor P2RY12 regulates osteoclast function and pathologic bone remodeling.

The adenosine diphosphate (ADP) receptor P2RY12 (purinergic receptor P2Y, G protein coupled, 12) plays a critical role in platelet aggregation, and P2RY12 inhibitors are used clinically to prevent cardiac and cerebral thrombotic events. Extracellular ADP has also been shown to increase osteoclast (OC) activity, but the role of P2RY12 in OC biology is unknown. Here, we examined the role of mouse P2RY12 in OC function. Mice lacking P2ry12 had decreased OC activity and were partially protected from age-associated bone loss. P2ry12-/- OCs exhibited intact differentiation markers, but diminished resorptive function. Extracellular ADP enhanced OC adhesion and resorptive activity of WT, but not P2ry12-/-, OCs. In platelets, ADP stimulation of P2RY12 resulted in GTPase Ras-related protein (RAP1) activation and subsequent αIIbß3 integrin activation. Likewise, we found that ADP stimulation induced RAP1 activation in WT and integrin ß3 gene knockout (Itgb3-/-) OCs, but its effects were substantially blunted in P2ry12-/- OCs. In vivo, P2ry12-/- mice were partially protected from pathologic bone loss associated with serum transfer arthritis, tumor growth in bone, and ovariectomy-induced osteoporosis: all conditions associated with increased extracellular ADP. Finally, mice treated with the clinical inhibitor of P2RY12, clopidogrel, were protected from pathologic osteolysis. These results demonstrate that P2RY12 is the primary ADP receptor in OCs and suggest that P2RY12 inhibition is a potential therapeutic target for pathologic bone loss.

Hedgehog signaling inhibition blocks growth of resistant tumors through effects on tumor microenvironment.

Hedgehog (Hh) signaling is implicated in bone development and cellular transformation. Here we show that inhibition of Hh pathway activity inhibits tumor growth through effects on the microenvironment. Pharmacologic inhibition of the Hh effector Smoothened (Smo) increased trabecular bone in vivo and inhibited osteoclastogenesis in vitro. In addition, enhanced Hh signaling due to heterozygosity of the Hh inhibitory receptor Patched (Ptch1(+/-)) increased bone resorption, suggesting direct regulation of osteoclast (OC) activity by the Hh pathway. Ptch1(+/-) mice had increased bone metastatic and subcutaneous tumor growth, suggesting that increased Hh activation in host cells promoted tumor growth. Subcutaneous growth of Hh-resistant tumor cells was inhibited by LDE225, a novel orally bioavailable SMO antagonist, consistent with effects on tumor microenvironment. Knockdown of the Hh ligand Sonic Hh (SHH) in these cells decreased subcutaneous tumor growth and decreased stromal cell production of interleukin-6, indicating that tumor-derived Hh ligands stimulated tumor growth in a paracrine fashion. Together our findings show that inhibition of the Hh pathway can reduce tumor burden, regardless of tumor Hh responsiveness, through effects on tumor cells, OCs, and stromal cells within the tumor microenvironment. Hh may be a promising therapeutic target for solid cancers and bone metastases.

Dissection of platelet and myeloid cell defects by conditional targeting of the beta3-integrin subunit.

The purpose of this work was to determine platelet and myeloid cell-specific requirements for beta3-containing integrins in hemostasis, bone resorption, and tumor growth. LoxP-flanked mice were generated to study the conditional deletion of beta3-integrin in platelets [knockout in platelets (KOP)] and myeloid cells [knockout in myeloid (KOM)]. Using the beta3KOP and beta3KOM strains of mice, we studied the role of beta3-integrin in hemostasis, bone resorption, and subcutaneous tumor growth. Tissue-specific deletion of platelet beta3-integrins in beta3KOP mice did not affect bone mass but resulted in a severe bleeding phenotype. No growth difference of tumor xenografts or in neoangiogenesis were found in beta3KOP mice, in contrast to the defects observed in germline beta3(-/-) mice. Conditional deletion of myeloid beta3-integrins in beta3KOM mice resulted in osteopetrosis but had no effect on hemostasis or mortality. Tumor growth in beta3KOM mice was increased and accompanied by decreased macrophage infiltration, without increase in blood vessel number. Platelet beta3-integrin deficiency was sufficient to disrupt hemostasis but had no effect on bone mass or tumor growth. Myeloid-specific beta3-integrin deletion was sufficient to perturb bone mass and enhance tumor growth due to reduced macrophage infiltration in the tumors. These results suggest that beta3-integrins have cell-specific roles in complex biological processes.-Morgan, E. A., Schneider, J. G., Baroni, T. E., Uluçkan, O., Heller, E., Hurchla, M. A., Deng, H., Floyd, D., Berdy, A., Prior, J. L., Piwnica-Worms, D., Teitelbaum, S. L., Ross, F. P., Weilbaecher, K. N. Dissection of platelet and myeloid cell defects by conditional targeting of the beta3-integrin subunit.

The ARF tumor suppressor regulates bone remodeling and osteosarcoma development in mice.

The ARF tumor suppressor regulates p53 as well as basic developmental processes independent of p53, including osteoclast activation, by controlling ribosomal biogenesis. Here we provide evidence that ARF is a master regulator of bone remodeling and osteosarcoma (OS) development in mice. Arf(-/-) mice displayed increased osteoblast (OB) and osteoclast (OC) activity with a significant net increase in trabecular bone volume. The long bones of Arf(-/-) mice had increased expression of OB genes while Arf(-/-) OB showed enhanced differentiation in vitro. Mice transgenic for the Tax oncogene develop lymphocytic tumors with associated osteolytic lesions, while Tax+Arf(-/-) mice uniformly developed spontaneous OS by 7 months of age. Tax+Arf(-/-) tumors were well differentiated OS characterized by an abundance of new bone with OC recruitment, expressed OB markers and displayed intact levels of p53 mRNA and reduced Rb transcript levels. Cell lines established from OS recapitulated characteristics of the primary tumor, including the expression of mature OB markers and ability to form mineralized tumors when transplanted. Loss of heterozygosity in OS tumors arising in Tax+Arf(+/-) mice emphasized the necessity of ARF-loss in OS development. Hypothesizing that inhibition of ARF-regulated bone remodeling would repress development of OS, we demonstrated that treatment of Tax+Arf(-/-) mice with zoledronic acid, a bisphosphonate inhibitor of OC activity and repressor of bone turnover, prevented or delayed the onset of OS. These data describe a novel role for ARF as a regulator of bone remodeling through effects on both OB and OC. Finally, these data underscore the potential of targeting bone remodeling as adjuvant therapy or in patients with genetic predispositions to prevent the development of OS.

Interferon-gamma targets cancer cells and osteoclasts to prevent tumor-associated bone loss and bone metastases.

Interferon-gamma (IFN-gamma) has been shown to enhance anti-tumor immunity and inhibit the formation of bone-resorbing osteoclasts. We evaluated the role of IFN-gamma in bone metastases, tumor-associated bone destruction, and hypercalcemia in human T cell lymphotrophic virus type 1-Tax transgenic mice. Compared with Tax(+)IFN-gamma(+/+) mice, Tax(+)IFN-gamma(-/-) mice developed increased osteolytic bone lesions and soft tissue tumors, as well as increased osteoclast formation and activity. In vivo administration of IFN-gamma to tumor-bearing Tax(+)IFN-gamma(-/-) mice prevented new tumor development and resulted in decreased bromodeoxyuridine uptake by established tumors. In vitro, IFN-gamma directly decreased the viability of Tax(+) tumor cells through inhibition of proliferation, suppression of ERK phosphorylation, and induction of apoptosis and caspase 3 cleavage. IFN-gamma also inhibited macrophage colonystimulating factor-mediated proliferation and survival of osteoclast progenitors in vitro. Administration of IFN-gamma to C57BL/6 mice decreased Tax(+) tumor growth and prevented tumor-associated bone loss and hypercalcemia. In contrast, IFN-gamma treatment failed to protect IFN-gammaR1(-/-) mice from Tax(+) tumor-induced skeletal complications, despite decreasing tumor growth. These data demonstrate that IFN-gamma suppressed tumor-induced bone loss and hypercalcemia in Tax(+) mice by inhibiting both Tax(+) tumor cell growth and host-induced osteolysis. These data suggest a protective role for IFN-gamma in patients with bone metastases and hypercalcemia of malignancy.

Ligation of B and T lymphocyte attenuator prevents the genesis of experimental cerebral malaria.

B and T lymphocyte attenuator (BTLA; CD272) is a coinhibitory receptor that is predominantly expressed on T and B cells and dampens T cell activation. In this study, we analyzed the function of BTLA during infection with Plasmodium berghei ANKA. Infection of C57BL/6 mice with this strain leads to sequestration of leukocytes in brain capillaries that is associated with a pathology resembling cerebral malaria in humans. During the course of infection, we found an induction of BTLA in several organs, which was either due to up-regulation of BTLA expression on T cells in the spleen or due to infiltration of BTLA-expressing T cells into the brain. In the brain, we observed a marked induction of BTLA and its ligand herpesvirus entry mediator during cerebral malaria, which was accompanied by an accumulation of predominantly CD8+ T cells, but also CD4+ T cells. Application of an agonistic anti-BTLA mAb caused a significantly reduced incidence of cerebral malaria compared with control mice. Treatment with this Ab also led to a decreased number of T cells that were sequestered in the brain of P. berghei ANKA-infected mice. Our findings indicate that BTLA-herpesvirus entry mediator interactions are functionally involved in T cell regulation during P. berghei ANKA infection of mice and that BTLA is a potential target for therapeutic interventions in severe malaria.

Unexpected role of B and T lymphocyte attenuator in sustaining cell survival during chronic allostimulation.

B and T lymphocyte attenuator (BTLA; CD272) can deliver inhibitory signals to B and T cells upon binding its ligand herpesvirus entry mediator. Because CD28, CTLA-4, programmed death-1, and ICOS regulate the development of acute graft-vs-host disease (GVHD), we wished to assess if BTLA also played a role in this T cell-mediated response. In the nonirradiated parental-into-F1 model of acute GVHD, BTLA+/+ and BTLA-/- donor lymphocytes showed equivalent engraftment and expansion during the first week of the alloresponse. Unexpectedly, BTLA-/- donor T cells failed to sustain GVHD, showing a decline in surviving donor cell numbers beginning at day 9 and greatly reduced by day 11. Similarly, inhibition of BTLA-herpesvirus entry mediator engagement by in vivo administration of a blocking anti-BTLA Ab also caused reduced survival of donor cells. Microarray analysis revealed several genes that were differentially expressed by BTLA-/- and BTLA+/+ donor CD4+ T cells preceding the decline in BTLA-/- donor T cells. Several genes influencing Th cell polarization were differentially expressed by BTLA+/+ and BTLA-/- donor cells. Additionally, the re-expression of the IL-7Ralpha subunit that occurs in BTLA+/+ donor cells after 1 wk of in vivo allostimulation was not observed in BTLA-/- donor CD4+ cells. The striking loss of BTLA-/- T cells in this model indicates a role for BTLA activity in sustaining CD4+ T cell survival under the conditions of chronic stimulation in the nonirradiated parental-into-F1 GVHD.

B and T lymphocyte attenuator exhibits structural and expression polymorphisms and is highly Induced in anergic CD4+ T cells.

B and T lymphocyte attenuator (BTLA) was initially identified as expressed on Th1 cells and B cells, but recently reported to be expressed by macrophages, dendritic cells, and NK cells as well. To address this discrepancy we generated a panel of BTLA-specific mAbs and characterized BTLA expression under various activation conditions. We report the existence of three distinct BTLA alleles among 23 murine strains, differing both in Ig domain structure and cellular distribution of expression on lymphoid subsets. The BALB/c and MRL/lpr alleles differ at one amino acid residue, but C57BL/6 has nine additional differences and alters the predicted cysteine bonding pattern. The BALB/c BTLA allele is also expressed by B cells, T cells, and dendritic cells, but not macrophages or NK cells. However, C57BL/6 BTLA is expressed on CD11b+ macrophages and NK cells. Finally, in CD4+ T cells, BTLA is expressed most highly following Ag-specific induction of anergy in vivo, and unlike programmed death-1 and CTLA-4, not expressed by CD25+ regulatory T cells. These results clarify discrepancies regarding BTLA expression, suggest that structural and expression polymorphisms be considered when analyzing BTLA in various murine backgrounds, and indicate a possible role in anergic CD4+ T cells.

B and T lymphocyte attenuator regulates T cell activation through interaction with herpesvirus entry mediator.

B and T lymphocyte attenuator (BTLA) provides an inhibitory signal to B and T cells. Previously, indirect observations suggested that B7x was a ligand for BTLA. Here we show that BTLA does not bind B7x; instead, we identify herpesvirus entry mediator (HVEM) as the unique BTLA ligand. BTLA bound the most membrane-distal cysteine-rich domain of HVEM, distinct from regions where the ligands LIGHT and lymphotoxin-alpha bound HVEM. HVEM induced BTLA tyrosine phosphorylation and association of the tyrosine phosphatase SHP-2 and repressed antigen-driven T cell proliferation, providing an example of reverse signaling to a non-tumor necrosis factor family ligand. The conservation of the BTLA-HVEM interaction between mouse and human suggests that this system is an important pathway regulating lymphocyte activation and/or homeostasis in the immune response.

BTLA is a lymphocyte inhibitory receptor with similarities to CTLA-4 and PD-1.

During activation, T cells express receptors for receiving positive and negative costimulatory signals. Here we identify the B and T lymphocyte attenuator (BTLA), an immunoglobulin domain-containing glycoprotein with two immunoreceptor tyrosine-based inhibitory motifs. BTLA is not expressed by naive T cells, but it is induced during activation and remains expressed on T helper type 1 (T(H)1) but not T(H)2 cells. Crosslinking BTLA with antigen receptors induces its tyrosine phosphorylation and association with the Src homology domain 2 (SH2)-containing protein tyrosine phosphatases SHP-1 and SHP-2, and attenuates production of interleukin 2 (IL-2). BTLA-deficient T cells show increased proliferation, and BTLA-deficient mice have increased specific antibody responses and enhanced sensitivity to experimental autoimmune encephalomyelitis. B7x, a peripheral homolog of B7, is a ligand of BTLA. Thus, BTLA is a third inhibitory receptor on T lymphocytes with similarities to cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) and programmed death 1 (PD-1).