TREM1 activation of myeloid cells promotes antitumor immunity.

Myeloid cells in the tumor microenvironment (TME) can exist in immunosuppressive and immunostimulatory states that impede or promote antitumor immunity, respectively. Blocking suppressive myeloid cells or increasing stimulatory cells to enhance antitumor immune responses is an area of interest for therapeutic intervention. Triggering receptor expressed on myeloid cells-1 (TREM1) is a proinflammatory receptor that amplifies immune responses. TREM1 is expressed on neutrophils, subsets of monocytes and tissue macrophages, and suppressive myeloid populations in the TME, including tumor-associated neutrophils, monocytes, and tumor-associated macrophages. Depletion or inhibition of immunosuppressive myeloid cells, or stimulation by TREM1-mediated inflammatory signaling, could be used to promote an immunostimulatory TME. We developed PY159, an afucosylated humanized anti-TREM1 monoclonal antibody with enhanced FcγR binding. PY159 is a TREM1 agonist that induces signaling, leading to up-regulation of costimulatory molecules on monocytes and macrophages, production of proinflammatory cytokines and chemokines, and enhancement of T cell activation in vitro. An antibody against mouse TREM1, PY159m, promoted antitumor efficacy in syngeneic mouse tumor models. These results suggest that PY159-mediated agonism of TREM1 on tumoral myeloid cells can promote a proinflammatory TME and offer a promising strategy for immunotherapy.

Targeting TREM2 on tumor-associated macrophages enhances immunotherapy.

Converting checkpoint inhibitor (CPI)-resistant individuals to being responsive requires identifying suppressive mechanisms. We identify TREM2+ tumor-associated macrophages (TAMs) as being correlated with exhausted CD8+ tumor-infiltrating lymphocytes (TILs) in mouse syngeneic tumor models and human solid tumors of multiple histological types. Fc domain-enhanced anti-TREM2 monoclonal antibody (mAb) therapy promotes anti-tumor immunity by elimination and modulation of TAM populations, which leads to enhanced CD8+ TIL infiltration and effector function. TREM2+ TAMs are most enriched in individuals with ovarian cancer, where TREM2 expression corresponds to disease grade accompanied by worse recurrence-free survival. In an aggressive orthotopic ovarian cancer model, anti-TREM2 mAb therapy drives potent anti-tumor immunity. These results highlight TREM2 as a highly attractive target for immunotherapy modulation in individuals who are refractory to CPI therapy and likely have a TAM-rich tumor microenvironment.

Blockade of nonhormonal fibroblast growth factors by FP-1039 inhibits growth of multiple types of cancer.

The fibroblast growth factor (FGF) pathway promotes tumor growth and angiogenesis in many solid tumors. Although there has long been interest in FGF pathway inhibitors, development has been complicated: An effective FGF inhibitor must block the activity of multiple mitogenic FGF ligands but must spare the metabolic hormone FGFs (FGF-19, FGF-21, and FGF-23) to avoid unacceptable toxicity. To achieve these design requirements, we engineered a soluble FGF receptor 1 Fc fusion protein, FP-1039. FP-1039 binds tightly to all of the mitogenic FGF ligands, inhibits FGF-stimulated cell proliferation in vitro, blocks FGF- and vascular endothelial growth factor (VEGF)-induced angiogenesis in vivo, and inhibits in vivo growth of a broad range of tumor types. FP-1039 antitumor response is positively correlated with RNA levels of FGF2, FGF18, FGFR1c, FGFR3c, and ETV4; models with genetic aberrations in the FGF pathway, including FGFR1-amplified lung cancer and FGFR2-mutated endometrial cancer, are particularly sensitive to FP-1039-mediated tumor inhibition. FP-1039 does not appreciably bind the hormonal FGFs, because these ligands require a cell surface co-receptor, klotho or ß-klotho, for high-affinity binding and signaling. Serum calcium and phosphate levels, which are regulated by FGF-23, are not altered by administration of FP-1039. By selectively blocking nonhormonal FGFs, FP-1039 treatment confers antitumor efficacy without the toxicities associated with other FGF pathway inhibitors.

Chronic administration of belimumab, a BLyS antagonist, decreases tissue and peripheral blood B-lymphocyte populations in cynomolgus monkeys: pharmacokinetic, pharmacodynamic, and toxicologic effects.

The tolerability, pharmacodynamic effects, and pharmacokinetics of belimumab (LymphoStat-B) were evaluated in cynomolgus monkeys. Belimumab is a fully human IgG1lambda antibody directed against B-lymphocyte stimulator (BLyS) protein. BLyS is a TNF family member that supports B-lymphocyte maturation and survival and has been implicated in the pathogenesis of autoimmune diseases and B-lymphocyte malignancies. Belimumab was developed to antagonize BLyS activity in autoimmune diseases and B-lymphocyte malignancies, where undesirable effects of B-lymphocyte activity may cause or contribute to disease. Pharmacodynamic effects of belimumab were monitored by immunophenotyping of peripheral blood. Pathology end points, including tissue immunophenotyping, are described after 13 and 26 weeks of treatment and after a 34-week treatment-free (recovery) period. Belimumab was safe and well tolerated in repeat-dose toxicology studies at 5-50 mg/kg for up to 26 weeks. Monkeys exposed to belimumab had significant decreases in peripheral blood B lymphocytes by 13 weeks of exposure, continuing into the recovery period, despite total lymphocyte counts similar to the controls. There were concomitant decreases in spleen and lymph node B-lymphocyte representation after 13 or 26 weeks of treatment with belimumab. Microscopically, monkeys treated with belimumab for 13 or 26 weeks had decreases in the number and size of lymphoid follicles in the white pulp of the spleen. All findings were generally reversible within a 34-week recovery period. These data confirm the specific pharmacologic activity of belimumab in reducing B lymphocytes in the cynomolgus monkey. The favorable safety profile and lack of treatment-related infections also support continued clinical development of belimumab.

BLyS--an essential survival factor for B cells: basic biology, links to pathology and therapeutic target.

A paradigm shift in our understanding of autoimmune disease pathology is underway; B cells are now considered to play a central role in disease pathogenesis. Targeting B cells may prove to be an effective route for the development of novel therapeutics. BLyS, a member of the TNF family of cytokines, is an essential survival factor for B cells. Constitutive BLyS overexpression in mice leads to an autoimmune phenotype similar to lupus nephritis. Clinically, BLyS is elevated in patients with systemic autoimmune diseases including rheumatoid arthritis and systemic lupus erythematosus. BLyS ablation results in a block of B cell development in which mature B cells are absent. BLyS binds to three receptors, BR3, TACI and BCMA. Analysis of the receptors suggests that the major pro-survival signals are mediated by BR3, while TACI is involved in negative signaling. BCMA is required for survival of long-lived plasma cells. BLyS signaling results in upregulation of anti-apoptotic bcl-2 family members. In animal models of autoimmune disease, BLyS antagonists reduce disease severity and delay disease progression. BLyS is an attractive target for antagonism in autoimmune diseases. Multiple approaches are being taken to antagonize BLyS including a fully human antibody and soluble BLyS receptors. These approaches are currently being tested in clinical trials.

B lymphocyte stimulator overexpression in patients with systemic lupus erythematosus: longitudinal observations.

OBJECTIVE: To assess the overexpression of B lymphocyte stimulator (BLyS) over time in patients with systemic lupus erythematosus (SLE). METHODS: Sixty-eight SLE patients were followed up longitudinally for a median 369 days. At each physician encounter, disease activity was assessed by the Systemic Lupus Erythematosus Disease Activity Index, and blood was collected for determination of the serum BLyS level, blood BLyS messenger RNA (mRNA) level, and cell surface BLyS expression. Twenty normal control subjects underwent similar laboratory evaluations. RESULTS: In contrast to the uniformly normal serum BLyS and blood BLyS mRNA phenotypes in control subjects, SLE patients displayed marked heterogeneity, with 50% and 61% of patients manifesting persistently or intermittently elevated serum BLyS and blood BLyS mRNA phenotypes, respectively. Surface BLyS expression by SLE peripheral blood mononuclear cells was also often increased. Treatment of patients who had elevated serum BLyS levels with intensive courses of high-dose corticosteroids resulted in marked reductions in serum BLyS levels, and tapering of the corticosteroid dosage often resulted in increases in serum BLyS levels. Serum BLyS levels generally correlated with anti-double-stranded DNA (anti-dsDNA) titers (in those with detectable anti-dsDNA titers), but changes in serum BLyS levels did not correlate with changes in disease activity in individual patients. Serum BLyS phenotype did not associate with specific organ system involvement. CONCLUSION: Dysregulation of BLyS over extended periods of time is common in patients with SLE. Neutralization of BLyS activity with an appropriate BLyS antagonist may be therapeutically beneficial.

Generation and characterization of LymphoStat-B, a human monoclonal antibody that antagonizes the bioactivities of B lymphocyte stimulator.

OBJECTIVE: To identify and characterize a fully human antibody directed against B lymphocyte stimulator (BLyS), a tumor necrosis factor-related cytokine that plays a critical role in the regulation of B cell maturation and development. Elevated levels of BLyS have been implicated in the pathogenesis of autoimmune diseases. METHODS: A human phage display library was screened for antibodies against human BLyS. A human monoclonal antibody, LymphoStat-B, specific for human BLyS was obtained from the library screening and subsequent affinity optimization mutagenesis. The antibody was tested for inhibition of human BLyS in vitro and in an in vivo murine model. Additionally, the consequences of BLyS inhibition were tested in vivo by administration of LymphoStat-B to cynomolgus monkeys. RESULTS: LymphoStat-B bound with high affinity to human BLyS and inhibited the binding of BLyS to its 3 receptors, TACI, BCMA, and BLyS receptor 3/BAFF-R. LymphoStat-B potently inhibited BLyS-induced proliferation of B cells in vitro, and administration of LymphoStat-B to mice prevented human BLyS-induced increases in splenic B cell numbers and IgA titers. In cynomolgus monkeys, administration of LymphoStat-B resulted in decreased B cell representation in both spleen and mesenteric lymph nodes. CONCLUSION: A fully human monoclonal antibody has been isolated that binds to BLyS with high affinity and neutralizes human BLyS bioactivity in vitro and in vivo. Administration of this antibody to cynomolgus monkeys resulted in B cell depletion in spleen and lymph node. This antibody may prove therapeutically useful in the treatment of autoimmune diseases in humans.

BLyS and APRIL form biologically active heterotrimers that are expressed in patients with systemic immune-based rheumatic diseases.

BLyS and APRIL are two members of the TNF superfamily that are secreted by activated myeloid cells and have costimulatory activity on B cells. BLyS and APRIL share two receptors, TACI and BCMA, whereas a third receptor, BAFF-R, specifically binds BLyS. Both BLyS and APRIL have been described as homotrimeric molecules, a feature common to members of the TNF superfamily. In this study, we show that APRIL and BLyS can form active heterotrimeric molecules when coexpressed and that circulating heterotrimers are present in serum samples from patients with systemic immune-based rheumatic diseases. These findings raise the possibility that active BLyS/APRIL heterotrimers may play a role in rheumatic and other autoimmune diseases and that other members of the TNF ligand superfamily may also form active soluble heterotrimers.