Signal Regulatory Protein Alpha Research Articles

Updates from Ongoing, First-in-Human Phase 1 Dose Escalation and Expansion Study of TTI-621, a Novel Biologic Targeting CD47, in Patients with Relapsed or Refractory Hematologic Malignancies

Updates from Ongoing, First-in-Human Phase 1 Dose Escalation and Expansion Study of TTI-621, a Novel Biologic Targeting CD47, in Patients with Relapsed or Refractory Hematologic Malignancies

Activating Macrophage-Mediated Cancer Immunotherapy by Genetically Edited Nanoparticles.

Immunomodulation of macrophages against cancer has emerged as an encouraging therapeutic strategy. However, there exist two major challenges in effectively activating macrophages for antitumor immunotherapy. First, ligation of signal regulatory protein alpha (SIRPα) on macrophages to CD47, a "don't eat me" signal on cancer cells, prevents macrophage phagocytosis of cancer cells. Second, colony stimulating factors, secreted by cancer cells, polarize tumor-associated macrophages (TAMs) to a tumorigenic M2 phenotype. Here, it is reported that genetically engineered cell-membrane-coated magnetic nanoparticles (gCM-MNs) can disable both mechanisms. The gCM shell genetically overexpressing SIRPα variants with remarkable affinity efficiently blocks the CD47-SIRPα pathway while the MN core promotes M2 TAM repolarization, synergistically triggering potent macrophage immune responses. Moreover, the gCM shell protects the MNs from immune clearance; and in turn, the MN core delivers the gCMs into tumor tissues under magnetic navigation, effectively promoting their systemic circulation and tumor accumulation. In melanoma and breast cancer models, it is shown that gCM-MNs significantly prolong overall mouse survival by controlling both local tumor growth and distant tumor metastasis. The combination of cell-membrane-coating nanotechnology and genetic editing technique offers a safe and robust strategy in activating the body's immune responses for cancer immunotherapy.

CD47/SIRPα blocking peptide identification and synergistic effect with irradiation for cancer immunotherapy

BackgroundImmunotherapy has achieved remarkable advances via a variety of strategies against tumor cells that evade immune surveillance. As important innate immune cells, macrophages play important roles in maintaining homeostasis, preventing...

Hybrid cellular membrane nanovesicles amplify macrophage immune responses against cancer recurrence and metastasis

Effectively activating macrophages against cancer is promising but challenging. In particular, cancer cells express CD47, a ‘don’t eat me’ signal that interacts with signal regulatory protein alpha (SIRPα) on macrophages to prevent phagocytosis. Also, cancer cells secrete stimulating factors, which polarize tumor-associated macrophages from an antitumor M1 phenotype to a tumorigenic M2 phenotype. Here, we report that hybrid cell membrane nanovesicles (known as hNVs) displaying SIRPα variants with significantly increased affinity to CD47 and containing M2-to-M1 repolarization signals can disable both mechanisms. The hNVs block CD47-SIRPα signaling axis while promoting M2-to-M1 repolarization within tumor microenvironment, significantly preventing both local recurrence and distant metastasis in malignant melanoma models. Furthermore, by loading a stimulator of interferon genes (STING) agonist, hNVs lead to potent tumor inhibition in a poorly immunogenic triple negative breast cancer model. hNVs are safe, stable, drug loadable, and suitable for genetic editing. These properties, combined with the capabilities inherited from source cells, make hNVs an attractive immunotherapy.

Abstract 4317: Prognostic significance of SIRPa+ macrophages in esophageal squamous cell carcinoma

Abstract While the immune checkpoint blockade has revolutionized the cancer treatment with potent and durable anti-tumor immunity, the benefits remained limited in many occasions, highlighting the needs for predictive biomarkers and improved patient stratification strategies. Here, we aimed to evaluate the clinical relevance of inhibitory receptor signal regulatory protein alpha (SIRPα), predominantly expressed in macrophages in patients with esophageal squamous cell carcinoma (ESCC). For this purpose, tissue microarrays (TMA) were constructed, comprising a total of 249 ESCC patients who underwent radical surgery in 2013. Macrophages associated in situ immune contexture were deciphered by quantitative multiplex fluorescence immunohistochemistry (mFIHC) using Vectra3™ multispectral imaging platform and digital pathology workstation (HALO™). CD68+ macrophages were identified with or without co-expression of SIRPα and PDL1, while tumor cells (CK+) found with differential expressed inhibitory CD47 and PDL1. A comprehensive profiling including density, percentage and spatial/neighborhood association of all the subsets was performed and correlated for prognostic significance. The univariate and multivariate analysis showed that pT, pN stage, tumor length, macrophage density, ratio of SIRPα+ macrophages to total macrophages (rSIRPα), PDL1+ tumor cell density appeared as independent prognostic factors. Log-rank test showed that more infiltration of macrophages had a better overall survival (OS) (P=.004). Lower rSIRPα instead of the density of SIRPα+ macrophages could predict a better OS (P=.027). These indicate that the survival of ESCC patient could be significantly influenced by both the density and the status of macrophages. Furthermore, rSIRPα and PDL1+ cell density was used to stratify patients with similar state of innate or adaptive immunity. Within the subgroup of SIRPαloPDL1hi patients, patients with lower number of SIRPα + macrophages in a radius of 60µm of CD47+ tumor cell (SIRPα60µm) had a significantly better OS (P=.030) while in the subgroup of rSIRPαlo patients, lymph node metastasis was more frequent and broader in patients with higher CD47+ tumor cell density (P=.041). In conclusion, this study revealed the clinical significance of the density and location of SIRPα+ macrophages in ESCC. We found that higher rSIRPα indicated a worse survival. Moreover, within the subgroup of rSIRPαloPDL1hi patients, higher SIRPα60µm indicated a worse survival. These findings highlighted a differential immune paradigm direct the prognostic trajectories and must not be ignored for patients with therapeutic resistance. Along with the correlation between CD47+ tumor cells and metastasis, we spotted high heterogeneity among ESCC patients and therefore suggesting more filtered stratification according to immune network for personalized treatment selection to predict robust anti-tumor immune response. Citation Format: Yida Li, Li Chu, Xi, Yang, Xiao Chu, Jianjiao Ni, Zhengfei Zhu. Prognostic significance of SIRPa+ macrophages in esophageal squamous cell carcinoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4317.

Clinicopathological analysis of immunohistochemical expression of CD47 and SIRPα in adult T-cell leukemia/lymphoma.

The interaction of CD47 and signal-regulatory protein alpha (SIRPα) induces "don't eat me signal", leading suppression of phagocytosis. This signal can affect the clinical course of malignant disease. Although CD47 and SIRPα expression are associated with clinicopathological features in several neoplasms, the investigation for adult T-cell leukemia/lymphoma (ATLL) has not been well-documented. This study aimed to declare the association between CD47 and SIRPα expression and clinicopathological features in ATLL. We performed immunostaining on 73 biopsy samples and found that CD47 is primarily expressed in tumor cells, while SIRPα is expressed in non-neoplastic stromal cells. CD47 positive cases showed significantly higher FoxP3 (P = .0232) and lower CCR4 (P = .0214). SIRPα positive cases presented significantly better overall survival than SIRPα negative cases (P = .0132). SIRPα positive cases showed significantly HLA class I (P = .0062), HLA class II (P = .0133), microenvironment PD-L1 (miPD-L1) (P = .0032), and FoxP3 (P = .0229) positivity. In univariate analysis, SIRPα expression was significantly related to prognosis (Hazard ratio [HR] 0.470; 95% confidence interval [CI] 0.253-0.870; P = .0167], although multivariate analysis did not show SIPRα as an independent prognostic factor. The expression of SIRPα on stromal cells reflects activated immune surveillance mechanism in tumor microenvironment and induce good prognosis in ATLL. More detailed studies for gene expression or genomic abnormalities will disclose clinical and biological significance of the CD47 and SIRPα in ATLL.

Bromodomain Epigenetic Protein Promotes Metastatic Potential in Melanoma Cells through Increased Invasiveness and Decreased Macrophage-Mediated Phagocytosis

Bromodomain Epigenetic Protein Promotes Metastatic Potential in Melanoma Cells through Increased Invasiveness and Decreased Macrophage-Mediated Phagocytosis

Ongoing, first-in-human, phase I dose escalation study of the investigational CD47-blocker TTI-622 in patients with advanced relapsed or refractory lymphoma.

3030 Background: CD47 is an immune checkpoint that binds signal regulatory protein alpha (SIRPα) and delivers a "do not eat" signal to suppress macrophage phagocytosis. Cancer cells frequently overexpress CD47 to escape immune surveillance. TTI-622 is a fusion protein consisting of the CD47-binding domain of human SIRPα linked to the Fc region of human IgG4. TTI-622 acts as a decoy receptor, preventing CD47 from delivering its inhibitory signal and enabling macrophage activation and anti-cancer activity via pro-phagocytic signals present on cancer cells. Unlike many CD47-blocking antibodies, TTI-622 does not bind to human erythrocytes and thus may not cause anemia in patients. Methods: In phase 1A, patients with advanced relapsed or refractory lymphoma received IV TTI-622 once per week with dose increased based on traditional 3+3 escalation. Dosing was on a mg/kg basis with the third and subsequent weekly doses approximately 2-fold higher than the first 2 doses (e.g., 0.05, 0.05, and 0.1 mg/kg for weeks 1, 2 and 3). Blood samples were obtained for PK analysis and assessment of CD47 receptor occupancy (RO) on peripheral T cells. Results: At data cut-off, 19 patients (11 M, 8 F) of median age 62 years (range, 24-86) with the following lymphomas: DLBCL 10; HL 6; and TCL, MCL and FL, 1 each, with a median of 3 prior therapies (range, 1-8) were enrolled. No DLTs have been observed in 5 dose levels (0.05 to 4.0 mg/kg). Grade ≥3 related neutropenia occurred in 2 patients; other related AEs occurring in 2 patients each included abdominal pain, fatigue, and nausea; no patients experienced a related SAE. Acute, post-dose platelet decreases occurred transiently and generally were Grade 1- 2; no related Grade ≥3 thrombocytopenia or anemia AEs have been observed. Preliminary PK data indicate a dose-proportional increase in exposure and a T1/2 of approximately 4-5 days following repeat infusions (Week 6). Preliminary biomarker data reveal approximately 60% RO at the end of the first infusion of 2 mg/kg and more sustained 24-hour RO at 1 and 2 mg/kg vs ≤ 0.8 mg/kg. To date, 1 patient with stage 4 non-GCB DLBCL (5 prior therapies) initially achieved PR by Wk 8 and CR by Wk 36, with response ongoing. Conclusions: TTI-622 is well tolerated at doses up to 4 mg/kg per week. Preliminary data indicate dose-dependent increases in PK exposure and target engagement with 1 DLBCL patient having achieved a durable, ongoing CR. Dose escalation is ongoing and additional safety, PK, biomarker and response data will be available at the time of meeting presentation. Clinical trial information: NCT03530683 .

Functional cytotoxic T cells exhibit tissue-specific phenotypic differences during chronic Friend virus infection

Abstract Friend virus (FV) is a murine retroviral complex that establishes chronic infection characterized by the induction of CD4+Foxp3+ Tregs and prolonged exposure to antigenic stimulation. This leads to a state of diminished CD8+ T cell function, termed “exhaustion”, in the spleens of FV-infected mice. We report that during exhaustion there is a subset of functional CD8+ T cells defined by surface expression of signal regulatory protein alpha (SIRPα), whose expression had previously been reported on neurons, myeloid and hematopoietic stem cells but not T cells. This subset of SIRPα+ CD8+ T cells has high expression of multiple inhibitory receptors including PD-1, Tim3 and Fas, while maintaining high expression of activation/stimulatory molecules including ICOS and CD43. In addition, SIRPα+CD8+ T cells exhibit enhanced proliferation and maintain cytolytic capability, despite the conditions of exhaustion existing within the spleens of chronically infected mice. Furthermore, target cells that express the ligand for SIRPα, CD47, are more susceptible to CD8+ T cell-killing in vivo. We now demonstrate that SIRPα expression on CD8+ T cells is tissue specific, occurring in the spleen but not liver. This is interesting as we have previously reported that the liver has a 10-fold reduction of chronic FV levels, which correlates with reduced Treg-mediated suppression and increased CD8+ T cell function. Furthermore, the SIRPα− CD8+ T cells from the liver of chronically infected mice appear equivalently cytolytic to SIRPα+ CD8+ T cells from the spleen. Therefore, SIRPα expression identifies functional cytotoxic T cells in the spleen but not the liver during chronic exhaustion, highlighting tissue-specific differences of viral control.

Versatile activatable vSIRPα-probe for cancer-targeted imaging and macrophage-mediated phagocytosis of cancer cells

Signal-regulatory protein alpha (SIRPα) engaged by CD47, that is overexpressed in a wide range of human solid tumors, serves as a ‘Don't eat me’ signal for phagocytic cells such as macrophages and dendritic cells. The SIRPα-CD47 interactions have recently attracted increasing attention in both cancer diagnosis and cancer immunotherapy. Herein, we designed and suggested a lysosomal enzyme-activatable vSIRPα-probe (vSIRPα-probe) capable of facilitating CD47-targeted cancer imaging and eliciting anti-cancer immune responses depending on phagocytosis as a versatile platform for potential cancer theranostic applications. For more efficient and precise cancer targeting, a recombinant SIRPα variant (vSIRPα) having a 50,000-fold higher binding affinity to CD47 than wild-type SIRPα was used to fabricate the vSIRPα-probe by conjugating to a dark-quenched fluorogenic peptide that is a substrate of lysosomal endopeptidases. The vSIRPα-probe could specifically bind to CD47 in different types of cancer cells and be activated by dequenching after cellular internalization. By interrupting the SIRPα-CD47 interaction between macrophages and cancer cells, the vSIRPα-probe promoted the destruction of cancer cells by macrophage-mediated phagocytosis, which was highly comparable to the un-modified vSIRPα recombinant protein. In the mouse tumor-xenografts treated with intravenous injection of the vSIRPα-probe, its enhanced in vivo tumor-targeting and imaging abilities drastically diminished after blocking the SIRPα-CD47 interaction via intratumoral administration of anti-CD47 antibodies. This study demonstrates that our vSIRPα-probe provides a promising tumor-targeted immunotheranostic probe for a novel cancer diagnostic and therapeutic strategy.

Macrophage checkpoint blockade: results from initial clinical trials, binding analyses, and CD47-SIRPα structure-function.

The macrophage checkpoint is an anti-phagocytic interaction between signal regulatory protein alpha (SIRPα) on a macrophage and CD47 on all types of cells – ranging from blood cells to cancer cells. This interaction has emerged over the last decade as a potential co-target in cancer when combined with other anti-cancer agents, with antibodies against CD47 and SIRPα currently in preclinical and clinical development for a variety of hematological and solid malignancies. Monotherapy with CD47 blockade is ineffective in human clinical trials against many tumor types tested to date, except for rare cutaneous and peripheral lymphomas. In contrast, pre-clinical results show efficacy in multiple syngeneic mouse models of cancer, suggesting that many of these tumor models are more immunogenic and likely artificial compared to human tumors. However, combination therapies in humans of anti-CD47 with agents such as the anti-tumor antibody rituximab do show efficacy against liquid tumors (lymphoma) and are promising. Here, we review such trials as well as key interaction and structural features of CD47-SIRPα.

Molecular Mechanisms of Stem Cell Reprogramming by CD47 Antagonists in Primary Human Cells

CD47 is a ubiquitously expressed transmembrane receptor whose interaction with signal regulatory protein alpha on macrophages initiates anti‐phagocytic signaling. Additionally, thrombospondin‐1 (THBS1) binding to CD47 induces cell‐autonomous signaling that regulates cell proliferation, differentiation, and recovery from genotoxic stress. Previous studies showed that CD47‐ or THBS1‐null primary lung endothelial cells exposed to ionizing radiation have higher viability than primary wildtype cells. The mechanisms that enhance the viability of CD47‐null primary cells include enhanced autophagy, anabolic metabolism, and increased expression of c‐Myc and other stem cell transcription factors. The latter enable null cells to spontaneously form embryoid bodies. These results suggest that loss of CD47 may generally facilitate cell reprogramming and self‐renewal. Induced pluripotent stem cells (iPS) can be induced by introducing Yamanaka stem cell factors (MYC, KLF4, SOX2, and OCT4) into primary somatic cells, but iPS cells can form teratomas and thus pose risk of cancer when used for regenerative medicine. Therefore, alternative approaches are needed to overcome these limitations. We propose that CD47 gene knock out (KO) via CRISPR or treating with CD47 antagonists from primary human cells could be a new, simpler, and more effective way to develop multipotent stem cells. To investigate this, we have studied the effects of CD47 knockout and antagonists on embryoid body formation and mRNA expression of stem cell factors using fibroblasts, adipocytes, and human umbilical vein cells (HUVEC). Reprogramming was measured by quantifying embryoid body formation, cell viability, and mRNA expression using real‐time PCR. Preliminary results with HUVEC, fibroblast, and adipocyte primary cells treated with CD47 knockout or antagonists have shown enhanced cell proliferation and expression of stem cell factors similar to murine cd47‐null lung endothelial cells. These results suggest that CD47 plays a key regulatory role in stem cell reprogramming of human primary cells.Support or Funding InformationThis work was supported by the Intramural Research Program of the NIH/National Cancer Institute.

The Fully human anti-CD47 antibody SRF231 exerts dual-mechanism antitumor activity via engagement of the activating receptor CD32a

BackgroundCD47 is a broadly expressed cell surface glycoprotein associated with immune evasion. Interaction with the inhibitory receptor signal regulatory protein alpha (SIRPα), primarily expressed on myeloid cells, normally serves to...

In Vivo Analysis of Human Immune Responses in Immunodeficient Rats.

Humanized immune system immunodeficient mice have been extremely useful for the in vivo analyses of immune responses in a variety of models, including organ transplantation and graft versus host disease (GVHD) but they have limitations. Rat models are interesting complementary alternatives presenting advantages over mice, such as their size and their active complement compartment. Immunodeficient rats have been generated but human immune responses have not yet been described. We generated immunodeficient Rat Rag-/- Gamma chain-/- human signal regulatory protein alpha-positive (RRGS) rats combining Rag1 and Il2rg deficiency with the expression of human signal regulatory protein alpha, a negative regulator of macrophage phagocytosis allowing repression of rat macrophages by human CD47-positive cells. We then immune humanized RRGS animals with human peripheral blood mononuclear cells (hPBMCs) to set up a human acute GVHD model. Treatment of GVHD was done with a new porcine antihuman lymphocyte serum active through complement-dependent cytotoxicity. We also established a tumor xenograft rejection model in these hPBMCs immune system RRGS animals by subcutaneous implantation of a human tumor cell line. RRGS animals receiving hPBMCs showed robust and reproducible reconstitution, mainly by T and B cells. A dose-dependent acute GVHD process was observed with progressive weight loss, tissue damage, and death censoring. Antihuman lymphocyte serum (L1S1) antibody completely prevented acute GVHD. In the human tumor xenograft model, detectable tumors were rejected upon hPBMCs injection. hPBMC can be implanted in RRGS animals and elicit acute GVHD or rejection of human tumor cells and these are useful models to test new immunotherapies.

Development of AO-176, a Next-Generation Humanized Anti-CD47 Antibody with Novel Anticancer Properties and Negligible Red Blood Cell Binding.

Inhibitors of adaptive immune checkpoints have shown promise as cancer treatments. CD47 is an innate immune checkpoint receptor broadly expressed on normal tissues and overexpressed on many tumors. Binding of tumor CD47 to signal regulatory protein alpha (SIRPα) on macrophages and dendritic cells triggers a "don't eat me" signal that inhibits phagocytosis enabling escape of innate immune surveillance. Blocking CD47/SIRPα interaction promotes phagocytosis reducing tumor burden in numerous xenograft and syngeneic animal models. We have developed a next-generation humanized anti-CD47 antibody, AO-176, that not only blocks the CD47/SIRPα interaction to induce tumor cell phagocytosis, but also induces tumor cytotoxicity in hematologic and solid human tumor cell lines, but not normal noncancerous cells, by a cell autonomous mechanism (not ADCC). AO-176 also binds preferentially to tumor versus many normal cell types. In particular, AO-176 binds negligibly to RBCs in contrast to tumor cells, even at high concentrations up to 200 μg/mL and does not agglutinate RBCs up to 1 mg/mL in vitro These properties are expected not only to decrease the antigen sink, but also to minimize on-target clinical adverse effects observed following treatment with other reported RBC-binding anti-CD47 antibodies. When tested in cynomolgus monkeys, AO-176 was well tolerated with no adverse effects. Finally, we show that AO-176 demonstrates dose-dependent antitumor activity in tumor xenograft models. Taken together, the unique properties and antitumor activity of our next-generation anti-CD47 antibody, AO-176, distinguishes it from other CD47/SIRPα axis targeting agents in clinical development.

Exciting progress of cancer immunotherapy focusing on immune checkpoints

Immune checkpoints blockade (ICB) has made revolutionary progress in cancer therapy recently. The development of blocking agents to checkpoints on coinhibitory pathway, which prevents inflammation-induced tissue damage but also induces the cancer immune evasion, and retrieves the productive immune responses against tumors. The striking clinical trial results of ICB, by targeting the cytotoxic T lymphocyte–associated protein 4 (CTLA-4), the programmed cell death 1 (PD-1) or PD-1 ligand 1 (PD-L1), has promoted the approval of multiple antibodies for several cancer types by the US Food and Drug Administration (FDA). In addition, the combination of multiple types of blockade even increased the efficacy of tumor regression. Following the previous success, other immune checkpoints have also been verified, such as lymphocyte-activated gene-3 (LAG-3) and Signal-regulatory Protein alpha (SIRPα). However, not all patients can get benefits from ICB and the mechanisms of these coinhibitory pathways are not quite clear. Therefore, understanding the mechanisms of ICB is a formidable challenge that could have far reaching guidelines for therapeutic strategies in cancer. This article summarizes the literature to date regarding ICB that may help more patients get benefit from immunotherapy.

Blocking CD47 efficiently potentiated therapeutic effects of anti-angiogenic therapy in non-small cell lung cancer

BackgroundInhibitors targeting VEGF and VEGFR are commonly used in the clinic, but only a subset of patients could benefit from these inhibitors and the efficacy was limited by multiple relapse mechanisms. In this work, we aimed to investigate the role of innate immune response in anti-angiogenic therapy and explore efficient therapeutic strategies to enhance efficacy of anti-angiogenic therapy against non-small cell lung cancer (NSCLC).MethodsThree NSCLC tumor models with responses to VEGF inhibitors were designed to determine innate immune-related underpinnings of resistance to anti-angiogenic therapy. Immunofluorescence staining, fluorescence-activated cell sorting and immunoblot analysis were employed to reveal the expression of immune checkpoint regulator CD47 in refractory NSCLC. Metastatic xenograft models and VEGFR1-SIRPα fusion protein were applied to evaluate the therapeutic effect of simultaneous disruption of angiogenetic axis and CD47-SIRPα axis.ResultsUp-regulation of an innate immunosuppressive pathway, CD47, the ligand of the negative immune checkpoint regulator SIRPα (signal regulatory protein alpha), was observed in NSCLC tumors during anti-angiogenic therapy. Further studies revealed that CD47 upregulation in refractory lung tumor models was mediated by TNF-α/NF-κB1 signal pathway. Targeting CD47 could trigger macrophage-mediated elimination of the relapsed NSCLC cells, eliciting synergistic anti-tumor effect. Moreover, simultaneously targeting VEGF and CD47 by VEGFR1-SIRPα fusion protein induced macrophages infiltration and sensitized NSCLC to angiogenesis inhibitors and CD47 blockade.ConclusionsOur research provided evidence that CD47 blockade could sensitize NSCLC to anti-angiogenic therapy and potentiate its anti-tumor effects by enhancing macrophage infiltration and tumor cell destruction, providing novel therapeutics for NSCLC by disrupting CD47/SIRPα interaction and angiogenetic axis.

A Phase I Study of CC-90002, a Monoclonal Antibody Targeting CD47, in Patients with Relapsed and/or Refractory (R/R) Acute Myeloid Leukemia (AML) and High-Risk Myelodysplastic Syndromes (MDS): Final Results

A Phase I Study of CC-90002, a Monoclonal Antibody Targeting CD47, in Patients with Relapsed and/or Refractory (R/R) Acute Myeloid Leukemia (AML) and High-Risk Myelodysplastic Syndromes (MDS): Final Results

Evaluation of a Bifunctional Sirpα-CD123 Fusion Antibody for the Elimination of Acute Myeloid Leukemia Stem Cells

Background: Despite considerable advances in the development of novel strategies for the treatment of acute myeloid leukemia (AML) the relapse rate is still high with only limited treatment options. Relapse occurs due to the persistence of chemotherapy-resistant leukemic stem cells (LSCs), which re-initiate outgrowth of the disease, highlighting the need of targeting LSCs to improve overall survival. Immunotherapies represent a promising strategy to target chemotherapy-resistant LSCs in AML. LSCs are characterized by the expression of the interleukin-3 receptor α, also known as CD123. CD123 is expressed on AML blasts and LSCs, and shows only a moderate expression on normal hematopoietic stem cells, claiming CD123 as a suitable target antigen (Haubner et al, Leukemia 2019). CD47, known as a marker of self, is also highly expressed on LSCs as immune escape mechanism. CD47 transmits a "don't eat me" signal upon its interaction with the myeloid-specific signal regulatory protein alpha (SIRPα) receptor on macrophages, thus inhibiting phagocytosis. In order to efficiently eliminate LSCs and provide AML patients a possibility for prolonged relapse-free survival, we have designed a bifunctional antibody that specifically targets CD123 and simultaneously blocks CD47. Importantly, our strategy restricts the benefits of the CD47 blockade to CD123 positive AML cells. Thus, we hypothesize a lower risk for on-target off-leukemia toxicity. Methods: The bifunctional SIRPα-CD123 antibody was generated by fusing the endogenous extracellular domain of SIRPα, which functions as the CD47 blocking domain, to an CD123 antibody CD123. We assessed the selective binding of the bifunctional antibody to CD123+CD47+ AML-derived cells and the ability to block CD47 on CD123+ cells in vitro. Furthermore, the biological activity of the SIRPα-CD123 antibody was examined using the AML-derived cell line MOLM-13, patient-derived xenografted (PDX) AML cells as well as primary cells from patients with newly diagnosed or relapsed AML. Results: We engrafted the endogenous SIRPα V-like domain to an antibody targeting CD123, which improved the binding of the bifunctional SIRPα-CD123 antibody to AML cells compared to a conventional CD123 antibody (MFI ratioCD123 = 2.46 0.25 vs MFI ratioSIRPα-CD123 = 4.44 0.60). The SIRPα-CD123 antibody enhanced the elimination of the AML-derived MOLM-13 cells by antibody-dependent cellular cytotoxicity (EC50CD123 = 38.5 pM vs EC50SIRPα-CD123 = 10.1 pM, n = 9). Additionally, the cytotoxicity was confirmed using primary patient-derived AML cells ex vivo. Further, an improved ex vivo cytotoxicity towards AML PDX cells was observed with the SIRPα-CD123 antibody (% lysis at 100 nM: 14.27 5.40 vs 42.94 10.21 for CD123 and SIRPα-CD123 antibodies respectively, n = 3). With regards to the inhibition of CD47 signaling, we were able to show a blockade of CD47 on CD123+CD47+ positive cells by the SIRPα-CD123 antibody. Correspondingly, a significant increase in phagocytosis of primary patient-derived AML cells mediated by monocyte-derived macrophages was observed in allogenic as well as autologous settings (% phagocytosis, normalized to isotype control and maximum phagocytosis in an autologous setting: 20.11 4.59 vs 90.37 6.22, n = 5 for CD123 and SIRPα-CD123 antibodies, respectively). We were further able to show a preferential binding to MOLM-13 in the presence of a 20-fold excess of red blood cells indicating a potential low on-target off-leukemia toxicity. Taken together, our in vitro data supports the elimination of the CD123+CD47+ positive AML LSC compartment by a synergistic effect of avidity-dependent binding to CD123 and CD47 and the simultaneous inhibition of the innate immune CD47-SIRPα signaling pathway. Conclusions: The SIRPα-CD123 is a bifunctional antibody with the potential to deplete CD123+CD47+ AML LSCs by a dual mode of action mechanism resulting in NK cell dependent cytotoxicity and macrophage-mediated phagocytosis. By combining a high affinity binding to CD123+ cells and a low affinity CD47 blockade that is restricted to CD123+ cancer cells we effectively minimize the risk for CD47-related on-target off-leukemia toxicity. The results of our in vitro assays using AML cell lines are consistent with the data from PDX and primary AML samples and support further preclinical testing of the SIRPα-CD123 antibody in vivo. Disclosures Subklewe: Miltenyi: Research Funding; Pfizer: Consultancy, Honoraria; Gilead: Consultancy, Honoraria, Research Funding; AMGEN: Consultancy, Honoraria, Research Funding; Oxford Biotherapeutics: Research Funding; Roche: Consultancy, Research Funding; Celgene: Consultancy, Honoraria; Morphosys: Research Funding; Janssen: Consultancy.

Signal regulatory protein alpha initiates cachexia through muscle to adipose tissue crosstalk.

BackgroundMuscle wasting from chronic kidney disease (CKD) or from defective insulin signalling results in morbidity and, ultimately, mortality. We have identified an endogenous mediator of insulin resistance, signal regulatory protein alpha (SIRPα), which leads to cachexia in mice and is associated with cachexia in patients with CKD.MethodsWe assessed insulin signalling and mechanisms causing muscle atrophy plus white adipose tissue (WAT) metabolism in mouse models of CKD or acute diabetes (streptozotocin treatment). We then examined these factors in mice with global knockout (KO) of SIRPα and sought mediators of metabolic responses in muscle and adipose tissues of mice with either muscle‐specific or adipose tissue‐specific KO of SIRPα. Metabolic responses were confirmed in primary cultures of adipose cells.ResultsIn mice with CKD, SIRPα expression was increased in WAT (three‐fold, P < 0.05), and this was associated with precursors of cachexia: ‘pathologic browning', thermogenesis, and a two‐fold activation of protein kinase A (P < 0.05 vs. control mice) plus loss of adipose tissue mass. In contrast, mice with SIRPα global KO and CKD or acute diabetes experienced improved insulin signalling and activation of pAkt plus ‘physiologic browning' of WAT. These mice avoided losses of muscle and adipose tissues and experienced a 31% improvement in survival (P < 0.05) than did wild‐type mice with CKD. In muscle‐specific SIRPα KO mice with CKD, we uncovered that serum SIRPα levels (P < 0.05) were suppressed and were associated with improved insulin signalling both in skeletal muscles and in WAT. These changes were accompanied by physiologic WAT browning. However, in adipose‐specific SIRPα KO mice with CKD, levels of serum SIRPα were increased over two‐fold (P < 0.05), while muscle losses were minimally inhibited. Clinical implications of SIRPα signalling are suggested by our findings that include increased SIRPα expression in muscle and adipose tissues (P < 0.05 vs. healthy controls) plus higher SIRPα levels in the serum of patients with CKD (2.4‐fold, P=0.000017 vs. healthy controls).ConclusionsOur results show that SIRPα plays an important role as an anti‐insulin mediator regulating pathways to cachexia. In muscle‐specific SIRPα KO, changes in SIRPα serum levels seem to improve insulin signalling in muscle and WAT, suggesting crosstalk between muscle and adipose tissue. Therefore, targeting SIRPα may prevent cachexia in patients with CKD or acute diabetes.