AO-176, a Differentiated Clinical-Stage Anti-CD47 Antibody, Demonstrates Potent Anti-Tumor Activity across Multiple Preclinical Models of B Cell Neoplasms

Upregulation of CD47, the "don't eat me" signal, on the surface of tumors to evade immune surveillance is a common escape mechanism utilized during hematological malignancy and solid tumor development, progression, and relapse. We recently reported that AO-176, a clinical stage humanized anti-CD47 IgG2 antibody, possesses differentiated characteristics such as preferential binding of tumor cells compared to normal cells, negligible binding to red blood cells, non-ADCC direct tumor killing and elicits immunogenic cell death and DAMP induction, all in addition to single-agent phagocytosis. In vivo, AO-176 has exhibited broad anti-tumor activity in preclinical xenograft models of multiple myeloma (MM), acute myeloid leukemia, T cell acute lymphoblastic leukemia, and Burkitt lymphoma. In this study, the anti-tumor activity of AO-176 in an expanded set of preclinical models of B cell neoplasms was evaluated. We assessed In vivo anti-tumor activity in a diffuse large B cell lymphoma (DLBCL) preclinical xenograft model by inoculating Toledo cells into NSG mice and treating once weekly with either 25 mg/kg AO-176 or human IgG2 isotype control. Treatment with AO-176 resulted in profound tumor shrinkage, achieved complete responses in 8/10 mice, and extended survival for all treated mice through the 46 day dosing period, compared to all isotype control treated tumors reaching endpoint by day 21. Having previously observed significant tumor shrinkage and extension of survival in subcutaneous xenograft models of MM, we sought to evaluate anti-tumor activity of AO-176 in an orthotopic model of MM. Luciferase expressing RPMI-8226 cells were inoculated via intratibial injection into NOD-SCID mice and treated with either 25 mg/kg of AO-176 or human IgG2 isotype control once weekly. AO-176-treated mice showed significant reductions of bioluminescence on study days 7, 21, 35, and 41, and serum paraprotein at study end. Evaluation of bone lesions by x-ray showed significantly reduced average bone lysis score in the AO-176 treatment group at study day 41. We then compared the anti-tumor activity of AO-176 against the second generation proteosome inhibitor carfilzomib in a myeloma xenograft model. AO-176 dosed at 25 mg/kg once weekly achieved 72% TGI, compared to 47% and 27% TGI for tumors treated with 5 mg/kg and 2.5 mg/kg carfilzomib at day 29 post treatment. To elucidate the pathways and processes that may be underpinning the anti-tumor activity of AO-176, we performed bulk RNA sequencing on AO-176 or isotype control-treated tumors harvested at multiple time points from a MM xenograft model we previously reported as exhibiting profound sensitivity to AO-176 in vivo. Murine transcripts from harvested tumor RNA were evaluated to assess differences in immune infiltrate resulting from AO-176 treatment. Days 3 and 7 post treatment with AO-176 showed the greatest number of differentially expressed genes compared to control treated tumors. The top enriched pathway on day 3 was microglia phagocytosis. Principal component analysis of gene expression indicated partitioning of day 3 post AO-176 treatment from the rest of the groups. Furthermore, deconvolution of abundances of infiltrating immune cells using CIBERSORT via TIMER analytical tool showed an enrichment of macrophages relative to other cell types on day 3 post treatment. To extend our RNA sequencing findings, we then sought to evaluate intratumoral immune cell populations after AO-176 treatment in a subcutaneous MM xenograft model. MM cells were inoculated into NOD-SCID mice, then treated with 25 mg/kg AO-176 or human IgG2 isotype control. At 48 hours post treatment, tumors were harvested, and we observed an increase of macrophages in the AO-176 treated tumors, confirming our previous results. In summary, the robust preclinical data in DLBCL and MM warrants further development of AO-176 for treatment of hematological malignancies. AO-176 is being evaluated in phase 1/2 clinical trials for the treatment of patients with solid tumors (NCT03834948) and with MM (NCT04445701). Disclosures Wilson: Arch Oncology: Current Employment. Richards: Arch Oncology: Current Employment. Andrejeva: Arch Oncology: Current Employment. Capoccia: Arch Oncology: Current Employment. Puro: Arch Oncology: Current Employment. Donio: Arch Oncology: Current Employment. Hiebsch: Arch Oncology: Current Employment. Kashyap: Arch Oncology: Current Employment. Pereira: Arch Oncology: Current Employment.

A Novel Lair-1 Antibody Selectively Targets Acute Myeloid Leukemia (AML) Stem Cells

Extensive research has led to recent approval of novel therapies such as mylotarg, venetoclax, glasdegib and CC486, and small molecule inhibitors against actionable mutations such as ivosidenib (IDH1), enasidenib (IDH2), gliteritinib and midostaurin (FLT3) in AML. However, the mainstay of treatment in AML remains unchanged since the 1970s. There is a significant unmet need for AML patients that fail to respond to or relapse after standard-of-care (SOC) treatments including allogeneic stem cell transplantation and targeting actionable mutations. In addition, a large fraction of SOC patients invariably relapse due to persistence of chemotherapy-resistant leukemia stem cells (LSCs) or immune evasion. Therefore, identification of unique therapies that preferentially target elusive LSCs and promote immune responses to AML to prevent relapse are highly sought after. Unlike, targeting acute lymphoblastic leukemia (ALL) with CD19 or CD22 with various modalities, when developing AML therapies, it is of paramount importance to differentiate LSCs from hematopoietic stem cells (HSCs) to lessen or abolish unavoidable cytopenias. Leukocyte-associated immunoglobulin-like receptor 1 (LAIR-1) is an immune checkpoint receptor on T cells and myeloid cells that delimits immune cell activation through binding to endogenous collagen ligands. In addition, LAIR-1 is universally expressed on AML blasts and may sustain AML survival signals. We demonstrated using multi-color flow cytometry that LAIR-1 is highly expressed in AML blasts (n=9 of 9) and that LAIR-1 expression in LSCs (markers: CD34 +CD38 -CD90 -CD45RA +/- or CD34 -CD117 +CD244 +/-) is high compared with negligible expression of LAIR-1 in HSCs (markers: CD34 +CD38 -CD90 +CD99 -) (n=3) (Figure 1). Based on these findings, we hypothesized that a LAIR-1 monoclonal antibody (mAb) would disrupt LAIR-1 mediated survival signaling and preferentially target LAIR-1 expressing AML LSCs and blast cells but not HSCs. To test this, we developed a novel LAIR-1 targeting mAb with a functional human IgG 1 isotype that blocks LAIR-1 binding to its ligands (including collagens, complement component C1q, MBL and SP-D) To characterize the anti-leukemic effect of the LAIR-1 mAb we performed an in vitro antibody dependent cell cytotoxicity (ADCC) assay with LAIR-1 expressing AML cells (MOLT4 and MV-4-11). Compared with isotype control, the LAIR-1 mAb significantly increased leukemia cell death (MV411 = 17% above isotype, and MOLT4 = 29.24% above isotype at 15 µg/ml), suggesting that the LAIR-1 mAb confers ADCC activity against LAIR1 + AML cells (Figure 2). To elucidate if the LAIR-1 mAb has a direct signaling effect on LAIR-1 + AML cells, a colony forming unit assay using primary AML cells was carried out. Interestingly, the LAIR-1 mAb inhibited colony formation by AML CD34 + cells (40-60% decreased compared with isotype control, N=4), but not normal CD34 + cells. These data suggests that our LAIR-1 mAb stimulated LAIR-1 signaling that inhibits LSC self-renewal. We then tested the in vivo anti-leukemia effect of the mAb in cell line derived xenograft (CDX) models (immune deficient mice transplanted with MV-4-11 expressing luciferase). In vivo bioluminescence imaging indicated that the LAIR-1 mAb significantly inhibited in vivo AML growth (91% reduction of total flux)(Figure 3). A significant increase in cell death was observed in the presence of the mAb in the blood (47%), spleen (89.4%) and bone marrow (27.6%). Similar to the anti-leukemic effect in CDX AML models, the LAIR-1 mAb significantly suppressed in vivo growth of AML patient derived xenografts (5 different primary AML donors) (10-90% human CD33 + AML cells in isotype control treatment vs 0.5-5% CD33 + AML cells in anti-LAIR-1 treatment, N=3) (Figure 4), while minimally impacting normal immune cells. Taken together, our studies suggest that the LAIR-1 mAb we generated is a novel AML immunomedicine that preferentially eradicates AML LSCs and blasts while preserving healthy HSCs through disruption of AML survival signals and clearance of AML through ADCP and ADCC. Additional studies are currently evaluating if this novel LAIR-1 mAb has other mechanisms of action that contribute to overall in vivo activity, including reduction of AML niche implantation, regulation of bone marrow homing and regulation of anti-tumor immunity. Figure 1 Figure 1. Disclosures Tian: NextCure: Ended employment in the past 24 months. Paucarmayta: NextCure: Current Employment. Lovewell: NextCure: Current Employment. Maloveste: NextCure: Current Employment. Copeland: NextCure: Current Employment. O'Neill: NextCure: Current Employment. Patel: NextCure: Current Employment. Liu: NextCure: Current Employment, Current holder of stock options in a privately-held company. Myint: NextCure: Current Employment, Current holder of stock options in a privately-held company. Langermann: NextCure: Current Employment, Current holder of stock options in a privately-held company. Flies: NextCure: Current Employment, Current holder of stock options in a privately-held company. Kim: Nextcure: Research Funding.

Treatment with DC/AML Fusion Vaccine and CD3xCD123 Bi-Specific T-Cell Engager (CD123-CODV-TCE) for Treatment of Acute Myeloid Leukemia

Introduction: Immunotherapy for AML holds promise in overcoming chemotherapy resistance and in preserving immunologic memory necessary for durable remissions.A bispecific T-cell engaging antibody targeting CD3 and CD123 (CD123-CODV-TCE) has been shown to stimulate T cells to target CD123-expressing leukemic cells in vitroand in mouse models 1. While the short-term immune stimulation mediated by the CD123TCE has the potential to result in clinical response, long-term disease control will require the development of immune memory. We have developed a personalized cancer vaccine in which patient's dendritic cells are fused with autologous leukemia cells resulting in presentation of a wide range of antigens to the immune system. Here, we describe a novel combination of CD123TCE with a DC/AML fusion vaccine ex vivo and in a xenograft murine model. We hypothesized that the CD123TCE will direct the vaccine-educated T cells to not only more effectively eradicate target leukemia cells but also evoke a repertoire of memory T cells and long-term response. Methods/Results: AML cells expressing CD123 were isolated from bone marrow mononuclear cells (BMMCs) from AML patients (n=3). DCs were generated from autologous adherent peripheral blood mononuclear cells (PBMCs) obtained at the time of disease remission as previously described 2,3. Concurrently, CD3+ T cells were isolated from the non-adherent fraction of PBMCs using magnetic bead separation. Fusion cells were generated by co-culturing the DC and tumor cells at a ratio of 3:1 in the presence of polyethylene glycol (PEG). Vaccine educated T cells were then generated by co-culture of T cells with the autologous fusion cells at a ratio of 10:1 for 5-7 days followed by T cell expansion via CD3/CD28 ligation. The capacity of the vaccine-educated T cells to target autologous leukemia cells with the addition of CD123TCE was assessed. The results demonstrated a statistically significant increase in Granzyme B activity in the target AML cells following co-culture with vaccine-educated T cells and the addition of the CD123TCE, compared to T cells + isotype control (n=3). Furthermore, vaccine stimulation in combination with CD123TCE led to a robust increase in induction of tumor specific activated T cells as detected by CD137 expression and intracellular IFN-γ production after co-culture of vaccine-educated T cells with autologous tumor cells in the presence of CD123TCE. The addition of CD123TCE to vaccine-educated T cells resulted in mean 25.4% and 9.6% intracellular IFN-γ expression for CD8 and CD4 T cells, respectively, compared to 8.5 and 3.1% IFN-γ expression following the addition of isotype control (n=3). Next, we examined the efficacy of the combined treatment with vaccine-educated T cells and CD123TCE in-vivo, in two independent xenograft experiments. NSG mice were irradiated with 300rads and challenged with 1x10 6 patient-derived CD123+ tumor cells via retro-orbital injections. After detection of human AML engraftment in the PB on day 76, the mice were inoculated IV with 1X10 6 resting, or ex vivo fusion vaccine educated autologous T cells IV. Subsequently, cohorts of mice were treated with CD123TCE or an appropriate isotype control every 3 days IP. A significant decrease in human leukemia burden was detected in the peripheral blood, spleen and bone marrows of analyzed animals after treatment with vaccine educated T cells and isotype control, or resting T cells and CD123TCE, compared to untreated mice (n=5). Strikingly, no detectable AML was found in peripheral blood, spleens and bone marrows of mice treated with vaccine educated T cells in combination with TCE (n=5). Of note, treatment with vaccine educated T cells led to an expansion of human CD3+ T cells in tissues obtained from the analyzed animals. These human T cells persisted in mice treated with the CD123TCE with a two-fold increase in tumor-specific CD8+ T cells, as assessed by intracellular IFN-γ secretion following ex vivo stimulation with autologous tumor lysate. Conclusions: We demonstrated that the combination of DC/AML fusion vaccine and CD123TCE led to increase in tumor specific T cell immunity, both ex-vivo and in a xenograft murine model when compared to uneducated T cells with CD123TCE or educated T cells with isotype control molecule. Most significantly, the combination treatment was shown to eradicate AML in this model with all animals remaining disease-free several months post inoculation. Disclosures Stroopinsky: The Blackstone Group: Consultancy. Nahas: Kite Pharma: Current Employment. Fraenkel: Sanofi: Current Employment. Yildirim: Sanofi: Current Employment. Bonnevaux: Sanofi: Current Employment. Guerif: Sanofi: Current Employment. Kufe: Genus Oncology: Current equity holder in publicly-traded company; Canbas: Consultancy; REATA: Consultancy, Current equity holder in publicly-traded company; Hillstream BioPharma: Current equity holder in publicly-traded company. Rosenblatt: Parexel: Consultancy; Wolters Kluwer Health: Consultancy, Patents & Royalties; Bristol-Myers Squibb: Research Funding; Karyopharm: Membership on an entity's Board of Directors or advisory committees; Imaging Endpoints: Consultancy; Attivare Therapeutics: Consultancy. Avigan: Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Pharmacyclics: Research Funding; Kite Pharma: Consultancy, Research Funding; Juno: Membership on an entity's Board of Directors or advisory committees; Partner Tx: Membership on an entity's Board of Directors or advisory committees; Karyopharm: Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Aviv MedTech Ltd: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; Legend Biotech: Membership on an entity's Board of Directors or advisory committees; Chugai: Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy; Parexcel: Consultancy; Takeda: Consultancy; Sanofi: Consultancy.

Immune Checkpoint Inhibitors (ICI) Enhance Cancer Associated Thrombosis (CAT) in Murine Model of Colon Carcinoma

Abstract Background: Venous thromboembolism (VTE) is an important immune-related adverse event (irAE) associated with immune checkpoint inhibitors (ICI) cancer therapy. To better understand the pathogenesis of ICI-induced VTE during ICI treatment, we utilized a murine model of cancer associated thrombosis (CAT) to examine the impact of ICI treatment on the development of flow restriction-induced thrombosis. Methods A syngeneic colon carcinoma murine model (CT26) on BALB/c background was utilized to evaluate venous thrombosis following inferior vena cava (IVC) ligation. Non-tumor-bearing and tumor-bearing animals were treated with therapeutic doses of ICI: anti-programmed cell death receptor 1 antibody (anti-PD1) and cytotoxic T-lymphocyte-associated protein 4 (anti-CTLA4) or isotype control antibodies. Mice underwent surgical treatment for IVC ligation followed by surgical retrieval of thrombus. Western blot analysis was performed on plasma cleaved high molecular weight kininogen (cHK), and citrullinated histone H3 (CitH3). Results Tumor-bearing mice undergoing IVC ligation after anti-PD1 and anti-CTLA4 infusion developed larger thrombi compared to mice treated with isotype control IgG. Thrombus weights in CT26 tumor-bearing mice treated with ICI (19.56±4.41 mg) were significantly increased compared to those in mice treated with isotype control IgG (14.67±2.76 mg) (P=0.043). The weight of thrombi in non-tumor-bearing mice was not affected by ICI treatment (9.25±2.22 mg with control IgG vs 9.33±1.15 mg with ICI). In addition, there was a significant increase in thrombus length in mice treated with ICI (9±1.02 mm vs 7.61±0.99 mm with IgG, P=0.039). Cleaved high molecular weight kininogen (cHK), an indicator of contact activation was increased in plasma pre-IVC occlusion from ICI-treated mice compared to IgG-treated mice (68% vs 38% in HK cleavage). Citrullinated histone H3 (CitH3), a NETosis marker, was elevated in plasma (and in thrombus) post-IVC occlusion from ICI-treated mice compared to that of IgG-treated mice. Conclusions ICI treatment of tumor-bearing mice undergoing flow restriction-induced thrombosis resulted in enhanced clot formation. Larger thrombi in ICI treated mice was accompanied with enhanced contact activation and NETosis marker CitH3. Figure 1 Figure 1. Disclosures Khorana: Halozyme: Consultancy, Honoraria; Bristol Myers Squibb: Consultancy, Honoraria; Sanofi: Consultancy, Honoraria; Pfizer: Consultancy, Honoraria; Bayer: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; Anthos: Consultancy, Honoraria. McCrae: Dova, Novartis, Rigel, and Sanofi Genzyme: Consultancy; Sanofi, Novartis, Alexion, and Johnson & Johnson: Consultancy, Honoraria.

991. Blockade of the PD-1/PD-L1 Immune Checkpoint Pathway Improves Mortality, Infection Severity, and Fungal Clearance in an Immunosuppressed Murine Model of Invasive Pulmonary Mucormycosis

Background Emerging experimental evidence suggests that immune checkpoint inhibitors (ICIs) enhance antifungal immunity. In addition, there is anecdotal evidence of potential benefit of adjunct PD-1 pathway blockade in patients with intractable mucormycosis. However, proof-of-concept data in animal models are lacking. Therefore, we compared the efficacy of PD-1 and PD-L1 inhibition in an immunosuppressed murine model of invasive pulmonary mucormycosis (IPM). Methods Female 8-9-week-old BALB/c mice were immunosuppressed with cyclophosphamide (150 mg/kg on days -4 and -1, 100 mg/kg on day +3) and cortisone acetate (300 mg/kg on day -1) and infected intranasally with 50,000 Rhizopus arrhizus spores (clinical isolate Ra-749, day 0). On days 0, +2, +4, and +6, mice received intraperitoneal injections of 250 µg/kg PD-1 or PD-L1 blocking antibodies versus (vs.) 250 µg/kg of the corresponding isotype antibodies (all antibodies from Leinco Technologies). Survival was monitored for 7 days post-infection. Infection severity was scored using the murine sepsis score (MSS, 0 = healthy to 3 = moribund). Fungal burden in lung tissue was determined by an 18S quantitative PCR assay on day +7 or upon death. 20 mice per treatment were assessed in 2 independent experiments. Results Control mice with IPM receiving either of the unspecific isotype antibodies developed severe infection (median MSS on day 7, 2.5-3.0) and had a high 7-day mortality (50-55%). Compared to the corresponding isotype control, PD-L1 inhibition provided a strong therapeutic benefit, significantly improving morbidity (median MSS = 1.0 vs. 2.5, p = 0.002), 7-day mortality (15% vs. 50%, p = 0.02), and fungal burden (3.6k vs. 27.2k spore equivalents/lung, p < 0.001). In contrast, blockade of-PD-1 modestly yet non-significantly reduced infection severity (median MSS = 2.1 vs. 3.0, p = 0.48), 7-day mortality (35% vs, 55%, p = 0.12), and fungal burden (5.6k vs. 40.7k spore equivalents/lung, p = 0.09) compared to isotype control. Conclusion Even without concomitant antifungals, blockade of PD-L1 and to a lesser extent of PD-1 improved mortality, infection severity, and fungal clearance in immunosuppressed mice with IPM. Immune phenotyping studies are in progress to better understand the protective antifungal activity of ICIs in IPM. Disclosures Dimitrios P. Kontoyiannis, MD, Astellas (Consultant)Cidara Therapeutics (Advisor or Review Panel member)Gilead Sciences (Consultant, Grant/Research Support, Other Financial or Material Support, Honoraria)

577 Non-clinical efficacy, pharmacokinetics, and pharmacodynamics of a novel bi-functional anti-CD73-TGFβRII-trap molecule in combination with immune checkpoint therapy

BackgroundA novel murine bi-functional molecule, G04-trap, comprised of an anti-CD73 antibody fused to the extracellular domain of TGFβ receptor II, is designed to potently antagonize two prominent immunosuppressive and pro-tumorigenic pathways present across a variety of cancer types. Inhibition of both CD73-adenosine and TGFβ pathways is expected to create favorable conditions within the tumor microenvironment and restore antitumor immune responses.MethodsG04-trap was evaluated in Detroit562, MC38, and Hepa1-6 efficacy tumor models. Tumor growth inhibition (TGI) was determined when >/=9 animals were alive in each group. Tumor-bearing mice received isotype control (200 microgram), G04-trap (246 microgram), anti-PD-(L)1 (200 microgram) or G04-trap + anti-PD-(L)1 twice per week for 3 weeks. Pharmacokinetic (PK) and pharmacodynamic (PD) assessment was performed on MC38 tumor-bearing mice dosed with 3 mg/kg, 10 mg/kg, or 30 mg/kg G04-trap. Plasma and tumor PK, CD73 target occupancy on T cells, plasma TGFβ, plasma free-sCD73, and tumor CD73 activity were measured after a single dose administration of G04-trapResultsAdministration of G04-trap to mice harboring TGFβ-dependent human pharyngeal Detroit562 xenograft tumors led to a dose-dependent anti-tumor response (83% TGI, at 246 microgram vs. isotype control on day 21). In addition, treatment with G04-trap in combination with immune checkpoint inhibition showed anti-tumor activity in MC38 and Hepa1-6 syngeneic mouse models. In MC38 on day 18, there was a statistically significant TGI with G04-trap + anti-PD-L1 (99% TGI vs. isotype control or 98% TGI vs. anti-PD-L1 alone). A more modest effect was observed in Hepa1-6, with 47% TGI in mice receiving G04-trap + anti-PD-1 vs. isotype control on day 27. To further interpret the efficacy observed in the MC38 tumor model, we performed in-depth PK/PD analysis. Intravenous administration of G04-trap at 3-30 mg/kg resulted in 10% tumor-to-plasma exposure ratio. Full TGFβ target coverage and full CD73 target occupancy on blood T cells was sustained for >3 days, supporting a BIW dosing schedule in non-clinical studies. Treatment also resulted in a dose-dependent inhibition of CD73 activity in tumors. In contrast to cellular CD73, a dose-dependent increase in free sCD73 concentration above baseline was measured in the plasma, consistent with previous reports evaluating anti-CD73 antibodies [1].ConclusionsDual inhibition of CD73 and TGFβ in combination with immune checkpoint blockade resulted in enhanced anti-tumor activity in xenograft and syngeneic tumor models. These results suggest that further exploration of this approach is warranted.ReferencesZhao Y, Gu H, Postelnek J, DeMichele M, Yuan L, Zhang YJ, et al. Fit-for-purpose protein biomarker assay validation strategies using hybrid immunocapture-liquid chromatography-tandem-mass spectrometry platform: Quantitative analysis of total soluble cluster of differentiation 73. Anal Chim Acta. 2020;1126:144–53.

Effect of immune modulation on the skeletal muscle mitochondrial exercise response: An exploratory study in mice with cancer

Cancer causes mitochondrial alterations in skeletal muscle, which may progress to muscle wasting and, ultimately, to cancer cachexia. Understanding how exercise adaptations are altered by cancer and cancer treatment is important for the effective design of exercise interventions aimed at improving cancer outcomes. We conducted an exploratory study to investigate how tumor burden and cancer immunotherapy treatment (anti-PD-1) modify the skeletal muscle mitochondrial response to exercise training in mice with transplantable tumors (B16-F10 melanoma and EO771 breast cancer). Mice remained sedentary or were provided with running wheels for ~19 days immediately following tumor implant while receiving no treatment (Untreated), isotype control antibody (IgG2a) or anti-PD-1. Exercise and anti-PD-1 did not alter the growth rate of either tumor type, either alone or in combination therapy. Untreated mice with B16-F10 tumors showed increases in most measured markers of skeletal muscle mitochondrial content following exercise training, as did anti-PD-1-treated mice, suggesting increased mitochondrial content following exercise training in these groups. However, mice with B16-F10 tumors receiving the isotype control antibody did not exhibit increased skeletal muscle mitochondrial content following exercise. In untreated mice with EO771 tumors, only citrate synthase activity and complex IV activity were increased following exercise. In contrast, IgG2a and anti-PD-1-treated groups both showed robust increases in most measured markers following exercise. These results indicate that in mice with B16-F10 tumors, IgG2a administration prevents exercise adaptation of skeletal muscle mitochondria, but adaptation remains intact in mice receiving anti-PD-1. In mice with EO771 tumors, both IgG2a and anti-PD-1-treated mice show robust skeletal muscle mitochondrial exercise responses, while untreated mice do not. Taken together, we postulate that immune modulation may enhance skeletal muscle mitochondrial response to exercise in tumor-bearing mice, and suggest this as an exciting new avenue for future research in exercise oncology.

Bioinformatic analysis of PD 1 checkpoint blockade responsive immune microenvironment in severe influenza infection

Background: The programmed cell death 1 (PD-1)/PD-1 ligand 1 (PD-L1) signaling pathway is significantly upregulated in severe influenza virus infection, which impairs the immune system and causes increased tissue inflammation and damage. Blocking this signaling pathway will reduce the damage, lower the virus titer in lung tissue, and alleviate the symptoms of infection to promote recovery. The aim of this study was to identify the key factors and regulatory mechanisms in the PD-1 checkpoint blockade–responsive immune microenvironment in severe influenza infection. Methods: A BALB/c mouse model of severe influenza A/H1N1 infection was constructed, and whole-transcriptome sequencing of mice treated with PD-1 checkpoint blockade before severe A/PR8(H1N1) influenza infection and IgG2a isotype control before infection were performed. Subsequently, the differential expression of nucleic acids between these two groups was analyzed, followed by functional interaction prediction analysis to investigate gene-regulatory circuits. Results: In total, 84 differentially expressed (dif) mRNAs, 36 dif-microRNAs (miRNAs), 90 dif‑lncRNAs (long noncoding RNAs), and 22 dif-circRNAs (circular RNAs) were found in PD-1 antagonist treated A/PR8(H1N1) influenza infection lung compared with the controls (IgG2a isotype control treated before infection). In spleens between the above two groups, 45 dif-mRNAs, 36 dif-miRNAs, 57 dif-lncRNAs, and 24 dif-circRNAs were identified. Direct function enrichment analysis of dif-mRNAs and dif-miRNAs showed that these genes were mainly involved in myocardial damage related to viral infection, mitogen activated protein kinase (MAPK) signaling pathways, RAP1 (Ras-related protein 1) signaling pathway, and Axon guidance. Finally, 595 interaction pairs were obtained for the lungs and 462 interaction pairs for the spleen were obtained in the competing endogenous RNA (ceRNA) complex network, in which the downregulated mmu‑miR-7043-3p and Vps39-204 were enriched significantly. Conclusions: The present study provided a basis for the identification of potential pathways and hub genes that might be involved in the PD-1 checkpoint blockade–responsive immune microenvironment in severe influenza infection.

BSCI-17. Targeting SIRPα as a therapeutic strategy for the treatment of breast cancer brain metastasis

Triple-negative breast cancer (TNBC) is a highly aggressive subtype of breast cancer characterized by the lack of druggable targets and an incidence of brain metastasis from the primary site of approximately 35%. There is no standard treatment for managing brain metastasis associated with TNBC; therefore, new strategies are urgently needed to overcome disease mortality. The CD47/SIRPα signaling pathway is implicated in tumor progression due to bypassing innate and adaptive immune surveillance. Most strategies targeting this pathway focus on targeting the receptor CD47; however, targeting SIRPα as a potential strategy to mitigate tumor burden remains understudied. Analysis of gene expression database shows that SIRPα expression is significantly elevated in invasive breast cancer when compared to primary. Furthermore, single-cell data indicates that SIRPα is expressed in basal epithelial cells in TNBC tumors aside from the myeloid compartment. Our immune staining against SIRPα in patient biopsies shows a five-fold increase in SIRPα expression in metastatic brain tumors compared to the primary lesions. Therefore, targeting SIRPα may be a new immunotherapeutic strategy to treat breast cancer brain metastases. Anti-SIRPα treatment of mice bearing brain metastatic 4T1br3 orthotopic tumors showed reduced tumor volume and tumor weight by over 50% compared to isotype control-treated mice. Furthermore, in a model of intracardial brain metastasis, treatment with SIRPα antibody was associated with a 60% increase in survival compared to isotype control-treated mice. RNA sequencing of tumors indicated that SIRPα blockade is associated with a reduction in genes linked to mitochondrial respiratory chain and increases in negative regulation of the cell cycle. Furthermore, in vitro SIRPα targeting enhanced the cell-mediated cytotoxicity of microglia against 4T1Br3 breast cancer cells. This suggests that SIRPα blockade may influence both tumor and innate immune cells to limit brain metastatic breast cancer growth and enhance survival.

ELISA detection of MPO-DNA complexes in human plasma is error-prone and yields limited information on neutrophil extracellular traps formed in vivo

Over the past years, neutrophil extracellular traps (NETs) were shown to contribute to states of acute and chronic inflammatory disease. They are composed of expelled chromatin and decorated by neutrophil-derived proteins. Therefore, the analysis of DNA complexes with myeloperoxidase (MPO) by ELISA has become an attractive tool to measure NET formation in in vitro and in vivo samples. When we used a published MPO-DNA ELISA protocol and included an isotype control for the anti-MPO coating antibody, we observed high assay specificity for in vitro prepared NET samples, whereas the specificity for in vivo plasma samples was low. In addition, the assay failed to detect in vitro generated MPO-DNA complexes when spiked into plasma. Therefore, we set out to improve the specificity of the MPO-DNA ELISA for plasma samples. We found that the use of Fab fragments or immunoglobulins from different species or reversal of the antibody pair led to either a high background or a low dynamic range of detection that did not improve the specificity for plasma samples. Also, the use of higher plasma dilutions or pre-clearing of plasma immunoglobulins were ineffective. Finally, we found that a commercial reagent designed to block human anti-mouse antibodies and multivalent substances increased the detection window between the MPO antibody and isotype control for highly diluted plasma. We applied this modified ELISA protocol to analyze MPO-DNA complexes in human blood samples of acute and chronic inflammatory conditions. While markers of neutrophil activation and NET formation such as MPO, elastase and citrullinated histone H3 correlated significantly, we observed no correlation with the levels of MPO-DNA complexes. Therefore, we conclude that ELISA measurements of MPO-DNA complexes in human plasma are highly questionable regarding specificity of NET detection. In general, plasma analyses by ELISA should more frequently include isotype controls for antibodies to demonstrate target specificity.