The interaction of amyloid-beta (Aβ) and tau in the pathogenesis of Alzheimer's disease is a subject of intense inquiry, with the bulk of evidence indicating that changes in tau are downstream of Aβ. It has been shown however, that human tau overexpression in amyloid precursor protein transgenic mice increases Aβ plaque deposition. Here, we confirm that human tau increases Aβ levels. To determine if the observed changes in Aβ levels were because of intracellular or extracellular secreted tau (eTau for extracellular tau), we affinity purified secreted tau from Alzheimer's disease patient-derived cortical neuron conditioned media and analyzed it by liquid chromatography-mass spectrometry. We found the extracellular species to be composed predominantly of a series of N-terminal fragments of tau, with no evidence of C-terminal tau fragments. We characterized a subset of high affinity tau antibodies, each capable of engaging and neutralizing eTau. We found that neutralizing eTau reduces Aβ levels in vitro in primary human cortical neurons where exogenously adding eTau increases Aβ levels. In vivo, neutralizing human tau in 2 human tau transgenic models also reduced Aβ levels. We show that the human tau insert sequence is sufficient to cause the observed increase in Aβ levels. Our data furthermore suggest that neuronal hyperactivity may be the mechanism by which this regulation occurs. We show that neuronal hyperactivity regulates both eTau secretion and Aβ production. Electrophysiological analysis shows for the first time that secreted eTau causes neuronal hyperactivity. Its induction of hyperactivity may be the mechanism by which eTau regulates Aβ production. Together with previous findings, these data posit a novel connection between tau and Aβ, suggesting a dynamic mechanism of positive feed forward regulation. Aβ drives the disease pathway through tau, with eTau further increasing Aβ levels, perpetuating a destructive cycle.

Key Points Cold agglutinin–driven classical pathway activity terminates prior to the initiation of the terminal cascade in CAD patient blood. By inhibiting cold agglutinin–mediated complement deposition on the cellular membrane, TNT003 prevents RBCs from being phagocytosed.

, et al. Improved topical delivery of tacrolimus: a novel composite hydrogel formulation for the treatment of psoriasis. J Controlled Release 2016;242: 16e24. Hawkes JE, Gudjonsson JE, Ward NL. The snowballing literature on imiquimod-induced skin inflammation in mice: a critical appraisal. J Invest Dermatol 2017;137: 546e9. Jain A, Doppalapudi S, Domb AJ, Khan W. Tacrolimus and curcumin co-loaded liposphere gel: synergistic combination towards management of psoriasis. J Controlled Release 2016;243:132e45.

Cold agglutinin disease (CAD) is an autoimmune hemolytic anemia in which autoantibodies bind to red blood cells (RBC) at temperatures below 37°C, resulting in activation of the classical complement pathway (CCP). CCP activation leads to hemolysis either intravascularly, by formation of the membrane attack complex, or extravascularly, when C3/C4 fragment deposition onto the RBC surface results in sequestration by the reticuloendothelial system. Here we describe the in vitro and in vivo activity of TNT003 and TNT009, inhibitors of a serine protease specific to the CCP, in pre-clinical models of CAD. TNT003 is a mouse monoclonal IgG2a antibody with sub-nanomolar affinity. TNT009 is the humanized form (IgG4) of TNT003 and retains affinity and specificity to its target. In vitro assays using IgM-sensitized sheep RBC and human or non-human primate (NHP) serum showed that TNT003 and TNT009 potently inhibited antibody-mediated hemolysis in a concentration dependent manner. Additionally, TNT003 and TNT009 inhibited CCP-mediated production of the anaphylatoxins C4a, C3a, and C5a. Flow cytometry analysis showed that both antibodies also prevented C3 fragment deposition on the RBC surface. Activity was proportional to the amount of serum used, and at 80% human or NHP serum, TNT003 completely inhibited hemolysis with an IC50 of ∼13 µg/mL. Using an ELISA-based assay, TNT003 inhibited C5b-9 deposition driven by the CCP but not by the alternative (CAP) or lectin (CLP) pathways. These data suggest that TNT003 and TNT009 are specific and potent inhibitors of the CCP. To demonstrate the utility of a CCP inhibitor in disease, we tested the ability of TNT003 and TNT009 to inhibit the CCP in ex vivo hemolysis assays using CAD patient autoantibodies. Type O- RBC were incubated in the presence of CAD plasma to sensitize the cells with autoantibody. RBC were then washed and 25% normal human serum (NHS) added as a source of complement. Thirteen of the seventeen CAD samples tested (76%) mediated C3 fragment deposition on the RBC surface as determined by flow cytometry. TNT003 significantly inhibited C3 fragment deposition by all patient samples that deposited complement (88 ± 2.6% inhibition, n = 13) with an average IC50 of 4.7 ± 0.4 µg/mL. One patient sample induced complement-dependent hemolysis of ∼50% of the RBC upon addition of NHS. In a concentration dependent manner, TNT003 and TNT009, but not control IgG, completely inhibited CAD autoantibody-mediated hemolysis (Fig. 1), as well as C4a, C3a and C5a generation. We further characterized each patient sample to determine cold agglutinin titer. We found that cold agglutinin titer correlated with the percent RBC staining positive for cell surface C3 fragments (R2 = 0.3566; p < .01; n = 17 samples; Fig. 2).Figure 1TNT003 and TNT009 inhibit CAD autoantibody-mediated hemolysisFigure 1. TNT003 and TNT009 inhibit CAD autoantibody-mediated hemolysisFigure 2Cold agglutinin titers correlate with C3 fragment deposition on RBCFigure 2. Cold agglutinin titers correlate with C3 fragment deposition on RBC Extravascular hemolysis of C3 fragment-coated RBC by liver macrophages is believed to be the primary mechanism of RBC destruction in CAD. We therefore tested the hypothesis that CAD patient plasma-induced C3 fragment deposition on RBC would promote phagocytosis by the monocytic cell line THP-1. We found that RBC sensitized in CAD plasma and exposed to NHS were engulfed in an FcgR-independent mechanism by THP-1 cells. RBC phagocytosis was significantly inhibited if NHS exposure occurred in the presence of TNT003 (100 µg/mL), but not a control IgG. The selective CCP inhibitory activity of TNT003 was evaluated in vivo in cynomolgus monkeys. TNT003 administered as a single IV injection at 30 mg/kg resulted in a Cmax of ∼330 µg/mL and detectable serum TNT003 thru ≥72 hours. Using an ELISA-based assay, we observed specific inhibition (≥95%) of the CCP for ≥72 hours. In contrast, CAP activity was modestly and transiently inhibited for 4 - 8 hours. At Cmax, endogenous C4a levels were reduced by >90% and returned to baseline levels by ≥96 hours. Serum samples containing TNT003 showed complete (100%) inhibition of hemolysis and C3 fragment deposition in vitro. CCP activity was completely restored to baseline after TNT003 concentrations fell below a predictable, threshold level. Collectively, these data indicate that TNT003 and TNT009 are potent and specific inhibitors of CCP activity and C3 fragment deposition in vitro and in vivo. These findings support the preclinical development of TNT009 for the treatment of CCP-mediated diseases including CAD. Disclosures: Panicker: True North Therapeutics, Inc.: Employment, Equity Ownership. Shi:True North Therapeutics, Inc.: Employment, Equity Ownership. Rose:True North Therapeutics, Inc.: Employment, Equity Ownership. Hussain:True North Therapeutics, Inc.: Employment, Equity Ownership. Tom:True North Therapeutics, Inc.: Employment, Equity Ownership. Strober:True North Therapeutics, Inc.: Employment. Sloan:True North Therapeutics, Inc.: Consultancy. Parry:True North Therapeutics, Inc.: Employment, Equity Ownership. Stagliano:True North Therapeutics, Inc.: Employment, Equity Ownership, Membership on an entity’s Board of Directors or advisory committees.

No abstract

Autoantibody mediated classical complement pathway (CP) activation has been hypothesized to drive hemolytic anemia in cold agglutinin disease (CAD) patients. Red blood cell (RBC) destruction is believed to occur as a result of C3 opsonin mediated extravascular hemolysis in the liver. We recently reported that TNT009, a humanized monoclonal antibody targeting the CP specific serine protease C1s, rapidly restores hemoglobin levels in severely anemic CAD patients. Here we describe the pharmacodynamic changes in the complement profile of patients to provide a mechanistic understanding of the hematological responses and therapeutic benefit observed following TNT009 treatment. In a Phase 1b trial, we enrolled 5 female CAD patients with severe anemia, one of whom had a lymphoplasmacytic lymphoma with >70% bone marrow infiltration and no measurable CP activity prior to dosing. This patient did not respond to TNT009 while on study and will be omitted from subsequent analyses. Patients were given an initial 10 mg/kg test dose of TNT009 on Day 1, followed by four weekly doses of 60 mg/kg on Day 2 or Day 5. Patients were followed for 4 weeks following the last dose (washout). Plasma and serum samples were collected throughout the study to measure TNT009 concentrations and to monitor serological markers of anemia and hemolysis. Additionally, futhan-containing plasma samples were collected to assess the levels of CP specific components including C1s, C1s-C1INH, and C1q by ELISA. RBCs were collected to monitor cell surface complement deposition (C3 fragments) via flow cytometry. Finally, C4 levels and an ELISA-based readout of CP activity were examined as measures of the pharmacodynamic effect of TNT009. Baseline levels of circulating C4 were either low or undetectable in CAD patients. Accordingly, serum CP activity was reduced compared to normal human serum samples. Following the first 60 mg/kg TNT009 dose, CP activity was immediately and completely inhibited within 15 minutes of dosing in all patients and remained inhibited for 3 weeks after the last dose. During this period of inhibition, C4 levels rose from a median circulating concentration of <90 mcg/mL (range: <70 - 145) to 251 mcg/mL (range: 238 - 353; p < .001). Plasma C1s levels, on the other hand, decreased from a median plasma concentration of 53.3 mcg/mL (range: 49.4 - 60.3) to a nadir of <3.13 mcg/mL, the lower limit of quantification (LLOQ), (p < .001). Similarly, C1s-C1INH decreased from a median value of 4.5 mcg/mL (range: 4.2 - 5.3) to a nadir of <0.16 mcg/mL (LLOQ; p < .001). Notably, circulating plasma C1q levels were unaffected. Classical pathway inhibition led to a significant increase in reticulocytes in all patients by, on average, 69% within 24 hours of dosing (p < .05). Interestingly, within 1 week after the first TNT009 dose, reticulocyte counts returned to pre-treatment levels and continued to decrease throughout the study, as expected when hemoglobin normalizes. Similarly, within 24 hours of the first dose of TNT009, bilirubin levels dropped from a median value of 2.1 mg/dL (range 1.6 - 3.8) to 0.7 mg/dL (range 0.6 - 1.2), resulting in an average reduction of 66% from baseline levels (p < .05) and returning to pre-treatment levels following washout. Finally, we monitored in vivo complement activation by staining for C3 fragment deposition on RBCs. In general, we observed a gradual reduction in the percentage of C3 fragment positive RBCs over the course of the study from a median value of 49% (range: 37 - 81) to 29% (range: 20 - 38) before washout of TNT009. The decrease in opsonized RBCs was concomitant with the rise in hemoglobin (example shown in Figure 1). Figure 1: Elevation of hemoglobin is associated with a decrease in C3 fragment coated erythrocytes Here we report that TNT009 administration depletes circulating C1s and immediately halts in vivo CP activity, normalizing plasma C4 levels in CAD patients. The abrupt increase in reticulocyte count within 24 hours of dosing suggests that cold agglutinin mediated complement activation affects reticulocyte survival, preventing their maturation into erythrocytes. The observed reduction in C3 opsonized RBCs suggests that TNT009 ameliorates anemia by preventing complement mediated hepatic RBC sequestration, supported by the immediate normalization of circulating bilirubin levels. These results provide a mechanistic interpretation of the therapeutic effects of TNT009 in CAD patients. Figure 1. Figure 1. Disclosures Panicker: True North Therapeutics, Inc.: Employment, Equity Ownership. Hussain:True North Therapeutics, Inc.: Employment, Equity Ownership. Parry:Truenorth Therapeutics, Inc.: Employment, Equity Ownership. Gilbert:Truenorth Therapeutics, Inc.: Employment, Equity Ownership. Jaeger:Janssen: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses.

No abstract

No abstract