Immunotherapeutic approach to reduce senescent cells and alleviate senescence-associated secretory phenotype in mice

Accumulation of senescent cells (SNCs) with a senescence-associated secretory phenotype (SASP) has been implicated as a major source of chronic sterile inflammation leading to many age-related pathologies. Herein, we provide evidence that a bifunctional immunotherapeutic, HCW9218, with capabilities of neutralizing TGF-β and stimulating immune cells, can be safely administered systemically to reduce SNCs and alleviate SASP in mice. In the diabetic db/db mouse model, subcutaneous administration of HCW9218 reduced senescent islet β cells and SASP resulting in improved glucose tolerance, insulin resistance, and aging index. In naturally aged mice, subcutaneous administration of HCW9218 durably reduced the level of SNCs and SASP, leading to lower expression of pro-inflammatory genes in peripheral organs. HCW9218 treatment also reverted the pattern of key regulatory circadian gene expression in aged mice to levels observed in young mice and impacted genes associated with metabolism and fibrosis in the liver. Single-nucleus RNA Sequencing analysis further revealed that HCW9218 treatment differentially changed the transcriptomic landscape of hepatocyte subtypes involving metabolic, signaling, cell-cycle, and senescence-associated pathways in naturally aged mice. Long-term survival studies also showed that HCW9218 treatment improved physical performance without compromising the health span of naturally aged mice. Thus, HCW9218 represents a novel immunotherapeutic approach and a clinically promising new class of senotherapeutic agents targeting cellular senescence-associated diseases.

A novel interleukin-2-based fusion molecule, HCW9302, differentially promotes regulatory T cell expansion to treat atherosclerosis in mice

Atherosclerosis is a chronic inflammatory disease caused by deposition of oxidative low-density lipoprotein (LDL) in the arterial intima which triggers the innate immune response through myeloid cells such as macrophages. Regulatory T cells (Tregs) play an important role in controlling the progression or regression of atherosclerosis by resolving macrophage-mediated inflammatory functions. Interleukin-2 (IL-2) signaling is essential for homeostasis of Tregs. Since recombinant IL-2 has an unfavorable pharmacokinetic profile limiting its therapeutic use, we constructed a fusion protein, designated HCW9302, containing two IL-2 domains linked by an extracellular tissue factor domain. We found that HCW9302 exhibited a longer serum half-life with an approximately 1000-fold higher affinity for the IL-2Rα than IL-2. HCW9302 could be administered to mice at a dosing range that expanded and activated Tregs but not CD4⁺ effector T cells. In an ApoE^-/- mouse model, HCW9302 treatment curtailed the progression of atherosclerosis through Treg activation and expansion, M2 macrophage polarization and myeloid-derived suppressor cell induction. HCW9302 treatment also lessened inflammatory responses in the aorta. Thus, HCW9302 is a potential therapeutic agent to expand and activate Tregs for treatment of inflammatory and autoimmune diseases.

Robust human regulatory T cell expansion with fusion proteins HCW9302 and HCW9213 circumvents need for magnetic-bead or feeder cell approaches for adoptive cell therapy

Regulatory T cells (CD4+CD25+FoxP3+) (Tregs) are a subset of CD4 T cells that suppress the activities of other immune cells and have applications in the treatment of autoimmune and inflammatory diseases. Their use as an adoptive cell therapy has been limited by the practicality of expanding and purifying clinically sufficient numbers of cells. HCW9213 and HCW9302 are fusion proteins based on HCW Biologics’ TOBI™ technology platform, consisting of anti-CD3/anti-CD28 antibody domains and IL-2 domains, respectively. When used in combination, these fusion proteins were capable of expanding human Treg cells in vitro without the use of anti-CD3/CD28 magnetic beads and/or feeder cells, improving the overall yield, process efficiency and overcoming regulatory hurdles in manufacturing. Tregs generated with these molecules displayed similar phenotypes and suppressive cytokine production as Tregs expanded with recombinant human IL-2. Using a proprietary anti-CD39 antibody to isolate CD39+ Tregs, we have also been able to generate a Treg population with twice the suppressive activity against CD4+ T responder cells as traditional CD4+CD25+CD127lo Tregs. Thus, using its novel fusion proteins, HCW Biologics has been able to develop a superior Treg cell product ideal for the use in adoptive cell transfer. Additionally, this Treg platform can potentially be further optimized with addition of disease-targeted chimeric antigen receptors (CAR).

A feeder cell-free activation and expansion strategy to generate memory-like NK cells sufficient for off-the-shelf multi-dose adoptive cell therapy

Adoptive cell therapy (ACT) using NK cells is a promising armament in the fight against cancer. Cytokine induced memory like (CIML) NK cells have been shown in clinical studies to have potent antitumor activity with superior in vivo persistence. Currently, the expansion of NK cells for clinical development is mainly based on feeder cells, which imposes significant regulatory hurdles and increases the costs for manufacturing. We have developed fusion proteins, HCW9201 and HCW9206 comprising of IL-15/IL-18/IL-12 and IL15/IL-7/IL-21, respectively, capable of priming memory-like differentiation and expanding CIML NK cell products without using feeder cells. This “Kick and Expand” strategy allows greater than 100x expansion of CIML NK cells from donor PBMCs in as little as 14 days without the use of exogenous feeder cells. Continued expansion can yield sufficient CIML NK cells for cryopreservation and multiple ACT infusions. The NK cells generated have bona fide memory-like properties: enhanced antitumor activity across multiple cancer cell lines, higher metabolic capacity, stable epigenetic demethylation of the IFN-γ promoter and increased persistence in NSG mice, when compared to conventional NK cells. In conclusion, this “Kick and Expand” process supports generation of abundant CIML NK cells for multiple ACT infusions and provides simpler, more regulatory friendly, off-the-shelf platform for generating NK cell products, including those with chimeric antigen receptor (CAR) constructs.

A Fusion Protein Complex that Combines IL-12, IL-15, and IL-18 Signaling to Induce Memory-Like NK Cells for Cancer Immunotherapy

Natural killer (NK) cells are a promising cellular therapy for cancer, with challenges in the field including persistence, functional activity, and tumor recognition. Briefly, priming blood NK cells with recombinant human (rh)IL-12, rhIL-15, and rhIL-18 (12/15/18) results in memory-like NK cell differentiation and enhanced responses against cancer. However, the lack of available, scalable Good Manufacturing Process (GMP)-grade reagents required to advance this approach beyond early-phase clinical trials is limiting. To address this challenge, we developed a novel platform centered upon an inert tissue factor scaffold for production of heteromeric fusion protein complexes (HFPC). The first use of this platform combined IL-12, IL-15, and IL-18 receptor engagement (HCW9201), and the second adds CD16 engagement (HCW9207). This unique HFPC expression platform was scalable with equivalent protein quality characteristics in small- and GMP-scale production. HCW9201 and HCW9207 stimulated activation and proliferation signals in NK cells, but HCW9207 had decreased IL-18 receptor signaling. RNA sequencing and multidimensional mass cytometry revealed parallels between HCW9201 and 12/15/18. HCW9201 stimulation improved NK cell metabolic fitness and resulted in the DNA methylation remodeling characteristic of memory-like differentiation. HCW9201 and 12/15/18 primed similar increases in short-term and memory-like NK cell cytotoxicity and IFNγ production against leukemia targets, as well as equivalent control of leukemia in NSG mice. Thus, HFPCs represent a protein engineering approach that solves many problems associated with multisignal receptor engagement on immune cells, and HCW9201-primed NK cells can be advanced as an ideal approach for clinical GMP-grade memory-like NK cell production for cancer therapy.

Bifunctional TGF-β trap/IL-15 Protein Complex Elicits Potent NK Cell and CD8+ T Cell Immunity Against Solid Tumors

Advances in immunostimulatory and anti-immunosuppressive therapeutics have revolutionized cancer treatment. However, novel immunotherapeutics with these dual functions are not frequently reported. Here we describe the creation of a heterodimeric bifunctional fusion molecule, HCW9218, constructed using our soluble tissue factor-based scaffold technology. This complex comprises extracellular domains of the human transforming growth factor-β (TGF-β) receptor II and a human interleukin (IL)-15/IL-15 receptor α complex. HCW9218 can be readily expressed in CHO cells and purified using antibody-based affinity chromatography in a large-scale manufacturing setting. HCW9218 potently activates mouse natural killer (NK) cells and CD8⁺ T cells in vitro and in vivo to enhance cell proliferation, metabolism and antitumor cytotoxic activities. Similarly, human immune cells become activated with increased cytotoxicity following incubation with HCW9218. This fusion complex also exhibits TGF-β neutralizing activity in vitro and sequesters plasma TGF-β in vivo. In a syngeneic B16F10 melanoma model, HCW9218 displayed strong antitumor activity mediated by NK cells and CD8⁺ T cells, and increased their infiltration into tumors. Repeat-dose subcutaneous administration of HCW9218 was well tolerated by mice, with a half-life sufficient to provide long lasting biological activity. Thus, HCW9218 may serve as a novel therapeutic to simultaneously provide immunostimulation and lessen immunosuppression associated with tumors.

Phase I Trial of ALT-803, A Novel Recombinant IL15 Complex, in Patients with Advanced Solid Tumors

Purpose: IL15 induces the activation and proliferation of natural killer (NK) and memory CD8⁺ T cells and has preclinical antitumor activity. Given the superior activity and favorable kinetics of ALT-803 (IL15N72D:IL15RαSu/IgG1 Fc complex) over recombinant human IL15 (rhIL15) in animal models, we performed this first-in-human phase I trial of ALT-803 in patients with advanced solid tumors.Patients and Methods: Patients with incurable advanced melanoma, renal cell, non-small cell lung, and head and neck cancer were treated with ALT-803 0.3 to 6 μg/kg weekly intravenously or 6 to 20 μg/kg weekly subcutaneously for 4 consecutive weeks, every 6 weeks. Immune correlates included pharmacokinetics, immunogenicity, and lymphocyte expansion and function. Clinical endpoints were toxicity and antitumor activity.Results: Twenty-four patients were enrolled; 11 received intravenous and 13 received subcutaneous ALT-803. Of these patients, nine had melanoma, six renal, three head and neck, and six lung cancer. Although total lymphocyte and CD8⁺ T-cell expansion were modest, NK cell numbers rose significantly. Neither anti-ALT-803 antibodies nor clinical activity were observed. Overall, ALT-803 was well tolerated, with adverse effects including fatigue and nausea most commonly with intravenous administration, whereas painful injection site wheal was reported most commonly with subcutaneous ALT-803.Conclusions: Subcutaneous ALT-803 produced the expected NK cell expansion and was well tolerated with minimal cytokine toxicities and a strong local inflammatory reaction at injection sites in patients with advanced cancer. These data, together with compelling evidence of synergy in preclinical and clinical studies, provide the rationale for combining ALT-803 with other anticancer agents. Clin Cancer Res; 24(22); 5552-61. ©2018 AACR.

First-in-human phase 1 clinical study of the IL-15 superagonist complex ALT-803 to treat relapse after transplantation

New therapies for patients with hematologic malignancies who relapse after allogeneic hematopoietic cell transplantation (allo-HCT) are needed. Interleukin 15 (IL-15) is a cytokine that stimulates CD8+ T-cell and natural killer (NK) cell antitumor responses, and we hypothesized this cytokine may augment antileukemia/antilymphoma immunity in vivo. To test this, we performed a first-in-human multicenter phase 1 trial of the IL-15 superagonist complex ALT-803 in patients who relapsed >60 days after allo-HCT. ALT-803 was administered to 33 patients via the IV or subcutaneous (SQ) routes once weekly for 4 doses (dose levels of 1, 3, 6, and 10 μg/kg). ALT-803 was well tolerated, and no dose-limiting toxicities or treatment-emergent graft-versus-host disease requiring systemic therapy was observed in this clinical setting. Adverse events following IV administration included constitutional symptoms temporally related to increased serum IL-6 and interferon-γ. To mitigate these effects, the SQ route was tested. SQ delivery resulted in self-limited injection site rashes infiltrated with lymphocytes without acute constitutional symptoms. Pharmacokinetic analysis revealed prolonged (>96 hour) serum concentrations following SQ, but not IV, injection. ALT-803 stimulated the activation, proliferation, and expansion of NK cells and CD8+ T cells without increasing regulatory T cells. Responses were observed in 19% of evaluable patients, including 1 complete remission lasting 7 months. Thus, ALT-803 is a safe, well-tolerated agent that significantly increased NK and CD8+ T cell numbers and function. This immunostimulatory IL-15 superagonist warrants further investigation to augment antitumor immunity alone and combined with other immunotherapies. This trial was registered at www.clinicaltrials.gov as #NCT01885897.

ALT-803, an IL-15 superagonist, in combination with nivolumab in patients with metastatic non-small cell lung cancer: a non-randomised, open-label, phase 1b trial

BACKGROUND

Immunotherapy with PD-1 or PD-L1 blockade fails to induce a response in about 80% of patients with unselected non-small cell lung cancer (NSCLC), and many of those who do initially respond then develop resistance to treatment. Agonists that target the shared interleukin-2 (IL-2) and IL-15Rβγ pathway have induced complete and durable responses in some cancers, but no studies have been done to assess the safety or efficacy of these agonists in combination with anti-PD-1 immunotherapy. We aimed to define the safety, tolerability, and activity of this drug combination in patients with NSCLC.

METHODS

In this non-randomised, open-label, phase 1b trial, we enrolled patients (aged ≥18 years) with previously treated histologically or cytologically confirmed stage IIIB or IV NSCLC from three academic hospitals in the USA. Key eligibility criteria included measurable disease, eligibility to receive anti-PD-1 immunotherapy, and an Eastern Cooperative Oncology Group performance status of 0 or 1. Patients received the anti-PD-1 monoclonal antibody nivolumab intravenously at 3 mg/kg (then 240 mg when US Food and Drug Administration [FDA]-approved dosing changed) every 14 days (either as new treatment or continued treatment at the time of disease progression) and the IL-15 superagonist ALT-803 subcutaneously once per week on weeks 1-5 of four 6-week cycles for 6 months. ALT-803 was administered at one of four escalating dose concentrations: 6, 10, 15, or 20 μg/kg. The primary endpoint was to define safety and tolerability and to establish a recommended phase 2 dose of ALT-803 in combination with nivolumab. Analyses were per-protocol and included any patients who received at least one dose of study treatment. This trial is registered with ClinicalTrials.gov, number NCT02523469; phase 2 enrolment of patients is ongoing.

FINDINGS

Between Jan 18, 2016, and June 28, 2017, 23 patients were enrolled and 21 were treated at four dose levels of ALT-803 in combination with nivolumab. Two patients did not receive treatment because of the development of inter-current illness during enrolment, one patient due to leucopenia and one patient due to pulmonary dysfunction. No dose-limiting toxicities were recorded and the maximum tolerated dose was not reached. The most common adverse events were injection-site reactions (in 19 [90%] of 21 patients) and flu-like symptoms (15 [71%]). The most common grade 3 adverse events, occurring in two patients each, were lymphocytopenia and fatigue. A grade 3 myocardial infarction occurred in one patient. No grade 4 or 5 adverse events were recorded. The recommended phase 2 dose of ALT-803 is 20 μg/kg given once per week subcutaneously in combination with 240 mg intravenous nivolumab every 2 weeks.

INTERPRETATION

ALT-803 in combination with nivolumab can be safely administered in an outpatient setting. The promising clinical activity observed with the addition of ALT-803 to the regimen of patients with PD-1 monoclonal antibody relapsed and refractory disease shows evidence of anti-tumour activity for a new class of agents in NSCLC.

FUNDING

Altor BioScience (a NantWorks company), National Institutes of Health, and Medical University of South Carolina Hollings Cancer Center.

Comparison of the Superagonist Complex, ALT-803, to IL15 as Cancer Immunotherapeutics in Animal Models

IL15, a potent stimulant of CD8(+) T cells and natural killer (NK) cells, is a promising cancer immunotherapeutic. ALT-803 is a complex of an IL15 superagonist mutant and a dimeric IL15 receptor αSu/Fc fusion protein that was found to exhibit enhanced biologic activity in vivo, with a substantially longer serum half-life than recombinant IL15. A single intravenous dose of ALT-803, but not IL15, eliminated well-established tumors and prolonged survival of mice bearing multiple myeloma. In this study, we extended these findings to demonstrate the superior antitumor activity of ALT-803 over IL15 in mice bearing subcutaneous B16F10 melanoma tumors and CT26 colon carcinoma metastases. Tissue biodistribution studies in mice also showed much greater retention of ALT-803 in the lymphoid organs compared with IL15, consistent with its highly potent immunostimulatory and antitumor activities in vivo. Weekly dosing with 1 mg/kg ALT-803 in C57BL/6 mice was well tolerated, yet capable of increasing peripheral blood lymphocyte, neutrophil, and monocyte counts by >8-fold. ALT-803 dose-dependent stimulation of immune cell infiltration into the lymphoid organs was also observed. Similarly, cynomolgus monkeys treated weekly with ALT-803 showed dose-dependent increases of peripheral blood lymphocyte counts, including NK, CD4(+), and CD8(+) memory T-cell subsets. In vitro studies demonstrated ALT-803-mediated stimulation of mouse and human immune cell proliferation and IFNγ production without inducing a broad-based release of other proinflammatory cytokines (i.e., cytokine storm). Based on these results, a weekly dosing regimen of ALT-803 has been implemented in multiple clinical studies to evaluate the dose required for effective immune cell stimulation in humans.

Intravesical ALT-803 and BCG treatment reduces tumor burden in a carcinogen induced bladder cancer rat model; a role for cytokine production and NK cell expansion

Intravesical Bacillus Calmette-Guérin (BCG) has been shown to induce a specific immunologic response (i.e., activation of IL-2 and effector T-cells), while preclinical studies using ALT-803 (mutated IL-15 analogue combined with IL-15Rα-Fc fusion) have shown promising results by prolonging the agent's half-life and stimulating CD8+ T-cells. Based on these results, we hypothesized that the intravesical administration of ALT-803 along with BCG will generate an immunologic response leading to significant bladder tumor burden reduction. Using a well-established carcinogen induced rat non-muscle invasive bladder cancer (NMIBC) model, we studied the effects of intravesical ALT-803 with and without BCG. Rat tissues were evaluated to document treatment response. Intravesical ALT-803 was safe and well tolerated alone and in combination with BCG. As a single treatment agent, ALT-803 reduced tumor burden by 35% compared to control whereas BCG alone only reduced tumor burden by 15%. However, the combination of ALT-803 plus BCG reduced tumor burden by 46% compared to control. Immune monitoring suggested that the antitumor response was linked to the production and secretion of IL-1α, IL-1β and RANTES, which in turn, induced the proliferation and activation of NK cells. Lastly, tumoral responses of the combinational treatment were associated with 76% reduction in angiogenesis, which is significantly higher than when assessed with either agent alone. The enhanced therapeutic index seen with this duplet provides justification for the development of this regimen for future clinical trials.

Inhibition of acute vascular thrombosis in chimpanzees by an anti-human tissue factor antibody targeting the factor X binding site

Tissue factor (TF) antagonists targeting the factor VII (FVII) binding domain have been shown to interrupt acute vascular thrombus formation without impairing haemostasis in non-human primates. In this study, we evaluate whether a human/mouse chimeric monoclonal antibody (ALT-836, formerly known as Sunol-cH36) blocking the factor X/factor IX (FX/FIX) binding site of tissue factor could achieve similar clinical benefits in an arterial thrombosis model induced by surgical endarterectomy in chimpanzees. In this model, sequential surgical endarterectomies on right and left superficial femoral arteries were performed 30 days apart in five chimpanzees. A bolus (1 mg/kg) of ALT-836 was injected intravenously immediately preceding the restoration of flow in the endarterectomised femoral artery. Pre-surgical labelling of autologous platelets using (111)In-Oxine and post-surgical gamma camera imaging of (111)In-platelet deposition at endarterectomy sites was performed. The manipulated arterial segments were harvested for patency analysis 30 days following surgery. The results indicate that ALT-836 was highly effective at reducing acute vascular thrombosis, with no significant variations in surgical blood loss and template-bleeding time in the treated group compared to the control animals. These data suggest that ALT-836 is an effective and safe antithrombotic agent in preventing TF-initiated vascular thrombogenesis without compromising haemostasis.

Novel human interleukin-15 agonists

IL-15 is an immunostimulatory cytokine trans-presented with the IL-15 receptor alpha-chain to the shared IL-2/IL-15Rbeta and common gamma-chains displayed on the surface of T cells and NK cells. To further define the functionally important regions of this cytokine, activity and binding studies were conducted on human IL-15 muteins generated by site-directed mutagenesis. Amino acid substitutions of the asparagine residue at position 72, which is located at the end of helix C, were found to provide both partial agonist and superagonist activity, with various nonconservative substitutions providing enhanced activity. Particularly, the N72D substitution provided a 4-5-fold increase in biological activity of the IL-15 mutein compared with the native molecule based on proliferation assays with cells bearing human IL-15Rbeta and common gamma-chains. The IL-15N72D mutein exhibited superagonist activity through improved binding ability to the human IL-15Rbeta-chain. However, the enhanced potency of IL-15N72D was not observed with cells expressing the mouse IL-15Ralpha-IL-15Rbeta-gamma(c) complex, suggesting that this effect is specific to the human IL-15 receptor. The enhanced biological activity of IL-15N72D was associated with more intense phosphorylation of Jak1 and Stat5 and better anti-apoptotic activity compared with the wild-type IL-15. IL-15N72D superagonist activity was also preserved when linked to a single-chain TCR domain to generate a tumor-specific fusion protein. Thus, the human IL-15 superagonist muteins and fusions may create opportunities to construct more efficacious immunotherapeutic agents with clinical utility.

The regulation of clotting factors

Blood clotting involves a multitude of proteins that act in concert in response to vascular injury to produce the procoagulant enzyme alpha-thrombin, which in turn is responsible for the generation of the fibrin plug. However, while generation of the fibrin plug is required for the arrest of excessive bleeding, unregulated clotting will result in the occlusion of the blood vessels and thrombosis. Thus, the regulation of the delicate balance between the procoagulant and anticoagulant mechanisms is of extreme importance for survival. While the majority of proteins involved in blood coagulation circulate as inactive zymogens that require proteolytic activation in order to function, approximately 1% of the circulating factor VII molecules are active. Factor VIIa, possess a serine protease active site, has poor catalytic activity, and is not inhibited by the circulating stoichiometric protease inhibitors. Following injury to the vasculature and subsequent exposure of the integral membrane glycoprotein, tissue factor (TF), the circulating factor VIIa molecules can bind to the exposed TF forming the extrinsic tenase complex (TF/factor VIIa) and initiate the blood coagulation process. Formation of the TF/factor VIIa complex increases the catalytic efficiency of the enzyme by four orders of magnitude when compared with factor VIIa alone. This cell-associated enzymatic complex initiates a series of enzymatic reactions, leading to the generation of alpha-thrombin and ultimately to the formation of the fibrin plug. The procoagulant enzymatic complexes (i.e., prothrombinase, intrinsic tenase, and extrinsic tenase) are similar in structure and composed of an enzyme, a cofactor, and the substrate associated on a cell surface in the presence of divalent metal ions. While the activity of the extrinsic tenase complex is limited by the availability (exposure) of its cell-associated cofactor (TF) it is remarkable that the activities of both the prothrombinase complex (factor Va/factor Xa) as well as the intrinsic tenase complex (factor VIIIa/factor IXa) are limited by the presence of the two soluble, nonenzymatic cofactors, factor Va and factor VIIIa. Factor Va and factor VIIIa, which are very similar in structure and function, are required for prothrombinase and intrinsic tenase activities, respectively, because both cofactors express a dual function in their respective complexes, acting as an enzyme receptor and catalytic effector on the cell surface. The cofactors derive from inactive plasma precursors by regulatory proteolytic events that involve alpha-thrombin. In general, bleeding tendencies are usually associated with defects in the activation of one of the zymogens or the cofactors of the procoagulant complexes. However, the activity of all of the complexes is also limited by the availability of an adequate membrane surface provided by endothelial cells, platelets, and monocytes. The cell surface provides a site for the recruitment of the appropriate proteins and allows for fast and efficient clot formation. In the absence of an appropriate membrane surface, the procoagulant complexes have limited catalytic efficiency. Thus, timely exposure of the adequate membrane surface is an additional step in the regulation of alpha-thrombin formation. alpha-Thrombin participates in its own down-regulation by binding to the endothelial cell receptor thrombomodulin, initiating the protein C pathway, which in turn leads to the formation of activated protein C (APC). APC is required for efficient neutralization of factor Va cofactor activity, which results in the inactivation of the prothrombin-activating complex. This inactivation can only occur in the presence of the appropriate membrane surface. Thus, while following alpha-thrombin activation, factor VIIIa is rapidly and spontaneously inactivated by dissociation of the A2 domain from the rest of the cofactor, APC is required for down-regulation of alpha-thrombin formation by prothrombinase. (ABSTRACT

The effect of Arg306-->Ala and Arg506-->Gln substitutions in the inactivation of recombinant human factor Va by activated protein C and protein S

Factor Va (fVa) is inactivated by activated protein C (APC) by cleavage of the heavy chain at Arg306, Arg506, and Arg679. Site-directed mutagenesis of human factor V cDNA was used to substitute Arg306-->Ala (rfVa306A) and Arg506-->Gln (rfVa506Q). Both the single and double mutants (rfVa306A/506Q) were constructed. The activation of these procofactors by alpha-thrombin and their inactivation by APC were assessed in coagulation assays using factor V-deficient plasma. All recombinant and wild-type proteins had similar initial cofactor activity and identical activation products (a factor Va molecule composed of light and heavy chains). Inactivation of factor Va purified from human plasma (fVaPLASMA) in HBS Ca2+ +0.5% BSA or in conditioned media by APC in the presence of phospholipid vesicles resulted in identical inactivation profiles and displayed identical cleavage patterns. Recombinant wild-type factor Va (rfVaWT) was inactivated by APC in the presence of phospholipid vesicles at an overall rate slower than fVaPLASMA. The rfVa306A and rfVa506Q mutants were each inactivated at rates slower than rfVaWT and fVaPLASMA. Following a 90-min incubation with APC, rfVa306A and rfVa506Q retain approximately 30-40% of the initial cofactor activity. The double mutant, rfVa306A/506Q, was completely resistant to cleavage and inactivation by APC retaining 100% of the initial cofactor activity following a 90-min incubation in the presence of APC. Recombinant fVaWT, rfVa306A, rfVa506Q, and rfVa306A/506Q were also used to evaluate the effect of protein S on the individual cleavage sites of the cofactor by APC. The initial rates of rfVaWT and rfVa306A inactivation in the presence of protein S were unchanged, indicating cleavage at Arg506 is not affected by protein S. The initial rate of rfVa506Q inactivation was increased, suggesting protein S slightly accelerates the cleavage at Arg306. Overall, the data demonstrate high specificity with respect to cleavage sites for APC on factor Va and demonstrate that cleavages of the cofactor at both Arg306 and Arg506 are required for efficient factor Va inactivation.

Regulation and activities of alpha-fetoprotein

alpha-Fetoprotein (AFP) is one of the major serum proteins in the early life of mammals. The function of this protein is not yet fully understood. AFP is an oncodevelopmental gene product which is expressed at high levels in the embryonic yolk sac and fetal liver. The synthesis of AFP decreases dramatically after birth. Only trace amounts of AFP are synthesized in the adult liver. However, expression of the AFP gene is reactivated in the adult during liver regeneration and hepatocarcinogenesis. AFP is an excellent model system for studying the temporal and tissue-specific regulation of oncodevelopmental gene expression. Experiments with transgenic mice and DNA transfection studies have revealed several transcriptional control regions and cis-acting elements in the AFP gene. A large number of trans-acting protein factors interacting with these cis-acting elements have also been identified. Recent studies demonstrated that expression of AFP is regulated by at least two major signal transduction pathways in response to extracellular stimuli. The interactions between steroid hormone receptors and transcriptional factors which respond to separate signal transduction pathways result in transcriptional regulation of AFP gene expression. Trans-acting protein factors or steroid receptors complexed with given response elements can display different activities in different cell types due to cross-talk among both local protein-protein interactions within the DNA-binding domain, and distal protein-protein interactions. However, the detailed mechanisms of AFP gene expression are still not completely understood.

Regulation and regulatory role of gamma-carboxyglutamic acid containing clotting factors

Blood coagulation is initiated following damage of the vessel wall. The large number of proteins that participate in the reactions that regulate blood coagulation must behave in a concerted manner to generate alpha-thrombin. This most abundant enzyme product of the coagulation process acts on the soluble blood protein fibrinogen to create the insoluble fibrin clot, trigger platelet activation, and initiate a variety of vascular processes ranging from coagulation inhibition and activation of fibrinolysis to cell growth. The majority of enzymes that participate in the blood-clotting process circulate in blood as inactive zymogens and procofactors. Following mechanical injury to the vessel wall, a cell-associated protein, tissue factor, is exposed and initiates a series of enzymatic reactions localized on a membrane surface generally provided by cells and accumulating platelets. The binding of the enzymes and zymogen substrates to the exposed membrane surface and their activation are in part governed by the gamma-carboxyglutamic acid residues (gla) of each protein. Recently, it has been demonstrated that the gla residues are necessary for Ca2+ binding and subsequent exposure of the hydrophobic membrane binding regions to the cell bilayer. Thus, the gla residues play a preeminent role during the blood-clotting process. Absence of gamma-carboxylation of one or more of the critical glutamic acid residues results in an impaired coagulation/anticoagulation process which may lead to a bleeding diathesis or thrombosis.

Factor VNew Brunswick: Ala221-to-Val substitution results in reduced cofactor activity

We have characterized the factor V protein and cDNA of a patient displaying factor V deficiency (parahemophilia) and correlated the reduced activity with a missense mutation of Ala221-to-Val. Plasma from the subject individual (C1) presented reduced factor V antigen (39% of normal) that displayed reduced activity (approximately 26% of normal). Factor V purified from this individual by standard techniques shows normal migration on sodium dodecyl sulfate gels and a normal pattern of activation by thrombin. Purified antigen from sibling C2 gives a much reduced specific activity of 263 U/mg (17% of normal). Sibling C3, the mother, and the father have antigen within the normal range (57% to 200%) that has approximately normal specific activity. The cDNA encoding the factor Va heavy and light chains of the subject individual was polymerase chain reaction-amplified and sequenced and revealed an A-to-G substitution at position 3 of codon 51 (silent mutation), a C-to-T substitution in position 2 of codon 221 (Ala221-Val), a T-to-C substitution at position 3 of codon 708 (silent mutation), and a G-to-A substitution at position 1 of codon 2185 (Thr2185-Ala). The latter mutation was also observed in control individuals and is proposed to be a possible polymorphism. Restriction analyses demonstrated the presence of one mutant and one normal allele in the father. The subject individual (C1) and sibling C2 carry only the mutant allele. The mother and sibling C3 carry only the normal allele. The inheritance pattern suggests the presence of a missing or nonexpressed allele in the mother that is passed on to all the siblings. Expression of only the mutant allele by the subject individual (C1) and sibling C2 is consistent with reduced factor V antigen and activity in these patients. We have designated this mutant as Factor VNew Brunswick.

Hepatitis B virus DNA integration and expression of an erb B-like gene in human hepatocellular carcinoma

Southern blot studies on Hepatitis B Virus (HBV) DNA integration in 13 human hepatocellular carcinomas (HCCs) patients revealed the presence of several distinct HBV integration sites in different human liver disease patients. In one HCC patient the DNA fragment containing the HBV integration also hybridized to an erb B probe. The erb B/HBV co-migrating DNA fragment was cloned and sequenced, and showed that HBV DNA is integrated next to a cellular DNA fragment which is homologous to the tyrosine protein kinase domain of the human epidermal growth factor receptor gene and other cell surface receptor genes. The virus-integrated cellular DNA sequence is expressed in this HCC patient, suggesting a possible role for this gene in hepatocarcinogenesis.

A micro-enzymatic method to measure cholesterol and triglyceride in lipoprotein subfractions separated by density gradient ultracentrifugation from 200 microliters of plasma or serum

A micro-enzymatic method was developed to measure total cholesterol (CHOL) and triglyceride (TG) in lipoproteins and their subfractions separated by density gradient ultracentrifugation. This method had a detection limit and sensitivity below 2 mg/dl and accuracy (bias to reference sera) and imprecision (coefficient of variation) of less than 3% between 2 and 30 mg/dl for both CHOL and TG. In addition, the method was in good agreement with standardized Abell-Kendall CHOL (r = 0.98) and enzymatic TG (r = 0.99) methods. Lipoproteins from 200 microliters of plasma or serum were separated by either equilibrium (EQ)- or rate zonal (RZ)-density gradient ultracentrifugation and the resulting fractions were analyzed for CHOL and TG by the micro-enzymatic method. Lipoprotein measurements by these micro-enzymatic/density gradient methods were highly correlated with standardized Lipid Research Clinic (LRC) procedures and preparative ultracentrifugation. The EQ-density gradient procedure also allowed determination of CHOL and TG in LDL and HDL subfractions within any desired density interval. These methods will facilitate the measurements and study of lipoproteins and their subfractions especially in infants, children, the elderly, and small animals. In addition, the micro-enzymatic method may be adapted to other modes of lipoprotein separation such as liquid chromatography, electrophoresis, and precipitation. CHOL or TG determinations could be made on approximately 500 density gradient fractions per hour.