Background Plasmodium falciparum Apical Membrane Antigen 1 (PfAMA1) is a candidate vaccine antigen expressed by merozoites and sporozoites. It plays a key role in red blood cell and hepatocyte invasion that can be blocked by antibodies.Methodology/Principal FindingsWe assessed the safety and immunogenicity of recombinant PfAMA1 in a dose-escalating, phase Ia trial. PfAMA1 FVO strain, produced in Pichia pastoris, was reconstituted at 10 µg and 50 µg doses with three different adjuvants, Alhydrogel™, Montanide ISA720 and AS02 Adjuvant System. Six randomised groups of healthy male volunteers, 8–10 volunteers each, were scheduled to receive three immunisations at 4-week intervals. Safety and immunogenicity data were collected over one year. Transient pain was the predominant injection site reaction (80–100%). Induration occurred in the Montanide 50 µg group, resulting in a sterile abscess in two volunteers. Systemic adverse events occurred mainly in the AS02 groups lasting for 1–2 days. Erythema was observed in 22% of Montanide and 59% of AS02 group volunteers. After the second dose, six volunteers in the AS02 group and one in the Montanide group who reported grade 3 erythema (>50 mm) were withdrawn as they met the stopping criteria. All adverse events resolved. There were no vaccine-related serious adverse events. Humoral responses were highest in the AS02 groups. Antibodies showed activity in an in vitro growth inhibition assay up to 80%. Upon stimulation with the vaccine, peripheral mononuclear cells from all groups proliferated and secreted IFNγ and IL-5 cytokines.Conclusions/SignificanceAll formulations showed distinct reactogenicity profiles. All formulations with PfAMA1 were immunogenic and induced functional antibodies.Trial RegistrationClinicaltrials.gov NCT00730782
Several attempts to attack tumours in experimental systems have been made using conjugates of chemotherapeutic agents or potent toxins with antibodies (immunotoxins). In vitro studies have been highly successful, showing target specificity of a high order in some cases. However, so far, such conjugates have been inadequate in vivo, probably for two main reasons. First, conventional heteroclonal antibodies are perhaps inappropriate, because purification by biochemical methods leaves a large amount of non-antibody gamma-globulins. The use of monoclonal antibodies may overcome this problem. Second, when whole toxins have been conjugated to antibodies there has been a strong residual nonspecific cytotoxicity due to the binding capacity of a subunit, the B-piece of the toxin. (Diphtheria toxin or ricin consist of two polypeptide subunits. The A-piece is responsible for inhibition of protein synthesis on ribosomes, and the B-piece binds to galactose residues on the cell membrane and facilitates the transmembrane passage of the A-piece.) In the present work the problem of nonspecific binding by the B-piece has been circumvented by using the A-piece only as the toxin component of immunotoxins; these immunotoxins are active both in vitro and in vivo.
In recent years, antibody -ricin-A-chain immunotoxins have been investigated as anti-neoplastic agents. To achieve in vivo therapy it is necessary that the immunotoxin remains in circulation at a sufficiently high level for a sufficiently long time to allow binding to tumor cells to occur. Therefore, examination of the pharmacology of immunotoxins may elucidate the reasons for the poor in vivo tumoricidal effect of immunotoxin described before. In this study the plasma clearance of antibody -ricin-A-chain immunotoxins, after intravenous injection in animals of different species, has been examined. Sensitive and reproducible techniques were developed to monitor the level of immunotoxin and its constituents in the blood. It is shown that immunotoxins are rapidly eliminated from the bloodstream. Neither the properties of the antibody moiety nor the nature of the linkage binding rich A-chain to antibody account for the disappearance of immunotoxin from the plasma. On the other hand, we found that the rapid clearance of immunotoxin is due to the mannose residues on the rich A-chain moiety which are specifically recognized by liver cells. When immunotoxin is administrated together with yeast mannan, which enhances the level of active immunotoxin in circulation by inhibition of liver uptake, the anti-cancer efficacy of immunotoxin in vivo is drastically improved.Progress has been made in rendering monoclonal antibodies highly cytotoxic by coupling them to the A-chain subunit of the phytotoxin ricin (RTA). Such hybrid molecules, termed immunotoxins (ITS), are now currently prepared according to standardized methods and their biological properties have been studied in detail [l -41. Although these conjugates showed specific cytotoxicity, their efficiency varies greatly from one IT to another. Obviously, the most attractive use of the IT is its in vivo application as a therapeutic agent for cancer. However, the results of initial trials in which ITS have been used therapeutically in animals showed, with one exception [3], that, even when the tumor load was small, the anti-cancer effects were relatively unimpressive [lo, 111. To improve the cancerocidal action of these conjugates, a detailed examination of potential agonists of the action of IT in vivo is needed. Site-specific toxin delivery requires the fulfillment of two sequential steps. First, IT should localize on the desired target site and subsequently bind to the relevant cell surface antigen; secondly, the toxin subunit should be translocated into the cytoplasm to inhibit protein synthesis and thus induce cell death.It has been shown from in vitro studies that to achieve high efficiency of this latter step it is necessary to administer most ITS together with IT enhancers. It has recently been demonstrated that IT enhancers that promote RTA delivery into the cytosol could also be effective in vivo (unpublished work). In order to achieve efficient binding, the IT must remain in the systemic circulation, in its active form, a sufficiently long time and at a sufficie...
Five patients with B-cell chronic lymphocytic leukemia (B-CLL) were treated with 6 courses of the anti-CD5 immunotoxin T101-ricin A chain (T101-RTA). Each course consisted of 8 bi-weekly infusions of T101-RTA (7 or 14 mg/m2). The immunotoxin was well tolerated in all cases with no major toxicities. Though saturation of circulating leukemic cell-associated target antigen was demonstrated by FACS analysis in all patients, no intact immunotoxin was detected in bone-marrow or lymph-node aspirates. Pharmacokinetic studies revealed rapid clearance of T101-RTA, with a half-life of 43 min. None of the patients developed detectable titers of antibody against either T101 murine antibody or ricin A chain. Clinical response was limited to a rapid and transient fall in WBC count lasting less than 24 hr, most likely secondary to the antibody portion of the conjugate. In vitro, fresh B-CLL cells were resistant to T101-RTA at concentrations up to 10(-8)M, while fresh malignant T-cells with a 10-fold increase in expression of CD5 antigen were sensitive. In the presence of the enhancing agent human serum albumin-monensin, fresh B-CLL cells were sensitive to T101-RTA, with an ID50 more than 2 logs below the maximal concentration of immunotoxin achieved in vivo. We conclude that T101-RTA is a potentially useful agent in the treatment of T-cell leukemias. In the presence of HSA-monensin, this spectrum of activity may be extended to B-CLL.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.