Advances in neglected tropical disease vaccines: Developing relative potency and functional assays for the Na-GST-1/Alhydrogel hookworm vaccine

Abstract

A new generation of vaccines for the neglected tropical diseases (NTDs) have now advanced into clinical development, with the Na-GST-1/Alhydrogel Hookworm Vaccine already being tested in Phase 1 studies in healthy adults. The current manuscript focuses on the often overlooked critical aspects of NTD vaccine product development, more specifically, vaccine stability testing programs. A key measure of vaccine stability testing is "relative potency" or the immunogenicity of the vaccine during storage. As with most NTD vaccines, the Na-GST-1/Alhydrogel Hookworm Vaccine was not developed by attenuation or inactivation of the pathogen (Necator americanus), so conventional methods for measuring relative potency are not relevant for this investigational product. Herein, we describe a novel relative potency testing program and report for the first time on the clinical lot of this NTD vaccine during its first 60 months of storage at 2–8°C. We also describe the development of a complementary functional assay that measures the ability of IgG from animals or humans immunized with Na-GST-1/Alhydrogel to neutralize this important hookworm enzyme. While 90% inhibition of the catalytic activity of Na-GST-1 was achieved in animals immunized with Na-GST-1/Alhydrogel, lower levels of inhibition were observed in immunized humans. Moreover, anti-Na-GST-1 antibodies from volunteers in non-hookworm endemic areas were better able to inhibit catalytic activity than anti-Na-GST-1 antibodies from volunteers resident in hookworm endemic areas. The results described herein provide the critical tools for the product development of NTD vaccines.

Twenty-five-year research progress in hookworm excretory/secretory products

“…Although a 90% blockage of Na-GST-1 catalytic activity has been attained in animals vaccinated with stored Na-GST-1, a lower blockage percentage has been detected in immunized humans. Additionally, anti-Na-GST-1 antibodies obtained from volunteers from a hookworm nonendemic area exhibited more potent catalytic activity inhibition than those from volunteers from a hookwormendemic area [160].…”

“…The Na-GST-1/Alhydrogel vaccine has been proposed to act through the induction of IgG antibodies, that could be ingested by the hookworms developing inside the host intestine to block the detoxifying action of parasite Na-GST-1, thus allowing free heme to accumulate and damage the worm [95]. Recently, Brelsford et al [160] have tested Na-GST-1/Alhydrogel vaccine immunogenicity and relative potency during storage. Although a 90% blockage of Na-GST-1 catalytic activity has been attained in animals vaccinated with stored Na-GST-1, a lower blockage percentage has been detected in immunized humans.…”

Potency testing for a recombinant protein vaccine early in clinical development: Lessons from the Schistosoma mansoni Tetraspanin 2 vaccine

“…The first (#11-69F-003) and second (#1975) clinical lots of Sm -TSP-2/Al, manufactured four years apart to meet product needs during early clinical testing, were tested for potency over their first 84 and 36 months, respectively, after cGMP production. As Sm -TSP-2/Al does not induce sterilizing immunity against its target pathogen ( Sm ) in an animal model, potency was estimated by serological substitution using a compliance approach and the relative potency (RP) metric, as has been done for other recombinant protein vaccines developed by our group [11] , [12] . Three alternatives to the compliance approach for potency testing were then applied using the same potency dataset: (i) a least-squares regression fitted to a first-order linear decay model [10] followed by joinpoint regression to identify segments of time when potency deviated from first-order decay; (b) control charting of stability slopes, followed by assessment of their conformity to the Westgard rules of quality control; and (c) bootstrap models of potency over time and by cGMP manufactured lot, including a bootstrap simulation of a sub-potent lot of Sm -TSP-2/Al.…”

A highly expressed intestinal cysteine protease of Ancylostoma ceylanicum protects vaccinated hamsters from hookworm infection

“…caninum gave 33–53% decreased hookworm burdens [26,27,29]. However, in a phase 1a trial, although rNaGST1 was safe and immunogenic in human volunteers [30], IgG had negligible neutralizing effect on rNaGST1 enzymatic activity, despite the observation that IgG from immunized mice were highly neutralizing [31]; these results suggest a decreased potential for this vaccine in human trials. It remains crucial that further and expanded efforts be undertaken to develop new hookworm vaccines.…”