Efficacy of Na-GST-1/Alhydrogel Hookworm Vaccine Assessed by Controlled Challenge Infection

Double blind, randomized, controlled, Phase 2 clinical trial in hookworm-unexposed adults living in the metropolitan area of Washington, DC. Subjects will receive three doses of the assigned vaccine formulation, or saline placebo, delivered intramuscularly on approximately Days 0, 56, and 112.

Subjects will be challenged with 50 infectious N. americanus larvae 4 weeks after 3rd vaccination. Fecal samples will be collected weekly starting 4 weeks post-challenge. Albendazole will be administered 20 weeks post-challenge to cure infections. Subjects will be followed until 10 months after their final vaccination.

Safety of vaccination will be measured from the time of each study vaccination (Day 0) through 14 days after each study vaccination by the occurrence of solicited injection site and systemic reactogenicity events. Safety of CHHI will be measure from the time of larval application (Day 140) through the first day of treatment with albendazole (Day 280).

Unsolicited non-serious adverse events (AEs) will be collected until approximately 1 month following each study vaccination and from study Day 140 (day of CHHI) through Day 280.

New-onset chronic medical conditions and Serious Adverse Events (SAEs) will be collected from the time of the first study vaccination through approximately 10 months after the third study vaccination (final visit). Clinical laboratory evaluations for safety will be performed on venous blood collected approximately 14 days after each vaccination and CHHI.

Immunogenicity testing will include IgG antibody responses to Na-GST-1, by a qualified indirect enzyme-linked immunosorbent assay (ELISA), on serum obtained prior to each study vaccination and CHHI, and at time points after each vaccination and after CHHI (see Appendix A); the affinity of vaccine-induced antibodies against Na-GST-1 using Surface Plasmon Resonance; the functional activity of vaccine-induced antibodies via in vitro enzyme neutralization assay; antigen-specific memory B cell responses; and, the innate immune responses to each of the TLR receptor immunostimulants.

Parasitological testing will include microscopic fecal egg detection by a qualified saline flotation technique, fecal egg counts by the McMaster method, fecal PCR for hookworm DNA, and peripheral eosinophil counts.

Recruitment and enrollment into the study will occur on an ongoing basis, with each group being recruited and vaccinated in sequence.

48 subjects will be enrolled into 4 groups of 12. Subjects will be enrolled sequentially and upon enrollment will be randomized to one of the following IP assignments in a double-blind fashion:

• Group 1 IP allocation (n=12 subjects): 12 subjects will receive 100µg Na-GST-1/Alhydrogel® delivered by IM injection in the deltoid muscle.
• Group 2 IP allocation (n=12): 12 subjects will receive Na-GST-1/Alhydrogel® plus 500µg CpG 10104 delivered by IM injection in the deltoid muscle.
• Group 3 IP allocation (n=12): 12 subjects will receive Na-GST-1/Alhydrogel® plus 5µg GLA-AF delivered by IM injection in the deltoid muscle.
• Group 4 IP allocation (n=12): 12 subjects will receive sterile saline delivered by IM injection in the deltoid muscle.

Inclusion criteria

• Males and non-pregnant females between 18 and 45 years, inclusive.
• Good general health as determined by means of the screening procedures1.
• Available for the duration of individual subject study participation (14 months).
• Willingness to participate in the study as evidenced by signing the informed consent document.
• Able to understand and comply with planned study procedures.

Exclusion criteria

• Pregnancy as determined by a positive urine human choriogonadotropin (hCG) test (if female).
• Subject unwilling to use effective contraception for a minimum of 30 days prior to vaccination and up until documentation of clearance of hookworm infection post-CHHI (if female and not surgically sterile, abstinent from intercourse with a male partner, in a monogamous relationship with a vasectomized partner, at least 2 years post-menopausal, or determined otherwise by medical evaluation to be sterile).
• Currently lactating and breast-feeding or plans to breastfeed at any given time from the first study vaccination until clearance of hookworm infection post-CHHI (if female).
• Evidence of clinically significant neurologic, cardiac, pulmonary, hepatic, rheumatologic, autoimmune, gastrointestinal, diabetes, or renal disease by history, physical examination, and/or laboratory studies.
• Has a diagnosis of schizophrenia, bipolar disease or other major psychiatric condition that would make compliance with study visits/procedures difficult (e.g., subject with psychoses or history of suicide attempt or gesture in the 3 years before study entry, ongoing risk for suicide).
• Known or suspected immunodeficiency or immunosuppression as a result of an underlying illness or treatment (causes for immunosuppression may include, but are not limited to, poorly-controlled diabetes mellitus, chronic liver disease, renal insufficiency, active neoplastic disease or a history of hematologic malignancy, connective tissue disease, organ transplant).
• Laboratory evidence of liver disease (alanine aminotransferase [ALT] greater than 1.25-times the upper reference limit).
• Laboratory evidence of renal disease (serum creatinine greater than 1.25-times the upper reference limit, or urine dipstick testing positive for glucose or more than trace protein).
• Laboratory evidence of hematologic disease (hemoglobin <11.1 g/dl [females] or <12.5 g/dl [males]; absolute leukocyte count <3400/mm3 or >10.8 x 103/mm3; absolute eosinophil count <500/mm3; or platelet count <140,000/mm3).
• Other condition that in the opinion of the investigator would jeopardize the safety or rights of a volunteer participating in the trial or would render the subject unable to comply with the protocol.
• Planned participation in another investigational vaccine or drug trial within 30 days of starting this study or until the last study visit (this may include other licensed or unlicensed vaccines, drugs, biologics, devices, blood products, or medications).
• Volunteer has had medical, occupational, or family problems as a result of alcohol or illicit drug use during the past 24 months.
• Positive fecal occult blood test at screening.
• Infection with a pathogenic intestinal helminth as determined by stool examination for ova and parasites at screening.
• History of iron deficiency anemia or laboratory evidence of iron deficiency (serum ferritin concentration below the lower reference limit).
• History of hypoalbuminemia.
• History of a severe allergic reaction or anaphylaxis.
• Severe asthma as defined by the need for daily use of inhalers, or emergency clinic visit or hospitalization within 6 months of the volunteer's expected first vaccination in the study.
• Positive test for hepatitis B surface antigen (HBsAg).
• Positive confirmatory test for HIV infection.
• Positive confirmatory test for hepatitis C virus (HCV) infection.
• Using or intends to continue using oral or parenteral corticosteroids, high-dose inhaled corticosteroids (>800 μg/day of beclomethasone dipropionate or equivalent) or other immunosuppressive or cytotoxic drugs within 30 days of the volunteer's expected first vaccination in this study or planned use during the study.
• Receipt of a live vaccine within 4 weeks or a killed vaccine within 2 weeks prior to the volunteer's expected first vaccination in the study.
• Receipt of immunoglobin or other blood products (with exception of Rho D immunoglobulin) within 90 days of the planned first study vaccination.
• Known allergy to albendazole, amphotericin B or gentamicin.
• History of previous infection with hookworm or continuous residence for more than 6 months in a community where hookworm is endemic.
• Current or past scars, tattoos, or other disruptions of skin integrity at the intended site of larval application.
• Previous receipt of the Na-GST-1/Alhydrogel® hookworm vaccine.
• History of a surgical splenectomy.
• Pre-existing autoimmune or antibody-mediated diseases including but not limited to: systemic lupus erythematosis, rheumatoid arthritis, multiple sclerosis, Sjogren's syndrome, autoimmune thrombocytopenia; or laboratory evidence of possible autoimmune disease determined by a positive anti-dsDNA titer, positive rheumatoid factor, and/or proteinuria (greater than trace protein on urine dipstick testing).