Trial Design and Participants
VRC 614 was a phase 1, open-label, dose-escalation clinical trial. The primary objectives of the trial were to evaluate the safety and side-effect profile of L9LS administered at intravenous doses of 1, 5, and 20 mg per kilogram of body weight and at a subcutaneous dose of 5 mg per kilogram. The secondary objectives were to evaluate the pharmacokinetic properties and protective efficacy of L9LS after controlled human malaria infection approximately 2 to 6 weeks after the participants had received L9LS.
Eligible participants were healthy adults who were 18 to 50 years of age and had not previously had malaria or received a vaccine for malaria. Full details of the inclusion and exclusion criteria are provided in the protocol, available with the full text of this article at NEJM.org.
The trial was designed, funded, and conducted by the Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health (NIH), at the NIH Clinical Center in Bethesda, Maryland. Controlled human malaria infection was conducted at the U.S. Army facility at the Walter Reed Army Institute of Research in Silver Spring, Maryland. The NIH institutional review board approved the clinical trial protocol. All the participants provided written informed consent, and the trial followed the Department of Health and Human Services guidelines for the protection of human research participants. Data were collected and analyzed by the Vaccine Research Center and the Walter Reed Army Institute of Research. All the authors vouch for the accuracy and completeness of the data and analyses and for the adherence of the trial to the protocol.
L9LS, a human IgG1 monoclonal antibody that was produced in accordance with current good manufacturing practices by cell-culture expression in a recombinant Chinese hamster ovary cell line, consists of purified, formulated L9LS glycoprotein. Processes and analytic methods were developed at the Vaccine Research Center Vaccine Production Program and transferred to the Vaccine Clinical Materials Program, operated under contract with Leidos Biomedical Research in Frederick, Maryland, for current good manufacturing practices production and vialing in a buffered formulation at a concentration of 150 mg per milliliter.
L9LS was administered intravenously over a period of 30 minutes at a dose of 1 mg per kilogram of body weight, 5 mg per kilogram, or 20 mg per kilogram. Participants who received subcutaneous injections received 5 mg per kilogram, with the total dose divided into one or two injections, not exceeding 2.0 ml each, according to the weight of the participant. Most injections were abdominal, but the upper arm could be used if preferred by the participant and clinician. Participants were observed in the clinic for 1 to 2 hours after administration of L9LS.
Interim safety data reviews were conducted to assess for any dose-related safety concerns before escalation to doses of 5 mg per kilogram and 20 mg per kilogram. Unsolicited adverse events were recorded for 28 days after L9LS administration and controlled human malaria infection and were graded according to a modified Division of Acquired Immunodeficiency Syndrome Table for Grading the Severity of Adult and Pediatric Adverse Events.14 Serious adverse events and new chronic medical conditions were recorded for the entire duration of the trial.
Participants were followed for 24 weeks after L9LS administration. Control participants were followed for 7 weeks after controlled human malaria infection.
Controlled Human Malaria Infection
Participants were exposed to bites on the forearm from Anopheles stephensi mosquitoes infected with P. falciparum (3D7 strain). The participants met standard infectivity criteria consisting of five qualifying bites from mosquitoes with a salivary gland score of 2 or greater (scores range from 0 to 4, with higher scores indicating more microscopically observed sporozoites).15 The participants were evaluated by means of two telephone calls in the first 7 days after controlled human malaria infection, followed by in-clinic visits on days 7 through 17 and on day 21 to assess for parasitemia with a highly sensitive and specific polymerase-chain-reaction (PCR) test to detect early blood-stage malaria infection.15-17 Day 21 was chosen as the upper end of the range of assessment days in order to minimize the risk of exposure to coronavirus disease 2019 while ensuring sufficient time to assess for parasitemia.
Parasitemia was defined as a single positive PCR result. Participants were considered protected if parasitemia did not develop through day 21 after controlled human malaria infection. Directly observed therapy with a standard treatment of 1 g of atovaquone and 400 mg of proguanil hydrochloride for 3 consecutive days was initiated in all the participants either on confirmation of parasitemia or on day 21 if the participant had not already been treated.
Serum concentrations of L9LS were quantified with the use of an L9LS anti-idiotype antibody on the Meso Scale Discovery platform, as previously described, at prespecified time points up to 8 weeks after administration of the monoclonal antibody.3 Pharmacokinetic analysis of L9LS concentrations was performed with both compartmental and noncompartmental approaches. Descriptive statistics for the maximum serum concentration (Cmax) and for the time of maximum concentration (Tmax), along with the concentrations at trial days 28 and 56, were calculated on the basis of observed data. The area under the curve was calculated with the use of the linear trapezoid method. Additional details of the quantification method and pharmacokinetic analysis are described in the Supplemental Methods section in the Supplementary Appendix, available at NEJM.org.
The target sample size was determined on the basis of the probability of observing serious adverse events. The efficacy analysis included all enrolled participants who underwent controlled human malaria infection. The primary efficacy analysis was performed with the use of a two-sided Barnard test in which the percentage of participants who had malaria infection among those who had received L9LS was compared with the percentage among control participants. The secondary efficacy analysis was based on the time to parasitemia; Kaplan–Meier curves were provided for each group and compared with the use of a log-rank test. To assess the comparability of the challenge between the treatment and control groups, the median and interquartile ranges of the salivary gland scores were reported for each group. Owing to the exploratory nature of the trial, no adjustment was made for multiplicity.
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