Trial design and participants
VRC 614 was a Phase 1, open-label, dose-escalation clinical trial. The primary objectives of the study were to evaluate the safety and adverse event 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 received L9LS.
Eligible participants were healthy adults ages 18 to 50 who had not previously had malaria or received a malaria vaccine. Full details of the inclusion and exclusion criteria can be found 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 US 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 participants gave written informed consent, and the trial followed Department of Health and Human Services guidelines for protecting participants in human research. Data was collected and analyzed by the Vaccine Research Center and the Walter Reed Army Institute of Research. All authors warrant the accuracy and completeness of the data and analyzes and adherence to the process by the protocol.
L9LS, a human IgG1 monoclonal antibody 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 analytical methods were developed in the Vaccine Research Center Vaccine Production Program and transferred to the Vaccine Clinical Materials Program, conducted under contract with Leidos Biomedical Research in Frederick, Maryland, for the current production of good manufacturing practices and vials 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 of no more than 2.0 ml each, depending on the participant’s weight. Most injections were abdominal, but the upper arm could be used if the participant and physician preferred. Participants were observed in the clinic for 1 to 2 hours after L9LS administration.
Interim safety data reviews were performed to assess any dose-related safety concerns before scaling up to doses of 5 mg per kilogram and 20 mg per kilogram. Unsolicited adverse reactions were recorded for 28 days after L9LS administration and controlled human malaria infection and were assessed according to a modified format of the acquired immunodeficiency syndrome table to assess the severity of adverse reactions in adults and children.14 Serious adverse events and new chronic medical conditions were recorded for the entire duration of the study.
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 of Anopheles Stephensic 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 higher (scores range from 0 to 4, with higher scores indicating more microscopically observed sporozoites).15 The participants were evaluated through two phone calls in the first 7 days after controlled human malaria infection, followed by clinic visits on days 7 through 17 and on day 21 to assess for parasitemia with a highly sensitive and specific polymerase chain. – reaction test (PCR) to detect early blood stage malaria infection.15-17 Day 21 was chosen as the upper end of the assessment days range to minimize the risk of exposure to 2019 coronavirus disease while providing sufficient time to assess for parasiticemia.
Parasitemia was defined as a single positive PCR result. Participants were considered protected if parasitemia did not develop until day 21 after controlled human malaria infection. Directly observed therapy with a standard regimen of 1 g atovaquone and 400 mg proguanil hydrochloride for 3 consecutive days was initiated in all participants, either upon confirmation of parasitemia, or at day 21 if the participant was untreated.
Serum concentrations of L9LS were quantified using an L9LS anti-idiotype antibody on the Meso Scale Discovery platform, as previously described, at pre-specified time points up to 8 weeks after monoclonal antibody administration.3 Pharmacokinetic analysis of L9LS concentrations was performed using both compartmental and non-compartmental approaches. Descriptive statistics for the maximum serum concentration (Cmax) and for the time of maximum concentration (Tmax), along with the concentrations on trial days 28 and 56, were calculated from observed data. The area under the curve was calculated using the linear trapezoidal method. Additional details of the quantification method and pharmacokinetic analysis are described in the Additional Methods section in the Supplementary Appendix, available at NEJM.org.
The target sample size was determined based on the probability of detecting serious adverse events. The efficacy analysis included all enrolled participants who underwent controlled human malaria infection. The primary efficacy analysis was performed using a two-tailed Barnard test comparing the percentage of participants with a malaria infection among those who received L9LS with the percentage among control participants. The secondary efficacy analysis was based on time to parasitemia; For each group, Kaplan-Meier curves were provided and compared using a log-rank test. To assess the comparability of challenge between the treatment and control groups, the median and interquartile ranges of the salivary gland scores for each group were reported. Due to the explorative nature of the trial, no adjustment was made for multiplicity.