A highly protective malaria vaccine would greatly facilitate the prevention and elimination of malaria and containment of drug-resistant parasites1. A high level (more than 90%) of protection against malaria in humans has previously been achieved only by immunization with radiation-attenuated Plasmodium falciparum (Pf) sporozoites (PfSPZ) inoculated by mosquitoes2,3,4; by intravenous injection of aseptic, purified, radiation-attenuated, cryopreserved PfSPZ (‘PfSPZ Vaccine’)5,6; or by infectious PfSPZ inoculated by mosquitoes to volunteers taking chloroquine7,8,9,10 or mefloquine11 (chemoprophylaxis with sporozoites). We assessed immunization by direct venous inoculation of aseptic, purified, cryopreserved, non-irradiated PfSPZ (‘PfSPZ Challenge’12,13) to malaria-naive, healthy adult volunteers taking chloroquine for antimalarial chemoprophylaxis (vaccine approach denoted as PfSPZ-CVac)14. Three doses of 5.12 × 104 PfSPZ of PfSPZ Challenge12,13 at 28-day intervals were well tolerated and safe, and prevented infection in 9 out of 9 (100%) volunteers who underwent controlled human malaria infection ten weeks after the last dose (group III). Protective efficacy was dependent on dose and regimen. Immunization with 3.2 × 103 (group I) or 1.28 × 104 (group II) PfSPZ protected 3 out of 9 (33%) or 6 out of 9 (67%) volunteers, respectively. Three doses of 5.12 × 104 PfSPZ at five-day intervals protected 5 out of 8 (63%) volunteers. The frequency of Pf-specific polyfunctional CD4 memory T cells was associated with protection. On a 7,455 peptide Pf proteome array, immune sera from at least 5 out of 9 group III vaccinees recognized each of 22 proteins. PfSPZ-CVac is a highly efficacious vaccine candidate; when we are able to optimize the immunization regimen (dose, interval between doses, and drug partner), this vaccine could be used for combination mass drug administration and a mass vaccination program approach to eliminate malaria from geographically defined areas.
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The authors thank the vaccine trial participants for their contribution and commitment to vaccine research. We thank F. Adomat, S. Adukpo, M. Aldejohann, S. Bolte, S. Borrmann, A. Bouyoukou Hounkpatin, S. Brückner, E. Bruske, J. Fernandes, P. Granados Bayón, J. Hass, S. Jeyaraj, J. Keim, A. Knoblich, R. Köllner, A. Kreidenweiss, D. N. Ndungu, R. Ritter, J. A. Selvaraj, Z. Sulyok, S. Theil, N. Theurer, and I. Westermann for support in conducting the trial, and P. Darrah and M. Roederer for assistance with the interpretation of the T-cell data. We thank the Sanaria and Protein Potential teams for manufacture and shipping of investigational products, PfSPZ Challenge and diluents, regulatory, quality, and clinical site activities, and legal and administrative support, including especially D. Cheney (née Padilla), Y. Abebe, E. Saverino, Y. Wu, E. Fomumbod, A. Awe, M. King, M. Orozco, A. Patil, Y. Wen, K. Nelson, J. Overby, S. Matheny, V. Pitch, B. Jiang, L. Gao, R. Xu, T. T. Wai, S. Monsheimer, P. De La Vega, M. Laskowski, H. Huang, M. Marquette, J. Jackson, F. Beams, R. Douglas, R. C. Thompson, D. Dolberg and A. Hoffman. We thank J. Inglese and P. Dranchak of the National Center for Advancing Translational Sciences (NCATS), NIH for support with the automated immunofluorescence assay and inhibition of sporozoite invasion assays. We appreciate the expert reviews of the Safety Monitoring Committee (W. Chen, P. Coyne and P. Zanger). The clinical trial was funded by the German Federal Ministry of Education and Research (BMBF) through the German Center for Infection Research (DZIF). Manufacture of investigational product by Sanaria was supported in part by the National Institute of Allergy and Infectious Diseases of the National Institutes of Health under SBIR award numbers 5R44AI058375 and 5R44AI055229. T cell studies were supported by the intramural research program of the VRC, NIAID, NIH. Proteome microarray studies were supported by NIAID SBIR grant 5R44AI066791 and funding from the Bill & Melinda Gates Foundation.
S.C., A.J.R., E.R.J., P.F.B., N.K, A.M., T.M., A.G., A.G.E., T.L., R.E.S, M.L., T.L.R., B.K.L.S. and S.L.H. are salaried employees of Sanaria Inc., the developer and owner of PfSPZ Challenge and the sponsor of the clinical trial. In addition, S.L.H. and B.K.L.S. have a financial interest in Sanaria Inc. J.J.C. is an Antigen Discovery Employee. P.L.F. owns stock and is a board member at Antigen Discovery, Inc. All other authors declare no conflicts of interest.
Reviewer Information Nature thanks L. Rénia and the other anonymous reviewer(s) for their contribution to the peer review of this work.
Extended data figures and tables
a, b, The number of adverse events (AEs) regardless of attribution to investigational product. Each bar represents one volunteer sorted on the number of adverse events from the time of first injection with normal saline (controls) or PfSPZ-CVac until the time of CHMI, approximately 17 weeks later (a) and adverse events in the same volunteers from initiation of CHMI until the end of follow-up (b). Mild (grade 1) adverse events are depicted in grey, moderate (grade 2) in yellow and severe (grade 3) in blue. Non-protected volunteers are marked with an ‘M’ on the x axis.
PBMCs from subjects were drawn 14 days after third immunization (post-imm) or 1 day before CHMI (pre-CHMI), stimulated with PfSPZ, PfRBC, or stimulation controls, and stained for intracellular cytokine expression. a, b, The pie charts show the proportion of memory CD4 T cells expressing any combination of IFN-γ, IL-2, or TNF-α for each dose group after stimulation with PfSPZ (a) or PfRBC (b). Responses are background subtracted from control antigen stimulations 1% HSA or uninfected erythrocytes. c, d, The magnitude of the memory CD4 T-cell response for each combination of cytokines is shown in c and d. There is a trend towards higher polyfunctionality as dose increases. e, f, The median fluorescence intensity (MFI) for IFN-γ is shown for the different combination of IFN-γ+ cells following PfSPZ or PfRBC stimulation. Cells that simultaneously produce IFN-γ, IL-2, and TNF-α have the highest IFN-γ MFI.
a, b, Memory CD4 T cells producing IL-4 (a) or IL-10 (b) after PfRBC stimulation. Memory γδ T cells producing IFN-γ, IL-2, or TNF-α following PfSPZ (c) or PfRBC stimulation (d). For a–d, results are the percentage of cytokine-producing cells after incubation with PfSPZ minus the percentage of cells after incubation with vaccine diluent (medium with 1% HSA) as control or percentage of cytokine-producing cells after incubation with asexual Pf-infected red blood cells (PfRBC) minus uninfected RBCs as control. e, f, Total memory γδ T cells assessed before immunization (pre-imm) and 14 days after third immunization (post-imm) for the percentage of cells expressing CD38. The absolute frequencies are shown in e and the change from pre-vaccination to post-vaccination is shown in f. For a–d, within a dose group, the difference from pre-vaccine was assessed by two-way ANOVA with Bonferroni correction. Data are median ± interquartile range. For e, f, difference from pre-vaccine was assessed by Wilcoxon signed rank test. P values were corrected for multiple comparisons by the Bonferroni method. *P < 0.05, *P < 0.01. Data are median ± interquartile range. Pre-imm, 3 days before first immunization; post-imm, 14 days after third immunization; pre-CHMI, 1 day before CHMI.
a–f, The frequency of the circulating γδ T-cell subsets as a percentage of total lymphocytes was assessed in unstimulated PBMCs before the first immunization (pre-imm), 2 weeks after final immunization (post-imm), and the day before CHMI (pre-CHMI). Fold change compared to pre-imm is shown for total memory γδ T cells (a), Vγ9+Vδ2+ (b), Vγ9+Vδ1+ (c), Vγ9−Vδ1+ (d), Vγ9+Vδ1−Vδ2− (e), and Vγ9−Vδ1−Vδ2− (f) subfamilies. The frequency of Vγ9−Vδ2+ subset is low to undetectable. Within a dose group, the difference from pre-imm was assessed by two-way ANOVA with Bonferroni correction. *P < 0.05, **P < 0.01. Data are geometric mean ± 95% CI.
Extended Data Figure 6 Anti-plasmodial antibody responses in vaccinated volunteers who were immunized with three doses of 5.12 × 104 PfSPZ at 28-day, 14-day, or 5-day intervals.
Antibodies to PfCSP by ELISA were assessed in sera taken before any immunizations (pre-immunization), two weeks following last immunization (post-immunization) and 10 weeks after last immunization, which was one day before CHMI (pre-CHMI). PfCSP ELISA results are reported as net OD 1.0; the reciprocal serum dilution at which the optical density was 1.0 in post-immunization or pre-CHMI sera minus the OD 1.0 in pre-immunization sera. All values met criteria for positivity. Protected volunteers are represented by yellow circles and unprotected volunteers by grey circles.
Radiation-attenuated PfSPZ in PfSPZ Vaccine invade hepatocytes and partially develop, but do not replicate. They are metabolically active and non-replicating. Infectious PfSPZ in PfSPZ-CVac invade hepatocytes and fully develop. A single PfSPZ replicates exponentially producing more than 104 merozoites. These merozoites are released into the circulation, and each merozoite can invade a different erythrocyte. Chloroquine prevents complete parasite development within erythrocytes, thereby preventing the development of merozoites that can invade new erythrocytes.
Parasitaemia measured by qPCR over 22 days. The subjects who were protected and not protected against CHMI are in yellow and grey, respectively. The times of PfSPZ inoculations are shown as vertical red lines and the time of last CQ administration as a vertical blue line. CQ was given as 10 mg kg−1 (maximum 620 mg) loading dose on day 0 followed by 5 mg kg−1 (maximum 310 mg) chloroquine base on days 5, 10, and 15.
This file contains Supplementary Figure 1, Supplementary Tables 1-5 and 7-9. (PDF 804 kb)
Supplementary Table 6 shows logistic regression of peak antibody levels (2 weeks after final immunization) and baseline antibody levels on probability of sterile protection against CHMI, adjusted by dose of PfSPZ-CVac. (PDF 1802 kb)
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Mordmüller, B., Surat, G., Lagler, H. et al. Sterile protection against human malaria by chemoattenuated PfSPZ vaccine. Nature 542, 445–449 (2017). https://doi.org/10.1038/nature21060
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