Naturally acquired immunity among Kenyan adults suppresses the West African P. falciparum NF54 strain in controlled human malaria infection (CHMI)

We used controlled human malaria infection (CHMI) to study naturally acquired immunity of Kenyan adults. We administered 3.2×10[3][1] cryopreserved Plasmodium falciparum sporozoites (SPZ, NF54 West African strain) and undertook clinical monitoring and serial quantitative PCR (qPCR). Of the 142 volunteers who were eligible for analysis: 26 (18.3%) had febrile symptoms and were treated; 30 (21.1%) reached ≥500 parasites/μl and were treated; 53 (37.3%) had parasitaemia without meeting thresholds for treatment and; 33 (23.2%) remained qPCR negative. We find that the immunity acquired by some Kenyan adults can completely suppress in vivo growth of a parasite strain originating from outside Kenya. ### Competing Interest Statement All authors declare no conflicts of interest except for the following: Y. A., P. F. B., S. L. H, E.R.J., T. L. R., and B. K. L. S. are salaried, full-time employees of Sanaria Inc., the manufacturer of Sanaria PfSPZ Challenge. Thus, all authors associated with Sanaria Inc have potential conflicts of interest. ### Clinical Trial NCT02739763 ### Clinical Protocols ### Funding Statement This work was supported by a Wellcome Trust grant (107499). The funder had no role in the design of the study, volunteer recruitment and selection, data collection, analysis and interpretation, preparation of the manuscript, or decision to publish. All named authors and the corresponding author have full access to the study data and are responsible for the publication. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The study received ethical approval from the KEMRI Scientific and Ethics Review Unit (KEMRI//SERU/CGMR-C/029/3190) and the University of Oxford Tropical Research Ethics Committee (OxTREC 2-16). All necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes Volunteer data will be made available including data dictionaries after de-identification of the volunteer data that represent the results reported in this article. The data will be available to researchers who will need to submit proposals to dgc@kemri-wellcome.org to gain access to the data following a signed data access agreement. The study protocol, informed consent forms, and all other associated documents have been previously published. [1]: #ref-3