Beyond Blood Smears: Qualification of Plasmodium 18S rRNA as a Biomarker for Controlled Human Malaria Infections.

Abstract

18S rRNA is a biomarker that provides an alternative to thick blood smears in controlled human malaria infection (CHMI) trials. We reviewed data from CHMI trials at non-endemic sites that used blood smears and Plasmodium 18S rRNA/rDNA biomarker nucleic acid tests (NATs) for time to positivity. We validated a multiplex quantitative reverse transcription-polymerase chain reaction (qRT-PCR) for Plasmodium 18S rRNA, prospectively compared blood smears and qRT-PCR for three trials, and modeled treatment effects at different biomarker-defined parasite densities to assess the impact on infection detection, symptom reduction, and measured intervention efficacy. Literature review demonstrated accelerated NAT-based infection detection compared with blood smears (mean acceleration: 3.2-3.6 days). For prospectively tested trials, the validated Plasmodium 18S rRNA qRT-PCR positivity was earlier (7.6 days; 95% CI: 7.1-8.1 days) than blood smears (11.0 days; 95% CI: 10.3-11.8 days) and significantly preceded the onset of grade 2 malaria-related symptoms (12.2 days; 95% CI: 10.6-13.3 days). Discrepant analysis showed that the risk of a blood smear-positive, biomarker-negative result was negligible. Data modeling predicted that treatment triggered by specific biomarker-defined thresholds can differentiate complete, partial, and non-protective outcomes and eliminate many grade 2 and most grade 3 malaria-related symptoms post-CHMI. Plasmodium 18S rRNA is a sensitive and specific biomarker that can justifiably replace blood smears for infection detection in CHMI trials in non-endemic settings. This study led to biomarker qualification through the U.S. Food and Drug Administration for use in CHMI studies at non-endemic sites, which will facilitate biomarker use for the qualified context of use in drug and vaccine trials.

• Authors: Annette M Seilie, Ming Chang, Amelia E Hanron, Zachary P Billman, Brad C Stone, Kevin Zhou, Tayla M Olsen, Glenda Daza, Jose Ortega, Kurtis R Cruz, Nahum Smith, Sara A Healy, Jillian Neal, Carolyn K Wallis, Lisa Shelton, Tracie VonGoedert Mankowski, Sharon Wong-Madden, Sebastian A Mikolajczak, Ashley M Vaughan, Stefan H I Kappe, Matt Fishbaugher, Will Betz, Mark Kennedy, Jen C C Hume, Angela K Talley, Stephen L Hoffman, Sumana Chakravarty, B Kim Lee Sim, Thomas L Richie, Anna Wald, Christopher V Plowe, Kirsten E Lyke, Matthew Adams, Gary A Fahle, Elliot P Cowan, Patrick E Duffy, James G Kublin, Sean C Murphy
• Journal: The American journal of tropical medicine and hygiene (Am J Trop Med Hyg) Vol. 100 Issue 6 Pg. 1466-1476 (06 2019) ISSN: 1476-1645 [Electronic] United States
• PMID: 31017084 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't, Validation Study)

Chemical References

• Biomarkers
• RNA, Protozoan
• RNA, Ribosomal, 18S

Topics

• Biomarkers (blood)
• Humans
• Malaria (diagnosis)
• Multiplex Polymerase Chain Reaction
• Plasmodium (genetics, isolation & purification)
• RNA, Protozoan (genetics)
• RNA, Ribosomal, 18S (blood, genetics)
• Real-Time Polymerase Chain Reaction
• Reproducibility of Results
• Reverse Transcriptase Polymerase Chain Reaction