Assays to Support Development of Malaria Transmission Blocking Vaccines

National Institute Of Allergy And Infectious Diseases

Investigators

Linked publications & trials

Abstract

We published the following findings in FY2023: Sagara I, Healy SA, Assadou MH, Kone M, Swihart BJ, Kwan JL, Fintzi J, Sissoko K, Kamate B, Samake Y, Guindo MA, Doucoure M, Niar K, Dolo A, Diarra B, Rausch KM, Narum DL, Jones DS, MacDonald NJ, Zhu D, Gorres JP, Imeru A, Mohan R, Thera I, Zaidi I, Salazar-Miralles F, Duan J, Neal J, Morrison RD, Muratova O, Sylla D, OConnell EM, Wu Y, Hume JCC, Coulibaly MB, Anderson CF, Traore SF, Doumbo OK, Duffy PE. A randomized controlled phase 1 trial of malaria transmission-blocking vaccines Pfs230D1-EPA and Pfs25-EPA in Alhydrogel in healthy Malian adults. 2023. Lancet Infectious Diseases. In press. We compared gamete vaccine Pfs230D1-EPA/Alhydrogel to zygote vaccine Pfs25-EPA/Alhydrogel in malaria-experienced Malians (ClinicalTrials.gov NCT02334462) who were enrolled in a pilot dose-escalation then double-blind, block-randomised, comparator-controlled main-phase trial in malaria-intense Bancoumana, Mali. 18-50-year-old healthy non-pregnant, non-breastfeeding consenting adult residents were randomly assigned (1:1:1:1) to receive four doses at months 0, 1, 45, and 165 of either 47 g Pfs25, 40 g Pfs230D1 or comparator (Twinrix or Menactra)all co-administered with normal saline for blindingor 47 g Pfs25 plus 40 g Pfs230D1 co-administered. We documented safety and tolerability (primary endpoint in the as-treated populations) and immunogenicity (secondary endpoint in the as-treated populations: ELISA, standard-membrane-feeding assay, and mosquito direct skin feed assay). Most vaccinees became seropositive after two Pfs230D1 or three Pfs25 doses; peak titres increased with each dose thereafter. Functional activity (mean peak transmission-reducing activity) appeared for Pfs230D1 alone and for Pfs25 plus Pfs230D1 after the third dose and after the fourth dose, but not for Pfs25 alone. Pfs230D1 transmission-reducing activity persisted 10 weeks after the fourth dose. Transmission-reducing activity of 80% was estimated at 1659 ELISA units for Pfs25, 218 for Pfs230D1, and 223 for Pfs230D1 plus Pfs25. After 3850 direct skin feed assays, 35 participants (12 Pfs25, eight Pfs230D1, five Pfs25 plus Pfs230D1, and ten comparator) had transmitted parasites at least once. The proportion of positive assays in vaccine groups did not differ from that of the comparator, nor did Pfs230D1 and combination groups differ. Pfs230D1 but not Pfs25 vaccine induced durable serum functional activity in Malian adults. Direct skin feed assays detected parasite transmission to mosquitoes but increased event rates are needed to assess vaccine effectiveness. Miura K, Pham TP, Lee S, Plieskatt J, Diouf A, Sagara I, Coelho CH, Duffy PE, Wu Y, Long CA. Development and qualification of an antigen integrity assay for a Plasmodium falciparum malaria transmission blocking vaccine candidate, Pfs230. 2022. Vaccines. Sep 28. While potency of Pfs230 protein can be determined by a standard membrane-feeding assay (SMFA) using antibodies from immunized subjects, the precision of a general in vivo potency study is known to be poor and is also time-consuming. Therefore, we contributed to a collaborative project led by Dr. Miura from LMIV/NIAID that developed a sandwich ELISA-based in vitro potency assay, called the Antigen Integrity Assay (AIA), using a well-characterized Pfs230 recombinant protein and two human anti-Pfs230 monoclonal antibodies (mAbs) developed at LMIV, which had functional activity indicated by SMFA. Multiple validation parameters of AIA were evaluated to qualify the assay following International Conference on Harmonization (ICH) Q2(R1) guidelines. The AIA is a high throughput assay and demonstrated excellent precision (3.2 and 5.4% coefficients of variance for intra- and inter-assay variability, respectively) and high sensitivity (>12% impurity in a sample can be detected). General methodologies and the approach to assay validation described herein are amenable to any subunit vaccine as long as more than two functional, non-competing mAbs are available. Thus, this study supports future subunit vaccine development. Tang WK, Coelho CH, Miura K, Tentokam BCN, Salinas ND, Narum DL, Healy SA, Sagara I, Long CA, Duffy PE, Tolia NH. Human antibody epitope map of a malaria transmission blocking vaccine. 2023. Immunity. Feb 14. 56(2):433-443.e5. doi: 10.1016/j.immuni.2023.01.012. Pfs230 domain 1 (Pfs230D1) is an advanced malaria transmission-blocking vaccine antigen demonstrating high functional activity in clinical trials. However, the structural and functional correlates of transmission-blocking activity are not defined. Here, we characterized a panel of human monoclonal antibodies (hmAbs) elicited in vaccinees immunized with Pfs230D1. These hmAbs exhibited diverse transmission-reducing activity, yet all bound to Pfs230D1 with nanomolar affinity. We compiled epitope-binning data for seventeen hmAbs and structures of nine hmAbs complexes to construct a high-resolution epitope map and revealed that potent transmission-reducing hmAbs bound to one face of Pfs230D1, while non-potent hmAbs bound to the opposing side. The structure of Pfs230D1D2 revealed that non-potent transmission-reducing epitopes were occluded by the second domain. The hmAb epitope map delineated binary hmAb combinations that synergized for extremely high-potency, transmission-reducing activity. This work provides a high-resolution guide for structure-based design of enhanced immunogens and informs diagnostics that measure the transmission-reducing response.