# Role of nonstructural protein in limited genetic diversity of yellow fever 17D vaccine virus

> **NIH NIH R21** · UNIVERSITY OF TEXAS MED BR GALVESTON · 2022 · $200,000

## Abstract

ABSTRACT
Many successful live attenuated vaccines (LAVs) were derived empirically and little is known about their
mechanisms of attenuation. The best characterized of these LAVs is poliovirus where attenuation has been
mapped to the 5’NCR and capsid genes. Increased understanding the mechanism of attenuation of licensed
LAVs will help in the rational development of future LAVs. The disease yellow fever is controlled by the use of a
live attenuated vaccine, strain 17D, derived from wild-type (WT) strain Asibi, and differ by 20 amino acids; 9 in
the structural genes and 11 in the nonstructural (NS) genes. Our overall goal is to understand the mechanism of
attenuation of 17D vaccine, which is poorly understood. Next Generation Sequencing (NGS) technology has
great applications to vaccine development and quality control and safety of LAVs. We have compared WT Asibi
and 17D vaccine by NGS and found that Asibi is a typical RNA virus with a quasispecies population while,
surprisingly, 17D vaccine has very little evidence of quasispecies, and we believe that this may contribute to the
attenuated phenotype of the vaccine virus. We have shown that the restricted quasispecies in 17D vaccine virus
is due to mutation(s) in the NS proteins of the replication complex as a whole, rather than the RNA dependent
RNA polymerase (RdRp) alone. In addition, ribavirin is an antiviral drug that introduces mutations into RNA
genomes during replication due to the lack of fidelity of the viral RdRp. We have shown that WT Asibi virus is
sensitive to ribavirin while 17D vaccine virus is relatively resistant suggesting that a high fidelity replication
complex potentially contributes to the attenuated phenotype of 17D vaccine. We believe that investigation of the
mechanism of limited quasispecies in 17D vaccine virus may have important applications to understanding the
molecular basis of attenuation of 17D vaccine, other LAVs, and development of future flavivirus LAVs. In this
application we will identify the viral genes that contribute to limited quasispecies of 17D vaccine. We hypothesize
that the restricted quasispecies in 17D vaccine virus is due to multiple mutations in the NS proteins of the
replication complex as a whole, rather than the RdRp alone, encodes an attenuated phenotype, and multiple
mutations contribute to the very low rate of reversion to virulence. The objective of this proposal is to perform
targeted studies to identify which YFV NS genes contribute to the restricted quasispecies of 17D vaccine to
propose a hypothesis to investigate the role of NS genes in the mechanism of attenuation of 17D vaccine. This
will be achieved via three specific aims: Aim 1 will investigate the quasispecies population and ribavirin sensitivity
of Asibi/17D mutants to identify residues in NS genes that contribute to restricted quasispecies population and
ribavirin resistance of 17D vaccine; Aim 2 will generate Asibi mutants that are resistant to ribavirin, identify the
nucleotid...

## Key facts

- **NIH application ID:** 10372589
- **Project number:** 1R21AI156059-01A1
- **Recipient organization:** UNIVERSITY OF TEXAS MED BR GALVESTON
- **Principal Investigator:** Alan D.T. Barrett
- **Activity code:** R21 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $200,000
- **Award type:** 1
- **Project period:** 2022-04-22 → 2024-03-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10372589

## Citation

> US National Institutes of Health, RePORTER application 10372589, Role of nonstructural protein in limited genetic diversity of yellow fever 17D vaccine virus (1R21AI156059-01A1). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10372589. Licensed CC0.

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