# vsgseq2: an updated pipeline for analysis of the diversity and abundance of population-wide Trypanosoma brucei VSG expression

## TL;DR

vsgseq2 is an improved tool for analyzing how the parasite Trypanosoma brucei changes its surface proteins to evade the immune system.

## Contribution

vsgseq2 introduces a more efficient and reproducible workflow for analyzing VSG expression in Trypanosoma brucei populations.

## Key findings

- vsgseq2 accurately reconstructs population-wide VSG repertoires and expression proportions.
- vsgseq2 improves computational efficiency and reproducibility in VSGSeq data analysis.
- vsgseq2 enhances data utilization for studying immune evasion mechanisms in T. brucei.

## Abstract

Trypanosoma brucei is an extracellular eukaryotic parasite that causes sleeping sickness in humans and Nagana, Surra and Dourine in livestock, game animals and horses. The parasite displays an extensive immune evasion mechanism, utilising the expression and ability to switch antigenically distinct variant surface glycoprotein (VSG) coats. VSG encoding genes account for ~10% of the
T. brucei genome, and mosaic VSGs, assembled from distinct incomplete VSG gene copies, can be produced from this VSG library, generating an almost infinite VSG repertoire, which enables chronic infections. Each parasite expresses just one VSG at a time, but within a host, many VSGs can be expressed simultaneously. Understanding patterns of VSG expression is therefore central to studying parasite dynamics, tissue tropism, and infection persistence. VSGSeq is an amplicon sequencing approach that enables surveillance of the population-wide diversity and abundance of expressed VSGs. We present vsgseq2, an updated and fully reproducible workflow for analysing VSGSeq data. Implemented in Nextflow, vsgseq2 integrates modern tools for transcript assembly and quantification, improves computational efficiency. Benchmarking against defined
T. brucei VSG expression datasets demonstrated that vsgseq2 accurately reconstructs population-wide VSG repertoires and better recapitulates VSG expression proportions. Analyses of in vivo infection data further confirmed that vsgseq2 enhances reproducibility and improves data utilisation, and improves computational efficiency. vsgseq2 enables researchers to efficiently and reproducibly analyse complex VSG expression data and the mechanisms driving immune evasion in
T. brucei.

African trypanosomes, such as
Trypanosoma brucei, are parasites that cause deadly diseases in humans and livestock. They survive in their host's blood by constantly changing a protective coat of proteins, known as variant surface glycoproteins (VSGs). Switching VSG makes it very hard for the immune system to keep up, allowing infections to last for months or even years. At any one time, each parasite uses only one VSG, but across the whole population inside a host, many different VSGs are used simultaneously. To study how parasites change their coats, a method called VSGSeq was developed, which shows the genetic basis that makes the VSG coat. This research introduces vsgseq2, which provides an enhanced workflow for population-scale analysis of VSG expression, helping future research to understand how trypanosomes evade their host's immune attack.