Zimvo Obasa Poster 2023

Dr Zimvo Obasa

Stellenbosch University, South Africa

An ex vivo model for understanding the impact of vaccination on Mycobacterial persister Populations

Poster Abstract

This project aims to adapt an ex vivo model of mycobacterial growth inhibition to study the effect of immune status on Mycobacterium tuberculosis (Mtb) persister formation. Ex vivo mycobacterial growth inhibition assays (MGIAs) have been successfully exploited to assess vaccine efficacy, probe immune mechanisms underlying protective efficacy, and determine the combined impact of drug treatment and vaccination on mycobacterial killing. Persisters are defined here as non or slowly growing, reversibly drug-tolerant (not genetically resistant) organisms. During TB treatment, the majority of drug susceptible Mtb is killed within the first few days of treatment, but the small remaining (persister) population takes much longer to eradicate, necessitating a minimum treatment period of 6 months. Whether they form after TB treatment or because of host pressure, persisters pose a subsequent threat of reactivation disease, a particular concern in HIV-co-infected individuals.

We have recently developed a dual fluorescent replication reporter system and applied this to demonstrate M. tuberculosis persister formation in infected macrophages. The reporter strain in combination with flow cytometry provide a rapid means of monitoring population wide Mtb growth, killing kinetics and phenotypes on a single cell level. In this work, we are adapting MGIAs to assess the impact of the change in immune cell populations after vaccination on mycobacterial persister populations. We are investigating the hypothesis that a change in immune status through effective vaccination will reduce the formation of Mtb persister cells. This work could provide new insights into the impact of host factors on persister formation, and vice versa. This would help to rationally design new vaccines and adjunct therapies that reduce persister formation and therefore increase long-term protection against TB.

Biography

Dr Zimvo Obasa is a postdoctoral researcher at Stellenbosch University. She has a BSc degree in Human Life Sciences (2014), an MSc in Human Physiology (2017) and a PhD in Molecular Biology (2021). Her PhD research focused on understanding the host immune responses elicited by Mycobacterium tuberculosis persisters in macrophage cultures and she also developed and validated a trackable murine model for the studying of Mycobacterium persister formation in Balb/c mice. Her postdoctoral research focuses on assessing in vivo response to and efficacy of novel nanoparticle (NP) formulations as a host-directed therapy for the eradication of Mycobacterium tuberculosis in C3HeB/FeJ (Kramink) mice. Utilising the Kramnik mouse strain provides a valuable opportunity to assess the influence of NPs on immuno-pathology (and vice versa). Knowledge gained from this project could ultimately contribute to improved TB control strategies, specifically more effective drug treatment regimens. Dr Obasa is also contributing to the VALIDATE Pump-Priming project that focuses on the use of an ex vivo model for understanding the impact of vaccination on Mycobacterial persister populations. The results obtained in this project could provide new insights into how host factors influence persister formation, and vice versa. This would help to rationally design new vaccines and therapies that reduce persister formation and therefore increase long-term protection against TB.