Jessica Home is a PhD candidate in the McFadden Lab at the University of Melbourne. Her research focuses on resistance to clindamycin, an apicoplast translational inhibitor, in malaria parasites. Using both human and rodent malaria models, Jessica is investigating the mechanisms underlying clindamycin resistance and the transmission efficiency of resistant parasites across the life cycle.
Talk title: Unravelling clindamycin resistance in Plasmodium
Clindamycin is a well-tolerated antibiotic that kills malaria parasites by targeting the apicoplast prokaryotic translational machinery, but mechanisms of resistance in Plasmodium remain largely unknown.
We selected for clindamycin resistance in P. falciparum (in vitro) and in P. berghei (in vivo). Clindamycin resistant P. falciparum had acquired point mutations in the apicoplast-encoded 23S ribosomal RNA—the canonical mechanism of clindamycin resistance in bacteria. Notably, these mutants exhibited impaired development in mosquitoes, suggesting a fitness cost associated with disruption of the apicoplast translational machinery that should restrict spread of such resistance. In contrast, two independently generated clindamycin resistant P. berghei lines lacked mutations in the apicoplast-encoded translational machinery. Rather, sequencing revealed apparent loss-of-function mutations in nucleus-encoded genes encoding enzymes responsible for formylating the initiator methionine on tRNA. Formyl methionine is required for efficient translation initiation and protein stability in prokaryotes and thus likely occurs in the prokaryote-derived apicoplast. Intriguingly, changes to the machinery generating formyl methionine have never been connected to clindamycin resistance in any organism.
To validate this novel resistance mechanism, we disrupted initiator methionine formylation genes in both P. berghei and P. falciparum and confirmed clindamycin resistance. Interestingly, methionine formylation mutants conferred lower resistance levels than 23S rRNA mutants but had no mosquito transmission impairment, suggesting weaker resistance but more facile spread. Clindamycin resistance in Plasmodium is thus more complex than anticipated, and further investigation of the methionine formylation pathway is imperative to dissect this new resistance mechanism.
Jem Murdoch is a PhD student in the school of biomedical sciences at UNSW under the supervision of Prof. Jake Baum and co-supervisor Dr Deborah Burnett. Prior to his PhD he was Jake’s MRes student at Imperial studying molecular and cellular biosciences. His current research is focused on studying B cell immunology in the context of a Plasmodium falciparum pre-erythrocytic infection to identify novel non-CSP antigen targets through single-cell B cell receptor sequencing.
Talk title: Seeing the Wood for the Trees: Looking beyond the immunodominance of the malaria parasite surface protein CSP
Abstract: Human infection with malaria begins with the injection of sporozoites by the feeding mosquito. The sporozoite surface has a dense layer of one, immunodominant protein, called circumsporozoite protein (CSP) at ~1 million copies per cell. This protein contains 38 NANP amino acid tandem repeats which are highly immunogenic. The current licensed malaria vaccines being rolled out in Africa (RTS,S and R21) both target CSP, however they require multiple boosters to maintain high antibody titre, with vaccine efficacy waning overtime. Given CSP’s immunodominance and prevalence, could it be acting as an immunological decoy, evolved to evade an immune response from other critical cell surface proteins on the parasite? Here, we have developed a CSP-tolerant mouse model, immunising mice with human infective Plasmodium falciparum sporozoites to induce an immune response that potentially selectively targets other sporozoite surface proteins. We have performed 10x single-cell sequencing of the expanded B cell clones from immunized mice and generated a panel of monoclonal antibodies. Using these monoclonals, we hope to identify immunogenic non-CSP sporozoite specific antigens as potential targets for next generation malaria vaccines.
