Leishmania tarentolae: Taxonomic classification and its application as a promising biotechnological expression host

In this review, we summarize the current knowledge concerning the eukaryotic protozoan parasite Leishmania tarentolae, with a main focus on its potential for biotechnological applications. We will also discuss the genus, subgenus, and species-level classification of this parasite, its life cycle and geographical distribution, and similarities and differences to human-pathogenic species, as these aspects are relevant for the evaluation of biosafety aspects of L. tarentolae as host for recombinant DNA/protein applications. Studies indicate that strain LEM-125 but not strain TARII/UC of L. tarentolae might also be capable of infecting mammals, at least transiently. This could raise the question of whether the current biosafety level of this strain should be reevaluated. In addition, we will summarize the current state of biotechnological research involving L. tarentolae and explain why this eukaryotic parasite is an advantageous and promising human recombinant protein expression host. This summary includes overall biotechnological applications, insights into its protein expression machinery (especially on glycoprotein and antibody fragment expression), available expression vectors, cell culture conditions, and its potential as an immunotherapy agent for human leishmaniasis treatment. Furthermore, we will highlight useful online tools and, finally, discuss possible future applications such as the humanization of the glycosylation profile of L. tarentolae or the expression of mammalian recombinant proteins in amastigote-like cells of this species or in amastigotes of avirulent human-pathogenic Leishmania species. Author summary Recent studies indicate that the classification of Leishmania species into one of the four currently recognized subgenera (L. [Leishmania], L. [Sauroleishmania], L. [Viannia], and L. [Mundinia]), or even the related genera, can be a challenging task. A monotonous morphology of this group is coupled with a high genetic variability in nature, a multitude of clinical manifestations, and a propensity for rapid evolution in culture. As some geographic regions have not been adequately sampled, the known biodiversity of this group may be an underestimate of its true dimensions. Therefore, the taxonomic classification of the genus Leishmania and its close relatives is not definitively settled. In this review, we will focus on biotechnological applications of L. tarentolae, a protozoan parasite of geckos. As this species belongs to the genus Leishmania and subgenus L. (Sauroleishmania), and because many Leishmania are human-pathogenic, the taxonomic status and phylogenetic position of L. tarentolae are relevant for biosafety and also discussed herein. The subgenus of L. (Sauroleishmania) mostly contains species that are infectious to reptiles, but some species and strains, such as L. adleri and L. tarentolae strain LEM-125, were also shown to be (transiently) infectious to humans. However, most strains of L. tarentolae are nonpathogenic to humans and can be easily handled as laboratory culture. Therefore, this species has been a successful model system for representing other Leishmania in basic research. It has also been of great interest for the scientific community, as it represents a promising host for the expression of human recombinant proteins (including glycoproteins and its future application for the expression of full-length antibodies) and immunotherapy agent for human leishmaniasis treatment. These two topics will also be discussed.