Leishmania tarentolae as an Antigen Delivery Platform: Dendritic Cell Maturation after Infection with a Clone Engineered to Express the SARS-CoV-2 Spike Protein

Abstract

Background: Protozoa of the genus Leishmania are characterized by their capacity to target macrophages and Dendritic Cells (DCs). These microorganisms could thus be exploited for the delivery of antigens to immune cells. Leishmania tarentolae is regarded as a non-pathogenic species; it was previously used as a biofactory for protein production and has been considered as a candidate vaccine or as an antigen delivery platform. However, results on the type of immune polarization determined by L. tarentolae are still inconclusive. Methods: DCs were derived from human monocytes and exposed to live L. tarentolae, using both the non-engineered P10 strain, and the same strain engineered for expression of the spike protein from SARS-CoV-2. We then determined: (i) parasite internalization in the DCs; and (ii) the capacity of the assayed strains to activate DCs and the type of immune polarization. Results: Protozoan parasites from both strains were effectively engulfed by DCs, which displayed a full pattern of maturation, in terms of MHC class II and costimulatory molecule expression. In addition, after parasite infection, a limited release of Th1 cytokines was observed. Conclusions: Our results indicate that L. tarentolae could be used as a vehicle for antigen delivery to DCs and to induce the maturation of these cells. The limited cytokine release suggests L. tarentolae as a neutral vaccine vehicle that could be administered in association with appropriate immune-modulating molecules.

Leishmania tarentolae: a vaccine platform to target dendritic cells and a surrogate pathogen for next generation vaccine research in leishmaniases and viral infections

“…However, the expression of M2 markers in human macrophages, after stimulation with L. tarentolae, was also observed [74]. A recent in vitro study on human DCs reported moderate production of Th1-type cytokines after stimulation by living promastigotes of L. tarentolae and also confirmed the penetration of L. tarentolae into DCs and their maturation, with expression of surface markers of activation, including MHC class II and co-stimulatory molecules [44]. The capacity of DCs to engulf L. tarentolae, the maturation of these cells after exposure to the parasite and evidence for the production, even though moderate, of Th1-associated cytokines are all coherent with the possibility that L. tarentolae possesses some of the characteristics required by an anti-Leishmania vaccine.…”

“…However, several genes possibly associated with virulence are lacking in L. tarentolae, compared to pathogenic Leishmania species [67], which is reassuring in relation to safety issues. Third, current evidence indicates that L. tarentolae is not pathogenic to mammals, while still being capable of infecting macrophages and DCs, reaching the amastigote state [41,44,68]. Finally, the evidence for a circulation of L. tarentolae in dogs, and the absence of any evidence for its association with pathological outcomes, further emphasizes the potential utility of this parasite in anti-Leishmania vaccination (see [11] and section on L. tarentolae natural history and the evidence of infectivity in mammalian hosts).…”

“…It is interesting to note that another species belonging to the subgenus Sauroleishmania, Leishmania adleri, while primarily associated with ectothermic hosts, may infect humans causing transient skin lesions, similar to those observed in cutaneous leishmaniasis [39], and has also been detected in asymptomatic hamsters and mice [40]. Additionally, under laboratory conditions, L. tarentolae promastigotes differentiate into an amastigote-like form after uptake by mammalian DCs and macrophages [41][42][43][44], hinting at the possibility of natural infection in mammals. In Mediterranean countries, human and canine leishmaniases are endemic, and L. tarentolae has been isolated from different species of reptiles [12,45,46] and sand flies [28], and its DNA has also been detected by molecular methods in mammals [29,38,46,47].…”

Efficacy of mucosal vaccination using a protozoan parasite as a vehicle for antigen delivery: IgG and neutralizing response after rectal administration of LeCoVax-2, a candidate vaccine against COVID-19

“…In a recent in vitro study, we showed that the Lt-spike clone of L. tarentolae, engineered for the surface expression of the spike antigen of SARS-CoV-2, effectively delivers the spike antigen into DCs [26]. This L. tarentolae clone thus represents a potential COVID-19 vaccine candidate, suitable for further testing in in vivo assays.…”

“…Indeed, the major niche for survival and replication of Leishmania species infecting mammals is represented by phagocytic myeloid cells, including DCs and macrophages [23,24]. This propensity to be phagocytized by mammalian DCs and macrophages has also been demonstrated for L. tarentolae [25,26]. In addition, commercial kits are available for the genetic transformation of L. tarentolae, for the production of recombinant proteins [12,13].…”