Purification and production of Plasmodium falciparum zygotes from in vitro culture using magnetic column and Percoll density gradient

Full maturation of in vitro Plasmodium falciparum oocysts using the AlgiMatrix 3D culture system

BACKGROUND

Plasmodium falciparum oocysts undergo growth and maturation in a unique setting within the mosquito midgut, firmly situated between the epithelium and the basal lamina. This location exposes them to specific nutrient exchange and metabolic processes while in direct contact with the mosquito haemolymph. The limited availability of in vitro culture systems for growth of the various P. falciparum mosquito stages hampers study of their biology and impedes progress in combatting malaria.

METHODS

An artificial in vitro environment was established to mimic this distinctive setting, transitioning from a 2D culture system to a 3D model capable of generating fully mature oocysts that give rise to in vitro sporozoites.

RESULTS

A two-dimensional (2D) chamber slide was employed along with an extracellular matrix composed of type IV collagen, entactin, and gamma laminin. This matrix facilitated development of the optimal medium composition for cultivating mature P. falciparum oocysts in vitro. However, the limitations of this 2D culture system in replicating the in vivo oocyst environment prompted a refinement of the approach by optimizing a three-dimensional (3D) alginate matrix culture system. This new system offered improved attachment, structural support, and nutrient exchange for the developing oocysts, leading to their maturation and the generation of sporozoites.

CONCLUSIONS

This technique enables the in vitro growth of P. falciparum oocysts and sporozoites.

Cross-reactivity of rPvs48/45, a recombinant Plasmodium vivax protein, with sera from Plasmodium falciparum endemic areas of Africa

Background

Ps48/45, a Plasmodium gametocyte surface protein, is a promising candidate for malaria transmission-blocking (TB) vaccine. Due to its relevance for a multispecies vaccine, we explored the cross-reactivity and TB activity of a recombinant P. vivax Ps48/45 protein (rPvs48/45) with sera from P. falciparum-exposed African donors.

Methods

rPvs48/45 was produced in Chinese hamster ovary cell lines and tested by ELISA for its cross-reactivity with sera from Burkina Faso, Tanzania, Mali, and Nigeria - In addition, BALB/c mice were immunized with the rPvs48/45 protein formulated in Montanide ISA-51 and inoculated with a crude extract of P. falciparum NF-54 gametocytes to evaluate the parasite-boosting effect on rPvs48/45 antibody titers. Specific anti-rPvs48/45 IgG purified from African sera was used to evaluate the ex vivo TB activity on P. falciparum, using standard mosquito membrane feeding assays (SMFA).

Results

rPvs48/45 protein showed cross-reactivity with sera of individuals from all four African countries, in proportions ranging from 94% (Tanzania) to 40% (Nigeria). Also, the level of cross-reactive antibodies varied significantly between countries (p<0.0001), with a higher antibody level in Mali and the lowest in Nigeria. In addition, antibody levels were higher in adults (≥ 17 years) than young children (≤ 5 years) in both Mali and Tanzania, with a higher proportion of responders in adults (90%) than in children (61%) (p<0.0001) in Mali, where male (75%) and female (80%) displayed similar antibody responses. Furthermore, immunization of mice with P. falciparum gametocytes boosted anti-Pvs48/45 antibody responses, recognizing P. falciparum gametocytes in indirect immunofluorescence antibody test. Notably, rPvs48/45 affinity-purified African IgG exhibited a TB activity of 61% against P. falciparum in SMFA.

Conclusion

African sera (exposed only to P. falciparum) cross-recognized the rPvs48/45 protein. This, together with the functional activity of IgG, warrants further studies for the potential development of a P. vivax and P. falciparum cross-protective TB vaccine.

CRISPR/Cas9-engineered inducible gametocyte producer lines as a valuable tool for Plasmodium falciparum malaria transmission research

The malaria parasite Plasmodium falciparum replicates inside erythrocytes in the blood of infected humans. During each replication cycle, a small proportion of parasites commits to sexual development and differentiates into gametocytes, which are essential for parasite transmission via the mosquito vector. Detailed molecular investigation of gametocyte biology and transmission has been hampered by difficulties in generating large numbers of these highly specialised cells. Here, we engineer P. falciparum NF54 inducible gametocyte producer (iGP) lines for the routine mass production of synchronous gametocytes via conditional overexpression of the sexual commitment factor GDV1. NF54/iGP lines consistently achieve sexual commitment rates of 75% and produce viable gametocytes that are transmissible by mosquitoes. We also demonstrate that further genetic engineering of NF54/iGP parasites is a valuable tool for the targeted exploration of gametocyte biology. In summary, we believe the iGP approach developed here will greatly expedite basic and applied malaria transmission stage research.