Characterization of merozoite-specific thrombospondin-related anonymous protein (MTRAP) in Plasmodium vivax and P. knowlesi parasites.

Plasmodium vivax, the most widespread human malaria parasite, and P. knowlesi, an emerging Plasmodium that infects humans, are the phylogenetically closest malarial species that infect humans, which may induce cross-species reactivity across most co-endemic areas in Southeast Asia. The thrombospondin-related anonymous protein (TRAP) family is indispensable for motility and host cell invasion in the growth and development of Plasmodium parasites. The merozoite-specific TRAP (MTRAP), expressed in blood-stage merozoites, is supposed to be essential for human erythrocyte invasion. We aimed to characterize MTRAPs in blood-stage P. vivax and P. knowlesi parasites and ascertain their cross-species immunoreactivity. Recombinant P. vivax and P. knowlesi MTRAPs of full-length ectodomains were expressed in a mammalian expression system. The MTRAP-specific immunoglobulin G, obtained from immune animals, was used in an immunofluorescence assay for subcellular localization and invasion inhibitory activity in blood-stage parasites was determined. The cross-species humoral immune responses were analyzed in the sera of patients with P. vivax or P. knowlesi infections. The MTRAPs of P. vivax (PvMTRAP) and P. knowlesi (PkMTRAP) were localized on the rhoptry body of merozoites in blood-stage parasites. Both anti-PvMTRAP and anti-PkMTRAP antibodies inhibited erythrocyte invasion of blood-stage P. knowlesi parasites. The humoral immune response to PvMTRAP showed high immunogenicity, longevity, and cross-species immunoreactivity with P. knowlesi. MTRAPs are promising candidates for development of vaccines and therapeutics against vivax and knowlesi malaria.

Characterisation of the merozoite thrombospondin related anonymous protein (MTRAP) of Plasmodium berghei as a transmission-blocking antigen

BACKGROUND Malaria is an infectious disease caused by protozoan parasites belonging to the genus Plasmodium. Human-to-human transmission depends on a mosquito vector; thus, the interruption of parasite transmission from humans to mosquitoes is an important approach in the fight against malaria. The parasite stages infectious to mosquitoes are the gametocytes, sexual stages that are ingested by the vector during a blood meal and transform into male and female gametes in the midgut. Immunity against sexual stage antigens expressed by gametocytes, gametes, and the zygote formed after fertilisation can interrupt the parasite sexual cycle in the mosquito. This transmission blocking immunity is mediated by specific antibodies ingested during the mosquito blood feed, inhibiting the parasite development in the midgut. Merozoite thrombospondin related anonymous protein (MTRAP) is a merozoite and gametocyte surface protein essential for gamete egress from erythrocytes and for parasite transmission to mosquitoes. OBJECTIVES Here, we evaluated the potential of the P. berghei MTRAP to elicit antibodies with the ability to inhibit gamete fertilisation in vitro. METHODS We expressed a soluble recombinant PbMTRAP and used it to immunise BALB/c mice. The transmission blocking activity of the anti-rPbMTRAP antibodies was tested through in vivo challenge experiments followed by in vitro conversion assays. FINDINGS Immunisations with the rPbMTRAP induced a strong antibody response and the antibodies recognised the native protein by Western Blot and IFA. Anti-rPbMTRAP present in the blood stream of immunised mice partially inhibited gamete conversion into ookinetes. CONCLUSION Our results indicate that antibodies to PbMTRAP may reduce but are not sufficient to completely block transmission.

M-TRAP: Safety and performance of metastatic tumor cell trap device in advanced ovarian cancer patients.

OBJECTIVE: Despite radical surgery and chemotherapy, most patients with ovarian cancer die due to disease progression. M-Trap is an implantable medical device designed to capture peritoneal disseminated tumor cells with the aim to focalize the disease. This trial analyzed the safety and performance of the device. METHODS: This first-in-human prospective, multi-center, non-blinded, single-arm study enrolled 23 women with high-grade serous advanced ovarian cancer. After primary or interval debulking surgery, 3 M-Trap devices were placed in the peritoneum of the abdominal cavity. 18-months post-implantation or at disease progression, devices were initially removed by laparoscopy. The primary safety endpoint was freedom from device and procedure-related major adverse events (MAEs) through 6-months post-implantation compared to an historical control. The primary performance endpoint was histopathologic evidence of tumor cells capture. RESULTS: Only one major adverse event was attributable to the device. 18 women were free of device and procedure related MAEs (78.3%). However, the primary safety endpoint was not achieved (p = 0.131), primarily attributable to the greater surgical complexity of the M-Trap patient population. 62% of recurrent patients demonstrated tumor cell capture in at least one device with a minimal tumor cell infiltration. No other long-term device-related adverse events were reported. The secondary performance endpoint demonstrated a lack of disease focalization. CONCLUSIONS: The M-Trap technology failed to meet its primary safety objective, although when adjusted for surgical complexity, the study approved it. Likewise, the devices did not demonstrate the anticipated benefits in terms of tumor cell capture and disease focalization in recurrent ovarian cancer.