Evidences of protection against blood-stage infection of Plasmodium falciparum by the novel protein vaccine SE36.

An effective malaria vaccine is a public health priority. Proteins expressed during the blood-stage of the parasite life cycle have been proposed as good vaccine candidates. No such blood-stage vaccine, however, is available against Plasmodium falciparum, the deadliest Plasmodium species. We show here that P. falciparum serine repeat antigen 5 (SERA5) is a potential vaccine immunogen. We have constructed a new recombinant molecule of SERA5, namely SE36, based on previously reported SE47' molecule by removing the serine repeats. Epidemiological study in the holo-endemic population of Solomon Islands shows highly significant correlation of sero-conversion and malaria protective immunity against this antigen. Animal experiments using non-human primates, and a human phase 1a clinical trial assessed SE36 vaccine immunogenicity. Vaccination of squirrel monkeys with SE36 protein and aluminum hydroxyl gel (SE36/AHG) conferred protection against high parasitemia and boosted serum anti-SE36 IgG after P. falciparum parasite challenge. SE36/AHG was highly immunogenic in chimpanzees, where serum anti-SE36 IgG titers last more than one year. Phase 1a clinical trial (current controlled trials, ISRCTN78679862) demonstrated the safety and immunogenicity of SE36/AHG with 30 healthy adults and 10 placebo controls. Three subcutaneous administrations of 50 and 100microg dose of SE36/AHG were well-tolerated, with no severe adverse events; and resulted in 100% sero-conversion in both dose arms. The current research results for SE36/AHG provide initial clinical validation for future trials and suggest clues/strategies for further vaccine development.

Plant cultured cells expressing human beta1,4-galactosyltransferase secrete glycoproteins with galactose-extended N-linked glycans.

Previously, we generated transgenic tobacco BY2 suspension-cultured cells (GT6 cells) that produced human beta1,4-galactosyltransferase. In this study, we analyze the N-glycan structures of glycoproteins secreted from GT6 cells to the spent medium. The N-glycans were liberated by hydrazinolysis, and the resulting oligosaccharides were labeled with 2-aminopyridine (PA). The pyridylaminated glycans were purified by reversed-phase and size-fractionation HPLC. The structures of the PA sugar chains were identified by the combined use of 2D PA sugar chain mapping, MS/MS analysis, and exoglycosidase digestion. The distribution of proposed N-glycan structures of GT6-secreted glycoproteins (GalGNM5 [26.8%], GalGNM4 [18.4%], GalGNM3 [19.6%], and GalGNM3X [35.2%]) is different from that found in intracellular glycoproteins (M7A [9.3%], M7B [15.9%], M6B [19.5%], M5 [1.4%], M3X [6.6%], GalGNM5 [35.5%], and GalGNM3 [11.8%]). In vitro, sialic acid was transferred to sugar chains of extracellular glycoproteins from the GT6 spent medium. The results suggest that sugar chains of extracellular glycoproteins from the GT6 spent medium are candidates for substrates of sialic acid transfer.