A Plasmodium berghei sporozoite-based vaccination platform against human malaria

There is a pressing need for safe and highly effective Plasmodium falciparum (Pf) malaria vaccines. The circumsporozoite protein (CS), expressed on sporozoites and during early hepatic stages, is a leading target vaccine candidate, but clinical efficacy has been modest so far. Conversely, whole-sporozoite (WSp) vaccines have consistently shown high levels of sterilizing immunity and constitute a promising approach to effective immunization against malaria. Here, we describe a novel WSp malaria vaccine that employs transgenic sporozoites of rodent P. berghei (Pb) parasites as cross-species immunizing agents and as platforms for expression and delivery of PfCS (PbVac). We show that both wild-type Pb and PbVac sporozoites unabatedly infect and develop in human hepatocytes while unable to establish an infection in human red blood cells. In a rabbit model, similarly susceptible to Pb hepatic but not blood infection, we show that PbVac elicits cross-species cellular immune responses, as well as PfCS-specific antibodies that efficiently inhibit Pf sporozoite liver invasion in human hepatocytes and in mice with humanized livers. Thus, PbVac is safe and induces functional immune responses in preclinical studies, warranting clinical testing and development.

A genetically engineered parasite, related to malaria-causing Plasmodium falciparum, excels as a vaccine in preclinical tests. A team led by Miguel Prudêncio, of the University of Lisbon, Portugal, developed a genetically altered vaccine candidate based on Plasmodium berghei, which is pathogenic to rodents but, in humans, fails to progress from a harmless, transient liver infection to causing full, blood-borne malaria. The candidate expresses a human form of ‘circumsporozoite protein,’ a known antigen, and is designed to provoke a more comprehensive immune response as it presents a whole pathogen to the host. In preclinical tests, the candidate generated antibodies able to neutralize infection in human hepatocytes and also provoked a cellular immune response in rabbits. The team’s candidate proved safe and efficacious, warranting further trials and clinical testing.

Chronic depression of hypothalamic paraventricular neuronal activity produces sustained hypotension in hypertensive rats

Changes in the sympathetic nervous system are responsible for the initiation, development and maintenance of hypertension. An important central sympathoexcitatory region is the paraventricular nucleus (PVN) of the hypothalamus, which may become more active in hypertensive conditions, as shown in acute studies previously. Our objective was to depress PVN neuronal activity chronically by the overexpression of an inwardly rectifying potassium channel (hKir2.1), while evaluating the consequences on blood pressure (BP) and its reflex regulation. In spontaneously hypertensive rats (SHRs) and Wistar rats (WKY) lentiviral vectors (LVV-hKir2.1; LV-TREtight-Kir-cIRES-GFP5 4 × 10(9) IU and LV-Syn-Eff-G4BS-Syn-Tetoff 6.2 × 10(9) IU in a ratio 1:4) were stereotaxically microinjected bilaterally into the PVN. Sham-treated SHRs and WKY received bilateral PVN microinjections of LVV-eGFP (LV-Syn-Eff-G4BS-Syn-Tetoff 6.2 × 10(9) IU and LV-TREtight-GFP 5.7 × 10(9) IU in a ratio 1:4). Blood pressure was monitored continuously by radio-telemetry and evaluated over 75 days. Baroreflex gain was evaluated using phenylephrine (25 μg ml(-1), i.v.), whereas lobeline (25 μg ml(-1), i.v.) was used to stimulate peripheral chemoreceptors. In SHRs but not normotensive WKY rats, LVV-hKir2.1 expression in the PVN produced time-dependent and significant decreases in systolic (from 158 ± 3 to 132 ± 6 mmHg; P < 0.05) and diastolic BP (from 135 ± 4 to 113 ± 5 mmHg; P < 0.05). The systolic BP low-frequency band was reduced (from 0.79 ± 0.13 to 0.42 ± 0.09 mmHg(2); P < 0.05), suggesting reduced sympathetic vasomotor tone. Baroreflex gain was increased and peripheral chemoreflex depressed after PVN microinjection of LVV-hKir2.1. We conclude that the PVN plays a major role in long-term control of BP and sympathetic nervous system activity in SHRs. This is associated with reductions in both peripheral chemosensitivity and respiratory-induced sympathetic modulation and an improvement in baroreflex sensitivity. Our results support the PVN as a powerful site to control BP in neurogenic hypertension.