Restoration of virulence in the attenuated Candid#1 vaccine virus requires reversion at both positions 168 and 427 in the envelope glycoprotein GPC

Live-attenuated virus vaccines provide long-lived protection against viral disease but carry inherent risks of residual pathogenicity and genetic reversion. The live-attenuated Candid#1 vaccine was developed to protect Argentines against lethal infection by the Argentine hemorrhagic fever arenavirus, Junín virus. Despite its safety and efficacy in Phase III clinical study, the vaccine is not licensed in the US, in part due to concerns regarding the genetic stability of attenuation. Previous studies had identified a single F427I mutation in the transmembrane domain of the Candid#1 envelope glycoprotein GPC as the key determinant of attenuation, as well as the propensity of this mutation to revert upon passage in cell culture and neonatal mice. To ascertain the consequences of this reversion event, we introduced the I427F mutation into recombinant Candid#1 (I427F rCan) and investigated the effects in two validated small-animal models: in mice expressing the essential virus receptor (human transferrin receptor 1; huTfR1) and in the conventional guinea pig model. We report that I427F rCan displays only modest virulence in huTfR1 mice and appears attenuated in guinea pigs. Reversion at another attenuating locus in Candid#1 GPC (T168A) was also examined, and a similar pattern was observed. By contrast, virus bearing both revertant mutations (A168T+I427F rCan) approached the lethal virulence of the pathogenic Romero strain in huTfR1 mice. Virulence was less extreme in guinea pigs. Our findings suggest that genetic stabilization at both positions is required to minimize the likelihood of reversion to virulence in a second-generation Candid#1 vaccine.IMPORTANCELive-attenuated virus vaccines, such as measles/mumps/rubella and oral poliovirus, provide robust protection against disease but carry with them the risk of genetic reversion to the virulent form. Here, we analyze the genetics of reversion in the live-attenuated Candid#1 vaccine that is used to protect against Argentine hemorrhagic fever, an often-lethal disease caused by the Junín arenavirus. In two validated small-animal models, we find that restoration of virulence in recombinant Candid#1 viruses requires back-mutation at two positions specific to the Candid#1 envelope glycoprotein GPC, at positions 168 and 427. Viruses bearing only a single change showed only modest virulence. We discuss strategies to genetically harden Candid#1 GPC against these two reversion events in order to develop a safer second-generation Candid#1 vaccine virus.

Modeling Heartland virus disease in mice and therapeutic intervention with 4'-fluorouridine

Heartland virus (HRTV) is an emerging tick-borne bandavirus that causes a febrile illness of varying severity in humans, with cases reported in eastern and midwestern regions of the United States. No vaccines or approved therapies are available to prevent or treat HRTV disease. Here, we describe the genetic changes, natural history of disease, and pathogenesis of a mouse-adapted HRTV (MA-HRTV) that is uniformly lethal in 7- to 8-week-old AG129 mice at low challenge doses. We used this model to assess the efficacy of the ribonucleoside analog, 4'-fluorouridine (EIDD-2749), and showed that once-daily oral treatment with 3 mg/kg of drug, initiated after the onset of disease, protects mice against lethal MA-HRTV challenge and reduces viral loads in blood and tissues. Our findings provide insights into HRTV virulence and pathogenesis and support further development of EIDD-2749 as a therapeutic intervention for HRTV disease.

IMPORTANCE

More than 60 cases of HRTV disease spanning 14 states have been reported to the United States Centers for Disease Control and Prevention. The expanding range of the Lone Star tick that transmits HRTV, the growing population of at-risk persons living in geographic areas where the tick is abundant, and the lack of antiviral treatments or vaccines raise significant public health concerns. Here, we report the development of a new small-animal model of lethal HRTV disease to gain insight into HRTV pathogenesis and the application of this model for the preclinical development of a promising new antiviral drug candidate, EIDD-2749. Our findings shed light on how the virus causes disease and support the continued development of EIDD-2749 as a therapeutic for severe cases of HRTV infection.

Iron deficiency in ethnic minorities: associations with dietary fibre and phytate

Routine full blood counts and serum ferritin determinations were carried out after admission to hospital in 112 children which included a white caucasian group (n = 65) and two ethnic minority groups of West Indians (n = 24) and Asians (n = 23). In these 3 groups those children between the ages of 1 week and 6 months were found to have similar haemoglobin, mean corpuscular volume, and ferritin levels. In the remaining children (aged from 7 months to 14 years 5 months) serum ferritin levels were lower in the ethnic minority groups than in white caucasians, but the haemoglobin and mean corpuscular volume were not significantly different. Children with lower height centiles had reduced ferritin levels, irrespective of their ethnic origins. A nutritional survey between the ages of 7 months and 14 years 5 months showed that mean daily dietary intakes of energy, protein, and iron in white caucasions were similar to those in West Indian and Asian children. The differences noted were in larger phytate and fibre intakes in the ethnic minority groups. Asian diets appeared to differ in containing meat less often as a source of iron, while pulses and chapattis provided more phytate and fibre. It is suggested that dietary intakes of phytate and fibre are important in causing lower ferritin levels by reducing iron absorption.

The role of the cellular sodium pump in human granulopoiesis in vitro

The specific sodium pump antagonist ouabain was used to study the effect of sodium pump inhibition on granulopoietic colony formation by normal human bone marrow cells cultured in soft agar for 7 d. Suppression of colony formation was dose-dependent and occurred at a low and reproducible concentration. The use of an extended range of concentrations (1 X 10(-19) M to 1 X 10(-4) M) revealed no additional effect. Inhibition occurred when colony formation was stimulated by either normal human white blood cells in a soft agar underlayer, or the inclusion of pre-formed colony-stimulating activity. Sensitivity to inhibition was similar under either set of conditions, the 50% inhibitory concentrations being 2.70 +/- 0.43 (SE) X 10(-8) M and 2.83 +/- 0.21 (SE) X 10(-8) M respectively. This is interpreted as showing an effect primarily on the colony-forming cells rather than on the cellular production of colony-stimulating activity. Inhibition of colony formation by ouabain was opposed by the addition of extra potassium to the culture medium, confirming that the inhibition was mediated via a perturbation of monovalent cation exchange. Inhibition by 2 X 10(-7) M ouabain appeared to be reversible by simple washing after exposure for up to 24 h, suggesting that the inhibitory effect of ouabain is not primarily cytotoxic.