Augmentation of immune responses to HIV-1 and simian immunodeficiency virus DNA vaccines by IL-2/Ig plasmid administration in rhesus monkeys.

The potential utility of plasmid DNA as an HIV-1 vaccination modality currently is an area of active investigation. However, recent studies have raised doubts as to whether plasmid DNA alone will elicit immune responses of sufficient magnitude to protect against pathogenic AIDS virus challenges. We therefore investigated whether DNA vaccine-elicited immune responses in rhesus monkeys could be augmented by using either an IL-2/Ig fusion protein or a plasmid expressing IL-2/Ig. Sixteen monkeys, divided into four experimental groups, were immunized with (i) sham plasmid, (ii) HIV-1 Env 89.6P and simian immunodeficiency virus mac239 Gag DNA vaccines alone, (iii) these DNA vaccines and IL-2/Ig protein, or (iv) these DNA vaccines and IL-2/Ig plasmid. The administration of both IL-2/Ig protein and IL-2/Ig plasmid induced a significant and sustained in vivo activation of peripheral T cells in the vaccinated monkeys. The monkeys that received IL-2/Ig plasmid generated 30-fold higher Env-specific antibody titers and 5-fold higher Gag-specific, tetramer-positive CD8+ T cell levels than the monkeys receiving the DNA vaccines alone. IL-2/Ig protein also augmented the vaccine-elicited immune responses, but less effectively than IL-2/Ig plasmid. Augmentation of the immune responses by IL-2/Ig was evident after the primary immunization and increased with subsequent boost immunizations. These results demonstrate that the administration of IL-2/Ig plasmid can substantially augment vaccine-elicited humoral and cellular immune responses in higher primates.

Malpais spring virus: a new vesiculovirus from mosquitoes collected in New Mexico and evidence of infected indigenous and exotic ungulates.

Two virus isolates, 1 each from Aedes campestris and Psorophora signipennis mosquitoes collected in south central New Mexico in August 1985, were shown by neutralization tests to be identical to each other, but not to any of more than 250 arthropod-borne and other viruses. Electron microscopy of 1 isolate (85-488NM, chosen as the prototype) indicated that this strain shares morphologic characteristics with viruses of the family Rhabdoviridae. Indirect fluorescent antibody tests indicated that this virus is a member of the genus Vesiculovirus, but is not closely related to any of the North American or other rhabdoviruses with which it was tested, including vesicular stomatitis (Indiana) and vesicular stomatitis (New Jersey) viruses. The name Malpais Spring virus is proposed for this newly recognized vesiculovirus. A serologic survey indicated that Malpais Spring virus infects indigenous (mule deer and pronghorn) and exotic (gemsbok) ungulates at and near the sites where the mosquitoes from which the virus strains were isolated were collected. Antibody prevalence in wild animals indicates that the pronghorn and gemsbok may play roles as hosts for Malpais Spring, epizootic hemorrhagic disease (New Jersey), and bluetongue viruses in this area.

Antibody response of sandhill and whooping cranes to an eastern equine encephalitis virus vaccine.

As a possible strategy to protect whooping cranes (Grus americana) from fatal eastern equine encephalitis (EEE) viral infection, studies were conducted to determine the immune response of this species and sandhill cranes (Grus canadensis) to a formalin-inactivated EEE viral vaccine. Viral-specific neutralizing antibody was elicited in both species after intramuscular (IM) vaccination. Subcutaneous and intravenous routes of vaccination failed to elicit detectable antibody in sandhill cranes. Among the IM vaccinated cranes, the immune response was characterized by nondetectable or low antibody titers that waned rapidly following primary exposure to the vaccine. However, one or more booster doses consistently elicited detectable antibody and/or increased antibody titers in the whooping cranes. In contrast, cranes with pre-existing EEE viral antibody, apparently induced by natural infection, exhibited a rapid increase and sustained high-antibody titers. Even though EEE virus vaccine induced neutralizing antibody and produced no adverse side effects, further studies will be required to determine the protective efficacy of the antibody.

Identification of Aedes campestris from New Mexico: with notes on the isolation of western equine encephalitis and other arboviruses.

An arbovirus survey was conducted during August 1985 at White Sands Missile Range in southcentral New Mexico following a suspected arboviral disease epizootic among feral horses. A total of 20,566 mosquitoes (18,505 females and 2,061 males) and 8,900 biting gnats were collected and assayed for virus. Female mosquitoes were principally Aedes campestris (54.8%), Aedes dorsalis (30.4%) and Culex tarsalis (13.2%). Arboviruses were not isolated from biting gnats, but mosquitoes yielded a total of 37 viral isolates, including western equine encephalitis (WEE) (18), California serogroup (15), Cache Valey (1), and Hart Park (1) viruses in addition to 2, as yet unidentified, rhabdoviruses. Isolates of WEE virus were from 9 pools of Ae. campestris, 6 of Cx. tarsalis and 3 of Ae. dorsalis. California serogroup viruses, including 2 subtypes, were obtained from 7 pools of females and 1 pool of males of Ae. campestris and from 4 pools of Ae. dorsalis. Cache Valley and Hart Park viruses were isolated from single pools of Ae. dorsalis and Cx. tarsalis, respectively, and the rhabdoviruses were obtained from Ae. campestris and Psorophora signipennis.

Mortality of captive whooping cranes caused by eastern equine encephalitis virus.

Of 39 captive whooping cranes (Grus americana), 7 died during a 7-week period (Sept 17 through Nov 4, 1984) at the Patuxent Wildlife Research Center, Laurel, Md. Before their deaths, 4 cranes did not develop clinical signs, whereas the other 3 cranes were lethargic and ataxic, with high aspartate transaminase, gamma-glutamyl transferase, and lactic acid dehydrogenase activities, and high uric acid concentrations. Necropsies indicated that the birds had ascites, intestinal mucosal discoloration, fat depletion, hepatomegaly, splenomegaly, and visceral gout. Microscopically, extensive necrosis and inflammation were seen in many visceral organs; the CNS was not affected. Eastern equine encephalitis (EEE) virus was isolated from specimens of the livers, kidneys, lungs, brains, and intestines of 4 of the 7 birds that died, and EEE virus-neutralizing antibody was detected in 14 (44%) of the 32 surviving birds. Other infectious or toxic agents were not found. Morbidity or mortality was not detected in 240 sandhill cranes (Grus canadensis) interspersed among the whooping cranes; however, 13 of the 32 sandhill cranes evaluated had EEE virus-neutralizing antibody. Of the 41 wild birds evaluated in the area, 3 (4%) had EEE virus-neutralizing antibody. Immature Culiseta melanura (the most probable mosquito vector) were found in scattered foci 5 km from the research center.

Absence of La Crosse virus in the presence of Aedes triseriatus on the Delmarva Peninsula.

Between 1980 and 1984, field studies were conducted in 2 areas on the Delmarva Peninsula to identify the presence of La Crosse (LAC) virus. Ovitraps were used to collect eggs of Aedes triseriatus complex mosquitoes. No virus was obtained from 969 pools containing 22,370 adult mosquitoes reared from eggs. Only 1 of 143 raccoon serum samples had neutralizing antibody to LAC virus; 36 sentinel domestic goats, and 99 other wild mammal serum samples were negative. The apparent absence of LAC virus may be due to the uncommon occurrence of the eastern chipmunk, a species which has been shown to be an amplifying host for this virus, on the Peninsula.

Glucan-induced enhancement of host resistance to selected infectious diseases.

We conducted studies with mice, rats, and monkeys which demonstrated the ability of glucan to induce either nonspecific or specific enhancement of host resistance to infectious diseases. Intravenous pretreatment of mice with glucan significantly enhanced the survival of mice challenged with either Venezuelan equine encephalomyelitis (VEE) virus or Rift Valley fever virus. Pretreatment was beneficial when initiated 3 days before challenge with VEE virus and 7 days before challenge with Rift Valley fever virus. Treatment of mice after VEE challenge did not increase their survival compared with controls. Glucan pretreatment of rats provided increased resistance to both intraperitoneal and low-dose aerosol challenges with virulent Francisella tularensis when the glucan was given intravenously, but not when it was administered intranasally. In contrast, intranasal glucan pretreatment enhanced the survival of mice when they were challenged by aerosol with Pseudomonas pseudomallei, whereas intravenous glucan pretreatment did not increase survival. mice given glucan combined with a marginally immunogenic dose of VEE vaccine were more resistant to homologous virus challenge than were mice given either Freund complete adjuvant plus vaccine or vaccine alone. Similarly, both primary and secondary VEE antibody titers in cynomolgus monkeys given glucan with VEE vaccine were significantly greater than titers in vaccine controls.

Evaluation of a formalin-inactivated Rift Valley fever vaccine in sheep.

A formalin-inactivated Rift Valley fever (RVF) vaccine prepared in cell culture for human use was immunogenic in sheep. Vaccine was administered as a single dose of diluted (1:5) or undiluted vaccine with or without an adjuvant. Serum-neutralizing antibodies induced by RVF vaccine persisted for at least 7 months. Seven of 11 vaccinated sheep with prechallenge plaque-reduction neutralization (PRN80) antibody titers of less than or equal to 10 were protected against challenge exposure with 10(6) plaque-forming units of Zagazig 501 strain of RVF virus. Challenge exposure induced abortion in 2 of 2 pregnant sheep. Five sheep with PRN80 titers greater than or equal 1:20 were protected from detectable viremia after challenge exposure. Additionally, 5 of 6 lambs (3 months old) were protected (by maternal antibodies) against challenge exposure. Challenge control sheep developed clinical disease and detectable viremia after exposure. Virus was isolated from saliva of 1 challenge control sheep and virus was transmitted by contact exposure to 1 of 4 seronegative contact-control sheep. Immunization of sheep with formalin-inactivated RVF vaccine induced a priming effect against RVF viral antigens. Challenge exposure with RVF virus resulted in significantly higher neutralizing titers in vaccinated sheep than in nonvaccinated sheep.

Adjuvant activity of a novel metabolizable lipid emulsion with inactivated viral vaccines.

Studies were conducted in mice, hamsters, sheep, and two species of nonhuman primates which demonstrate the adjuvant activity of a new metabolizable lipid emulsion with marginally immunogenic doses of Formalin-inactivated viral vaccines. The lipid base consists of highly refined peanut oil emulsified in aqueous vaccines with glycerol and lecithin. Hamsters and mice inoculated with lipid emulsion plus western or Venezuelan equine encephalitis vaccine were significantly more resistant than vaccinated controls to lethal homologous virus challenge. Sheep given one dose of lipid emulsion plus Rift Valley fever vaccine developed significantly higher antibody titers than control sheep receiving only vaccine. Cynomolgous monkeys inoculated with lipid emulsion plus Rift Valley fever vaccine developed 16-fold greater peak primary and 20-fold greater secondary antibody titers than those of vaccine controls. Similar lipid emulsion-Rift Valley fever studies in rhesus monkeys resulted in 37- and 300-fold increases in primary and secondary titers, respectively, compared with monkeys given vaccine alone. Neither the sequence of combining antigen with lipid nor the exact ratio of aqueous phase to lipid phase affected the survival of Venezuelan equine encephalitis-vaccinated mice challenged with homologous lethal virus. This lipid formulation has several advantages over other water-in-oil adjuvants for potential use in humans. The components are metabolizable or normal host constituents, it is easily emulsified with aqueous vaccines by gentle agitation, and it is relatively nonreactogenic in recipients.

Adjuvant effects of low doses of a nuclease-resistant derivative of polyinosinic acid . polycytidylic acid on antibody responses of monkeys to inactivated Venezuelan equine encephalomyelitis virus vaccine.

Polyriboinosinic.polyribocytidylic acid [poly(I).poly(C)] stabilized with poly-l-lysine and carboxymethylcellulose [poly(ICLC)] has been previously shown to be a compound with marked adjuvant activity when given in high doses with inactivated Venezuelan equine encephalomyelitis (VEE) virus vaccine. This study investigated the effects of much lower doses of poly(ICLC) on the magnitude and kinetics of the primary and secondary humoral antibody responses of rhesus monkeys to inactivated VEE virus vaccine. Monkeys given a single injection of vaccine developed very low neutralizing antibody titers, whereas those given adjuvant plus vaccine had 30- to 100-fold-higher titers which remained elevated for longer than 6 months. Low doses of poly(ICLC) given with VEE virus vaccine resulted in a profound but transient increase in priming of secondary antibody responses to the antigen. In contrast, the administration of poly-l-lysine and carboxymethylcellulose alone without the poly(I).poly(C) component of the complex had no adjuvant effect on antibody responses of monkeys to VEE virus vaccine. The temporal development of antibody by class (immunoglobulin M-immunoglobulin G) in monkeys given two injections of adjuvant-vaccine was not different from that with vaccine alone. Serial hematological and clinical chemistry determinations on monkeys given single or multiple doses of poly(ICLC) with vaccine were not different from values in monkeys given vaccine alone.

Inactivated Venezuelan equine encephalomyelitis virus vaccine complexed with specific antibody: enhanced primary immune response and altered pattern of antibody class elicited.

Complexes of formalinized Venezuelan equine encephalomyelitis (VEE) virus vaccine and specific IgG formed at antigen-antibody equivalence enhanced the immune responses of rhesus monkeys (Macaca mulatta). The predomonant class of antibody elicited by complexes was IgG. In contrast, lower titers of antibody and a more biphasic (IgG-IgM) response were observed after exposure of monkeys to the vaccine alone. In comparison to the response of monkeys primed with antigen, a more rapid secondary response was obtained in monkeys primed with the complexes of antigen and antibody formed at equivalence. A sustained level of protection of 88% was afforded mice 24 hr after immunization with antigen-antibody complexes; development of protection after administration of antigen required eight days to reach this level. Passive protection (80%-100%) was conferred by IgG controls for seven to eight days after immunization. This level of protection was not significantly affected by X-irradiation 24 hr prior to administration of IgG; however, protection in mice similarly irradiated prior to immunization with antigen-antibody complexes was significantly decreased. Early protection afforded by the complexes was not nonspecific (interferon) but was mediated by specific immunologic mechanisms and may be caused by an early formation of IgG.

Modified polyriboinosinic-polyribocytidylic acid, an immunological adjuvant.

Stabilization of polyriboinosinic-polyribocytidylic acid against enzymatic hydrolysis by addition of poly-1-lysine and carboxymethylcellulose (PICLC) resulted in a compound with marked adjuvanticity. The primary antibody response of rhesus monkeys to formalin-inactivated Venezuelan equine encephalomyelitis virus vaccine was significantly potentiated if the vaccine was combined with PICLC prior to vaccination. The antibody response was maintained at a significantly higher level than controls for 2.5 months postvaccination and paralleled immunological responses reported for live, attenuated (TC-83) vaccine.

Adjuvant effects of diethylaminoethyl-dextran.

Diethylaminoethyl-dextran exhibited a significant effect on the primary immune response of rhesus monkeys to formalin-inactivated Venezuelan equine encephalomyelitis virus vaccine (IVEE). Antibody formed to IVEE and adjuvant followed a classic immunoglobulin M-immunoglobulin G pattern; however, as compared with vaccine alone, use of this adjuvant with IVEE reduced the time required for onset of immunoglobulin G synthesis.

Transplacental transmission of Venezuelan equine encephalomyelitis virus in mice.

Transplacental infection of mouse fetuses with Venezuelan equine encephalomyelitis was produced by intraperitoneal injection of dams at various stages of gestation with 10(3) suckling mouse intracerebral median lethal doses of an attenuated strain (TC-83). Virus inoculation, at times ranging from 6 days prior to mating to 9 days after conception, had no effect on conception rate, litter size, or survival of the newborn. Inoculation of the dam from the 10th to 13th days of gestation resulted in decreased litter size, an increase in stillbirths, and a decrease in birth-to-weaning survival. Inoculation of the dams later in gestation only decreased the birth-to-weaning survival. No evidence of morphologic abnormality was noted in any of the newborn.