Study Of Respiratory And Flavivirus Vaccines In Voluntee

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Abstract

Studies in volunteers have been initiated with a live attenuated dengue 1 (DEN1del30). The live attenuated DEN1 vaccine candidate virus rDEN1del30 has been evaluated in preclinical animal models and found to be attenuated and immunogenic. These promising preclinical studies have identified rDEN1del30 as a candidate DEN1 vaccine virus for further testing in a human Phase I clinical trial. rDEN1del30 at a dose of 1000 pfu was administered as a single inoculation to twenty healthy adult volunteers. Eight additional volunteers received placebo. Volunteers were monitored closely for adverse events and serum was collected on study days 0, 28, 42, and 180 for determination of neutralizing antibody titer. The vaccine was well tolerated by the vaccinees. The most common adverse events observed were a transient asymptomatic rash in 40% of vaccinees and a mild neutropenia in 45% of vaccinees. No vaccinee developed a dengue-like illness. The vaccine was highly infectious and immunogenic with 95% of vaccinees developing a 4-fold rise in serum neutralizing antibody titer against DEN1 that persisted throughout the six month duration of the trial. The rDEN1del30 vaccine is safe and induced a potent and durable antibody response against DEN1. It is a promising vaccine candidate for inclusion in a tetravalent dengue vaccine formulation. [unreadable] [unreadable] Studies were initiated with a dengue 2 (rDEN2/4del30) virus vaccine and with a rDEN4del30 vaccine that contains further attenuating mutations. The rDEN2/4del30 at a dose of 1000 pfu has been completed and data is being analyzed, but preliminary results indicate that the vaccine was safe and immunogenic..[unreadable] [unreadable] Additional, Clinical trial materials (vaccine candidates) have been prepared for a not lot of the DEN1 and DEN2 virus vaccines; one DEN3 virus vaccine; and two DEN4 vaccine candidates. [unreadable] [unreadable] Vaccine for West Nile Virus[unreadable] Studies in volunteers have been initiated with a live attenuated West Nile virus (WN/DEN4del30) vaccine and dose ranging studies are in progress.[unreadable] [unreadable] Vaccine for Tick-borne Encephalitis Virus[unreadable] Studies in volunteers have been initiated with a live attenuated tick-borne encephalitis Virus vaccine (LGT/DEN4). The 1000 pfu dose was highly infectious and safe, and a follow-up study with two doses is being planned.[unreadable] [unreadable] Vaccine for Respiratory Syncytial Virus[unreadable] [unreadable] Respiratory syncytial virus (RSV), a leading cause of severe respiratory illness in the elderly, young children and infants, is a priority for vaccine development. The primary strategy for RSV vaccine development has been to identify live attenuated RSV vaccines for intranasal administration that are satisfactorily attenuated and induce a protective immune response in the targeted age group. The live, intranasal approach is based on observations that mucosal immunity plays an important role in protection against RSV and is optimally stimulated by intranasal immunization. The original live attenuated RSV vaccine candidate was derived by passage of wild type RSV in vitro at sub-optimal temperatures, yielding the cold-passaged (cp) attenuated cpRSV. Chemical mutagenesis of cpRSV yielded further-attenuated temperature-sensitive (ts) derivatives referred to as RSVcpts viruses. One virus, designated RSVcpts248/404, was evaluated in the target group for pediatric vaccine use, the 1-2 month old infant. In this age group, intranasal immunization induced a significant antibody response and conferred protective immunity against a second vaccine dose. [unreadable] [unreadable] RSV vaccine development became much less empiric with the introduction of reverse genetic techniques that allow the production of infectious RSV entirely from cloned cDNAs. The cDNA intermediate provides a means for introducing defined mutations into infectious RSV to make ?designer? attenuated vaccine candidates. The attenuating mutations in the lineage of RSVcp and RSVcpts viruses were identified using reverse genetics, and new attenuating mutations were created by deletion of non-essential accessory genes including the small hydrophobic (SH) surface protein, the M2-2 protein involved in regulating RNA synthesis, and the NS1 and NS2 nonstructural proteins that are described further below. [unreadable] [unreadable] Reverse genetics was used to combine the attenuating mutations from the above-mentioned RSVcpts248/404 virus with a point mutation (designated 1030) from another virus along with a deletion of the SH gene. Last year it was reported that the resulting recombinant virus, called rA2cp248/404/1030delSH, was well tolerated and immunogenic in 1- to 2-month old infants, although some of the viral vaccine specimens recovered from vaccines exhibited loss of a single attenuating point mutation suggesting that greater genetic stability was desirable. Gene deletions are particularly attractive stabilizing genetic mutations because they presumably cannot undergo reversion during the limited duration of in vivo replication characteristic of RSV. Attenuation resulting from a gene deletion identifies the deleted gene product as an important virulence factor. Importantly, NIH has entered into a CRADA with Medimmune to further develop live attenuated RSV, HPIV1-3 (Human parainfluenza viruses types 1, 2, and 3), and HMPV vaccines. A proof of principle Phase IIb efficacy study with rA2cp248/404/1030delSH is being considered. [unreadable] [unreadable] Other gene deletion RSV vaccines are being developed for evaluation in humans.[unreadable] [unreadable] [unreadable] Vaccines for Parainfluenza Virus [unreadable] [unreadable] A study was conducted that examined the transmissibility between young children of an intranasally administered live attenuated human parainfluenza virus type 3 (HPIV3)-cp45 vaccine candidate that has passed Phase II trials in humans. Eighty subjects were enrolled in play groups among which there was at least one infected vaccinee in close contact with a seronegative placebo recipient over 21 days without a confounding infection with wtHPIV3. Following vaccination viral cultures were obtained on 9 occasions to detect shedding and transmission of HPIV3cp45. Serum antibody titers were measured before and 7 weeks after vaccination. No child fulfilled the criteria for transmission of HPIV3cp45 giving a risk of transmission of 0.04 (95%C.I. 0.01-0.19), hence establishing that HPIV3cp45 is less infectious than wtHPIV3 and risk of transmission is not a limitation to further clinical development of this vaccine candidate.[unreadable] [unreadable] Clinical trial materials (vaccine candidates) have been being prepared for two recombinant live attenuated PIV3 virus vaccines, rHPIV3cp45 and rB/HPIV3. INDs have been filed for both vaccines, and a clinical trial with rHPIV3cp45 has been initiated. A proof of principle Phase IIb efficacy study with rHPIV3cp45 is being considered.