Progress has been made toward the development of a trivalent live attenuated virus vaccine consisting of (1) a respiratory syncytial virus (RSV) subgroup A component; (2) a RSV subgroup B component; and (3) a parainfluenza virus type 3 (PIV3) vaccine component. Recombinant chimeric RSV subgroup A and B viruses bearing more attenuating mutations than the A2cpts248/404 vaccine candidate, that previously has been shown to retain mild reactogenicity for the upper respiratory tract of seronegative pediatric subjects, are being evaluated in volunteers. Importantly, the vaccine candidate, rA2cpts248/404/1030 with a deletion of the SH gene, is replicating in the upper respiratory tract of infants and young children to about a 10-fold lower mean virus titer than the cpts248/404 vaccine candidate suggesting that it is more attenuated than cpts248/404. Studies with this vaccine have been initiated in 2 month old infants this year. Studies with recombinant RSV subgroup B candidate vaccine viruses have been initiated this past year. A live attenuated PIV3 candidate vaccine, JS cp45, produced by our CRADA partner, Wyeth-Lederle-Praxis, in qualified Vero cells is satisfactorily attenuated, phenotypically stable, poorly transmissible, and immunogenic in seronegative infants and children greater than 6 months old as well as in two month old infants. A high level of immunity to a second dose of vaccine was observed one month later, and only moderate immunity was seen when the second dose was given three months later. Phase II trials have almost been completed and indicate that the satisfactory safety profile seen in Phase I trials has been maintained. The recombinant dengue virus type 4 vaccine candidate, 2Adel30, was attenuated in rhesus monkeys due to an engineered 30 nucleotide deletion (del) in the 3' untranslated region of the viral genome. A clinical trial to evaluate the safety and immunogenicity of a single dose of 2Adel30 was conducted with 20 adult human volunteers. The vaccine candidate was well tolerated and did not cause systemic illness in any of the 20 volunteers. Viremia was detectable in 14 volunteers at a mean level of 1.6 log10pfu/ml, although all 20 volunteers seroconverted with a seven-fold or greater rise in serum neutralizing antibody titer on day 28 (mean titer = 1:580). A mild asymptomatic macular rash developed in 10 volunteers, and a transient elevation in the level of ALT in the serum was noted in 5 volunteers. The low level of reactogenicity and high degree of immunogenicity of this vaccine candidate warrant its further evaluation and its use as a vector to create chimeric vaccine viruses expressing the structural genes of dengue virus types 1, 2, and 3. To assess the transmissibility of 2Adel30 by mosquitoes, we compared its in vivo replication in mosquitoes with that of its wild type DEN-4 parent. Both the vaccine candidate and wild type virus were equally able to infect the mosquito Toxorhynchites splendens after intrathoracic inoculation. Relative to its wild type parent, 2Adel30 was slightly restricted in its ability to infect the midgut of Aedes aegypti mosquitoes fed on an artificial bloodmeal and was even more restricted in its ability to disseminate from the midgut to the salivary glands. Thus the 30 nucleotide deletion rendered the vaccine candidate more sensitive than its wild type parent to the mosquito midgut escape barrier. Most significantly, 2Adel30 was not transmitted to 352 Aedes albopictus mosquitoes fed on ten vaccinees, all of whom were infected with the vaccine candidate. A human papilloma virus (HPV) type 16 virus-like particle vaccine was shown to be safe and highly immunogenic in adult seronegative volunteers and phase II trials are continuing.
