Alan R. Davis

A further attenuated derivative of a cold-passaged temperature-sensitive mutant of human respiratory syncytial virus retains immunogenicity and protective efficacy against wild-type challenge in seronegative chimpanzees.

A cold-passage (cp), temperature-sensitive (ts) RSV mutant designated RSV cpts-248 (shut-off temperature 38 degrees C), which possesses host-range mutations acquired during 52 passages at low temperature in bovine tissue culture and a ts phenotype introduced by subsequent chemical mutagenesis, was found previously to be attenuated, immunogenic, and protective against wild-type challenge in seronegative chimpanzees. We sought to introduce additional attenuating mutations such as small-plaque (sp) and ts mutations into RSV cpts-248 by chemical mutagenesis with 5-fluorouracil with the intent of obtaining cpts-248 derivatives that are more attenuated in mice or chimpanzees and that are more genetically stable following replication in vivo. Ten mutants of RSV cpts-248 which had acquired a sp phenotype or a second ts mutation were generated by chemical mutagenesis. Five cpts-248 derivatives which had acquired mutations that specified a 36 degrees C shut-off temperature for plaque formation and one which had acquired only a sp phenotype were more restricted in replication in Balb/c mice than the cpts-248 parental strain. One mutant, designated RSV cpts-248/404 (shut-off temperature 36 degrees C), was 100 times more restricted in replication in the nasal turbinates of mice and 100 times more restricted in the nasopharynx of seronegative chimpanzees than its cpts-248 parent. The cpts-248/404 mutant was completely restricted in replication in the lower respiratory tract of chimpanzees even following direct intratracheal administration. The ts phenotype of the cpts-248/404 mutant was stable during replication in vivo in mice and chimpanzees.(ABSTRACT TRUNCATED AT 250 WORDS)

Satisfactorily attenuated and protective mutants derived from a partially attenuated cold-passaged respiratory syncytial virus mutant by introduction of additional attenuating mutations during chemical mutagenesis

A cold-passaged RSV mutant, designated cp-RSV, which acquired host range mutations during 52 passages at low temperature in bovine tissue culture, was completely attenuated for seropositive adults and children but retained the capacity to cause upper respiratory disease in seronegative infants. We sought to introduce additional attenuating mutations, such as temperature-sensitive (ts) and small-plaque (sp) mutations, into the cp-RSV mutant, which is a ts+ virus, in order to generate a mutant which would be satisfactorily attenuated in seronegative infants and young children. Nine mutants of cp-RSV, which had acquired either the ts or small-plaque sp phenotype, were generated by chemical mutagenesis with 5-fluorouracil. The two ts mutants with the lowest in vitro shut-off temperature, namely the cpts-248 (38 degrees C) and cpts-530 (39 degrees C) mutants, were the most restricted of the nine cp-RSV mutant progeny tested for efficiency of replication in Balb/c mice. In seronegative chimpanzees, the cpts-248 mutant replicated fourfold less efficiently in the nasopharynx and caused significantly less rhinorrhoea than its cp-RSV parent. The cpts-248 mutant virus, like its cp-RSV parent, was 1000-fold restricted in replication in the trachea compared with wild-type RSV. Previously, another candidate RSV live attenuated vaccine strain, a mutant designated ts-1, exhibited some instability of its ts phenotype following replication in susceptible humans or chimpanzees. Hence, we sought cp-RSV ts progeny that exhibited a greater degree of stability of the ts phenotype than the prototype ts-1 mutant.(ABSTRACT TRUNCATED AT 250 WORDS)

Initial safety and immunogenicity studies of an oral recombinant adenohepatitis B vaccine.

Orally administered adenovirus may be a useful vaccine carrier of cloned antigens of other pathogens. A recombinant adenohepatitis vaccine Wy-Ad7HZ6-1, which expressed hepatitis B surface antigen and contained a large deletion in early region 3 (E3), was constructed and studied in humans. Volunteers received Wy-Ad7HZ6-1 (n = 3), adenovirus type 7 vaccine (n = 3) or placebo (n = 3). Recipients of Wy-Ad7HZ6-1 shed less vaccine virus in the stool for a shorter period and had a lower titre of anti-adenovirus type 7 antibodies than recipients of the adenovirus 7 vaccine. None of the three Wy-Ad7HZ6-1 vaccinees developed antibody to hepatitis B surface antigen after this one dose primary immunization regimen. The E3 region may be required for optimal enteric growth of adenovirus-vectored vaccines.

Oral Adenoviruses as the Carriers for Human Immunodeficiency Virus or Hepatitis B Virus Surface Antigen Genes

The development of virus vaccines based on live recombinant adenoviruses has received increasing attention in the recent past because live virus-vectored vaccines possess significant advantages for immunization against viral diseases relative to inactivated or subunit vaccines. A major strength of the adenovirus vector approach is immunization by oral administration of vaccine. An adenovirus recombinant vaccine is administered as an enteric-coated tablet, which ensures safe passage of virus to the intestines where asymptomatic replication occurs. Foreign viral proteins are thus expressed in the context of an infection of the gut. We believe that presentation of viral antigens in this manner is likely to evoke substantial humoral immunity, including secretory responses, as well as significant cell-mediated immunity. In addition, adenoviruses represent an attractive viral vector system for vaccine development because they exhibit several characteristics that allow for high expression of foreign viral genes. In this chapter several features of the adenovirus vector system as applied to its use for vaccination purposes will be reviewed, with an emphasis on the use of adenoviruses as vaccine vectors for diseases caused by hepatitis B virus (HBV) and human immunodeficiency virus (HIV).