The concern about bioterrorism with smallpox has raised the possibility of widespread vaccination, but the greater prevalence of immunocompromised individuals today requires a safer vaccine, and the mechanisms of protection are not well understood. Here we show that, at sufficient doses, the protection provided by both modified vaccinia Ankara and NYVAC replication-deficient vaccinia viruses, safe in immunocompromised animals, was equivalent to that of the licensed Wyeth vaccine strain against a pathogenic vaccinia virus intranasal challenge of mice. A similar variety and pattern of immune responses were involved in protection induced by modified vaccinia Ankara and Wyeth viruses. For both, antibody was essential to protect against disease, whereas neither effector CD4 ؉ nor CD8 ؉ T cells were necessary or sufficient. However, in the absence of antibody, T cells were necessary and sufficient for survival and recovery. Also, T cells played a greater role in control of sublethal infection in unimmunized animals. These properties, shared with the existing smallpox vaccine, provide a basis for further evaluation of these replication-deficient vaccinia viruses as safer vaccines against smallpox or against complications from vaccinia virus.

Natural HIV transmission occurs through mucosa, but it is debated whether mucosal cytotoxic T lymphocytes (CTLs) can prevent or reduce dissemination from the initial mucosal site to the systemic circulation. Also, the role of CTL avidity in mucosal AIDS viral transmission is unknown. To address these questions, we used delay in acute-phase peak viremia after intrarectal challenge as an indicator of systemic dissemination. We found that a peptide-prime/poxviral boost vaccine inducing high levels of high-avidity mucosal CTLs can have an impact on dissemination of intrarectally administered pathogenic SHIV-ku2 in macaques and that IntroductionThe gastrointestinal and vaginal mucosae are the primary sites of natural HIV transmission and the former is also a major reservoir for HIV replication. [1][2][3][4] This mucosa-centric nature of HIV infection provides a strong rationale for development of mucosal HIV vaccines to induce sufficient mucosal response to clear virus from mucosal tissues. [5][6][7] Indeed, we previously demonstrated that intrarectal immunization of macaques with a peptide vaccine was superior to subcutaneous immunization both in the induction of mucosal CD8 ϩ cytotoxic T lymphocyte (CTL) responses and in limiting viral titers in the blood and intestine. 8,9 In addition, control of viremia in SIV/SHIV/HIV infection correlates with and is dependent on CD8 ϩ CTLs in macaques and chimpanzees. [10][11][12] However, it has been debated whether CTLs in the mucosa can eliminate the first round of virally infected cells fast enough to prevent or reduce dissemination of virus to the systemic circulation. Data from several laboratories show that virus remains in the mucosa from 2 to 7 days before spreading to other sites, 2,13 suggesting that if CTLs are present at the local site of infection early enough, it may be possible to eradicate the initial nidus of infection before it spreads. However, no data have been available to test this hypothesis, which is important to understand the role of mucosal CTLs in protection and thus in the design of mucosal AIDS vaccines. Here, we use the delay in acute-phase appearance of virus in the systemic circulation after intrarectal inoculation as an indicator of such dissemination from the mucosa to test this hypothesis in rhesus macaques immunized intrarectally with an experimental vaccine.In murine studies, high-avidity CD8 ϩ CTLs are more effective than low-avidity CD8 ϩ CTLs in clearance of viral infections. [14][15][16][17] However, only limited indirect information has been available in primates, 18 and the role of CTL avidity has not been studied explicitly in the mucosa. Here, while comparing mucosal vaccine regimens in macaques for protection against mucosal transmission of an AIDS virus, we made the unexpected observation that peptide priming increased mucosal CTL avidity, and further found a correlation between levels of high-avidity mucosal CTLs and delayed appearance of circulating plasma viral particles, which we interpret to reflect dissemination of virus f...