A whole-cell killed unencapsulated pneumococcal vaccine given by the intranasal route with cholera toxin as an adjuvant was tested in two animal models. This vaccination was highly effective in preventing nasopharyngeal colonization with an encapsulated serotype 6B strain in mice and also conferred protection against illness and death in rats inoculated intrathoracically with a highly encapsulated serotype 3 strain. When the serotype 3 challenge strain was incubated in the sera of immunized rats, it was no longer virulent in an infant-rat sepsis model, indicating that the intranasal immunization elicited protective systemic antibodies. These studies suggest that killed whole-cell unencapsulated pneumococci given intranasally with an adjuvant may provide multitypic protection against capsulated pneumococci.Streptococcus pneumoniae (pneumococcus) annually causes 10 million deaths worldwide, including the deaths of 1 million children in low-income countries (26). Type-specific immunity, based on the capsular polysaccharides (PS), is well established (20). The licensed 23-valent PS vaccine, however, is not efficacious in children younger than 2 years. The newly licensed heptavalent PS conjugate vaccine protects against 90% of pneumococcal invasive disease in infancy in the United States (28) but includes fewer serotypes than the PS vaccine and omits several that are prevalent worldwide (10). Other drawbacks of the conjugate vaccine include a limited effect on otitis media (2, 11), high costs, and the potential for serotype replacement, which has already been suggested in recent clinical trials (11, 17; R. Dagan, N. Givon, P. Yagupsky, N. Porat, J. Janco, I. Chang, et al., Program Abstr. 38th Intersci. Conf. Antimicrob. Agents Chemother., abstr. S52, 1998).Several investigators have identified protective antigens common to pneumococci of many or all serotypes. Several such "species" antigens in purified or vectored form have shown protection in animal models (4-6, 8, 18, 19, 23, 25), but it is uncertain whether, when, and at what cost any of these will be developed as an effective vaccine for humans, particularly in low-income countries. As an alternative presentation of species antigens, we have studied unencapsulated whole cells, which should present a number of such antigens in native configuration unoccluded by capsule. In addition, the intranasal route of immunization might elicit mucosal immunity and, with suitable adjuvant, systemic immunity as well. Finally, of importance to low-income countries, a mucosally administered whole-cell preparation has the possible advantage of low cost of production and administration, without the need for sterile injection devices. In the present study we tested killed, unencapsulated cells applied intranasally with cholera toxin (CT) as an adjuvant (R. Malley, S. Pelton, A. Stack, R. Saladino, D. E. Briles, and P. Anderson, 2nd Int. Symp. Pneumococci Pneumococcal Dis., abstr. P25, 2000), using two animal models: nasopharyngeal colonization of mice with type 6B and lethal intrat...