The potential to use PspA and other pneumococcal proteins to elicit protection against pneumococcal infection

Pneumococcal proteins, alone, in combination with each other, or in combination with capsular polysaccharide-protein conjugates may be useful pneumococcal vaccine components. Four proteins with a potential for use in vaccines are PspA, pneumolysin, PsaA, and PspC. In a mouse model of carriage, PsaA and PspC were the most efficacious vaccine proteins. Of these, PsaA was the best at eliciting protection against carriage. However, a combination of PspA and pneumolysin may elicit stronger immunity to pulmonary infection and possibly sepsis than either protein alone. Recently, a phase one trial of a recombinant family 1 PspA was completed in man. PspA was observed to be safe and immunogenic. Injection of 0.1 ml of immune serum diluted to 1/400 was able to protect mice from fatal infection with S. pneumoniae. Under these conditions, pre-immune serum was not protective. The immune human serum protected mice from infections with pneumococci expressing either of the major PspA families (1 and 2) and both of the pneumococcal capsular types tested: 3 and 6.