ENHANCED PROTECTIVE ANTIBODY-RESPONSES TO PSPA AFTER INTRANASAL OR SUBCUTANEOUS INJECTIONS OF PSPA GENETICALLY FUSED TO GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR OR INTERLEUKIN-2

Antibody to pneumococcal surface protein A (PspA) has been shown to be protective for Streptococcus pneumoniae infections in mice. In an att empt to define a model for inducing protective antibody to PspA in the absence of adjuvant, we designed two genetic fusions, PspA-interleuki n-2 [IL-2]) and PspA-granulocyte-macrophage colony-stimulating factor (GM-CSF). These constructs maintained high cytokine function in vitro, as tested by their activity on IL-2 or GM-CSP-dependent cell lines. W hile intranasal immunization with PspA induced no detectable anti-PspA response, both PspA-IL-2 and PspA-GM-CSF stimulated high immunoglobul in G1 (IgG1) antibody responses, Interestingly, only the PspA-IL-2, no t the PspA-GM-CSF, construct stimulated IgG2a antibody responses, sugg esting that this construct directed the response along a TH1-dependent pathway. Comparable enhancement of the anti-PspA response with simila r isotype profiles was observed after subcutaneous immunization as wel l. The enhancement observed with PspA-IL-2 was dependent on IL-2 activ ity in that it was not seen in IL-2 receptor knockout mice, while PspA in alum induced high-titer antibody in these mice, The antibody was t ested for its protective activity in a mouse lethality model using S. pneumoniae WU-R2. Passive transfer of 1:90 dilutions of sera from mice immunized with PspA-IL-2 and PspA-GM-CSF elicited protection of CBA/N mice against intravenous challenge with over 170 50% lethal doses of capsular type 3 strain WU2, Only 0.17 mu g or less of IgG antibody to PspA was able to provide passive protection against otherwise fatal ch allenge with S. pneumoniae. The data demonstrate that designing protei n-cytokine fusions may be a useful approach for mucosal immunization a nd can induce high-titer systemic protective antibody responses.