Functional activity of anti-neisserial surface protein a monoclonal antibodies against strains of Neisseria meningitidis serogroup B

Neisserial surface protein A (NspA) is currently being investigated with hu mans as a candidate vaccine for the prevention of meningococcal disease. Al though NspA is highly conserved, the ability of anti-NspA antibodies to bin d to or elicit complement-mediated bactericidal activity against diverse Ne isseria meningitidis serogroup B strains is controversial, To evaluate stra in differences in NspA surface accessibility and susceptibility to bacteric idal activity, we prepared murine immunoglobulin G2a anti-NspA monoclonal a ntibodies (MAds) and evaluated their functional activity against 10 genetic ally diverse N. meningitidis serogroup B strains. By colony Western blot, a il 10 strains expressed NspA as detected by one or more MAbs. By flow cytom etry, two MAbs were found to bind to the bacterial surface of 6 of the 10 s trains, In addition, two strains showed variable NspA surface accessibility for the MAbs despite being uniformly positive for NspA expression by colon y Western blotting. Only 4 of the 10 strains were susceptible to anti-NspA complement-mediated bacteriolysis, Passively administered MAb protected inf ant rats from developing bacteremia after challenge with N. meningitidis se rogroup B strain 8047 (surface binding positive, susceptible to anti-NspA b acteriolysis), was poorly:protective against strain BZ232 (surface binding variable, resistant to bacteriolysis), and did not protect against strain M 986 (surface binding negative, resistant to bacteriolysis). Finally, NspA d oes not appear to be critical for causing bacteremia, as an NspA knockout f rom strain 8047 was highly virulent in infant rats. Taken together, these f indings suggest that an NspA-based vaccine will need to incorporate additio nal antigens to elicit broad protection against N. meningitidis serogroup B .