Concomitant administration of Mycobacterium bovis BCG with the meningococcal C conjugate vaccine to neonatal mice enhances antibody response and protective efficacy

Abstract

Mycobacterium bovis BCG is administered to human neonates in many countries worldwide. The objective of the study was to assess if BCG could act as an adjuvant for polysaccharide-protein conjugate vaccines in newborns and thereby induce protective immunity against encapsulated bacteria in early infancy when susceptibility is high. We assessed whether BCG could enhance immune responses to a meningococcal C (MenC) conjugate vaccine, MenC-CRM(197), in mice primed as neonates, broaden the antibody response from a dominant IgG1 toward a mixed IgG1 and IgG2a/IgG2b response, and increase protective efficacy, as measured by serum bactericidal activity (SBA). Two-week-old mice were primed subcutaneously (s.c.) with MenC-CRM(197). BCG was administered concomitantly, a day or a week before MenC-CRM(197). An adjuvant effect of BCG was observed only when it was given concomitantly with MenC-CRM(197), with increased IgG response (P = 0.002) and SBA (8-fold) after a second immunization with MenC-CRM(197) without BCG, indicating increased T-cell help. In neonatal mice (1 week old) primed s.c. with MenC-CRM(197) together with BCG, MenC-polysaccharide (PS)-specific IgG was enhanced compared to MenC-CRM(197) alone (P = 0.0015). Sixteen days after the second immunization with MenC-CRM(197), increased IgG (P < 0.05), IgG1 (P < 0.05), IgG2a (P = 0.06), and IgG2b (P < 0.05) were observed, and only mice primed with MenC-CRM(197) plus BCG showed affinity maturation and detectable SBA (SBA > 128). Thus, vaccination with a meningococcal conjugate vaccine (and possibly with other conjugates) may benefit from concomitant administration of BCG in the neonatal period to accelerate and enhance production of protective antibodies, compared to the current infant administration of conjugate which follows BCG vaccination at birth.

Fig. 1.

Antibody response of mice immunized with MenC-CRM₁₉₇ at 2 weeks of age with or without BCG treatment and receiving a second immunization with MenC-CRM₁₉₇. Mice received BCG a week before (−7d), a day before (−1d), or at the same time that MenC-CRM₁₉₇ was given at 2 weeks of age or did not receive BCG. Sixteen days later the mice received a second immunization with MenC-CRM_197. Control mice received saline at both times. (a) MenC-PS-specific IgG levels 2 weeks after priming (light gray columns) and 2 weeks after the second immunization (dark gray columns). The results are presented as mean + SD for each group (n = 8 per group) for one of two independent experiments showing comparable results. *, P < 0.05 compared to saline, MenC-CRM₁₉₇, and other groups. (b) MenC-PS-specific IgG1 and IgG2a antibody levels 2 weeks after the second immunization with MenC-CRM₁₉₇. The results are presented as mean + SD for each group (n = 8 per group) for one of two independent experiments showing comparable results.

Fig. 2.

Effect of BCG on MenC-PS-specific IgG response and protective capacity when administered with MenC-CRM₁₉₇ to neonatal mice. Mice received BCG at the same time as the priming with MenC-CRM₁₉₇ at 1 week of age. Sixteen days later the mice received a second immunization with MenC-CRM₁₉₇ without BCG. (a) MenC-PS-specific IgG levels 2 weeks after priming (light gray columns) and 2 weeks after the second immunization with MenC-CRM₁₉₇ (dark gray columns). The results are presented as mean + SD for each group (n = 8 per group) for one of three independent experiments showing comparable results. *, P < 0.05 compared to saline and MenC-CRM₁₉₇ groups. (b) SBA induced by priming neonatal mice with MenC-CRM₁₉₇ with or without BCG, 2 weeks after the second immunization with MenC-CRM₁₉₇. Immunizations are indicated at bottom. SBA was measured in pooled sera (equal volumes from each mouse within group; n = 8 per group). SBA detection limit is 16 and is indicated with a dotted line. Samples with undetectable SBA are arbitrarily assigned an SBA titer of 8, corresponding to half the detection limit.

Fig. 3.

The effect of BCG on IgG subclasses and avidity of MenC-PS-specific antibodies. (a) IgG subclasses of MenC-PS-specific antibodies 2 weeks after the second immunization with MenC-CRM₁₉₇. Mice received BCG at the same time as the priming with MenC-CRM₁₉₇ at 1 week of age. Sixteen days later the mice received a second immunization with MenC-CRM₁₉₇ without BCG. Immunizations are indicated at bottom. IgG subclass levels (mean + SD) are presented for each group (n = 8 per group) for one of three independent experiments showing comparable results. *, P < 0.05 compared to MenC-CRM₁₉₇ group. (b) AI of MenC-PS-specific IgG 2 weeks after the second immunization with MenC-CRM₁₉₇. Immunizations are indicated at bottom. AIs (expressed as M KSCN) are shown for individual mice, and a line indicates the mean for each group. Results are presented for one of three independent experiments showing comparable results. The AI detection limit was 0.117 (0.117 M KSCN).