Immunologic memory induced by a glycoconjugate vaccine in a murine adoptive lymphocyte transfer model

Abstract

We have developed an adoptive cell transfer model in mice to study the ability of a glycoprotein conjugate vaccine to induce immunologic memory for the polysaccharide moiety. We used type III capsular polysaccharide from the clinically relevant pathogen group B streptococci conjugated to tetanus toxoid (GBSIII-TT) as our model vaccine. GBS are a major cause of neonatal infections in humans, and type-specific antibodies to the capsular polysaccharide protect against invasive disease. Adoptive transfer of splenocytes from mice immunized with the GBSIII-TT conjugate vaccine conferred anti-polysaccharide immunologic memory to naive recipient mice. The transfer of memory occurred in a dose-dependent manner. The observed anamnestic immune response was characterized by (i) more rapid kinetics, (ii) isotype switching from immunoglobulin M (IgM) to IgG, and (iii) 10-fold-higher levels of type III-specific IgG antibody than for the primary response in animals with cells transferred from placebo-immunized mice. The adoptive cell transfer model described in this paper can be used for at least two purposes: (i) to evaluate conjugate vaccines with different physicochemical properties for their ability to induce immunologic memory and (ii) to study the cellular interactions required for an immune response to these molecules.

FIG. 1

Transfer of immunologic memory for GBSIII PS. BALB/c mice were immunized twice with GBSIII-TT conjugate vaccine, and 4 weeks later 2 × 10⁸ spleen cells were adoptively transferred into groups of six naive recipients (solid line). In control animals, 2 × 10⁸ naive spleen cells were transferred (dotted line). All recipient mice were immunized 24 h later with GBSIII-TT, and the antibody response to the GBSIII PS in serum was measured 0, 7, 14, and 28 days after immunization. (A) GBSIII-specific IgG response; (B) GBSIII-specific IgM response. Lines represent the median levels, and error bars indicate the range. The results of two independent experiments are shown. ∗, P < 0.01 compared with recipients of splenocytes from placebo-immunized donors (Mann-Whitney test).

FIG. 2

GBSIII-specific IgG subclass antibodies in naive mice transferred with splenocytes from GBSIII-TT-immunized donors. BALB/c mice were immunized twice 3 weeks apart with GBSIII-TT conjugate vaccine; 4 weeks after the second immunization, 2 × 10⁸ spleen cells were adoptively transferred into six naive recipients. All recipient mice were immunized 24 h later with GBSIII-TT, and the IgG subclass response to the GBSIII PS was measured in serum taken 28 days after immunization. The levels of GBSIII-specific IgG subclass antibodies are reported in nanograms per milliliter.

FIG. 3

Transfer of immunologic memory for GBSIII PS. BALB/c mice were immunized twice 3 weeks apart with GBSIII-TT conjugate vaccine, and 4 weeks after the second immunization, 2 × 10⁸ spleen cells were adoptively transferred into six naive recipients. All recipient mice were immunized 24 h later with saline (first immunization) and 28 days later with GBSIII-TT (second immunization), and the antibody response to GBSIII PS was measured in serum taken 0, 7, 14, and 28 days after these two immunizations. (A) GBSIII-specific IgG response; (B) GBSIII-specific IgM response. Lines represent the median levels, and error bars indicate the range.

FIG. 4

Dose response following adoptive transfer of spleen cells from mice primed with GBSIII-TT conjugate vaccine. BALB/c mice were immunized with GBSIII-TT conjugate vaccine, and 2 × 10⁸, 1 × 10⁸, 2 × 10⁷, or 2 × 10⁶ spleen cells from these primed mice were adoptively transferred into naive recipients (groups of six mice). In the control group, 2 × 10⁸ naive spleen cells were transferred (hatched bars). All recipient mice were immunized with GBSIII-TT, and blood was taken 0, 7, and 14 days after immunization. (A) GBSIII PS-specific IgG antibodies; (B) TT-specific IgG antibodies. The levels of GBSIII-specific and carrier TT-specific IgG antibodies after the transfer of spleen cells are reported as medians. ∗, P < 0.01 compared with recipients of splenocytes from placebo-immunized donors (Mann-Whitney test).