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The Divergent CD8+ T Cell Adjuvant Properties of LT-IIb and LT-IIc, Two Type II Heat-Labile Enterotoxins, Are Conferred by Their Ganglioside-Binding B Subunits.

Hu JC, Greene CJ, King-Lyons ND, Connell TD - PLoS ONE (2015)

Bottom Line: Comparing the immune potentiating characteristics of both native and chimeric HLT adjuvants, it was found that not all the adjuvant characteristics of the HLT adjuvants were modulated by the respective B subunits.However, induction of IL-1 from macrophages and the capacity to intoxicate cells in a mouse Y1 adrenal cell bioassay did not correlate with the B subunits.Therefore, it is likely that additional factors other than the B subunits contribute to the effects elicited by the HLT adjuvants.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology & Immunology, The Witebsky Center for Microbial Pathogenesis and Immunology, The University at Buffalo, Buffalo, New York, United States of America.

ABSTRACT
Poor immune responses elicited by vaccine antigens can be enhanced by the use of appropriate adjuvants. Type II heat-labile enterotoxins (HLT) produced by Escherichia coli are extremely potent adjuvants that augment both humoral and cellular immunity to co-administered antigens. Recent findings demonstrate that LT-IIb and LT-IIc, two type II HLT adjuvants, exhibit potent, yet distinguishable CD8(+) T cell adjuvant properties. While LT-IIc elicits a robust and rapid response at one week after administration, LT-IIb engenders a more gradual and slower expansion of antigen-specific CD8(+) T cells that correlates with improved immunity. The variations in immune effects elicited by the HLT adjuvants have been generally attributed to their highly divergent B subunits that mediate binding to various gangliosides on cell surfaces. Yet, HLT adjuvants with point mutations in the B subunit that significantly alter ganglioside binding retain similar adjuvant functions. Therefore, the contribution of the B subunits to adjuvanticity remains unclear. To investigate the influence of the B subunits on the enhancement of immune responses by LT-IIb and LT-IIc, chimeric HLT were engineered in which the B subunits of the two adjuvants were exchanged. Comparing the immune potentiating characteristics of both native and chimeric HLT adjuvants, it was found that not all the adjuvant characteristics of the HLT adjuvants were modulated by the respective B subunits. Specifically, the differences in the CD8(+) T cell kinetics and protective responses elicited by LT-IIb and LT-IIc did indeed followed their respective B subunits. However, induction of IL-1 from macrophages and the capacity to intoxicate cells in a mouse Y1 adrenal cell bioassay did not correlate with the B subunits. Therefore, it is likely that additional factors other than the B subunits contribute to the effects elicited by the HLT adjuvants.

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CD8+ T cell responses to chimeric HLT adjuvants.OVA-specific CD8+ T cells in the peripheral blood post-immunization utilizing 50 μg of OVA and 1.0 μg of WT or chimeric HLT adjuvants. (A) Staining of OVA-specific CD8+ T cells from peripheral blood 28 days after immunization. Cells gated from live TCRβ+CD8+ population. (B) OVA-specific CD8+ T cells from PBMCs after 7, 14, and 28 days post-immunization. Data shown (n = 8). Statistical analysis: One-way ANOVA with Bonferroni post-test compared to OVA, unless otherwise noted. *P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001. Results shown as the arithmetic mean with error bars denoting SEM.
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pone.0142942.g004: CD8+ T cell responses to chimeric HLT adjuvants.OVA-specific CD8+ T cells in the peripheral blood post-immunization utilizing 50 μg of OVA and 1.0 μg of WT or chimeric HLT adjuvants. (A) Staining of OVA-specific CD8+ T cells from peripheral blood 28 days after immunization. Cells gated from live TCRβ+CD8+ population. (B) OVA-specific CD8+ T cells from PBMCs after 7, 14, and 28 days post-immunization. Data shown (n = 8). Statistical analysis: One-way ANOVA with Bonferroni post-test compared to OVA, unless otherwise noted. *P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001. Results shown as the arithmetic mean with error bars denoting SEM.

Mentions: The immunomodulatory differences exhibited by the various HLTs is hypothesized to be determined by the highly divergent B subunits that target the adjuvant to different immune cells or cellular compartments due to the HLTs’ different ganglioside preferences [13]. While both LT-IIb and LT-IIc enhance an antigen-specific CD8+ T response, LT-IIb induces a slower and longer expansion phase and promotes better vaccine efficacy upon pathogen challenge [12]. Therefore, to determine the contribution of the A and B subunits of LT-IIb and LT-IIc to these CD8+ T cell adjuvant characteristics, the responses elicited by both WT and chimeric HLT adjuvants in an intradermal immunization model were investigated. Mice were immunized with 1 μg of HLT adjuvant and 50 μg of ovalbumin (OVA), a model antigen. OVA-specific CD8+ T cells in the peripheral blood, identified by use of OVA dextramer staining (Fig 4A), were analyzed on days 7, 14, and 28 post-immunization. LT-IIbc exhibited CD8+ T cell expansion and contraction kinetics that were similar to those of wild-type LT-IIc with an early peak at day 7 followed by contraction for the duration of the experiment (Fig 4B). In contrast, the kinetics of the CD8+ T cell response was similar in cells treated with either LT-IIcb or WT LT-IIb, with a gradual expansion and contraction of OVA-specific CD8+ T cells (Fig 4B). Full expansion was not attained until 2 weeks after immunization. Amplitude differences, however, were observed when the responses to administration of LT-IIb and LT-IIcb were compared (Fig 4B).


The Divergent CD8+ T Cell Adjuvant Properties of LT-IIb and LT-IIc, Two Type II Heat-Labile Enterotoxins, Are Conferred by Their Ganglioside-Binding B Subunits.

Hu JC, Greene CJ, King-Lyons ND, Connell TD - PLoS ONE (2015)

CD8+ T cell responses to chimeric HLT adjuvants.OVA-specific CD8+ T cells in the peripheral blood post-immunization utilizing 50 μg of OVA and 1.0 μg of WT or chimeric HLT adjuvants. (A) Staining of OVA-specific CD8+ T cells from peripheral blood 28 days after immunization. Cells gated from live TCRβ+CD8+ population. (B) OVA-specific CD8+ T cells from PBMCs after 7, 14, and 28 days post-immunization. Data shown (n = 8). Statistical analysis: One-way ANOVA with Bonferroni post-test compared to OVA, unless otherwise noted. *P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001. Results shown as the arithmetic mean with error bars denoting SEM.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4643920&req=5

pone.0142942.g004: CD8+ T cell responses to chimeric HLT adjuvants.OVA-specific CD8+ T cells in the peripheral blood post-immunization utilizing 50 μg of OVA and 1.0 μg of WT or chimeric HLT adjuvants. (A) Staining of OVA-specific CD8+ T cells from peripheral blood 28 days after immunization. Cells gated from live TCRβ+CD8+ population. (B) OVA-specific CD8+ T cells from PBMCs after 7, 14, and 28 days post-immunization. Data shown (n = 8). Statistical analysis: One-way ANOVA with Bonferroni post-test compared to OVA, unless otherwise noted. *P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001. Results shown as the arithmetic mean with error bars denoting SEM.
Mentions: The immunomodulatory differences exhibited by the various HLTs is hypothesized to be determined by the highly divergent B subunits that target the adjuvant to different immune cells or cellular compartments due to the HLTs’ different ganglioside preferences [13]. While both LT-IIb and LT-IIc enhance an antigen-specific CD8+ T response, LT-IIb induces a slower and longer expansion phase and promotes better vaccine efficacy upon pathogen challenge [12]. Therefore, to determine the contribution of the A and B subunits of LT-IIb and LT-IIc to these CD8+ T cell adjuvant characteristics, the responses elicited by both WT and chimeric HLT adjuvants in an intradermal immunization model were investigated. Mice were immunized with 1 μg of HLT adjuvant and 50 μg of ovalbumin (OVA), a model antigen. OVA-specific CD8+ T cells in the peripheral blood, identified by use of OVA dextramer staining (Fig 4A), were analyzed on days 7, 14, and 28 post-immunization. LT-IIbc exhibited CD8+ T cell expansion and contraction kinetics that were similar to those of wild-type LT-IIc with an early peak at day 7 followed by contraction for the duration of the experiment (Fig 4B). In contrast, the kinetics of the CD8+ T cell response was similar in cells treated with either LT-IIcb or WT LT-IIb, with a gradual expansion and contraction of OVA-specific CD8+ T cells (Fig 4B). Full expansion was not attained until 2 weeks after immunization. Amplitude differences, however, were observed when the responses to administration of LT-IIb and LT-IIcb were compared (Fig 4B).

Bottom Line: Comparing the immune potentiating characteristics of both native and chimeric HLT adjuvants, it was found that not all the adjuvant characteristics of the HLT adjuvants were modulated by the respective B subunits.However, induction of IL-1 from macrophages and the capacity to intoxicate cells in a mouse Y1 adrenal cell bioassay did not correlate with the B subunits.Therefore, it is likely that additional factors other than the B subunits contribute to the effects elicited by the HLT adjuvants.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology & Immunology, The Witebsky Center for Microbial Pathogenesis and Immunology, The University at Buffalo, Buffalo, New York, United States of America.

ABSTRACT
Poor immune responses elicited by vaccine antigens can be enhanced by the use of appropriate adjuvants. Type II heat-labile enterotoxins (HLT) produced by Escherichia coli are extremely potent adjuvants that augment both humoral and cellular immunity to co-administered antigens. Recent findings demonstrate that LT-IIb and LT-IIc, two type II HLT adjuvants, exhibit potent, yet distinguishable CD8(+) T cell adjuvant properties. While LT-IIc elicits a robust and rapid response at one week after administration, LT-IIb engenders a more gradual and slower expansion of antigen-specific CD8(+) T cells that correlates with improved immunity. The variations in immune effects elicited by the HLT adjuvants have been generally attributed to their highly divergent B subunits that mediate binding to various gangliosides on cell surfaces. Yet, HLT adjuvants with point mutations in the B subunit that significantly alter ganglioside binding retain similar adjuvant functions. Therefore, the contribution of the B subunits to adjuvanticity remains unclear. To investigate the influence of the B subunits on the enhancement of immune responses by LT-IIb and LT-IIc, chimeric HLT were engineered in which the B subunits of the two adjuvants were exchanged. Comparing the immune potentiating characteristics of both native and chimeric HLT adjuvants, it was found that not all the adjuvant characteristics of the HLT adjuvants were modulated by the respective B subunits. Specifically, the differences in the CD8(+) T cell kinetics and protective responses elicited by LT-IIb and LT-IIc did indeed followed their respective B subunits. However, induction of IL-1 from macrophages and the capacity to intoxicate cells in a mouse Y1 adrenal cell bioassay did not correlate with the B subunits. Therefore, it is likely that additional factors other than the B subunits contribute to the effects elicited by the HLT adjuvants.

Show MeSH
Related in: MedlinePlus