Wanda G. H. Han

Roads to the development of improved pertussis vaccines paved by immunology

Current acellular pertussis vaccines have various shortcomings, which may contribute to their suboptimal efficacy and waning immunity in vaccinated populations. This calls for the development of new pertussis vaccines capable of inducing long-lived protective immunity. Immunization with whole cell pertussis vaccines and natural infection with Bordetella pertussis induce distinct and more protective immune responses when compared with immunization with acellular pertussis vaccines. Therefore, the immune responses induced with whole cell vaccine or after infection can be used as a benchmark for the development of third-generation vaccines against pertussis. Here, we review the literature on the immunology of B. pertussis infection and vaccination and discuss the lessons learned that will help in the design of improved pertussis vaccines.

Modulation of the CD4(+) T cell response after acellular pertussis vaccination in the presence of TLR4 ligation.

Whole cell pertussis (wP) vaccines are gradually being replaced by aluminum salt-adjuvanted acellular pertussis (aP) vaccines. These promote CD4(+) T cell responses with a non-protective Th2 component, while protective immune mechanisms to B. pertussis may rather involve long-lived Th1/Th17 type CD4(+) T cells. Here we asked whether addition of a non-toxic meningococcal LPS derivative, LpxL1, as adjuvant can favorably modulate the aP-induced pertussis-specific CD4(+) T cell response in mice. To assess the effect of TLR4 ligation, Th type, quantity, and memory potential of pertussis-specific CD4(+) T cells were determined at the single-cell level after aP and aP+LpxL1 vaccination using intracellular cytokine staining and MHC class II tetramers. Adding LpxL1 to the aP vaccine weakened the Th2 component and strengthened the Th1/Th17 component of the specific CD4(+) T cell response. Notably, LpxL1 addition also induced higher frequencies of tetramer positive CD4(+) T cells in draining lymph nodes or blood, depending on the phase after vaccination. Moreover, there was a net profit in the number of CD4(+) T cells with a central memory phenotype, preferred for long-term immunity. Thus, adding a TLR4 ligand as adjuvant to a current aP vaccine was associated with a more favorable pertussis-specific CD4(+) T cell response.

Molecular Signatures of the Evolving Immune Response in Mice following a Bordetella pertussis Infection

Worldwide resurgence of pertussis necessitates the need for improvement of pertussis vaccines and vaccination strategies. Since natural infections induce a longer-lasting immunity than vaccinations, detailed knowledge of the immune responses following natural infection can provide important clues for such improvement. The purpose was to elucidate the kinetics of the protective immune response evolving after experimental Bordetella pertussis (B. pertussis) infection in mice. Data were collected from (i) individual analyses, i.e. microarray, flow cytometry, multiplex immunoassays, and bacterial clearance; (ii) twelve time points during the infection; and (iii) different tissues involved in the immune responses, i.e. lungs, spleen and blood. Combined data revealed detailed insight in molecular and cellular sequence of events connecting different phases (innate, bridging and adaptive) of the immune response following the infection. We detected a prolonged acute phase response, broad pathogen recognition, and early gene signatures of subsequent T-cell recruitment in the lungs. Activation of particular transcription factors and specific cell markers provided insight into the time course of the transition from innate towards adaptive immune responses, which resulted in a broad spectrum of systemic antibody subclasses and splenic Th1/Th17 memory cells against B. pertussis. In addition, signatures preceding the local generation of Th1 and Th17 cells as well as IgA in the lungs, considered key elements in protection against B. pertussis, were established. In conclusion, molecular and cellular immunological processes in response to live B. pertussis infection were unraveled, which may provide guidance in selecting new vaccine candidates that should evoke local and prolonged protective immune responses.

Waning and aging of cellular immunity to Bordetella pertussis

While it is clear that the maintenance of Bordetella pertussis-specific immunity evoked both after vaccination and infection is insufficient, it is unknown at which pace waning occurs and which threshold levels of sustained functional memory B and T cells are required to provide long-term protection. Longevity of human cellular immunity to B. pertussis has been studied less extensively than serology, but is suggested to be key for the observed differences between the duration of protection induced by acellular vaccination and whole cell vaccination or infection. The induction and maintenance of levels of protective memory B and T cells may alter with age, associated with changes of the immune system throughout life and with accumulating exposures to circulating B. pertussis or vaccine doses. This is relevant since pertussis affects all age groups. This review summarizes current knowledge on the waning patterns of human cellular immune responses to B. pertussis as addressed in diverse vaccination and infection settings and in various age groups. Knowledge on the effectiveness and flaws in human B. pertussis-specific cellular immunity ultimately will advance the improvement of pertussis vaccination strategies.

Bordetella pertussis outer membrane vesicle vaccine confers equal efficacy in mice with milder inflammatory responses compared to a whole-cell vaccine

The demand for improved pertussis vaccines is urgent due to the resurgence of whooping cough. A deeper understanding of the mode of action of pertussis vaccines is required to achieve this improvement. The vaccine-induced effects of a candidate outer membrane vesicle vaccine (omvPV) and a classical protective but reactogenic whole cell vaccine (wPV) were comprehensively compared in mice. The comparison revealed essential qualitative and quantitative differences with respect to immunogenicity and adverse effects for these vaccines. Both vaccines stimulated a mixed systemic Th1/Th2/Th17 response. Remarkably, omvPV evoked higher IgG levels, lower systemic pro-inflammatory cytokine responses and enhanced splenic gene expression than wPV. The omvPV-induced transcriptome revealed gene signatures of the IFN-signaling pathway, anti-inflammatory signatures that attenuate LPS responses, anti-inflammatory metabolic signatures, and IgG responses. Upon intranasal challenge, both immunized groups were equally efficient in clearing Bordetella pertussis from the lungs. This study importantly shows that immunization with omvPV provides a milder inflammatory responses but with equal protection to bacterial colonization and induction of protective antibody and Th1/Th17 type immune responses compared to wPV. These results emphasize the potential of omvPV as a safe and effective next-generation pertussis vaccine.

Loss of Multi-Epitope Specificity in Memory CD4+ T Cell Responses to B. Pertussis with Age

Pertussis is still occurring in highly vaccinated populations, affecting individuals of all ages. Long-lived Th1 CD4+ T cells are essential for protective immunity against pertussis. For better understanding of the limited immunological memory to Bordetella pertussis, we used a panel of Pertactin and Pertussis toxin specific peptides to interrogate CD4+ T cell responses at the epitope level in a unique cohort of symptomatic pertussis patients of different ages, at various time intervals after infection. Our study showed that pertussis epitope-specific T cell responses contained Th1 and Th2 components irrespective of the epitope studied, time after infection, or age. In contrast, the breadth of the pertussis-directed CD4+ T cell response seemed dependent on age and closeness to infection. Multi-epitope specificity long-term after infection was lost in older age groups. Detailed knowledge on pertussis specific immune mechanisms and their insufficiencies is important for understanding resurgence of pertussis in highly vaccinated populations.

Immunological signatures after Bordetella Pertussis infection demonstrate importance of pulmonary innate immune cells

Effective immunity against Bordetella pertussis is currently under discussion following the stacking evidence of pertussis resurgence in the vaccinated population. Natural immunity is more effective than vaccine-induced immunity indicating that knowledge on infection-induced responses may contribute to improve vaccination strategies. We applied a systems biology approach comprising microarray, flow cytometry and multiplex immunoassays to unravel the molecular and cellular signatures in unprotected mice and protected mice with infection-induced immunity, around a B. pertussis challenge. Pre-existing systemic memory Th1/Th17 cells, memory B-cells, and mucosal IgA specific for Ptx, Vag8, Fim2/3 were detected in the protected mice 56 days after an experimental infection. In addition, pre-existing high activity and reactivation of pulmonary innate cells such as alveolar macrophages, M-cells and goblet cells was detected. The pro-inflammatory responses in the lungs and serum, and neutrophil recruitment in the spleen upon an infectious challenge of unprotected mice were absent in protected mice. Instead, fast pulmonary immune responses in protected mice led to efficient bacterial clearance and harbored potential new gene markers that contribute to immunity against B. pertussis. These responses comprised of innate makers, such as Clca3, Retlna, Glycam1, Gp2, and Umod, next to adaptive markers, such as CCR6+ B-cells, CCR6+ Th17 cells and CXCR6+ T-cells as demonstrated by transcriptome analysis. In conclusion, besides effective Th1/Th17 and mucosal IgA responses, the primary infection-induced immunity benefits from activation of pulmonary resident innate immune cells, achieved by local pathogen-recognition. These molecular signatures of primary infection-induced immunity provided potential markers to improve vaccine-induced immunity against B. pertussis.

Transcriptome signature for dampened Th2 dominance in acellular pertussis vaccine-induced CD4+ T cell responses through TLR4 ligation

Current acellular pertussis (aP) vaccines promote a T helper 2 (Th2)-dominated response, while Th1/Th17 cells are protective. As our previous study showed, after adding a non-toxic TLR4 ligand, LpxL1, to the aP vaccine in mice, the Bordetella pertussis-specific Th2 response is decreased and Th1/Th17 responses are increased as measured at the cytokine protein level. However, how this shift in Th response by LpxL1 addition is regulated at the gene expression level remains unclear. Transcriptomics analysis was performed on purified CD4+ T cells of control and vaccinated mice after in vitro restimulation with aP vaccine antigens. Multiple key factors in Th differentiation, including transcription factors, cytokines, and receptors, were identified within the differentially expressed genes. Upregulation of Th2- and downregulation of follicular helper T cell-associated genes were found in the CD4+ T cells of both aP- and aP+LpxL1-vaccinated mice. Genes exclusively upregulated in CD4+ T cells of aP+LpxL1-vaccinated mice included Th1 and Th17 signature cytokine genes Ifng and Il17a respectively. Overall, our study indicates that after addition of LpxL1 to the aP vaccine the Th2 component is not downregulated at the gene expression level. Rather an increase in expression of Th1- and Th17-associated genes caused the shift in Th subset outcome.

Ex vivo peptide-MHC II tetramer analysis reveals distinct end-differentiation patterns of human pertussis-specific CD4(+) T cells following clinical infection.

Pertussis is occurring in highly vaccinated populations, suggesting insufficient protective memory CD4(+) T cells to Bordetella (B.) pertussis. P.69 Pertactin (P.69 Prn) is an important virulence factor of B. pertussis, and P.69 Prn7-24 is an immunodominant CD4(+) T cell epitope in mice and broadly recognized in humans. P.69 Prn7-24 peptide-MHC II tetramers (DRB4*0101/IVKT) were designed to ex vivo interrogate the presence and differentiation state of P.69 Prn7-24 specific CD4(+) T cells in six symptomatic pertussis cases. Cases with relatively more CD45RA(-)CCR7(+) central memory CD4(+)DRB4*0101/IVKT(+) T cells secreted Th1 cytokines, while cases with more CD45RA(-)CCR7(-) effector memory CD4(+)DRB4*0101/IVKT(+) T cells secreted both Th1 and Th2 cytokines upon peptide stimulation. CD45RA(+)CCR7(-) terminal differentiation pattern was associated with low or non-functionality based on cytokine secretion. This study provides proof of principle for further peptide-MHC II tetramer guided approaches in the elucidation of limited immunological memory to B. pertussis and the resurgence of pertussis.

In vitro innate immune cell based models to assess whole cell Bordetella pertussis vaccine quality: a proof of principle.

Lot release testing of vaccines is primarily based on animal models that are costly, time-consuming and sometimes of questionable relevance. In order to reduce animal use, functional in vitro assays are being explored as an alternative approach for the current lot release testing paradigm. In this study, we present an evaluation of APC platforms assessing innate immune activation by whole cell Bordetella pertussis (wP) vaccines. Primary monocytes, monocyte-derived DC (moDC) and human monocyte/DC cell lines (MonoMac6 and MUTZ-3) were compared for their capacity to respond to wP vaccines of varying quality. To produce such vaccines, the production process of wP was manipulated, resulting in wP vaccines covering a range of in vivo potencies. The responses of MUTZ-3 cells and primary monocytes to these vaccines were marginal and these models were therefore considered inappropriate. Importantly, moDC and MonoMac6 cells responded to the wP vaccines and discriminated between vaccines of varying quality, although slight variations in the responses to wP vaccines of similar quality were also observed. This study provides a proof of principle for the use of in vitro APC platforms as part of a new strategy to assess wP vaccine lot consistency, though careful standardisation of assay conditions is necessary.