The Gram-negative bacterium Bordetella pertussis causes whooping cough (pertussis), a severe respiratory disease, especially in young children, which is resurgent despite high vaccine coverage. The current acellular pertussis vaccine prevents severe disease but does not prevent nasal infection with B. pertussis. This parenterally delivered vaccine induces potent circulating antibody responses but limited respiratory tissue-resident memory T cells and IgA responses. Here we developed a vaccine approach based on respiratory delivery of antibiotic-inactivated B. pertussis (AIBP). Ciprofloxacin-treated B. pertussis potently activated antigen-presenting cells to drive T cell responses. AIBP immunization via aerosol or intranasal administration conferred a high level of protection against lung and nasal infection. The AIBP vaccine induced B. pertussis-specific interleukin (IL)-17-producing CD4 tissue-resident memory T cells that recruited neutrophils to the respiratory tract. Protection was abrogated by depletion of CD4 T cells or neutralization of IL-17 in mice. Unlike a parenterally delivered whole-cell pertussis vaccine, which induced high levels of serum IL-1β, IL-6, tumour necrosis factor and C-reactive protein, aerosol immunization with the AIBP vaccine did not promote systemic pro-inflammatory responses. We present preclinical evidence of a safe and effective respiratory-delivered vaccine platform for inducing T cell-mediated sterilizing immunity against a respiratory pathogen.

Bordetella pertussis causes whooping cough (pertussis), a respiratory infectious disease that is resurgent despite high vaccine coverage. Research on the mechanisms of immunity to B. pertussis have demonstrated protective roles for innate immune cells, antibodies and T cells in immunity induced by natural infection. Studies in animal models have demonstrated that IL-17-secreting respiratory tissue-resident memory CD4+ T (TRM) cells and associated recruitment of neutrophils play a critical role in clearance of bacteria from nasal mucosa. However, current acellular pertussis (aP) vaccines, while inducing potent serum antibody responses and protecting against pertussis disease, fail to induce local immune responses in the respiratory tract, thus allowing transmission of the bacteria from vaccinated individuals. Motivated by the resurgence of pertussis and the limitations of the current aP vaccines, several research groups involved in the design of more effective third generation pertussis vaccines are focusing on nasal-delivery approaches that induce respiratory TRM cells and mucosal IgA, as well as circulating antibodies.

Tissue-resident memory T (TRM) cells play a key role in sustained protective immunity against Bordetella pertussis infection of the nasal mucosa. Current alum-adjuvanted acellular pertussis (aP) vaccines protect against severe pertussis disease but fail to prevent nasal infection with B. pertussis. Here we demonstrate that immunization of mice with an aP vaccine failed to generate respiratory TRM cells, but did induce antigen-specific CD4+ Treg cells that expressed Foxp3, CD49b, PD-1 and LAG-3, and CD8+ Treg cells that expressed CD122, PD-1, and IL-10. B. pertussis-specific CD4+ and CD8+ T cell lines established from aP-immunized mice expressed the regulatory markers and suppressed activation of Th1 and Th17 cells. Blockade of IL-10 signaling during aP immunization or B. pertussis challenge promoted the induction of IL-17-secreting CD4+ TRM responses and enhanced bacterial clearance from the nose. Addition of the adjuvant LP-GMP, comprising TLR2 and STING agonists, to the aP vaccine and delivery by the nasal route promoted the induction of antigen-specific IL-17-producing CD4+ TRM cells and enhanced vaccine efficacy. Our findings demonstrate that aP vaccines suppress the induction of protective TRM cells in part through the induction of CD4+ and CD8+ Treg cells, which can be overcome using a potent adjuvant and delivery of the vaccine intranasally.

Cytomegalovirus (CMV) induces a unique T-cell response, where antigen-specific populations do not contract, but rather inflate during viral latency. It has been proposed that subclinical episodes of virus reactivation feed the inflation of CMV-specific memory cells by intermittently engaging T-cell receptors (TCRs), but evidence of TCR engagement has remained lacking. Nuclear factor of activated T cells (NFAT) is a family of transcription factors, where NFATc1 and NFATc2 signal downstream of TCR in mature T lymphocytes. We show selective impacts of NFATc1 and/or NFATc2 genetic ablations on the long-term inflation of MCMV-specific CD8 T-cell responses despite largely maintained responses to acute infection. NFATc1 ablation elicited robust phenotypes in isolation, but the strongest effects were observed when both NFAT genes were missing. CMV control was impaired only when both NFATs were deleted in CD8 T cells used in adoptive immunotherapy of immunodeficient mice. Transcriptome analyses revealed that T-cell intrinsic NFAT is not necessary for CD8 T-cell priming, but rather for their maturation towards effector-memory and in particular the effector cells, which dominate the pool of inflationary cells.

Whooping cough, caused by Bordetella pertussis, is still a major cause of morbidity and mortality worldwide. Current acellular pertussis (aP) vaccines induce potent circulating IgG and prevent severe disease in children/adults and in infants born to vaccinated mothers. However, they do not prevent nasal infection, allowing asymptomatic transmission of B. pertussis. Studies in animal models have demonstrated that, unlike natural infection, immunization with aP vaccines fails to induce secretory immunoglobulin A (IgA) or interleukin-17 (IL-17)-secreting tissue-resident memory CD4 T (TRM) cells, required for sustained sterilizing immunity in the nasal mucosa. Live-attenuated vaccines or aP vaccines formulated with novel adjuvants that induce respiratory IgA and TRM cells, especially when delivered by the nasal route, are in development and have considerable promise as next-generation vaccines against pertussis.

Tissue-resident memory CD4 T (TRM ) cells induced by infection with Bordetella pertussis persist in respiratory tissues and confer long-term protective immunity against reinfection. However, it is not clear how they are maintained in respiratory tissues. Here, we demonstrate that B. pertussis-specific CD4 TRM cells produce IL-17A in response to in vitro stimulation with LPS or heat-killed Klebsiella pneumoniae (HKKP) in the presence of dendritic cells. Furthermore, IL-17A-secreting CD4 TRM cells expand in the lung and nasal tissue of B. pertussis convalescent mice following in vivo administration of LPS or HKKP. Bystander activation of CD4 TRM cells was suppressed by anti-IL-12p40 but not by anti-MHCII antibodies. Furthermore, purified respiratory tissue-resident, but not circulating, CD4 T cells from convalescent mice produced IL-17A following direct stimulation with IL-23 and IL-1β or IL-18. Intranasal immunization of mice with a whole-cell pertussis vaccine induced respiratory CD4 TRM cells that were reactivated following stimulation with K. pneumoniae. Furthermore, the nasal pertussis vaccine conferred protective immunity against B. pertussis but also attenuated infection with K. pneumoniae. Our findings demonstrate that CD4 TRM cells induced by respiratory infection or vaccination can undergo bystander activation and confer heterologous immunity to an unrelated respiratory pathogen.

Whooping cough (pertussis) remains a global health problem despite widespread vaccination. Infection with Bordetella pertussis induces tissue-resident memory CD4 T cells (TRM) with Th1/Th17 phenotype, which confer protective immunity against re-infection. Current alum-adjuvanted acellular pertussis (aP) vaccines (aP/alum) protect against lung infection but induce limited cellular immunity or expansion of respiratory TRM cells and fail to prevent infection of the nasal mucosa or bacterial transmission. This study aims to elucidate the mechanisms by which aP/alum vaccines fail to recruit TRM cells to the nasal tissue and how novel adjuvants may overcome this deficit. Immunization of mice with aP/alum vaccine induced antibody responses but failed to induce systemic Th1 or Th17 responses and TRM cells in nasal tissue after B. pertussis challenge. In contrast, immunization of mice with aP/alum vaccine induced IL-10 production in draining lymph nodes. Immunization of IL-10-deficient mice with an aP/alum vaccine promoted induction of respiratory IFN-γ and IL-17-secreting TRM cells and conferred protection against B. pertussis infection of the nasal cavity. Substitution or adding a novel adjuvant LP-GMP, comprising TLR2 and STING agonists, to an aP vaccine generated respiratory TRM cells and promoted bacterial clearance from the nasal mucosa. These findings suggest that IL-10 may play a role in the failure of aP/alum vaccines to protect against B. pertussis infection of the nasal mucosa by suppressing activation and recruitment of TRM cells, but this can be overcome by adding the potent adjuvant LP-GMP to the aP/alum vaccine formulation.

The potential of memory T cells to provide protection against reinfection is beyond question. Yet, it remains debated whether long-term T cell memory is due to long-lived memory cells. There is ample evidence that blood-derived memory phenotype CD8+ T cells maintain themselves through cell division, rather than through longevity of individual cells. It has recently been proposed, however, that there may be heterogeneity in the lifespans of memory T cells, depending on factors such as exposure to cognate Ag. CMV infection induces not only conventional, contracting T cell responses, but also inflationary CD8+ T cell responses, which are maintained at unusually high numbers, and are even thought to continue to expand over time. It has been proposed that such inflating T cell responses result from the accumulation of relatively long-lived CMV-specific memory CD8+ T cells. Using in vivo deuterium labeling and mathematical modeling, we found that the average production rates and expected lifespans of mouse CMV-specific CD8+ T cells are very similar to those of bulk memory-phenotype CD8+ T cells. Even CMV-specific inflationary CD8+ T cell responses that differ 3-fold in size were found to turn over at similar rates.

Understanding the mechanism of protective immunity in the nasal mucosae is central to the design of more effective vaccines that prevent nasal infection and transmission of Bordetella pertussis. We found significant infiltration of IL-17-secreting CD4(+) tissue-resident memory T (T-RM) cells and Siglec-F+ neutrophils into the nasal tissue during primary infection with B. pertussis. Il17A(-/-) mice had significantly higher bacterial load in the nasal mucosae, associated with significantly reduced infiltration of Siglec-F+ neutrophils. Re-infected convalescent mice rapidly cleared B. pertussis from the nasal cavity and this was associated with local expansion of IL-17-producing CD4(+) T-RM cells. Depletion of CD4 T cells from the nasal tissue during primary infection or after re-challenge of convalescent mice significantly delayed clearance of bacteria from the nasal mucosae. Protection was lost in Il17A(-/-) mice and this was associated with significantly less infiltration of Siglec-F+ neutrophils and antimicrobial peptide (AMP) production. Finally, depletion of neutrophils reduced the clearance of B. pertussis following re-challenge of convalescent mice. Our findings demonstrate that IL-17 plays a critical role in natural and acquired immunity to B. pertussis in the nasal mucosae and this effect is mediated by mobilizing neutrophils, especially Siglec-F+ neutrophils, which have high neutrophil extracellular trap (NET) activity.

Adaptive evolution is a key feature of T cell immunity. During acute immune responses, T cells harboring high-affinity T cell antigen receptors (TCRs) are preferentially expanded, but whether affinity maturation by clonal selection continues through the course of chronic infections remains unresolved. Here we investigated the evolution of the TCR repertoire and its affinity during the course of infection with cytomegalovirus, which elicits large T cell populations in humans and mice. Using single-cell and bulk TCR sequencing and structural affinity analyses of cytomegalovirus-specific T cells, and through the generation and in vivo monitoring of defined TCR repertoires, we found that the immunodominance of high-affinity T cell clones declined during the chronic infection phase, likely due to cellular senescence. These data showed that under conditions of chronic antigen exposure, low-affinity TCRs preferentially expanded within the TCR repertoire, with implications for immunotherapeutic strategies.

Bordetella pertussis causes whooping cough (pertussis), a severe and sometimes fatal respiratory infectious disease, especially in young infants. Pertussis can be prevented in infants and children by immun-ization with either whole-cell pertussis (wP) or acellular pertussis (aP) vaccines; however, its incidence is increasing in many countries despite high vaccine coverage. This resurgence in populations immun-ized with aP vaccines has been attributed to (1) genetic changes in circulating strains of B. pertussis resulting from vaccinedriven immune selection, (2) waning protective immunity due to poor induction of immunological memory, or (3) a failure of aP vaccines to induce the appropriate arm(s) of the cellular immune responses required to prevent infection. Studies in a baboon model have suggested that previous infection prevents reinfection as well as disease, whereas aP vaccines fail to prevent nasal - colonization and transmission of B. pertussis. Studies in the mouse model have demonstrated that immun-ization with wP vaccines induces Th1 and Th17 responses, whereas aP vaccines promote Th2-skewed responses and high antibody titres. Thus, while aP vaccine-induced antibodies may prevent pertussis, they may not prevent nasal colonization or transmission. Emerging data have suggested that replacing alum with novel adjuvants based on pathogen-associated molecular patterns has the capacity to switch the responses induced with aP vaccines to the more protective Th1/Th17 responses and may also enhance immunological memory. It is likely that third-generation pertussis vaccines will be based on live attenuated bacteria or aP formulations with novel adjuvants, which prevent nasal and lung infection and induce sustained immunity through induction of memory T cells.

Protective immunity wanes rapidly after immunization of children with acellular pertussis (aP) vaccines and these vaccines do not prevent nasal colonization or transmission of Bordetella pertussis in baboons. In this study, we examined the role of tissue-resident memory T (TRM) cells in persistent protective immunity induced by infection or immunization with aP and whole-cell pertussis (wP) vaccines in mice. Immunization of mice with a wP vaccine protected against lung and nasal colonization, whereas an aP vaccine failed to protect in the nose. IL-17 and IFN-γ-secreting CD69+CD4+ TRM cells were expanded in the lung and nasal tissue after B. pertussis challenge of mice immunized with wP, but not aP vaccines. However, previous infection induced the most persistent protection against nasal colonization and this correlated with potent induction of nasal tissue TRM cells, especially IL-17-secreting TRM cells. Blocking T cell migration to respiratory tissue during immunization with a wP vaccine impaired bacterial clearance, whereas transfer of TRM cells from convalescent or wP-immunized mice conferred protection to naïve mice. Our findings reveal that previous infection or wP vaccination are significantly more effective than aP vaccination in conferring persistent protective immunity against B. pertussis and that this is mediated by respiratory TRM cells.

Cytomegalovirus (CMV) is a ubiquitous β-herpesvirus that establishes life-long latent infection in a high percentage of the population worldwide. CMV induces the strongest and most durable CD8+ T cell response known in human clinical medicine. Due to its unique properties, the virus represents a promising candidate vaccine vector for the induction of persistent cellular immunity. To take advantage of this, we constructed a recombinant murine CMV (MCMV) expressing an MHC-I restricted epitope from influenza A virus (IAV) H1N1 within the immediate early 2 (ie2) gene. Only mice that were immunized intranasally (i.n.) were capable of controlling IAV infection, despite the greater potency of the intraperitoneally (i.p.) vaccination in inducing a systemic IAV-specific CD8+ T cell response. The protective capacity of the i.n. immunization was associated with its ability to induce IAV-specific tissue-resident memory CD8+ T (CD8TRM) cells in the lungs. Our data demonstrate that the protective effect exerted by the i.n. immunization was critically mediated by antigen-specific CD8+ T cells. CD8TRM cells promoted the induction of IFNγ and chemokines that facilitate the recruitment of antigen-specific CD8+ T cells to the lungs. Overall, our results showed that locally applied MCMV vectors could induce mucosal immunity at sites of entry, providing superior immune protection against respiratory infections.

BPZE1 is a live attenuated Bordetella pertussis vaccine for nasal administration to mimic the natural route of infection. Here, we studied the mechanism of BPZE1-induced immunity in the murine nasal cavity in contrast to acellular vaccine (aPV), although both vaccines protected against lung colonization. Transfer of splenocytes or serum from BPZE1-vaccinated or aPV-vaccinated mice protected naïve mice against lung colonization but not against nasal colonization. However, transfer of nasal washes from BPZE1-vaccinated mice resulted in protection against nasal colonization, which was lost in IgA-deficient or poly-Ig receptor-deficient mice, indicating that it depends on secretory IgA (SIgA) induction induced in the nose. BPZE1-induced protection against nasal colonization was long-lived despite the relatively rapid decay of SIgA, indicating a potent BPZE1-induced local memory response, likely due to CD4 + tissue-resident memory T cells induced in the nose by BPZE1. These cells produced interleukin-17 (IL-17), known to be important for SIgA secretion. Furthermore, BPZE1 failed to protect Il17 −/ − mice against nasal colonization by B. pertussis and induced only background levels of nasal SIgA. Thus, our results show important differences in the protective mechanism between the upper and the lower murine respiratory tract and demonstrate an IL-17-dependent SIgA-mediated mechanism of BPZE1-induced protection against B. pertussis nasopharyngeal colonization.

Effector-memory T-cells (TEM) are assumed to be short-lived cells that poorly proliferate upon antigenic restimulation, thus depending on central-memory T-cells (TCM) to replenish their numbers during homeostasis, largely depending on adoptive transfer evidence. Here we analyzed T cells in their natural environment and observed robust long-term in vivo cycling within the TEM subset that was stronger than the one in the TCM subset. We compared the non-persistent vaccinia virus and the persisting murine Cytomegalovirus (MCMV), which induces inflationary TEM responses that remain high during viral latency. We analyzed Ki67 expression during acute, resolved and latent infection and found Ki67hiBcl2lo TEM in acutely or latently infected mice, arguing for antigen-driven TEM proliferation. In vivo labeling with deuterium showed that TEM acquired deuterium more rapidly than TCM, and were rapidly lost during chase. Similarly, antibody-mediated depletion of primed CD8 T cells in latenly infected mice revealed that TEM replenished more rapidly than TCM, suggesting that TEM cycle faster than TCM. Finally, we utilized the ability of Tamoxifen-induced Cre-ERT2 recombinase to induce chromosomal translocations when large amounts of Tamoxifen are administered for an extended time, which resulted in a selective depletion of proliferating Ki67hi cells that hardly affected the TCM subset, but drove a selective loss of Ki67hiBcl2lo effector T-cells, and an increase in the death of TEM in the spleen, arguing that TEM preferentially proliferate in the spleen. Since our results contradicted previous evidence from adoptive transfer experiments, we tested T cell homing to the spleen upon adoptive transfer. TEM homing was substantially poorer than the one of TCM, likely explaining the previously reported expansions of TCM, but not TEM, upon transfer into latently infected mice. In conclusion, our data suggest that memory inflation is largely maintained by splenic proliferation of antigen-specific TEM, rather than by continued expansion and differentiation of TCM.