Kaimei Song

Superior T memory stem cell persistence supports long-lived T cell memory

Long-lived memory T cells are able to persist in the host in the absence of antigen; however, the mechanism by which they are maintained is not well understood. Recently, a subset of human T cells, stem cell memory T cells (TSCM cells), was shown to be self-renewing and multipotent, thereby providing a potential reservoir for T cell memory throughout life. However, their in vivo dynamics and homeostasis still remain to be defined due to the lack of suitable animal models. We identified T cells with a TSCM phenotype and stem cell-like properties in nonhuman primates. These cells were the least-differentiated memory subset, were functionally distinct from conventional memory cells, and served as precursors of central memory. Antigen-specific TSCM cells preferentially localized to LNs and were virtually absent from mucosal surfaces. They were generated in the acute phase of viral infection, preferentially survived in comparison with all other memory cells following elimination of antigen, and stably persisted for the long term. Thus, one mechanism for maintenance of long-term T cell memory derives from the unique homeostatic properties of TSCM cells. Vaccination strategies designed to elicit durable cellular immunity should target the generation of TSCM cells.

Characterization of CCR9 Expression and CCL25/Thymus-Expressed Chemokine Responsiveness During T Cell Development: CD3highCD69+ Thymocytes and γδTCR+ Thymocytes Preferentially Respond to CCL25

CCR9 mediates chemotaxis of thymocytes in response to CCL25/thymus-expressed chemokine, and its mRNA is selectively expressed in thymus and small intestine, the two known sites of T lymphopoiesis. To examine the expression of CCR9 during lymphocyte development, we generated polyclonal Ab that recognizes murine CCR9. CCR9 was expressed on the majority of immature CD4+CD8+ (double-positive) thymocytes, but not on immature CD4−CD8− (double-negative) thymocytes. CCR9 was down-regulated during the transition of double-positive thymocytes to the CD4+ or CD8+ (single-positive) stage, and only a minor subset of CD8+ lymph node T cells expressed CCR9. All CCR9+ thymocyte subsets migrated in response to CCL25; however, CD69+ thymocytes demonstrated enhanced CCL25-induced migration compared with CD69− thymocytes. Ab-mediated TCR stimulation also enhanced CCL25 responsiveness, indicating that CCL25-induced thymocyte migration is augmented by TCR signaling. Approximately one-half of all γδTCR+ thymocytes and peripheral γδTCR+ T cells expressed CCR9 on their surface, and these cells migrated in response to CCL25. These findings suggest that CCR9 may play an important role in the development and trafficking of both αβTCR+ and γδTCR+ T cells.

Characterization of subsets of CD4+ memory T cells reveals early branched pathways of T cell differentiation in humans

The pathways for differentiation of human CD4+ T cells into functionally distinct subsets of memory cells in vivo are unknown. The identification of these subsets and pathways has clear implications for the design of vaccines and immune-targeted therapies. Here, we show that populations of apparently naïve CD4+ T cells express the chemokine receptors CXCR3 or CCR4 and demonstrate patterns of gene expression and functional responses characteristic of memory cells. The proliferation history and T cell receptor repertoire of these chemokine-receptor+ cells suggest that they are very early memory CD4+ T cells that have “rested down” before acquiring the phenotypes described for “central” or “effector” memory T cells. In addition, the chemokine-receptor+ “naïve” populations contain Th1 and Th2 cells, respectively, demonstrating that Th1/Th2 differentiation can occur very early in vivo in the absence of markers conventionally associated with memory cells. We localized ligands for CXCR3 and CCR4 to separate foci in T cell zones of tonsil, suggesting that the chemokine-receptor+ subsets may be recruited and contribute to segregated, polarized microenvironments within lymphoid organs. Importantly, our data suggest that CD4+ T cells do not differentiate according to a simple schema from naïve → CD45RO+ noneffector/central memory → effector/effector memory cells. Rather, developmental pathways branch early on to yield effector/memory populations that are highly heterogeneous and multifunctional and have the potential to become stable resting cells.

Reduced Protection from Simian Immunodeficiency Virus SIVmac251 Infection Afforded by Memory CD8+ T Cells Induced by Vaccination during CD4+ T-Cell Deficiency

ABSTRACT Adaptive CD4+ and CD8+ T-cell responses have been associated with control of human immunodeficiency virus/simian immunodeficiency virus (HIV/SIV) replication. Here, we have designed a study with Indian rhesus macaques to more directly assess the role of CD8 SIV-specific responses in control of viral replication. Macaques were immunized with a DNA prime-modified vaccinia virus Ankara (MVA)-SIV boost regimen under normal conditions or under conditions of antibody-induced CD4+ T-cell deficiency. Depletion of CD4+ cells was performed in the immunized macaques at the peak of SIV-specific CD4+ T-cell responses following the DNA prime dose. A group of naïve macaques was also treated with the anti-CD4 depleting antibody as a control, and an additional group of macaques immunized under normal conditions was depleted of CD8+ T cells prior to challenge exposure to SIVmac251. Analysis of the quality and quantity of vaccine-induced CD8+ T cells demonstrated that SIV-specific CD8+ T cells generated under conditions of CD4+ T-cell deficiency expressed low levels of Bcl-2 and interleukin-2 (IL-2), and plasma virus levels increased over time. Depletion of CD8+ T cells prior to challenge exposure abrogated vaccine-induced protection as previously shown. These data support the notion that adaptive CD4+ T cells are critical for the generation of effective CD8+ T-cell responses to SIV that, in turn, contribute to protection from AIDS. Importantly, they also suggest that long-term protection from disease will be afforded only by T-cell vaccines for HIV that provide a balanced induction of CD4+ and CD8+ T-cell responses and protect against early depletion of CD4+ T cells postinfection.

Genetic immunization in the lung induces potent local and systemic immune responses

Successful vaccination against respiratory infections requires elicitation of high levels of potent and durable humoral and cellular responses in the lower airways. To accomplish this goal, we used a fine aerosol that targets the entire lung surface through normal respiration to deliver replication-incompetent recombinant adenoviral vectors expressing gene products from several infectious pathogens. We show that this regimen induced remarkably high and stable lung T-cell responses in nonhuman primates and that it also generated systemic and respiratory tract humoral responses of both IgA and IgG isotypes. Moreover, strong immunogenicity was achieved even in animals with preexisting antiadenoviral immunity, overcoming a critical hurdle to the use of these vectors in humans, who commonly are immune to adenoviruses. The immunogenicity profile elicited with this regimen, which is distinct from either intramuscular or intranasal delivery, has highly desirable properties for protection against respiratory pathogens. We show that it can be used repeatedly to generate mucosal humoral, CD4, and CD8 T-cell responses and as such may be applicable to other mucosally transmitted pathogens such as HIV. Indeed, in a lethal challenge model, we show that aerosolized recombinant adenoviral immunization completely protects ferrets against H5N1 highly pathogenic avian influenza virus. Thus, genetic immunization in the lung offers a powerful platform approach to generating protective immune responses against respiratory pathogens.

CCR2 Identifies a Stable Population of Human Effector Memory CD4+ T Cells Equipped for Rapid Recall Response

Because T cells act primarily through short-distance interactions, homing receptors can identify colocalizing cells that serve common functions. Expression patterns for multiple chemokine receptors on CD4+ T cells from human blood suggested a hierarchy of receptors that are induced and accumulate during effector/memory cell differentiation. We characterized CD4+CD45RO+ T cells based on expression of two of these receptors, CCR5 and CCR2, the principal subsets being CCR5−CCR2− (∼70%), CCR5+CCR2− (∼25%), and CCR5+CCR2+ (∼5%). Relationships among expression of CCR5 and CCR2 and CD62L, and the subsets’ proliferation histories, suggested a pathway of progressive effector/memory differentiation from the CCR5−CCR2− to CCR5+CCR2− to CCR5+CCR2+ cells. Sensitivity and rapidity of TCR-mediated activation, TCR signaling, and effector cytokine production by the subsets were consistent with such a pathway. The subsets also showed increasing responsiveness to IL-7, and the CCR5+CCR2+ cells were CD127bright and invariably showed the greatest response to tetanus toxoid. CCR5+CCR2+ cells also expressed the largest repertoire of chemokine receptors and migrated to the greatest number of chemokines. By contrast, the CCR5+CCR2− cells had the greatest percentages of regulatory T cells, activated/cycling cells, and CMV-reactive cells, and were most susceptible to apoptosis. Our results indicate that increasing memory cell differentiation can be uncoupled from susceptibility to death, and is associated with an increase in chemokine responsiveness, suggesting that vaccination (or infection) can produce a stable population of effector-capable memory cells that are highly enriched in the CCR5+CCR2+ subset and ideally equipped for rapid recall responses in tissue.

Comparison of systemic and mucosal vaccination: impact on intravenous and rectal SIV challenge.

Mucosal tissues are the primary route of transmission for most respiratory and sexually transmitted diseases, including human immunodeficiency virus. We aimed to generate strong mucosal immune responses to simian immunodeficiency virus (SIV) in rhesus macaques by targeting recombinant adenovirus serotype 5 (rAd5) to the lung. The immunogenicity and efficacy of aerosol (AE) vaccination was compared with intramuscular (IM) delivery in either an intravenous (IV) or intrarectal (IR) SIVmac251 challenge model. Aerosolized rAd5 induced strong cellular responses in the lung and systemic humoral responses equivalent to IM. Strikingly, all immunization groups controlled acute viremia in the IV challenge model by 1–2 logs. By contrast, after IR challenge, only peak viremia was reduced by immunization, with no significant effect on SIV infection acquisition rate or mucosal CD4+ T-cell preservation. Improved disease outcome was associated with pre-challenge cellular and humoral responses, while post-challenge T-cell responses were highly correlated with viremia control. The similar outcomes achieved by systemic and airway mucosal immunization support AE delivery as a safe, effective, and less invasive alternative to parenteral vaccination.

Trafficking, Persistence, and Activation State of Adoptively Transferred Allogeneic and Autologous Simian Immunodeficiency Virus-Specific CD8+ T Cell Clones during Acute and Chronic Infection of Rhesus Macaques

Despite multiple lines of evidence suggesting their involvement, the precise role of CD8+ T cells in controlling HIV replication remains unclear. To determine whether CD8+ T cells can limit retroviral replication in the absence of other immune responses, we transferred 1–13 × 109 allogeneic in vitro expanded SIV-specific CD8+ T cell clones matched for the relevant restricting MHC-I allele into rhesus macaques near the time of i.v. SIV challenge. Additionally, in vitro expanded autologous SIV-specific CD8+ T cell clones were infused 4–9 mo postinfection. Infused cells did not appreciably impact acute or chronic viral replication. The partially MHC-matched allogeneic cells were not detected in the blood or most tissues after 3 d but persisted longer in the lungs as assessed by bronchoalveolar lavage (BAL). Autologous cells transferred i.v. or i.p. were found in BAL and blood samples for up to 8 wk postinfusion. Interestingly, despite having a nominally activated phenotype (CD69+HLA-DR+), many of these cells persisted in the BAL without dividing. This suggests that expression of such markers by T cells at mucosal sites may not reflect recent activation, but may instead identify stable resident memory T cells. The lack of impact following transfer of such a large number of functional Ag-specific CD8+ T cells on SIV replication may reflect the magnitude of the immune response required to contain the virus.

Early immunologic and virologic predictors of clinical HIV-1 disease progression.

Objective:To identify early determinants of HIV-1 disease progression, which could potentially enable individualized patient treatment, and provide correlates of progression applicable as reference phenotypes to evaluate breakthrough infections in vaccine development. Design:High-throughput technologies were employed to interrogate multiple parameters on cryopreserved, retrospective peripheral blood mononuclear cell (PBMC) samples from 51 individuals from São Paulo, Brazil, obtained within 1 year of diagnosing early Clade B HIV-1 infection. Fast Progressors, Slow Progressors, and Controllers were identified based on a 2-year clinical follow-up. Methods:Phenotypic and functional T-cell parameters were tested by flow cytometry and qPCR to identify potential early determinants of subsequent HIV-1 disease progression. Results:Major differences were observed between Controllers and Progressors, especially in cell-associated viral load (CAVL), the differentiation pattern and CD38 expression of CD8+ T cells, and the cytokine pattern and activation phenotype of HIV-1-specific CD8+ T cells. Despite remarkably few other differences between the two Progressor groups, the CAVL had predictive power independent of plasma viral load. Conclusion:Analysis of three parameters (% CD38+ CD8+ T cells, total CAVL, % CCR5+ CD8+ T cells) was sufficient to predict subsequent disease progression (P < 0.001). Use of such prognostic correlates may be crucial when early CD4+ T-cell counts and plasma viral load levels fail to discriminate among groups with differing subsequent clinical progression.

Priming T-cell responses with recombinant measles vaccine vector in a heterologous prime-boost setting in non-human primates

Abstract Licensed live attenuated virus vaccines capable of expressing transgenes from other pathogens have the potential to reduce the number of childhood immunizations by eliciting robust immunity to multiple pathogens simultaneously. Recombinant attenuated measles virus (rMV) derived from the Edmonston Zagreb vaccine strain was engineered to express simian immunodeficiency virus (SIV) Gag protein for the purpose of evaluating the immunogenicity of rMV as a vaccine vector in rhesus macaques. rMV-Gag immunization alone elicited robust measles-specific humoral and cellular responses, but failed to elicit transgene (Gag)-specific immune responses, following aerosol or intratracheal/intramuscular delivery. However, when administered as a priming vaccine to a heterologous boost with recombinant adenovirus serotype 5 expressing the same transgene, rMV-Gag significantly enhanced Gag-specific T lymphocyte responses following rAd5 immunization. Gag-specific humoral responses were not enhanced, however, which may be due to either the transgene or the vector. Cellular response priming by rMV against the transgene was highly effective even when using a suboptimal dose of rAd5 for the boost. These data demonstrate feasibility of using rMV as a priming component of heterologous prime-boost vaccine regimens for pathogens requiring strong cellular responses.