Evaluation of CD62L expression as a marker for vaccine-elicited memory cytotoxic T lymphocytes

The development of successful vaccination strategies for eliciting cytotoxic T lymphocytes (CTLs) will be facilitated by the definition of strategies for subdividing CTLs into functionally distinct subpopulations. We assessed whether surface expression of a number of cell‐surface proteins could be used to define functionally distinct subpopulations of memory CTLs in mice immunized with a recombinant vaccinia virus expressing human immunodeficiency virus (HIV)‐1 envelope (Env). We found changes in cell‐surface expression of CD11a, CD44, CD45RB, CD49d, CD54 and CD62L on Env‐specific CD8⁺ T cells that appeared to differentiate them from other CD8⁺ T cells within 1 week to 1 month following immunization. Further, we saw an up‐regulation of CD62L surface expression on Env‐specific CD8⁺ memory T cells several months after immunization. However, CD62L expression did not correlate with differences in the abilities of CTLs to proliferate or produce interferon gamma (IFN‐γ) and tumour necrosis factor alpha (TNF‐α) in vitro in response to Env peptide stimulation. Moreover, the expression of CD62L did not allow differentiation of CTLs into subpopulations with distinct expansion kinetics in vivo after adoptive transfer into naïve mice and subsequent boosting of these mice with a recombinant adenovirus expressing HIV‐1 Env. Therefore, the definition of memory CD8⁺ T‐cell subpopulations on the basis of CD62L expression in mice does not allow the delineation of functionally distinct CTL subpopulations.     

Tumor‐mediated down‐regulation of MHC class II in DC development is attributable to the epigenetic control of the CIITA type I promoter

In patients with cancer, DC express significantly lower amounts of MHC class II compared with those of normal individuals. However, the underlying mechanisms for this have not yet been fully defined. In the present study, we found that IL‐10 plays a major role in the tumor‐conditioned medium (TCM)‐mediated decrease of MHC class II expression on BM‐derived DC. IL‐10 inhibited the expression of type I CIITA during DC differentiation. GM‐CSF‐mediated histone (H3 and H4) acetylation at the type I promoter (pI) locus of the CIITA gene was markedly increased during DC differentiation and this increase was blocked by IL‐10. We also found that STAT5 bound to the CIITA pI locus during DC differentiation, and the binding was markedly attenuated by TCM or IL‐10. Altogether, these findings suggest that (i) the down‐regulation of MHC class II in tumor microenvironments is most likely attributable to IL‐10 in the TCM and (ii) IL‐10‐mediated MHC class II down‐regulation results from the inhibition of type I CIITA expression. This inhibition is most likely due to blocking of the STAT5‐associated epigenetic modifications of the CIITA pI locus during the entire period of DC differentiation from BM cells, as opposed to a simple inhibition of MHC class II expression at the DC stage.     

Differential requirements of CD4+ T‐cell signals for effector cytotoxic T‐lymphocyte (CTL) priming and functional memory CTL development at higher CD8+ T‐cell precursor frequency

Increased CD8⁺ T‐cell precursor frequency (PF) precludes the requirement of CD4⁺ helper T (Th) cells for primary CD8⁺ cytotoxic T‐lymphocyte (CTL) responses. However, the key questions of whether unhelped CTLs generated at higher PF are functional effectors, and whether unhelped CTLs can differentiate into functional memory cells at higher PF are unclear. In this study, ovalbumin (OVA) ‐pulsed dendritic cells (DC_OVA) derived from C57BL/6, CD40 knockout (CD40^?/?) or CD40 ligand knockout (CD40L^?/?) mice were used to immunize C57BL/6, Ia^b?/?, CD40^?/? or CD40L^?/? mice, whose PF was previously increased with transfer of 1 × 10⁶ CD8⁺ T cells derived from OVA‐specific T‐cell receptor (TCR) transgenic OTI, OTI(CD40^?/?) or OTI(CD40L^?/?) mice. All the immunized mice were then assessed for effector and memory CTL responses. Following DC immunization, relatively comparable CTL priming occurred without CD4⁺ T‐cell help and Th‐provided CD40/CD40L signalling. In addition, the unhelped CTLs were functional effectors capable of inducing therapeutic immunity against established OVA‐expressing tumours. In contrast, the functional memory development of CTLs was severely impaired in the absence of CD4⁺ T‐cell help and CD40/CD40L signalling. Finally, unhelped memory CTLs failed to protect mice against lethal tumour challenge. Taken together, these results demonstrate that CD4⁺ T‐cell help at higher PF, is not required for effector CTL priming, but is required for functional memory CTL development against cancer. Our data may impact the development of novel preventive and therapeutic approaches in cancer patients with compromised CD4⁺ T‐cell functions.     

Granzyme A expression reveals distinct cytolytic CTL subsets following influenza A virus infection

CTL mediate anti‐viral immunity via targeted exocytosis of cytolytic granules containing perforin and members of the granzyme (grz) serine protease family. Here, we provide the first analysis of grzA protein expression by murine anti‐viral CTL. During the progression of influenza A virus infection, CTL expressed two divergent cytolytic phenotypes: grzA^?B⁺ and grzA⁺B⁺. CTL lacked grzA expression during the initial rounds of antigen‐driven division. High levels of grzA were expressed by influenza‐specific CTL early post infection (day 6), particularly in tissues associated with the infected respiratory tract (bronchoalveolar lavage, lung). Following resolution of influenza infection, a small population of memory CTL expressed grzA. Interestingly, individual influenza A virus‐derived epitope‐specific CTL expressed different levels of grzA. The grzA expression hierarchy was determined to be K^bPB1₇₀₃=D^bF2₆₂=K^bNS2₁₁₄>D^bNP₃₆₆=D^bPA₂₂₄ and inversely correlated with CTL magnitude. Therefore following influenza infection, a CTL cytolytic hierarchy was established relating to the different profiles of antigen expression and relative immunodominance. Analysis of CTL grzA expression during influenza virus immunity has enabled a more detailed insight into the cytolytic mechanisms of virus elimination.     

GATA-binding protein-3 regulates T helper type 2 cytokine and ifng loci through interaction with metastasis-associated protein 2

GATA‐binding protein‐3 (GATA‐3) regulates the T helper type 2 (Th2) cytokine locus through induction of chromatin remodelling. However, the molecular mechanism for this is poorly understood. To understand this mechanism better, we screened GATA‐3 interacting proteins using affinity purification and mass spectrometry. We found that GATA‐3 bound to metastasis‐associated protein 2 (MTA‐2), a component of the NuRD chromatin remodelling complex. GATA‐3 and MTA‐2 in turn bound to several regulatory regions of the Th2 cytokine locus and the ifng promoter. Cell transfection assay showed that MTA‐2 acted as an antagonist with GATA‐3 in the expression of Th2 cytokines, but co‐operated with GATA‐3 in the repression of the ifng gene expression. These results suggest that GATA‐3 interacts with MTA‐2 to co‐ordinately regulate Th2 cytokine and ifng loci during T helper cell differentiation.     

Suppression of murine tumour growth through CD8+ cytotoxic T lymphocytes via activated DEC‐205+ dendritic cells by sequential administration of α‐galactosylceramide in vivo

Cancer immunity is mediated through the effective priming and activation of tumour‐specific class I MHC molecule‐restricted CD8⁺ cytotoxic T lymphocytes (CTLs). DEC‐205⁺ dendritic cells (DCs) can cross‐present the epitope(s) of captured tumour antigens associated with class I MHC molecules alongside co‐stimulatory molecules to prime and activate tumour‐specific CD8⁺ CTLs. Immunosuppressive tolerogenic DCs with reduced co‐stimulatory molecules may be a cause of impaired CTL induction. Hepa1‐6‐1 cells were established from the mouse hepatoma cell line Hepa1‐6; these cells grow continuously after subcutaneous implantation into syngeneic C57BL/6 (B6) mice and do not prime CD8⁺ CTLs. In this study, we show that the growth of ongoing tumours was suppressed by activated CD8⁺ CTLs with tumour‐specific cytotoxicity through the administration of the glycolipid α‐galactosylceramide (α‐GalCer), which is a compound known to stimulate invariant natural killer T (iNKT) cells and selectively activate DEC‐205⁺ DCs. Moreover, we demonstrated that sequential repetitive intraperitoneal inoculation with α‐GalCer every 48 hr appeared to convert tolerogenic DEC‐205⁺ DCs into immunogenic DCs with a higher expression of co‐stimulatory molecules and a stronger cross‐presentation capacity, which primed CTL precursors and induced tumour‐specific CD8⁺ CTLs within the tumour environment without activating iNKT cells. These findings provide a new basis for cancer immunotherapy to convert tolerogenic DEC‐205⁺ DCs within tumours into immunogenic DCs through the sequential administration of an immuno‐potent lipid/glycolipid, and then activated immunogenic DCs with sufficient expression of co‐stimulatory molecules prime and activate tumour‐specific CD8⁺ CTLs within the tumour to control tumour growth.     

Induction of hepatitis B virus surface antigen‐specific cytotoxic T lymphocytes can be up‐regulated by the inhibition of indoleamine 2, 3‐dioxygenase activity

Cytotoxic T lymphocytes (CTLs) are thought to be major effectors involved in viral clearance during acute infections, including hepatitis B virus (HBV) infection. A persistent HBV infection is characterized by a lack of or a weak CTL response to HBV, which may be reflective of tolerance to HBV. Efficient induction of HBV‐specific CTLs leads to the clearance of HBV in patients with a chronic HBV infection. Previously, we reported that α‐galactosylceramide (α‐GalCer), a specific natural killer T (NKT) cell agonist, enhanced the induction of HBV surface antigen (HBsAg)‐specific CTLs. In the present study, we found that inhibition of indoleamine 2,3‐dioxygenase (IDO) activity enhanced the induction of HBsAg‐specific CTLs after immunization with HBsAg and α‐GalCer. The administration of HBsAg and α‐GalCer increased the production of interleukin‐2 and interleukin‐12b, which are crucial for the induction of HBsAg‐specific CTLs. The production of these cytokines was more strongly enhanced in IDO knockout mice compared with wild‐type mice. In addition, α‐GalCer induced the production of IDO in CD11b⁺ cells, and these cells inhibited proliferation of HBsAg‐specific CTLs. Our results lead to strategies for improving the induction of HBsAg‐specific CTLs.     

Embryonic stem cell‐derived haematopoietic progenitor cells down‐regulate the CD3 ξ chain on T cells,abrogating alloreactive T cells

Murine embryonic stem (ES) cell‐derived haematopoietic progenitor cells (HPCs) engraft and populate lymphoid organs. In vivo, HPCs engraft across MHC barriers protecting donor‐type allografts from rejection. However, the underlying phenomenon remains elusive. Here, we sought to determine the mechanism by which ES cell‐derived HPCs regulate alloreactive T cells. We used the 2C mouse, which expresses a transgenic T‐cell receptor against H2‐L^d to determine whether HPCs are deleted by cytotoxic T lymphocytes (CTLs). Previously, we reported that HPCs express MHC class I antigens poorly and do not express class II antigens. In vitro stimulated 2C CTLs failed to lyse H2‐L^d HPCs in a standard 4‐hr ⁵¹chromium release assay. Similarly, when the HPCs were tested in an ELISPOT assay measuring the release of interferon‐γ by CTLs, HPCs failed to induce CTL degranulation. In addition, mice that were injected with HPCs showed a marked decrease in T‐cell responses to alloantigen and CD3 stimulation, but showed a normal response to PMA/ionomycin, suggesting that HPCs impaired T‐cell signalling through the T‐cell receptor/CD3 complex. Here, we show that HPCs secrete arginase, an enzyme that scavenges l ‐arginine, leading to metabolites that down‐regulate CD3 ζ chain. Indeed an arginase inhibitor partially restored expression of the CD3 ζ chain, implicating arginase 1 in the down‐regulation of T cells. This previously unrecognized property of ES cell‐derived HPCs could positively enhance the engraftment of ES cell‐derived HPCs across MHC barriers by preventing rejection.     

Recognition of the PB1, neuraminidase, and matrix proteins of influenza virus A/NT/60/68 by cytotoxic T lymphocytes

We have investigated the recognition of the PB1, neuraminidase, and matrix (Ml) proteins of influenza virus A/NT/ 60/68 (H3N2 subtype) by secondary in vitro stimulated polyclonal cytotoxic T lymphocyte (CTL) populations. While these three proteins have different functions and cellular locations, they can all be recognized as target antigens. However, the immunogenicity of these proteins for CTLs is under strict genetic control. Thus, PB1 protein is recognized as a cross-reactive target antigen by CTLs raised in CBA (H-2^k) but not BALB/c (H-2^d) mice. CBA, but not BALB/c mice, also generate a low-level CTL response to the neuraminidase. This latter response was only detectable following in vivo priming of CBA mice with a recombinant vaccinia virus expressing neuraminidase (N2-VACC). The matrix protein, expressed from recombinant vaccinia virus M-VACC, was not recognized as an antigen by CTL generated from either CBA or BALB/c strains of mice. By contrast, human HLA-A2-restricted influenza virus-specific CTLs were shown to recognize this matrix protein as a target antigen. Endogenous expression of as little as 90 amino acids of the matrix protein was sufficient to render target cells susceptible to lysis by such CTLs.     

Changes in histone acetylation and methylation that are important for persistent but not transient expression of CCR4 in human CD4+ T cells

Although regulation of CXCR3 and CCR4 is related to Th1 and Th2 differentiation, respectively, many CXCR3⁺ and CCR4⁺ cells do not express IFN‐γ and/or IL‐4, suggesting that the chemokine receptor genes might be inducible by mechanisms that are lineage‐independent. We investigated the regulation of CXCR3 versus IFNG, and CCR4 versus IL4 in human CD4⁺ T cells by analyzing modifications of histone H3. In naïve cord‐blood cells, under nonpolarizing conditions not inducing IL4, CCR4 was induced to high levels without many of the activation‐associated changes in promoter histone H3 found for both IL4 and CCR4 in Th2 cells. Importantly, CCR4 expression was stable in Th2 cells, but fell in nonpolarized cells after the cells were rested; this decline could be reversed by increasing histone acetylation using sodium butyrate. Patterns of histone H3 modifications in CXCR3⁺CCR4^? and CXCR3^?CCR4⁺ CD4⁺ T‐cell subsets from adult blood matched those in cells cultured under polarizing conditions in vitro. Our data show that high‐level lineage‐independent induction of CCR4 can occur following T‐cell activation without accessibility‐associated changes in histone H3, but that without such changes expression is transient rather than persistent.