Co-stimulatory members of the TNFR family: keys to effective T-cell immunity?

Manipulating dendritic cell biology for the active immunotherapy of cancer

Dendritic cells (DCs) are specialized antigen-presenting cells (APCs) that have an unequaled capacity to initiate primary immune responses, including tolerogenic responses. Because of the importance of DCs in the induction and control of immunity, an understanding of their biology is central to the development of potent immunotherapies for cancer, chronic infections, autoimmune disease, and induction of transplantation tolerance. This review discusses recent advances in DC research and the application of this knowledge toward new strategies for the clinical manipulation of DCs for cancer immunotherapy.

Extremely rapid and intense induction of apoptosis in human eosinophils by anti-CD30 antibody treatment in vitro

Apoptosis is an important cellular mechanism for controlling cell viability and proliferation. With respect to eosinophils, cytokines prolong their survival, whereas corticosteroids reduce their survival in vitro. CD30, a member of the TNFR family, is expressed on the surface of many cell types, including Hodgkin's lymphoma cells. CD30 is capable of inducing apoptosis after Ab treatment in some cell lines. To determine whether this surface structure is involved in apoptosis of human eosinophils, we examined its expression and the effect of anti-CD30 Ab treatment on the viability of eosinophils. Purified human eosinophils expressed low, but consistently detectable, levels of CD30. Immobilized, but not soluble, forms of anti-CD30 Abs (HRS-4 and Ber-H8) or recombinant mouse CD30 ligand exhibited an extremely rapid and intense survival-reducing effect on the eosinophils in the presence of exogenous IL-5; this effect was both concentration and time dependent. Furthermore, high concentrations of IL-5 could not reverse the reduced survival rates. After treatment with anti-CD30 Ab, gel electrophoresis of DNA extracted from the eosinophils demonstrated changes consistent with apoptosis. The immobilized F(ab')(2) of the anti-CD30 Ab failed to induce eosinophil apoptosis. The addition of anti-CD18 Ab also completely abrogated the induction of eosinophil apoptosis. Further examination using specific signal transduction inhibitors suggested the involvement of p38, mitogen-activated protein kinase kinase 1/2, and specific tyrosine kinase, but not NF-kappaB, in the induction of CD30-mediated eosinophil apoptosis. These data demonstrate that CD30 can modify eosinophil survival by causing an extremely rapid and intense induction of apoptosis through a tightly regulated intracellular signaling pathway.

Memory T cells in transplantation: generation, function, and potential role in rejection

The adaptive immune system is endowed with long-lived memory to recall previous antigen encounters and respond more effectively to them. Memory immune responses are mediated by antigen-specific memory T lymphocytes that exhibit enhanced function compared with naïve T cells that have never encountered antigen. While the generation of memory T cells specific for pathogens is beneficial in providing protective immunity, memory T cells specific for alloantigens can be deleterious to the recipient of a transplanted organ. In graft rejection, memory T cells mediate accelerated, "second-set" rejection and their presence has been associated with increased propensity for early rejection. Recent findings have demonstrated that alloreactive memory T cells can be generated via exposure to alloantigens, as well as stimuli that are cross-reactive with alloantigens, and are therefore likely present in "naïve" individuals. This review focuses on the characteristics of memory T cells which make them of special interest to the transplant community, including differential activation requirements, broad homing properties, and resistance to tolerance induction. The multiple ways in which memory T cells can contribute to early and late graft rejection are discussed, as well as potential targets for combating alloreactive memory to be considered in the future design of tolerance induction strategies.

Emerging paradigms of T-cell co-stimulation

The analysis of recent data reveals that T-cell co-stimulation is a hierarchical process with elements of mutual interdependence between individual co-stimulators. The expression and function of co-stimulatory molecules is biased on various T-cell subsets and is dependent on the T-cell differentiation state. The classical paradigm of T-cell co-stimulation by professional antigen-presenting cells has to incorporate the newly recognized concept of T-cell co-stimulation in the interaction with peripheral tissues, such as endothelial or epithelial cells. The two signal paradigm of T-cell co-stimulation is being replaced by a multisignal integration concept of central and peripheral co-stimulation.

Targeted delivery of adenoviral vectors by cytotoxic T cells

Effective targeting of vectors to tumor cells that have metastasized to multiple different tissue sites remains a major challenge for gene therapy. Tumor-specific cytotoxic T lymphocytes (CTLs) have been shown in animal models and in humans to be able to cross tissue barriers and traffic to tumor cells. However, their capacity to eliminate malignancy has been limited by tumor immune evasion strategies. We now use a model of Epstein-Barr virus-mediated malignancy to show that human CTLs themselves may be modified to release therapeutic vectors following engagement of their antigen-specific receptors and that these vectors will effectively transduce and destroy tumor targets. We generated EBV-specific CTLs that were transgenic for the adenoviral E1 gene under the control of the cell activation-dependent CD40 ligand (CD40L) promoter. Following transduction with E1-deficient adenoviral vectors, these CTLs produced infectious virus when exposed to HLA-matched EBV-expressing targets, but not on exposure to major histocompatibility complex (MHC)-mismatched or otherwise irrelevant cells. This approach provides a means of delivering oncolytic/therapeutic vectors not only to locally accessible macroscopic tumors as is presently the case, but also to disseminated metastatic disease, while avoiding the risks associated with systemic administration of large doses of adenoviral vectors.

Adenovirus Vector-Mediated in Vivo Gene Transfer of OX40 Ligand to Tumor Cells Enhances Antitumor Immunity of Tumor-Bearing Hosts

OX40 ligand (OX40L), the ligand for OX40 on activated CD4+ T cells, has adjuvant properties for establishing effective T-cell immunity, a potent effector arm of the immune system against cancer. The hypothesis of this study is that in vivo genetic engineering of tumor cells to express OX40L will stimulate tumor-specific T cells by the OX40L-OX40 engagement, leading to an induction of systemic antitumor immunity. To investigate this hypothesis, s.c. established tumors of three different mouse cancer cells (B16 melanoma, H-2b; Lewis lung carcinoma, H-2b; and Colon-26 colon adenocarcinoma, H-2d) were treated with intratumoral injection of a recombinant adenovirus vector expressing mouse OX40L (AdOX40L). In all tumor models tested, treatment of tumor-bearing mice with AdOX40L induced a significant suppression of tumor growth along with survival advantages in the treated mice. The in vivo AdOX40L modification of tumors evoked tumor-specific cytotoxic T lymphocytes in the treated host correlated with in vivo priming of T helper 1 immune responses in a tumor-specific manner. Consistent with the finding, the antitumor effect provided by intratumoral injection of AdOX40L was completely abrogated in a CD4+ T cell-deficient or CD8+ T cell-deficient condition. In addition, ex vivo AdOX40L-transduced B16 cells also elicited B16-specific cytotoxic T lymphocyte responses, and significantly suppressed the B16 tumor growth in the immunization-challenge experiment. All of these results support the concept that genetic modification of tumor cells with a recombinant OX40L adenovirus vector may be of benefit in cancer immunotherapy protocols.

TNF Receptor-Associated Factor 5 Limits the Induction of Th2 Immune Responses

The TNF receptor-associated factor (TRAF) family of molecules acts as adapter proteins for signaling pathways initiated by several members of the TNF receptor (TNFR) superfamily. TRAF5(-/-) animals are viable and have normal development of the immune system despite interacting with several TNFR family members. A clear role for TRAF5 has yet to emerge. OX40 (CD134) interacts with TRAF5, suggesting that this pathway could be involved in regulating T cell differentiation into Th1 or Th2 cells. In tissue culture, OX40 stimulation of TRAF5(-/-) T cells resulted in a pronounced Th2 phenotype with elevated levels of IL-4 and IL-5. Similarly, in vivo immunization with protein in adjuvant in the presence of an agonist anti-OX40 Ab resulted in enhanced Th2 development in TRAF5(-/-) mice. Additionally, lung inflammation induced by T cells, which is critically controlled by OX40, was more pronounced in TRAF5(-/-) mice, characterized by higher levels of Th2 cytokines. These results suggest that TRAF5 can limit the induction of Th2 responses, and that TRAF5 can play a role in modulating responses driven by OX40 costimulation.

Expression and function of 4-1BB during CD4 versus CD8 T cell responsesin vivo

4-1BBL(-/-) mice have a defect in recall CD8+ T cell responses to viruses, whereas CD4+ T cell responses to virus are unimpaired in these mice. In contrast, both CD4+ and CD8+ T cells respond to 4-1BB ligand (4-1BBL) in vitro. To clarify the role of 4-1BB/4-1BBL in CD4+ versus CD8+ T cell responses in vivo, we compared CD4 (OT-II) and CD8 (OT-I) TCR transgenic T cells responding to the same antigen in an in vivo adoptive transfer model in 4-1BBL(+/+) versus 4-1BBL(-/-) mice. During primary and secondary responses, expression of 4-1BB on in vivo-activated TCR transgenic T cells was earlier and more transient than previously observed in vitro, correlating with expression of the early activation antigen CD69 and preceding the transition to the CD44hi state. Although 4-1BB is expressed early in the primary response, there was no effect of 4-1BBL deficiency on initial CD8 T cell expansion and only a minor effect on initial CD4 T cell expansion. The major effect of 4-1BB/4-1BBL interaction is on the T cell recall response. This is due to effects of 4-1BBL on maintenance of T cell numbers at the end of the primary response with additional effects of 4-1BBL on secondary expansion of T cells.

The costimulation-regulated duration of PKB activation controls T cell longevity

A brief antigenic stimulus can promote T cell proliferation, but the duration and nature of intracellular signals required for survival are unclear. Here we show that in the absence of OX40 costimulation, antigen-activated CD4+ cells are short-lived because the activity of protein kinase B (PKB; also known as Akt) is not maintained over time. Activated T cells that express a dominant-negative variant of PKB also undergo apoptosis, reproducing the OX40-deficient phenotype. In contrast, an active form of PKB prevents downregulation of antiapoptotic proteins in OX40-deficient T cells, rescues antigen-induced cell survival in vivo, and controls inflammation in recall responses. Thus, sustained and periodic PKB signaling has an integral role in regulating T cell longevity.

The role of ICOS and other costimulatory molecules in allergy and asthma

Activation and differentiation of T cells play a critical role in the pathogenesis of allergies and asthma. Upon encounter with specific antigen, naïve T helper precursor (ThP) cells become activated, an event that is regulated not only by engagement of the T cell receptor (TCR) with peptide presented in the context of MHC class II molecules, but also by a number of costimulatory signals. CD28 engagement by B7-1 and B7-2 on resting ThP cells provides a critical signal for initial cell cycle progression, interleukin-2 production and clonal expansion. However, in recent years, other related members of the immunoglobulin (Ig) family, such as inducible costimulatory molecules (ICOS) and the TNF receptor family members which include OX40, have also been demonstrated to play an important role in providing unique and complementary signals that regulate the outcome of immune responses. These positive costimulatory signals are counterbalanced by signals that dampen down immune responses and include CTLA-4, PD-1 and the recently described Ig superfamily members BTLA and TIM-3. This review discusses the role of these costimulatory signals and their potential involvement in the pathogenesis of asthma and allergic responses.

IL-1-regulated responses in astrocytes: Relevance to injury and recovery

In the central nervous system (CNS), the cellular processes of astrocytes make intimate contact with essentially all areas of the brain. They have also been shown to be functionally coupled to neurons, oligodendrocytes, and other astrocytes via both contact-dependent and non-contact-dependent pathways. These observations have led to the suggestion that a major function of astrocytes in the CNS is to maintain the homeostatic environment, thus promoting the proper functioning of the neuronal network. Inflammation in the CNS disrupts this process either transiently or permanently and, as such, is thought to be tightly regulated by both astrocytes and microglia. The remarkable role that single cytokines, such as TNF and IL-1, may play in this process has now been well accepted, but the extent of the reprogramming of the transcriptional machinery initiated by these factors remains to be fully appreciated. With the advent of microarray technology, a more comprehensive analysis of this process is now available. In this report we review data obtained with this technology to provide an overview of the extent of changes induced in astrocytes by the cytokine IL-1.