IL-2-activated CD8+CD44high cells express both adaptive and innate immune system receptors and demonstrate specificity for syngeneic tumor cells

Treatment of leishmaniasis with chemotherapy and vaccine: a mathematical model

Leishmaniasis, an infectious disease, manifests itself mostly in two forms, cutaneous leishmaniasis (CL) and, a more severe and potentially deadly form, visceral leishmaniasis (VL). The current control strategy for leishmaniasis relies on chemotherapy drugs such as sodium antimony gluconate (SAG) and meglumine antimoniate (MA). However, all these chemotherapy compounds have poor efficacy, and they are associated with toxicity and other adverse effects, as well as drug resistance. While research in vaccine development for leishmaniasis is continuously progressing, no vaccine is currently available. However, some experimental vaccines such as LEISH-F1+MPL-SE (V) have demonstrated some efficacy when used as drugs for CL patients. In this paper we use a mathematical model to address the following question: To what extent vaccine shots can enhance the efficacy of standard chemotherapy treatment of leishmaniasis? Starting with standard MA treatment of leishmaniasis and combining it with three injections of V , we find, by Day 84, that efficacy increased from 29% to 65-91% depending on the amount of the vaccine. With two or just one injection of V , efficacy is still very high, but there is a definite resurgence of the disease by end-time.

Bystander Memory T Cells and IMiD/Checkpoint Therapy in Multiple Myeloma: A Dangerous Tango?

In this review article we discuss the role of the memory T cells in multiple myeloma (MM) and how they may influence immune responses in patients that received immunomodulating drugs and check point therapy.

Leishmaniasis diagnosis: an update on the use of parasitological, immunological and molecular methods

Diagnosis of leishmaniasis has always been a major challenge as its clinical features resemble some other commonly occurring diseases such as tuberculosis, typhoid, and malaria. Reliable laboratory methods become important for differential diagnosis. Demonstration of the parasites in stained preparations of bone marrow and splenic aspirates being risky and invasive is still the gold standard for diagnosis. Serological tests utilizing rapid immunochromatographic formats or rK39 in enzyme linked immune sorbent assay, immunoblotting, direct agglutination test have complications related to high proportions of positive asymptomatic individuals and the inability to diagnose a relapse. Among the molecular techniques, polymerase chain reaction is the most commonly used technique that is successfully implied for diagnosis. This review provides updated information on the recent developments in the field of diagnosis in leishmaniasis, various methods utilized with their advantages and limitations.

Bystander T Cells: A Balancing Act of Friends and Foes

T cell responses are essential for appropriate protection against pathogens. T cell immunity is achieved through the ability to discriminate between foreign and self-molecules, and this relies heavily on stringent T cell receptor (TCR) specificity. Recently, bystander activated T lymphocytes, that are specific for unrelated epitopes during an antigen-specific response, have been implicated in diverse diseases. Numerous infection models have challenged the classic dogma of T cell activation as being solely dependent on TCR and major histocompatibility complex (MHC) interactions, indicating an unappreciated role for pathogen-associated receptors on T cells. We discuss here the specific roles of bystander activated T cells in pathogenesis, shedding light on the ability of these cells to modulate disease severity independently from TCR recognition.

The role of CMV in glioblastoma and implications for immunotherapeutic strategies

Controversy surrounds the role of cytomegalovirus (CMV) in glioblastoma (GBM). However, several studies have shown that CMV nucleic acids and proteins are present within GBM tumor tissue. CMV has been implicated in GBM pathogenesis by affecting tumor stem cell factors, angiogenesis and immune pathways. Anti-viral therapy has not been found to definitively improve outcomes for patients with GBM. Several studies have leveraged CMV by targeting CMV antigens using ex-vivo expanded T cells or dendritic cell vaccines. The initial results from these studies are promising and larger studies are underway.

The anti-tumor role of NK cells in vivo pre-activated and re-stimulated by interleukins in acute lymphoblastic leukemia

Although natural killer cells (NK cells) were traditionally classified as members of the innate immune system, NK cells have recently been found also to be an important player in the adaptive immune systems. In this context, in vitro activation of NK cells by cytokines leads to generation of NK cells with memory-like properties characterized by increased interferon-γ (IFNγ) production. However, it remains to be defined whether these memory-like NK cells exist in vivo after cytokine activation. Furthermore, it is also unclear whether such memory-like NK cells induced in vivo by cytokines could have effective anti-leukemia response. To address these issues, we used an in vivo pre-activation and re-stimulation system that was able to produce NK cells with increased IFNγ secretion. It was found that after in vivo pre-activation and re-stimulation with interleukins (ILs), NK cells retained a state to produce increased amount of IFNγ. Of note, whereas this intrinsic capacity of enhanced IFNγ production after in vivo IL pre-activation and re-stimulation could be transferred to the next generation of NK cells and was associated with prolonged survival of the mice with acute lymphoid leukemia. Moreover, the anti-leukemia activity of these memory-like NK cells was associated with IFNγ production and up-regulation of NK cells activation receptor-NK Group 2 member D (NKG2D). Together, these findings argue strongly that in vivo IL pre-activation and re-stimulation is capable to induce memory-like NK cells as observed previously in vitro, which are effective against acute lymphoblastic leukemia, likely via NKG2D-dependent IFNγ production, in intact animals.

Fusion Proteins of NKG2D/NKG2DL in Cancer Immunotherapy

NKG2D (natural killer group 2, member D) is an important activating receptor in natural killer (NK) cells and some T cells. NKG2D ligands (NKG2DLs) are specifically expressed on most tumor cells. The engagement of these ligands on tumor cells to NKG2D on NK cells will induce cell-mediated cytotoxicity and have target cells destroyed. This gives NKG2D/NKG2DLs great potential in cancer therapeutic application. The creation of NKG2D/NKG2DL-based multi-functional fusion proteins is becoming one of the most promising strategies in immunotherapy for cancer. Antibodies, cytokines, and death receptors have been fused with NKG2D or its ligands to produce many powerful fusion proteins, including NKG2D-based chimeric antigen receptors (CARs). In this article, we review the recent developments of the fusion proteins with NKG2D/NKG2DL ligands in cancer immunotherapy.

Diacylglycerol Kinase ζ Limits Cytokine-dependent Expansion of CD8+ T Cells with Broad Antitumor Capacity

Interleukin-2 and -15 drive expansion/differentiation of cytotoxic CD8⁺ T cells that eliminate targets via antigen-independent killing. This property is clinically relevant for the improvement of T cell-based antitumor therapies. Diacylglycerol kinase α and ζ (DGKα/ζ) metabolize the diacylglycerol generated following antigen recognition by T lymphocytes. Enhanced expression of these two lipid kinases in tumor-infiltrating CD8⁺ T cells promotes a hyporesponsive state that contributes to tumor immune escape. Inhibition of these two enzymes might thus be of interest for potentiating conventional antigen-directed tumor elimination. In this study, we sought to characterize the contribution of DGKα and ζ to antigen-independent cytotoxic functions of CD8⁺ T cells. Analysis of DGKζ-deficient mice showed an increase in bystander memory-like CD8⁺ T cell populations not observed in DGKα-deficient mice. We demonstrate that DGKζ limits cytokine responses in an antigen-independent manner. Cytokine-specific expansion of DGKζ-deficient CD8⁺ T cells promoted enhanced differentiation of innate-like cytotoxic cells in vitro, and correlated with the more potent in vivo anti-tumor responses of DGKζ-deficient mice engrafted with the murine A20 lymphoma. Our studies reveal a isoform-specific function for DGKζ downstream of IL-2/IL-15-mediated expansion of innate-like cytotoxic T cells, Pharmacological manipulation of DGKζ activity is of therapeutic interest for cytokine-directed anti-tumor treatments.

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DGKζ, a well-characterized negative regulator of TCR signals, also limits IL-2/15 function.

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DGKζ impairs cytokine-induced differentiation of cytotoxic T cell populations with innate-like ability to kill targets.

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As a result, DGKζ-deficient mice demonstrate enhanced rejection of implanted B cell lymphoma compared to wild type mice.

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Targeting DGKζ activity might be of interest to enhance cytokine-mediated antitumor therapies.

The immune system defends the body from foreign invaders. In cancer, tumors disguise as self-body cells and evade immune attack. For this reason it is important to identify the mechanism that stop T lymphocytes from recognize and destroy tumors. In this study we investigate the role of Diacylglycerol kinase zeta (DGKζ) as an inhibitor of antitumor T cell functions. We demonstrate that lymphoma cells injected in mice genetically modified to lack DGKζ expression develop smaller tumors that resolve more rapidly than those grown in normal mice. Our studies suggest that inhibition of DGKζ could help to reinforce the antitumor capacity of immune T lymphocytes.

Regulation of NKG2D+CD8+ T-cell-mediated antitumor immune surveillance: Identification of a novel CD28 activation-mediated, STAT3 phosphorylation-dependent mechanism

The natural killer (NK) group 2D (NKG2D) receptor, which displays on mouse and human NK cells, activates CD8⁺ T cells and small subsets of other T cells. NKG2D⁺CD8⁺ T cells play critical roles in both innate and adaptive immunity upon engagement with NKG2D ligands to eliminate tumor and infected cells. Despite the important role of NKG2D⁺CD8⁺ T cells in immune surveillance, the mechanisms of how NKG2D expression on CD8⁺ T cells is regulated remain poorly defined. We treated mouse and human CD8⁺ T cells with CD80 recombinant protein, plus a pharmacologic model with small molecular inhibitors to determine which signaling pathway leads to NKG2D regulation on CD8⁺T cells. This study revealed that CD28 activation gives rise to sustained NKG2D expression on both mouse and human CD8⁺ T cells in a signal transducer and activator of transcription 3 (STAT3) phosphorylation-dependent manner. Further, we found that CD28 activation stimulated sustained activation of the tyrosine kinase Lck, which recruits and triggers Janus kinase/STAT3 signaling to phosphorylate STAT3, and in turn increases NKG2D expression. Moreover, NKG2D induction on CD8⁺ T cells exerts cytolytic activity against target tumor cells in vitro, as well as significantly improves the antitumor therapeutic effects in vivo in an NKG2D-dependent manner. Taken together, these results elucidated a novel mechanism of NKG2D regulation by phosphorylated STAT3 (pSTAT3) on CD8⁺ T cells upon CD28 activation. This mechanism may shed light on the effectiveness of CD80-based, NKG2D-dependent antitumor immunotherapy.

Influence of In Vitro IL-2 or IL-15 Alone or in Combination with Hsp 70 Derived 14-Mer Peptide (TKD) on the Expression of NK Cell Activatory and Inhibitory Receptors on Peripheral Blood T Cells, B Cells and NKT Cells

Previous studies from Multhoff and colleagues reported that plasma membrane Hsp70 acts as a tumour-specific recognition structure for activated NK cells, and that the incubation of NK cells with Hsp70 and/or a 14-mer peptide derived from the N-terminal sequence of Hsp70 (TKDNNLLGRFELSG, TKD, aa 450–463) plus a low dose of IL-2 triggers NK cell proliferation and migration, and their capacity to kill cancer cells expressing membrane Hsp70. Herein, we have used flow cytometry to determine the influence of in vitro stimulation of peripheral blood mononuclear cells from healthy individuals with IL-2 or IL-15, either alone or in combination with TKD peptide on the cell surface expression of CD94, NK cell activatory receptors (CD16, NK2D, NKG2C, NKp30, NKp44, NKp46, NKp80, KIR2DL4, DNAM-1 and LAMP1) and NK cell inhibitory receptors (NKG2A, KIR2DL2/L3, LIR1/ILT-2 and NKR-P1A) by CD3+CD56+ (NKT), CD3+CD4+, CD3+CD8+ and CD19+ populations. NKG2D, DNAM-1, LAMP1 and NKR-P1A expression was upregulated after the stimulation with IL-2 or IL-15 alone or in combination with TKD in NKT, CD8+ T cells and B cells. CD94 was upregulated in NKT and CD8+ T cells. Concurrently, an increase in a number of CD8+ T cells expressing LIR1/ILT-2 and CD4+ T cells positive for NKR-P1A was observed. The proportion of CD8+ T cells that expressed NKG2D was higher after IL-2/TKD treatment, when compared with IL-2 treatment alone. In comparison with IL-15 alone, IL-15/TKD treatment increased the proportion of NKT cells that were positive for CD94, LAMP1 and NKRP-1A. The more potent effect of IL-15/TKD on cell surface expression of NKG2D, LIR1/ILT-2 and NKRP-1A was observed in B cells compared with IL-15 alone. However, this increase was not of statistical significance. IL-2/TKD induced significant upregulation of LAMP1 in CD8+ T cells compared with IL-2 alone. Besides NK cells, other immunocompetent cells present within the fraction of peripheral blood mononuclear cells were influenced by the treatment with low-dose interleukins themselves or in combination with hsp70 derived (TKD) peptide.

Immune response to infection by Leishmania: A mathematical model

Leishmaniasis is a disease caused by the Leishmania parasites. The injection of the parasites into the host occurs when a sand fly, which is the vector, bites the skin of the host. The parasites, which are obligate, take advantage of the immune system response and invade both the classically activated macrophages (M1) and the alternatively activated macrophages (M2). In this paper, we develop a mathematical model to explain the evolution of the disease. Simulations of the model show that, M2 macrophages steadily increase and M1 macrophages steadily decrease, while M1+M2 reach a steady state which is approximately the same as at healthy state of the host. Furthermore, the ratio of Leishmania parasites to macrophages depends homogeneously on their ratio at the time of the initial infection, in agreement with in vitro experimental data. The model is used to simulate treatment by existing or potential new drugs, and to compare the efficacy of different schedules of drug delivery.

The effects of polymorphisms in IL-2, IFN-γ, TGF-β2, IgL, TLR-4, MD-2, and iNOS genes on resistance to Salmonella enteritidis in indigenous chickens

Salmonella Enteritidis is a major cause of food poisoning worldwide, and poultry products are the main source of S. Enteritidis contamination for humans. Among the numerous strategies for disease control, improving genetic resistance to S. Enteritidis has been the most effective approach. We investigated the association between S. Enteritidis burden in the caecum, spleen, and liver of young indigenous chickens and seven candidate genes, selected on the basis of their critical roles in immunological functions. The genes included those encoding interleukin 2 (IL-2), interferon-γ (IFN-γ), transforming growth factor β2 (TGF-β2), immunoglobulin light chain (IgL), toll-like receptor 4 (TLR-4), myeloid differentiation protein 2 (MD-2), and inducible nitric oxide synthase (iNOS). Two Malaysian indigenous chicken breeds were used as sustainable genetic sources of alleles that are resistant to salmonellosis. The polymerase chain reaction restriction fragment-length polymorphism technique was used to genotype the candidate genes. Three different genotypes were observed in all of the candidate genes, except for MD-2. All of the candidate genes showed the Hardy-Weinberg equilibrium for the two populations. The IL-2-MnlI polymorphism was associated with S. Enteritidis burden in the caecum and spleen. The TGF-β2-RsaI, TLR-4-Sau 96I, and iNOS-AluI polymorphisms were associated with the caecum S. Enteritidis load. The other candidate genes were not associated with S. Enteritidis load in any organ. The results indicate that the IL-2, TGF-β2, TLR-4, and iNOS genes are potential candidates for use in selection programmes for increasing genetic resistance against S. Enteritidis in Malaysian indigenous chickens.

The biography of the immune system and the control of cancer: from St Peregrine to contemporary vaccination strategies

BACKGROUND

The historical basis and contemporary evidence for the use of immune strategies for prevention of malignancies are reviewed. Emphasis is focussed on the Febrile Infections and Melanoma (FEBIM) study on melanoma and on malignancies that seem to be related to an overexpression of human endogenous retrovirus K (HERV-K).

DISCUSSION

It is claimed that, as a result of recent observational studies, measures for prevention of some malignancies such as melanoma and certain forms of leukaemia are already at hand: vaccination with Bacille Calmette-Guérin (BCG) of new-borns and vaccination with the yellow fever 17D (YFV) vaccine of adults. While the evidence of their benefit for prevention of malignancies requires substantiation, the observations that vaccinations with BCG and/or vaccinia early in life improved the outcome of patients after surgical therapy of melanoma are of practical relevance as the survival advantage conferred by prior vaccination is greater than any contemporary adjuvant therapy.

SUMMARY

The reviewed findings open a debate as to whether controlled vaccination studies should be conducted in patients and/or regions for whom/where they are needed most urgently. A study proposal is made and discussed. If protection is confirmed, the development of novel recombinant vaccines with wider ranges of protection based, most likely, on BCG, YFV or vaccinia, could be attempted.

The ThPOK transcription factor differentially affects the development and function of self-specific CD8(+) T cells and regulatory CD4(+) T cells

The zinc finger transcription factor ThPOK plays a crucial role in CD4 T-cell development and CD4/CD8 lineage decision. In ThPOK-deficient mice, developing T cells expressing MHC class II-restricted T-cell receptors are redirected into the CD8 T-cell lineage. In this study, we investigated whether the ThPOK transgene affected the development and function of two additional types of T cells, namely self-specific CD8 T cells and CD4(+) FoxP3(+) T regulatory cells. Self-specific CD8 T cells are characterized by high expression of CD44, CD122, Ly6C, 1B11 and proliferation in response to either IL-2 or IL-15. The ThPOK transgene converted these self-specific CD8 T cells into CD4 T cells. The converted CD4(+) T cells are no longer self-reactive, lose the characteristics of self-specific CD8 T cells, acquire the properties of conventional CD4 T cells and survive poorly in peripheral lymphoid organs. By contrast, the ThPOK transgene promoted the development of CD4(+) FoxP3(+) regulatory T cells resulting in an increased recovery of CD4(+) FoxP3(+) regulatory T cells that expressed higher transforming growth factor-β-dependent suppressor activity. These studies indicate that the ThPOK transcription factor differentially affects the development and function of self-specific CD8 T cells and CD4(+) FoxP3(+) regulatory T cells.

Structure and inducing tumor cell apoptosis activity of polysaccharides isolated from Lentinus edodes

In this study, five novel polysaccharides SLNT1, SLNT2, JLNT1, JLNT2, and JLNT3 were isolated from the fruit body of Lentinus edodes. Chemical and physical analyses showed that the five polysaccharides consist of glucose with the structure of β-(1→3)-d-glucose main chains and β-(1→6)-d-glucose side chains. Moreover, all of them had triple-helical conformation and different molecular weight distributions. Animal studies further demonstrated that the antitumor effects were remarkably improved by SLNT1 and JLNT1 treatments with the inhibitory rates of 65.41% and 61.07% in H22-bearing mice, respectively. Additionally, both of them significantly increased the levels of serum IL-2 and TNF-α production and induced the tumor cell apoptosis. Taken together, our findings revealed that the involved antitumor mechanisms possibly in part were mediated not only by enhancing the immunity but also by directly killing the tumor and the induction of tumor cell apoptosis in H22-bearing mice.

Immunoediting and antigen loss: overcoming the achilles heel of immunotherapy with antigen non-specific therapies

Cancer immunotherapy has emerged as a mainstream therapy option in the battle against cancer. Pre-clinical data demonstrates the ability of immunotherapy to harness the immune system to fight disseminated malignancy. Clinical translation has failed to recapitulate the promising results of pre-clinical studies although there have been some successes. In this review we explore some of the short-comings of cancer immunotherapy that have limited successful clinical translation. We will give special consideration to what we consider the most formidable hurdle to successful cancer immunotherapy: tumor-induced immune suppression and immune escape. We will discuss the need for antigen-specific immune responses for successful immunotherapy but also consider the need for antigen specificity as an Achilles heel of immunotherapy given tumor heterogeneity, immune editing, and antigen loss. Finally, we will discuss how combinatorial strategies may overcome some of the pitfalls of antigen specificity and highlight recent studies from our lab which suggest that the induction of antigen non-specific immune responses may also produce robust anti-tumor effects and bypass the need for antigen specificity.

Distinct populations of innate CD8+ T cells revealed in a CXCR3 reporter mouse

CXCR3, expressed mainly on activated T and NK cells, is implicated in a host of immunological conditions and can contribute either to disease resolution or pathology. We report the generation and characterization of a novel CXCR3 internal ribosome entry site bicistronic enhanced GFP reporter (CIBER) mouse in which enhanced GFP expression correlates with surface levels of CXCR3. Using CIBER mice, we identified two distinct populations of innate CD8(+) T cells based on constitutive expression of CXCR3. We demonstrate that CXCR3(+) innate CD8(+) T cells preferentially express higher levels of Ly6C and CD122, but lower levels of CCR9 compared with CXCR3(-) innate CD8(+) T cells. Furthermore, we show that CXCR3(+) innate CD8(+) T cells express higher transcript levels of antiapoptotic but lower levels of proapoptotic factors, respond more robustly to IL-2 and IL-15, and produce significantly more IFN-γ and granzyme B. Interestingly, CXCR3(+) innate CD8(+) T cells do not respond to IL-12 or IL-18 alone, but produce significant amounts of IFN-γ on stimulation with a combination of these cytokines. Taken together, these findings demonstrate that CXCR3(+) and CXCR3(-) innate CD8(+) T cells are phenotypically and functionally distinct. These newly generated CIBER mice provide a novel tool for studying the role of CXCR3 and CXCR3-expressing cells in vivo.

Human NKG2D-ligands: cell biology strategies to ensure immune recognition

Immune recognition mediated by the activating receptor NKG2D plays an important role for the elimination of stressed cells, including tumors and virus-infected cells. On the other hand, the ligands for NKG2D can also be shed into the sera of cancer patients where they weaken the immune response by downmodulating the receptor on effector cells, mainly NK and T cells. Although both families of NKG2D-ligands, major histocompatibility complex class I-related chain (MIC) A/B and UL16 binding proteins (ULBPs), are related to MHC molecules and their expression is increased after stress, many differences are observed in terms of their biochemical properties and cell trafficking. In this paper, we summarize the variety of NKG2D-ligands and propose that selection pressure has driven evolution of diversity in their trafficking and shedding, but not receptor binding affinity. However, it is also possible to identify functional properties common to individual ULBP molecules and MICA/B alleles, but not generally conserved within the MIC or ULBP families. These characteristics likely represent examples of convergent evolution for efficient immune recognition, but are also attractive targets for pathogen immune evasion strategies. Categorization of NKG2D-ligands according to their biological features, rather than their genetic family, may help to achieve a better understanding of NKG2D-ligand association with disease.

The role of antigen-specific and non-specific immunotherapy in the treatment of cancer

Immunotherapy in the treatment of cancer is increasing, particularly with the recent FDA approval of sipuleucel-T and ipilimumab. The efficacy of anti-tumor immunotherapies has been modest compared to their theoretical and pre-clinical promise. This review evaluates the promise and pitfalls of immunotherapy and highlight some of the obstacles to improving anti-tumor immunotherapy: the need for technical refinement of therapies, the need for an increased understanding of how best to combine therapies with traditional cytotoxic therapies, the inability of patients to mount an effective immune response either due to disease burden or tumor induced immune suppression, the significant toxicities associated with many immunotherapies, and the lack of strongly immunogenic antigens required by many therapies. Further, antigen-non-specific immunotherapies, including cytokines such as interleukins and interferons, immuno-stimulatory agents such as CpG oligonucleotides, or BCG, antibodies targeted against receptors such as the agonistic CD40 or inhibitory CTLA-4 antibodies, and enzyme inhibitors such as those targeting cyclo-oxygenase or indolamine-2,3-dioxygenase are discussed. In addition, potential mechanisms of these therapies such as direct anti-tumor effects, reversal of immune suppression, activation of innate immunity, and antigen-non-specific T-cell activation are reviewed. We also appraise the potential of these antigen-non-specific therapies to overcome some of the previously described pitfalls of immunotherapy. Lastly, we discuss a recent series of studies from our laboratory demonstrating the importance of antigen-non-specific 'bystander activation' of memory T-lymphocytes by immunomodulatory therapies such as interleukin-2 and the antigen-non-specific anti-tumor effects of these cells.

Targeting NKG2D in tumor surveillance

INTRODUCTION

NKG2D (natural killer group 2, member D) is expressed on the surface of all mouse and human NK cells, and subpopulation of T cells. Stimulation of NK cells through NKG2D triggers cell-mediated cytotoxicity and induces the production of cytokines. NKG2D binds to family of unique ligands with structurally similar to MHC class I, however, NKG2D ligands can be up-regulated in their expression on stressed cells including tumor cells unlike conventional MHC class I molecules. Mounting evidences clearly implicate that NKG2D recognition plays an important role in tumor immune surveillance.

AREAS COVERED

While NKG2D detect for potentially dangerous cells, various inhibitory and/or escape mechanisms counteract immune surveillance system and thereby limit effective elimination of transformed tumor cells. In addition, tumors often generate an immunosuppressive microenvironment where inhibitory molecules or cytokines negatively effect the function of anti-tumor immune responses. NKG2D ligand expression can be up-regulated by transcriptional or posttranscriptional mechanisms, therefore, certain therapy targeting those regulatory mechanisms could regain the expression of NKG2D ligands on tumor cells to be detected by the host immune responses.

EXPERT OPINION

Our knowledge in the precise mechanism of anti-tumor immunity is rapidly increasing. While NKG2D is known as primary cytotoxicity receptor in NK cell activation by recognizing 'induced-self' ligands on stressed cells including tumor cells, there are increasing evidences that NKG2D recognition can result in both immune activation and immune silencing. Future combined application of conventional cancer therapy and new therapy utilizing such stress-induced recognition systems will provide a novel opportunity to control malignant tumor progression of cancer disease.

Lack of IL-7 and IL-15 signaling affects interferon-γ production by, more than survival of, small intestinal intraepithelial memory CD8+ T cells

Survival of antigen-specific CD8(+) T cells in peripheral lymphoid organs during viral infection is known to be dependent predominantly on IL-7 and IL-15. However, little is known about a possible influence of tissue environmental factors on this process. To address this question, we studied survival of memory antigen-specific CD8(+) T cells in the small intestine. Here, we show that 2 months after vaccinia virus infection, B8R(20-27) /H2-K(b) tetramer(+) CD8(+) T cells in the small intestinal intraepithelial (SI-IEL) layer are found in mice deficient in IL-15 expression. Moreover, SI-IEL and lamina propria lymphocytes do not express the receptor for IL-7 (IL-7Rα/CD127). In addition, after in vitro stimulation with B8R(20-27) peptide, SI-IEL cells do not produce high amounts of IFN-γ neither at 5 days nor at 2 months postinfection (p.i.). Importantly, the lack of IL-15 was found to shape the functional activity of antigen-specific CD8(+) T cells, by narrowing the CTL avidity repertoire. Taken together, these results reveal that survival factors, as well as the functional activity, of antigen-specific CD8(+) T cells in the SI-IEL compartments may markedly differ from their counterparts in peripheral lymphoid tissues.

Delineation of antigen-specific and antigen-nonspecific CD8(+) memory T-cell responses after cytokine-based cancer immunotherapy

Memory T cells exhibit tremendous antigen specificity within the immune system and accumulate with age. Our studies reveal an antigen-independent expansion of memory, but not naive, CD8(+) T cells after several immunotherapeutic regimens for cancer resulting in a distinctive phenotype. Signaling through T-cell receptors (TCRs) or CD3 in both mouse and human memory CD8(+) T cells markedly up-regulated programmed death-1 (PD-1) and CD25 (IL-2 receptor α chain), and led to antigen-specific tumor cell killing. In contrast, exposure to cytokine alone in vitro or with immunotherapy in vivo did not up-regulate these markers but resulted in expanded memory CD8(+) T cells expressing NKG2D, granzyme B, and possessing broadly lytic capabilities. Blockade of NKG2D in mice also resulted in significantly diminished antitumor effects after immunotherapy. Treatment of TCR-transgenic mice bearing nonantigen expressing tumors with immunotherapy still resulted in significant antitumor effects. Human melanoma tissue biopsies obtained from patients after topically applied immunodulatory treatment resulted in increased numbers of these CD8(+) CD25(-) cells within the tumor site. These findings demonstrate that memory CD8(+) T cells can express differential phenotypes indicative of adaptive or innate effectors based on the nature of the stimuli in a process conserved across species.

Tumor antigen-dependent and tumor antigen-independent activation of antitumor activity in T cells by a bispecific antibody-modified tumor vaccine

New approaches of therapeutic cancer vaccination are needed to improve the antitumor activity of T cells from cancer patients. We studied over the last years the activation of human T cells for tumor attack. To this end, we combined the personalized therapeutic tumor vaccine ATV-NDV—which is obtained by isolation, short in vitro culture, irradiation, and infection of patient's tumor cells by Newcastle Disease Virus (NDV)—with bispecific antibodies (bsAbs) binding to this vaccine and introducing anti-CD3 (signal 1) and anti-CD28 (signal 2) antibody activities. This vaccine called ATV-NDV/bsAb showed the unique ability to reactivate a preexisting potentially anergized antitumor memory T cell repertoire. But it also activated naive T cells to have antitumor properties in vitro and in vivo. This innovative concept of direct activation of cancer patients' T cells via cognate and noncognate interactions provides potential for inducing strong antitumor activities aiming at overriding T cell anergy and tumor immune escape mechanisms.

Multiple sclerosis: are protective immune mechanisms compromised by a complex infectious background?

The immunological background of multiple sclerosis (MS) manifests as an altered reactivity against a diverse range of infections, particularly with the Epstein-Barr virus. Although this could be only an epiphenomenon of a more generalised dysfunction of the immune system in MS, it is also possible that a complex infectious background forms the basis of a specific immune dysregulation finally causing the disease. It is thus suggested that the complex infectious background bears the key for an understanding of the immune pathogenesis of the disease. It appears probable that improved standards of hygiene cause regulatory defects in the immune system, allowing the abnormal expression of human endogenous retroviral (HERV) genes. On the basis of epidemiological observations we describe how a failure of expansion or an eclipse of a subfraction of self-antigen-specific CD8(+) T cells mediating immune repair, and a deleterious mode of action of HERV gene products, could underlie the pathogenesis of MS.

Melanoma, Darwinian medicine and the inner world

INTRODUCTION

A diverse range of human diseases, including allergy, asthma, autoimmune disease, cancer and chronic neurologic diseases, notably multiple sclerosis and endogenous depression, is becoming more prevalent in industrialized countries. It has been postulated that environmental factors associated with improved standards of hygiene play a leading role in this process since the immune system seems to need extrinsic challenges for its proper maturation.

THE INNER WORLD

An added dimension has now emerged--the impact on disease of the inner world, principally the numerous endogenous retroviruses (HERVs) within the human genome. Taking melanoma as an example, we propose a framework for understanding how a complex infectious and immunological background can induce or inhibit expression of a HERV-related disease process. The central role of a failure to induce or to maintain certain populations of self-specific CD8(+) T-cells mediating immune surveillance, the expression of HERV-encoded peptides on affected cells and pathological mechanisms directly attributable to HERV proteins are discussed.

CONCLUSIONS

The presented concepts explain events preceding the clinical manifestation of diseases by several years and provide a rationale for the use of currently available vaccines to protect against certain HERV-induced diseases, especially melanoma. Criteria for establishing the causal role of HERVs in a given disease are proposed.

TNFR2-deficient memory CD8 T cells provide superior protection against tumor cell growth

TNF receptor-2 (TNFR2) plays a critical role in promoting the activation and survival of naive T cells during the primary response. Interestingly, anti-CD3 plus IL-2 activated TNFR2(-/-) CD8 T cells are highly resistant to activation-induced cell death (AICD), which correlates with high expression levels of prosurvival molecules such as Bcl-2, survivin, and CD127 (IL-7Ralpha). We determined whether the resistance of activated TNFR2(-/-) CD8 T cells to AICD contributes to more effective protection against tumor cell growth. We found that during a primary tumor challenge, despite initial inferiority in controlling tumor cell growth, TNFR2(-/-) mice were able to more effectively control tumor burden over time compared with wild-type (WT) mice. Furthermore, vaccination of TNFR2(-/-) mice with recombinant Listeria monocytogenes that express OVA confers better protection against the growth of OVA-expressing E.G7 tumor cells relative to similarly vaccinated WT mice. The enhanced protection against tumor cell growth was not due to more effective activation of OVA-specific memory CD8 T cells in vaccinated TNFR2(-/-) mice. In vitro studies indicate that optimally activated OVA-specific TNFR2(-/-) CD8 T cells proliferated to the same extent and possess similar cytotoxicity against E.G7 tumor cells as WT CD8 T cells. However, relative to WT cells, activated OVA-specific TNFR2(-/-) CD8 T cells were highly resistant to AICD. Thus, the enhanced protection against E.G7 in TNFR2(-/-) mice is likely due to the recruitment and activation of OVA-specific memory TNFR2(-/-) CD8 T cells and their prolonged survival at the tumor site.

IL-15 is critical for the maintenance and innate functions of self-specific CD8(+) T cells

IL-15 is a pleiotropic cytokine involved in host defense as well as autoimmunity. IL-15-deficient mice show a decrease of memory phenotype (MP) CD8(+) T cells, which develop naturally in naïve mice and whose origin is unclear. It has been shown that self-specific CD8(+) T cells developed in male H-Y antigen-specific TCR transgenic mice share many similarities with naturally occurring MP CD8(+) T cells in normal mice. In this study, we found that H-Y antigen-specific CD8(+) T cells in male but not female mice decreased when they were crossed with IL-15-deficient mice, mainly due to impaired peripheral maintenance. The self-specific TCR transgenic CD8(+) T cells developed in IL-15-deficient mice showed altered surface phenotypes and reduced effector functions ex vivo. Bystander activation of the self-specific CD8(+) T cells was induced in vivo during infection with Listeria monocytogenes, in which proliferation but not IFN-gamma production was IL-15-dependent. These results indicated important roles for IL-15 in the maintenance and functions of self-specific CD8(+) T cells, which may be included in the naturally occurring MP CD8(+) T-cell population in naïve normal mice and participate in innate host defense responses.

Preferential development of CD4 and CD8 T regulatory cells in RasGRP1-deficient mice

RasGRP1 and Sos are two Ras-guanyl-nucleotide exchange factors that link TCR signal transduction to Ras and MAPK activation. Recent studies demonstrate positive selection of developing thymocytes is crucially dependent on RasGRP1, whereas negative selection of autoreactive thymocytes appears to be RasGRP1 independent. However, the role of RasGRP1 in T regulatory (Treg) cell development and function is unknown. In this study, we characterized the development and function of CD4(+)CD25(+)Foxp3(+) and CD8(+)CD44(high)CD122(+) Treg lineages in RasGRP1(-/-) mice. Despite impaired CD4 Treg cell development in the thymus, the periphery of RasGRP1(-/-) mice contained significantly increased frequencies of CD4(+)Foxp3(+) Treg cells that possessed a more activated cell surface phenotype. Furthermore, on a per cell basis, CD4(+)Foxp3(+) Treg cells from mutant mice are more suppressive than their wild-type counterparts. Our data also suggest that the lymphopenic environment in the mutant mice plays a dominant role of favored peripheral development of CD4 Treg cells. These studies suggest that whereas RasGRP1 is crucial for the intrathymic development of CD4 Treg cells, it is not required for their peripheral expansion and function. By contrast to CD4(+)CD25(+)Foxp3(+) T cells, intrathymic development of CD8(+)CD44(high)CD122(+) Treg cells is unaffected by the RasGRP1(-/-) mutation. Moreover, RasGRP1(-/-) mice contained greater numbers of CD8(+)CD44(high)CD122(+) T cells in the spleen, relative to wild-type mice. Activated CD8 Treg cells from RasGRP1(-/-) mice retained their ability to synthesize IL-10 and suppress the proliferation of wild-type CD8(+)CD122(-) T cells, albeit at a much lower efficiency than wild-type CD8 Treg cells.

Regulation of human DAP10 gene expression in NK and T cells by Ap-1 transcription factors

Human NKG2D/DAP10 is an activation receptor expressed by NK and subsets of T cells, whose ligands include MHC class I chain-related (MIC) protein A and protein B and UL16-binding proteins that are often up-regulated by stress or pathological conditions. DAP10 is required for NKG2D/DAP10 cell surface expression and signaling capacity. Little is known about the mechanisms that regulate DAP10 gene expression. We describe the existence of multiple transcriptional start sites upstream of DAP10 exon 1 and identify the location of the basic promoter upstream of these starting sites. The promoter is active in NK and CD8+ T cells, but not in CD4+ T cells. We demonstrate TCR-mediated up-regulation of DAP10 transcription and found that a 40 bp region within the DAP10 promoter, containing an Ap-1 binding site, is largely responsible for this increased transcription. Using pull-down and chromatin immunoprecipitation assays, we show that the DAP10 promoter interacts with Ap-1 transcription factors in primary CD8+ T and NK cells in vitro and in vivo. Overexpression of c-Jun or c-Fos in NK and T cells led to enhanced DAP10 promoter activity and DAP10 protein expression. Taken together, our data indicate that Ap-1 is an important transcription factor for regulating DAP10 gene expression in human NK and T cells, and that Ap-1 plays a key role in the transactivation of DAP10 promoter following TCR stimulation.

NKG2D receptor signaling enhances cytolytic activity by virus-specific CD8+ T cells: evidence for a protective role in virus-induced encephalitis

Inoculation with the neurotropic JHM strain of mouse hepatitis virus (JHMV) into the central nervous system (CNS) of mice results in an acute encephalitis associated with an immune-mediated demyelinating disease. During acute disease, infiltrating CD8(+) T cells secrete gamma interferon (IFN-gamma) that controls replication in oligodendrocytes, while infected astrocytes and microglia are susceptible to perforin-mediated lysis. The present study was undertaken to reveal the functional contributions of the activating NKG2D receptor in host defense and disease following JHMV infection. NKG2D ligands RAE-1, MULT1, and H60 were expressed within the CNS following JHMV infection. The immunophenotyping of infiltrating cells revealed that NKG2D was expressed on approximately 90% of infiltrating CD8(+) T cells during acute and chronic disease. Blocking NKG2D following JHMV infection resulted in increased mortality that correlated with increased viral titers within the CNS. Anti-NKG2D treatment did not alter T-cell infiltration into the CNS or the generation of virus-specific CD8(+) T cells, and the expression of IFN-gamma was not affected. However, cytotoxic T-lymphocyte (CTL) activity was dependent on NKG2D expression, because anti-NKG2D treatment resulted in a dramatic reduction in lytic activity by virus-specific CD8(+) T cells. Blocking NKG2D during chronic disease did not affect either T-cell or macrophage infiltration or the severity of demyelination, indicating that NKG2D does not contribute to virus-induced demyelination. These findings demonstrate a functional role for NKG2D in host defense during acute viral encephalitis by selectively enhancing CTL activity by infiltrating virus-specific CD8(+) T cells.

Inhibition of prostate carcinogenesis by combined active immunoprophylaxis

The aim of this study is to investigate whether an active immunoprophylactic approach combining specific antigens and adjuvant stimuli would be able to inhibit prostate carcinogenesis in transgenic TRAMP mice. A vaccine consisting of allogeneic large T antigen (TAg)-positive SV40-transformed cells combined with systemic recombinant IL-12 was administered to TRAMP mice, starting from when they were still tumor-free at 5-6 weeks of age. The combined vaccine significantly inhibited prostate carcinogenesis, giving a more than doubled median latency time of prostatic tumors (53 weeks in comparison to 26 weeks in control mice). Vaccination with cells alone or IL-12 treatment alone was poorly effective (median latency of 30 and 39 weeks, respectively). The combined vaccine induced a very high CD4 response biased toward the Th1 pathway, with the induction of a humoral response that included TAg-specific antibodies. Therefore, such active immunoprophylactic approach based on the combination of allogeneic SV40 TAg-positive cells and systemic administration of recombinant IL-12 significantly delayed autochthonous urogenital carcinogenesis driven by SV40 TAg in TRAMP mice.

Self-antigen maintains the innate antibacterial function of self-specific CD8 T cells in vivo

Self-specific CD8 T cells, which are selected by high-affinity interactions with self-Ags, develop into a lineage distinct from conventional CD8 T cells. We have previously shown that these self-specific cells acquire phenotypic and functional similarities to cells of the innate immune system including the expression of functional receptors associated with NK cells. In this study, we show that these self-specific cells have the ability to produce large amounts of IFN-gamma in response to infection with Listeria monocytogenes in a bystander fashion. The rapid production of IFN-gamma is associated with a dramatic reduction in the number of viable bacteria at the peak of infection. Self-specific CD8 T cells provide only marginal innate protection in the absence of self-Ag; however, the presence of self-Ag dramatically increases their protective ability. Exposure to self-Ag is necessary for the maintenance of the memory phenotype and responsiveness to inflammatory cytokines such as IL-15. Significantly, self-specific CD8 T cells are also more efficient in the production of IFN-gamma and TNF-alpha, thus providing more cytokine-dependent protection against bacterial infection when compared with NK cells. These findings illustrate that self-reactive CD8 T cells can play an important innate function in the early defense against bacterial infection.

IL-2 in vivo activities and antitumor efficacy enhanced by an anti-IL-2 mAb

IL-2 is a potent immunostimulant and has been tested for clinical use, including in immunotherapy for cancers and HIV infection. Here we show that a widely used neutralizing anti-murine IL-2 mAb (S4B6) exhibits unexpected activities that enhance the treatment effects of IL-2 in vivo. Coinjection of the anti-IL-2 mAb with a plasmid carrying murine IL-2 cDNA significantly increased the serum IL-2 levels and induced a substantial increase in the division of CD8+ T and NK1.1(high) cells in vivo. Injection of the mAb premixed with recombinant murine IL-2 showed the same enhanced effect. A 5-day treatment with the anti-IL-2 mAb alone gradually increased the CD44(high)CD8+ population, and the increased population was maintained for >300 days, suggesting that the mAb can gradually maintain and potentially enhance the bioactivity of endogenous IL-2 for extended periods. Furthermore, combined treatment with the anti-IL-2 mAb plus the IL-2 plasmid markedly enhanced Ag-specific CTL activity in vivo and partially protected mice from tumor metastasis to the lungs, compared with the anti-IL-2 mAb or IL-2 plasmid alone. These results demonstrated IL-2-enhancing effects of the anti-IL-2 mAb in vivo and suggest that combining a neutralizing anti-IL-2 Ab with IL-2 gene delivery might be used effectively to enhance IL-2 functions in clinical applications.

ITK and IL-15 support two distinct subsets of CD8+ T cells

CD8(+) T cells are commonly divided into naïve CD44(lo)CD122(lo) and "memory phenotype" CD44(hi)CD122(hi) cells. Here we show data suggesting that these two cell populations represent independent CD8(+) T cell subsets. Whereas IL-15(-/-) mice lack CD44(hi)CD122(hi) CD8(+) T cells, mice deficient in the kinase ITK lack CD44(lo)CD122(lo) cells among CD8(+) T cells. The same defects were observed during thymus development. CD44(hi)CD122(hi) cells were found among double-positive thymocytes and increased in frequency during CD8 development in wild-type mice. At the mature stage, IL-15(-/-) mice harbored virtually no CD44(hi)CD122(hi) CD8(+) thymocytes. In contrast, ITK(-/-) mice lacked CD44(lo)CD122(lo) CD8(+) cells at this stage. We generated mice with genetic deletions in both IL-15 and ITK and observed a severe reduction of all CD8(+) T cells. The two CD44(lo)CD122(lo) and CD44(hi)CD122(hi) CD8(+) T cell subsets differed in the periphery in that natural killer (NK) receptor expression was found only on CD44(hi)CD122(hi) CD8(+) T cells. This expression was paralleled by their ability to respond to both T cell receptor and NK receptor engagements. In contrast, CD44(lo)CD122(lo) CD8(+) T cells mounted stronger responses to T cell receptor stimulation but failed to recognize NK receptor ligands. Thus, whereas ITK-dependent CD44(lo)CD122(lo) CD8(+) T cells appear to represent conventional CD8(+) T cells, IL-15-dependent CD44(hi)CD122(hi) CD8(+) T cells may have functions in both adaptive and innate immunity.

The assembly of diverse immune receptors is focused on a polar membrane-embedded interaction site

The majority of receptors responsible for activation of distinct cell types within the immune system assemble with dimeric signaling modules through interaction of a basic transmembrane residue with a pair of acidic residues of the signaling dimer. Because assembly of other membrane proteins requires specific interactions along extended stretches of transmembrane helices, we examined how transmembrane sequences flanking the polar interaction site contribute to assembly for three receptors that associate with different signaling modules—the natural killer cell receptors KIR and NKG2D and the Fc receptor for IgA, FcαRI. The KIR and NKG2D receptors assembled with the DAP12 and DAP10 dimers, respectively, even when the entire KIR or NKG2D transmembrane domains were replaced by polyleucine sequences with a properly positioned basic residue. In contrast, a high degree of specificity for the basic side chain could be observed because the KIR–DAP12 and FcαRI–Fcγ interactions favored lysine or arginine, respectively. Steric hindrance among incompatible extra-membranous domains and competition for signaling modules also contributed to specificity of assembly. These results demonstrate that these interactions are focused on the polar site created by three ionizable transmembrane residues, and explain how the DAP12 and Fcγ signaling modules can assemble with large, non-overlapping sets of receptors that have highly divergent transmembrane sequences.

By mutating all residues but one to polyleucine in diverse immune receptors, the authors find that only one polar interaction embedded in the membrane is required for their specificity and assembly.

The role of CD8 T cells in innate immunity and in antigen non-specific protection

The role of CD8 T cells in adaptive immune responses is well understood. These lymphocytes respond through their T cell receptors to diverse antigens presented by MHC class I molecules by proliferating, secreting cytokines and chemokines, and directly lysing infected cells. Recently, a role for CD8 T cells in the innate immune response has become apparent. Independent of T cell receptor ligation, CD8 T cells can mount a response against pathogens by secreting cytokines and can defend against tumors by directly killing transformed cells. This innate response has been shown to be beneficial in controlling several types of bacterial infections. However, a subset of CD8 T cells that have innate non-antigen-specific capabilities has been implicated in self-reactivity, which could lead to autoimmunity.

Thymus-dependent memory phenotype CD8 T cells in naive B6.H-2Kb-/-Db-/- animals mediate an antigen-specific response against Listeria monocytogenes

B6.H-2Kb-/-Db-/- (DKO) mice have greatly reduced numbers of mature CD8alphabeta T cells in their periphery. However, these non-class Ia-selected CD8alphabeta T cells are able to mediate immune responses to a number of pathogens. Approximately 60% of the CD8alphabeta T cells in the spleen and peripheral lymph nodes of naive DKO mice display a memory (CD44high) phenotype. To investigate the origins of these non-class Ia-selected CD8alphabetaCD44high cells, we traced the phenotype of recent thymic emigrants and found that most were CD44low. We also determined whether their appearance was thymus dependent and found that only a small percentage of non-class Ia-selected CD8alphabetaCD44high cells develop in a thymus-independent pathway. Functionally, CD8alphabetaCD44high cells from DKO mice are able to secrete IFN-gamma in response to IL-12 and IL-18 in the absence of cognate Ag. When challenged with anti-CD3 in vivo, nearly half of these cells produce IFN-gamma within 3 h. When purified CD8alphabetaCD44high cells from Thy1.2.DKO mice were transferred into Thy1.1 DKO recipients and then challenged with Listeria monocytogenes, an Ag-specific anti-L. monocytogenes response was observed 6 days later. Our data suggest that non-class Ia-selected CD8alphabetaCD44high cells in naive animals can respond rapidly to Ag and play a role in the innate as well as the early phase of the acquired immune response.

T Cells Gene-engineered with DAP12 Mediate Effector Function in an NKG2D-dependent and Major Histocompatibility Complex-independent Manner

NKG2D is an important activating/co-stimulatory receptor harnessed by NK and T cells in immune surveillance. In contrast to NK cells, T cells fail to express the activation-signaling molecule DAP12 even when activated and, therefore, ligation of NKG2D alone is insufficient to induce T cell cytolytic function. To test whether we could endow T cells with NK cell-like effector function, we have engineered DAP12 into T cells by retroviral transduction (T-DAP12). T-DAP12 cells were demonstrated to specifically secrete interferon-gamma following receptor ligation and to mediate potent and specific lysis of the NKG2D ligand (NKG2D-L) (Rae-1beta) expressing MHC class I-deficient and class I-sufficient tumors. To circumvent the inability of T-DAP12 cells to proliferate following NKG2D ligation by Rae-1beta expressing tumors, DAP12 was engineered into OT-1 cells with an endogenous T cell receptor specific for chicken ovalbumin peptide (amino acids 257-264). Importantly, following a period of proliferation through endogenous T cell receptor ligation, OT-1-DAP12 cells retained specificity against NKG2D-L expressing major histocompatibility complex class I-deficient tumor. In adoptive transfer experiments, T-DAP12 cells enhanced the survival of NK cell-depleted RAG-1-deficient mice inoculated with RMA-S-Rae-1beta but not parental RMA-S tumors. Overall, this study demonstrated the significant potential of suppressing tumors and other cellular targets expressing NKG2D-L by endowing T cells with innate NK cell-like function.

IL-2 responsiveness of CD4 and CD8 lymphocytes: further investigations with human IL-2Rbeta transgenic mice

Responsiveness to IL-2 varies from one lympho-mononuclear subset to another. NK lymphocytes and monocytes spontaneously respond to IL-2 whereas it is generally accepted that T and B lymphocytes need to be activated to fully acquire this competence. To further investigate this phenomenon, we studied human IL-2Rbeta (hIL-2Rbeta) transgenic mice constitutively expressing heterospecific, intermediate-affinity IL-2R (hIL-2Rbeta/mouse IL-2Rgamma(c)). We noted that the B lymphocytes and monocytes from spleens of these hIL-2Rbeta transgenic animals failed to grow when cultured in IL-2-containing medium. Under the same experimental conditions, CD4 lymphocytes survived, again without growth, whereas CD8 lymphocytes and NK cells were able to proliferate and develop potent LAK cytotoxicity. The properties of these CD4 and CD8 lymphocytes were then compared after purification. Both subsets expressed functional IL-2R able to induce global protein phosphorylation and, more precisely, signal transducer and activation of transcription 5 and Erk phosphorylation. Therefore, the differential growth potential of these CD4 and CD8 lymphocytes cannot be explained by the lack of IL-2R-dependent early signaling events. When the entrance of purified CD4 and CD8 lymphocytes into the cell cycle was analyzed, we found that the CD4 lymphocytes were unable to enter the G1 phase in the absence of anti-CD3 stimulation. This correlates with the effect of IL-2 on cyclin-dependent kinase inhibitor p27(kip1). In CD4 lymphocytes, IL-2 does not affect p27(kip1) expression. But in CD8 lymphocytes, IL-2 down-modulates p27(kip1). These results indicate that, aside from IL-2R expression and function, IL-2 responsiveness is also controlled by lineage-specific mechanisms.

Requirement of homotypic NK-cell interactions through 2B4(CD244)/CD48 in the generation of NK effector functions

2B4 belongs to the CD2 subset of the IgG family of receptors. Members in this family have been shown to function as coreceptors via homophilic or heterophilic interactions. Both 2B4 and CD2 bind to CD48, another member of this family. Because all 3 molecules are expressed on natural killer (NK) cells, it raises a possibility that the binding of 2B4 and CD2 to CD48 among NK cells may have functional consequences. Using specific monoclonal antibodies and gene-deficient NK cells, we found that 2B4/CD48, but not CD2/CD48, interaction is essential for IL-2-driven expansion and activation of murine NK cells. In the absence of 2B4/CD48 interaction, NK cytotoxicity and IFN-gamma secretion on tumor target exposure is severely impaired. Impaired activation of NK cells in 2B4-deficient mice was also demonstrated by poor NK-mediated clearance of syngeneic tumor cells in these mice. Functional impairment of NK cells in the absence of 2B4/CD48 interactions was accompanied by defective calcium signaling, suggesting that the early signaling pathway of NK receptors is inhibited. Finally, homotypic interactions among NK cells through 2B4/CD48 was visualized by specific localization of GFP-tagged 2B4 onto NK-NK conjugation sites. Thus, these data identify a novel mechanism whereby NK effector function is regulated via homotypic 2B4/CD48 interactions.

Engagement of NKG2D by cognate ligand or antibody alone is insufficient to mediate costimulation of human and mouse CD8+ T cells

CD8+ T cells require a signal through a costimulatory receptor in addition to TCR engagement to become activated. The role of CD28 in costimulating T cell activation is well established. NKG2D, a receptor found on NK cells, CD8+ alphabeta-TCR+ T cells, and gammadelta-TCR+ T cells, has also been implicated in T cell costimulation. In this study we have evaluated the role of NKG2D in costimulating mouse and human naive and effector CD8+ T cells. Unexpectedly, in contrast to CD28, NKG2D engagement by ligand or mAb is not sufficient to costimulate naive or effector CD8+ T cell responses in conventional T cell populations. While NKG2D did not costimulate CD8+ T cells on its own, it was able to modify CD28-mediated costimulation of human CD8+ T cells under certain contitions. It is, therefore, likely that NKG2D acts as a costimulatory molecule only under restricted conditions or requires additional cofactors.

The low affinity Fc receptor for IgG functions as an effective cytolytic receptor for self-specific CD8 T cells

We have recently described a population of self-Ag-specific murine CD8(+) T cells with a memory phenotype that use receptors of both the adaptive and innate immune systems in the detection of transformed and infected cells. In this study we show that upon activation with IL-2 with or without Ag, between 10 and 20% of the activated self-specific CD8(+) T cells express the low affinity FcR for IgG. By contrast, all IL-2-activated NK cells express high levels of this FcR. The FcR comprises the FcgammaRIIIalpha and FcRgamma subunits. However, the FcRgamma subunit also associates with the CD3 complex, and this association probably contributes to the low expression of FcR in activated cells. Although the FcR is expressed at a low level on activated self-specific CD8(+) T cells, it functions very efficiently as a cytolytic receptor in ADCC. FcR-dependent killing occurred in the absence of TCR stimulation, but could be augmented by concurrent stimulation of the TCR. In addition to mediating ADCC, engagement of the FcR on self-specific CD8(+) T cells results in the production of both IFN-gamma and TNF-alpha. This is the first report of an activating FcR on self-specific murine CD8(+)alphabeta TCR(+) T cells and establishes the importance of innate immune system receptors in the function of these self-specific CD8(+) T cells.

CD1d-unrestricted human NKT cells release chemokines upon Fas engagement

Attempts at inducing allograft immune privilege by enforced Fas ligand expression have shown accelerated rejection mediated by neutrophils. While it has been proposed that Fas ligand was directly chemotactic toward neutrophils, several lines of evidence argue for an indirect recruitment mechanism. This question was addressed by using in vitro migration assays that used highly purified human leukocyte subsets. Granulocytes did not migrate in response to Fas engagement and required the presence of T cells expressing several natural killer (NK) cell markers. These rare CD8 memory T cells expressed T and NK cell markers and were not restricted to CD1d, showing that they are distinct from conventional natural killer T (NKT) cells. These cells were able to kill both NK-sensitive and -insensitive targets and secreted several CC and CXC chemokines active toward granulocytes, monocytes, and NK cells upon Fas engagement. Chemotactic factor release depended on caspase activity, in the absence of NKT cell apoptosis. The ability of CD1d-unrestricted NKT cells to recruit innate immune system cells might play a role in cancer cell eradication and contribute to inflammatory diseases.

Potential Role of Natural Killer Cell Receptor-Expressing Cells in Immunotherapy for Leukemia

Natural killer cell receptor (NKR)-expressing cells have cytolytic activity against leukemic cells, and solid tumor cells escape from T-cell recognition because of the low expression levels of class I HLA molecules in both allogeneic and autologous settings. This characteristic feature of NK cell recognition of target cells in contrast with that of T-cells provides a strategy to overcome tolerance in the tumor-bearing host. Furthermore, inhibitory NKR-expressing cells may have cytolytic activity and immunoregulatory functions. Several methods can be used to expand NKR-expressing cells for adoptive immunotherapy for leukemia and other malignant diseases. We review recent developments in the biology and clinical application of NKR-expressing cells, such as NK cells, lymphokine-activated killer cells, cytokine-induced killer cells, NKT cells, and other NKR-expressing cells.

Self-reactive memory-phenotype CD8 T cells exhibit both MHC-restricted and non-MHC-restricted cytotoxicity: a role for the T-cell receptor and natural killer cell receptors

We have recently shown that interleukin-2 (IL-2)-activated CD8(+)CD44(hi) cells from normal mice express both adaptive and innate immune system receptors and specifically kill syngeneic tumor cells, particularly those that express NKG2D ligands. Here we show that CD8+ T cells from antigen-expressing H-Y T-cell receptor (TCR) transgenic mice also exhibit characteristics of both T cells and natural killer (NK) cells. Interaction with cognate self-antigen was required for the optimal expansion of these cells in peripheral lymphoid tissues. Although these cells possess a higher activation threshold relative to naive T cells, they can be activated by cytokine alone in vitro. They also undergo bystander proliferation in response to a bacterial infection in vivo. Interestingly, upon activation, the cells express the NKG2D receptor as well as the DNAX activation protein 12 (DAP12) adaptor protein. We provide evidence that NKG2D can act additively with the TCR in the killing of target cells, and it can also function as a directly activating receptor in non-major histocompatibility complex (MHC)-restricted killing of target cells. These properties of CD8+ T cells from H-Y TCR transgenic mice are remarkably similar to CD8(+)CD44(hi) cells that are found in normal mice. The H-Y TCR transgenic mice provide a well-defined system for characterizing the developmental biology and function of these cells.