Immunology: Paper alert

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Immunology Paper alert A selection of interesting papers that were published in the two months before our press date in major journals most likely to report significant results in immunology. • ••

of special interest of outstanding interest

Current Opinion in Immunology 2001, 13:511–520

Contents (chosen by) 511 Antigen processing and recognition (Elliott) 512 Innate immunity (Bonneville) 512 Lymphocyte development (Kruisbeek) 513 Tumour immunology (Walker) 514 Lymphocyte activation and effector functions (Essayan) 515 Immunity to infection (Glaichenhaus and Vyakarnam) 517 Immunogenetics (Casanova) 517 Immunotherapy (Liu) 518 Transplantation (Auchincloss, Waneck and LeGuern) 519 Allergy and hypersensitivity (Akdis) 520 Autoimmunity (Green)

Antigen processing and recognition Selected by Tim Elliott University of Southampton, Southampton, UK e-mail: [email protected]

• IFN-γγ affects both the stability and the intracellular transport of class I MHC complexes. Fromm SV, Ehrlich R: J Interferon Cytokine Res 2001, 21:199-208. Significance: Selection of high-affinity peptide epitopes capable of stabilising MHC class I molecules at the cell surface, from an internal pool of peptides with diverse binding affinities, is an important principle in the presentation of antigens to cytotoxic T cells. It is likely to influence the longevity of the immunostimulatory MHC−peptide ligand on an antigen-presenting cell and consequently the repertoire of presentable epitopes. This paper shows that treatment of antigen-presenting cells with the inflammatory cytokine IFN-γ may enhance T cell responses by increasing the cell surface expression of stable MHC-class-I−peptide complexes. Findings: Treatment of cells with IFN-γ increased the expression of TAP, LMP, β2m and MHC class I heavy chain 2−4-fold, and cell surface expression of MHC class I molecules by 3−4-fold. The stability of cell surface MHC class I molecules was assessed by FACS over four hours and was shown to be greater for IFN-γ-treated cells. Although it was not always easy to see from the data presented, the authors indicate that the rate at which assembled heavy-chain− β2m complexes leave the ER and travel to the cell surface was slower in IFN-γ-treated cells. The authors argue that IFN-γ has a general retarding effect on trafficking from the ER to the medial Golgi, which results in more-rigorous quality control in the ER and editing of the peptide repertoire in favour of high-affinity peptides.

• Discrete cleavage motifs of constitutive and immunoproteasomes revealed by quantitative analysis of cleavage products. Toes REM, Nussbaum AK, Degermann S, Schirle M, Emmerich NPN, Kraft M, Laplace C, Swinderman A, Dick TP, Muller J et al.: J Exp Med 2001,194:1-12. Significance: The major cytosolic protease in mammalian cells (the proteasome) generates peptides for presentation to cytotoxic T lymphocytes. ‘Constitutive’ proteasomes undergo a change in their subunit structure upon IFN-γ stimulation, giving rise to the ‘immunoproteasome’. To date, the significance of this has been obscure. The study shows that the immunoproteasome generates a partially overlapping but different repertoire of peptides which influences T cell responses. Findings: Constitutive proteasomes from LMP2,7−/− cells and immunoproteasomes from a related EBV-transformed cell line were exposed to the substrate enolase 1 for 48 hours. The degradation products were analysed by HPLC followed by MALDITOF-MS (which is not quantitative) and Edman degradation (which is quantitative) in order to compile a digestion map. Of the cleavages generated by the constitutive proteasome, 50% are not made by the immunoproteasome. Of cleavages generated by the immunoproteasome, 25% were found for the constitutive proteasome. Of those generated by the constitutive proteasome, 30% were identical to those for the immunoproteasome. Quantitation of the generated peptides allowed the most frequently used sites to be mapped and hence the characteristics of cleavage sites preferred by the constitutive proteasomes and immunoproteasomes could be compared. Both of them liberated peptides of between seven and nine amino acids. Both preferred a scissile bond between leucine at P1 and alanine at P1′ with aspartic acid (D) at P2′. The preference for leucine at P1 was stronger for the immunoproteasome, reflecting its increased chymotryptic activity. The constitutive proteasome disfavoured serine at P3, lysine at P1 and lysine at P2′. The immunoproteasome disfavoured isoleucine, leucine and valine at P1′. LMP7−/− mice (i.e. mice lacking LMP7 but with normal LMP2) responded to wildtype cells of the same genetic background (in both skin-graft and mixed-lymphocyte-culture experiments) but not vice versa. This was further indication that the immunoproteasome generates new peptides that are not normally made by the LMP7−/− mice. • ER aminopeptidases generate a unique pool of peptides for MHC class I molecules. Serwold T, Gaw S, Shastri N: Nat Immunol 2001, 2:644-651. Significance: Amino-terminal trimming of precursor peptide epitopes transported into the ER by TAP has been demonstrated but the physiological significance of this was hitherto unknown. This paper identifies an inhibitable N-aminopeptidase activity and shows for the first time that ER trimming contributes to the generation of an optimal repertoire of peptides for many MHC class I molecules and, for those that bind to peptides with proline close to the amino terminus, ER trimming may be obligatory for expression. Findings: Using precursor peptides expressed from transfected minigenes and targeted to the ER with a leader sequence, and a cellular readout for the generation for the optimal sequence, the authors show that proline added immediately to the amino terminus of the epitope blocked trimming due to the inability of the

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aminopeptidase to cleave X−P. H2-Ld binds to peptides with an X−P−Xn motif, as do 20% of all MHC molecules. Leucinethiol (which was shown to be a selective and potent inhibitor of microsomal immunoproteases, including N-aminopeptides) blocked Ld expression by 80% in P815 cells treated for 13 hours. It inhibited Dd by 40% and Kd by 35%. Neither of these alleles binds peptides with an X−P−Xn motif. It inhibited to varying degrees the presentation of three out of nine Kb- or Db-restricted T cell hybridomas and enhanced two out of nine, indicating that ER aminopeptidases may be involved in destroying some epitopes. Inhibition of presentation of specifically targeted amino-extended epitope precursors was also observed. • Structural features of nonpeptide prenyl pyrophosphates that determine their antigenicity for human γδ T cells. Morita CT, Lee HK, Wang H, Hongmin L, Mariuzza A, Tanaka Y: J Immunol 2001, 167: 36-41. Significance: γδ T cells recognise nonpeptide antigens and play an important role in immunity to infection and to tumours; Vγ2Vδ2TCR-bearing cells expand to very high levels in the peripheral blood of humans in response to many different bacterial and protozal antigens. This paper identifies the exact structural features of prenyl pyrophosphate (pp) recognised by these cells and proposes a binding site for pp in the TCR. Findings: Using chemical analogues of pp, the authors found that the core antigenic unit was isoprenyl pyrophosphate, with ethylphosphate being the minimal antigenic unit. The first alkyl chain was key to recognition. Groups such as nucleotides could be tolerated when added to the pyrophosphate unit. Saturated carbon chains longer than two were not active as antigens; nor were aromatic substitutions but, when unsaturated chains were tested, isoprenyl groups of up to 16 carbons (geranylgeranyl) were recognised, but at a much reduced level (two orders of magnitude lower). The sequence comparison of Vγ2Vδ2 TCRs studied to date indicated a conserved CDR3 length, a conserved lysine in the Jγ1.2 region and a conserved hydrophobic residue in the δ2 CDR3. Further modelling of the Vβ2Vδ2 TCR led the authors to suggest that three conserved lysine residues in the CDR2 of δ2 were important in binding the pyrophosphate group and that a hydrophobic pocket created between the Vγ2 CDR2 and Vδ2 CDR3 could accommodate the isoprenyl chains.

Innate immunity Selected by Marc Bonneville Institut de Biologie, Nantes, France e-mail: [email protected]

•• TREM-1 amplifies inflammation and is a crucial mediator of septic shock. Bouchon A, Facchetti F, Weigand MA, Colonna M: Nature 2001, 410:1103-1107. Significance: This study describes a novel receptor on myeloid cells that plays a major role in acute inflammatory responses to bacteria and fungi. Targeting this receptor could be a new therapeutic tool for the treatment of septic shock. Findings: This group recently identified a triggering receptor on neutrophils and monocytes, termed TREM-1. Here they show that TREM-1 expression is upregulated on monocytes and neutrophils by extracellular bacteria in vitro, and on peritoneal neutrophils of patients with microbial sepsis. TREM-1 amplifies the inflammatory response of neutrophils to microbial products. Furthermore, blockade of TREM-1 protects mice from

LPS-induced shock and septic shock in two models of microbial peritonitis and sepsis. •• Vital involvement of a natural killer cell activation receptor in resistance to viral infection. Brown MG, Dokun AO, Heusel JW, Smith HRC, Beckman DL, Blattenberger EA, Dubbelde CE, Stone LR, Scalzo AA, Yokoyama WM: Science 2001, 292:934-937. •• Murine cytomegalovirus is regulated by a discrete subset of natural killer cells reactive with monoclonal antibody to Ly49H. Daniels KA, Devora G, Lai WC, O’Donnell CL, Bennett M, Welsh RM: J Exp Med 2001, 194:29-44. Significance: These two studies provide new, important insights into the mechanism of viral control by NK cells. They also show for the first time that discrete NK cell subsets can fulfil distinct functions in vivo, thus suggesting an unexpected resemblance between NK cells and conventional lymphoid effectors of adaptive immunity. Findings: Susceptibility of some mouse strains to infection by murine cytomegalovirus (MCMV) was previously shown to be controlled by a single autosomal dominant locus, termed Cmv1. Brown et al. provide strong genetic evidence that susceptibility to CMV infections is due to deficient expression in Ly49H, an activation receptor expressed on a subset of NK cells. Furthermore, both studies show that in vivo treatment with monoclonal antibodies specific for Ly49H dramatically impairs control of MCMV replication by resistant strains, thus demonstrating a key contribution of Ly49H+ NK cells in the control of this viral infection. • Staphylococcus aureus resistance to human defensins and evasion of neutrophil killing via the novel virulence factor MprF is based on modification of membrane lipids with L-lysine. Peschel A, Jack RW, Otto M, Colling LV, Staubitz P, Nicholson G, Kalbacher H, Nieuwenhuizen WF, Jung G, Tarkowski A: J Exp Med 2001, 193:1067-1076. Significance: This study demonstrates a key role for defensinmediated resistance in the pathogenicity of S. aureus and identifies a new virulence factor that could represent an interesting therapeutic target against multidrug-resistant bacteria. Findings: Defensins, which are antimicrobial peptides produced by epithelial cells and phagocytes, contribute to the innate defence of mucosa and skin against bacterial infections. S. aureus resists many antimicrobial peptides, including α- and β-defensins, by virtue of an as-yet-unknown mechanism. This study describes a novel staphylococcal gene, termed mprF, whose inactivation leads to increased sensitivity to defensins and other cationic antibacterial peptides, to increased susceptibility to neutrophil killing in vitro and to attenuated virulence in mice. Evidence is provided that MprF modulates the electrostatic properties of the cell envelope through lysination of phospholipids, thus affecting binding of cationic antibacterial peptides.

Lymphocyte development Selected by Ada Kruisbeek The Netherlands Cancer Institute, Amsterdam, The Netherlands e-mail: [email protected]

• Negative selection at the pre-BCR checkpoint elicited by human µ heavy chains with unusual CDR3 regions. Minegishi Y, Conley ME: Immunity 2001, 14:631-641.

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Significance: Once correctly rearranged immunoglobulin µ heavy chains have been formed in pro-B cells, they are expressed on the cell surface together with the surrogate light chain and the Igα−Igβ signal transduction module. This so-called pre-BCR triggers essential signals for survival and expansion, and orchestrates the transition from the pro-B to the pre-B cell stage. In the process of evaluating early stages of B cell differentiation in patients with defects in B cell development, these authors discovered an unusual group of VDJ rearrangements that encode in-frame µ heavy chains. These can be expressed on the cell surface without surrogate or conventional light chains, but do not support transition from the pro-B to the pre-B cell stage. Findings: Around 9% of in-frame µ heavy chain transcripts found in normal human pro-B cells encode intact heavy-chain proteins that are expressed on the surface in the absence of surrogate light chains. Such transcripts exhibit preferential usage of certain VH genes, a significantly higher proportion of basic amino acids in the CDR3 region and under-represented D-region reading frames. Since these aberrant µ heavy chains are not found in preB cells or mature B cells, it is proposed they induce negative selection at the pro-B cell stage. This remains to be confirmed for pro-B cells (only transfection experiments that confirm this notion with Jurkat T cell lines are performed), but the findings suggest a novel quality-control mechanism for B cell development. • Essential requirement for c-kit and common γ chain in thymocyte development cannot be overruled by enforced expression of Bcl-2. Rodewald H-R, Waskow C, Haller C: J Exp Med 2001, 193:1431-1437. Significance: The receptor tyrosine kinase c-kit and the common cytokine-receptor γ chain (γc) provide essential synergistic survival signals in pro-T cells. As a consequence, the thymus of mice lacking both these receptors is alymphoid, but the downstream events triggered by these receptors remain to be fully defined. Upregulation of the anti-apoptotic mediator Bcl-2 has been suggested to be one mechanism through which c-kit and γc receptors act, but conflicting results have been obtained so far. The present study evaluates the effects of transgene-driven expression of Bcl-2 in mice lacking c-kit, γc or both. Findings: First, the authors validate whether the Bcl-2 transgene functions as a thymocyte survival factor ex vivo in c-kit- or γc-mutant mice (double mutants could not be tested, since they are totally alymphoid). Indeed, Bcl-2 does promote survival both of total thymocytes and of pro-thymocytes ex vivo. Still, Bcl-2 transgene expression in vivo was unable to rescue thymic cellularity in either the single or double c-kit/γc-mutant mice. Also, the phenotypic block at the CD25+CD44+/− stage of development is not released. The authors did notice a remarkably broad range in thymic cellularity, with the numbers of thymocytes spread over more than two logs. This phenotypic heterogeneity (probably a result of modifier genes) may account for the discrepancies between this and other studies. Nevertheless, the data show that Bcl-2-mediated survival signals are unable to substitute for crucial c-kit and γc signals in pro-thymocyte development. • T cell-specific loss of Pten leads to defects in central and peripheral tolerance. Suzuki A, Yamaguchi MT, Ohteki T, Sasaki T, Kaisho T, Kimura Y, Yoshida R, Wakeham A, Higuchi T, Fukumoto M et al.: Immunity 2001, 14:523-534. Significance: When thymocytes with self-reactive TCRs interact with intrathymic self-antigens, they undergo apoptosis. Self-reactive thymocytes that escape negative selection in the thymus and migrate to the peripheral lymphoid organs may also

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undergo clonal deletion, but the mechanisms underlying both thymic and peripheral tolerance remain to be fully defined. Here, the tumor-suppressor gene PTEN is implicated in the regulation of both T cell tolerance and T cell homeostasis. It was already known that PTEN regulates PKB/Akt activation and apoptosis in embryonic fibroblasts and that PTEN is constitutively expressed in T cells. Also, mice heterozygous for a null mutation in PTEN (homozygous PTEN-deficiency is embryonically lethal) often develop lymphoid hyperplasia, and sometimes T cell lymphomas and autoimmunity. The present study provides a better understanding of these findings. Findings: Using the Cre-LoxP system, mice with a T cell specific deletion in PTEN were generated. Apart from developing T cell lymphomas, these mice exhibit defects in both thymic and peripheral tolerance, as shown in TCR-transgenic mice and superantigen-induced deletion experiments. A molecular explanation for this observation is found: defects in the in vitro apoptotic response of thymocytes and peripheral T cells occur, as does inappropriate activation of the PI3K/PKB/Akt pathway. It remains to be seen whether the dramatic increase in the size of the DP compartment in the PTEN-deficient thymus also represents, as the authors suggest, a manifestation of a defect in negative selection. A plausible alternative explanation would be the accelerated or exaggerated transition from the DN to the DP stage. This might occur if the survival signals triggered by the pre-TCR are also regulated by PTEN; that possibility remains to be tested.

Tumour immunology Selected by Paul R Walker University Hospital Geneva, Geneva, Switzerland e-mail: [email protected]

•• Roles of tumour localization, second signals and cross priming in cytotoxic T-cell induction. Ochsenbein AF, Sierro S, Odermatt B, Pericin M, Karrer U, Hermans J, Hemmi S, Hengartner H, Zinkernagel RM: Nature 2001, 411:1058-1064. Significance: This major publication brings together data obtained from multiple tumour models to address an issue seldom tackled by other groups, namely tumour localisation, and to force a reassessment of other concepts (co-stimulation and cross-priming) that are often investigated, but for which alternative interpretations are possible. Hopefully these results will stimulate an equally rigorous examination of these processes by other groups using different models and ultimately be used in the study of human cancer. Findings: Ochsenbein et al. used MC57G and D2 fibrosarcomas, EL4 lymphoma, Lewis lung carcinoma, B16 melanoma and P815 mastocytoma, all transfected with antigens derived from lymphocytic choriomeningitis virus. Cell lines growing as solid tumours were in some cases transplanted as fragments, facilitating the study of responses to tumours remaining strictly outside lymphoid organs. In such cases, even antigenic, B7-expressing tumours failed to prime (or delete) cytotoxic T lymphocytes (CTLs). Successful CTL priming and protective immunity were achieved when sufficient cells from a tumour reached secondary lymphoid organs early in tumour growth. Conversely, the authors propose that the poor immunogenicity of tumours such as B16 melanoma and Lewis lung carcinoma is the result of barrier formation (maintained by collagen and haemostasis factors), isolating them from T cells. Perhaps the most surprising and potentially controversial findings were that CTLs were directly induced by tumour cells

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rather than by the cross-presentation of tumour antigen on host antigen-presenting cells and that, despite this role of tumour cells, the presence or absence of B7.1 on the tumour had little influence on either induction or deletion of specific CTLs. • Hepatocyte growth factor ameliorates acute graft-versushost disease and promotes hematopoietic function. Kuroiwa T, Kakishita E, Hamano T, Kataoka Y, Seto Y, Iwata N, Kaneda Y, Matsumoto K, Nakamura T, Ueki T et al.: J Clin Invest 2001, 107:1365-1373. • LPS antagonism reduces graft-versus-host disease and preserves graft-versus-leukemia activity after experimental bone marrow transplantation. Cooke KR, Gerbitz A, Crawford JM, Teshima T, Hill GR, Tesolin A, Rossignol DP, Ferrara JL: J Clin Invest 2001, 107:1581-1589. • Adoptive transfer of minor histocompatibility antigen-specific T lymphocytes eradicates leukemia cells without causing graft-versus-host disease. Fontaine P, Roy-Proulx G, Knafo L, Baron C, Roy DC, Perreault C: Nat Med 2001, 7:789-794. Significance: Probably the most successful cancer immunotherapy in current clinical practice is the treatment of certain leukaemias by allogeneic haematopoietic stem-cell transplantation. A T-cell-mediated graft-versus-leukemia (GVL) effect can potentially totally eradicate malignant cells. However, one major limitation of this therapy is the occurrence of graft-versus-host disease (GVHD), also mediated by T cells in the graft. Ways of minimising GVHD whilst maintaining an efficacious GVL effect are urgently sought. In these new murine studies, encouraging data suggest new approaches for reducing GVHD (Kuroiwa et al. and Cooke et al.), whereas Fontaine et al. suggest that transfer of monospecific T cells may allow GVL activity in the total absence of GVHD. Findings: Donor T cell recognition of host minor histocompatibility antigens is an important cause of GVHD, but its severity depends upon inflammation. Using a gene therapy approach in a GVHD model, Kuroiwa et al. were able to protect gut epithelial cells (a target of GVHD) from apoptosis by injection of cDNA encoding hepatocyte growth factor (a pleiotropic factor, with antiapoptotic functions amongst others), resulting in diminished levels of inflammatory cytokines and reduced GVHD. Cooke et al. also tackled the problem of gut damage (and consequent endotoxin release into the circulation) as an amplifier of GVHD, by blocking endotoxin with a competitive antagonist (B975). This reduced GVHD without compromising an antileukaemic effect against P815 cells. Finally, Fontaine et al. describe what may be the ideal situation: a GVL effect without any GVHD. In elegant experiments with congenic mice and tumours expressing defined minor histocompatibility antigens, malignant cells could be totally eliminated in the absence of GVHD when CTLs specific for a single immunodominant minor antigen were adoptively transferred; cotransfer of other T cells led to GVHD. • Activated granulocytes and granulocyte-derived hydrogen peroxide are the underlying mechanism of suppression of T-cell function in advanced cancer patients. Schmielau J, Finn OJ: Cancer Res 2001, 61:4756-4760. Significance: Many potential mechanisms of tumour-mediated immunosuppression have been proposed for different cancers, but it has been difficult to explain how these may influence T cells not in the local tumour microenvironment. This is the first study to suggest the activated granulocyte as an intermediate mediator of immunosuppression that can modulate systemic T cell function. Findings: In advanced cancer patients, large numbers of activated granulocytes copurified with peripheral blood

mononuclear cells. These granulocytes are possibly activated by the high serum concentrations of TNF-α and IL-8 found in some cancer patients. Patient T cells, or normal T cells incubated with activated granulocytes, had a diminished capacity to secrete cytokines. This effect was mediated by H2O2, liberated during the oxidative burst of granulocytes. • Comprehensive analysis of the frequency of recognition of melanoma-associated antigen (MAA) by CD8 melanoma infiltrating lymphocytes (TIL): implications for immunotherapy. Benlalam H, Labarrière N, Linard B, Derré L, Diez E, Pandolfino M-C, Bonneville M, Jotereau F: Eur J Immunol 2001, 31:2007-2015. Significance: Detailed studies of T cell recognition of tumourassociated antigens in human cancer have generally focused on a limited number of epitopes restricted by even fewer HLA alleles. This study analyses a large number of patient-derived T cell lines to detect dominant specificities in the spontaneous antitumour response. It provides an impetus for defining new epitopes within previously identified melanoma antigens and suggests possibilities for improving immunotherapies that aim to reinforce existing immune responses. Findings: Tumour-infiltrating lymphocyte (TIL)-derived cell lines were tested for reactivity against COS cells transfected with cDNAs encoding an array of 28 melanoma-associated antigens and the relevant HLA alleles expressed by each patient (31 alleles in total). About half of the TIL lines reacted with 1−3 antigens in the context of 1−3 different HLA molecules, although there was frequently a single, dominant epitope and HLA-restriction element for each line. Furthermore many TIL responses (particularly for MAGE, LAGE and GAGE proteins) were in novel HLA contexts.

Lymphocyte activation and effector functions Selected by David Essayan US Food and Drug Administration, Rockville, MD, USA e-mail: [email protected]

• Physiological regulation of the immunological synapse by agrin. Khan AA, Bose C, Yam LS, Soloski MJ, Rupp F: Science 2001, 292:1681-1686. Significance: Similarities between neuronal and immune cell signal-transduction are underscored by this description of the first protein family that induces receptor aggregation and lipid microdomain reorganization at synapses in both systems. Findings: A splice variant of agrin (the Z+ isoform) is used by motor neurons to induce local aggregation of proteins at the neuromuscular junction. A Z− isoform was shown to be selectively expressed and regulated upon activation in lymphocytes, to induce lipid raft formation at the immunological synapse and to lower the threshold for lymphocyte activation. • IL-18 transgenic mice: in vivo evidence of a broad role for IL-18 in modulating immune function. Hoshino T, Kawase Y, Okamoto M, Yokota K, Yoshino K, Yamamura K, Miyazaki J, Young HA, Oizumi K: J Immunol 2001, 166:7014-7018. Significance: This is the most compelling study to date demonstrating a complex role for IL-18 that is not specific for Th1 induction. Findings: IL-18-transgenic mice were generated with IL-18 under the control of the mouse Ig promoter. These mice demonstrated

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increased numbers of CD8+ T cells and macrophages, decreased numbers of splenic B cells and increased serum IgE, IL-4 and IFN-γ levels. Splenic T cells from transgenic mice also produced more IL-5, IL-13 and IFN-γ than their wild-type controls. • IL-4 and IL-13 induce myofibroblastic phenotype of human lung fibroblasts through c-Jun NH2-terminal kinase-dependent pathway. Hashimoto S, Gon Y, Takeshita I, Maruoka S, Horie T: J Allergy Clin Immunol 2001, 107:1001-1008. Significance: This is an important new link in the association of Th2 cells and their cytokines with the tissue remodeling and fibrosis associated with chronic asthma. Findings: Using an in vitro model, IL-4 and IL-13 induced a time- and dose-dependent increase in the myofibroblast marker, α smooth muscle actin, in cultured human lung fibroblasts; IL-4 and IL-13 also increased JNK and Erk phosphorylation and activity, but not p38 MAP-kinase activity. Using the selective inhibitors CEP-1347 and PD 98059, the effects on α smooth muscle actin were specifically JNK dependent. • The common γ-chain is an indispensable subunit of the IL-21 receptor complex. Asao H, Okuyama C, Kumaki S, Ishii N, Tsuchiya S, Foster D, Sugamura K: J Immunol 2001, 167:1-5. Significance: This is the first demonstration that IL-21 signaling through the IL-21R complex requires the γc chain, the same chain common to signal transduction for IL-2, -4, -7, -9 and -15. Findings: IL-21 bound to γc-deficient ED40515− cells through the IL-21R, but was unable to induce signaling. If γc was transfected into these cells, IL-21 binding was associated with activation of JAK1, JAK3, STAT1 and STAT3. Direct binding of IL-21 to the γc chain was demonstrated by DSS cross-linking of biotinylated cytokine and γc immunoprecipitation. • Importance of ICOS-B7RP-1 costimulation in acute and chronic allograft rejection. Ozkaynak E, Gao W, Shemmeri N, Wang C, Gutierrez-Ramos J-C, Amaral J, Qin S, Rottman JB, Coyle AJ, Hancock WW: Nat Immunol 2001, 2:591-596. • ICOS is critical for T helper cell-mediated lung mucosal inflammatory responses. Gonzalo JA, Tian J, Delaney T, Corcoran J, Rottman JB, Lora J, Al-garawi A, Kroczek R, Gutierrez-Ramos J-C, Coyle AJ: Nat Immunol 2001, 2:597-604. • The costimulatory molecule ICOS plays an important role in the immunopathogenesis of EAE. Rottman JB, Smith T, Tonra JR, Ganley K, Bloom T, Silva R, Pierce B, Gutierrez-Ramos J-C, Ozkaynak E, Coyle AJ: Nat Immunol 2001, 2:605-611. • ICOS costimulation: it’s not just for TH2 cells anymore. Sperling AI, Bluestone JA: Nat Immunol 2001, 2:573-574. Significance: This series of papers demonstrates the importance of ICOS signaling in Th1 activation and effector functions in vivo. Findings: Ozkaynak et al. demonstrate that inhibition of ICOS signaling prolonged allograft survival and decreased intragraft T cell activation in a transplantation model; combination with cyclosporin A led to long-term engraftment. Gonzalo et al. report that inhibition of ICOS signaling preferentially attenuated effector T cell responses in a lung mucosal inflammation model. Rottman et al. demonstrate that ICOS blockade during the effector phase of murine experimental autoimmune encephalomyelitis abrogated disease whereas ICOS blockade during antigen priming exacerbated disease; both humoral and cellular arms of the immune response were affected by ICOS blockade. Finally, Sperling and Bluestone contribute an excellent “News & Views” article.

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• Increases in circulating and lymphoid tissue interleukin-10 in autoimmune lymphoproliferative syndrome are associated with disease expression. Lopatin U, Yao X, Williams RK, Bleesing JJH, Dale JK, Wong D, Teruya-Feldstein J, Fritz S, Morrow MR, Fuss I et al.: Blood 2001, 97:3161-3170. Significance: The first suggestion that IL-10 may play an important role in autoimmune lymphoproliferative syndrome (ALPS). Findings: Circulating and tissue levels of IL-10 were significantly increased in subjects with ALPS. Disproportionately high levels of IL-10 were found in the CD4–CD8– T cell population that is pathognomonic for ALPS. Interestingly, in vitro studies failed to demonstrate an effect of IL-10 on CD4–CD8– T cell survival. • A viral protein that selectively downregulates ICAM-1 and B7-2 and modulates T cell costimulation. Coscoy L, Ganem D: J Clin Invest 2001, 107:1599-1606. Significance: The first example of a virus-derived modulator of T cell costimulation and immunological synapse formation. Findings: The K5 protein product of Kaposi’s-sarcoma-associated herpesvirus (KSHV) reduced ICAM-1 and CD86 surface expression without affecting the surface expression of CD80; this effect was reversed by coexpression of a dominant-negative mutant of dynamin, implicating enhanced endocytosis as the mechanism of downregulation. K5-transfected B cells were impaired in their ability to activate T cells. • Treatment of allergic airway inflammation and hyperresponsiveness by antisense-induced local blockade of GATA-3 expression. Finotto F, De Sanctis GT, Lehr HA, Herz U, Buerke M, Schipp M, Bartsch B, Atreya R, Schmitt E, Galle PR et al.: J Exp Med 2001, 193:1247-1260. Significance: Compelling in vivo evidence of the importance of GATA-3 signaling in allergic pulmonary responses. Findings: Intrapulmonary blockade of GATA-3 expression using antisense oligonucleotides in a murine model of asthma downregulated Th2 cytokine production, pulmonary infiltration by eosinophils and antigen-induced airway hyper-responsiveness; these effects were not seen in the non-sense oligonucleotide controls.

Immunity to infection Selected by Nicolas Glaichenhaus Institut de Pharmacologie Moléculaire et Cellulaire, Valbonne, France e-mail: [email protected]

•• Susceptibility to mouse cytomegalovirus is associated with deletion of an activating natural killer cell receptor of the C-type lectin superfamily. Lee S-H, Girard S, Macina D, Busa M, Zafer A, Belouchi A, Gros P, Vidal SM: Nat Genet 2001, 28:42-46. •• Vital involvement of a natural killer cell activation receptor in resistance to viral infection. Brown MG, Dokun AO, Heusel JW, Smith HRC, Beckman DL, Blattenberger EA, Dubbelde CE, Stone LR, Scalzo AA, Yokoyama WM: Science 2001, 292:934-937. •• Murine cytomegalovirus is regulated by a discrete subset of natural killer cells reactive with monoclonal antibody to Ly49H. Daniels KA, Devora G, Lai WC, O’Donnell CL, Bennet M, Welsh RM: J Exp Med 2001, 194:29-44.

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Significance: These studies provide direct evidence that a distinct subset of NK cells plays a critical role in controlling a virus infection in vivo. Findings: Whereas some strains of mice, such as C57BL/6, are resistant to infection with murine cytomegalovirus (MCMV), other strains such as DBA/2 and BALB/c are susceptible. Previous studies have shown that MCMV susceptibility is controlled by Cmv1, a locus on chromosome 6 that regulates NK cell activity against virally infected targets. Lee et al. used a mouse strain, BXD-8 (derived from DBA/2 and C57BL/6), in which a recombination event conferred high susceptibility to infection by MCMV while conserving the C57BL/6 Cmv1 haplotype. Using a positional cloning strategy, these authors found that MCMV susceptibility was associated with a 23 kb deletion that included the Klra8 gene (formerly known as Ly49h). In an independent study, Brown et al. found that NK cells from BXD-8 mice were selectively deficient in the expression of the NK cell activation receptor Ly49H. They further demonstrated that the depletion of cells expressing Ly49H in resistant C57BL/6 mice dramatically altered their survival upon infection with MCMV. Similar findings were reported by Daniels et al. • Antibodies against merozoite surface protein (MSP)-119 are a major component of the invasion-inhibitory response in individuals immune to malaria. O’Donnell RA, de Koning-Ward F, Burt RA, Bockarie M, Reeder JC, Cowman AF, Crabb BS: J Exp Med 2001, 193:1403-1412. Significance: Several studies have shown that the sera of some, but not all, individuals living in malaria-endemic regions contain antibodies that inhibit the growth of blood stage Plasmodium falciparum in vitro. Here, the authors show that this inhibitory effect is mainly contributed by antibodies directed to the P. falciparum merozoite surface protein (MSP)-119. This study supports a significant role for MSP-119-specific antibodies in immunity to malaria in highly exposed individuals and suggests that efforts in the development of MSP119-based vaccines must be continued. Findings: Using an elegant allelic replacement strategy, the authors constructed a P. falciparum parasite line, D10-PcMEGF, that expresses the antigenically distinct MSP-119 domain from P. chabaudi. Using three different approaches, they further showed that sera from P.-falciparum-immune individuals were much less efficient in inhibiting the growth of D10-PcMEGF than those of the parental P. falciparum line. The opposite result was obtained with sera from P.-chabaudi-immune mice. •• Induction of M3-cytotoxic T lymphocyte responses by N-formylayted peptides derived from Mycobacterium tuberculosis. Chun T, Serbina NV, Nolt D, Wang B, Chiu NM, Flynn JL, Wang C-R: J Exp Med 2001, 193:1213-1220. Significance: Because bacteria, but not mammals, initiate protein synthesis with N-formyl methionine, the recognition of N-formylated peptides is one of the stratagems that mammals can use to ‘sense’ the presence of bacteria. To achieve this goal, mice express M3, which is an MHC class Ib molecule that preferentially presents N-formyl peptides to CD8+ T cells. In this study, the authors scanned the genome of Mycobacterium tuberculosis (Mtb) for peptides that were able to bind M3 molecules. Some of these epitopes were eventually found to be the targets of the T cell immune response directed to Mtb, a result that demonstrated the success of this approach for identifying new T cell antigens. Findings: The authors searched the Mtb genome for N-formylated mycobacterial peptides with sequence homology to other M3-binding peptides. Out of the 40 peptides identified, 4 were

shown to bind to M3 and to be presented at the surface of Mtb-infected macrophages. Further experiments showed that the lungs, the spleen and the lymph nodes of Mtb-infected mice contained T cells that had been primed by these formylated peptides and that were eventually able to rapidly secrete IFN-γ in response to antigenic stimulation in vitro. • Leishmania major induces differential expression of costimulatory molecules on mouse epidermal cells. Mbow ML, DeKrey GK, Titus RG: Eur J Immunol 2001, 31:1400-1409. Significance: Results from this study show that antigen-presenting cells (APCs) from different strains of mice express different levels of costimulatory molecules. The differential expression of these molecules may be one of the parameters that determine the ability of different strains of mice to mount a protective immune response to intracellular pathogens. Findings: Whereas C3H mice are resistant to the intracellular parasite L. major and develop a Th1-dominated response, BALB/c mice are susceptible and mount a Th2-polarized response. In this study, the authors show that the expression of CD80 was downregulated on BALB/c Langerhans cells (LCs) upon infection with L. major promastigotes in vitro. In contrast, infection with L. major induced LCs from C3H mice to downregulate CD86. •• Role of the parasite-derived prostaglandin D2 in the inhibition of epidermal Langerhans cell migration during schistosomiasis infection. Angeli V, Faveeuw C, Roye O, Fontaine J, Teissier E, Capron A, Wolowczuk I, Capron M, Trottein F: J Exp Med 2001, 193:1135-1147. Significance: This study demonstrates that pathogens can evade the immune response by inhibiting the migration of epidermal LCs from the skin to the draining lymph nodes. Findings: Although the injection of the helminth parasite Schistosoma mansoni into the skin of C57BL/6 mice induced the activation of LCs, the authors of this study found that activated LCs did not migrate to the draining lymph nodes. Further experiments showed that the binding of soluble lipophilic factors released by the parasites to the adenylate-cyclase-coupled prostaglandin (PG)D2 receptor was responsible for the inhibition of LC migration. • CD4+ T cell epitope escape mutant virus selected in vivo. Curea A, Hunziker L, Martinic MMA, Oxenius A, Hengartner H, Zinkernagel RM: Nat Med 2001, 7:795-800. Significance: This study is the first to show that viruses exhibiting mutations in CD4+ T cell epitopes can be selected in mammalian hosts as the result of an efficient immune response directed to these epitopes. This phenomenon of immune evasion may be beneficial for both the pathogen, by allowing its persistence, and for the host, by avoiding the development of detrimental CD4+ T cell mediated immunopathology. Findings: Lymphocytic choriomeningitis virus (LCMV) is a noncytopathic virus, which induces a strong T cell mediated immune response upon infection of C57BL/6 mice. However, although CD8+ T cells have been shown to be critical for virus clearance, a direct role of CD4+ T cells in the control of virus replication remained to be demonstrated. Here, the authors adoptively transfered relatively high numbers of LCMV-specific CD4+ TCR-transgenic T cells to mice that had been persistently infected with LCMV. Whereas some mice died as a consequence of CD4+ T cell mediated immunopathology, other mice survived and viruses were isolated from their blood. Further studies

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showed that these viruses displayed mutations within the epitope recognized by the TCR-transgenic T cells and that they exhibited an increased ability to replicate in immunocompetent hosts. Selected by Anna Vyakarnam King’s College London, London, UK e-mail: [email protected]

• Identification and antigenicity of broadly cross-reactive and conserved human immunodeficiency virus type 1-derived helper T-lymphocyte epitopes. Wilson CC, Palmer B, Southwood S, Sidney J, Higashimoto Y, Appella E, Chestnut R, Sette A, Livingston BD: J Virol 2001, 75:4195-4207. Significance: It is becoming increasingly clear that HIV-specific CD4+ T cells are critical in antiviral immunity as helper cells in the induction and maintenance of an effective HIV-specific cytotoxic T cell response. However, little is known of the specificity and function of CD4+ T cells in HIV infection and few CD4+ epitopes in HIV have been mapped. This paper documents several highly conserved and immunogenic CD4+ T cell epitopes in HIV and thereby contributes to the design of an effective HIV vaccine. Findings: Amino acid sequences of HIV structural and regulatory proteins were screened for the presence of HLA-DR supermotifs. HLA-DR types that represent the vast majority of humans irrespective of ethnicity were selected. A subset of motif-bearing peptides were selected for analysis based on conservancy in >50% of clade B HIV-1. Thus eleven highly cross-reactive HLA-DR-binding peptides that would be predicted to be antigenic in HIV-1-infected subjects were identified. These peptides were shown to induce proliferation of blood mononuclear cells from HIV+ subjects. Of the 22 subjects tested, 13 responded and of the responders several recognised multiple epitopes. The HLA-DR restriction of the response was confirmed by antibody-mediated blocking of the proliferative response. The ability of the peptides to induce IFN-γ was confirmed by intracytoplasmic staining. The antigenicity of the peptides correlated with recognition of naturally processed antigen — cells from the majority of peptide responders also proliferated to recombinant HIV proteins. Finally, the lack of response correlated with an overall defect in recall response to HIV proteins. These data provide evidence that the peptides selected on the basis of HLA-DR-binding supermotifs are antigenic, activate functional CD4+ T cells and are cross-reactive and therefore of likely importance in vaccine design. • Identification and functional characterization of human CD4+CD25+ T cells with regulatory properties isolated from peripheral blood. Jonuleit H, Schmitt E, Stassen M, Tuettenberg A, Knop J, Enk AH: J Exp Med 2001, 193:1285-1294. Significance: Immune regulatory CD4+CD25+ T cells have been shown to play an important role in self-tolerance and are essential for T cell homeostasis and the prevention of autoimmunity in murine models. A similar population is now described in humans. Findings: By flow cytometry, the authors define a subpopulation of CD4+CD25+ memory (CD45RO+) cells that constitutively express human HLA-DR (reflecting recently activated cells) and intracellular CTLA4 (cytotoxic T lymphocyte associated antigen 4). These cells were isolated using antibody-coated magnetic beads and characterised in vitro along with total CD4+ T cells. Unlike total CD4+ cells, CD4+CD25+ cells showed low rates of proliferation when stimulated with allogeniec dendritic cells (DCs) that could not be overcome by addition of anti-CD3, antiCD28 or PHA. These anergic CD4+CD25+ cells produced low levels of IL-2, IL-4, IFN-γ and IL-10 in the above allo-stimulation

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assays. This anergic state did not correlate with increased apoptosis as measured by annexin V staining. The refractory state of CD4+CD25+ cells was partially reversed by addition of high concentrations of IL-2 (200 IU/ml) or IL-4 (500 IU/ml) and significantly so by the combination of both. The CD4+CD25+ population was shown to inhibit the proliferation and cytokine (IL-2 and IFN-γ) production of CD4+ cells in co-culture assays where cells were stimulated with allogeneic DCs. This inhibitory effect was contact-dependent and antigen-non-specific (CD4+CD25+ cells could be induced to inhibit other cells following stimulation with anti-CD3 antibody). Finally CD4+CD25+ cells were shown to have two subpopulations — CD45RO+ and CD45RO− cells —with the former but not the latter having anergic and suppressive characteristics. This study now opens up further analysis of the CD4+CD25+ memory subset in T cell homeostasis in normal and disease conditions.

Immunogenetics Selected by Jean-Laurent Casanova Laboratory of Human Genetics of Infectious Disease, Necker-Enfants Malades Medical School, Paris, France e-mail: [email protected]

α • Familial CD8 deficiency due to a mutation in the CD8α gene. De la Calle-Martin O, Hernandez M, Ordi J, Casamitjana N, Arostegui JI, Caragol I, Ferrando M, Labrador M, RodriguezSanchez JL, Espanol T: J Clin Invest 2001, 108:117-123. Significance: This is the first report of patients without CD8+ T cells due to a germline mutation in the gene encoding CD8α. Findings: A 25-year-old patient with recurrent bacterial infections was investigated. The blood immunological phenotype was unremarkable, with the notable exception of a lack of CD8+ T cells and an increase in CD4−CD8− α/β T cells. Two healthy younger siblings were found to lack CD8+ T cells as well. A homozygous mis-sense mutation was identified in the CD8A gene, encoding the CD8α subunit shared by the two types of CD8 dimers (CD8α−CD8α and CD8α−CD8β). The mutation is not a polymorphism, as it was not found in control individuals. It is recessive, as only the three siblings who were homozygous for the mutation lacked CD8+ T cells. It is a loss-of-function effect, as transfection of the mutant CD8A allele, unlike that of the wild-type allele, was unable to complement defective recipient cells. Intriguingly, CD8α-deficient patients, like previously reported HLA-I-deficient patients (with low numbers of CD8+ T cells), do not seem to be particularly vulnerable to viral diseases, suggesting that compensatory mechanisms ensure optimal protection from viruses. More surprisingly, the recurrence of severe diseases caused by extracellular encapsulated bacteria raises the question of the role of CD8+ T cells in antibacterial immunity.

Immunotherapy Selected by Yang Liu Ohio State University, Columbus, OH, USA e-mail: [email protected]

•• Adoptive transfer of minor histocompatibility antigen-specific T lymphocytes eradicates leukemia cells without causing graft-versus-host disease. Fontaine P,

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Roy-Proulx G, Knafo L, Baron C, Roy DC, Perreault C: Nat Med 2001, 7:789-794. Significance: An elegant demonstration for selective induction of graft-versus-leukemia (GVL) effects in the absence of overt graft-versus-host disease (GVHD). Findings: Mice that lack a particular minor histocompatibility antigen (B6dom1) have significantly enhanced immunity to EL4 leukemia, which bears this antigen, even without prior immunization. Adoptive transfer of primed or unprimed T cells into B6dom1 incompatible hosts causes tumor rejection but not GVHD. This protection correlates with increased number of CD8+ T cells specific for this antigen. • LPS antagonism reduces graft-versus-host disease and preserves graft-versus-leukemia activity after experimental bone marrow transplantation. Cooke KR, Gerbitz A, Crawford JM, Teshima T, Hill GR, Tesolin A, Rossignol DP, Ferrara JL: J Clin Invest 2001, 107:1581-1589. Significance: A novel approach to reduce GVHD without affecting GVL effects in fully allogeneic chimera mice by manipulating innate immunity. Findings: Administration of B975, a synthetic lipid-A analogue, reduced TNF-α levels and decreased intestinal histopathology but not donor T cell responses to host antigens. Most importantly, this treatment significantly improved leukemia-free survival of the recipient mice.

Transplantation Selected by Hugh Auchincloss Jr*, Gerry Waneck and Christian LeGuern Massachusetts General Hospital, Boston, MA, USA *e-mail: [email protected]

• Ex vivo isolation and characterization of CD4(+)CD25(+) T cells with regulatory properties from human blood. Dieckmann D, Plottner H, Berchtold S, Berger T, Schuler G: J Exp Med 2001, 193:1303-1310. • Human CD25(+)CD4(+) T regulatory cells suppress naive and memory T cell proliferation and can be expanded in vitro without loss of function. Levings MK, Sangregorio R, Roncarolo MG: J Exp Med 2001, 193:1295-1302. • Identification and functional characterization of human CD4(+)CD25(+) T cells with regulatory properties isolated from peripheral blood. Jonuleit H, Schmitt E, Stassen M, Tuettenberg A, Knop J, Enk AH: J Exp Med 2001, 193:1285-1294. Significance: Human T cells regulate too! The identification of CD4+CD25+ regulatory T cells (T-reg) in humans will help to understand the mechanism of peripheral T cell tolerance and will undoubtedly lead to important implications for therapy. Findings: CD4+CD25+CD45RO+ T-reg were identified by these three groups in the blood of healthy donors. These cells resemble their murine counterparts — they constitutively express CTLA-4 (CD152) and are poorly stimulated by allogeneic antigen-presenting cells. The refractory/anergic state is reversible with the addition of IL-2, IL-4 or IL-15. T-reg-mediated suppression of naive and memory CD4+ T cell proliferative responses requires cell-to-cell contact but IL-10, TGF-β or CTLA-4 are not involved in suppression. • Importance of ICOS-B7RP-1 costimulation in acute and chronic allograft rejection. Ozkaynak E, Gao W, Shemmeri N,

Wang C, Gutierrez-Ramos JC, Amaral J, Qin S, Rottman JB, Coyle AJ, Hancock WW: Nat Immunol 2001, 2:591-596. Significance: Although blockade of recipient CTLA-4 and CD28 T cell costimulatory pathways allows prolongation of allograft survival, such treatment does not prevent chronic rejection. The present study demonstrates that the combined use of cyclosporine A and an anti-I-COS (inducible costimulator) monoclonal antibody (mAb) provides permanent survival without signs of chronic rejection. This approach may foster new therapies for treatment of chronic rejection. Findings: Contrary to CD28 and CTLA-4, which are two key membrane signals for the initial activation of T cells, the I-COS T cell activation signal is recruited during the effector phase and thereby may be implicated in chronic rejection. This hypothesis was proven in this study, which shows that fully allogeneic murine heart grafts are accepted long-term (>100 days) in recipients conditioned with a combination of cyclosporine A and anti-I-COS mAb whereas the use of either immunosuppressive agent alone leads to <25-day graft survival. Accepted tissues show no histological signs of chronic rejection. • Failure to induce neonatal tolerance in mice that lack both IL-4 and IL-13 but not in those that lack IL-4 alone. Inoue Y, Konieczny BT, Wagener ME, McKenzie ANJ, Lakkis FG: J Immunol 2001, 167:1125-1128. Significance: Genetic demonstration that the immuno-regulatory mechanism implicated in neonatal tolerance is mediated through the Th2 pathway. Findings: Mice with a double knockout, for the IL-4 and IL-13 genes — which both control the Th2 T cell differentiation pathway — are resistant to the induction of neonatal tolerance to the H-Y minor antigen. Tolerance resistance is associated with the synthesis of high levels of IFN-γ in adult mutant mice that have been re-challenged with the male antigen. • Different mechanisms of cardiac allograft rejection in wildtype and CD28-deficient mice. Szot GL, Zhou P, Rulifson I, Wang J, Guo Z, Kim O, Newell KA, Thistlethwaite JR, Bluestone JA, Alegre M-L: Amer J Transplant 2001, 1:38-46. Significance: This study emphasizes the importance of CD8+-cell-dependent mechanisms in graft rejection when CD4+ T cell function is impaired by various strategies. Findings: Although CD28-deficient mice reject cardiac allografts, the authors demonstrate that the cellular mechanisms are different compared with wild-type mice. Rejection by CD28-deficient recipients depends on CD8+ T cells and on the continued presence of CD4+ T cells, both of which are not true in wild-type recipients. Thus, tolerogenic and immunosuppressive strategies that affect primarily CD4+ T cells may not be successful if CD8+ T cell responses are not targeted as well. • Regulatory functions of self-restricted MHC class II allopeptide-specific Th2 clones in vivo. Waaga AM, Gasser M, Kist-van Holthe JE, Najafian N, Muller A, Vella JP, Womer KL, Chandraker A, Khoury SJ, Sayegh MH: J Clin Invest 2001, 107:909-916. Significance: These studies describe alloreactive T cell clones that have an indirect specificity and a Th2 phenotype and that show regulatory function both in vitro and in vivo. Findings: The authors derived T cell clones from mice that had rejected allografts or from recipients that had been rendered tolerant by co-stimulatory blockade. Both sets of clones were

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specific for the same donor MHC peptide presented on a self MHC molecule. The clones from the rejecting recipients had a Th1 phenotype whereas those from the tolerant recipients had a Th2 phenotype. Co-culture experiments in vitro and adoptivetransfer DTH experiments in vivo showed that the Th2 clones could alter the responses of the Th1 clones. • CD4+ T cell recognition of a single discordant HLA-A2-transgenic molecule through the indirect antigen presentation pathway induces acute rejection of murine cardiac allografts. Smith CR, Jaramillo A, Liu W, Tu Y, Kaleem Z, Swanson CJ, Mohanakumar T: Transplantation 2001, 71:1640-1648. Significance: Indirect allorecognition of donor MHC class I molecules leads to rejection of cardiac allografts in this unique transplant model, in which there is a single MHC discordance between donor and recipient. Findings: Cardiac allografts from HLA-A2-transgenic C57BL/6 (HLA-A2+) mice were transplanted into normal C57BL/6, CD4-knockout (KO) C57BL/6 mice, CD8-KO C57BL/6 mice, fully allogeneic BALB/c mice and syngeneic HLA-A2+ C57BL/6 mice. HLA-A2+ grafts were acutely rejected by BALB/c mice, normal C57BL/6 mice and CD8-KO mice. In contrast, HLA-A2+ grafts were not rejected by CD4KO mice or HLA-A2+ mice. CD8-KO recipients treated with an anti-CD4 mAb, but not those treated with an anti-NK-cell mAb, failed to reject their allografts. Spleen cells from mice rejecting HLA-A2+ allografts failed to lyse HLA-A2+ target cells, indicating that CD8+ T cells were not involved in the rejection process. In contrast, spleen cells from rejecting animals proliferated significantly to both HLA-A2+ cells and to a peptide derived from the HLA-A2 molecule.

Allergy and hypersensitivity Selected by Cezmi Akdis Swiss Institute of Allergy and Asthma Research, Davos, Switzerland e-mail: [email protected]

•• Regulation of mast cell survival by IgE. Asai K, Kitaura J, Kawakami Y, Yamagata N, Tsai M, Carbone DP, Liu F-T, Galli SJ, Kawakami T: Immunity 2001, 14:791-800. Significance: Mast cells are major effector cells in IgE-dependent immediate-hypersensitivity reactions, as well as IgE-mediated immune responses to certain parasites. Mast cell numbers in the tissues can change during the course of allergic reactions. Although the death of certain cells can lead to functional deficiencies, prolonged survival of some effector cells can cause tissue injury and play a role on the pathogenesis of disease. This study demonstrates that monomeric IgE can promote the survival of mast cells under conditions of growth factor limitation, demonstrating an essential pathophysiological loop and the importance of targeting high IgE levels for the treatment of allergic diseases. Findings: Monomeric IgE binding to its receptor, FcεRI, prolongs the survival of bone-marrow-derived mast cells (BMMCs) without increasing proliferation. In addition, IgE protects mast cells from apoptosis induced by growth factor (IL-3 and stem cell factor) depletion. In contrast, FcεRI cross-linking does not promote the survival of BMMCs. The anti-apoptotic effect of monomeric IgE does not involve autocrine growth factor secretion and blockage of the Fas/Fas-ligand apoptosis pathway.

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Although the mechanism of action is unknown as yet, intracellular signaling by monomeric IgE differs from FcεRI cross-linking. • Treatment of allergic airway inflammation and hyperresponsiveness by antisense-induced local blockage of GATA-3 expression. Finotto S, De Sanctis GT, Lehr HA, Herz U, Buerke M, Schipp M, Bartsch B, Atreya R, Schmitt E, Galle PR et al.: J Exp Med 2001, 193:1247-1260. Significance: GATA-3 is a transcription factor expressed in T cells, mast cells, eosinophils, basophils, and embryonic brain and kidney. It has been shown to be essential for the development of T cell progenitors and is selectively expressed in Th2 but not in Th1 cells. Recently, the demonstration of increased expression of GATA-3 mRNA in human asthmatic airways suggested that it may be involved in the regulation of Th2 cytokine responses in asthma. Findings: Increased local production of GATA-3 was observed in ovalbumin-induced allergic airway inflammation in mice. Local treatment of mice with specific anti-sense phosphorothioate oligonucleotide to the translation start site of GATA-3 inhibited the GATA-3 protein expression in the lungs. This was paralleled with decreased airway inflammation, as demonstrated by decreased eosinophil infiltration, decreased mucus-producing cell numbers and suppressed airway hyper-reactivity. • Fractalkine (CX3CL1) as an amplification circuit of polarized Th1 responses. Fraticelli P, Sironi M, Bianchi G, D’Ambrosio D, Albanesi C, Stoppacciaro A, Chieppa M, Allavena P, Ruco L, Girolomoni G et al.: J Clin Invest 2001, 107:1173-1181. Significance: Fractalkine (FKN, CX3CL1) is a unique CX3C chemokine found in membrane bound and secreted forms and induced by primary proinflammatory signals in vascular endothelial cells. It utilizes a G-protein-coupled, pertussis-toxin-sensitive receptor, CX3CR1. Chemokines represent an important component of polarized Th1 and Th2 responses, as demonstrated in this paper, in which FKN is shown to participate in Th1 responses. Findings: FKN was induced by proinflammatory signals such as LPS, IL-1, TNF, CD40-ligand and IFN-γ. The Th2 cytokines IL-4 and IL-13 significantly suppressed FKN expression in human umbilical vein endothelial cells. NK cells and Th1 cells preferentially expressed the FKN receptor CX3CR1. As an in vivo support for the findings, FKN was expressed in the lesions of Th1-mediated disorders such as psoriasis and Mycobacteriumtuberculosis-induced granulomatous lymphadenitis. • Essential role of lymph nodes in contact hypersensitivity α-deficient mice. Rennert PD, revealed in lymphotoxin-α Hochman PS, Flavell RA, Chaplin DD, Jayaraman S, Browning JL, Fu Y-X: J Exp Med 2001, 193:1227-1238. Significance: Although immune responses are induced in lymph nodes (LNs) by antigen exposure, it is not known whether LNs are essential for acquired immunity. Lymphotoxin (LT)α−/− and LTβ−/− mice lack LNs due to developmental defects in LN genesis. LNs appear to be required for generating contact hypersensitivity (CH) in response to hapten application. In contrast, the spleen can not mediate CH, because antigen-bearing epidermal Langerhans cells do not access splenic white pulp. Findings: LTα−/− mice and LTβ−/− mice can not develop CH response to haptens. LTα−/− mice can be induced to develop LNs by using the agonist anti-LT-receptor mAb and they were able to show a CH response. Conversely, loss of LNs following use of LT-receptor antagonists in normal mice leads to the loss of the CH response.

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Autoimmunity Selected by Allison Green Wellcome Trust Center for Molecular Mechanisms in Disease, Addenbrooke’s Hospital, Cambridge, UK e-mail: [email protected]

•• Migratory activity and functional changes of green fluorescent effector cells before and during experimental autoimmune encephalomyelitis. Flügel A, Berkowicz T, Ritter T, Labeur M, Jenne DE, Li Z, Ellwart JW, Willem M, Lassmann H, Wekerle H: Immunity 2001, 14:547-560. Significance: The authors take an interesting approach to monitor the migration pattern of autoreactive CD4+ T cells during the development of EAE. Their unique protocol for transfecting autoreactive cells with a retroviral vector encoding green fluorescent effector protein (GFP) could potentially provide a powerful tool to monitor specific subsets of T cells in vivo over a long period of time. Findings: Primary myelin basic protein (MBP)-specific CD4+ T cells were transfected with retroviral constructs encoding GFP and injected into Lewis rats. Control rats received similarly transfected OVA-specific T cells. FACS, PCR and histology techniques determined that both MBP-specific and OVA-specific T cells migrated into the parathymic lymph node within 12−36 hours post-injection, and into the blood and spleen by 60 hours. At this time-point, MBP-specific T cells en masse migrated into the central nervous system (CNS) — no MBP-specific T cells were detectable in any other organs, including lymphoid organs. OVA-specific cells remained in the lymphoid organs. FACS analysis of MBP-specific T cells isolated from the blood, spleen and parathymic lymph node 36–60 hours post-injection determined that CD25 and OX-40 (activation markers for rat T cells) were downregulated and that chemokine receptors CCR-1, CCR-2b, CCR-3, CCR-5 and CXCR-4 were upregulated. Upon entry into the CNS, MBP-specific T cells became re-activated and produced an array of inflammatory cytokines. •• TACI-ligand interactions are required for T cell activation and collagen-induced arthritis in mice. Wang H, Marsters SA, Baker T, Chan B, Lee WP, Fu L, Tumas D, Yan M, Dixit VM, Ashenazi A, Grewal IS: Nat Immunol 2001, 2:632-636. Significance: The authors demonstrate that, in addition to the importance of B lymphocyte stimulator (BLyS) and proliferationinducing ligand (APRIL) in the development of B cell mediated

autoimmunities, these molecules can also play a critical role in T cell mediated arthritis. Findings: Using a transmembrane activator and CAML interactor (TACI)−Fc fusion protein, which blocks TACI−BLyS and TACI−APRIL interactions, they demonstrated that TACI− BLyS/APRIL interactions are critical for T cell activation in vitro following stimulation with anti-CD3. In vivo, animals treated with TACI−Fc showed decreased T cell recall responses to keyhole limpet haemocyanin (KLH) compared with mice receiving isotype-control antibodies. In a murine model for rheumatoid arthritis (RA), radiological and histological analysis determined that TACI−Fc injection into DBA/I mice primed with type II collagen substantially inhibited RA progression compared with isotype-control-treated mice. Indeed, TACI−Fc-treated mice showed minimal inflammation in their joints, with little evidence of osteolysis. Thus, TACI−BLyS/APRIL interactions are likely to be critical in the initiation phase of RA. • The costimulatory molecule ICOS plays an important role in the immunopathogenesis of EAE. Rottmen JB, Smith T, Tonra JR, Ganley K, Bloom T, Silva R, Pierce B, Gutierrez-Ramos J-C, Özkaynak E, Coyle AJ: Nat Immunol 2001, 2:605-611. Significance: The authors provide new evidence that the ICOS−B7RP-1 costimulatory pathway has both a positive and negative impact in the development of EAE. Findings: Using the SJL model for EAE, mRNA levels for ICOS and its receptor B7RP-1 increased in the brain 10 days after immunization with proteolipid protein PLP(139–151), and remained high until day 20. FACS, histological and RNAse protection assays confirmed that ICOS expression was restricted to 12% of CD3+ T cells that infiltrated the brain during the course of EAE. Blockade of ICOS using mAb 12A8 during the priming phase (1–10 days post-immunization) resulted in enhanced infiltration of the CNS and upregulation of certain chemokines (CCR1, RANTES, MIP-2 and MCP-1) as well as IL-1α, IL-β, IL-6, IL-12p35 and IFN-γ compared with control mice. All these changes contributed to more-severe pathology in the CNS and rapid progression of EAE. In striking contrast, animals treated with mAb 12A8 during the efferent phase (9–20 days post-immunization) had no CNS infiltration and did not develop EAE; PLP-specific T cells isolated from the mice produced little IFN-γ upon stimulation in vitro. However, protection was not absolute as 50% of mice went on to develop disease 20 days post-immunization and this correlated with the development of neutralizing antibodies to mAb 12A8.