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Eight years have passed since the approval of belimumab, a monoclonal antibody directed against B lymphocyte stimulation and the first targeted therapy approved for systemic lupus. erythematous (SLE). While well tolerated, the efficacy of belimumab remains limited and is not recommended for patients suffering severe nephritis, a life threatening complication of SLE. We sought to explore alternative targets of autoreactive B lymphocytes through manipulation of affinity maturation. The BXSB model is a long established model of human SLE developing elevated antinuclear antibodies and immune complex nephritis along with other manifestations of autoimmune disease. We used CRISPR-Cas9 to inactivate Activation Induced Cytidine Deaminase (Aicda, AID) directly in the BXSB background and found greatly improved survival. While mice continued to develop plasma cells, follicular structure was restored and renal pathology was reduced. While antinuclear antibody concentrations were reduced in knockout mice, renal immune complex deposition was grossly the same as wild type while complement deposition was very limited in the knockout mice. Mice develop expanded germinal center B cell populations as in other models of AID deficiency without concurrent expansion of follicular T cells. The prolonged survival in these mice appears to be attributed to the reduced renal pathology warranting further exploration as current therapeutics targeting lupus nephritis are limited and thus in great demand.

A recent publication questions the suitability of mice as a model for the human inflammatory response and has fueled the continuing debate about the suitability of mice as models for human disease. We discuss recent advances in disease modeling using mice, and the genetic factors that need to be considered when trying to recapitulate aspects of human disease. Failure to appreciate the important differences between human and mouse biology and genetics underlying attempts to generate faithful models frequently leads to poor outcomes. Closely coordinated human and model organism studies are essential to provide traction for translational research.

The pleiotropic cytokine IL-21 is implicated in the pathogenesis of human systemic lupus erythematosus by polymorphisms in the molecule and its receptor (IL-21R). The systemic lupus erythematosus-like autoimmune disease of BXSB.Yaa mice is critically dependent on IL-21 signaling, providing a model for understanding IL-21/IL-21R signaling in lupus pathogenesis. In this study, we generated BXSB.Yaa mice selectively deficient in IL-21R on B cells, on all T cells, or on CD8+ T cells alone and examined the effects on disease. We found that IL-21 signaling to B cells is essential for the development of all classical disease manifestations, but that IL-21 signaling also supports the expansion of central memory, CD8+ suppressor cells and broadly represses the cytokine activity of CD4+ T cells. These results indicate that IL-21 has both disease-promoting and disease-suppressive effects in the autoimmune disease of BXSB.Yaa mice.

Interleukin-7 (IL-7) is essential to T-cell survival as well as homeostatic proliferation, and clinical trials that exploit the mitogenic effects of IL-7 have achieved success in treating human diseases. In mice, the in vivo potency of IL-7 improves dramatically when it is administered as a complex with the anti-IL-7 neutralizing monoclonal antibody clone M25. However, the mechanism whereby M25 augments IL-7 potency is unknown. We have analyzed the discrete contributions of the antibody constant (Fc) and IL-7-binding (Fab) domains to the mechanism. By engaging the neonatal Fc receptor the Fc domain extends the in vivo lifespan of IL-7/M25 complexes and accounts for the majority of their activity. Unexpectedly, the IL-7-neutralizing Fab domain provides an additional, albeit smaller, contribution, possibly by serving as a cytokine depot. This study is the first to demonstrate that the neutralizing aspect of the monoclonal antibody is directly involved in enhancing the potency of a cytokine with a single form of receptor. Lessons from the mechanism of IL-7/M25 complexes inform the design of next-generation cytokine therapeutics.

Therapeutic monoclonal antibodies are widely recognized to be a most promising means to treat an increasing number of human diseases, including cancers and autoimmunity. To a large extent, the efficacy of monoclonal antibody treatment is because IgG antibodies have greatly extended persistence in vivo. However, conventional rodent models do not mirror human antibody pharmacokinetics. The key molecule responsible for the extended persistence antibodies is the major histocompatibility complex class I family Fc receptor, FcRn. We describe human FcRn transgenic mouse models and how they can be exploited productively for the preclinical pharmacokinetic evaluation of therapeutic antibodies.

Careful regulation of the body’s immunoglobulin G (IgG) and albumin concentrations is necessitated by the importance of their respective functions. As such, the neonatal Fc receptor (FcRn), as a single receptor, is capable of regulating both of these molecules and has become an important focus of investigation. In addition to these essential protection functions, FcRn possesses a number of other functions that are equally as critical and are increasingly coming to attention. During the very first stages of life, FcRn mediates the passive transfer of IgG from mother to offspring both before and after birth. In the adult, FcRn regulates the persistence of both IgG and albumin in the serum as well as the movement of IgG, and any bound cargo, between different compartments of the body via transcytosis across polarized cells. FcRn is also expressed by hematopoietic cells; consistent with this, FcRn regulates MHC class II presentation and MHC class I cross-presentation by dendritic cells. As such, FcRn plays an important role in immune surveillance throughout adult life. The increasing appreciation for FcRn in both homeostatic and pathological conditions is generating an intense interest in the potential for therapeutic modulation of FcRn binding to IgG and albumin.

Background: FcRn regulates the serum half-life of IgG. Results: Fc engineering of scFv-Fc affects binding to mFcRn and hFcRn differently, which reflects blood clearance in WT and transgenic mice. Conclusion: Modulating FcRn binding to scFv-Fc reveals cross-species differences that determine blood clearance. Significance: This work provides insights into FcRn binding that must be considered prior to pre-clinical evaluation of engineered IgGs., Serum half-life of IgG is controlled by the neonatal Fc receptor (FcRn) that interacts with the IgG Fc region and may be increased or decreased as a function of altered FcRn binding. Preclinical evaluations of modified IgGs are frequently carried out in mice, but such IgGs may bind differently to mouse and human FcRn (mFcRn and hFcRn). Here, we report a detailed characterization of a matched set of mouse-human chimeric T84.66 scFv-Fc variants with specificity for the tumor carcinoembryonic antigen and mutations in the FcRn-binding site. Binding to soluble mFcRn and hFcRn was measured using in vitro assays, and the results were compared with blood clearance in vivo in normal (mFcRn bearing) and hFcRn transgenic mice. All variants bound better to mFcRn than to hFcRn. The loss of affinity varied among the mutants, however, and also the hierarchy of binding differed depending on the receptor. The mutations had no major impact on binding to the classical Fcγ receptors. Importantly, the trend of blood clearance in both strains of mice correlated with the hierarchy of binding obtained using soluble FcRn. Consequently, in vitro interaction analysis of engineered IgGs regarding their cross-species FcRn binding ability provides information for prediction of in vivo pharmacokinetics.

Donor T cells contribute to the success of allogeneic hematopoietic stem cell transplantation (alloSCT). Alloreactive donor T cells attack leukemia cells, mediating the GVL effect. Donor T cells, including the memory T cells (TM) that are generated after infection, also promote immune reconstitution. Nonetheless, leukemia relapse and infection are major sources of treatment failure. Efforts to augment GVL and immune reconstitution have been limited by GVHD, the attack by donor T cells on host tissues. One approach to augmenting GVL has been to infuse ex vivo–generated T cells with defined specificities; however, this requires expertise that is not widely available. In the present study, we tested an alternative approach, adoptive immunotherapy with CD8+ TM from donors vaccinated against a single minor histocompatibility antigen (miHA) expressed by leukemia cells. Vaccination against the miHA H60 greatly augmented TM-mediated GVL against mouse chronic-phase (CP-CML) and blast crisis chronic myeloid leukemia (BC-CML). TM-mediated GVL was antigen specific and was optimal when H60 expression was hematopoietically restricted. Even when H60 was ubiquitous, donor H60 vaccination had a minimal impact on GVHD. TM from lymphocytic choriomeningitis virus (LCMV)–immune and H60-vaccinated donors augmented GVL and protected recipients from LCMV. These data establish a strategy for augmenting GVL and immune reconstitution without elaborate T-cell manipulation.

Dysregulation of the T cell-dependent Ab response can lead to numerous immunological disorders, ranging from systemic lupus erythematosus to B cell lymphomas. Cellular processes governed by MHC class II proteins play a major role in this response and its dysregulation. The extent to which processes controlled by the diverse family of MHC class I proteins impact such autoimmune and neoplastic disorders, however, is less clear. In this study, we genetically dissect the contributions of individual MHC class I family members and the pathological processes under their control in the systemic lupus erythematosus-like disease of BXSB.Yaa mice and B cell lymphomagenesis of SJL mice. This study reveals a powerful repressive regulatory axis comprised of MHC class I-dependent CD8+ T cells and NK cells. These results indicate that the predominant role of the MHC class I protein family in such immunological disorders is to protect from more aggressive diseases.

Strategies to prevent the sexual transmission of HIV include vaccines that elicit durable, protective mucosal immune responses. A key to effective mucosal immunity is the capacity for antigens administered locally to cross epithelial barriers. Given the role of neonatal Fc receptor (FcRn) in transferring IgG across polarized epithelial cells which line mucosal surfaces, FcRn might be useful for delivering HIV vaccine antigens across mucosal epithelial barriers to the underlying antigen-presenting cells. Chimeric proteins composed of HIV Gag (p24) fused to the Fc region of IgG (Gag-Fc) bind efficiently to airway mucosa and are transported across this epithelial surface. Mice immunized intranasally with Gag-Fc plus CpG adjuvant developed local and systemic immunity, including durable B and T cell memory. Gag-specific immunity was sufficiently potent to protect against an intravaginal challenge with recombinant vaccinia virus expressing the HIV Gag protein. Intranasal administration of a Gag-Fc/CpG vaccine protected at a distal mucosal site. Our data suggest that targeting of FcRn with chimeric immunogens may be an important strategy for mucosal immunization and should be considered a new approach for preventive HIV vaccines.

Cytoplasmic Ags derived from viruses, cytosolic bacteria, tumors, and allografts are presented to T cells by MHC class I or class II molecules. In the case of class II-restricted Ags, professional APCs acquire them during uptake of dead class II-negative cells and present them via a process called indirect presentation. It is generally assumed that the cytosolic Ag-processing machinery, which supplies peptides for presentation by class I molecules, plays very little role in indirect presentation of class II-restricted cytoplasmic Ags. Remarkably, upon testing this assumption, we found that proteasomes, TAP, and endoplasmic reticulum-associated aminopeptidase associated with Ag processing, but not tapasin, partially destroyed or removed cytoplasmic class II-restricted Ags, such that their inhibition or deficiency led to dramatically increased Th cell responses to allograft (HY) and microbial (Listeria monocytogenes) Ags, both of which are indirectly presented. This effect was neither due to enhanced endoplasmic reticulum-associated degradation nor competition for Ag between class I and class II molecules. From these findings, a novel model emerged in which the cytosolic Ag-processing machinery regulates the quantity of cytoplasmic peptides available for presentation by class II molecules and, hence, modulates Th cell responses.

The FcγRs found on macrophages (Mϕs) and dendritic cells (DCs) efficiently facilitate the presentation or cross-presentation of immune-complexed Ags to T cells. We found that the MHC class I-related neonatal FcR for IgG (FcRn) in both Mϕs and DCs failed to have a strong effect on the cross-presentation of immune complex (IC) OVA Ag to CD8+ T cells. Interestingly, endosomal FcRn enhanced the presentation of the monomeric OVA-IC to CD4+ T cells robustly, whereas FcRn in phagosomes exerted distinctive effects on Ag presentation between Mϕs and DCs. The presentation of phagocytosed OVA-ICs to CD4+ T cells was considerably enhanced on wild-type versus FcRn-deficient Mϕs, but was not affected in FcRn-deficient DCs. This functional discrepancy was associated with the dependence of IgG–FcRn binding in an acidic pH. Following phagocytosis, the phagosomal pH dropped rapidly to

Vaccine strategies to prevent invasive mucosal pathogens are being sought because 80–90% of infectious diseases are initiated at mucosal surfaces. However, our ability to deliver an intact vaccine antigen across a mucosal barrier for induction of effective immunity is limited. The neonatal Fc receptor (FcRn) mediates the transport of IgG across polarized epithelial cells lining mucosal surfaces. By mimicking IgG transfer at mucosal surfaces, intranasal immunization with a model antigen, herpes simplex virus type-2 (HSV-2) glycoprotein gD fused with an IgG Fc fragment, in combination with the adjuvant CpG, resulted in complete protection of wild type, but not FcRn knockout, mice that were intravaginally challenged with virulent HSV-2 186. This immunization strategy induced efficient mucosal and systemic antibody, B and T cell immune responses, including memory immune responses, which remained stable at least 6 months post-vaccination and conferred protection for a majority of animals. These results demonstrate that the FcRn-IgG transcellular transport pathway may represent a novel mucosal vaccine delivery route for a subunit vaccine against abundant mucosal pathogens.

The immune system includes a subpopulation of CD8 + T cells equipped to inhibit the expansion of follicular T helper (T FH ) cells, resulting in suppression of autoantibody production and associated lupus-like disease. These CD8 + T regulatory (Treg) cells recognize Qa-1/peptide complexes on target T FH cells and depend on the IL-15 cytokine for development and function. Here we show that these CD8 + Treg cells express a triad of surface receptors—CD44, CD122, and the class I MHC receptor Ly49—and account for + T cells. Moreover, the development of systemic lupus erythematosus-like disease in B6- Yaa mutant mice is associated with a pronounced defect in CD8 + Treg cell activity, suggesting that this regulatory subset may represent an effective therapeutic approach to systemic lupus erythematosus-like autoimmune disease.

A number of C57BL/6 (B6) substrains are commonly used by scientists for basic biomedical research. One of several B6 strain-specific background diseases is focal alopecia that may resolve or progress to severe, ulcerative dermatitis. Clinical and progressive histologic changes of skin disease commonly observed in C57BL/6J and preliminary studies in other closely related substrains are presented. Lesions develop due to a primary follicular dystrophy with rupture of severely affected follicles leading to formation of secondary foreign body granulomas (trichogranulomas) in affected B6 substrains of mice. Histologically, these changes resemble the human disease called central centrifugal cicatrical alopecia (CCCA). Four B6 substrains tested have a polymorphism in alcohol dehydrogenase 4 ( Adh4) that reduces its activity and potentially affects removal of excess retinol. Using immunohistochemistry, differential expression of epithelial retinol dehydrogenase (DHRS9) was detected, which may partially explain anecdotal reports of frequency differences between B6 substrains. The combination of these 2 defects has the potential to make high dietary vitamin A levels toxic in some B6 substrains while not affecting most other commonly used inbred strains.

Background: The cytokine-deficiency-induced colitis susceptibility (Cdcs)1 locus is a major modifier of murine inflammatory bowel disease (IBD) and was originally identified in experimental crosses of interleukin-10-deficient (Il10−/−) mice. Congenic mice, in which this locus was reciprocally transferred between IBD-susceptible C3H/HeJBir-Il10−/− and resistant C57BL/6J-Il10−/− mice, revealed that this locus likely acts by inducing innate hypo- and adaptive hyperresponsiveness, associated with impaired NF-κB responses of macrophages. The aim of the present study was to dissect the complexity of Cdcs1 by further development and characterization of reciprocal Cdcs1 congenic strains and to identify potential candidate genes in the congenic interval. Methods: In total, 15 reciprocal congenic strains were generated from Il10−/− mice of either C3H/HeJBir or C57BL/6J genetic backgrounds by 10 cycles of backcrossing. Colitis activity was monitored by histological grading. Candidate genes were identified by fine mapping of congenic intervals, sequencing, microarray analysis, and a high-throughput real-time reverse-transcription polymerase chain reaction (RT-PCR) approach using bone marrow-derived macrophages. Results: Within the originally identified Cdcs1-interval, 3 independent regions were detected that likely contain susceptibility-determining genetic factors (Cdcs1.1, Cdcs1.2, and Cdcs1.3). Combining results of candidate gene approaches revealed Fcgr1, Cnn3, Larp7, and Alpk1 as highly attractive candidate genes with polymorphisms in coding or regulatory regions and expression differences between susceptible and resistant mouse strains. Conclusions: Subcongenic analysis of the major susceptibility locus Cdcs1 on mouse chromosome 3 revealed a complex genetic structure. Candidate gene approaches revealed attractive genes within the identified regions. (Inflamm Bowel Dis 2009;)

Activation-Induced Cytidine Deaminase (AID) mutates and modifies the IgH locus. However, it also initiates double-strand breaks (DSBs) throughout the genome. This effect of AID is balanced by RAD51-dependent homologous recombination repair. Importantly, we previously showed that inhibition of RAD51 function by a small-molecule inhibitor leads to cell death of AID-positive neoplastic cells. While we have used AID-RAD51 imbalance as a potential chemotherapy approach, the efficacy of current RAD51 inhibitors can be further improved. Studies have shown a relationship between glycolysis and RAD51 function, and therefore targeting the glycolytic pathway is a viable strategy to enhance RAD51 inhibitor efficacy. Here we show that glycolytic inhibitor 2DG and RAD51 inhibitor DIDS act synergistically to reduce B-lymphocyte human chronic lymphocytic leukemia proliferation ex vivo, and mice xenografted with this cell line showed significant reduction in the tumor burden in the presence of both 2DG and DIDS. These data suggest that the glycolytic pathway and DNA repair can be simultaneously targeted to produce better chemotherapies against B-lymphoid cancers. Citation Format: Muneer G. Hasham, Kin-hoe Chow, John Wilson, Nathan LaBrie, Bryant Perkins, Jane Branca, Thomas Sproule, Derry Roopenian. Targeting glycolysis and RAD51-dependent repair in B-lymphoid cancers [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr A115.

BCL10, required for nuclear factor κB (NF-κB) activation during antigen-driven lymphocyte responses, is aberrantly expressed in mucosa-associated lymphoid tissue-type marginal zone (MZ) lymphomas because of chromosomal translocations. Eμ-driven human BCL10 transgenic (Tg) mice, which we created and characterize here, had expanded populations of MZ B cells and reduced follicular and B1a cells. Splenic B cells from Tg mice exhibited constitutive activation of both canonical and noncanonical NF-κB signaling pathways is associated with increased expression of NF-κB target genes. These genes included Tnfsf13b, which encodes the B-cell activating factor (BAFF). In addition, levels of BAFF were significantly increased in sera from Tg mice. MZ B cells of Tg mice exhibited reduced turnover in vivo and enhanced survival in vitro, indicative of lymphoaccumulation rather than lymphoproliferation as the cause of MZ expansion. In vivo antibody responses to both T-independent, and especially T-dependent, antigens were significantly reduced in Tg mice. Mortality was accelerated in Tg animals, and some mice older than 8 months had histologic and molecular findings indicative of clonal splenic MZ lymphoma. These results suggest that, in addition to constitutive activation of BCL10 in MZ B cells, other genetic factors or environmental influences are required for short latency oncogenic transformation.

Aside from Myc-activating translocations characteristic of plasmacytomas (PCT), little is known about genetic factors and signaling pathways responsible for the development of spontaneous B-cell lineage lymphomas of mice. Here, we characterized the transcriptional profiles of PCT, centroblastic diffuse large B-cell lymphomas (CBL), and high-grade splenic marginal zone B-cell lymphoma (MZL++) using high-throughput quantitative reverse transcription-PCR. Expression profiles of CBL and MZL++ were strikingly similar and quite unlike that of PCT. Among the genes expressed at significantly higher levels by PCT were a number involved in NOTCH signaling, a finding supported by gene set enrichment analyses of microarray data. To investigate the importance of this pathway, NOTCH signaling was blocked in PCT cell lines by treatment with a γ-secretase inhibitor (GSI) or transduction of a dominant-negative mutant of MAML1. These treatments resulted in reduced expression of NOTCH transcriptional targets in association with impaired proliferation and increased apoptosis. GSI treatment of transformed plasma cells in a primary PCT also induced apoptosis. These results integrate NOTCH activation with oncogenic signaling pathways downstream of translocated Myc in the pathogenesis of mouse PCT, two signaling pathways also implicated in development of human multiple myeloma and T-cell lymphoblastic lymphoma. [Cancer Res 2008;68(22):9202–11]

Inbred mouse strains are routinely used as genetically defined animal models for studying a wide assortment of biological and pathological processes, including immune system function. However, no studies have presented large-scale data on the immune cell populations among the inbred strains in physiological conditions. Here we present a systematic, quantitative analysis of peripheral blood cell phenotypes of 30 mouse strains assessed by flow cytometry. This cohort of mice represents a wide range of genetic origins and includes most of the strains used in genetic, physiological, and immunological studies. We evaluated the relative percentages of peripheral blood leukocyte subtypes (lymphocytes, granulocytes, and monocytes) and lymphocyte subpopulations (CD4+ T, CD8+ T, B220+ B, and natural killer cells) of mature (6-mo-old) mice. Our comprehensive study demonstrated: 1) marked differences in the relative proportions of blood cell populations among the strains at this age, 2) considerable variation of each immune trait with more than twofold difference between strains with the highest and the lowest trait values, and 3) haplotype analysis revealed a strong correlation between eosinophil percentage and a single region on chromosome 14 containing two candidate genes. The strain differences described here provide important information for researchers applying immunophenotyping of peripheral blood in immunological and genetic studies. The data from this study are available as part of the Mouse Phenome Database at http://www.jax.org/phenome .

The glomerular filtration barrier prevents large serum proteins from being lost into the urine. It is not known, however, why the filter does not routinely clog with large proteins that enter the glomerular basement membrane (GBM). Here, we provide evidence that an active transport mechanism exists to remove immunoglobulins that accumulate at the filtration barrier. We found that FcRn, an IgG and albumin transport receptor, is expressed in podocytes and functions to internalize IgG from the GBM. Mice lacking FcRn accumulated IgG in the GBM as they aged, and tracer studies showed delayed clearance of IgG from the kidneys of FcRn-deficient mice. Supporting a role for this pathway in disease, saturating the clearance mechanism potentiated the pathogenicity of nephrotoxic sera. These studies support the idea that podocytes play an active role in removing proteins from the GBM and suggest that genetic or acquired impairment of the clearance machinery is likely to be a common mechanism promoting glomerular diseases.

The neonatal Fc receptor for IgG (FcRn) has been well characterized in the transfer of passive humoral immunity from a mother to her fetus. In addition, throughout life, FcRn protects IgG from degradation, thereby explaining the long half-life of this class of antibody in the serum. In recent years, it has become clear that FcRn is expressed in various sites in adults, where its potential function is now beginning to emerge. In addition, recent studies have examined the interaction between FcRn and the Fc portion of IgG with the aim of either improving the serum half-life of therapeutic monoclonal antibodies or reducing the half-life of pathogenic antibodies. This Review summarizes these two areas of FcRn biology.

Homologues of the SHARPIN (SHANK-associated RH domain-interacting protein) gene have been identified in the human, rat and mouse genomes. SHARPIN and its homologues are expressed in many tissues. SHARPIN protein forms homodimers and associates with SHANK in the post-synaptic density of excitatory neurotransmitters in the brain. SHARPIN is hypothesized to have roles in the crosslinking of SHANK proteins and in enteric nervous system function. We demonstrate that two independently arising spontaneous mutations in the mouse Sharpin gene, cpdm and cpdm(Dem), cause a chronic proliferative dermatitis phenotype, which is characterized histologically by severe inflammation, eosinophilic dermatitis and defects in secondary lymphoid organ development. These are the first examples of disease-causing mutations in the Sharpin gene and demonstrate the importance of SHARPIN protein in normal immune development and control of inflammation.

We have compared histologic features and gene expression profiles of newly identified plasmacytomas from NFS.V+ congenic mice with plasmacytomas of IL6 transgenic, Fasl mutant, and SJL-β2M−/− mice. NFS.V+ tumors comprised an overlapping morphologic spectrum of high-grade/anaplastic, intermediate-grade/plasmablastic, and low-grade/plasmacytic cases with similarities to subsets of human multiple myeloma and plasmacytoma. Microarray and immunohistochemical analyses of genes expressed by the most prevalent tumors, plasmablastic plasmacytomas, showed them to be most closely related to immunoblastic lymphomas, less so to plasmacytomas of Fasl mutant and SJL mice, and least to plasmacytic plasmacytomas of IL6 transgenic mice. Plasmablastic tumors seemed to develop in an inflammatory environment associated with gene signatures of T cells, natural killer cells, and macrophages not seen with plasmacytic plasmacytomas. Plasmablastic plasmacytomas from NFS.V+ and SJL-β2M−/− mice did not have structural alterations in Myc or T(12;15) translocations and did not express Myc at high levels, regular features of transgenic and pristane-induced plasmacytomas. These findings imply that, as for human multiple myeloma, Myc-independent routes of transformation contribute to the pathogenesis of these tumors. These findings suggest that plasma cell neoplasms of mice and humans exhibit similar degrees of complexity. Mouse plasmacytomas, previously considered to be homogeneous, may thus be as diverse as their human counterparts with respect to oncogenic mechanisms of plasma cell transformation. Selecting specific types of mouse plasmacytomas that relate most closely to subtypes of human multiple myeloma may provide new opportunities for preclinical testing of drugs for treatment of the human disease. [Cancer Res 2007;67(6):2439–47]

Genes at the centromeric end of the human leukocyte antigen region influence adaptive autoimmune diseases and cancer. In this study, we characterized protein expression of HKE2, a gene located in the centromeric portion of the class II region of the major histocompatibility complex encoding subunit 6 of prefoldin. Immunohistochemical analysis using an anti-HKE2 antibody indicated that HKE2 protein expression is dramatically upregulated as a consequence of activation. In a tissue microarray and in several tumors, HKE2 was overexpressed in certain cancers compared with normal counterparts. The localization of the HKE2 gene to the class II region, its cytoplasmic expression and putative protein-binding domain suggest that HKE2 may function in adaptive immunity and cancer.

CD8+ T cells activated without CD4+ T-cell help are impaired in memory expansion. To understand the underlying cellular mechanism, here we track the dynamics of helper-deficient CD8+ T-cell response to a minor histocompatibility antigen by phenotypic and in vivo imaging analyses. Helper-deficient CD8+ T cells show reduced burst expansion, rapid peripheral egress, delayed antigen clearance and continuous activation, and are eventually exhausted. Contrary to the general consensus that CD4 help encodes memory programmes in CD8+ T cells and helper-deficient CD8+ T cells are abortive, these cells can differentiate into effectors and memory precursors. Importantly, accelerating antigen clearance or simply increasing the burst effector size enables generation of memory cells by CD8+ T cells, regardless of CD4 help. These results suggest that the memory programme is CD8+ T-cell-intrinsic, and provide insight into the role of CD4 help in CD8+ T-cell responses., Persistent antigen stimulation can cause exhaustion and unresponsiveness of CD8 cells, impairing the immune response. Here the authors show that increasing the number of CD8 cells, decreasing the antigen load or providing CD4 help can overcome the exhaustion and establish a memory response.

SJL/J mice exhibit a high incidence of mature B-cell lymphomas that require CD4(+) T cells for their development. We found that their spleens and lymph nodes contained increased numbers of germinal centers and T follicular helper (TFH) cells. Microarray analyses revealed high levels of transcripts encoding IL-21 associated with high levels of serum IL-21. We developed IL-21 receptor (IL21R)-deficient Swiss Jim Lambart (SJL) mice to determine the role of IL-21 in disease. These mice had reduced numbers of TFH cells, lower serum levels of IL-21, and few germinal center B cells, and they did not develop B-cell tumors, suggesting IL-21-dependent B-cell lymphomagenesis. We also noted a series of features common to SJL disease and human angioimmunoblastic T-cell lymphoma (AITL), a malignancy of TFH cells. Gene expression analyses of AITL showed that essentially all cases expressed elevated levels of transcripts for IL21, IL21R, and a series of genes associated with TFH cell development and function. These results identify a mouse model with features of AITL and suggest that patients with the disease might benefit from therapeutic interventions that interrupt IL-21 signaling.

Infection with the helminth Schistosoma mansoni results in hepatointestinal granulomatous inflammation mediated by CD4 T cells directed against parasite eggs. The severity of disease varies greatly in humans and mice; however, the genetic basis of such a heterogenous immune response remains poorly understood. Here we show that, despite their close genetic relationship, C57BL/10SnJ (B10) mice developed significantly more pronounced immunopathology and higher T helper 17 cell responses than C57BL/6J (B6) mice. Similarly, live egg-stimulated B10-derived dendritic cells (DCs) produced significantly more IL-1β and IL-23, resulting in higher IL-17 production by CD4 T cells. Gene expression analysis disclosed a heightened proinflammatory cytokine profile together with a strikingly lower expression of Ym1 in B10 versus B6 mice, consistent with failure of B10 DCs to attain alternative activation. To genetically dissect the differential response, we developed and analyzed congenic mouse strains that capture major regions of allelic variation, and found that the level of inflammation was controlled by a relatively small number of genes in a locus mapping to chromosome 4 117-143 MB. Our study has thus identified novel genomic regions that regulate the severity of the schistosome infection by way of controlling the mode of DC activation and consequent CD4 T-cell subset development.

The MHC class I-like Fc receptor FcRn plays an essential role in extending the half-life (t(1/2)) of IgG antibodies and IgG-Fc-based therapeutics in the circulation. The goal of this study was to analyze the effect of human IgG1 (hIgG1) antibodies with enhanced in vitro binding to FcRn on their in vivo t(1/2) in mice expressing human FcRn (hFcRn). Mutants of the humanized monoclonal Herceptin antibody (Hu4D5-IgG1), directed against human epidermal growth factor receptor 2 (p185 (HER2)), show altered pH-dependent binding to hFcRn in vitro. Two engineered IgG1 mutants (N434A and T307A/E380A/N434A) showed a considerably extended t(1/2) in vivo compared with wild-type antibody in mice expressing an hFcRn transgene (Tg) but not in mice expressing the endogenous mouse FcRn. The efficiency of hFcRn-mediated protection was dependent on hFcRn Tg copy number. Moreover, when injected into FcRn-humanized mice at a concentration sufficient to partially saturate hFcRn, the engineered IgG1 mutants with an extended serum t(1/2) were most effective in reducing the t(1/2) of a tracer hIgG1 antibody. Finally, administration of mutant with high binding to hFcRn ameliorated arthritis induced by passive transfer with human pathogenic plasma. These results indicate that Fc regions modified for high binding affinity to hFcRn increases serum persistence of therapeutic antibodies, that the same approach can be exploited as an anti-autoimmune therapy to promote the clearance of endogenous pathogenic IgG and that FcRn-humanized mice are a promising surrogate for hIgG therapeutic development.

The neonatal Fc receptor for IgG (FcRn) plays a major role in regulating host IgG levels and transporting IgG and associated antigens across polarized epithelial barriers. Selective expression of FcRn in the epithelium is shown here to be associated with secretion of IgG into the lumen that allows for defense against an epithelium-associated pathogen (Citrobacter rodentium). This pathway of host resistance to a bacterial pathogen as mediated by FcRn involves retrieval of bacterial antigens from the lumen and initiation of adaptive immune responses in regional lymphoid structures. Epithelial-associated FcRn, through its ability to secrete and absorb IgG, may thus integrate luminal antigen encounters with systemic immune compartments and as such provide essential host defense and immunoregulatory functions at the mucosal surfaces.

The purpose of this study was to prepare a tetravalent anti-human CD22 recombinant antibody with improved antitumor activity and a half life longer than that of its divalent counterpart. We compared the ability of tetravalent vs. divalent antibody to associate/dissociate to/from CD22-positive Daudi cells, to interact with murine and human Fcgamma receptors (FcgammaR), to bind human complement component C1q, to inhibit the growth of tumor cells, to diffuse into various tissues, to be internalized by Daudi cells, to react with human neonatal Fc receptors (FcRn), and to persist in the circulation of normal mice. As compared to the murine or chimeric divalent antibodies, the chimeric tetravalent counterpart has a longer half life in mice. It also has an affinity for FcRns that is identical to that of human IgG. The tetravalent antibody has increased antitumor activity in vitro and completely conserved effector functions (binding to FcgammaR-positive cells and to C1q) in vitro. Despite its 33% higher molecular weight, it penetrates mouse tissues as well as its divalent antibody counterpart. Based on the improved in vitro performance and pharmacokinetics of the tetravalent antibody it will now be tested for its antitumor activity in vivo.

Rheumatoid arthritis (RA) is a complex autoimmune disease with a poorly understood pathogenesis. The disease is associated with polyclonal B cell activation and the production of autoantibodies (autoAbs), but there is a longstanding controversy as to whether such Abs contribute to, or are secondary to, the pathogenesis of RA. To address the potential pathogenicity of human RA–associated Abs, we developed a passive transfer model involving mice deficient in the low-affinity inhibitory Fc receptor, FcγRIIB. We report that plasma or serum from patients with active RA can induce inflammation and histological lesions in FcγRIIB−/− mice consistent with arthritis, and that this pathogenic activity is caused by the immunoglobulin G–rich fraction. Our results suggest that humoral autoimmunity can contribute directly to autoimmune arthritis, and that FcγRIIB−/− mice are a promising model to evaluate the arthritogenic potential of human autoAbs.

Numerous mechanisms of action have been proposed for intravenous Ig (IVIG). In this study, we used IgG passive transfer murine models of bullous pemphigoid (BP), pemphigus foliaceus (PF), and pemphigus vulgaris (PV) to test the hypothesis that the effect of IVIG in autoantibody-mediated cutaneous bullous diseases is to accelerate the degradation of pathogenic IgG by saturation of the MHC-like Fc receptor neonatal Fc receptor (FcRn). BP, PF, and PV are organ-specific antibody-mediated diseases in which autoantibodies target the hemidesmosomal antigen BP180 and desmosomal antigens Dsg1 and Dsg3, respectively. Antibodies against BP180, Dsg1, and Dsg3, when injected into neonatal mice, induce the BP, PF, and PV disease phenotypes, respectively. We found that FcRn-deficient mice were resistant to experimental BP, PF, and PV. Circulating levels of pathogenic IgG in FcRn-deficient mice were significantly reduced compared with those in WT mice. Administration of high-dose human IgG (HDIG) to WT mice also drastically reduced circulating pathogenic IgG levels and prevented blistering. In FcRn-deficient mice, no additional protective effect with HDIG was realized. These data demonstrate that the therapeutic efficacy of HDIG treatment in the pemphigus and pemphigoid models is dependent on FcRn. Thus, FcRn is a promising therapeutic target for treating such IgG-mediated autoimmune diseases.

The role of NKT cells during immune responses is diverse, ranging from antiviral and antitumor activity to the regulation of autoimmune diseases; however, the regulatory function of CD1d-dependent NKT cells in rejection responses against allogeneic graft is uncertain. In this study, we demonstrated the direct regulatory effects of CD1d-dependent NKT cells using an allogeneic skin transplantation model. H-Y-mismatched skin graft survival was shortened in CD1d−/− recipients compared with wild-type recipients. Adoptive transfer of syngeneic NKT cells via splenocytes or hepatic mononuclear cells into CD1d−/− recipients restored graft survival times to those of wild-type recipients. α-Galactosylceramide, a specific activator of NKT cells, further prolonged graft survival. Although CD1d-dependent NKT cells did not extend skin graft survival in either major or complete minor histocompatibility-mismatched models, these cells affected graft survival in minor Ag mismatch models according to the magnitude of the antigenic difference. The afferent arm of NKT cell activation during transplantation required CD1d molecules expressed on host APCs and the migration of CD1d-dependent NKT cells into grafts. Moreover, the regulatory effects of CD1d-dependent NKT cells against alloantigen were primarily IL-10 dependent. Taken together, we concluded that CD1d-dependent NKT cells may directly affect the outcome of allogeneic skin graft through an IL-10-dependent regulatory mechanism.

Germline mutations in Fas and Fasl induce nonmalignant T cell hyperplasia and systemic autoimmunity and also greatly increase the risk of B cell neoplasms. B lymphomas occurring in Fasl mutant (gld) mice usually are immunoglobulin (Ig) isotype switched, secrete Ig, and are plasmacytoid in appearance but lack Myc translocations characteristic of other plasma cell (PC) neoplasms. Here, we explore the relationship between B cell autoreactivity and transformation and use gene expression profiling to further classify gld plasmacytoid lymphomas (PLs) and to identify genes of potential importance in transformation. We found that the majority of PLs derive from antigen-experienced autoreactive B cells producing antinuclear antibody or rheumatoid factor and exhibit the skewed Ig V gene repertoire and Ig gene rearrangement patterns associated with these specificities. Gene expression profiling revealed that both primary and transplanted PLs share a transcriptional profile that places them at an early stage in PC differentiation and distinguishes them from other B cell neoplasms. In addition, genes were identified whose altered expression might be relevant in lymphomagenesis. Our findings provide a strong case for targeted transformation of autoreactive B cells in gld mice and establish a valuable model for understanding the relationship between systemic autoimmunity and B cell neoplasia.

IL-21 is a type I cytokine whose receptor is expressed on T, B, and NK cells. Within the B cell lineage, IL-21 regulates IgG1 production and cooperates with IL-4 for the production of multiple Ab classes in vivo. Using IL-21-transgenic mice and hydrodynamics-based gene delivery of IL-21 plasmid DNA into wild-type mice as well as in vitro studies, we demonstrate that although IL-21 induces death of resting B cells, it promotes differentiation of B cells into postswitch and plasma cells. Thus, IL-21 differentially influences B cell fate depending on the signaling context, explaining how IL-21 can be proapoptotic for B cells in vitro yet critical for Ag-specific Ig production in vivo. Moreover, we demonstrate that IL-21 unexpectedly induces expression of both Blimp-1 and Bcl-6, indicating mechanisms as to how IL-21 can serve as a complex regulator of B cell maturation and terminal differentiation. Finally, BXSB-Yaa mice, which develop a systemic lupus erythematosus-like disease, have greatly elevated IL-21, suggesting a role for IL-21 in the development of autoimmune disease.

Periodontal disease is one of the most prevalent chronic inflammatory diseases. There is a genetic component to susceptibility and resistance to this disease. Using a mouse model, we investigated the progression of alveolar bone loss by gene expression profiling of susceptible and resistant mouse strains (BALB/cByJ and A/J, respectively). We employed a novel and sensitive quantitative real-time PCR method to compare basal RNA transcription of a 48-gene set in the gingiva and the spleen and the subsequent changes in gene expression due to Porphyromonas gingivalis oral infection. Basal expression of interleukin-1 beta ( Il1b ) and tumor necrosis factor alpha ( Tnf ) mRNA was higher in the gingiva of the susceptible BALB/cByJ mice than in the gingiva of resistant A/J mice. Gingival Il1b gene expression increased further and Stat6 gene expression was turned on after P. gingivalis infection in BALB/cByJ mice but not in A/J mice. The basal expression of interleukin-15 ( Il15 ) in the gingiva and the basal expression of p-selectin ( Selp ) in the spleen were higher in the resistant A/J mice than in the susceptible BALB/cByJ mice. In the resistant A/J mice the expression of no genes detectably changed in the gingiva after infection. These results suggest a molecular phenotype in which discrete sets of differentially expressed genes are associated with genetically determined susceptibility ( Il1b , Tnf , and Stat6 ) or resistance ( Il15 and Selp ) to alveolar bone loss, providing insight into the genetic etiology of this complex disease.

The MHC class I family-like Fc receptor, FcRn, is normally responsible for extending the life span of serum IgG Ab's, but whether this molecule contributes to autoimmune pathogenesis remains speculative. To determine directly whether this function contributes to humoral autoimmune disease, we examined whether a deficiency in the FcRn heavy chain influences autoimmune arthritis in the K/BxN mouse model. FcRn deficiency conferred either partial or complete protection in the arthritogenic serum transfer and the more aggressive genetically determined K/BxN autoimmune arthritis models. The protective effects of an FcRn deficiency could be overridden with excessive amounts of pathogenic IgG Ab's. The therapeutic saturation of FcRn by high-dose intravenous IgG (IVIg) also ameliorated arthritis, directly implicating FcRn blockade as a significant mechanism of IVIg's anti-inflammatory action. The results suggest that FcRn is a potential therapeutic target that links the initiation and effector phases of humoral autoimmune disease.

Minor histocompatibility antigens (minor H antigen) elicit strong T-cell-mediated responses during both graft rejection and graft versus leukemia (GvL) among MHC-matched individuals (where MHC is major histocompatibility complex). Employing expression-cloning methodology, we have identified a cDNA clone, MI-35, encoding the immunodominant H4b minor H antigen within the classical mouse H4 complex. The minimal antigenic epitope derived from H4b presented on Kb class I MHC is SGIVYIHL (SYL8) and the polymorphism is due to C-->T nucleotide modification in p3 resulting in the change of threonine (ACT) to isoleucine (ATT). The results presented here demonstrate that amino acid variation in the allelic epitopes results in the low abundance of H4a peptide. The differential peptide copy number resulted in an immunodominant cytotoxic T cells (CTL) response directed against H4b while the anti-B6 response directed against H4a was easily dominated. These results provide a molecular mechanism for the H4 minor H antigen and suggest a novel mechanism by which alloantigenic disparity caused by conservative amino acid changes can be augmented by posttranslational antigen processing events.

Minor histocompatibility (H) Ag disparities result in graft-vs-host disease and chronic solid allograft rejection in MHC-identical donor-recipient combinations. Minor H Ags are self protein-derived peptides presented by MHC class I molecules. Most arise as a consequence of allelic variation in the bound peptide (p) that results in TCR recognizing the p/MHC as foreign. We used a combinational peptide screening approach to identify the immune dominant H2Kb-restricted epitope defining the mouse H4b minor H Ag. H4b is a consequence of a P3 threonine to isoleucine change in the MHC-bound peptide derived from epithelial membrane protein-3. This allelic variation also leads to phosphorylation of the H4b but not the H4a epitope. Further, ex vivo CD8+ T lymphocytes bind phosphorylated Ag tetramers with high efficiency. Although we document the above process in the minor H Ag system, posttranslational modifications made possible by subtle amino acid changes could also contribute to immunogenicity and immune dominance in tumor immunotherapeutic settings.

Abs of the IgG isotype are efficiently transported from mother to neonate and have an extended serum t1/2 compared with Abs of other isotypes. Circumstantial evidence suggests that the MHC class I-related protein, the neonatal FcR (FcRn), is the FcR responsible for both in vivo functions. To understand the phenotypes imposed by FcRn, we produced and analyzed mice with a defective FcRn gene. The results provide direct evidence that perinatal IgG transport and protection of IgG from catabolism are mediated by FcRn, and that the latter function is key to IgG homeostasis, essential for generating a potent IgG response to foreign Ags, and the basis of enhanced efficacy of Fc-IgG-based therapeutics. FcRn is therefore a promising therapeutic target for enhancing protective humoral immunity, treating autoimmune disease, and improving drug efficacy.

Background. Murine orthotopic corneal allografts experience immune privilege and have good survival as compared with skin allografts. However, privilege is not complete, and some grafts are still rejected. Unexpectedly, corneas expressing minor histocompatibility (H) alloantigens are rejected at a higher rate than major histocompatibility complex (MHC) disparate grafts. We hypothesize that certain immunodominant minor H alloantigens are extremely immunogenic when expressed in corneal tissue, terminate ocular immune privilege, and initiate corneal allograft rejection. Methods and Results. Corneal allograft survival and the role of CD4+ T cells and CD8+ T cells were examined in corneal transplants that expressed genetically defined minor H3 alloantigens. The H3 locus contains at least two minor H genes. H3a is presented by MHC class I and recognized exclusively by CD8+ T cells. H3b is presented by class II and recognized exclusively by CD4+ T cells. Congenic strains that differ from C57BL/10 at (1) H3a, (2) H3b, or (3) H3a+H3b were used for orthotopic corneal and skin transplants. Donor corneas expressing either H3a or H3a+H3b experienced immune privilege and survived longer than skin allografts. By contrast, donor corneas expressing H3b (recognized by CD4+ T cells) experienced vigorous rejection and were eliminated faster than skin allografts. Conclusion. There are minor H alloantigens that terminate ocular immune privilege and initiate corneal allograft rejection. These minor H alloantigens are more immunogenic when expressed in corneal tissue than when they are expressed in skin allografts.

The inverse relationship between serum albumin concentration and its half-life suggested to early workers that albumin would be protected from a catabolic fate by a receptor-mediated mechanism much like that proposed for IgG. We show here that albumin binds FcRn in a pH dependent fashion, that the lifespan of albumin is shortened in FcRn-deficient mice, and that the plasma albumin concentration of FcRn-deficient mice is less than half that of wild-type mice. These results affirm the hypothesis that the major histocompatibility complex–related Fc receptor protects albumin from degradation just as it does IgG, prolonging the half-lives of both.

Caroline G. McPhee1, F. Jason Duncan2, Kathleen A. Silva1, Lloyd E. King Jr.3, Harm HogenEsch4, Derry C. Roopenian1, Helen B. Everts2, and John P. Sundberg1,3 1The Jackson Laboratory, Bar Harbor, ME 2Department of Nutrition, The Ohio State University, Columbus, OH 3Division of Dermatology, Vanderbilt University, Nashville, TN 4Department of Comparative Pathobiology, Purdue University, West Lafayette, IN, Bar Harbor, Maine, USA

Epidermolysis bullosa (EB) describes a spectrum of rare, incurable, inherited mechanobullous disorders unified by the fact that they are caused by structural defects in the basement membrane zone which disrupt adhesion between the epidermis and dermis. Mouse models provide valuable tools to define the molecular basis of these diseases and to test novel therapeutic approaches. There is need for rapid, quantitative tests that measure the integrity of dermal-epidermal adhesions in such models. To address this need, we describe a novel quantitative method to determine the mechanical strength of the adhesion between tail skin epidermis and dermis. We show that this test reliably measures the force required to cause dermal-epidermal separation in tails of mice that are genetically predisposed to a form of non-Herlitz Junctional EB which develops as the result of a hypomorphic mutation in the laminin gamma 2 gene (Lamc2(jeb) ). This simple, quantitative method of directly measuring the tensile strength of dermal-epidermal adhesion provides a novel dimension to the pathophysiological screening, evaluation, and therapeutic treatment of mice that may develop progressive forms of EB and potentially other disorders that compromise cutaneous integrity.

The H60 minor histocompatibility (H) antigen peptide is derived from a glycoprotein that serves as a ligand for the stimulatory NKG2D receptor. We show that this peptide is remarkably immunodominant in that it competes effectively with MHC alloantigens, is efficiently crosspresented by host antigen-presenting cells (APCs), and readily elicits naive CD8 T cell responses in vitro. H60 immunodominance is neither a consequence of NKG2D engagement nor competition among minor H antigens on APCs. Instead, H60 immunodominance is a consequence of an abnormally high naive precursor frequency of H60 peptide reactive CD8 T cells. Understanding why the H60 peptide is so immunogenic has important implications in tissue transplantation and vaccine design.

The mouse H13 minor histocompatibility (H) Ag, originally detected as a barrier to allograft transplants, is remarkable in that rejection is a consequence of an extremely subtle interchange, P4Val/Ile, in a nonamer H2-Db-bound peptide. Moreover, H13 peptides lack the canonical P5Asn central anchor residue normally considered important for forming a peptide/MHC complex. To understand how these noncanonical peptide pMHC complexes form physiologically active TCR ligands, crystal structures of allelic H13 pDb complexes and a P5Asn anchored pDb analog were solved to high resolution. The structures show that the basis of TCRs to distinguish self from nonself H13 peptides is their ability to distinguish a single solvent-exposed methyl group. In addition, the structures demonstrate that there is no need for H13 peptides to derive any stabilization from interactions within the central C pocket to generate fully functional pMHC complexes. These results provide a structural explanation for a classical non-MHC-encoded H Ag, and they call into question the requirement for contact between anchor residues and the major MHC binding pockets in vaccine design.

Systemic lupus erythematosus (SLE) is an autoimmune disease mediated mainly by autoantibodies reactive to nuclear acids and proteins. These autoantibodies are mostly of IgG isotype, indicating that class-switch recombination (CSR) may play an important role in the development of SLE. CSR is initiated by the enzyme, activation-induced cytidine deaminase (AID) which induces double strand DNA breaks then repaired by homologous recombination using the RAD51 complex. We hypothesize that therapeutic targeting of CSR will retard the development of SLE by inducing cell death in AID-expressed B cells and reducing pathogenic IgG antibodies. The BXSB/MpJ mouse is a well characterized model of human SLE, exhibiting a robust germinal center response and copious production of immunoglobulins. 4,4’-diisothiocyanatostilbene-2-2’-disulfonic acid (DIDS) is a molecule which impairs homologous recombination by inhibiting the binding of RAD51 complex to DNA. In this study, male BXSB/MpJ mice were injected with DIDS or control. Treated mice showed a reduction in the germinal center B cell population and a corresponding decrease in follicular T helper cells. T1 B cell and follicular B cell populations were significantly decreased in DIDS treated mice but no changes were found in marginal zone B cells. Sera were analyzed for the immunoglobulin levels and antinuclear antibodies. These findings demonstrate that targeting CSR by DIDS reduces potentially pathogenic B lymphocyte populations and may be a viable novel therapeutic option in the treatment of SLE.