PP2A catalytic subunit alpha is critically required for CD8+ T cell homeostasis and anti-bacterial responses

While the functions of tyrosine phosphatases in T cell biology have been extensively studied, our knowledge on the contribution of serine/threonine phosphatases in T cells remains poor. Protein phosphatase 2A (PP2A) is one of the most abundantly expressed serine/threonine phosphatases. It is important in thymocyte development and CD4+ T cell differentiation. Utilizing a genetic model in which its catalytic subunit alpha isoform (PP2A Cα) is deleted in T cells, we investigated its contribution to CD8+ T cell homeostasis and effector functions. Our results demonstrate that T cell intrinsic PP2A Cα is critically required for CD8+ T cell homeostasis in secondary lymphoid organs and intestinal mucosal site. Importantly, PP2A Cα deficient CD8+ T cells exhibit reduced proliferation and survival. CD8+ T cell anti-bacterial response is strictly dependent on PP2A Cα. Expression of Bcl2 transgene rescues CD8+ T cell homeostasis in spleens, but not in intestinal mucosal site, nor does it restore the defective anti-bacterial responses. Finally, proteomics and phosphoproteomics analyses reveal potential targets dependent on PP2A Cα, including mTORC1 and AKT. Thus, PP2A Cα is a key modulator of CD8+ T cell homeostasis and effector functions.

Brain cancer induces systemic immunosuppression through release of non-steroid soluble mediators

Immunosuppression of unknown aetiology is a hallmark feature of glioblastoma and is characterized by decreased CD4 T-cell counts and downregulation of major histocompatibility complex class II expression on peripheral blood monocytes in patients. This immunosuppression is a critical barrier to the successful development of immunotherapies for glioblastoma. We recapitulated the immunosuppression observed in glioblastoma patients in the C57BL/6 mouse and investigated the aetiology of low CD4 T-cell counts. We determined that thymic involution was a hallmark feature of immunosuppression in three distinct models of brain cancer, including mice harbouring GL261 glioma, B16 melanoma, and in a spontaneous model of diffuse intrinsic pontine glioma. In addition to thymic involution, we determined that tumour growth in the brain induced significant splenic involution, reductions in peripheral T cells, reduced MHC II expression on blood leucocytes, and a modest increase in bone marrow resident CD4 T cells. Using parabiosis we report that thymic involution, declines in peripheral T-cell counts, and reduced major histocompatibility complex class II expression levels were mediated through circulating blood-derived factors. Conversely, T-cell sequestration in the bone marrow was not governed through circulating factors. Serum isolated from glioma-bearing mice potently inhibited proliferation and functions of T cells both in vitro and in vivo. Interestingly, the factor responsible for immunosuppression in serum is non-steroidal and of high molecular weight. Through further analysis of neurological disease models, we determined that the immunosuppression was not unique to cancer itself, but rather occurs in response to brain injury. Non-cancerous acute neurological insults also induced significant thymic involution and rendered serum immunosuppressive. Both thymic involution and serum-derived immunosuppression were reversible upon clearance of brain insults. These findings demonstrate that brain cancers cause multifaceted immunosuppression and pinpoint circulating factors as a target of intervention to restore immunity.

Conditional Silencing of H-2Db Class I Molecule Expression Modulates the Protective and Pathogenic Kinetics of Virus-Antigen-Specific CD8 T Cell Responses during Theiler's Virus Infection

Theiler's murine encephalomyelitis virus (TMEV) infection of the CNS is cleared in C57BL/6 mice by a CD8 T cell response restricted by the MHC class I molecule H-2D^b The identity and function of the APC(s) involved in the priming of this T cell response is (are) poorly defined. To address this gap in knowledge, we developed an H-2D^b LoxP-transgenic mouse system using otherwise MHC class I-deficient C57BL/6 mice, thereby conditionally ablating MHC class I-restricted Ag presentation in targeted APC subpopulations. We observed that CD11c⁺ APCs are critical for early priming of CD8 T cells against the immunodominant TMEV peptide VP2_121-130 Loss of H-2D^b on CD11c⁺ APCs mitigates the CD8 T cell response, preventing early viral clearance and immunopathology associated with CD8 T cell activity in the CNS. In contrast, animals with H-2D^b-deficient LysM⁺ APCs retained early priming of D^b:VP2_121-130 epitope-specific CD8 T cells, although a modest reduction in immune cell entry into the CNS was observed. This work establishes a model enabling the critical dissection of H-2D^b-restricted Ag presentation to CD8 T cells, revealing cell-specific and temporal features involved in the generation of CD8 T cell responses. Employing this novel system, we establish CD11c⁺ cells as pivotal to the establishment of acute antiviral CD8 T cell responses against the TMEV immunodominant epitope VP2_121-130, with functional implications both for T cell-mediated viral control and immunopathology.

CAR T cells generated in situ using gene therapy in naturally activated lymph node T cells

T cells expressing chimeric antigen receptors (CAR T cells) are manufactured outside the body using non-physiological activation and in vitro culture protocols. The procedure takes 3 weeks and costs approximately $450,000 to administer. We have devised a scheme using mouse models for manufacturing CAR T cells in just 3 days employing a natural, polyclonal anti-viral immune response inside a lymph node (LN) using off the shelf reagents that can be applied widely in populations. CAR T cells emerge from the LN within a week, invade solid tumor, and eliminate the targeted antigen-positive tumor cells. Polyclonal activation of T cells is achieved by modifying the antigen presenting properties of lymph node resident professional antigen presenting cells (APC) through viral expression of allogeneic major histocompatibility antigens. The ensuing polyclonal activation occurs in the context of virus activated APC within the normal aarchitecture of the LN and confers robust T cell activation signals directing the development of cytolytic T cells. During the course of T cell activation, the T cells are transduced in situ with retroviruses encoding selected CARs. This approach could be applied to any number of different CARs to target a variety of tumors. T cells activated in the lymph node are functionally distinct from those activated using standard CAR T manufacturing protocols. We anticipate that CAR T cells generated in situ to natural stimuli will exhibit more normal immune regulatory properties that will impact their therapeutic utility. Because our approach uses off the shelf reagents and is administered using standard clinical procedures, cost to patients should be lowered and access to therapy increased.

Anti-CD3 Mono-Fab co-potentiates TCR antigen recognition in human T cells

TCR mediated antigen recognition results in a signaling cascade leading to T cell activation. Antigen binding to its cognate TCR drives receptor aggregation and conformational changes that trigger signaling from the receptor. Conformational change in the CD3 complex (CD3Δc) is required for robust signaling and productive T cell responses. In contrast, weakly recognized antigens do not induce CD3Δc and the resulting T cell response is poor. Thus, T cell responses to weak antigens may be improved by induction of CD3Δc. We previously described an anti-mouse CD3ɛ monovalent Fab (Mono-7D6-Fab) that induced CD3Δc and synergized with weak antigens to enhance the T cell response, a process we termed co-potentiation. However, Mono-7D6-Fab did not induce classical T cell signaling in the absence of antigenic ligation. Mono-7D6-Fab effectively co-potentiated T cells against murine B16-F10 melanoma cells and reduced tumor burden in vivo in a T cell dependent manner. We exploited a model of human cytomegalovirus (CMV) to generate proof of concept that co-potentiation may enhance T cell antigen recognition in humans. Anti-human CD3ɛ monovalent Fab (Mono-OKT3-Fab) improved the CD8 T cell response to the CMV pp65495–503 peptide as measured by increased T cell proliferation, cytokine production, and the ability to kill target cells. Co-potentiation was dependent on antigen specificity, as 1) the effects were dampened when antigen recognition was impaired and 2) sequencing of the TCRs revealed a restricted number of expanded TCR clones. Our results suggest that Mono-OKT3-Fab may have therapeutic clinical applications to achieve a more robust antigen-specific T cell response in the context of diverse human disease, from cancer to chronic infection.

A generalized pathway of immunocompromise following central nervous system insult: the release of large immunosuppressive molecules and thymic involution

Immunosuppression following damage to the CNS is a common, yet poorly understood, feature of neurological diseases as diverse as stroke, traumatic brain injury, and glioblastoma. This immunosuppression is a barrier to successful patient outcomes. We sought to define the effect of various brain insults on the thymus and T-cell responses. We tested thymic function following various neurological insults, including viral infection, brain tumor, sterile inflammation, physical injury, and seizures. All brain insults resulted in significant thymic involution that was reversible if the insult was cleared. Thymic involution did not occur following similar peripheral insults. Using parabiosis, we demonstrated that thymic involution was transferable via circulatory routes from glioma-bearing to non-tumor-bearing parabionts. Similarly, serum obtained from mice with ongoing neurological insults potently inhibited T-cell proliferation in vitro. We next fractionated the serum based on molecular weight and tested the resulting fractions’ immunosuppressive potential. Interestingly, we found that serum fractions with large molecular weights of greater than 100 kiloDaltons were responsible for the immunosuppressive properties of serum obtained from glioma-bearing mice. In short, CNS-specific insults, regardless of nature, induce immunosuppression by prompting thymic involution and systemic immunosuppression mediated through circulating factors with large molecular weight. These studies provide evidence of the mechanisms leading to immune deficiencies observed in patients following neurological injuries.

MHC genotype, immune repertoire, and tumor immunity all influence spontaneous cancer development and metastasis in spontaneous breast cancer models

20 to 30% of breast cancers overexpress ERRB2, encoding the human epidermal growth factor-2 receptor (HER2). Overexpression of HER2 is associated with poorer prognosis, particularly in metastatic disease. Although HER2 therapeutics exists many patients eventually develop uncontrolled tumor growth. The BALB/c-neuT mouse has been a popular model for investigating HER2-positive breast cancer. We have found that immune responsiveness and MHC genotype are important factors in spontaneous tumor development and tumor rejection in the neuT model. To assess the influence of immune response potential on tumor biology we introduced the skg ZAP-70 mutation or the H-2b MHC haplotype into the neuT model. Spontaneous tumors appeared with decreased frequency and metastasis or increased frequency and metastasis, respectively, in comparison to the BALB/c model. H-2b tumors were readily transplantable into the breast fat pads of syngeneic BALB.B-neuT hosts which developed systemic immune abnormalities very similar to those observed in BALB/c - neuT or BALB/c WT mice bearing neuT tumors. However, BALB.B WT hosts initially accepted the grafts, but subsequently rejected them after they were established. Adoptive transfer of splenocytes from BALB.B WT mice which had rejected tumor conferred resistance to the tumor grafts, as well as to spontaneous tumors developing in BALB.B neuT littermates. The strong H-2b-mediated antitumor response in WT mice indicates efficient antigen presentation, and presumably leads to strong tolerance in neuT+ animals. The importance of an intact T cell signaling and MHC genotype indicate a critical role for T cell-mediated immunity and tolerance in the biology of the spontaneously developing tumor and metastasis.

The early proximal αβ TCR signalosome specifies thymic selection outcome through a quantitative protein interaction network

During αβ T cell development, T cell antigen receptor (TCR) engagement transduces biochemical signals through a protein-protein interaction (PPI) network that dictates dichotomous cell fate decisions. It remains unclear how signal specificity is communicated, instructing either positive selection to advance cell differentiation or death by negative selection. Early signal discrimination might occur by PPI signatures differing qualitatively (customized, unique PPI combinations for each signal), quantitatively (graded amounts of a single PPI series), or kinetically (speed of PPI pathway progression). Using a novel PPI network analysis, we found that early TCR-proximal signals distinguishing positive from negative selection appeared to be primarily quantitative in nature. Furthermore, the signal intensity of this PPI network was used to find an antigen dose that caused a classic negative selection ligand to induce positive selection of conventional αβ T cells, suggesting that the quantity of TCR triggering was sufficient to program selection outcome. Because previous work had suggested that positive selection might involve a qualitatively unique signal through CD3δ, we reexamined the block in positive selection observed in CD3δ⁰ mice. We found that CD3δ⁰ thymocytes were inhibited but capable of signaling positive selection, generating low numbers of MHC-dependent αβ T cells that expressed diverse TCR repertoires and participated in immune responses against infection. We conclude that the major role for CD3δ in positive selection is to quantitatively boost the signal for maximal generation of αβ T cells. Together, these data indicate that a quantitative network signaling mechanism through the early proximal TCR signalosome determines thymic selection outcome.

Abstract P4-09-03: Phenotypes of breast tumor cells and normal lymphocytes are determined by the integration of minor changes in expression of multiple genes: A new dimension in quantitative inheritance

Breast tumors develop under environmental pressures with phenotypically variant cells generated by mutation and epigenetic changes providing the substrate for clonal selection. Chromosomal mutations are a feature of spontaneous breast tumors in the BALB-neuT mouse model. However, there is little evidence that specific changes in chromosomal structure or ploidy confer selective advantage in these spontaneous tumors. The prominent exception is a consistent loss of chromosome 4, a little understood feature common to several mouse tumors. We previously measured heterozygosity in spontaneous breast tumors from FVB X BALB-neuT F1 mice using Illumina’s Golden Gate assay. In addition to the expected gain and loss of heterozygosity (LOH) evident throughout the genomes of a cohort of spontaneous tumors, the assay also detected wide-spread stochastic pseudo-“LOH” at 600 discrete loci spread throughout the genome in unique patterns among the tumors. Several of these positions were examined by sequence analysis revealing no deviations from the WT sequences, suggesting the detected “LOH” may have been generated by epigenetic modification of DNA which altered sequence detection. While, epigenetically modified DNA templates recapitulated the observed “LOH” signals, no canonical CpG motifs were present in the majority of the 600 loci probed, suggesting that an unusual DNA modification could be responsible for the unexpected wide-spread stochastic structural changes in the breast tumor DNA. We next assessed whether these putative epigenetic changes in DNA structure might impact gene regulation, and have reported that the stochastic pattern observed as “LOH” in DNA was recapitulated in the transcriptomes in unique patterns among the tumors. A direct correlation between the number of “LOH” variants and the down regulation of hundreds of non-polymorphic genes in the transcriptome also was noted. Furthermore, pathway analyses of the genes exhibiting changes in allelic ratios in these tumors revealed significant enrichments within gene networks regulating tissue homeostasis and antigen presentation, providing strong evidence that the perturbations in gene expression translated into selectable tumor cell phenotypes. We now have extended this study to examine the relationship between the magnitude of change in the expression of genes mapping within the pathways regulating tissue homeostasis (Molecular Mechanisms of Cancer). A remarkable feature of the flagged genes is that the magnitude of change in gene expression was not great in each case, yet the biological consequences were strongly reflected in the evolutionary history of the tumors. Importantly, the polymorphisms marking the parental alleles are mostly silent, not altering the structure of the encoded products. Therefore magnitude and timing of gene expression are the likely determinants of phenotypic variation. Each tumor contained several outliers within the pathways regulating tissue homeostasis, suggesting that the integration of multiple small perturbations in the expression of genes comprising functional networks could influence the biology properties of the tumor cells. Overall expression of the loci marked by allelic outliers was significantly below the average expression found among tumors in the cohort highlighting the importance of down regulation of one allele in the establishment of selectable traits. We find a similar direct correlation of multiple small changes in the transcriptome of normal lymphocytes with immune response phenotypes, suggesting this principle of integration of multiple small deviations in gene expression applies widely to the phenotypes of normal cells, tumors, and by extension to organismic traits.

Citation Format: Larry R Pease, Sara J Felts, Adam D Scheid, Xiaojia Tang, Krishna R Kalari. Phenotypes of breast tumor cells and normal lymphocytes are determined by the integration of minor changes in expression of multiple genes: A new dimension in quantitative inheritance [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P4-09-03.

Abstract P5-04-15: An immunogenic mouse model using BALB.B-MMTV-neuT breast cancers reveals spontaneous protective humoral immunity

The BALB/c-neuT mouse has been a faithful model for investigating metastatic breast cancer. Spontaneous breast tumors from BALB/c-neuT mice are readily transplantable orthotopically into syngeneic or rat neuT negative BALB/c WT hosts facilitating controlled studies of developing breast cancers. When introduced into the breast ducts of BALB/c WT hosts, lung metastases form similarly to how they appear in mice with spontaneous tumors. Tumor grafts grow out with comparable kinetics and induce similar systemic immune abnormalities in the spleens and lymph nodes of both lines of mice as seen in mice with spontaneous tumors. Factors inducing these abnormal immune cell configurations are not yet known. Immunization of BALB/c WT mice against the rat Her2 antigen can induce both T cell and antibody mediated rejection of the transplanted tumors, but these approaches have not been equally successful in syngeneic, rat neuT+ positive hosts, indicating tolerance to rat Her2 is a significant barrier to the induction of immunity against these breast tumors. The MHC encodes class I and class II antigen presenting molecules which are known to be highly polymorphic in both structure and function. We introduced the H-2b MHC haplotype into the MMTV-NeuT model to assess the influence of a different set of antigen presenting molecules on tumor biology. In BALB.B-neuT mice spontaneous tumors appeared with frequencies and in numbers similar to those seen in the BALB/c model. In anything, lung metastases are more frequent and more aggressive in BALB.B-neuT mice. Again, the tumors were readily transplantable into the breast fat pads of syngeneic BALB.B-neuT hosts which developed systemic immune abnormalities very similar to those observed in BALB/c -neuT or BALB/c WT mice. However, BALB.B WT hosts initially accepted the grafts, but subsequently rejected them after they were established. Mice that were in the process of rejecting the tumors retained normal cellularity within their spleens and lymph nodes indicating the importance of an ongoing immune response and/or tumor rejection in shaping the microenvironment in secondary lymphoid organs. Adoptive transfer of spleen cells from BALB.B WT mice which had rejected established tumor conferred resistance to the tumor grafts as long as B cells were included (P<0.01), indicating active humoral immunity was important to tumor rejection. A mechanistic understanding or how antibody-mediated immunotherapy works in patients is incomplete. This new model provides an opportunity to address this question. The Her2 ecto-domain is known to be shed from tumor cells. We propose a model in which the ecto-domain of rat neuT is shed, but is insufficiently immunogenic in BALB/c (H-2d) hosts, but highly immunogenic in BALB.B (H-2b) mice. Consistent with this model is the prediction using the Immune Epitope and Data Base Resource of the presence of a potentially immunogenic IAb-restricted class II epitope within the ecto-domain of rat Her2 neuT oncogene, but no such epitope restricted by IAd or IEd was identified. This provides a compelling hypothesis explaining why grafted spontaneous tumors grow in BALB/c, but not in BALB.B WT mice. An important prediction from this model is that linkage of a potent class II epitope to the Erbb2-encoded ecto-domain may provide a basis for a potent vaccine against Her2 positive breast tumors which should be a strategy adaptable to any MHC genotype. It also will be of interest to determine whether the presence of an antibody reactive against established tumor restores the normal cellular composition of secondary lymphoid organs which have been perturbed by established breast tumors.

Citation Format: Sarah Anne Castro, Alvaro Pena, Khashayarsha Khazaie, Larry R. Pease. An immunogenic mouse model using BALB.B-MMTV-neuT breast cancers reveals spontaneous protective humoral immunity [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P5-04-15.

SCIDOT-34. BRAIN INJURY SIGNALS SYSTEMIC IMMUNOSUPPRESSION THROUGH THYMIC INVOLUTION

Systemic immunosuppression following neurological insults including stroke, traumatic brain injury, and glioblastoma (GBM) causes mortality and leads to failure of immune-modulating therapies. Exact immunological nature and the underlying mechanisms of this immunosuppression are unknown. Our goal was to define effects of neurological insults given exclusively to the brain on the thymus. The thymus is the primary immune organ responsible for T-cell development and maintenance both in children and in adults. We evaluated the brain-thymus communication using the following neurological insults: physical injury, CNS viral infection, sterile injury, tumor implantation, and seizures. All insults resulted in significant thymic involution that was reversible upon clearance of the insult. Thymic involution did not occur following similar peripheral insults. We next demonstrated that the GL261 model of GBM recapitulates hallmark features of peripheral immunosuppression observed in GBM patients including low CD4 T-cell counts. Thus, we aimed to further study the immunosuppression affecting the thymus in this clinically relevant model. Principle component analysis following RNA-sequencing of thymi from naïve and glioma-bearing mice revealed unbiased separation of the groups suggesting that the thymus is directly affected by a brain tumor. To determine the extent to which thymic involution was caused by a soluble factor we employed parabiosis. We demonstrated that thymic involution was transferable from glioma-bearing to non-tumor-bearing parabionts. Similarly, serum taken from GL261 glioma-bearing mice potently inhibited proliferation of T-cells in vitro. Together our data demonstrate that CNS-specific insults, regardless of nature, cause immunosuppression by prompting thymic involution through circulating factors. This accounts at least partially for immune deficiencies observed following neurological injuries. Identification of this suppressive factor is crucial in designing future therapeutics for GBM patients, and patients with other acute and chronic neurological trauma.

Abstract 2898: Stochastic variation in gene expression is selected during clonal evolution of spontaneous mouse mammary tumors

Molecular and cellular diversity in cancer cells enables evolutionary processes that govern tumor progression and contributes to treatment failures, but the mechanisms governing this variability remain incompletely understood. We previously described tumor-specific epigenetic alterations in DNA devoid of canonical CpG methylation sites throughout the genomes of spontaneous breast tumors which arise in genetically uniform, yet heterozygous, [FVB X BALB/c MMTV-NeuT+] F1 mice. Those changes were detected in purified tumor DNA using a template-assisted quantitative ligation assay employing locus-specific and SNP-specific oligonucleotide genotyping probes, and the assay was subsequently shown to be sensitive to epigenetic modifications of the templates. We now describe losses of heterozygosity similarly distributed throughout the transcriptomes of tumors in this same model. We quantified expressed alleles across a population of clonal tumors and tested each expressed variant for the occurrence of allelic ratio outliers. The results revealed variegated patterns of expression in hundreds of genes, highly significantly enriched in pathways typically co-opted by tumors (Molecular Mechanisms of Cancer, P < 10-10, IPA analysis). An astounding 87% (2634 of 3044) of expressed genes that could be measured using this approach were represented in at least one tumor. Furthermore, the frequency of these outliers in any one individual tumor was found to correlate strongly with the transcriptional repression of an additional large set of non-polymorphic genes. These findings reveal underappreciated, latent mechanisms driving sporadic errors in epigenetic programming that promote repression of a multiple cis-linked transcripts. This genome-wide molecular chaos presents as dysregulated cellular homeostasis and is the foundation for heritable diversity as tumors evolve.

Citation Format: Sara J. Felts, Xiaojia Tang, Virginia P. Van Keulen, Krishna R. Kalari, Larry R. Pease. Stochastic variation in gene expression is selected during clonal evolution of spontaneous mouse mammary tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2898.

Stochastic changes in gene expression promote chaotic dysregulation of homeostasis in clonal breast tumors

Cells within tumors vary in phenotype as a result of changes in gene expression caused by a variety of mechanisms, permitting cancers to evolve under selective pressures from immune and other homeostatic processes. Earlier, we traced apparent losses in heterozygosity (LOH) of spontaneous breast tumors from first generation (F1) intercrossed mice to atypical epigenetic modifications in the structure of DNA across the tumor genomes. Here, we describe a parallel pattern of LOH in gene expression, revealed through quantitation of parental alleles across a population of clonal tumors. We found variegated patterns of LOH, based on allelic ratio outliers in hundreds of genes, enriched in regulatory pathways typically co-opted by tumors. The frequency of outliers was correlated with transcriptional repression of a large set of homozygous genes. These findings suggest stochastic losses in gene expression across the genome of tumors generate phenotypic variation among cells, allowing clonal selection during tumor development.

An engineered vaccine encompassing an MHC class I antigen presenting molecule induces self-reacting CTL in a setting of profound tolerance

Engineered antigen presenting molecules can promote allorecognition and activate CTL capable of recognizing weak or self-antigens in the context of self-MHC. Traditionally, allogeneic antigen presenting molecules differ from self MHC molecules in their interactions with the bound peptides and with TCR expressed in the immune repertoire to promote peptide dependent alloimmunity. Alloreactive T cells target their inducing alloantigens, as well as third-party alloantigens, but as a result of tolerance, generally not self-antigen presenting molecules. Certain residues located on the alpha-1/2 domains of class I antigen presenting molecules interface with TCR CDR loops and do not influence the nature or orientation of bound peptides. These residues are more conserved within and across species than are residues that determine peptide antigen binding properties. Class I variants designed with amino acid substitutions at key positions within the conserved helical structures at this MHC:TCR interface are found to provide strong activating signals to alloreactive CD8 T cells in the self tolerant immune repertoire. We demonstrate that CTL activated in this manner can break self-tolerance by reacting to self-peptides presented by native MHC. The ability to activate self-tolerant T cells capable of cross-reacting on self-peptide-MHC in vivo represents a novel approach for inducing autoimmunity, with possible application the development of cancer vaccines.

Exploring the effect of library preparation on RNA sequencing experiments

RNA sequencing (RNA-seq) has become the widely preferred choice for surveying the genome-wide transcriptome complexity in many organisms. However, the broad adaptation of this methodology into the clinic still needs further evaluation of potential effect of sample preparation factors on its analytical reliability using patient samples. In this study, we examined the impact of three major sample preparation factors (i.e., cDNA library storage time, the quantity of input RNA, and cryopreservation of cell samples) on sequence biases, gene expression profiles, and enriched biological functions using RNAs isolated from primary B cell and CD4+ cell blood samples of healthy subjects. Our comprehensive comparison results suggested that different cDNA library storage time, quantity of input RNA, and cryopreservation of cell samples did not significantly alter gene transcriptional expression profiles generated by RNA-seq experiments. These findings shed new lights on the potential applications of RNA-seq technique to patient samples in a regular clinical setting.

Integrative Genome-Wide Analysis of Long Noncoding RNAs in Diverse Immune Cell Types of Melanoma Patients

Genome-wide identification and characterization of long noncoding RNAs (lncRNA) in individual immune cell lineages helps us better understand the driving mechanisms behind melanoma and advance personalized patient treatment. To elucidate the transcriptional landscape in diverse immune cell types of peripheral blood cells (PBC) in stage IV melanoma, we used whole transcriptome RNA sequencing to profile lncRNAs in CD4+, CD8+, and CD14+ PBC from 132 patient samples. Our integrative computational approach identified 27,625 expressed lncRNAs, 2,744 of which were novel. Both T cells (i.e., CD4+ and CD8+ PBC) and monocytes (i.e., CD14+ PBC) exhibited differential transcriptional expression profiles between patients with melanoma and healthy subjects. Cis- and trans-level coexpression analysis suggested that lncRNAs are potentially involved in many important immune-related pathways and the programmed cell death receptor 1 checkpoint pathways. We also identified nine gene coexpression modules significantly associated with melanoma status, all of which were significantly enriched for three mRNA translation processes. Age and melanoma traits closely correlated with each other, implying that melanoma contains age-associated immune changes. Our computational prediction analysis suggests that many cis- and trans-regulatory lncRNAs could interact with multiple transcriptional and posttranscriptional regulatory elements in CD4+, CD8+, and CD14+ PBC, respectively. These results provide novel insights into the regulatory mechanisms involving lncRNAs in individual immune cell types in melanoma and can help expedite cell type-specific immunotherapy treatments for such diseases.Significance: These findings elucidate melanoma-associated changes to the noncoding transcriptional landscape of distinct immune cell classes, thus providing cell type-specific guidance to targeted immunotherapy regimens. Cancer Res; 78(15); 4411-23. ©2018 AACR.

Non-equivalent antigen presenting capabilities of dendritic cells and macrophages in generating brain-infiltrating CD8 + T cell responses

The contribution of antigen-presenting cell (APC) types in generating CD8+ T cell responses in the central nervous system (CNS) is not fully defined, limiting the development of vaccines and understanding of immune-mediated neuropathology. Here, we generate a transgenic mouse that enables cell-specific deletion of the H-2Kb MHC class I molecule. By deleting H-2Kb on dendritic cells and macrophages, we compare the effect of each APC in three distinct models of neuroinflammation: picornavirus infection, experimental cerebral malaria, and a syngeneic glioma. Dendritic cells and macrophages both activate CD8+ T cell responses in response to these CNS immunological challenges. However, the extent to which each of these APCs contributes to CD8+ T cell priming varies. These findings reveal distinct functions for dendritic cells and macrophages in generating CD8+ T cell responses to neurological disease.

Gene Expression Signatures Characterized by Longitudinal Stability and Interindividual Variability Delineate Baseline Phenotypic Groups with Distinct Responses to Immune Stimulation

Human immunity exhibits remarkable heterogeneity among individuals, which engenders variable responses to immune perturbations in human populations. Population studies reveal that, in addition to interindividual heterogeneity, systemic immune signatures display longitudinal stability within individuals, and these signatures may reliably dictate how given individuals respond to immune perturbations. We hypothesize that analyzing relationships among these signatures at the population level may uncover baseline immune phenotypes that correspond with response outcomes to immune stimuli. To test this, we quantified global gene expression in peripheral blood CD4⁺ cells from healthy individuals at baseline and following CD3/CD28 stimulation at two time points 1 mo apart. Systemic CD4⁺ cell baseline and poststimulation molecular immune response signatures (MIRS) were defined by identifying genes expressed at levels that were stable between time points within individuals and differential among individuals in each state. Iterative differential gene expression analyses between all possible phenotypic groupings of at least three individuals using the baseline and stimulated MIRS gene sets revealed shared baseline and response phenotypic groupings, indicating the baseline MIRS contained determinants of immune responsiveness. Furthermore, significant numbers of shared phenotype-defining sets of determinants were identified in baseline data across independent healthy cohorts. Combining the cohorts and repeating the analyses resulted in identification of over 6000 baseline immune phenotypic groups, implying that the MIRS concept may be useful in many immune perturbation contexts. These findings demonstrate that patterns in complex gene expression variability can be used to define immune phenotypes and discover determinants of immune responsiveness.

Definitive activation of endogenous antitumor immunity by repetitive cycles of cyclophosphamide with interspersed Toll-like receptor agonists

Many cancers both evoke and subvert endogenous anti-tumor immunity. However, immunosuppression can be therapeutically reversed in subsets of cancer patients by treatments such as checkpoint inhibitors or Toll-like receptor agonists (TLRa). Moreover, chemotherapy can leukodeplete immunosuppressive host elements, including myeloid-derived suppressor cells (MDSCs) and regulatory T-cells (Tregs). We hypothesized that chemotherapy-induced leukodepletion could be immunopotentiated by co-administering TLRa to emulate a life-threatening infection. Combining CpG (ODN 1826) or CpG+poly(I:C) with cyclophosphamide (CY) resulted in uniquely well-tolerated therapeutic synergy, permanently eradicating advanced mouse tumors including 4T1 (breast), Panc02 (pancreas) and CT26 (colorectal). Definitive treatment required endogenous CD8+ and CD4+ IFNγ-producing T-cells. Tumor-specific IFNγ-producing T-cells persisted during CY-induced leukopenia, whereas Tregs were progressively eliminated, especially intratumorally. Spleen-associated MDSCs were cyclically depleted by CY+TLRa treatment, with residual monocytic MDSCs requiring only continued exposure to CpG or CpG+IFNγ to effectively attack malignant cells while sparing non-transformed cells. Such tumor destruction occurred despite upregulated tumor expression of Programmed Death Ligand-1, but could be blocked by clodronate-loaded liposomes to deplete phagocytic cells or by nitric oxide synthase inhibitors. CY+TLRa also induced tumoricidal myeloid cells in naive mice, indicating that CY+TLRa's immunomodulatory impacts occurred in the complete absence of tumor-bearing, and that tumor-induced MDSCs were not an essential source of tumoricidal myeloid precursors. Repetitive CY+TLRa can therefore modulate endogenous immunity to eradicate advanced tumors without vaccinations or adoptive T-cell therapy. Human blood monocytes could be rendered similarly tumoricidal during in vitro activation with TLRa+IFNγ, underscoring the potential therapeutic relevance of these mouse tumor studies to cancer patients.

Human perforin gene variation is geographically distributed

Background

Deleterious mutations in PRF1 result in lethal, childhood disease, familial hemophagocytic lymphohistiocytosis type 2 (FHL 2). However, not all mutations in PRF1 are deleterious and result in FHL 2. Currently, these nondeleterious mutations are being investigated in the onset of numerous disorders, such as lymphomas and diabetes. Yet, there is still an overwhelmingly large amount of PRF1 mutations that are not associated with disease.

Methods

We conducted a post hoc analysis of the PRF1 mutations in the coding region using the recently published Exome Aggregation Consortium genomes, Leiden Open Variation Database, NCBI SNP database, and primary literature to better understand PRF1 variation in the human population.

Results

This study catalogs 460 PRF1 mutations in the coding region, and demonstrates PRF1 is more variant then previously predicted. We identify key PRF1 mutations with high allelic frequency and are only found in certain populations. Additionally, we define PRF1SNVs are geographically distributed.

Conclusions

This study concludes with a novel hypothesis that nondeleterious mutation in PRF1, which decreases perforin expression and/or activity, may be an example of selective advantage in the context of environmental stressors prevalent near the equator. Our studies illustrate how perforin deficiency can be protective from injuries resulting in blood–brain barrier (BBB) disruption.

Conditional silencing of the H-2Db class I molecule on CD11c+ Dendritic Cells inhibits the generation of antiviral CD8 T Cells during acute Theiler’s Murine Encephalomyelitis Virus (TMEV) infection in the CNS

The generation of an effective antiviral CD8 T cell response is required to protect C57BL/6 mice from Theiler’s murine encephalomyelitis virus (TMEV) induced demyelinating syndrome. Our group previously defined the VP2 121-130 peptide presented in the context of the H-2Db class I molecule as the immunodominant antigen recognized by the majority of brain infiltrating CD8 T cells during acute TMEV infection. Our group also determined that this Db:VP2 121-130 epitope specific CD8 T cell response was required for virus clearance. However, the mechanism by which virus antigen-specific CD8 T cells are generated in the brain remained undefined. Therefore, our laboratory generated a novel transgenic mouse system that enables conditional ablation of the H-2Db class I gene in specific antigen presenting cell types (APCs). Previously, analysis of class I-restricted antigen presentation required genetic disruption or depletion of entire APC subsets. We used this novel Cre-Lox transgenic mouse system to define the APC required to generate the immunodominant Db:VP2 121-130 epitope specific CD8 T cell response during acute TMEV infection. In the course of this analysis, we determined that silencing of class I-restricted antigen presentation on CD11c+ dendritic cells (DCs) did not affect thymic development of CD8 T cells. However, loss of Db expression by CD11c+ DCs completely abolished the generation of Db:VP2 121-130 epitope-specific CD8 T cell responses during acute TMEV infection. These findings demonstrate the importance of DCs in generating CD8 T cell responses against a neurotropic virus. We also provide a novel transgenic mouse for future studies involving class I-restricted antigen presentation.

A cancer-associated gene signature bifurcates healthy subjects into cancer-associated and cancer-distinct phenotypes

In the context of immunity, genomic sequence, epigenetic, and environmental factor diversity combine to propagate variable gene expression and immune function among individuals. We hypothesize that we can harness gene expression variability across people to study molecular immune phenotypes and predict individual responses to immune stimuli. To test this we used RNA-Seq to derive a set of genes whose expression is stable over time and differential among healthy people in peripheral blood CD4+ cells. This gene set, which we term the molecular immune response signature (MIRS), identifies transcriptomic “fingerprints” in each healthy person. The same gene set also identifies unique signatures in independent stage IV melanoma patients, and, intriguingly, groups the cancer patients with a particular subset of healthy people. We further clarified the subset by selecting MIRS genes that differentiate it from the other healthy subset. To test if a larger population of melanoma patients grouped with the same healthy subset we clustered additional independent patients with the healthy subsets using these genes. Each of the patient samples grouped with the cancer-associated healthy subset (p=0.00195). We also tested if the gene set would segregate an additional independent cohort of healthy donors into two subsets and found that it did. This, and the fact that no known demographics differentiate the healthy subsets, suggests the observed healthy phenotype may relate to a cancer-like phenotype. Pathway analysis implicates Th1-skewing in the cancer-associated healthy subset. Future directions include further understanding the biological impacts of the phenotype and using the MIRS to predict individual responses to immunotherapeutics.

Engineering MHC class I fine structure for activation of self-tolerant T cells

Central tolerance imposed during thymic development and mechanisms of peripheral tolerance result in a mature T cell repertoire capable of cross-reacting weakly on self, but usually incapable of activation. We have observed mutations in class I heavy chains capable of activating normally tolerant T cells which can then cross-react effectively on self. We hypothesized that mutation of the class I heavy chain, based on our understanding of MHC fine structure, could be used to generate engineered MHC molecules capable of activating T cells normally incapable of activation due to self-tolerance that could then cross-react effectively on self, but without altering the presentation of bound peptides. Known ternary complex (pMHC:TCR) crystal structures were modeled to predict amino acid substitutions within the class I heavy chain resulting in increased stable contacts between pMHC and TCR without altering the structure of bound peptides. Four substitutions within the class I heavy chain meeting these criteria were predicted by the structure based modeling. Cell lines were established which demonstrated stable surface expression of the engineered class I molecules. In a direct test of binding, a single chain TCR was detected with 20 fold greater intensity on the surface of cells expressing engineered MHC molecules compared with wild-type MHC, while competitive inhibition of binding a labeled peptide demonstrated unaltered peptide presentation. Stimulation of T cells with a weak antigen presented by the engineered MHC resulted in enhanced activation and proliferation compared with wild-type MHC. In an in vivo transplant model, protective immunity was induced against a native tumor after challenge with tumor expressing engineered MHC.

Widespread Non-Canonical Epigenetic Modifications in MMTV-NeuT Breast Cancer

Breast tumors in (FVB × BALB-NeuT) F1 mice have characteristic loss of chromosome 4 and sporadic loss or gain of other chromosomes. We employed the Illumina GoldenGate genotyping platform to quantitate loss of heterozygosity (LOH) across the genome of primary tumors, revealing strong biases favoring chromosome 4 alleles from the FVB parent. While allelic bias was not observed on other chromosomes, many tumors showed concerted LOH (C-LOH) of all alleles of one or the other parent on sporadic chromosomes, a pattern consistent with cytogenetic observations. Surprisingly, comparison of LOH in tumor samples relative to normal unaffected tissues from these animals revealed significant variegated (stochastic) deviations from heterozygosity (V-LOH) in every tumor genome. Sequence analysis showed expected changes in the allelic frequency of single nucleotide polymorphisms (SNPs) in cases of C-LOH. However, no evidence of LOH due to mutations, small deletions, or gene conversion at the affected SNPs or surrounding DNA was found at loci with V-LOH. Postulating an epigenetic mechanism contributing to V-LOH, we tested whether methylation of template DNA impacts allele detection efficiency using synthetic oligonucleotide templates in an assay mimicking the GoldenGate genotyping format. Methylated templates were systematically over-scored, suggesting that the observed patterns of V-LOH may represent extensive epigenetic DNA modifications across the tumor genomes. As most of the SNPs queried do not contain standard (CpG) methylation targets, we propose that widespread, non-canonical DNA modifications occur during Her2/neuT-driven tumorigenesis.

Combinatorial Immunoprofiling in Latent Tuberculosis Infection. Toward Better Risk Stratification

RATIONALE

Most immunocompetent patients diagnosed with latent tuberculosis infection (LTBI) will not progress to tuberculosis (TB) reactivation. However, current diagnostic tools cannot reliably distinguish nonprogressing from progressing patients a priori, and thus LTBI therapy must be prescribed with suboptimal patient specificity. We hypothesized that LTBI diagnostics could be improved by generating immunomarker profiles capable of categorizing distinct patient subsets by a combinatorial immunoassay approach.

OBJECTIVES

A combinatorial immunoassay analysis was applied to identify potential immunomarker combinations that distinguish among unexposed subjects, untreated patients with LTBI, and treated patients with LTBI and to differentiate risk of reactivation.

METHODS

IFN-γ release assay (IGRA) was combined with a flow cytometric assay that detects induction of CD25(+)CD134(+) coexpression on TB antigen-stimulated T cells from peripheral blood. The combinatorial immunoassay analysis was based on receiver operating characteristic curves, technical cut-offs, 95% bivariate normal density ellipse prediction, and statistical analysis. Risk of reactivation was estimated with a prediction formula.

MEASUREMENTS AND MAIN RESULTS

Sixty-five out of 150 subjects were included. The combinatorial immunoassay approach identified at least four different T-cell subsets. The representation of these immune phenotypes was more heterogeneous in untreated patients with LTBI than in treated patients with LTBI or unexposed groups. Patients with IGRA(+) CD4(+)CD25(+)CD134(+) T-cell phenotypes had the highest estimated reactivation risk (4.11 ± 2.11%).

CONCLUSIONS

These findings suggest that immune phenotypes defined by combinatorial assays may potentially have a role in identifying those at risk of developing TB; this potential role is supported by risk of reactivation modeling. Prospective studies will be needed to test this novel approach.

Calcium-Modulating Cyclophilin Ligand Is Essential for the Survival of Activated T Cells and for Adaptive Immunity

Calcium-modulating cyclophilin ligand (CAML) is an endoplasmic reticulum resident protein that is widely expressed. Although it has been demonstrated to participate in the tail-anchored protein insertion pathway, its physiological role in the mature immune system is unknown. In this work, we show that mature, peripheral T cells require CAML for survival specifically following TCR-induced activation. In this study, we examined mature T cells from spleen and lymph nodes of tamoxifen-inducible CAML knockout mice (tCAML(-/-)). Whereas CAML-deficient T cells were able to express the early activation markers CD25 and CD69, and produce IL-2 normally upon stimulation, deficient cells proliferated less and died. Cells did not require CAML for entry into the S phase of the cell cycle, thus implicating its survival function at a relatively late step in the T cell activation sequence. In addition, CAML was required for homeostatic proliferation and for Ag-dependent cell killing in vivo. These results demonstrate that CAML critically supports T cell survival and cell division downstream of T cell activation.

Co-potentiation of antigen recognition: A mechanism to boost weak T cell responses and provide immunotherapy in vivo

Adaptive immunity is mediated by antigen receptors that can induce weak or strong immune responses depending on the nature of the antigen that is bound. In T lymphocytes, antigen recognition triggers signal transduction by clustering T cell receptor (TCR)/CD3 multiprotein complexes. In addition, it hypothesized that biophysical changes induced in TCR/CD3 that accompany receptor engagement may contribute to signal intensity. Nonclustering monovalent TCR/CD3 engagement is functionally inert despite the fact that it may induce changes in conformational arrangement or in the flexibility of receptor subunits. We report that the intrinsically inert monovalent engagement of TCR/CD3 can specifically enhance physiologic T cell responses to weak antigens in vitro and in vivo without stimulating antigen-unengaged T cells and without interrupting T cell responses to strong antigens, an effect that we term as "co-potentiation." We identified Mono-7D6-Fab, which biophysically altered TCR/CD3 when bound and functionally enhanced immune reactivity to several weak antigens in vitro, including a gp100-derived peptide associated with melanoma. In vivo, Mono-7D6-Fab induced T cell antigen-dependent therapeutic responses against melanoma lung metastases, an effect that synergized with other anti-melanoma immunotherapies to significantly improve outcome and survival. We conclude that Mono-7D6-Fab directly co-potentiated TCR/CD3 engagement by weak antigens and that such concept can be translated into an immunotherapeutic design. The co-potentiation principle may be applicable to other receptors that could be regulated by otherwise inert compounds whose latent potency is only invoked in concert with specific physiologic ligands.

A Versatile Simple Capture Assay for Assessing the Structural Integrity of MHC Multimer Reagents

Antigen-specific T cell responses can be visualized using MHC:peptide multimers. In cases where robust T cell controls are not readily available to assess the integrity of multimer reagents prior to analyzing limited sample, the ability to assess the structural integrity of MHC multimers before their use in critical experiments would be useful. We present a method to probe the structural integrity of MHC multimers using antibodies specific for conformational determinants. Beads coated with anti-mouse Ig are incubated with conformation-specific mouse monoclonal antibody and then with fluorescently tagged MHC multimer. The ability of the bead to capture the labeled multimer can be measured semi-quantitatively by flow cytometry. In this manner, the correct folding of MHC multimers can be visualized and batches of multimer can be compared for quality control. Because there are multiple conformational epitopes formed by various molecular interactions among heavy chain, peptide, and β₂M, this capture assay can assess the fidelity of each aspect of multimer structure, depending on the availability of antibodies. The described approach could be particularly useful for studies using irreplaceable samples, including patient samples collected in clinical trials.

Gene expression patterns in CD4+ peripheral blood cells in healthy subjects and stage IV melanoma patients

Melanoma patients exhibit changes in immune responsiveness in the local tumor environment, draining lymph nodes, and peripheral blood. Immune-targeting therapies are revolutionizing melanoma patient care increasingly, and studies show that patients derive clinical benefit from these newer agents. Nonetheless, predicting which patients will benefit from these costly therapies remains a challenge. In an effort to capture individual differences in immune responsiveness, we are analyzing patterns of gene expression in human peripheral blood cells using RNAseq. Focusing on CD4+ peripheral blood cells, we describe multiple categories of immune regulating genes, which are expressed in highly ordered patterns shared by cohorts of healthy subjects and stage IV melanoma patients. Despite displaying conservation in overall transcriptome structure, CD4+ peripheral blood cells from melanoma patients differ quantitatively from healthy subjects in the expression of more than 2000 genes. Moreover, 1300 differentially expressed genes are found in transcript response patterns following activation of CD4+ cells ex vivo, suggesting that widespread functional discrepancies differentiate the immune systems of healthy subjects and melanoma patients. While our analysis reveals that the transcriptome architecture characteristic of healthy subjects is maintained in cancer patients, the genes expressed differentially among individuals and across cohorts provide opportunities for understanding variable immune states as well as response potentials, thus establishing a foundation for predicting individual responses to stimuli such as immunotherapeutic agents.

A natural human IgM that binds to gangliosides is therapeutic in murine models of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating, fatal neurological disease that primarily affects spinal cord anterior horn cells and their axons for which there is no treatment. Here we report the use of a recombinant natural human IgM that binds to the surface of neurons and supports neurite extension, rHIgM12, as a therapeutic strategy in murine models of human ALS. A single 200 µg intraperitoneal dose of rHIgM12 increases survival in two independent genetic-based mutant SOD1 mouse strains (SOD1G86R and SOD1G93A) by 8 and 10 days, delays the onset of neurological deficits by 16 days, delays the onset of weight loss by 5 days, and preserves spinal cord axons and anterior horn neurons. Immuno-overlay of thin layer chromatography and surface plasmon resonance show that rHIgM12 binds with high affinity to the complex gangliosides GD1a and GT1b. Addition of rHIgM12 to neurons in culture increases α-tubulin tyrosination levels, suggesting an alteration of microtubule dynamics. We previously reported that a single peripheral dose of rHIgM12 preserved neurological function in a murine model of demyelination with axon loss. Because rHIgM12 improves three different models of neurological disease, we propose that the IgM might act late in the cascade of neuronal stress and/or death by a broad mechanism.

Summary: A single peripheral dose of a recombinant natural human IgM increases lifespan and delays neurological deficits in mouse models of human ALS.

Immune-mediated injury of virus-infected oligodendrocytes A model of multiple sclerosis

The causes of primary demyelination in diseases such as multiple sclerosis are still unknown, but it is possible that immune attack triggered by virus infection may be responsible. Theiler's murine encephalitis is a popular animal model of demyelinating diseases, and in this article Moses Rodriguez and his colleagues describe a hypothetical scheme to explain differential susceptibility of inbred strains to infection. They propose a mechanism by which specific demyelination is produced when immune cells interact with viral antigen and major histocompatibility complex (MHC) antigens.

Naturally occurring antibodies as therapeutics for neurologic disease: can human monoclonal IgMs replace the limited resource IVIG?

Naturally occurring autoantibodies (NAbs) are common in normal humans. The majority of NAbs are IgMs, but a small proportion are IgGs. Therefore a certain portion of pooled whole human IgG (IVIG) can be considered NAbs. While the applications of IVIG to modulate human disease have increased dramatically, the use of IgMs as drugs has lagged. In fact, much of the contaminating IgM component of IVIG is disposed of as waste. However, a number of model studies, including those targeting Alzheimer and multiple sclerosis (MS) suggest that IgMs may better modulate disease at much lower doses than IVIG. Our own studies in a model of MS show that polyclonal human IgM promotes better remyelination than IVIG and that monoclonal IgMs promote greater remyelination than monoclonal IgGs containing identical variable region sequences. We propose that this difference is due to the ability of IgM to cross link cell surface antigens better than IgGs and induce signals in nervous system cells. Monoclonal antibodies (mAbs) that promote remyelination induce a transient Ca(2+) influx in myelin forming cells, whereas IgGs with identical variable sequences do not. MAbs that promote remyelination were identified in human serum and in EBV-immortalized human B-cell lines obtained from normal adults, fetal cord blood, and rheumatoid arthritis and MS patients. Therefore therapeutic mAbs are present and common in normal circulation. All therapeutic mAbs were IgMs and bound to nervous system cells, however, the tissue binding patterns suggest that binding any one of multiple antigens induces repair. An expression vector was constructed that can manufacture gram quantities of recombinant monoclonal human IgM. Therefore the technology exists to determine whether human monoclonal NAbs can modulate human disease. IVIG can modulate neurologic disease, but using IVIG to treat these chronic diseases is unsustainable. A long-term solution is to identify the functional component of IVIG and test whether a recombinant human monoclonal can replicate its efficacy.

Lineage(-)Sca1+c-Kit(-)CD25+ cells are IL-33-responsive type 2 innate cells in the mouse bone marrow

IL-33 promotes type 2 immune responses, both protective and pathogenic. Recently, targets of IL-33, including several newly discovered type 2 innate cells, have been characterized in the periphery. In this study, we report that bone marrow cells from wild-type C57BL/6 mice responded with IL-5 and IL-13 production when cultured with IL-33. IL-33 cultures of bone marrow cells from Rag1 KO and Kit(W-sh/W-sh) mice also responded similarly; hence, eliminating the possible contributions of T, B, and mast cells. Rather, intracellular staining revealed that the IL-5- and IL-13-positive cells display a marker profile consistent with the Lineage(-)Sca-1(+)c-Kit(-)CD25(+) (LSK(-)CD25(+)) cells, a bone marrow cell population of previously unknown function. Freshly isolated LSK(-)CD25(+) cells uniformly express ST2, the IL-33 receptor. In addition, culture of sorted LSK(-)CD25(+) cells showed that they indeed produce IL-5 and IL-13 when cultured with IL-33 plus IL-2 and IL-33 plus IL-7. Furthermore, i.p. injections of IL-33 or IL-25 into mice induced LSK(-)CD25(+) cells to expand, in both size and frequency, and to upregulate ST2 and α(4)β(7) integrin, a mucosal homing marker. Thus, we identify the enigmatic bone marrow LSK(-)CD25(+) cells as IL-33 responsive, both in vitro and in vivo, with attributes similar to other type 2 innate cells described in peripheral tissues.

A single dose of neuron-binding human monoclonal antibody improves spontaneous activity in a murine model of demyelination

Our laboratory demonstrated that a natural human serum antibody, sHIgM12, binds to neurons in vitro and promotes neurite outgrowth. We generated a recombinant form, rHIgM12, with identical properties. Intracerebral infection with Theiler's Murine Encephalomyelitis Virus (TMEV) of susceptible mouse strains results in chronic demyelinating disease with progressive axonal loss and neurologic dysfunction similar to progressive forms of multiple sclerosis. To study the effects of rHIgM12 on the motor function of TMEV-infected mice, we monitored spontaneous nocturnal activity over many weeks. Nocturnal behavior is a sensitive measure of rodent neurologic function because maximal activity changes are expected to occur during the normally active night time monitoring period. Mice were placed in activity boxes eight days prior to treatment to collect baseline spontaneous activity. After treatment, activity in each group was continuously recorded over 8 weeks. We chose a long 8-week monitoring period for two reasons: (1) we previously demonstrated that IgM induced remyelination is present by 5 weeks post treatment, and (2) TMEV-induced demyelinating disease in this strain progresses very slowly. Due to the long observation periods and large data sets, differences among treatment groups may be difficult to appreciate studying the original unfiltered recordings. To clearly delineate changes in the highly fluctuating original data we applied three different methods: (1) binning, (2) application of Gaussian low-pass filters (GF) and (3) polynomial fitting. Using each of the three methods we showed that compared to control IgM and saline, early treatment with rHIgM12 induced improvement in both horizontal and vertical motor function, whereas later treatment improved only horizontal activity. rHIgM12 did not alter activity of normal, uninfected mice. This study supports the hypothesis that treatment with a neuron-binding IgM not only protects neurons in vitro, but also influences functional motor improvement.

A human IgM signals axon outgrowth: coupling lipid raft to microtubules

Mouse and human IgMs support neurite extension from primary cerebellar granule neurons. In this study using primary hippocampal and cortical neurons, we demonstrate that a recombinant human IgM, rHIgM12, promotes axon outgrowth by coupling membrane domains (lipid rafts) to microtubules. rHIgM12 binds to the surface of neuron and induces clustering of cholesterol and ganglioside GM1. After cell binding and membrane fractionation, rHIgM12 gets segregated into two pools, one associated with lipid raft fractions and the other with the detergent-insoluble cytoskeleton-containing pellet. Membrane-bound rHIgM12 co-localized with microtubules and co-immuno precipitated with β3-tubulin. rHIgM12-membrane interaction also enhanced the tyrosination of α-tubulin indicating a stabilization of new neurites. When presented as a substrate, rHIgM12 induced axon outgrowth from primary neurons. We now demonstrate that a recombinant human mAb can induce signals in neurons that regulate membrane lipids and microtubule dynamics required for axon extension. We propose that the pentameric structure of the IgM is critical to cross-link membrane lipids and proteins resulting in signaling cascades.

Theiler's murine encephalomyelitis virus as a vaccine candidate for immunotherapy

The induction of sterilizing T-cell responses to tumors is a major goal in the development of T-cell vaccines for treating cancer. Although specific components of anti-viral CD8+ immunity are well characterized, we still lack the ability to mimic viral CD8+ T-cell responses in therapeutic settings for treating cancers. Infection with the picornavirus Theiler's murine encephalomyelitis virus (TMEV) induces a strong sterilizing CD8+ T-cell response. In the absence of sterilizing immunity, the virus causes a persistent infection. We capitalized on the ability of TMEV to induce strong cellular immunity even under conditions of immune deficiency by modifying the virus to evaluate its potential as a T-cell vaccine. The introduction of defined CD8+ T-cell epitopes into the leader sequence of the TMEV genome generates an attenuated vaccine strain that can efficiently drive CD8+ T-cell responses to the targeted antigen. This virus activates T-cells in a manner that is capable of inducing targeted tissue damage and glucose dysregulation in an adoptive T-cell transfer model of diabetes mellitus. As a therapeutic vaccine for the treatment of established melanoma, epitope-modified TMEV can induce strong cytotoxic T-cell responses and promote infiltration of the T-cells into established tumors, ultimately leading to a delay in tumor growth and improved survival of vaccinated animals. We propose that epitope-modified TMEV is an excellent candidate for further development as a human T-cell vaccine for use in immunotherapy.

Transgenic expression of viral capsid proteins predisposes to axonal injury in a murine model of multiple sclerosis

We used transgenic expression of capsid antigens to Theiler's murine encephalomyelitis virus (TMEV) to study the influence of VP1, VP2 or VP2(121-130) to either protection or pathogenesis to chronic spinal cord demyelination, axonal loss and functional deficits during the acute and chronic phases of infection. We used both mice that are normally susceptible (FVB) and mice normally resistant (FVB.D(b) ) to demyelination. Transgenic expression of VP2(121-130) epitope in resistant FVB.D(b) mice caused spinal cord pathology and virus persistence because the VP2(121-130) epitope is the dominant peptide recognized by D(b) , which is critical for virus clearance. In contrast, all three FVB TMEV transgenic mice showed more demyelination, inflammation and axonal loss as compared with wild-type FVB mice, even though virus load was not increased. Motor function measured by rotarod showed weak correlation with total number of midthoracic axons, but a strong correlation with large-caliber axons (>10µm(2) ). This study supports the hypothesis that expression of viral capsid proteins as self influences the extent of axonal pathology following Theiler's virus-induced demyelination. The findings provide insight into the role of axonal injury in the development of functional deficits that may have relevance to human demyelinating disease.

Invited article: human natural autoantibodies in the treatment of neurologic disease

Naturally occurring autoantibodies are molecules that are part of the normal immunoglobulin repertoire. This review focuses on three distinct groups of human monoclonal antibodies (mAb). These are human natural autoantibodies that, when injected into an animal model of human disease, stimulate remyelination in CNS demyelinating diseases, protect neurons and extend neuronal processes in CNS axonal disorders, and activate immune dendritic cells to produce cytotoxic T cells to clear metastatic tumors. Natural autoantibodies react to self antigens and are of relatively low affinity. They are derived from germline immunoglobulin genes and are usually polyreactive. Our experiments demonstrated CNS entry by autoradiography of labeled mAb and by MRI. Remyelinating mAb rHIgM22 clusters beta-integrin and mouse mAb O4 recognizes sulfatide. Neuronal outgrowth mAbs sHIgM42 and sHIgM12 appear to target carbohydrates on the surface of neurons. The mAb sHIgM12 (B7-DC-Xab) also is promising as therapeutic against metastatic tumors. It functions by binding and cross-linking the antigen B7-DC on dendritic cells, inducing tumor-specific cytotoxic T cells. All these mAbs activate a transient increase in intracellular calcium, signal via NFkappab, and prevent apoptosis. The mAbs engage downstream signaling events that induce the primary function of the cell (that is, remyelination for oligodendrocytes, axonal preservation and neurite extension for neurons, or antigen presentation for dendritic cells). Natural human auto mAbs are a potentially important therapeutic technique in combating a wide spectrum of disease processes.

Self-Reactive CTL Reveal a Strong Focus of the CD8+ T cell Receptor Repertoire on Self MHC (46.12)

Mouse CD8+ T cells can be activated to lyse targets expressing self class I molecules more potently than allogeneic targets. Self-reactive CTL express IL-17 and can be enriched following intracellular staining. Such CTL lyse targets in an MHC restricted fashion. This recognition is independent of the bound peptides, as demonstrated by cold-target inhibition studies. Activation of OT-1 transgenic T cells using traditional APC results in peptide specific CTL recognition, stimulation of the same T cells induces peptide independent, yet Kb-restricted recognition, irrespective of whether RAG sufficient or deficient mice were used. Self-reactive CTL efficiently lyse targets expressing wild type Kb or Kb-mutants with amino acid substitutions on the β-strands of the antigen binding groove, but not mutants with substitutions on the α1 and α2 helices, suggesting self MHC recognition is mediated by interactions of the CDR1 and CDR2 regions of the TCR with the α-helices of the class I molecules, and not by bound peptides. The ability of CTL to react in an MHC restricted, yet peptide independent, manner raises important questions about the nature of TCR-MHC interactions. We propose a novel "pre-positive selection" check point in thymic development and in peripheral T cell activation in recruitment of TCR-MHC complexes at the immunological synapse during T cell activation and homeostatic recognition.