Depletion of autoreactive plasma cells and treatment of lupus nephritis in mice using CEP-33779, a novel, orally active, selective inhibitor of JAK2.

Accumulating evidence suggests that autoreactive plasma cells play an important role in systemic lupus erythematosus (SLE). In addition, several proinflammatory cytokines promote autoreactive B cell maturation and autoantibody production. Hence, therapeutic targeting of such cytokine pathways using a selective JAK2 inhibitor, CEP-33779 (JAK2 enzyme IC(50) = 1.3 nM; JAK3 enzyme IC(50)/JAK2 enzyme IC(50) = 65-fold), was tested in two mouse models of SLE. Age-matched, MRL/lpr or BWF1 mice with established SLE or lupus nephritis, respectively, were treated orally with CEP-33779 at 30 mg/kg (MRL/lpr), 55 mg/kg or 100 mg/kg (MRL/lpr and BWF1). Studies included reference standard, dexamethasone (1.5 mg/kg; MRL/lpr), and cyclophosphamide (50 mg/kg; MRL/lpr and BWF1). Treatment with CEP-33779 extended survival and reduced splenomegaly/lymphomegaly. Several serum cytokines were significantly decreased upon treatment including IL-12, IL-17A, IFN-α, IL-1ß, and TNF-α. Anti-nuclear Abs and frequencies of autoantigen-specific, Ab-secreting cells declined upon CEP-33779 treatment. Increased serum complement levels were associated with reduced renal JAK2 activity, histopathology, and spleen CD138(+) plasma cells. The selective JAK2 inhibitor CEP-33779 was able to mitigate several immune parameters associated with SLE advancement, including the protection and treatment of mice with lupus nephritis. These data support the possibility of using potent, orally active, small-molecule inhibitors of JAK2 to treat the debilitative disease SLE.

The ubiquitin-like protein, ISG15, is a novel tumor-associated antigen for cancer immunotherapy.

The recent announcement of the first FDA-approved therapeutic vaccine for prostate cancer, Sipuleucel-T, is a watershed moment for the field of tumor immunotherapy. However, while Sipuleucel-T provides a powerful tool to clinicians for the most prevalent form of cancer in men, there remains an unmet need for a similar therapeutic strategy against breast cancer, the most prevalent cancer in women. While current breast cancer vaccines in development target several antigens, the most prevalent is the tumor-associated antigen, HER2. Initial results with HER2 vaccines appear promising in terms of efficacy; however, the lack of HER2 overexpression by a majority of breast tumors and the safety concerns associated with current HER2-targeted immunotherapy suggest that additional therapeutic strategies would be beneficial. Recently, several studies have identified ISG15 as a molecule highly expressed in numerous malignancies. ISG15 is a small ubiquitin-like protein regulated by type-I interferon and classically associated with viral defense. Elevated ISG15 expression in breast cancer is especially well documented and is independent of HER2, progesterone receptor, and estrogen receptor status. Additionally, high ISG15 expression in breast cancer correlates with an unfavorable prognosis and poor responses to traditional treatment strategies such as chemotherapy and radiation. To overcome these challenges, we employ a novel strategy to specifically target tumor-associated ISG15 expression with immunotherapy. We demonstrate that vaccination against ISG15 results in significant CD8-mediated reductions in both primary and metastatic mammary tumor burden. These results validate ISG15 as a tumor-associated antigen for cancer immunotherapy.

Secreted heat shock protein gp96-Ig and OX40L-Fc combination vaccine enhances SARS-CoV-2 Spike (S) protein-specific B and T cell immune responses.

Encouraging protection results from current mRNA-based SARS-CoV-2 vaccine platforms are primarily due to the induction of SARS- CoV-2- specific B cell antibody and CD4 + T cell. Even though, current mRNA vaccine platforms are adept in inducing SARS-CoV2-specific CD8 + T cell, much less is known about CD8 T cells contribution to the overall vaccine protection. Our allogeneic cellular vaccine, based on a secreted form of the heat-shock protein gp96-Ig, achieves high frequencies of polyclonal CD8 + T cell responses to tumor and infectious antigens through antigen cross-priming in vivo. We and others have shown that gp96-Ig, in addition to antigen-specific CD8 + T cell anti-tumor and anti-pathogen immunity, primes antibody responses as well. Here, we generated a cell-based vaccine that expresses SARS-Cov-2 Spike (S) protein and simultaneously secretes gp96-Ig and OX40L-Fc fusion proteins. We show that co-secretion of gp96-Ig-S peptide complexes and the OX40L-Fc costimulatory fusion protein in allogeneic cell lines results in enhanced activation of S protein-specific IgG antibody responses. These findings were further strengthened by the observation that this vaccine platform induces T follicular helper cells (TFH) and protein-S -specific CD8 + T cells. Thus, a cell-based gp96-Ig vaccine/OX40-L fusion protein regimen provides encouraging translational data that this vaccine platform induces pathogen-specific CD8+, CD4 + T and B cell responses, and may cohesively work as a booster for FDA-approved vaccines. Our vaccine platform can be rapidly engineered and customized based on other current and future pathogen sequences.

An anti-vascular endothelial growth factor receptor 2/fetal liver kinase-1 Listeria monocytogenes anti-angiogenesis cancer vaccine for the treatment of primary and metastatic Her-2/neu+ breast tumors in a mouse model.

Thirty years after angiogenesis was shown to play an enabling role in cancer, modern medicine is still trying to develop novel compounds and therapeutics to target the tumor vasculature. However, most therapeutics require multiple rounds of administration and can have toxic side effects. In this study, we use anti-angiogenesis immunotherapy to target cells actively involved in forming new blood vessels that support the growth and spread of breast cancer. Targeting a central cell type involved in angiogenesis, endothelial cells, we immunized against host vascular endothelial growth factor receptor 2 to fight the growth of Her-2/neu(+) breast tumors. Using the bacterial vector, Listeria monocytogenes (Lm), we fused polypeptides from the mouse vascular endothelial growth factor receptor 2 molecule (fetal liver kinase-1) to the microbial adjuvant, listeriolysin-O, and used Lm to deliver the Ags and elicit potent antitumor CTL responses. Lm-listeriolysin-O-fetal liver kinase-1 was able to eradicate some established breast tumors, reduce microvascular density in the remaining tumors, protect against tumor rechallenge and experimental metastases, and induce epitope spreading to various regions of the tumor-associated Ag Her-2/neu. Tumor eradication was found to be dependent on epitope spreading to HER-2/neu and was not solely due to the reduction of tumor vasculature. However, vaccine efficacy did not affect normal wound healing nor have toxic side effects on pregnancy. We show that an anti-angiogenesis vaccine can overcome tolerance to the host vasculature driving epitope spreading to an endogenous tumor protein and drive active tumor regression.

Novel method of monitoring trace cytokines and activated STAT molecules in the paws of arthritic mice using multiplex bead technology.

BACKGROUND: The use of mouse models to study human disease provides useful data that can provide support for research projects or an existing drug discovery program. How well a model recapitulates the human condition and the ease and reproducibility of data collected will determine how much confidence a scientist can place on results obtained. Designing new treatments for rheumatic diseases, such as rheumatoid arthritis (RA), requires complex immunocompetent models that depend on intricate cytokine networks. Using local cytokines, signal transduction and transcription factor molecules as potential biomarkers to monitor disease and treatment efficacy is the best method to follow the progression of tissue damage and repair when testing an unknown compound or biologic. Described here in this report, a novel method for the non-enzymatic extraction and measurement of cytokines and signal transducers and activators of transcription (STAT) molecules using Luminex® bead array technology in two different mouse models for human RA--collagen antibody-dependent arthritis (CAIA) and collagen-induced arthritis (CIA). RESULTS: Dynamic expression of several pro-inflammatory cytokines responsible for promoting disease augmentation overtime were monitored, such as IL-1ß, TNFα, IL-6 and IL-12, locally in the paws of affected animals directly ex vivo. Local cytokine responses could be matched with serum cytokine levels and joint pathology results. In addition, STAT1, 3, and 5a/b activation status could be monitored with confidence using specifically formulated extraction buffer that protected the phosphorylation site. STAT3 activation followed paw swelling and cytokine levels in both models and correlates of disease could be ablated upon treatment with dexamethasone. Here reported a novel method of extracting joint fluid from the paws of inflamed mice coupled with powerful multiplex bead technology allowing us to measure cytokine responses, pharmacodynamic markers such as STATs and pharmacokinetic analysis of dosed agent all from the same sample directly ex vivo. CONCLUSIONS: This method is powerful in that it is applicable to multiple autoimmunity model types, streamlines ex vivo readouts in a high-throughput manner, and allows multiplexing providing the investigator with an array of options and possible analytes when developing preclinical animal models to support drug discovery efforts in the search for new treatments for rheumatic diseases.

A novel human Her-2/neu chimeric molecule expressed by Listeria monocytogenes can elicit potent HLA-A2 restricted CD8-positive T cell responses and impact the growth and spread of Her-2/neu-positive breast tumors.

PURPOSE: The aim of this study was to efficiently design a novel vaccine for human Her-2/neu-positive (hHer-2/neu) breast cancer using the live, attenuated bacterial vector Listeria monocytogenes. EXPERIMENTAL DESIGN: Three recombinant L. monocytogenes-based vaccines were generated that could express and secrete extracellular and intracellular fragments of the hHer-2/neu protein. In addition, we generated a fourth construct fusing selected portions of each individual fragment that contained most of the human leukocyte antigen (HLA) epitopes as a combination vaccine (L. monocytogenes-hHer-2/neu chimera). RESULTS: Each individual vaccine was able to either fully regress or slow tumor growth in a mouse model for Her-2/neu-positive tumors. All three vaccines could elicit immune responses directed toward human leukocyte antigen-A2 epitopes of hHer-2/neu. The L. monocytogenes-hHer-2/neu chimera was able to mimic responses generated by the three separate vaccines and prevent spontaneous outgrowth of tumors in an autochthonous model for Her-2/neu-positive breast cancer, induce tumor regression in transplantable models, and prevent seeding of experimental lung metastases in a murine model for metastatic breast cancer. CONCLUSION: This novel L. monocytogenes-hHer-2/neu chimera vaccine proves to be just as effective as the individual vaccines but combines the strength of all three in a single vaccination. These encouraging results support future clinical trials using this chimera vaccine and may be applicable to other cancer types expressing the Her-2/neu molecule such as colorectal and pancreatic cancer.

Induction of SARS-CoV-2 Protein S-Specific CD8+ T Cells in the Lungs of gp96-Ig-S Vaccinated Mice.

Given the aggressive spread of COVID-19-related deaths, there is an urgent public health need to support the development of vaccine candidates to rapidly improve the available control measures against SARS-CoV-2. To meet this need, we are leveraging our existing vaccine platform to target SARS-CoV-2. Here, we generated cellular heat shock chaperone protein, glycoprotein 96 (gp96), to deliver SARS-CoV-2 protein S (spike) to the immune system and to induce cell-mediated immune responses. We showed that our vaccine platform effectively stimulates a robust cellular immune response against protein S. Moreover, we confirmed that gp96-Ig, secreted from allogeneic cells expressing full-length protein S, generates powerful, protein S polyepitope-specific CD4+ and CD8+ T cell responses in both lung interstitium and airways. These findings were further strengthened by the observation that protein-S -specific CD8+ T cells were induced in human leukocyte antigen HLA-A2.1 transgenic mice thus providing encouraging translational data that the vaccine is likely to work in humans, in the context of SARS-CoV-2 antigen presentation.

Immunoregulation of fetal and anti-paternal immune responses.

Immunological tolerance to the fetus is essential for fetal survival during pregnancy. The semi-allogeneic fetus expresses genes foreign to the mother that can be recognized by maternal T cells. Under times of stress or infection, deleterious immune responses can result in fetal destruction and/or maternal death. Exposure to non-maternal antigens begins as early as insemination and some of the mechanisms required to prevent maternal priming against these antigens are in place before sexual encounter. Continuous and overlapping regulatory mechanisms must cooperate to allow the best chances for fertilization, implantation, and healthy gestation, simultaneously protecting the fetus from maternal immune attack yet making minimal compromises in resistance to infection. Several types of immune cell from both the innate and adaptive arms of the immune system help protect both the mother and fetus during pregnancy. It's the intricate communication and interplay between the immune system and the endocrine system that will ultimately decide the success or fate of the developing fetus.

Cancer immunotherapy using Listeria monocytogenes and listerial virulence factors.

Our laboratory is interested in how immunogenicity may be modulated in vivo in order to better design more effective immunotherapeutics against cancer. Our main approach is to use a facultative intracellular bacterium, Listeria monocytogenes, which has the unusual ability to live and grow in the cytoplasm of the cell and is thus an excellent vector for targeting passenger antigens to the major histocompatibility complex (MHC) class I pathway of antigen processing with the generation of authentic CTL epitopes. We have used this approach to target tumor antigens expressed on breast, melanoma and cervical cancer. We are also exploring the role of Listerial virulence factors in potentiating adaptive immune responses by activating innate immunity. Specifically, we are using these proteins as adjuvants for B cell lymphomas.

The many faces of Janus kinase.

Janus kinases have proved to be essential for many immunological processes but there is growing evidence that they also play a critical role in pathogenesis of many diseases including inflammatory diseases and cancer where they promote multiple steps of tumorigenesis. Several companies are in late stage clinical programs for the development of JAK kinase inhibitors and the first small molecule JAK inhibitor, Jakafi® (ruxolitinib) has been just approved for treatment of myeloproliferative neoplasms. Several other molecules are on the rise to treat arthritis, psoriasis and multiple types of cancer. This commentary will provide a review of the JAK kinase field as it pertains to small molecule inhibition for the treatment of cancer and autoimmune diseases with an emphasis on JAK2. The use of experimental and clinical inhibitors of JAK will be discussed for solid tumor and hematological malignancies, lupus, arthritis, colitis, neurological disorders, pain, diabetes and cardiovascular disease. In addition, it will review current paradigms in the field and treatment programs which could be complemented by small molecule inhibitors of Janus kinase.

Novel, orally active, proteasome inhibitor, delanzomib (CEP-18770), ameliorates disease symptoms and glomerulonephritis in two preclinical mouse models of SLE.

Current therapies for late-stage systemic lupus erythematosus (SLE) are limited to cytotoxic agents. Delanzomib (CEP-18770) is an orally active, reversible P2 threonine boronic acid inhibitor of the 26S mammalian proteasome. Delanzomib was tested in a head-to-head comparison against bortezomib to protect and treat mice with fatal lupus nephritis (LN). Age matched MRL/lpr or NZBWF1 mice with established SLE or LN, respectively, were treated with delanzomib either 3 mg/kg once or twice weekly intravenously or orally at 10 mg/kg. Mice were also treated with reference agent bortezomib at 0.5 mg/kg, intraperitoneally, once a week or 0.3 mg/kg once or twice a week. Reductions in the frequencies of specific anti-chromatin, smith and dsDNA antibody secreting cells and levels of the corresponding circulating antinuclear antibodies, were observed following delanzomib treatment. Reductions in several serum pro-inflammatory cytokines were observed in delanzomib-treated animals. Delanzomib treatment suppressed the development and progression of renal tissue damage and extended the survival of ill mice. Proteinuria was significantly decreased and severity of various renal histopathologies reduced relative to vehicle-treated nephritic mice. Treatment of lupus in these models demonstrated that delanzomib treatment lead to greater tolerability and rate of response resulting in improved stabilization of disease.

Therapeutic efficacy of CEP-33779, a novel selective JAK2 inhibitor, in a mouse model of colitis-induced colorectal cancer.

Constitutively activated STAT3 and STAT5 are expressed in a wide variety of human malignancies including solid and hematopoietic cancers and often correlate with a poor prognosis and resistance to multiple therapies. Given the well established role of STAT3 in tumorigenesis, inhibition of Janus-activated kinase 2 (JAK2) activity might represent an attractive therapeutic approach. Using a mouse model of colitis-induced colorectal cancer, we show that a novel, orally active, selective JAK2 inhibitor, CEP-33779, induced regression of established colorectal tumors, reduced angiogenesis, and reduced proliferation of tumor cells. Histopathologic analysis confirmed reduced incidence of histologic-grade neoplasia by CEP-33779. Tumor regression correlated with inhibition of STAT3 and NF-κB (RelA/p65) activation in a CEP-33779 dose-dependent manner. In addition, the expression of proinflammatory, tumor-promoting cytokines interleukin (IL)-6 and IL-1ß was strongly reduced upon JAK2 inhibition. The ability of CEP-33779 to suppress growth of colorectal tumors by inhibiting the IL-6/JAK2/STAT3 signaling suggests a potential therapeutic utility of JAK2 inhibitors in multiple tumors types, particularly those with a strong inflammatory component.

Animal models of systemic lupus erythematosus (SLE) and ex vivo assay design for drug discovery.

Systemic Lupus Erythematosus (SLE) is a debilitating and often fatal autoimmune disease that involves multiple organ systems. It can develop for years before being diagnosed. Current treatments for SLE usually involve the use of cytotoxic or immunosuppressive agents that can lead to infection or cancer. The design of appropriate models and assays will determine the efficiency and speed with which an investigator can test a new chemical entity (NCE) or expect results to move a drug discovery program forward. This unit describes a series of preclinical assays for the identification of new agents for the treatment of SLE. Most importantly, this unit will guide the reader through a step-by-step process to select appropriate models, validation drugs, and readouts, depending on the objective of the study. The reader will acquire a working knowledge of what models are available and the potential advantages and disadvantages of each, including ex vivo assays relevant to the discovery of new SLE therapeutics.

A highly selective, orally active inhibitor of Janus kinase 2, CEP-33779, ablates disease in two mouse models of rheumatoid arthritis.

INTRODUCTION: Janus kinase 2 (JAK2) is involved in the downstream activation of signal transducer and activator of transcription 3 (STAT3) and STAT5 and is responsible for transducing signals for several proinflammatory cytokines involved in the pathogenesis of rheumatoid arthritis (RA), including interleukin (IL)-6, interferon γ (IFNγ) and IL-12. In this paper, we describe the efficacy profile of CEP-33779, a highly selective, orally active, small-molecule inhibitor of JAK2 evaluated in two mouse models of RA. METHODS: Collagen antibody-induced arthritis (CAIA) and collagen type II (CII)-induced arthritis (CIA) were established before the oral administration of a small-molecule JAK2 inhibitor, CEP-33779, twice daily at 10 mg/kg, 30 mg/kg, 55 mg/kg or 100 mg/kg over a period of 4 to 8 weeks. RESULTS: Pharmacodynamic inhibition of JAK2 reduced mean paw edema and clinical scores in both CIA and CAIA models of arthritis. Reduction in paw cytokines (IL-12, IFNγ and tumor necrosis factor α) and serum cytokines (IL-12 and IL-2) correlated with reduced spleen CII-specific T helper 1 cell frequencies as measured by ex vivo IFNγ enzyme-linked immunosorbent spot assay. Both models demonstrated histological evidence of disease amelioration upon treatment (for example, reduced matrix erosion, subchondral osteolysis, pannus formation and synovial inflammation) and reduced paw phosphorylated STAT3 levels. No changes in body weight or serum anti-CII autoantibody titers were observed in either RA model. CONCLUSIONS: This study demonstrates the utility of using a potent and highly selective, orally bioavailable JAK2 inhibitor for the treatment of RA. Using a selective inhibitor of JAK2 rather than pan-JAK inhibitors avoids the potential complication of immunosuppression while targeting critical signaling pathways involved in autoimmune disease progression.

Estradiol-induced vaginal mucus inhibits antigen penetration and CD8(+) T cell priming in response to intravaginal immunization.

Although vaginal immunization has been explored as a strategy to induce mucosal immunity in the female reproductive tract, this site displays unique immunological features that probably evolved to inhibit anti-paternal T cell responses after insemination to allow successful pregnancy. We previously demonstrated that estradiol, which induces an estrus-like state, prevented CD8(+) T cell priming during intravaginal immunization of mice. We now show that estradiol prevented antigen loading of vaginal antigen presenting cells (APCs) after intravaginal immunization. Histological examination confirmed that estradiol prevented penetration of peptide antigen into the vaginal wall. Removal of the estradiol-induced mucus barrier by mucinase partially restored antigen loading of vaginal APC and CD8(+) T cell proliferation in vivo. The estradiol-induced mucus barrier may thus prevent exposure to antigens delivered intravaginally, supplementing additional estradiol-dependent mechanism(s) that inhibit CD8(+) T cell priming after insemination or vaginal vaccination.

Antiangiogenesis immunotherapy induces epitope spreading to Her-2/neu resulting in breast tumor immunoediting.

Targeting tumors using cancer vaccine therapeutics has several advantages including the induction of long-term immunity, prime boost strategies for additional treatments and reduced side effects compared to conventional chemotherapeutics. However, one problem in targeting tumor antigens directly is that this can lead to antigen loss or immunoediting. We hypothesized that directing the immune response to a normal cell type required for tumor growth and survival could provide a more stable immunotherapeutic target. We thus examined the ability of an antiangiogenesis, Listeria monocytogenes (Lm)-based vector to deliver extracellular and intracellular fragments of the mouse vascular endothelial growth factor receptor-2/Flk-1 molecule, Lm-LLO-Flk-E1, and Lm-LLO-Flk-11 respectively, in an autochthonous model for Her-2/neu(+) breast cancer. We found that these vaccines could cause epitope spreading to the endogenous tumor protein Her-2/neu and significantly delay tumor onset. However, tumors that grew out overtime accumulated mutations in the Her-2/neu molecule near or within cytotoxic T lymphocytes epitopes. We show here for the first time how an antiangiogenesis immunotherapy can be used to delay the onset of a spontaneous tumor through epitope spreading and determine a possible mechanism of how immunoediting of an endogenous tumor protein can allow for tumor escape and outgrowth in an autochthonous mouse model for Her-2/neu(+) breast cancer.

Cancer immunotherapy targeting the high molecular weight melanoma-associated antigen protein results in a broad antitumor response and reduction of pericytes in the tumor vasculature.

The high molecular weight melanoma-associated antigen (HMW-MAA), also known as melanoma chondroitin sulfate proteoglycan, has been used as a target for the immunotherapy of melanoma. This antigen is expressed on the cell surface and has a restricted distribution in normal tissues. Besides its expression in a broad range of transformed cells, this antigen is also found in pericytes, which are important for tumor angiogenesis. We generated a recombinant Listeria monocytogenes (Lm-LLO-HMW-MAA-C) that expresses and secretes a fragment of HMW-MAA (residues 2,160-2,258) fused to the first 441 residues of the listeriolysin O (LLO) protein. Immunization with Lm-LLO-HMW-MAA-C was able to impede the tumor growth of early established B16F10-HMW-MAA tumors in mice and both CD4(+) and CD8(+) T cells were required for therapeutic efficacy. Immune responses to a known HLA-A2 epitope present in the HMW-MAA(2160-2258) fragment was detected in the HLA-A2/K(b) transgenic mice immunized with Lm-LLO-HMW-MAA-C. Surprisingly, this vaccine also significantly impaired the in vivo growth of other tumorigenic cell lines, such as melanoma, renal carcinoma, and breast tumors, which were not engineered to express HMW-MAA. One hypothesis is that the vaccine could be targeting pericytes, which are important for tumor angiogenesis. In a breast tumor model, immunization with Lm-LLO-HMW-MAA-C caused CD8(+) T-cell infiltration in the tumor stroma and a significant decrease in the number of pericytes in the tumor blood vessels. In conclusion, a Lm-based vaccine against HMW-MAA can trigger cell-mediated immune responses to this antigen that can target not only tumor cells but also pericytes in the tumor vasculature.

Paternal antigen-bearing cells transferred during insemination do not stimulate anti-paternal CD8+ T cells: role of estradiol in locally inhibiting CD8+ T cell responses.

Maternal immunological tolerance of the semiallogeneic fetus involves several overlapping mechanisms to balance maternal immunity and fetal development. Anti-paternal CD8+ T cells are suppressed during pregnancy in some but not all mouse models. Since semen has been shown to mediate immune modulation, we tested whether exposure to paternal Ag during insemination activated or tolerized anti-paternal CD8+ T cells. The uterine lumen of mated female mice contained male MHC I+ cells that stimulated effector, but not naive, CD8+ T cells ex vivo. Maternal MHC class I+ myeloid cells fluxed into the uterine lumen in response to mating and cross-presented male H-Y Ag to effector, but not naive, CD8+ T cells ex vivo. However, neither unprimed nor previously primed TCR-transgenic CD8+ T cells specific for either paternal MHC I or H-Y Ag proliferated in vivo after mating. These T cells subsequently responded normally to i.p. challenge, implicating ignorance rather than anergy as the main reason for the lack of response. CD8+ T cells responded to either peptide Ag or male cells delivered intravaginally in ovariectomized mice, but this response was inhibited by systemic estradiol (inducing an estrus-like state). Subcutaneous Ag induced responses in both cases. Allogeneic dendritic cells did not induce responses intravaginally even in ovariectomized mice in the absence of estradiol. These results suggest that inhibition of antiallogeneic responses is restricted both locally to the reproductive tract and temporally to the estrous phase of the menstrual cycle, potentially decreasing the risk of maternal immunization against paternal Ags during insemination.