Reduction of Murine Colon Tumorigenesis Driven by Enterotoxigenic Bacteroides fragilis Using Cefoxitin Treatment

BACKGROUND

Chronic inflammation and composition of the colon microbiota have been associated with colorectal cancer in humans. The human commensal enterotoxigenic Bacteroides fragilis (ETBF) is linked to both inflammatory bowel disease and colorectal cancer and, in our murine model, causes interleukin 17A (IL-17A)-dependent colon tumors. In these studies, we hypothesized that persistent colonization by ETBF is required for tumorigenesis.

METHODS

We established a method for clearing ETBF in mice, using the antibiotic cefoxitin. Multiple intestinal neoplasia mice were colonized with ETBF for the experiment duration or were cleared of infection after 5 or 14 days. Gross tumors and/or microadenomas were then evaluated. In parallel, IL-17A expression was evaluated in wild-type littermates.

RESULTS

Cefoxitin treatment resulted in complete and durable clearance of ETBF colonization. We observed a stepwise increase in median colon tumor numbers as the duration of ETBF colonization increased before cefoxitin treatment. ETBF eradication also significantly decreased mucosal IL-17A expression.

CONCLUSIONS

The timing of ETBF clearance profoundly influences colon adenoma formation, defining a period during which the colon is susceptible to IL-17A-dependent tumorigenesis in this murine model. This model system can be used to study the microbiota-dependent and molecular mechanisms contributing to IL-17A-dependent colon tumor initiation.

Redundant Innate and Adaptive Sources of IL17 Production Drive Colon Tumorigenesis

IL17-producing Th17 cells, generated through a STAT3-dependent mechanism, have been shown to promote carcinogenesis in many systems, including microbe-driven colon cancer. Additional sources of IL17, such as γδ T cells, become available under inflammatory conditions, but their contributions to cancer development are unclear. In this study, we modeled Th17-driven colon tumorigenesis by colonizing Min(Ap) (c+/-) mice with the human gut bacterium, enterotoxigenic Bacteroides fragilis (ETBF), to investigate the link between inflammation and colorectal cancer. We found that ablating Th17 cells by knocking out Stat3 in CD4(+) T cells delayed tumorigenesis, but failed to suppress the eventual formation of colonic tumors. However, IL17 blockade significantly attenuated tumor formation, indicating a critical requirement for IL17 in tumorigenesis, but from a source other than Th17 cells. Notably, genetic ablation of γδ T cells in ETBF-colonized Th17-deficient Min mice prevented the late emergence of colonic tumors. Taken together, these findings support a redundant role for adaptive Th17 cell- and innate γδT17 cell-derived IL17 in bacteria-induced colon carcinogenesis, stressing the importance of therapeutically targeting the cytokine itself rather than its cellular sources. Cancer Res; 76(8); 2115-24. ©2016 AACR.

Abstract A141: The vigorous immune microenvironment of microsatellite instable colon cancer isbalanced by multiple counter-inhibitory checkpoints

We examined the immune microenvironment of primary colorectal cancer (CRC) using immunohistochemistry, laser capture microdissection/qRT-PCR, flow cytometry and functional analysis of tumor infiltrating lymphocytes. A subset of CRC displayed high infiltration with activated CD8+ CTL as well as activated Th1 cells characterized by IFN-gamma production and the Th1 transcription factor Tbet. Parallel analysis of tumor genotypes revealed that virtually all of the tumors with this active Th1/CTL microenvironment had defects in mismatch repair, as evidenced by microsatellite instability (MSI). Counterbalancing this active Th1/CTL microenvironment, MSI tumors selectively demonstrated highly up-regulated expression of multiple immune checkpoints, including five - PD-1, PD-L1, CTLA-4, LAG-3 and IDO - currently being targeted clinically with inhibitors. These findings link tumor genotype with the immune microenvironment, and explain why MSI tumors are not naturally eliminated despite a hostile Th1/CTL microenvironment. They further suggest that blockade of specific checkpoints may be selectively efficacious in the MSI subset of CRC. Our findings are the first to demonstrate a link between a genetically defined subtype of cancer and its corresponding expression of immune checkpoints in the tumor microenvironment. The mismatch repair defective subset of CRC selectively up-regulates at least 5 checkpoint molecules that are targets of inhibitors currently being clinically tested. Furthermore, our results were clinically validated in a phase 2 study at Hopkins which showed mismatch-repair status as a predictor of clinical benefit to immune checkpoint blockade with pembrolizumab.

Citation Format: Nicolas J. Llosa, Franck Housseau, Elizabeth Wick, Hechenbleikner Lizzy, Michael Cruise, Robert Anders, Cynthia Sears, Drew M. Pardoll, Hongni Fan, Nicholas Siegel, Lee Blosser, Ada Tam, Hao Wang. The vigorous immune microenvironment of microsatellite instable colon cancer isbalanced by multiple counter-inhibitory checkpoints. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr A141.

Procarcinogenic regulatory T cells in microbial-induced colon cancer

Regulatory T cell (Treg) promote IL-17-mediated colon tumorigenesis in multiple intestinal neoplasia (Min) mice colonized with enterotoxigenic Bacteroides fragilis (ETBF). Although they retain their immunosuppressive function, mucosal Treg are instrumental to initiate ETBF-triggered IL-17 colitis by limiting the availability of IL-2 in the local microenvironment. However, the mechanisms that trigger the recruitment of the pro-carcinogenic Treg in ETBF-colonized colon remained to be elucidated.

Regulatory T-cell Response to Enterotoxigenic Bacteroides fragilis Colonization Triggers IL17-Dependent Colon Carcinogenesis

Many epithelial cancers are associated with chronic inflammation. However, the features of inflammation that are procarcinogenic are not fully understood. Regulatory T cells (Treg) typically restrain overt inflammatory responses and maintain intestinal immune homeostasis. Their immune-suppressive activity can inhibit inflammation-associated cancers. Paradoxically, we show that colonic Tregs initiate IL17-mediated carcinogenesis in multiple intestinal neoplasia mice colonized with the human symbiote enterotoxigenic Bacteroides fragilis (ETBF). Depletion of Tregs in ETBF-colonized C57BL/6 FOXP3(DTR) mice enhanced colitis but diminished tumorigenesis associated with shifting of mucosal cytokine profile from IL17 to IFNγ; inhibition of ETBF-induced colon tumorigenesis was dependent on reduced IL17 inflammation and was independent of IFNγ. Treg enhancement of IL17 production is cell-extrinsic. IL2 blockade restored Th17 responses and tumor formation in Treg-depleted animals. Our findings demonstrate that Tregs limit the availability of IL2 in the local microenvironment, allowing the Th17 development necessary to promote ETBF-triggered neoplasia, and thus unveil a new mechanism whereby Treg responses to intestinal bacterial infection can promote tumorigenesis.

SIGNIFICANCE

Tregs promote an oncogenic immune response to a common human symbiote associated with inflammatory bowel disease and colorectal cancer. Our data define mechanisms by which mucosal Tregs, despite suppressing excessive inflammation, promote the earliest stages of immune procarcinogenesis via enhancement of IL17 production at the expense of IFNγ production.

Enterotoxigenic Bacteroides fragilis induces oncogenic regulatory T cells (TUM9P.1000)

Enterotoxigenic Bacteroides fragilis (ETBF) is an occasional inducer of inflammatory diarrhea and acute colitis, and preliminary studies have recently demonstrated an association with inflammatory bowel disease and colorectal cancer in humans. The pathogenesis of ETBF can largely be attributed to the secretion of a toxin, BFT (B. fragilis toxin), which has a profound effect on the colonic microenvironment. BFT promotes cleavage of E-cadherin, activates NF-kB and Wnt/b-catenin signaling, and stimulates the secretion of pro-inflammatory cytokines, such as IL-6, IL-8, and TNF-a. The inflammation associated with ETBF is characterized by robust IL-17 cytokine secretion, and in MinAPC/+ mice, ETBF induces IL-17-dependent distal colon tumorigenesis. In an attempt to elucidate the immunologic differences between the distal and proximal colon, we found ETBF induced a greater density of Foxp3+ Tregs in the distal colon. Furthermore, those Tregs initiate the oncogenic IL-17 response to ETBF. While investigating the Treg and IL-17 responses to ETBF, we found that depletion of Tregs in ETBF-colonized C57BL/6 Foxp3DTR-GFP MinAPC/+ mice mitigated intestinal IL-17 production as well as colonic neoplasia. Antibody blockade of IL-2, but not genetic ablation of IFN-γ, restored ETBF-induced microadenoma formation. These findings unveil a new mechanism of cancer-induced inflammation whereby an overt Treg response to intestinal bacteria promotes colon tumorigenesis.

Immune checkpoint blockade in microsatellite instable colorectal cancers: Back to the clinic

The active Th1/CTL immune microenvironment of Microsatellite Instable colorectal cancer (CRC) is counterbalanced by up-regulated expression of multiple immune checkpoints, suggesting that defective mismatch repair may be a biomarker to select CRC patients for treatment with checkpoint inhibitors. This hypothesis is currently being tested in two clinical trials.

An unexpected journey: how cancer immunotherapy has paved the way for an HIV-1 cure

Over 30 million people worldwide are currently infected with human immunodeficiency virus type-1 (HIV-1). While HIV-1 infection was initially thought to be a death sentence, the advent of combination antiretroviral therapy (cART) in the mid-1990's resulted in decreases in viremia and an extended lifespan for infected persons. Despite this, long-term control of the virus in the absence of drug therapy has yet to be achieved, owing to the rebound in viral load and resumption of disease progression that follows removal of the patient from cART. Currently, the most promising candidates for an HIV-1 cure are immunotherapies that harness the patient's own immune system and induce cytotoxic T lymphocyte (CTL)-mediated clearance of infected cells. Most of these approaches were developed and optimized in the cancer setting and have had varying degrees of success, the findings from which have wide applications to various disease models. In this review, we evaluate the past successes and failures of cancer immunotherapy and how the findings have shaped our journey toward an HIV-1 cure.

The vigorous immune microenvironment of microsatellite instable colon cancer is balanced by multiple counter-inhibitory checkpoints

We examined the immune microenvironment of primary colorectal cancer using immunohistochemistry, laser capture microdissection/qRT-PCR, flow cytometry, and functional analysis of tumor-infiltrating lymphocytes. A subset of colorectal cancer displayed high infiltration with activated CD8(+) cytotoxic T lymphocyte (CTL) as well as activated Th1 cells characterized by IFNγ production and the Th1 transcription factor TBET. Parallel analysis of tumor genotypes revealed that virtually all of the tumors with this active Th1/CTL microenvironment had defects in mismatch repair, as evidenced by microsatellite instability (MSI). Counterbalancing this active Th1/CTL microenvironment, MSI tumors selectively demonstrated highly upregulated expression of multiple immune checkpoints, including five-PD-1, PD-L1, CTLA-4, LAG-3, and IDO-currently being targeted clinically with inhibitors. These findings link tumor genotype with the immune microenvironment, and explain why MSI tumors are not naturally eliminated despite a hostile Th1/CTL microenvironment. They further suggest that blockade of specific checkpoints may be selectively efficacious in the MSI subset of colorectal cancer.

SIGNIFICANCE

The findings reported in this article are the first to demonstrate a link between a genetically defined subtype of cancer and its corresponding expression of immune checkpoints in the tumor microenvironment. The mismatch repair-defective subset of colorectal cancer selectively upregulates at least five checkpoint molecules that are targets of inhibitors currently being clinically tested.

Bacteroides fragilis subverts mucosal biology: from symbiont to colon carcinogenesis

The human body comprises fewer host cells than bacterial cells, most of which are obligate anaerobes residing in the gut. The symbiont Bacteroides fragilis constitutes a relatively small proportion (up to 1%-2%) of cultured fecal bacteria, but colonizes most humans. There are 2 classes of B. fragilis distinguished by their ability to secrete a zinc-dependent metalloprotease toxin, B. fragilis toxin (BFT). Strains that do not secrete BFT are nontoxigenic B. fragilis (NTBF), and those that do are called enterotoxigenic B. fragilis (ETBF). ETBF can induce clinical pathology, including inflammatory diarrhea, although asymptomatic colonization may be common. Intestinal inflammation is mediated by BFT, as yet the only known virulence factor of ETBF. Recent experimental evidence demonstrating that ETBF-driven colitis promotes colon tumorigenesis has generated interest in the potential contribution of ETBF to human colon carcinogenesis. Critical questions about the epidemiology of chronic, subclinical human colonization with ETBF and its impact on the biology of the colon need to be addressed.

Oncogenic Kras activates a hematopoietic-to-epithelial IL-17 signaling axis in preinvasive pancreatic neoplasia

Many human cancers are dramatically accelerated by chronic inflammation. However, the specific cellular and molecular elements mediating this effect remain largely unknown. Using a murine model of pancreatic intraepithelial neoplasia (PanIN), we found that Kras(G12D) induces expression of functional IL-17 receptors on PanIN epithelial cells and also stimulates infiltration of the pancreatic stroma by IL-17-producing immune cells. Both effects are augmented by associated chronic pancreatitis, resulting in functional in vivo changes in PanIN epithelial gene expression. Forced IL-17 overexpression dramatically accelerates PanIN initiation and progression, while inhibition of IL-17 signaling using genetic or pharmacologic techniques effectively prevents PanIN formation. Together, these studies suggest that a hematopoietic-to-epithelial IL-17 signaling axis is a potent and requisite driver of PanIN formation.

Stat3 activation in murine colitis induced by enterotoxigenic Bacteroides fragilis

BACKGROUND

Enterotoxigenic Bacteroides fragilis (ETBF), a molecular subclass of the common human commensal, B. fragilis, has been associated with inflammatory bowel disease. ETBF colitis is characterized by the activation of Stat3 and a Th17 immune response in the colonic mucosa. This study was designed to investigate the time course and cellular distribution of Stat3 activation in ETBF-colonized mice.

METHODS

C57BL/6 wild-type, C57BL/6, or Rag-1 mice were inoculated with saline, nontoxigenic B. fragilis or ETBF. Histologic diagnosis and mucosal Stat activation (immunohistochemistry, Western blot, and/or electrophorectic mobility shift assay) were evaluated over time (6-24 h, 1-7 d, and 1-18 mo after inoculation). Mucosal permeability was evaluated at 16 hours, 1 day, and 3 days. Mucosal immune responses were evaluated at 1 week, and 12 and 18 months.

RESULTS

ETBF induced rapid-onset colitis that persisted for up to 1 year. Stat3 activation (pStat3) was noted in the mucosal immune cells within 16 hours, with colonic epithelial cell activation evident at 24 hours after inoculation. ETBF-induced increased mucosal permeability was first observed at 24 hours after inoculation, after which the initial immune cell pStat3 activation was noted. Immune cell pStat3 was present in the absence of epithelial pStat3 (C57BL/6). Epithelial pStat3 was present in the absence of T and B cells (Rag-1 mice). pStat3 persisted in the epithelial and immune cells for 1 year, characterized by isolated pStat3-positive cell clusters, with varying intensity distributed through the proximal and distal colon. Similarly, mucosal Th17 immune responses persisted for up to 1 year. Loss of fecal ETBF colonization was associated with the loss of mucosal pStat3 and Th17 immune responses.

CONCLUSIONS

ETBF rapidly induces immune cell pStat3, which is independent of epithelial pStat3. This occurs before ETBF-induced mucosal permeability, suggesting that ETBF, likely through B. fragilis toxin and its action on the colonic epithelial cell, triggers mucosal immune cell Stat3 activation. Peak mucosal Stat3 activation (immune and epithelial cells) occurs subsequently when other colonic bacteria may contribute to the ETBF-initiated immune response due to barrier dysfunction. ETBF induces long-lived, focal colonic Stat3 activation and Th17 immune responses dependent on the ongoing ETBF colonization. Further study is needed to evaluate the early mucosal signaling events, resulting in epithelial Stat3 activation and the sequelae of long-term colonic Stat3 activation.

Interleukin-17 and type 17 helper T cells in cancer management and research

Since their recent discovery, T helper 17 (Th17) cells have been frequently detected in the tumor microenvironment of many malignancies, but their clinical implications remain largely unknown. Interleukin-17 (IL-17) detection is commonly related with poor outcomes in colorectal cancers, yet its presence is associated with antitumor responses in ovarian carcinomas. Numerous experimental models illustrate the divergent roles of Th17 cells in tumor immunity, which appears to be mainly dependent on the tumor context (type, location, and stage of cancer). It is recognized that IL-17 is produced by a variety of cell types and that Th17 cells are endowed with a unique functional plasticity. Therefore, when trying to elucidate potential immune biomarkers and immunotargets, it is extremely important to make a clear dissociation between strategies targeting Th17 versus its hallmark cytokine, IL-17. In this review, we will summarize the data regarding the detection of IL-17 and Th17 in human cancers, consider the experimental evidence on their respective roles in antitumor activity, and discuss the potential of IL-17 as an immune target for therapeutic interventions.

Stat3 and Th17-mediated colitis promotes regional tumorigenesis in response to a common commensal bacterium: role of Foxp3+ Treg/Th17 balance (90.17)

Enterotoxigenic Bacteroides fragilis (ETBF) is an inducer of inflammatory diarrheal disease with acute colitis, and may even be linked to chronic colitis and colorectal cancer in humans. The pathogenesis of ETBF can largely be attributed to the secretion of a toxin, BFT (B. fragilis toxin), which has a profound effect on the colonic microenvironment. BFT promotes cleavage of E-cadherin, activates NF-kB and Wnt/b-catenin signaling, and stimulates the secretion of pro-inflammatory cytokines, such as IL-6, IL-8, and TNF-a. The inflammation associated with ETBF is characterized by widespread colonic Stat3 activation and IL-17 cytokine secretion. In Min mice, the Th17-mediated inflammation promotes the formation of distal colon tumors, as demonstrated by reduced tumorigenesis in response to IL-17 blockade. Our research has been focused on elucidating the immunologic differences between the distal and proximal colon in an attempt to determine why tumorigenesis is so regional. We have found that the proximal colon has a greater density of Foxp3+ Tregs than the distal colon. Furthermore, preliminary data suggests that the Th17 cytokines are differentially expressed in the two regions. We propose that increased Treg density in the proximal colon restrains Th17-mediated inflammation relative to the distal colon. We are currently studying the relationship between the Treg cells and infiltrating effector cells and how that affects tumorigenesis in response to ETBF.

IFN-producing killer dendritic cells are antigen-presenting cells endowed with T-cell cross-priming capacity

IFN-producing killer dendritic cells (IKDC) represent a recently discovered cell type in the immune system that possesses a number of functions contributing to innate and adaptive immunity, including production of type 1 and 2 IFNs, interleukin (IL)-12, natural killing, and ultimately antigen presentation to naïve T cells. Here, we compared in vitro and in vivo responses of mouse IKDC, conventional dendritic cells (DC), and natural killer (NK) cells to murine cytomegalovirus infection and found distinct functions among these cell subsets. Upon recognition of infected fibroblasts, IKDC, as well as NK, produced high level of IFN-gamma, but unlike NK, IKDC simultaneously produced IL-12p40 and up-regulated MHC class II (MHC-II) and costimulatory molecules. Using MHC-II molecule expression as a phenotypic marker to distinguish activated IKDC from activated NK, we further showed that highly purified MHC-II(+) IKDC but not NK cross-present MHC class I-restricted antigens derived from MCMV-infected targets to CD8(+) T cells in vitro and in vivo. Our findings emphasize the unique nature of IKDC as a killer antigen-presenting cell directly linking innate and adaptive immunity.

17beta-estradiol alters the activity of conventional and IFN-producing killer dendritic cells

Estrogens increase aspects of innate immunity and contribute to sex differences in the prevalence of autoimmune diseases and in response to infection. The goal of the present study was to assess whether exposure to 17beta-estradiol (E2) affects the development and function of bone marrow-derived dendritic cells and to determine whether similar changes are observed in CD11c(+) splenocytes exposed to E2 in vivo. E2 facilitated the differentiation of BM precursor cells into functional CD11c(+)CD11b(+)MHC class II(+) dendritic cells (DCs) with increased expression of the costimulatory molecules CD40 and CD86. Exposure of bone marrow-derived dendritic cells to E2 also enhanced production of IL-12 in response to the TLR ligands, CpG and LPS. In contrast, CD11c(+) cells isolated from the spleens of female C57BL/6 mice that were intact, ovariectomized, or ovariectomized with E2 replacement exhibited no differences in the number or activity of CD11c(+)CD11b(+)MHC class II(+) DCs. The presence of E2 in vivo, however, increased the number of CD11c(+)CD49b(+)NK1.1(low) cells and reduced numbers of CD11c(+)CD49b(+)NK1.1(high) cells, a surface phenotype for IFN-producing killer DCs (IKDCs). Ultrastructural analysis demonstrated that CD11c(+)NK1.1(+) populations were comprised of cells that had the appearance of both DCs and IKDCs. CD11c(+) splenocytes isolated from animals with supplemental E2 produced more IFN-gamma in response to IL-12 and IL-18. These data illustrate that E2 has differential effects on the development and function of DCs and IKDCs and provide evidence that E2 may strengthen innate immunity by enhancing IFN-gamma production by CD11c(+) cells.

Cutting Edge: An In Vivo Requirement for STAT3 Signaling in TH17 Development and TH17-Dependent Autoimmunity

STAT3 activation has been observed in several autoimmune diseases, suggesting that STAT3-mediated pathways promote pathologic immune responses. We provide in vivo evidence that the fundamental role of STAT3 signaling in autoimmunity relates to its absolute requirement for generating T(H)17 T cell responses. We show that STAT3 is a master regulator of this pathogenic T cell subtype, acting at multiple levels in vivo, including T(H)17 T cell differentiation and cytokine production, as well as induction of RORgamma t and the IL-23R. Neither naturally occurring T(H)17 cells nor T(H)17-dependent autoimmunity occurs when STAT3 is ablated in CD4 cells. Furthermore, ablation of STAT3 signaling in CD4 cells results in increased T(H)1 responses, indicating that STAT3 signaling skews T(H) responses away from the T(H)1 pathway and toward the T(H)17 pathway. Thus, STAT3 is a candidate target for T(H)17-dependent autoimmune disease immunotherapy that could selectively inhibit pathogenic immune pathways.

Interferon-producing killer dendritic cells provide a link between innate and adaptive immunity

Natural killer (NK) cells and dendritic cells (DCs) are, respectively, central components of innate and adaptive immune responses. We describe here a third DC lineage, termed interferon-producing killer DCs (IKDCs), distinct from conventional DCs and plasmacytoid DCs and with the molecular expression profile of both NK cells and DCs. They produce substantial amounts of type I interferons (IFN) and interleukin (IL)-12 or IFN-gamma, depending on activation stimuli. Upon stimulation with CpG oligodeoxynucleotides, ligands for Toll-like receptor (TLR)-9, IKDCs kill typical NK target cells using NK-activating receptors. Their cytolytic capacity subsequently diminishes, associated with the loss of NKG2D receptor (also known as Klrk1) and its adaptors, Dap10 and Dap12. As cytotoxicity is lost, DC-like antigen-presenting activity is gained, associated with upregulation of surface major histocompatibility complex class II (MHC II) and costimulatory molecules, which formally distinguish them from classical NK cells. In vivo, splenic IKDCs preferentially show NK function and, upon systemic infection, migrate to lymph nodes, where they primarily show antigen-presenting cell activity. By virtue of their capacity to kill target cells, followed by antigen presentation, IKDCs provide a link between innate and adaptive immunity.

In vivo costimulatory role of B7-DC in tuning T helper cell 1 and cytotoxic T lymphocyte responses

B7-DC, one of the recently described B7 family members, has the capacity to inhibit T cell responses via engagement of the immunoreceptor tyrosine-based inhibitory motif–containing inhibitory PD-1 receptor as well as enhance responses via an as yet unidentified costimulatory receptor. B7-DC is highly homologous to a coinhibitory B7 family member, B7-H1, which also binds PD-1. It is currently unclear which B7-DC function—costimulation or inhibition—predominates in vivo. To study in vivo functions of B7-DC, we evaluated immune responses in B7-DC knockout (KO) mice. Although not eliminated, interferon-γ (IFN-γ) production by CD4 T cells and IFN-γ–dependent humoral responses were reduced in B7-DC KO mice relative to wild type mice. Antigen-specific CD8 T cell responses and cytotoxic T lymphocyte (CTL) activity were also diminished in B7-DC KO mice. Hepatic tumors grew more quickly in B7-DC KO mice, associated with a decrease in intrahepatic tumor-specific CD8 T cells. These results highlight the contrasting in vivo roles of B7-DC and B7-H1 and indicate that B7-DC functions as a tuning molecule, selectively augmenting T helper 1 and CTL responses.

Cooperative B7-1/2 (CD80/CD86) and B7-DC costimulation of CD4+ T cells independent of the PD-1 receptor

B7-DC is a recently discovered member of the B7 family that binds to PD-1 and is selectively expressed by dendritic cells (DCs). It has been shown to either costimulate or inhibit T cell responses. To assess the role of B7-DC in DC-T cell interactions, DCs from B7-DC knockout (KO) mice were generated and compared with DCs from wild-type (WT) and B7-1/B7-2 double KO mice. B7-1/B7-2-deficient DCs, while strongly diminished in their ability to stimulate naive CD4+ T cells, nonetheless retain partial activity. DCs from B7-DC KO mice are diminished in their ability to activate CD4+ T cells, demonstrating that DC-expressed B7-DC serves a predominantly stimulatory rather than inhibitory function in the initiation of T cell responses. B7-DC costimulates expression of CD40L with faster kinetics than B7-1 and displays potent synergy with B7-1 and B7-2 for T cell proliferation and cytokine production, indicating that these B7 family members work in concert to stimulate T cells. Finally, costimulation with B7-DC alone or in conjunction with B7-1 is PD-1 independent, indicating that B7-DC costimulates T cells via a second receptor.

CD40-stimulated B lymphocytes pulsed with tumor antigens are effective antigen-presenting cells that can generate specific T cells

Although they are considered as antigen-presenting cells, the role of antigen-unspecific B lymphocytes in antigen presentation and T-lymphocyte stimulation remains controversial. In this paper, we tested the capacity of normal human peripheral activated B cells to stimulate T cells using melanoma antigens or melanoma cell lysates. B lymphocytes activated through CD40 ligation and then pulsed with tumor antigens efficiently processed and presented MHC class II-restricted peptides to specific CD4(+) T-cell clones. This suggests that CD40-activated B cells have the functional and molecular competence to present MHC class II epitopes when pulsed with exogenous antigens, thereby making them a relevant source of antigen-presenting cells to generate T cells. To test this hypothesis, CD40-activated B cells were pulsed with a lysate prepared from melanoma cells and used to stimulate peripheral autologous T cells. Interestingly, T cells specific to melanoma antigens were generated. Additional analysis of these T-cell clones revealed that they recognized MHC class II-restricted epitopes from tyrosinase, a known melanoma tumor antigen. The efficient antigen presentation by antigen-unspecific activated B cells was correlated with a down-regulation in the expression of HLA-DO, a B cell-specific protein known to interfere with HLA-DM function. Because HLA-DM is important in MHC class II peptide loading, the observed decrease in HLA-DO may partially explain the enhanced antigen presentation after B-cell activation. Results globally suggest that when they are properly activated, antigen-unspecific B-lymphocytes can present exogenous antigens by MHC class II molecules and stimulate peripheral antigen-specific T cells. Antigen presentation by activated B cells could be exploited for immunotherapy by allowing the in vitro generation of T cells specific against antigens expressed by tumors or viruses.

Prostate cancer chemoprevention agents exhibit selective activity against early stage prostate cancer cells

Preclinical models for the identification of prostate cancer chemoprevention agents are lacking. Based upon the notion that clinically useful chemoprevention agents should exhibit selective activity against early stage disease, studies were undertaken to assess whether chemoprevention agents selectively inhibited the growth of early stage prostate cancer, as compared to late stage cancer. First, a series of cell and molecular studies were performed, which, when taken together, validated the use of a panel of prostate cell lines as a model of the different stages of carcinogenesis. Next, therapeutic responsiveness to ten different cytotoxic or chemoprevention agents was evaluated. Chemoprevention agents exhibited selective activity against normal and early transformed prostate tissue, whereas cytotoxic agents were non-specific. Selective activity against early versus advanced prostate cancer cells is identified as a potential screening method for chemoprevention agents.Prostate Cancer and Prostatic Diseases (2001) 4, 81-91

Quantitative real-time RT-PCR as a method for monitoring T lymphocyte reactivity to full-length tyrosinase protein in vaccinated melanoma patients

The major goal of therapeutic cancer vaccine trials is to mediate tumor regression. However, it is critically important to devise in vitro immunological assays that correlate with clinical outcome, for use as surrogate markers of vaccine efficacy. To date, clinical emphasis has been placed on peptide vaccines, but trends towards the use of more complex immunogens such as whole proteins require the development of efficient and sensitive methods for monitoring their immunological effects. In the context of a vaccination trial using full-length tyrosinase (Ty) to immunize patients with metastatic melanoma, a monitoring technique was developed in which autologous dendritic cells (DC) infected with a recombinant adenovirus encoding the Ty protein were used to assess the Ty-specific reactivity of fresh peripheral blood lymphocytes (PBL) collected from patients at different intervals during therapy. Quantitative real-time RT-PCR (qRT-PCR) was used to measure the production of cytokine mRNA by T cells following a 2.5-h incubation with Ty-expressing DC. Two out of ten patients studied demonstrated Ty protein-specific reactivity that increased during and after the period of vaccination. While one of these patients also reacted to an HLA-A1-compatible Ty peptide, the second did not recognize any of the known Ty epitopes, highlighting the importance of this technique for monitoring the effects of complex vaccines.

Tumor-specific CD8+ T lymphocytes derived from the peripheral blood of prostate cancer patients by in vitro stimulation with autologous tumor cell lines

To identify tumor-associated antigens as putative targets for developing immunotherapies against prostate cancer, we investigated the ability of T cells derived from the peripheral blood lymphocytes of prostate cancer patients to recognize autologous tumor cells. The technical challenge of growing in vitro carcinoma cell lines from small prostate cancer samples was previously addressed by immortalization of early epithelial cell cultures with the HPV16 transforming proteins E6 and E7 and by genetic characterization of the carcinoma and normal prostate cell lines. In our study, peripheral blood lymphocytes were stimulated in vitro using autologous IFNgamma-treated prostate carcinoma cells transduced with the B7.1 molecule as a source of T-cell costimulation. Tumor-specific CD8+ T lymphocytes were obtained from 3 of 6 prostate cancer patients tested and included T cells restricted by classical and nonclassical HLA molecules. In 1 case, we demonstrated that the prostate cancer-reactive T cells were TCRalpha/beta+ and recognized autologous tumor cells but not autologous normal cells in the context of HLA-B or -C molecules. These results validate the approach of in vitro stimulation of peripheral blood lymphocytes from prostate cancer patients with autologous tumor cell lines to isolate prostate cancer-specific T cells and demonstrate the existence of a functionally diverse immune response against prostate cancer.

N-linked carbohydrates in tyrosinase are required for its recognition by human MHC class II-restricted CD4(+) T cells

Glycosylation of mammalian proteins is known to influence their intracellular trafficking, half life, and susceptibility to enzymatic degradation. Rare instances of natural T cell epitopes dependent upon glycosylation for recognition have been described. We report here on human CD4(+) T lymphocyte cultures and clones from two melanoma patients that recognize the melanoma-associated Ag tyrosinase in the context of HLA-DR4 and -DR8. These T cells recognize tyrosinase, normally a heavily glycosylated molecule, when expressed constitutively in melanoma cells or in COS-7 transfectants pulsed as lysates onto autologous APC. However, these T cells fail to recognize tyrosinase expressed in bacteria, nor do they react with overlapping peptides covering full-length tyrosinase, suggesting a critical role for glycosylation in the processing and / or composition of the stimulatory epitopes. The requirement for glycosylation was demonstrated by the failure of tyrosinase-specific CD4(+) T cells to recognize tyrosinase synthesized in the presence of glycosylation inhibitors, or deglycosylated enzymatically. Site-directed mutagenesis of each of seven potential N-glycosylation sites showed that four sites were required to generate forms of tyrosinase that could be recognized by individual T cell clones. These data indicate that certain carbohydrate moieties are required for processing the tyrosinase peptides recognized by CD4(+) T cells. Post-translational modifications of human tumor-associated proteins such as tyrosinase could be a critical factor for the development of antitumor immune responses.

Recognition of a shared human prostate cancer-associated antigen by nonclassical MHC-restricted CD8+ T cells

To identify prostate cancer-associated Ags, tumor-reactive T lymphocytes were generated using iterative stimulations of PBMC from a prostate cancer patient with an autologous IFN-gamma-treated carcinoma cell line in the presence of IL-2. A CD8+ T cell line and TCR alphabeta+ T cell clone were isolated that secreted IFN-gamma and TNF-alpha in response to autologous prostate cancer cells but not to autologous fibroblasts or lymphoblastoid cells. However, these T cells recognized several normal and malignant prostate epithelial cell lines without evidence of shared classical HLA molecules. The T cell line and clone also recognized colon cancers, but not melanomas, sarcomas, or lymphomas, suggesting recognition of a shared epithelium-associated Ag presented by nonclassical MHC or MHC-like molecules. Although Ag recognition by T cells was inhibited by mAb against CD8 and the TCR complex (anti-TCR alphabeta, CD3, Vbeta12), it was not inhibited by mAb directed against MHC class Ia or MHC class II molecules. Neither target expression of CD1 molecules nor HLA-G correlated with T cell recognition, but beta2-microglobulin expression was essential. Ag expression was diminished by brefeldin A, lactacystin, and cycloheximide, but not by chloroquine, consistent with an endogenous/cytosolic Ag processed through the classical class I pathway. These results suggest that prostate cancer and colon cancer cells can process and present a shared peptidic Ag to TCR alphabeta+ T cells via a nonclassical MHC I-like molecule yet to be defined.

Recognition of a Shared Human Prostate Cancer-Associated Antigen by Nonclassical MHC-Restricted CD8+ T Cells

To identify prostate cancer-associated Ags, tumor-reactive T lymphocytes were generated using iterative stimulations of PBMC from a prostate cancer patient with an autologous IFN-γ-treated carcinoma cell line in the presence of IL-2. A CD8+ T cell line and TCR αβ+ T cell clone were isolated that secreted IFN-γ and TNF-α in response to autologous prostate cancer cells but not to autologous fibroblasts or lymphoblastoid cells. However, these T cells recognized several normal and malignant prostate epithelial cell lines without evidence of shared classical HLA molecules. The T cell line and clone also recognized colon cancers, but not melanomas, sarcomas, or lymphomas, suggesting recognition of a shared epithelium-associated Ag presented by nonclassical MHC or MHC-like molecules. Although Ag recognition by T cells was inhibited by mAb against CD8 and the TCR complex (anti-TCR αβ, CD3, Vβ12), it was not inhibited by mAb directed against MHC class Ia or MHC class II molecules. Neither target expression of CD1 molecules nor HLA-G correlated with T cell recognition, but β2-microglobulin expression was essential. Ag expression was diminished by brefeldin A, lactacystin, and cycloheximide, but not by chloroquine, consistent with an endogenous/cytosolic Ag processed through the classical class I pathway. These results suggest that prostate cancer and colon cancer cells can process and present a shared peptidic Ag to TCR αβ+ T cells via a nonclassical MHC I-like molecule yet to be defined.

Contrasting patterns of regulation of the antioxidant selenoproteins, thioredoxin reductase, and glutathione peroxidase, in cancer cells

There is strong evidence that selenium protects against certain human cancers, but the underlying mechanism is unknown. Glutathione peroxidase (GPX1) and thioredoxin reductase (TR), the most abundant antioxidant selenium-containing proteins in mammals, have been implicated in this protection. We analyzed the expression of TR and GPX1 in the following model cancer systems: (1) liver tumors in TGFalpha/c-myc transgenic mice; (2) human prostate cell lines from normal and cancer tissues; and (3) p53-induced apoptosis in a human colon cancer cell line. TR was induced while GPX1 was repressed in malignancies relative to controls in transgenic mice and prostate cell lines. In the colon cell line, p53 expression resulted in elevated GPX1, but repressed TR. The data indicate that TR and GPX1 are regulated in a contrasting manner in the cancer systems tested and reveal the p53-dependent regulation of selenoprotein expression. The data suggest that additional studies on selenoprotein regulation in different cancers are required to evaluate future implementation of selenium as a dietary supplement in individuals at risk for developing certain cancers.

MHC-dependent cytolysis of autologous tumor cells by lymphocytes infiltrating urothelial carcinomas

Tumor-infiltrating lymphocytes (TIL) were grown from 23 urothelial carcinomas. Phenotyping analysis showed that the TIL cultures were mainly CD3+. Although CD4+ and CD8+ T-cell sub-sets were grown in culture, CD4+ T-cell sub-sets predominated over CD8+ T cells. Immunohistochemical studies performed on 5 tumor specimens confirmed this observation, and indicated that CD4+ T cells surrounded the tumor islets, whereas CD8+ T lymphocytes were localized among the tumor cells. Five short-term carcinoma cell lines established from these urothelial tumors were used as target cells in cytolysis assays in order to investigate the functional anti-tumor activity of autologous TIL. TIL from 4/5 tumors were lytic and 3 TIL lines displayed MHC-class-I-dependent cytotoxicity directed against autologous tumor cells. CD4+ T-cell-depletion experiments performed on TIL line 07 confirmed that CD8+ MHC-class-I-dependent CTL were the predominant effectors. Finally, experiments performed on 6 allogeneic urothelial-cancer cell lines matched for HLA-class-I molecules showed that TIL07 exhibited selective lytic activity toward tumor 07. These data indicate that CD8+ MHC-class-I-dependent CTL present in urothelial carcinomas are functional and may participate in the anti-tumor immune response.

Antigen-presenting function of murine gonadal epithelial cell lines

Murine Leydig (TM3) and Sertoli (TM4) cell lines were studied as nonprofessional antigen-presenting cells using the antigen model of human choriogonadotropin (hCG alpha/beta) and specific T-cell hybridomas. Both cell lines were treated with IFN-gamma to induce I-A(d) and I-E(d) molecules expression. Only the TM3 cell line, which expressed MHC-class II molecules upon IFN-gamma stimulation, was able to uptake, process, and present the human choriogonadotropin beta subunit to related T-cell hybridomas. Interestingly, the TM3 cell line was incapable of presenting the human choriogonadotropin alpha subunit, the presentation of which, by classical APC, is highly efficient. Using T-cell hybridomas directed against the immunogenic regions of hCG alpha/beta previously described in BALB/c mice, we showed that the TM3 cell line generated a narrower peptide repertoire than classical APC (i.e., B cells, macrophages, and dendritic cells). This experimental system suggests that Leydig cells could initiate, in vivo, an autoimmune process directed against gonadal tissues. In particular, such a mechanism has been evoked in experimental autoimmune orchitis.

Reaction of peripheral-blood lymphocytes to the human chorionic gonadotropin beta sub-unit in patients with productive tumors

Human chorionic gonadotropin (hCG) and its beta sub-unit (hCG beta) are secreted by trophoblast cells during pregnancy, and by tumoral cells of trophoblastic and non-trophoblastic origin. In contrast to hCG, the free hCG beta sub-unit is consistently undetectable in healthy non-pregnant subjects. With this in mind, we sought to determine whether an immune response to hCG beta can be detected in patients with bladder or germ-cell testis cancers. Peripheral-blood mononuclear cells (PBMC) from 31% of patients with hCG beta-productive bladder cancers and 33% of testis-tumor-bearing patients displayed an hCG beta-specific proliferative response, whereas no patients with non-hCG beta-productive cancers had a proliferative response. PBMC from pregnant women and healthy controls did not elicit significant reactivity. By the use of overlapping synthetic peptides, the immunogenic regions of hCG beta were delineated within the central 20-65 portion. Moreover, in 2 bladder-cancer patients with the HLA DR7, DQ2 haplotype, the T-cell response to hCG beta was focused on the hCG beta (20-47) peptide. Taken together, these results indicate that hCG beta is a tumor-associated antigen capable of inducing a cell-mediated immune response in patients with productive tumors.

Deficient antigen processing of a protein quaternary structure can be overcome by receptor-mediated uptake

Human chorionic gonadotropin (hCG) is a dimer of non-covalently associated alpha (hCG-alpha) and beta (hCG-beta) subunits. This molecule was used to study whether receptor-mediated uptake influences the presentation of a protein quaternary structure. Unprimed splenocytes and a B cell lymphoma were capable of presenting only the free (hCG-alpha) but not the combined (hCG) alpha subunit to hCG-alpha T cell hybridomas, while hCG-alpha-primed lymph node cells (LNC) responded to both hCG-alpha and hCG. As antigen (Ag)-specific antigen-presenting cells (APC) present in the hCG-alpha-primed LNC population may be potentially effective for presenting hCG, we investigated the role of specific Ag capture, through mIg and Fc gamma R, in the processing and presentation of hCG and hCG-alpha to HAG5, a T cell hybridoma directed against the immunodominant region (amino acids 61-81) of hCG-alpha. Results showed that only B cells bearing membrane immunoglobulin capable of recognizing hCG-alpha and hCG, and present in hCG-alpha-primed mice, were extremely effective in presenting the free as well as the combined alpha subunit. The effect of FcR-mediated uptake was analyzed using a B cell line transfected with the Fc gamma RII-B2 gene to present immune complexes of either hCG-alpha or hCG. We found that hCG-alpha and hCG were presented equally well, whatever the Ag-binding site of each antibody to hCG or its alpha subunit. Using HBG 6, an hCG-beta T cell hybridoma, we performed similar experiments with the Fc gamma RII-B2 cell line and determined that the potentiation of hCG presentation to HBG 6 was similar to that observed with HAG 5. Then kinetic experiments were performed to examine the effect of Ag uptake through FcR on processing. Results demonstrated that the uptake pathway drastically influenced the expression of alpha T cell determinants in the alpha/beta dimer. In addition, treatment with cycloheximide, a protein synthesis inhibitor, only impaired the ability of APC to present specifically captured Ag. Thus, the processing pathway for specifically captured Ag might be different from the pathway used to process nonspecifically captured Ag. This observation might explain why receptor-enhanced uptake bypasses the inefficient processing of the hCG quaternary structure and enables similar efficiency in the presentation of alpha and beta T cell specificities. These findings provide new insight into the antigenicity of oligomeric molecules, which is modified whether antigen capture is specific or not.

Influence of protein-quaternary structure on antigen processing

T cell recognition of the quaternary structure of human chorionic gonadotropin (hCG), resulting from the association between its alpha (hCG-alpha) and beta (hCG-beta) subunits, was analyzed using hCG-alpha and hCG-beta T cell hybridomas produced in BALB/c mice. First, the fine specificity of these T cell hybridomas was determined, enabling us to divide hCG-alpha-specific T cell hybridomas into two groups. Group I recognized the hCG-alpha(61-81) region, and group II responded to the hCG-alpha(50-70) part of the molecule. Two groups of hCG-beta-specific T cell hybridomas, designated groups III and IV, were analyzed and found to respond to the C- and the N-terminal parts of the hCG-beta(1-22) peptide, respectively. Moreover, we observed that the nature of APC influenced Ag recognition by hCG-beta T cell hybridomas from group IV, but not by other selected T cell hybridomas. We then showed that recognition of the hCG alpha/beta dimer by alpha-specific T cell hybridomas was dramatically reduced compared to both free hCG-alpha and heat-dissociated hCG alpha/beta molecules. In contrast, hCG-beta hybridomas exhibited comparable responses to the free beta subunit and the hCG dimer. Experiments using a dimeric molecule assembled from the alpha-subunit of human follicle-stimulating hormone, which is identical to hCG-alpha, and the beta-subunit of human follicle-stimulating hormone, which is homologous to hCG-beta, confirmed that the three-dimensional structure of the complex rather than the primary structure of the beta-subunit plays a critical role in the processing pathway. Finally, kinetic experiments showed that the presentation of hCG-alpha T cell epitopes differed depending upon whether the alpha-subunit was in its free or combined form. In contrast, the kinetic expression of hCG-beta T cell epitopes appeared to be independent of the quaternary structure of hCG. Thus, conformational alterations resulting from the alpha/beta subunit association mainly influenced processing of the alpha-subunit in its complexed form, rather than processing of the combined beta-subunit. The effect of protein-quaternary structure on T cell recognition may represent a new element in our understanding of the processing and presentation of oligomeric molecules.

Influence of protein-quaternary structure on antigen processing

T cell recognition of the quaternary structure of human chorionic gonadotropin (hCG), resulting from the association between its alpha (hCG-alpha) and beta (hCG-beta) subunits, was analyzed using hCG-alpha and hCG-beta T cell hybridomas produced in BALB/c mice. First, the fine specificity of these T cell hybridomas was determined, enabling us to divide hCG-alpha-specific T cell hybridomas into two groups. Group I recognized the hCG-alpha(61-81) region, and group II responded to the hCG-alpha(50-70) part of the molecule. Two groups of hCG-beta-specific T cell hybridomas, designated groups III and IV, were analyzed and found to respond to the C- and the N-terminal parts of the hCG-beta(1-22) peptide, respectively. Moreover, we observed that the nature of APC influenced Ag recognition by hCG-beta T cell hybridomas from group IV, but not by other selected T cell hybridomas. We then showed that recognition of the hCG alpha/beta dimer by alpha-specific T cell hybridomas was dramatically reduced compared to both free hCG-alpha and heat-dissociated hCG alpha/beta molecules. In contrast, hCG-beta hybridomas exhibited comparable responses to the free beta subunit and the hCG dimer. Experiments using a dimeric molecule assembled from the alpha-subunit of human follicle-stimulating hormone, which is identical to hCG-alpha, and the beta-subunit of human follicle-stimulating hormone, which is homologous to hCG-beta, confirmed that the three-dimensional structure of the complex rather than the primary structure of the beta-subunit plays a critical role in the processing pathway. Finally, kinetic experiments showed that the presentation of hCG-alpha T cell epitopes differed depending upon whether the alpha-subunit was in its free or combined form. In contrast, the kinetic expression of hCG-beta T cell epitopes appeared to be independent of the quaternary structure of hCG. Thus, conformational alterations resulting from the alpha/beta subunit association mainly influenced processing of the alpha-subunit in its complexed form, rather than processing of the combined beta-subunit. The effect of protein-quaternary structure on T cell recognition may represent a new element in our understanding of the processing and presentation of oligomeric molecules.

[Evans' syndrome caused by D-penicillamine in rheumatoid arthritis. Value of the corticoids-danazol combination]

The authors report the development of thrombocytopenia purpura in one patient with seropositive and erosive rheumatoid arthritis treated successfully for 11 months with D-penicillamine. Anti-platelet-bound antibodies were present, but also: anti-erythrocyte antibodies with hemolytic anemia (then defining Evans's syndrome): higher level of antinuclear antibodies; intermittent neutropenia. The responsibility of D-penicillamine is discussed, but thrombocytopenia purpura evolved for itself. Glucocorticoids alone, intravenous immunoglobulin, vincristine did not induced remission, which at least occurred under the association danazol-glucocorticoids, without toxicity, especially on the liver function.