Generation and decay of the immune response to a progressive fibrosarcoma. II. Failure to demonstrate postexcision immunity after the onset of T cell-mediated suppression of immunity

Capturing the dynamics of microbial interactions through individual-specific networks

Longitudinal analysis of multivariate individual-specific microbiome profiles over time or across conditions remains dauntin. Most statistical tools and methods that are available to study microbiomes are based on cross-sectional data. Over the past few years, several attempts have been made to model the dynamics of bacterial species over time or across conditions. However, the field needs novel views on handling microbial interactions in temporal analyses. This study proposes a novel data analysis framework, MNDA, that combines representation learning and individual-specific microbial co-occurrence networks to uncover taxon neighborhood dynamics. As a use case, we consider a cohort of newborns with microbiomes available at 6 and 9 months after birth, and extraneous data available on the mode of delivery and diet changes between the considered time points. Our results show that prediction models for these extraneous outcomes based on an MNDA measure of local neighborhood dynamics for each taxon outperform traditional prediction models solely based on individual-specific microbial abundances. Furthermore, our results show that unsupervised similarity analysis of newborns in the study, again using the notion of a taxon's dynamic neighborhood derived from time-matched individual-specific microbial networks, can reveal different subpopulations of individuals, compared to standard microbiome-based clustering, with potential relevance to clinical practice. This study highlights the complementarity of microbial interactions and abundances in downstream analyses and opens new avenues to personalized prediction or stratified medicine with temporal microbiome data.

Tumor resident memory CD8 T cells and concomitant tumor immunity develop independently of CD4 help

Tissue resident memory (Trm) CD8 T cells infiltrating tumors represent an enriched population of tumor antigen-specific T cells, and their presence is associated with improved outcomes in patients. Using genetically engineered mouse pancreatic tumor models we demonstrate that tumor implantation generates a Trm niche that is dependent on direct antigen presentation by cancer cells. However, we observe that initial CCR7-mediated localization of CD8 T cells to tumor draining lymph nodes is required to subsequently generate CD103+ CD8 T cells in tumors. We observe that the formation of CD103+ CD8 T cells in tumors is dependent on CD40L but independent of CD4 T cells, and using mixed chimeras we show that CD8 T cells can provide their own CD40L to permit CD103+ CD8 T cell differentiation. Finally, we show that CD40L is required to provide systemic protection against secondary tumors. These data suggest that CD103+ CD8 T cell formation in tumors can occur independent of the two-factor authentication provided by CD4 T cells and highlight CD103+ CD8 T cells as a distinct differentiation decision from CD4-dependent central memory.

The role of dendritic cells in radiation-induced immune responses

Dendritic cells perform critical functions in bridging innate and adaptive immunity. Their ability to sense adjuvant signals in their environment, migrate on maturation, and cross-present cell-associated antigens enables these cells to carry antigen from tissue sites to lymph nodes, and thereby prime naïve T cells that cannot enter tissues. Despite being an infrequent cell type in tumors, we discuss how dendritic cells impact the immune environment of tumors and their response to cancer therapies. We review how radiation therapy of tumors can impact dendritic cells, through transfer of cell associated antigens to dendritic cells and the release of endogenous adjuvants, resulting in increased antigen presentation in the tumor-draining lymph nodes. We explore how tumor specific factors can result in negative regulation of dendritic cell function in the tumor, and the impact of direct radiation exposure to dendritic cells in the treatment field. These data suggest an important role for dendritic cell subpopulations in activating new T cell responses and boosting existing T cell responses to tumor associated antigens in tumor draining lymph nodes following radiation therapy. It further justifies a focus on the needs of the lymph node T cells to improve systemic anti-immunity following radiation therapy.

The potential of regulatory T cell-based therapies for alopecia areata

Cytotoxic T lymphocyte has been a concern for the etiopathogenesis of alopecia areata (AA), some recent evidence suggests that the regulatory T (T_reg) cell deficiency is also a contributing factor. In the lesional scalp of AA, T_reg cells residing in the follicles are impaired, leading to dysregulated local immunity and hair follicle (HF) regeneration disorders. New strategies are emerging to modulate T_reg cells' number and function for autoimmune diseases. There is much interest to boost T_reg cells in AA patients to suppress the abnormal autoimmunity of HF and stimulate hair regeneration. With few satisfactory therapeutic regimens available for AA, T_reg cell-based therapies could be the way forward. Specifically, CAR-T_reg cells and novel formulations of low-dose IL-2 are the alternatives.

Associating resistance to immune checkpoint inhibitors with immunological escape in colorectal cancer

Colorectal cancer is a common malignant tumor that ranks third in incidence and second in mortality worldwide, and surgery in conjunction with chemotherapy and radiotherapy remains the most common treatment option. As a result of radiotherapy’s severe side effects and dismal survival rates, it is anticipated that more alternatives may emerge. Immunotherapy, a breakthrough treatment, has made significant strides in colorectal cancer over the past few years, overcoming specialized therapy, which has more selectivity and a higher survival prognosis than chemoradiotherapy. Among these, immune checkpoint inhibitor therapy has emerged as the primary immunotherapy for colorectal cancer nowadays. Nonetheless, as the use of immune checkpoint inhibitor has expanded, resistance has arisen inevitably. Immune escape is the primary cause of non-response and resistance to immune checkpoint inhibitors. That is the development of primary and secondary drug resistance. In this article, we cover the immune therapy-related colorectal cancer staging, the specific immune checkpoint inhibitors treatment mechanism, and the tumor microenvironment and immune escape routes of immunosuppressive cells that may be associated with immune checkpoint inhibitors resistance reversal. The objective is to provide better therapeutic concepts for clinical results and to increase the number of individuals who can benefit from colorectal cancer immunotherapy.

ICOS is upregulated on T cells following radiation and agonism combined with radiation results in enhanced tumor control

Multiple preclinical studies have shown improved outcomes when radiation therapy is combined with immune modulating antibodies. However, to date, many of these promising results have failed to translate to successful clinical studies. This led us to explore additional checkpoint and co-stimulatory pathways that may be regulated by radiation therapy. Here, we demonstrate that radiation increases the expression of inducible T cell co-stimulator (ICOS) on both CD4 and CD8 T cells in the blood following treatment. Moreover, when we combined a novel ICOS agonist antibody with radiation we observed durable cures across multiple tumor models and mouse strains. Depletion studies revealed that CD8 T cells were ultimately required for treatment efficacy, but CD4 T cells and NK cells also partially contributed to tumor control. Phenotypic analysis showed that the combination therapy diminished the increased infiltration of regulatory T cells into the tumor that typically occurs following radiation alone. Finally, we demonstrate in a poorly immunogenic pancreatic tumor model which is resistant to combined radiation and anti-PD1 checkpoint blockade that the addition of this novel ICOS agonist antibody to the treatment regimen results in tumor control. These findings identify ICOS as part of a T cell pathway that is modulated by radiation and targeting this pathway with a novel ICOS antibody results in durable tumor control in preclinical models.

The paradox of radiation and T cells in tumors

In this review we consider what appears to be a paradox in immunotherapies based around radiation therapy. The paradox is based on three main points. 1. That T cells are needed for radiation's efficacy; 2. That tumor-specific T cells are enriched in the field of treatment; and 3. That radiation kills T cells in the treatment field. We discuss evidence of the effect of radiation on T cells in the field given their ongoing movement in and out of tissues and the tumor, and how the movement of T cells impacts the treated primary tumor and untreated distant metastases. Given this evidence, we revisit the paradox to understand how the extraordinary efficacy of radiation and immunity in preclinical models is dependent on this radiation sensitive cell.

The Liver-Immunity Nexus and Cancer Immunotherapy

The impact of liver metastases on immune checkpoint-inhibitor effectiveness in patients with solid-tumor malignancies has been the focus of several recent clinical and translational studies. We review the literature describing the immune functions of the liver and particularly the mechanistic observations in these studies. The initial clinical observation was that pembrolizumab appeared to be much less effective in melanoma and non-small cell lung cancer (NSCLC) patients with liver metastasis. Subsequently other clinical studies have extended and reported similar findings with programmed death-1 (PD-1) and programmed death ligand-1 (PD-L1) inhibitors in many cancers. Two recent translational studies in animal models have dissected the mechanism of this systemic immune suppression. In both studies CD11b⁺ suppressive macrophages generated by liver metastasis in a two-site MC38 model appear to delete CD8⁺ T cells in a FasL-dependent manner. In addition, regulatory T-cell (Treg) activation was observed and contributed to the distal immunosuppression. Finally, we discuss some of the interventions reported to address liver immune suppression, such as radiation therapy, combination checkpoint blockade, and Treg depletion.

Defining Immunogenic and Radioimmunogenic Tumors

In the cancer literature tumors are inconsistently labeled as ‘immunogenic’, and experimental results are occasionally dismissed since they are only tested in known ‘responsive’ tumor models. The definition of immunogenicity has moved from its classical definition based on the rejection of secondary tumors to a more nebulous definition based on immune infiltrates and response to immunotherapy interventions. This review discusses the basis behind tumor immunogenicity and the variation between tumor models, then moves to discuss how these principles apply to the response to radiation therapy. In this way we can identify radioimmunogenic tumor models that are particularly responsive to immunotherapy only when combined with radiation, and identify the interventions that can convert unresponsive tumors so that they can also respond to these treatments.

Transcriptional Upregulation of NLRC5 by Radiation Drives STING- and Interferon-Independent MHC-I Expression on Cancer Cells and T Cell Cytotoxicity

Radiation therapy has been shown to enhance the efficacy of various T cell-targeted immunotherapies that improve antigen-specific T cell expansion, T regulatory cell depletion, or effector T cell function. Additionally, radiation therapy has been proposed as a means to recruit T cells to the treatment site and modulate cancer cells as effector T cell targets. The significance of these features remains unclear. We set out to determine, in checkpoint inhibitor resistant models, which components of radiation are primarily responsible for overcoming this resistance. In order to model the vaccination effect of radiation, we used a Listeria monocytogenes based vaccine to generate a large population of tumor antigen specific T cells but found that the presence of cells with cytotoxic capacity was unable to replicate the efficacy of radiation with combination checkpoint blockade. Instead, we demonstrated that a major role of radiation was to increase the susceptibility of surviving cancer cells to CD8+ T cell-mediated control through enhanced MHC-I expression. We observed a novel mechanism of genetic induction of MHC-I in cancer cells through upregulation of the MHC-I transactivator NLRC5. These data support the critical role of local modulation of tumors by radiation to improve tumor control with combination immunotherapy.

Tumor cure by radiation therapy and checkpoint inhibitors depends on pre-existing immunity

Radiation therapy is a source of tumor antigen release that has the potential to serve as an endogenous tumor vaccination event. In preclinical models radiation therapy synergizes with checkpoint inhibitors to cure tumors via CD8 T cell responses. To evaluate the immune response initiated by radiation therapy, we used a range of approaches to block the pre-existing immune response artifact initiated by tumor implantation. We demonstrate that blocking immune responses at tumor implantation blocks development of a tumor-resident antigen specific T cell population and prevents tumor cure by radiation therapy combined with checkpoint immunotherapy. These data demonstrate that this treatment combination relies on a pre-existing immune response to cure tumors, and may not be a solution for patients without pre-existing immunity.

Advances in the Study on the Relationship between Regulatory T cells and Human Papilloma Viral Infection

Regulatory T cells (Treg cells) are a group of negative regulatory cells that include non-specific immune regulation CD4+T cells. Treg cells inhibit the function of other immune cells. CD4+CD25+FOXP3+is a Treg cell that is co-expressed by CD25and FOXP3. The expression of Treg cells is up-regulated in the focal microenvironment and peripheral blood of patients infected with human papilloma virus (HPV). Further studies on Treg cells indicate that their potential clinical applications in the treatment of HPV infection.

FOXP3+ Tregs: heterogeneous phenotypes and conflicting impacts on survival outcomes in patients with colorectal cancer

The tumor microenvironment composites a mixture of immune lymphoid cells, myeloid cells, stromal cells with complex cytokines, as well as numerous lymphovascular vessels. Colorectal cancer (CRC) is a common malignancy and one of the leading causes of tumor-related death in the United States and worldwide. The immune status in the tumor microenvironment contributes to the survival of a patient with CRC. Regulatory T cells (Tregs) are considered a key factor in immune escape and immunotherapy failure among cancer patients. The transcription factor forkhead box P3 (FOXP3) is a crucial intracellular marker and also a key developmental and functional factor for CD4+CD25+ Tregs. Tregs are correlated with survival in various human neoplasms, and elevated proportions of Tregs are usually associated with unfavorable clinical outcomes. However, the role of Tregs in CRC remains controversial. High densities of tumor-infiltrating Tregs in CRC patients are reported to be correlated with worse or better outcomes. And Tregs may not be predictive of prognosis after resection of the primary tumor. The exact explanations for these discordant results remain unclear. The heterogeneous instincts of cell phenotype, gene expression, and functional activities of Tregs may partly contribute this contrasting result. Furthermore, the lack of a robust marker for identifying Tregs or due to the different techniques applied is also account. The Treg-specific demethylated region (TSDR) was recently reported to be a specific epigenetic marker for natural Tregs (nTregs), which can stably express FOXP3. The FOXP3-TSDR demethylation assay may be an promising technique for CRC-related nTregs studies.

Immunosuppressive Mechanisms of Malignant Gliomas: Parallels at Non-CNS Sites

The central nervous system (CNS) possesses powerful local and global immunosuppressive capabilities that modulate unwanted inflammatory reactions in nervous tissue. These same immune-modulatory mechanisms are also co-opted by malignant brain tumors and pose a formidable challenge to brain tumor immunotherapy. Routes by which malignant gliomas coordinate immunosuppression include the mechanical and functional barriers of the CNS; immunosuppressive cytokines and catabolites; immune checkpoint molecules; tumor-infiltrating immune cells; and suppressor immune cells. The challenges to overcoming tumor-induced immunosuppression, however, are not unique to the brain, and several analogous immunosuppressive mechanisms also exist for primary tumors outside of the CNS. Ultimately, the immune responses in the CNS are linked and complementary to immune processes in the periphery, and advances in tumor immunotherapy in peripheral sites may therefore illuminate novel approaches to brain tumor immunotherapy, and vice versa.

Understanding the function and dysfunction of the immune system in lung cancer: the role of immune checkpoints

Survival rates for metastatic lung cancer, including non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC), are poor with 5-year survivals of less than 5%. The immune system has an intricate and complex relationship with tumorigenesis; a groundswell of research on the immune system is leading to greater understanding of how cancer progresses and presenting new ways to halt disease progress. Due to the extraordinary power of the immune system-with its capacity for memory, exquisite specificity and central and universal role in human biology-immunotherapy has the potential to achieve complete, long-lasting remissions and cures, with few side effects for any cancer patient, regardless of cancer type. As a result, a range of cancer therapies are under development that work by turning our own immune cells against tumors. However deeper understanding of the complexity of immunomodulation by tumors is key to the development of effective immunotherapies, especially in lung cancer.

STAT3 Signaling Is Required for Optimal Regression of Large Established Tumors in Mice Treated with Anti-OX40 and TGFβ Receptor Blockade

In preclinical tumor models, αOX40 therapy is often successful at treating small tumors, but is less effective once the tumors become large. For a tumor immunotherapy to be successful to cure large tumors, it will most likely require not only an agonist to boost effector T-cell function but also inhibitors of T-cell suppression. In this study, we show that combining αOX40 antibodies with an inhibitor of the TGFβ receptor (SM16) synergizes to elicit complete regression of large established MCA205 and CT26 tumors. Evaluation of tumor-infiltrating T cells showed that SM16/αOX40 dual therapy resulted in an increase in proliferating granzyme B(+) CD8 T cells, which produced higher levels of IFNγ, compared with treatment with either agent alone. We also found that the dual treatment increased pSTAT3 expression in both CD4 and CD8 T cells isolated from tumors. Because others have published that STAT3 signaling is detrimental to T-cell function within the tumor microenvironment, we explored whether deletion of STAT3 in OX40-expressing cells would affect this potent combination therapy. Surprisingly, we found that deletion of STAT3 in OX40-expressing cells decreased the efficacy of this combination therapy, showing that the full therapeutic potential of this treatment depends on STAT3 signaling, most likely in the T cells of tumor-bearing mice.

Targeting macrophages in the tumour environment to enhance the efficacy of αOX40 therapy

The treatment of high-grade tumours must consider a tumour environment dominated by cells that support cancer growth. In addition to directing angiogenesis and invasion, alternatively activated macrophages in the tumour provide protection from adaptive immunity and permit tumour growth. Agonist antibodies to the tumour necrosis factor receptor family member OX40 are an effective therapy for cancer in a range of murine models; however, as with many immune therapies, αOX40 therapy is less effective as the tumour grows and develops an immune suppressive environment. We demonstrate that αOX40 directly activates T cells and that this T-cell activation alters macrophage differentiation in the tumour environment. We demonstrate that macrophages in the tumour limit the efficacy of αOX40 therapy, and that combining αOX40 therapy with inhibitors of arginase significantly enhances survival of tumour-bearing mice. These data demonstrate that macrophages in the tumour environment limit the effectiveness of OX40-based immunotherapy, and combination therapies that target both the cell-mediated immune response and the suppressive tumour environment will be required for translation of effective immunotherapies to patients with established tumours.

Expression of NF-κB p50 in tumor stroma limits the control of tumors by radiation therapy

Radiation therapy aims to kill cancer cells with a minimum of normal tissue toxicity. Dying cancer cells have been proposed to be a source of tumor antigens and may release endogenous immune adjuvants into the tumor environment. For these reasons, radiation therapy may be an effective modality to initiate new anti-tumor adaptive immune responses that can target residual disease and distant metastases. However, tumors engender an environment dominated by M2 differentiated tumor macrophages that support tumor invasion, metastases and escape from immune control. In this study, we demonstrate that following radiation therapy of tumors in mice, there is an influx of tumor macrophages that ultimately polarize towards immune suppression. We demonstrate using in vitro models that this polarization is mediated by transcriptional regulation by NFκB p50, and that in mice lacking NFκB p50, radiation therapy is more effective. We propose that despite the opportunity for increased antigen-specific adaptive immune responses, the intrinsic processes of repair following radiation therapy may limit the ability to control residual disease.

A positive-margin resection model recreates the postsurgical tumor microenvironment and is a reliable model for adjuvant therapy evaluation

Up to 30% of cancer patients undergoing curative surgery develop local recurrences due to positive margins. Patients typically receive adjuvant chemotherapy, immunotherapy and/or radiation to prevent such relapses. Interestingly, evidence supporting these therapies is traditionally derived in animal models of primary tumors, thus failing to consider surgically induced tumor microenvironment changes that may influence adjuvant therapy efficacy. To address this consideration, we characterized a murine model of local cancer recurrence. This model was reproducible and generated a postoperative inflammatory tumor microenvironment that resembles those observed following human cancer surgery. To further validate this model, antagonists of two pro-inflammatory mediators, TGFβ and COX-2, were tested and found to be effective in decreasing the growth of recurrent tumors. We appreciated that preoperative TGFβ inhibition led to wound dehiscence, while postoperative initiation of COX-2 inhibition resulted in a loss of efficacy. In summary, although not an exact replica of all human cancer surgeries, our proposed local recurrence approach provides a biologically relevant and reliable model useful for preclinical evaluation of novel adjuvant therapies. The use of this model yields results that may be overlooked using traditional preclinical cancer models that fail to incorporate a surgical component.

Tumor macrophages as a target for Capsaicin mediated immunotherapy

Tumor microenvironment contributes to a large extent for failure of immunological destruction of antigenic tumors. Most solid tumors adapt to the microenvironment and escape the host immune system. The dramatic and systemic effectiveness of neuro-immune ligand Capsaicin (CP) in regression of established solid tumors led us to investigate its immunomodulatory role in tumor microenvironment. In this report we demonstrate that CP induced tumor cell apoptosis leads to increased sensitization of the surrounding stroma manifested by enhanced antigen presentation by stromal macrophages and its destruction by tumor specific T-cells. Further, CP injection alters the tumor microenvironment with regards to tumor-infiltrating Treg cells as well as the cytokine milieu at the tumor site. Our data collectively demonstrates that injection of CP sets in motion, a cascade of several independent innate and adaptive immunological events initiated at the tumor environment.

The battle against immunopathology: infectious tolerance mediated by regulatory T cells

Infectious tolerance is a process whereby one regulatory lymphoid population confers suppressive capacity on another. Diverse immune responses are induced following infection or inflammatory insult that can protect the host, or potentially cause damage if not properly controlled. Thus, the process of infectious tolerance may be critical in vivo for exerting effective immune control and maintaining immune homeostasis by generating specialized regulatory sub-populations with distinct mechanistic capabilities. Foxp3(+) regulatory T cells (T(regs)) are a central mediator of infectious tolerance through their ability to convert conventional T cells into induced regulatory T cells (iT(regs)) directly by secretion of the suppressive cytokines TGF-β, IL-10, or IL-35, or indirectly via dendritic cells. In this review, we will discuss the mechanisms and cell populations that mediate and contribute to infectious tolerance, with a focus on the intestinal environment, where tolerance induction to foreign material is critical.

The Roles of CD4+ T Cells in Tumor Immunity

Activation of CD8+ cytotoxic T cells has long been regarded as a major antitumor mechanism of the immune system. Emerging evidence suggests that CD4+ T cells are required for the generation and maintenance of effective CD8+ cytotoxic and memory T cells, a phenomenon known as CD4+ T-cell help. CD4+ T-cell help facilitates the optimal expansion, trafficking, and effector function of CD8+ T cells, thereby enhancing tumor destruction. In addition, a specialized subset of CD4+ T cells, CD4+CD25+ regulatory T cells (TRegs), effectively hampers anti-tumor immune responses, which has been proposed to be one of the major tumor immune evasion mechanisms. Here, we review recent advances in deciphering how anti-tumor immune responses are orchestrated by CD4+ T cells. We will also discuss the immunotherapeutic potential of CD4+ T-cell manipulation in anti-tumor immune response.

IL-18 inhibits growth of murine orthotopic prostate carcinomas via both adaptive and innate immune mechanisms

Interleukin(IL)-18 is a pleiotrophic cytokine with functions in immune modulation, angiogenesis and bone metabolism. In this study, the potential of IL-18 as an immunotherapy for prostate cancer (PCa) was examined using the murine model of prostate carcinoma, RM1 and a bone metastatic variant RM1(BM)/B4H7-luc. RM1 and RM1(BM)/B4H7-luc cells were stably transfected to express bioactive IL-18. These cells were implanted into syngeneic immunocompetent mice, with or without an IL-18-neutralising antibody (αIL-18, SK113AE4). IL-18 significantly inhibited the growth of both subcutaneous and orthotopic RM1 tumors and the IL-18 neutralizing antibody abrogated the tumor growth-inhibition. In vivo neutralization of interferon-gamma (IFN-γ) completely eliminated the anti-tumor effects of IL-18 confirming an essential role of IFN-γ as a down-stream mediator of the anti-tumor activity of IL-18. Tumors from mice in which IL-18 and/or IFN-γ was neutralized contained significantly fewer CD4⁺ and CD8⁺ T cells than those with functional IL-18. The essential role of adaptive immunity was demonstrated as tumors grew more rapidly in RAG1^−/− mice or in mice depleted of CD4⁺ and/or CD8⁺ cells than in normal mice. The tumors in RAG1^−/− mice were also significantly smaller when IL-18 was present, indicating that innate immune mechanisms are involved. IL-18 also induced an increase in tumor infiltration of macrophages and neutrophils but not NK cells. In other experiments, direct injection of recombinant IL-18 into established tumors also inhibited tumor growth, which was associated with an increase in intratumoral macrophages, but not T cells. These results suggest that local IL-18 in the tumor environment can significantly potentiate anti-tumor immunity in the prostate and clearly demonstrate that this effect is mediated by innate and adaptive immune mechanisms.

Adjuvant therapy with agonistic antibodies to CD134 (OX40) increases local control after surgical or radiation therapy of cancer in mice

The tumor recurrence from residual local or micrometastatic disease remains a problem in cancer therapy. In patients with soft tissue sarcoma and the patients with inoperable nonsmall cell lung cancer, local recurrence is common and significant mortality is caused by the subsequent emergence of metastatic disease. Thus, although the aim of the primary therapy is curative, the outcome may be improved by additional targeting of residual microscopic disease. We display in a murine model that surgical removal of a large primary sarcoma results in local recurrence in approximately 50% of animals. Depletion of CD8 T cells results in local recurrence in 100% of animals, indicating that these cells are involved in the control of residual disease. We further show that systemic adjuvant administration of αOX40 at surgery eliminates local recurrences. In this model, αOX40 acts to directly enhance tumor antigen-specific CD8 T-cell proliferation in the lymph node draining the surgical site, and results in increased tumor antigen-specific cytotoxicity in vivo. These results are also corroborated in a murine model of hypofractionated radiation therapy of lung cancer. Administration of αOX40 in combination with radiation significantly extended the survival compared with either agent alone, and resulted in a significant proportion of long-term tumor-free survivors. We conclude that αOX40 increases tumor antigen-specific CD8 T-cell cytotoxic activity resulting in improved endogenous immune control of residual microscopic disease, and we propose that adjuvant αOX40 administration may be a valuable addition to surgical and radiation therapy for cancer.

Prognostic significance of regulatory T cells in tumor

Since entering the immunological stage several decades ago, regulatory T cell biology has been realized as fundamentally important in the prevention of autoimmune conditions, induction of transplant tolerance and the immune response to cancer. The role of regulatory T cells in tumor immunobiology is still being elucidated. Currently, regulatory T cells are implicated in the dampening of antitumor T-cell responses both through direct and indirect means. A number of investigators have demonstrated that regulatory T cell density and location may serve as independent prognostic factors in several types of cancer and are alternately detrimental or beneficial to patient survival. In this article, we will review the characteristics and functional phenotype of classical regulatory T cells, describe their distribution and quantification in tumor-bearing hosts and summarize recent studies investigating the prognostic significance of regulatory T cell number and locality in various cancers.

Cyclophosphamide enhances immunity by modulating the balance of dendritic cell subsets in lymphoid organs

Cyclophosphamide (CTX), a commonly used chemotherapeutic agent can enhance immune responses. The ability of CTX to promote the proliferation of effector T cells and abrogate the function of regulatory T cells (Tregs) has been described. In this study, we examined the effects of CTX treatment on dendritic cell (DC) subsets and the subsequent outcome on the effector and suppressive arms of adaptive immunity. In secondary lymphoid tissues, tissue-derived migratory DCs (migratory DCs), lymphoid tissue-resident DCs (resident DCs), and plasmacytoid DCs (pDCs) are well described. CTX has profound and selective cytotoxic effects on CD8(+) resident DCs, but not skin-derived migratory DCs or pDCs in lymph nodes (LNs) and spleen, causing an imbalance among these DC subsets. CTX treatment increases the potency of DCs in antigen presentation and cytokine secretion, and partially inhibits the suppressor activity of Tregs. Adoptive transfer of CD8(+) DCs can reconstitute this population in regional draining LNs and abrogate the immune-enhancing effects of CTX in vivo. These findings demonstrate that CTX may improve immune responses by preferentially depleting CD8(+) lymphoid-resident DCs, which leads to diminished Treg suppression and enhanced effector T-cell function in vivo.

Taming regulatory T cells by autologous T cell immunization: a potential new strategy for cancer immune therapy

Regulatory T cells (Tregs) play important roles in the maintenance of immune homeostasis, and is also involved in tumor immune tolerance. Dampening or elimination of Treg functions has been shown to lead to enhanced immune responses against tumors, and thus inhibition of tumor growth. Recently, we have developed a new immunization scheme, referred to as irradiated mitogen-activated autologous T cell vaccination (ATCV), and shown that such immunization could significantly enhance anti-tumor immunity in vivo. Mechanistically, the enhanced anti-tumor response appears to be due to reduced Treg functions and inhibition of activation-induced cell death (AICD) in effector T cells. Thus, ATCV may constitute a novel strategy in cancer immune therapy.

Regulatory-T-cell inhibition versus depletion: the right choice in cancer immunotherapy

Tumour-induced expansion of regulatory T (T(Reg)) cells is an obstacle to successful cancer immunotherapy. The potential benefit of T(Reg)-cell depletion through the interleukin-2 receptor is lost by the concurrent elimination of activated effector lymphocytes and possibly by the de novo induction of T(Reg)-cell replenishment. In theory, the functional inactivation of T(Reg) cells will maintain them at high numbers in tumours and avoid their replenishment from the peripheral lymphocyte pool, which has the capacity to further suppress the effector lymphocyte anti-tumour response.

Induction of postsurgical tumor immunity and T-cell memory by a poorly immunogenic tumor

The generation of protective CD8 T-cell memory against tumor-expressed self-antigens is an important but elusive goal of cancer immunotherapy. The possibility that a progressive, poorly immunogenic tumor can induce T-cell memory against self-antigens has not previously been studied. Herein, we report that growth of the poorly immunogenic B16 melanoma in the absence of regulatory T cells (T(reg)) generates CD8 T-cell responses that develop into functional memory after the tumor has been surgically excised. Tumor-primed memory T cells recognized melanocyte differentiation antigens TRP-2/DCT and gp100 and persisted for as long as 5 months following surgical tumor excision. Phenotypic analysis showed that these cells develop into both central and effector memory T-cell subsets, which produce IFN-gamma and interleukin-2 on reencounter with antigen. Most importantly, tumor-primed memory T cells mediated the rejection of intradermal and systemically disseminated challenge tumors given 30 to 60 days following surgery. Tumor-excised mice also developed autoimmune vitiligo, showing that T(reg) cells prevent tissue-specific autoimmunity in tumor-bearing hosts. This study establishes that T(reg) depletion in tumor-bearing hosts drives the natural development of protective T-cell memory. Generating such responses may aid in the clinical management of tumor recurrence and metastasis following surgery.

Tregs and rethinking cancer immunotherapy

Tumors express antigens that should induce immune-mediated rejection, but spontaneous rejection of established tumors is rare. Recent work demonstrates that one reason for the lack of tumor rejection is that tumors actively defeat host immunity. This concept forces us to rethink current approaches to harnessing potent, specific host immunity to battle cancer, most of which are based on the paradigm that inducing more antitumor immune cells alone is therapeutic. However, as I discuss in this Personal Perspective, a newer paradigm predicts that reducing tumor-driven immune suppression will be clinically beneficial. CD4+CD25+ Tregs are one mechanism of tumor-driven immune evasion that provide prototypical targets for testing novel anticancer treatment strategies within the newer paradigm.

Improving antitumor immune responses by circumventing immunoregulatory cells and mechanisms

Although numerous immunotherapeutic strategies have been studied in patients with cancer, consistent induction of clinical responses remains a formidable challenge. Cancer vaccines are often successful at generating elevated numbers of tumor-specific T lymphocytes in peripheral blood, however, despite this, tumors usually continue to grow unabated. Recent evidence suggests that endogenous regulatory cells, known to play a major role in the induction of immune tolerance to self and prevention of autoimmunity, as well as suppressive myeloid cells invoked in the tumor-bearing state, may be largely responsible for preventing effective antitumor immune responses. This review will focus on the major regulatory cell subtypes, including CD4(+)CD25(+) T-regulatory cells, type 1 regulatory T cells, natural killer T cells, and immature myeloid cells. Studies in humans and in animal models have shown a role for all of these cells in tumor progression, although the mechanisms by which they act to suppress immunity remain largely undefined. Elucidation of the dominant molecular mechanisms mediating immune suppression in vivo will allow more precise targeting of the relevant regulatory cell populations, as well as the development of novel strategies and clinical reagents that will directly block molecules that induce the suppression of antitumor immunity.

Cancer immunotherapy and preclinical studies: why we are not wasting our time with animal experiments

Experimental research on the immune response to transplanted tumors has led to pioneering discoveries that laid many of the foundations for the current field of immunology. Experimental research in oncology has proven that murine and human tumors have antigens that are truly cancer specific. This article discusses research investigating how can antigens on cancer cells be used to help eradicate cancer.

Inhibitory effects of B cells on antitumor immunity

B-cell functions in antitumor immunity are not well understood. In this study, we evaluated the role of B cells in the development of antitumor immunity using Friend murine leukemia virus gag-expressing mouse EL-4 (EL-4 gag), D5 mouse melanoma, or MCA304 mouse sarcoma cells. To screen tumors for susceptibility to B-cell-deficient immune environments, spleen cells from naive C57BL/6 [wild-type (WT)] and B-cell knockout (BKO) mice were cultured with irradiated tumor cells in vitro. When cells were stimulated with EL-4 gag or D5 (but not MCA304 tumors), IFN-gamma production from CD8 T cells and natural killer cells was markedly decreased in WT compared with BKO cultures. IFN-gamma production was correlated with CD40 ligand expression on the tumor and inversely with interleukin-10 (IL-10) production by B cells. Sorted WT B cells produced more IL-10 than CD40 knockout (CD40KO) B cells when cocultured with EL-4 gag or D5 (but not MCA304). IFN-gamma production by BKO cells was reduced by the addition of sorted naive WT B cells (partially by CD40KO B cells) or recombinant mouse IL-10. In vivo tumor progression mirrored in vitro studies in that WT mice were unable to control tumor growth whereas EL-4 gag and D5 tumors (but not MCA304) were eliminated in BKO mice. Robust in vivo antitumor CTLs developed only in BKO tumor-challenged mice. Our studies provide the first mechanistic basis for the concept that B-cell depletion could therapeutically enhance antitumor immune responses to certain tumors by decreasing IL-10 production from B cells.

Regulatory T cells, tumour immunity and immunotherapy

Tumours express a range of antigens, including self-antigens. Regulatory T cells are crucial for maintaining T-cell tolerance to self-antigens. Regulatory T cells are thought to dampen T-cell immunity to tumour-associated antigens and to be the main obstacle tempering successful immunotherapy and active vaccination. In this Review, I consider the nature and characteristics of regulatory T cells in the tumour microenvironment and their potential multiple suppressive mechanisms. Strategies for therapeutic targeting of regulatory T cells and the effect of regulatory T cells on current immunotherapeutic and vaccine regimens are discussed.

Tumor-infiltrating T lymphocytes: friends or foes?

The prognostic significance of tumor-infiltrating lymphocytes (TILs) has been a longstanding topic of debate. In cases where TILs have improved patient outcome, T lymphocytes are recognized as the main effectors of antitumor immune responses. However, recent studies have revealed that a subset of CD4(+) T cells, referred to as CD4(+)CD25(+) regulatory T cells (Treg), may accumulate in the tumor environment and suppress tumor-specific T-cell responses, thereby hindering tumor rejection. Hence, predicting tumor behavior on the basis of an indiscriminate evaluation of tumor-infiltrating T cells may result in inconsistent prognostic accuracy. The presence of infiltrating CD4(+)CD25(+) Treg may be detrimental to the host defense against the tumor, while the presence of effector T lymphocytes, including CD8(+) T cells and non-regulatory CD4(+) helper T cells may be beneficial. Enhanced recruitment of antitumor effector T lymphocytes to tumor tissue in addition to inhibition of local Treg, may therefore be an ideal target for improving cancer immunotherapy. This article reviews the antitumor functions of T-lymphocytes, with special attention given to CD4(+) regulatory T-cells within the tumor environment.

Intratumor depletion of CD4+ cells unmasks tumor immunogenicity leading to the rejection of late-stage tumors

Tumor environment can be critical for preventing the immunological destruction of antigenic tumors. We have observed a selective accumulation of CD4(+)CD25(+) T cells inside tumors. In a murine fibrosarcoma L(d)-expressing Ag104, these cells made up the majority of tumor-infiltrating lymphocytes at the late stage of tumor progression, and their depletion during the effector phase, rather than priming phase, successfully enhanced antitumor immunity. We show here that CD4(+)CD25(+) T cells suppressed the proliferation and interferon-gamma production of CD8(+) T cells in vivo at the local tumor site. Blockade of the effects of IL-10 and TGF-beta partially reversed the suppression imposed by the CD4(+) cells. Furthermore, local depletion of CD4(+) cells inside the tumor resulted in a change of cytokine milieu and led to the eradication of well-established highly aggressive tumors and the development of long-term antitumor memory. Therefore, CD4(+)CD25(+) T cells maintained an environment in the tumor that concealed the immunogenicity of tumor cells to permit progressive growth of antigenic tumors. Our study illustrates that the suppression of antitumor immunity by regulatory T cells occurs predominantly at the tumor site, and that local reversal of suppression, even at a late stage of tumor development, can be an effective treatment for well-established cancers.

Prevalence of regulatory T cells is increased in peripheral blood and tumor microenvironment of patients with pancreas or breast adenocarcinoma

Regulatory T cells (T(reg)) that prevent autoimmune diseases by suppression of self-reactive T cells may also suppress the immune response against cancer. In mice, depletion of T(reg) by Ab therapy leads to more efficient tumor rejection. T(reg)-mediated suppression of antitumor immune responses may partly explain the poor clinical response to vaccine-based immunotherapy for human cancer. In this study, we measured the prevalence of T(reg) that coexpress CD4 and CD25 in the PBLs, tumor-infiltrating lymphocytes, and regional lymph node lymphocytes from 65 patients with either pancreas or breast cancer. In breast cancer patients (n = 35), pancreas cancer patients (n = 30), and normal donors (n = 35), the prevalence of T(reg) were 16.6% (SE 1.22), 13.2% (SE 1.13), and 8.6% (SE 0.71) of the total CD4(+) cells, respectively. The prevalence of T(reg) were significantly higher in breast cancer patients (p < 0.01) and pancreas cancer patients (p < 0.01) when compared with normal donors. In tumor-infiltrating lymphocytes and lymph node lymphocytes, the T(reg) prevalence were 20.2% (SE 3.93) and 20.1% (SE 4.3), respectively. T(reg) constitutively coexpressed CTLA-4 and CD45RO markers, and secreted TGF-beta and IL-10 but did not secrete IFN-gamma. When cocultured with activated CD8(+) cells or CD4(+)25(-) cells, T(reg) potently suppressed their proliferation and secretion of IFN-gamma. We conclude that the prevalence of T(reg) is increased in the peripheral blood as well as in the tumor microenvironment of patients with invasive breast or pancreas cancers. These T(reg) may mitigate the immune response against cancer, and may partly explain the poor immune response against tumor Ags.

Activated lymphocytes from breast cancer patients express the characteristics of type 2 helper cells--a possible role for breast cancer-associated p43

P43, a breast cancer-associated antigen, has been repeatedly described as an immunosuppressive factor. The objective of the present study was to investigate whether immune dysregulation induced by p43 affects the profile of cytokines secreted by mitogen-stimulated lymphocytes in breast cancer patients as compared with stimulated lymphocytes in women with benign tumors. The study consisted of 32 women undergoing surgical excision for a suspicious lesion in their breast. Histology revealed malignant breast disease in 20 patients and benign lesions in 10 patients. Lymphocytes isolated from peripheral blood were activated by Conconavalin A (Con A) with and without the addition of p43 and the concentrations of cytokines (IL-2, TNF-alpha, IFN-gamma, IL-4, IL-10 and IL-6) secreted into the culture medium were determined. Lymphocytes of patients with malignant breast disease stimulated with Con A secreted a significantly higher concentration of IL-10 compared with lymphocytes of patients with benign tumors. No significant differences were found between the two groups regarding the levels of IL-2, TNF-alpha, IFN-gamma and IL-4. Cytokine concentrations were analyzed according to the type 1/type 2 cytokine profile (IL-2, TNF and IFN-gamma and IL-4, IL-6 and IL-10, respectively). This analysis revealed no significant differences in IL-2, TNF or IFN-gamma between benign and malignant tumors. However, in the type 2 cytokines, lymphocytes from cancer patients secreted significantly higher levels of IL-4 (27.3 +/- 7.2 U/ml) and IL-10 (44.1 +/- 22.3 U/ml) than did the lymphocytes from patients with benign disease (21.4 +/- 7.3 and 1.8 +/- 0.3 U/ml, respectively). The addition of p43 to the culture medium significantly enhanced the levels of IL-4 secreted by lymphocytes in both groups of patients (malignant disease, from 27.3 +/- 9.2 to 40.7 +/- 6.3 U/ml; benign disease, from 21.4 +/- 7.3 to 28.4 +/- 2.1 U/ml). P43 antigen significantly enhanced the low levels of IL-10 in the benign lymphocytes (from 1.8 +/- 0.4 to 8.4 +/- 1.5 U/ml) while the high levels of IL-10 secreted by the PBL in patients with malignant tumors were not significantly increased (44.1 +/- 22.3 versus 50.1 +/- 12.6 U/ml). The study showed a difference in the immune response of lymphocytes between malignant and benign tumors. When the current results were analyzed according to the type of response, i.e. in terms of whether at least two cytokines of either type 1 or type 2 were elevated, a significant type 2 response was observed in the PBL of patients with malignant breast cancer (IL-10 and IL-4). These results may explain why antitumor response is impaired in patients with breast cancer.

Mechanisms of tumor-induced immunosuppression: evidence for contact-dependent T cell suppression by monocytes

BACKGROUND

The progressive growth of tumors in mice is accompanied by down-regulation of specific T cell responses. The factors involved in this suppression are not completely understood. Here, we have developed a model to examine the role of host immune effector cells in the inhibition of T cell function. In this model, progressive growth of a colon carcinoma line, CT26, is accompanied by loss of T cell response to alloantigens in both cytolytic and proliferation assays.

MATERIALS AND METHODS

The CT26 tumor was inoculated into BALB/c syngeneic mice. Tumor growth, cytolytic T cell responses, lymphocyte proliferation, and flow cytometric analysis was performed in tumor-bearing animals 7 or 28 days after tumor inoculation.

RESULTS

Spleen cells from tumor-bearing mice were found to suppress the proliferative response of spleen cells from normal mice to alloantigens. Examination of the spleen cell population by FACS analysis revealed an increase in the percentage of monocytes as defined by expression of CD11b, the Mac-1 antigen. Removal of the Mac-1-positive cells from the tumor-bearing hosts spleen relieved suppression of the tumor-bearing mouse spleen cell proliferative response to alloantigens, and addition of the Mac-1-positive enriched cells suppressed proliferation of normal T cells in response to alloantigens. Cell contact was required for this inhibition.

CONCLUSIONS

Tumor induction of suppressive monocytes plays an important role in the general immunosuppression noted in animals bearing CT26 tumors. Identification of the mechanisms responsible for this effect and reversal of tumor-induced macrophage suppression may facilitate efforts to develop effective immunotherapy for malignancy.

Alterations in T cells of cancer-bearers: whence specificity?

T cells of tumor-bearing mice and cancer patients have been reported to have altered signal-transduction machinery. These alterations have been implicated in immunological suppression. Here, Daniel Levey and Pramod Srivastava critically examine the evidence for these alterations in the context of the tumor specificity of immunological unresponsiveness in tumor-bearing hosts.

T cells from late tumor-bearing mice express normal levels of p56lck, p59fyn, ZAP-70, and CD3 zeta despite suppressed cytolytic activity

Loss of T cell-associated signal transduction molecules has recently been implicated in immune suppression in tumor-bearing hosts. In the present study, we have examined this and related phenomenon extensively in a large number of tumor-bearing mice, analyzed individually. Splenic T cells from tumor-bearing mice were isolated and characterized with respect to the following: (a) levels of three tyrosine kinases, p56lck, p59fyn, and ZAP-70; (b) expression of CD3-zeta; (c) alloreactive responses; and (d) antigen-specific responses. Contrary to recent reports, T cells from tumor-bearing mice were observed to express normal levels of lck, fyn, ZAP-70, and CD3-zeta. Further, T cells showed healthy alloreactive and antigen-specific responses until approximately 3 wk after post tumor challenge, when the tumors constituted approximately 20% of the body weight. Alterations with respect to some parameters were observed only in mice that had been bearing larger tumors for a considerably longer period. As human tumors are unlikely to grow to such large sizes (e.g., > 20% of the total body weight), the significance of the alterations in T cell expression of lck, fyn, ZAP-70, or CD3-zeta in the immune status of cancer patients is unclear. Altogether, these results indicate that alterations in T cell signal transduction molecules do not account for the profound tumor-specific suppression observed during tumor growth.

Immunomodulation in an apparently non-immunogenic murine tumor

Madison lung carcinoma (M109), a murine tumor of spontaneous origin, appears to be non-immunogenic, according to 2 commonly employed tests for tumor immunogenicity. However, C.parvum-induced immunopotentiation during the growth of M109 tumor results in post-excision anti-tumor immunity to M109 tumor implants. The C.parvum-potentiated post-excision immunity to M109 is tumor-specific and T-cell-dependent. T cells from mice whose progressive M109 tumors have been excised are capable, on passive transfer, of inhibiting adoptive immunotherapy of T-cell-deficient recipients by spleen cells from mice immunized with an admixture of M109 cells and C.parvum. The data are interpreted as evidence supporting the hypothesis that the apparent lack of anti-tumor immunity in this tumor model is not due to the absence of tumor-associated antigens. We suggest that, instead, in this model the balance between the effector and suppressor arms of the immune response favors tumor-induced immunosuppression, resulting in a magnitude of anti-tumor immunity insufficient for detection by commonly employed tests for tumor immunogenicity. Our study shows that shifting the balance in favor of the effector arm by means of immunopotentiation results in a measurable immune response to an apparently non-immunogenic tumor.

Residual immunity of athymic NCr/Sed nude mice and the xenotransplantation of human tumors

This study assessed the residual immunity possessed by NCr/Sed (nu/nu) athymic nude mice and examined strategies to reduce it in order to enhance the transplantability of human tumors for experimentation. Adult (8-week-old) female mice had fewer T cells (11%) and more B and NK (asialo-GM1-positive [ASGM1+]) cells in their spleen than euthymic (nu/+) controls. The number of phenotypically mature T cells increased with age, peaking at 16 weeks. ASGM1+ cells also increased in number over time, although the NK-activity decreased after 12 weeks. B cells remained relatively constant in number. Athymic NCr/Sed nude mice displayed reactivity against a human squamous carcinoma xenograph (FaDu), in a Winn's test and TD50 assay. Immunity against xenografts (TD50 assay) was significantly lower (by a factor of 2) in 4-week-old than in 12-week-old nude mice. Similarly, a significant 2-fold reduction in TD50 was obtained after a single intraperitoneal injection of cyclophosphamide into 8-week-old animals. Chronic (greater than 8 weeks) exposure of the nude mice to subcutaneously administered beta-estradiol markedly reduced the number of splenic NK cells and their cytolytic activity, but the TD50 reduction was not statistically significant (p = 0.1). Six Gray whole-body irradiations (WBI) had been shown to produce a highly significant, 3-fold reduction in the TD50 for FaDu. Flow cytometric analysis of splenic lymphoid cells from whole-body-irradiated recipients revealed: (a) marked initial depletion in the absolute numbers of lymphoid cells; (b) marked and long-lasting depletion of T cells, with slow and minimal recovery only evident between 6 and 12 weeks; (c) rapid, almost complete, depletion of B cells with prompt and partial recovery after 2 weeks; (d) depletion of NK cells and NK activity, with recovery by 10 weeks. No change in the number or phagocytic capacity of resident peritoneal macrophages was seen. These data give further support to a postulated role for residual T cells in the xenoreactivity of NCr/Sed nude mice.

Specific unresponsiveness in rats with prolonged cardiac allograft survival after treatment with cyclosporine. III. Further characterization of the CD4+ suppressor cell and its mechanisms of action

The cellular basis of the specific unresponsiveness that develops in DA rats treated with cyclosporine (CSA) for 10 d after grafting a PVG heart was examined using an adoptive transfer assay. CD4+ cells from rats with long survival grafts specifically lack the capacity to restore PVG heart graft rejection, and can also inhibit the capacity of naive T cells to restore rejection, while in the first few weeks post-transplant, both CD4+ and CD8+ T cells from CSA-treated hosts have the capacity to effect PVG graft rejection. In this study, we demonstrated the CD4+ suppressor cells also had the capacity to inhibit restoration of rejection by CD4+ cells from CSA-treated DA rats recently transplanted with PVG hearts, and from rats sensitized to third party, but not from those specifically sensitized to PVG. They also inhibited the capacity of both naive CD8+ and sensitized CD8+ cells to effect rejection. These results showed that the CD4+ suppressor cell was capable of overriding the capacity to effect rejection of the CD4+ cell and activated CD8+ cells that were present in the CSA-treated host shortly after transplantation. The failure of naive CD8+ cells to augment suppression and the capacity of CD4+ suppressor cells to transfer unresponsiveness to irradiated hosts in which regeneration of CD8+ cells was abolished by thymectomy suggested that it was the CD4+ cell alone that mediated suppression. However, the failure of CD4+ suppressor cells to reinduce unresponsiveness in irradiated hosts whose CD8+ cells had been depleted by therapy with the mAb MRC Ox8 showed that a radioresistant CD8+ cell was required to reestablish the state of specific unresponsiveness. The induction of CD4+ suppressor cells in thymectomized hosts suggested that these cells were derived from long-lived CD4+ lymphocytes. However, their sensitivity to cyclophosphamide and their loss of suppressor function both after removal of the graft and after 3 d in culture demonstrated that the suppressor cell itself had a short lifespan. The CD4+ suppressor was shown to be MRC Ox22+ (CD45R+), MRC Ox17+ (MHC class II), and MRC Ox39+ (CD25, IL-2-R). These studies demonstrated the CD4+ suppressive cell identified in rats with specific unresponsiveness induced by CSA therapy had many features of the suppressor inducer cell identified in in vitro studies of the alloimmune response.(ABSTRACT TRUNCATED AT 400 WORDS)

Highly immunogenic regressor tumor cells can prevent development of postsurgical tumor immunity

Highly immunogenic malignant cells form small tumors that spontaneously regress after initial growth because the tumor induces specific immunity. However, variants may arise during the initial tumor growth that lose antigens, grow progressively, often become the predominant tumor population, and eventually kill the host. These progressively growing variants usually have not lost all tumor antigens and remain susceptible to rejection by T cells specific for antigens present on the parental tumor and retained by the progressively growing variants. Thus, it would seem logical for therapy to actively immunize with the parental highly immunogenic tumor (or sublines made similarly immunogenic by tumor heterogenization) after maximal surgical removal of the growing tumor. However, the present findings suggest that such a strategy may be ineffective and have adverse effects: the parental highly immunogenic tumor cells, either remaining or reintroduced, may perpetuate unresponsiveness to both the parental and the variant tumor. These findings suggest that unless tumor-induced suppression is first abrogated, immunization with highly immunogenic tumor cells may be counterproductive because this maneuver may maintain preexisting immune suppression and prevent development of postsurgical tumor immunity.

Antitumor effect of PSK: role of regional lymph nodes and enhancement of concomitant and sinecomitant immunity in the mouse

PSK, a Coriolus preparation, inhibited the growth of not only the right but also the left, non-treated tumor in a double grafted tumor system. In order to examine the role of lymph nodes and the spleen in the antitumor activity of PSK, regional (axillary and inguinal) lymph nodes and spleen were resected. Since in resected mice the antitumor activity of PSK against the right and left tumors was weakened, the regional lymph nodes and the spleen probably have a very important role in the antimetastatic effect of intratumoral administration of PSK. TIL (tumor-infiltrating lymphocytes) obtained from left and right side tumors treated with PSK were examined by Winn assay for their antitumor activity against Meth-A sarcoma in BALB/c mice. TIL from both sides clearly inhibited the growth of admixed Meth-A cells, but control TIL did not. A primary growth of Meth-A sarcoma inoculated into the right flank resulted in the generation of concomitant immunity to the growth of a second graft of the same tumor cells in the left flank. A significant inhibitory effect on the proliferation of the tumor cells inoculated secondarily was shown in mice bearing a primary right tumor that had previously been inoculated with PSK 3 times. After surgical excision of the primary tumor on day 6, daily oral administration of PSK significantly inhibited the growth of the secondary tumor inoculated on day 21, that is, PSK treatment also enhanced sinecomitant immunity. These observations suggest that presurgical intratumoral injection and postoperative oral administration of PSK are highly effective in eradicating metastatic tumors.

Chemotherapy of mice bearing syngeneic tumors with 1,3-bis (2-chloroethyl)-1-nitrosourea is effective only in normal, but not in irradiated or nude, mice: role of L3T4+ (CD4+) and Lyt-2+ (CD8+) T cells

We earlier demonstrated that treatment of C57BL/6 mice bearing a syngeneic tumor, LSA, with 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) resulted in over 90% survival of the mice, and 100% of the cured mice rejected secondary rechallenge with the homologous tumor but not with a heterologous syngeneic tumor such as EL-4. In the present study we investigated whether the host's immune system was also essential for successful chemotherapy with BCNU. It was observed that BCNU treatment was effective only in normal tumor-bearing mice (100% survival) but not in irradiated or nude tumor-bearing mice (0% survival), thereby suggesting that the immune system, particularly the T cells, was essential for effective treatment with BCNU. Since BCNU-cured mice lack demonstrable T suppressor (Ts) cells, these mice were next used as a model to investigate the phenotype of the T cells mediating tumor rejection. It was observed that L3T4+ (CD4+) or Lyt-2+ (CD8+) T cells from BCNU-cured mice could provide significant protection (80 and 40% survival, respectively) in irradiated or nude mice but not in normal mice. It was also observed that BCNU-cured LSA mice elicited tumor-specific delayed-type hypersensitivity (DTH) reaction, while, normal mice or LSA tumor-bearing mice failed to elicit DTH reaction. Also, only L3T4+ but not Lyt-2+ T cells from BCNU-cured mice when adoptively transferred into nude mice could elicit a DTH reaction. The present study suggests that for effective chemotherapy against a syngeneic tumor, with a tumoricidal drug such as BCNU, the presence of L3T4+ and Lyt-2+ T cells in the host is essential.