Combining radiotherapy and immunotherapy: a revived partnership

HPV-induced oropharyngeal cancer, immune response and response to therapy

Approximately 25% of head and neck squamous cell carcinoma (HNSCC) worldwide are associated with high-risk human papillomaviruses (HPV). HPV-positive HNSCCs have a more favorable outcome and greater response to therapy. While chronic HPV infection allows for the evolution of immune evasion mechanisms, viral antigens can still elicit an immune response. Moreover, a robust lymphocytic response is associated with better prognosis in a variety of tumor types including head and neck cancer. This article outlines several mechanisms whereby the observed improved response of HPV-positive tumors to radiotherapy may be related to enhancement of the immune response following radiotherapy.

Invariant natural killer T cells regulate breast cancer response to radiation and CTLA-4 blockade

PURPOSE

Immunoregulatory and suppressive mechanisms represent major obstacles to the success of immunotherapy in cancer patients. We have shown that the combination of radiotherapy to the primary tumor and CTL-associated protein 4 (CTLA-4) blockade induces antitumor immunity, inhibiting metastases and extending the survival of mice bearing the poorly immunogenic and highly metastatic 4T1 mammary carcinoma. Similarly to patients with metastatic cancer, however, mice were seldom cured. Here we tested the hypothesis that invariant natural killer T (iNKT) cells, a subset with unique regulatory functions, can regulate the response to radiotherapy and CTLA-4 blockade.

EXPERIMENTAL DESIGN

The growth of 4T1 primary tumors and lung metastases was compared in wild-type and iNKT cell-deficient (iNKT-/-) mice. Treatment was started on day 13 when the primary tumors were palpable. Mice received radiotherapy to the primary tumor in two doses of 12 Gy in combination or not with 9H10 monoclonal antibody against CTLA-4. Response to treatment was assessed by measuring primary tumor growth delay/regression, survival, and number of lung metastases.

RESULTS

The response to radiotherapy plus 9H10 was markedly enhanced in the absence of iNKT cells, with 50% of iNKT-/- versus 0% of wild-type mice showing complete tumor regression, long-term survival, and resistance to a challenge with 4T1 cells. Administration of the iNKT cell activator alpha-galactosylceramide did not enhance the response of wild-type mice to radiotherapy plus 9H10. Tumor-infiltrating iNKT cells were markedly reduced in wild-type mice treated with radiotherapy plus 9H10.

CONCLUSIONS

iNKT cells play a major role in regulating the response to treatment with local radiotherapy and CTLA-4 blockade.

Graft rejection occurring in post-liver transplant patients receiving cytotoxic chemotherapy: a case series

Liver transplant recipients are known to be at increased risk for the development of de novo neoplasms or the recurrence of preexisting malignancies, and this is possibly related to the use of immunosuppressive medication. Little is known about the effects of cytotoxic chemotherapy on graft function after transplantation. A retrospective chart and pathology database review was undertaken to identify post-liver transplant patients developing rejection during chemotherapy. All liver biopsies were reviewed by a hepatopathologist. Three patients were identified. All patients were diagnosed with cancer within 7 years of liver transplantation; two-thirds died soon after the diagnosis of malignancy. Rejection occurred soon after chemotherapy was started. All patients were receiving prednisone and tacrolimus (trough levels: 2.1-4.8 ng/mL). One patient developed plasma cell hepatitis (de novo autoimmune hepatitis). There was no histologic evidence of hepatotoxicity due to the chemotherapeutic agents. Cytotoxic chemotherapy should be used in liver transplant recipients with caution, and immunosuppressant doses should be maintained at therapeutic levels, as patients may be at risk for allograft rejection. Treatment of rejection or plasma cell hepatitis in this setting should be undertaken in a timely and aggressive fashion to prevent chronic ductopenic rejection.

Combining radiation and immunotherapy for synergistic antitumor therapy

The combination of radiation therapy and immunotherapy holds enticing promise as a strategy for cancer treatment. Preclinical studies have shown that radiation may act synergistically with immunotherapy to enhance or broaden antitumor immune responses, in part, because of radiation-induced phenotypic alterations of tumor cells that render them more susceptible to immune-mediated killing. Clinical trials utilizing the combination of therapeutic vaccines with radiation have supported many of these findings, and other clinical trials are both ongoing and planned. This review examines the evidence that radiation induces immunological death, the mechanisms by which radiation therapy can induce or augment antitumor immune responses, and translational studies demonstrating that immunotherapy can be effectively combined with radiation therapy. Finally, recent and current clinical trials combining radiation therapy with immunotherapy are reviewed.

Local control by radiotherapy: is that all there is?

Radiotherapy is a local treatment modality employed in breast cancer to reduce local recurrence following surgery. The observed association of optimal local control with improved survival was not expected in a disease characterized by early systemic spread. The underlying mechanisms whereby the application of ionizing radiation to the primary tumor site can have systemic effects remain unclear and are the subject of much debate. In the present article we discuss the hypothesis that radiotherapy has unique biological effects and that, in addition to killing residual neoplastic cells after surgery is performed, it might favorably alter the microenvironment at the primary tumor site during the process of wound healing and the development of antitumor immune responses.

Cryo-immunology: a review of the literature and proposed mechanisms for stimulatory versus suppressive immune responses

The use of cryosurgery to ablate tumors is expanding, primarily due to its technical ease and minimal morbidity. A potential secondary advantage to the in situ freezing of malignant disease is the cryo-immunologic response, the generation of an anti-tumor immune response triggered by the natural absorption of the malignant tissue. While initially proposed based on clinical observations of distant disease regressing after cryoablation of a primary tumor, results from preclinical studies have been mixed and the existence of a cryo-immunologic response has been controversial. Recent studies have shed light on the potential mechanism by which cryoablation may modulate the immune system, also reveals that both immunostimulatory and immunosuppressive responses may be triggered. This article reviews the existing evidence regarding tumor cryo-immunology and puts forward hypotheses regarding patient, tumor and technical factors that may influence the resultant immune response and warrant further investigation.

Radiation-induced CXCL16 release by breast cancer cells attracts effector T cells

Recruitment of effector T cells to inflamed peripheral tissues is regulated by chemokines and their receptors, but the factors regulating recruitment to tumors remain largely undefined. Ionizing radiation (IR) therapy is a common treatment modality for breast and other cancers. Used as a cytocidal agent for proliferating cancer cells, IR in combination with immunotherapy has been shown to promote immune-mediated tumor destruction in preclinical studies. In this study we demonstrate that IR markedly enhanced the secretion by mouse and human breast cancer cells of CXCL16, a chemokine that binds to CXCR6 on Th1 and activated CD8 effector T cells, and plays an important role in their recruitment to sites of inflammation. Using a poorly immunogenic mouse model of breast cancer, we found that irradiation increased the migration of CD8(+)CXCR6(+) activated T cells to tumors in vitro and in vivo. CXCR6-deficient mice showed reduced infiltration of tumors by activated CD8 T cells and impaired tumor regression following treatment with local IR to the tumor and Abs blocking the negative regulator of T cell activation, CTLA-4. These results provide the first evidence that IR can induce the secretion by cancer cells of proinflammatory chemotactic factors that recruit antitumor effector T cells. The ability of IR to convert tumors into "inflamed" peripheral tissues could be exploited to overcome obstacles at the effector phase of the antitumor immune response and improve the therapeutic efficacy of immunotherapy.

Synergistic tumoricidal effect of combined hMUC1 vaccination and hNIS radioiodine gene therapy

We examined the merits of combinatorial hMUC1 vaccination and hNIS radioiodine gene therapy and evaluated its tumoricidal effects in an animal tumor model. CMNF (CT26 expressing hMUC1, hNIS, and firefly luciferase) cells were transplanted into 28 mice, and 4 and 11 days after tumor challenge, tumor-bearing mice were immunized i.m. with pcDNA3.1 or pcDNA-hMUC1 vaccine and subsequently administered PBS or (131)I i.p. [four groups (7 mice per group): pcDNA3.1 + PBS, phMUC1 + PBS, pcDNA3.1 + (131)I, and phMUC1 + (131)I groups]. Thirty-two days after tumor challenge, we rechallenged mice in the pcDNA3.1 + (131)I and phMUC1 + (131)I groups with CMNF cells. Tumor progression and tumor-free mice (%) were monitored by bioluminescence. We investigated hMUC1-associated immune response generated by combination therapy. Marked tumor growth inhibition was observed in the phMUC1 + (131)I group by bioluminescence at 32 days after tumor challenge. Mice in phMUC1 + (131)I group showed complete hMUC1-expressing tumor suppression after tumor rechallenge, whereas mice in the pcDNA3.1 + (131)I group did not. The tumor-free mice (%) were much higher in the phMUC1 + (131)I group than in the other three groups. Levels of hMUC1-associated CD8(+)IFN-gamma(+) T cells were higher in the phMUC1 + (131)I group than in the other three groups. hMUC1-loaded CD11(+) cells in the phMUC1 + (131)I group were found to be most effective at generating hMUC1-associated CD8(+)IFN-gamma(+) T cells. The activities of hMUC1-associated cytotoxic T cells in the phMUC1 + (131)I group were higher than in the other three groups. Our data suggest that phMUC1 + (131)I combination therapy synergistically generates marked tumoricidal effects against established hMUC1-expressing cancers.

T-cell responses to survivin in cancer patients undergoing radiation therapy

PURPOSE

The goal of this study was to determine if radiation therapy (RT) of human cancer enhances or diminishes tumor-specific T-cell reactivity. This is important if immunotherapy is to be harnessed to improve the outcome of cancer radiotherapy.

EXPERIMENTAL DESIGN

Lymphocytes were isolated from colorectal cancer (CRC) patients before, during, and after presurgical chemoradiotherapy. Similar samples were taken from prostate cancer patients receiving standard RT. The level of CD8(+) T cells capable of binding tetramers for the tumor-associated antigen survivin, which is overexpressed in both cancer types, was enumerated in HLA-A*0201 patient samples. CD4(+), CD25(high), Foxp3(+) cells were also enumerated to evaluate therapy-induced changes in T(regulatory) cells. For CRC patients, most of whom were enrolled in a clinical trial, pathologic response data were available, as well as biopsy and resection specimens, which were stained for cytoplasmic and intranuclear survivin.

RESULTS

Survivin-specific CD8(+) T lymphocytes were detected in the peripheral blood of CRC and prostate cancer patients and increased after therapy in some, but not all, patients. Increases were more common in CRC patients whose tumor was downstaged after chemoradiotherapy. Biopsy specimens from this cohort generally had higher nuclear to cytoplasmic survivin expression. T(regulatory) cells generally increased in the circulation following therapy but only in CRC patients.

CONCLUSION

This study indicates that RT may increase the likelihood of some cancer patients responding to immunotherapy and lays a basis for future investigations aimed at combining radiation and immunotherapy.

Mechanisms involved in radiation enhancement of intratumoral dendritic cell therapy

We have previously reported that local tumor irradiation, without inducing cell death, can augment the therapeutic efficacy of intratumoral (IT) dendritic cell (DC) vaccination. This study examined potential mechanisms underlying radiation enhancement of IT DC therapy in this setting. Even though ionizing radiation did not mediate tumor cell killing, bone marrow-derived DCs acquired in vitro tumor antigens from irradiated D5 murine melanoma cells more efficiently than from untreated cells. This radiation-enhanced loading of DCs did not induce DC maturation, but was associated with improved cross-priming of T cells both in vitro and in vivo. Furthermore, in vivo pulsing of DCs with irradiated versus untreated tumor cells resulted in superior presentation of tumor antigens to T cells. In addition, tumor irradiation facilitated homing of IT administered DCs to the draining lymph node, possibly by down-regulating CCL21 expression within the tumor mass. Studies of the tumor microenvironment in irradiated versus untreated tumors did not reveal significant inflammatory changes. Moreover, radiation did not promote accumulation of CD4 or CD8 effector T cells within solid tumors. Our results indicate that, without inducing cytotoxicity, tumor irradiation can enhance the ability of DCs to capture tumor antigens, migrate to the draining lymph node, and present processed antigens to T cells. These findings may prove useful in designing future strategies for human cancer immunotherapy.

Radiotherapy augments the immune response to prostate cancer in a time-dependent manner

BACKGROUND

Cancer immunotherapy refers to an array of strategies intended to treat progressive tumors by augmenting a patient's anti-tumor immune response. As immunotherapy is eventually incorporated into oncology treatment paradigms, it is important to understand how these therapies interact with established cancer treatments such as chemotherapy or Radiotherapy (RT). To address this, we utilized a well-established, autochthonous murine model of prostate cancer to test whether RT could augment (or diminish) the CD4 T cell response to a tumor vaccine.

METHODS

Transgenic mice that develop spontaneous prostate cancer (TRAMP) which also express a unique tumor associated antigen (Influenza hemagglutinin) under the control of a prostate-specific promoter were given local RT in combination with immunotherapy. The immunological outcome of this combinatorial strategy was assayed by monitoring the effector response of adoptively transferred, prostate-specific CD4 T cells.

RESULTS

Neither RT nor immunotherapy alone was capable of priming an anti-tumor immune response in animals with evolving tumors. The combination of immunotherapy with RT resulted in anti-tumor T cell activation--this effect was profoundly dependent on the relative timing of RT and immunotherapy. Anti-tumor immune responses occurred when immunotherapy was administered 3-5 weeks post-RT, but such responses were undetectable when immunotherapy was administered either earlier (peri-radiotherapy) or later.

CONCLUSIONS

The therapeutic temporal window of immunotherapy post-RT suggests that highly aggressive, immuno-suppressive tumors might be most sensitive to immunotherapy in a fairly narrow time window; these results should help to guide future development of clinical combinatorial strategies.

Radiation-induced IFN-gamma production within the tumor microenvironment influences antitumor immunity

Alterations to the tumor microenvironment following localized irradiation may influence the effectiveness of subsequent immunotherapy. The objective of this study was to determine how IFN-gamma influences the inflammatory response within this dynamic environment following radiotherapy. B16/OVA melanoma cells were implanted into C57BL/6 (wild-type (WT)) and IFN-gamma-deficient (IFN-gamma-/-) mice. Seven days after implantation, mice received 15 Gy of localized tumor irradiation and were assessed 7 days later. Irradiation up-regulated the expression of VCAM-1 on the vasculature of tumors grown in WT but not in IFN-gamma-/- mice. Levels of the IFN-gamma-inducible chemokines MIG and IFN-gamma-inducible protein 10 were decreased in irradiated tumors from IFN-gamma-/- mice compared with WT. In addition to inducing molecular cues necessary for T cell infiltration, surface MHC class I expression is also up-regulated in response to IFN-gamma produced after irradiation. The role of IFN-gamma signaling in tumor cells on class I expression was tested using B16/OVA cells engineered to overexpress a dominant negative mutant IFN-gamma receptor (B16/OVA/DNM). Following implantation and treatment, expression of surface class I on tumor cells in vivo was increased in B16/OVA, but not in B16/OVA/DNM tumors, suggesting IFN-gamma acts directly on tumor cells to induce class I up-regulation. These increases in MHC class I expression correlated with greater levels of activated STAT1. Thus, IFN-gamma is instrumental in creating a tumor microenvironment conducive for T cell infiltration and tumor cell target recognition.

Use of radiolabeled monoclonal antibody to enhance vaccine-mediated antitumor effects

Radiolabeled monoclonal antibodies (mAb) have demonstrated measurable antitumor effects in hematologic malignancies. This outcome has been more difficult to achieve for solid tumors due, for the most part, to difficulties in delivering sufficient quantities of mAb to the tumor mass. Previous studies have shown that nonlytic levels of external beam radiation can render tumor cells more susceptible to T cell-mediated killing. The goal of these studies was to determine if the selective delivery of a radiolabeled mAb to tumors would modulate tumor cell phenotype so as to enhance vaccine-mediated T-cell killing. Here, mice transgenic for human carcinoembryonic antigen (CEA) were transplanted with a CEA expressing murine carcinoma cell line. Radioimmunotherapy consisted of yttrium-90 (Y-90)-labeled anti-CEA mAb, used either alone or in combination with vaccine therapy. A single dose of Y-90-labeled anti-CEA mAb, in combination with vaccine therapy, resulted in a statistically significant increase in survival in tumor-bearing mice over vaccine or mAb alone; this was shown to be mediated by engagement of the Fas/Fas ligand pathway. Mice receiving the combination therapy also showed a significant increase in the percentage of viable tumor-infiltrating CEA-specific CD8(+) T cells compared to vaccine alone. Mice cured of tumors demonstrated an antigen cascade resulting in CD4(+) and CD8(+) T-cell responses not only for CEA, but for p53 and gp70. These results show that systemic radiotherapy in the form of radiolabeled mAb, in combination with vaccine, promotes effective antitumor response, which may have implications in the design of future clinical trials.

Synergizing radiation therapy and immunotherapy for curing incurable cancers. Opportunities and challenges

The combination of radiation therapy and immunotherapy holds particular promise as a strategy for cancer therapeutics. Evidence suggests that immunotherapy is most beneficial alone when employed early in the disease process or in combination with standard therapies (eg, radiation) later in the disease process. Indeed, radiation may act synergistically with immunotherapy to enhance immune responses, inhibit immunosuppression, and/or alter the phenotype of tumor cells, thus rendering them more susceptible to immune-mediated killing. As monotherapies, both immunotherapy and radiation may be insufficient to eliminate tumor masses. However, following immunization with a cancer vaccine, the destruction of even a small percentage of tumor cells by radiation could result in crosspriming and presentation of tumor antigens to the immune system, thereby potentiating antitumor responses. Learning how to exploit radiation-induced changes to tumor-cell antigens, and how to induce effective immune responses to these cumulatively immunogenic stimuli, is an exciting frontier in cancer therapy research. This review examines mechanisms by which many forms of radiation therapy can induce or augment antitumor immune responses as well as preclinical systems demonstrating that immunotherapy can be effectively combined with radiation therapy. Finally, we review current clinical trials where standard-of-care radiation therapy is being combined with immunotherapy.

Multilineage hematopoietic recovery with concomitant antitumor effects using low dose Interleukin-12 in myelosuppressed tumor-bearing mice

BACKGROUND

Interleukin-12 (IL-12) is a cytokine well known for its role in immunity. A lesser known function of IL-12 is its role in hematopoiesis. The promising data obtained in the preclinical models of antitumor immunotherapy raised hope that IL-12 could be a powerful therapeutic agent against cancer. However, excessive clinical toxicity, largely due to repeat dose regimens, and modest clinical response observed in the clinical trials have pointed to the necessity to design protocols that minimize toxicity without affecting the anti-tumor effect of IL-12. We have focused on the lesser known role of IL-12 in hematopoiesis and hypothesized that an important clinical role for IL-12 in cancer may be as an adjuvant hematological cancer therapy. In this putative clinical function, IL-12 is utilized for the prevention of cancer therapy-related cytopenias, while providing concomitant anti-tumor responses over and above responses observed with the primary therapy alone. This putative clinical function of IL-12 focuses on the dual role of IL-12 in hematopoiesis and immunity.

METHODS

We assessed the ability of IL-12 to facilitate hematopoietic recovery from radiation (625 rad) and chemotherapy (cyclophosphamide) in two tumor-bearing murine models, namely the EL4 lymphoma and the Lewis lung cancer models. Antitumor effects and changes in bone marrow cellularity were also assessed.

RESULTS

We show herein that carefully designed protocols, in mice, utilizing IL-12 as an adjuvant to radiation or chemotherapy yield facile and consistent, multilineage hematopoietic recovery from cancer therapy-induced cytopenias, as compared to vehicle and the clinically-utilized cytokine granulocyte colony-stimulating factor (G-CSF) (positive control), while still providing concomitant antitumor responses over and above the effects of the primary therapy alone. Moreover, our protocol design utilizes single, low doses of IL-12 that did not yield any apparent toxicity.

CONCLUSION

Our results portend that despite its past failure, IL-12 appears to have significant clinical potential as a hematological adjuvant cancer therapy.

Differential induction from X-irradiated human peripheral blood monocytes to dendritic cells

Dendritic cells (DCs) are a type of antigen-presenting cell which plays an essential role in the immune system. To clarify the influences of ionizing radiation on the differentiation to DCs, we focused on human peripheral blood monocytes and investigated whether X-irradiated monocytes can differentiate into DCs. The non-irradiated monocytes and 5 Gy-irradiated monocytes were induced into immature DCs (iDCs) and mature DCs (mDCs) with appropriate cytokine stimulation, and the induced cells from each monocyte expressed each DC-expressing surface antigen such as CD40, CD86 and HLA-DR. However, the expression levels of CD40 and CD86 on the iDCs derived from the 5 Gy-irradiated monocytes were higher than those of iDCs derived from non-irradiated monocytes. Furthermore, the mDCs derived from 5 Gy-irradiated monocytes had significantly less ability to stimulate allogeneic T cells in comparison to the mDCs derived from non-irradiated monocytes. There were no significant differences in the phagocytotic activity of the iDCs and cytokines detected in the supernatants conditioned by the DCs from the non-irradiated and irradiated monocytes. These results suggest that human monocytes which are exposed to ionizing radiation can thus differentiate into DCs, but there is a tendency that X-irradiation leads to an impairment of the function of DCs.

Low-dose radiation potentiates the therapeutic efficacy of folate receptor-targeted hapten therapy

PURPOSE

Human cancers frequently overexpress a high-affinity cell-surface receptor for the vitamin folic acid. Highly immunogenic haptens can be targeted to folate receptor-expressing cell surfaces by administration of folate-hapten conjugates, rendering the decorated tumor cell surfaces more recognizable by the immune system. Treatment of antihapten-immunized mice with folate-hapten constructs results in elimination of moderately sized tumors by the immune system. However, when subcutaneous tumors exceed 300 mm(3) before initiation of therapy, antitumor activity is significantly decreased. In an effort to enhance the efficacy of folate-targeted hapten immunotherapy (FTHI) against large tumors, we explored the combination of targeted hapten immunotherapy with low-dose radiotherapy.

METHODS AND MATERIALS

Mice bearing 300-mm(3) subcutaneous tumors were treated concurrently with FTHI (500 nmol/kg of folate conjugated to fluorescein isothiocyanate, 20,000 U/dose of interleukin 2, and 25,000 U/dose of interferon alpha) and low-dose radiotherapy (3 Gy/dose focused directly on the desired tumor mass). The efficacy of therapy was evaluated by measuring tumor volume.

RESULTS

Tumor growth analyses show that radiotherapy synergizes with FTHI in antihapten-immunized mice, thereby allowing for cures of animals bearing tumors greater than 300 mm(3). More importantly, nonirradiated distal tumor masses in animals containing locally irradiated tumors also showed improved response to hapten immunotherapy, suggesting that not all tumor lesions must be identified and irradiated to benefit from the combination therapy.

CONCLUSIONS

These results suggest that simultaneous treatment with FTHI and radiation therapy can enhance systemic antitumor activity in tumor-bearing mice.

Radiation therapy and Toll-like receptor signaling: implications for the treatment of cancer

The identification of pathogen-associated molecular patterns, conserved microbial structures that act on Toll-like receptors, has led to a novel avenue of investigation aimed at developing a new generation of cancer immunotherapies. Ligation of Toll-like receptors results in the induction of robust immune responses that may be directed against tumor-associated antigens. Recent data suggest that such strategies may result in enhanced antitumor immunity. Nonetheless, as clinically effective immunotherapy for cancer remains a somewhat distant goal, attention has shifted toward multimodality approaches to cancer therapy, sometimes combining novel immune interventions and conventional treatments. The traditional view of radiation therapy as immunosuppressive has now been challenged, prompting a re-evaluation of its potential as an adjunct to immunotherapy. Radiation therapy can enhance the expression of tumor-associated antigens, induce immune-mediated targeting of tumor stroma, and diminish regulatory T cell activity. Recent evidence suggests that radiation therapy may also activate effectors of innate immunity through TLR-dependent mechanisms, thereby augmenting the adaptive immune response to cancer. In this paper, we will review evidence for enhanced tumor-directed immunity resulting from radiation exposure and early promising data suggesting synergistic effects of radiation and TLR-targeted immunotherapies.

Anti-OX40 monoclonal antibody therapy in combination with radiotherapy results in therapeutic antitumor immunity to murine lung cancer

The therapeutic effect of agonistic anti-OX40 (CD134) monoclonal antibody (mAb) in combination with radiotherapy was evaluated in a murine lung cancer model. After intradermal transplantation of ovalbumin (OVA)-transfected Lewis lung carcinoma, C57BL/6 mice were irradiated locally with a single dose of 20 Gy in combination with an intratumoral injection of anti-OX40 mAb at 50 microg on day 4 after transplantation, which is when the major axis of the inoculated tumor reached a diameter of 7-9 mm. On days 8, 11, and 14, the tumor-bearing mice were further treated with the same dose of anti-OX40 mAb. Anti-OX40 mAb in combination with radiotherapy prolonged survival and provided greater efficacy than either single treatment against well-established tumors. An in vivo depletion study suggested that therapeutic immunity was mainly CD8(+) T-cell dependent. OX40(+)CD8(+) T cells were augmented in draining lymph nodes obtained from irradiated mice compared with those from non-irradiated mice. OVA-major histocompatibility complex tetramer(+) CD8(+) T cells had been strongly recruited to the draining lymph nodes obtained from mice treated with anti-OX40 mAb in combination with radiotherapy, and strong antigen-specific cytotoxicity was confirmed by a (51)Cr-release assay. Moreover, a tumor-rechallenge model indicated that this combination therapy induced durable tumor immunity. Thus, anti-OX40 mAb in combination with radiotherapy may potentially help the management of patients with lung cancer.

TLR9 engagement on CD4 T lymphocytes represses gamma-radiation-induced apoptosis through activation of checkpoint kinase response elements

T cell-based therapies have much promise in cancer treatment. This approach may be enhanced if used in combination with radiotherapy provided that tumor-specific T cells can be protected against the effects of radiotherapy. Previously, we demonstrated that administration of TLR9 ligand into mice decreased activation- and serum deprivation-induced cell death in T cells. We hypothesized that TLR9 engagement on T lymphocytes decreased apoptosis after cellular stress. We show that TLR9 engagement on murine CD4 T cells reduces gamma-radiation-induced apoptosis as judged by decreased annexin-V/PI staining, caspase-3 activation, and PARP cleavage. TLR9-stimulated cells show heightened accumulation at the G2 cell-cycle phase and increased DNA repair rates. Irradiated, TLR9-engaged cells showed higher levels of phosphorylated Chk1 and Chk2. While the levels of activated ATM in response to IR did not differ between TLR9-stimulated and unstimulated cells, inhibition of ATM/ATR and Chk1/Chk2 kinases abolished the radioprotective effects in TLR9-stimulated cells. In vivo, TLR9-stimulated cells displayed higher radio resistance than TLR9-stimulated MyD88(-/-) T cells and responded to antigenic stimulation after total body irradiation. These findings show, for the first time, that TLR9 engagement on CD4 T cells reduces IR-induced apoptosis by influencing cell-cycle checkpoint activity, potentially allowing for combinatorial immunotherapy and radiotherapy.

The combination of ionizing radiation and peripheral vaccination produces long-term survival of mice bearing established invasive GL261 gliomas

PURPOSE

High-grade glioma treatment includes ionizing radiation therapy. The high invasiveness of glioma cells precludes their eradication and is responsible for the dismal prognosis. Recently, we reported the down-regulation of MHC class I (MHC-I) products in invading tumor cells in human and mouse GL261 gliomas. Here, we tested the hypothesis that whole-brain radiotherapy (WBRT) up-regulates MHC-I expression on GL261 tumors and enhances the effectiveness of immunotherapy.

EXPERIMENTAL DESIGN

MHC-I molecule expression on GL261 cells was analyzed in vitro and in vivo by flow cytometry and immunohistochemistry, respectively. To test the response of established GL261 gliomas to treatment, mice with measurable (at CT imaging) brain tumors were randomly assigned to four groups receiving (a) no treatment, (b) WBRT in two fractions of 4 Gy, (c) vaccination with irradiated GL261 cells secreting granulocyte-macrophage colony-stimulating factor, or (d) WBRT and vaccination. Endpoints were tumor response and survival.

RESULTS

An ionizing radiation dose of 4 Gy maximally up-regulated MHC-I molecules on GL261 cells in vitro. In vivo, WBRT induced the expression of the beta2-microglobulin light chain subunit of the MHC class I complex on glioma cells invading normal brain and increased CD4+ and CD8+ T cell infiltration. However, the survival advantage obtained with WBRT or vaccination alone was minimal. In contrast, WBRT in combination with vaccination increased long-term survival to 40% to 80%, compared with 0% to 10% in the other groups (P < 0.002). Surviving animals showed antitumor immunity by rejecting challenge tumors.

CONCLUSION

Ionizing radiation can be successfully combined with peripheral vaccination for the treatment of established high-grade gliomas.

The immune system--is it relevant to cancer development, progression and treatment?

The ability of the immune system to effectively respond to human tumours is a matter of long-term controversy. There is an increasing body of recent evidence to support a role for the immune system in eliminating pre-clinical cancers, an old concept termed 'immunosurveillance'. 'Immunoediting' is an updated hypothesis, in which selection pressures applied by the immune response to tumours modulate tumour immunogenicity and growth. Tumour infiltration by immune cells has been shown to have powerful prognostic significance in a host of cancer types. Paradoxically, in some circumstances the immune system can promote tumour development. Cytotoxic therapies, including radiotherapy and chemotherapy, induce potentially immunogenic cell death, releasing tumour-associated antigens in the context of a 'danger' signal to the immune system. An understanding of the interaction between immune cells, tumour cells and treatment modalities will therefore guide the future combination of immunotherapy with conventional therapy to achieve optimal anti-tumour effects.

Flow cytometry in radiation research: past, present and future

Flow cytometry is an invaluable technique in research and clinical laboratories. The technique has been applied extensively to many areas of radiation research at both the experimental and clinical level. In the past few years, there has been a significant increase in the capabilities of modern flow cytometers to undertake multicolor analysis in a user-friendly manner. The developments in cytometric technology are being matched by the rapid development of new reagents, new fluorochromes and new platforms such as bead arrays. These developments are facilitating many new applications in both basic and clinical research that have relevance for many fields of biology, including radiation research. This review provides a historical overview of the application of flow cytometry to radiobiology and an update on how technology and reagents have changed and cites examples of new applications relevant to radiation researchers. In addition, some entirely new flow instrumentation is currently under development that has significant potential for applications in radiation research.

Early experience with novel immunomodulators for cancer treatment

Immunotherapy involves the treatment of cancer by modification of the host-tumour relationship. It is now known that this relationship is quite complex and only some of the interactions have been elucidated. Early attempts at immunotherapy, such as Coley's toxins, were undertaken without an understanding of the processes mediating the effects. With a better understanding of the immunology of this anticancer response, recent trials have focussed on certain aspects of the process to stimulate an antitumour response. In this review, the authors discuss a number of novel biological response modifiers that work as general stimulants of the immune system, through varied mechanisms including induction of stimulatory cytokines (such as IFN-alpha, TNF-alpha and IL-12) and activation of T cells and the antigen-presenting dendritic cells. These compounds include Toll-like receptor agonists, several of which are in clinical trials at present. In addition to immunomodulatory activity, some compounds such as 5,6-dimethylxanthenone-4-acetic acid (DMXAA) and thalidomide and its analogues also target existing or developing tumour vasculature. Some of these compounds have single-agent activity in clinical trials, while others such as DMXAA have shown promise in combination with chemotherapy without increasing toxicity. Lactoferrin is another compound that has shown clinical activity with low toxicity. At present, accepted indications for immunotherapy are limited to a few cancers such as renal cell carcinoma and melanoma. This paper looks at some of the reasons for the limited impact of immunotherapy so far and suggest possible avenues for further research with a greater likelihood of success.

Standard treatments induce antigen-specific immune responses in prostate cancer

PURPOSE

Prostate tumors express antigens that are recognized by the immune system in a significant proportion of patients; however, little is known about the effect of standard treatments on tumor-specific immunity. Radiation therapy induces expression of inflammatory and immune-stimulatory molecules, and neoadjuvant hormone therapy causes prominent T-cell infiltration of prostate tumors. We therefore hypothesized that radiation therapy and hormone therapy may initiate tumor-specific immune responses.

EXPERIMENTAL DESIGN

Pretreatment and posttreatment serum samples from 73 men with nonmetastatic prostate cancer and 50 cancer-free controls were evaluated by Western blotting and SEREX (serological identification of antigens by recombinant cDNA expression cloning) antigen arrays to examine whether autoantibody responses to tumor proteins arose during the course of standard treatment.

RESULTS

Western blotting revealed the development of treatment-associated autoantibody responses in patients undergoing neoadjuvant hormone therapy (7 of 24, 29.2%), external beam radiation therapy (4 of 29, 13.8%), and brachytherapy (5 of 20, 25%), compared with 0 of 14 patients undergoing radical prostatectomy and 2 of 36 (5.6%) controls. Responses were seen within 4 to 9 months of initiation of treatment and were equally prevalent across different disease risk groups. Similarly, in the murine Shionogi tumor model, hormone therapy induced tumor-associated autoantibody responses in 5 of 10 animals. In four patients, SEREX immunoscreening of a prostate cancer cDNA expression library identified several antigens recognized by treatment-associated autoantibodies, including PARP1, ZNF707 + PTMA, CEP78, SDCCAG1, and ODF2.

CONCLUSION

We show for the first time that standard treatments induce antigen-specific immune responses in prostate cancer patients. Thus, immunologic mechanisms may contribute to clinical outcomes after hormone and radiation therapy, an effect that could potentially be exploited as a practical, personalized form of immunotherapy.

Induced sensitization of tumor stroma leads to eradication of established cancer by T cells

Targeting cancer cells, as well as the nonmalignant stromal cells cross-presenting the tumor antigen (Ag), can lead to the complete destruction of well-established solid tumors by adoptively transferred Ag-specific cytotoxic T lymphocytes (CTLs). If, however, cancer cells express only low levels of the Ag, then stromal cells are not destroyed, and the tumor escapes as Ag loss variants. We show that treating well-established tumors expressing low levels of Ag with local irradiation or a chemotherapeutic drug causes sufficient release of Ag to sensitize stromal cells for destruction by CTLs. This was shown directly using high affinity T cell receptor tetramers for visualizing the transient appearance of tumor-specific peptide–MHC complexes on stromal cells. Maximum loading of tumor stroma with cancer Ag occurred 2 d after treatment and coincided with the optimal time for T cell transfer. Under these conditions, tumor rejection was complete. These findings may set the stage for developing rational clinical protocols for combining irradiation or chemotherapy with CTL therapy.

The radiosensitizing effect of immunoadjuvant OM-174 requires cooperation between immune and tumor cells through interferon-gamma and inducible nitric oxide synthase

PURPOSE

To explore whether antitumor immunoadjuvant OM-174 can stimulate immune cells to produce interferon-gamma (IFN-gamma) and thereby radiosensitize tumor cells.

METHODS AND MATERIALS

Splenocytes from BALB/c mice were stimulated by OM-174 at plasma-achievable concentrations (0.03-3 mug/mL), and afterward analyzed for the expression and secretion of IFN-gamma by reverse transcriptase-polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. Stimulated splenocytes were used as a source of IFN-gamma to radiosensitize hypoxic EMT-6 tumor cells through the cytokine-inducible isoform of nitric oxide synthase (iNOS).

RESULTS

OM-174 activated the production of IFN-gamma at high levels that reached 70 ng/mL in normoxia (21% oxygen) and 27 ng/mL in tumor-relevant hypoxia (1% oxygen). This caused up to 2.1-fold radiosensitization of EMT-6 tumor cells, which was associated with the iNOS-mediated production of the radiosensitizing molecule nitric oxide, as confirmed by accumulation of its oxidative metabolite nitrite, Western blot analysis, and reverse transcriptase-polymerase chain reaction. Both iNOS activation and radiosensitization were counteracted by neutralizing antibodies against IFN-gamma. The same mechanism of radiosensitization through the IFN-gamma secretion pathway was identified for IL-12 + IL-18, which are known to mediate IFN-gamma responses. Hypoxia displayed a dual effect on the immune-tumor cell interaction, by downregulating the expression of the IFN-gamma gene while upregulating iNOS at transcriptional level.

CONCLUSION

Immunoadjuvant OM-174 is an efficient radiosensitizer of tumor cells through activation of the IFN-gamma secretion pathway in immune cells. This finding indicates a rationale for combining immunostimulatory and radiosensitizing strategies and extends the potential therapeutic applications of OM-174.

Update on clinical radiobiology

Radiation therapy is an important local cytotoxic modality for cancer treatment whose aim is to control the disease while minimising damage to normal tissue. The combination of different treatment modalities offers a more effective cure and reduction in normal tissue toxicity. However, the differences in genetic profiles can cause diverse treatment outcomes. Multidisciplinary research, where technologies and knowledge from different areas are integrated, is necessary to design the optimal regimen for individualised cancer treatment. This paper offers an overview of some new cancer treatment strategies; the impact of molecular imaging on radiation oncology; and a computer simulation model to optimise treatment planning based on patient information. It briefly discusses molecular targeted therapy, tumour microenvironment and bioreductive agents, and evidence for making individualised medicine a reality. Using DNA microarrays and proteomic technologies, information on defined molecular targets and genetic profiling for individual patients can be obtained and new algorithms for radiation oncology-related diagnosis, treatment response and prognosis can be developed.