Charlie T. Garnett

Sublethal Irradiation of Human Tumor Cells Modulates Phenotype Resulting in Enhanced Killing by Cytotoxic T Lymphocytes

Local radiation of tumor masses is an established modality for the therapy of a range of human tumors. It has recently been recognized that doses of radiation, lower than or equal to those that cause direct cytolysis, may alter the phenotype of target tissue by up-regulating gene products that may make tumor cells more susceptible to T-cell–mediated immune attack. Previously, we demonstrated that radiation increased Fas (CD95) gene expression in carcinoembryonic antigen (CEA)-expressing murine tumor cells, which consequently enhanced their susceptibility to CEA-specific CTL-mediated killing. The present study was designed to determine whether these phenomena also occur with human tumor cells. Here, 23 human carcinoma cell lines (12 colon, 7 lung, and 4 prostate) were examined for their response to nonlytic doses of radiation (10 or 20 Gy). Seventy-two hours postirradiation, changes in surface expression of Fas (CD95), as well as expression of other surface molecules involved in T-cell–mediated immune attack such as intercellular adhesion molecule 1, mucin-1, CEA, and MHC class I, were examined. Twenty-one of the 23 (91%) cell lines up-regulated one or more of these surface molecules postirradiation. Furthermore, five of five irradiated CEA+/A2+ colon tumor cells lines demonstrated significantly enhanced killing by CEA-specific HLA-A2–restricted CD8+ CTLs compared with nonirradiated counterparts. We then used microarray analysis to broaden the scope of observed changes in gene expression after radiation and found that many additional genes had been modulated. These up-regulated gene products may additionally enhance the tumor cells’ susceptibility to T-cell–mediated immune attack or serve as additional targets for immunotherapy. Overall, the results of this study suggest that nonlethal doses of radiation can be used to make human tumors more amenable to immune system recognition and attack and form the rational basis for the combinatorial use of cancer vaccines and local tumor irradiation.

Combination of Docetaxel and Recombinant Vaccine Enhances T-Cell Responses and Antitumor Activity: Effects of Docetaxel on Immune Enhancement

Purpose: Taxanes comprise some of the most widely used cancer chemotherapeutic agents. Members of this drug family, including docetaxel, are commonly used to treat breast, prostate, and lung cancers, among others. This study was designed to determine if this taxane has the ability to modulate components of the immune system independent of antitumor activity and to investigate the potential synergistic activities of the combination of docetaxel and vaccine therapy. Experimental Design: We examined the in vivo effects of docetaxel on immune-cell subsets and on the function of CD4+, CD8+, and regulatory T-cell (Treg) populations in response to antigen-specific vaccination. We also examined the antitumor effects of the combination of docetaxel and vaccine in a preclinical model in which docetaxel has no observable effect on tumor growth. Results: These studies show for the first time that (a) docetaxel modulates CD4+, CD8+, CD19+, natural killer cell, and Treg populations in non–tumor-bearing mice; (b) unlike cyclophosphamide, docetaxel does not inhibit the function of Tregs; (c) docetaxel enhances CD8+ but not CD4+ response to CD3 cross-linking; (d) docetaxel given after vaccination provides optimal enhancement of immune response to recombinant viral vaccines; (e) docetaxel combined with recombinant viral vaccine is superior to either agent alone at reducing tumor burden; and (f) docetaxel plus vaccine increases antigen-specific T-cell responses to antigen in the vaccine, as well as to cascade antigens derived from the tumor. Conclusions: These findings suggest potential clinical benefit for the combined use of docetaxel and recombinant cancer vaccines.

Multiple costimulatory modalities enhance CTL avidity

Recent studies in both animal models and clinical trials have demonstrated that the avidity of T cells is a major determinant of antitumor and antiviral immunity. In this study, we evaluated several different vaccine strategies for their ability to enhance both the quantity and avidity of CTL responses. CD8+ T cell quantity was measured by tetramer binding precursor frequency, and avidity was measured by both tetramer dissociation and quantitative cytolytic function. We have evaluated a peptide, a viral vector expressing the Ag transgene alone, with one costimulatory molecule (B7-1), and with three costimulatory molecules (B7-1, ICAM-1, and LFA-3), with anti-CTLA-4 mAb, with GM-CSF, and combinations of the above. We have evaluated these strategies in both a foreign Ag model using β-galactosidase as immunogen, and in a “self” Ag model, using carcinoembryonic Ag as immunogen in carcinoembryonic Ag transgenic mice. The combined use of several of these strategies was shown to enhance not only the quantity, but, to a greater magnitude, the avidity of T cells generated; a combination strategy is also shown to enhance antitumor effects. The results reported in this study thus demonstrate multiple strategies that can be used in both antitumor and antiviral vaccine settings to generate higher avidity host T cell responses.

Combination Chemotherapy and Radiation of Human Squamous Cell Carcinoma of the Head and Neck Augments CTL-Mediated Lysis

Purpose: The combination of systemic multiagent chemotherapy (5-fluorouracil + cisplatin) and tumor irradiation is standard of care for head and neck squamous cell carcinoma (HNSCC). Furthermore, it has been shown that sublethal doses of radiation or chemotherapeutic drugs in diverse cancer types may alter the phenotype or biology of neoplastic cells, making them more susceptible to CTL-mediated cytotoxicity. However, little is known about the potential synergistic effect of drug plus radiation on CTL killing. Here, we examined whether the combination of two chemotherapeutics and ionizing radiation enhanced CTL-mediated destruction of HNSCC more so than either modality separately, as well as the basis for the enhanced tumor cell lysis. Experimental Design: Several HNSCC cell lines with distinct biological features were treated with sublethal doses of cisplatin and 5-fluorouracil for 24 hours and with 10-Gy irradiation. Seventy-two hours postirradiation, tumor cells were exposed to an antigen-specific CD8+ CTL directed against carcinoembryonic antigen or MUC-1. Results: In three of three tumor cell lines tested, enhanced CTL activity was observed when the two modalities (chemotherapy and radiation) were combined as compared with target cells exposed to either modality separately. CTL-mediated lysis was MHC restricted and antigen specific and occurred almost entirely via the perforin pathway. Moreover, the combination treatment regimen led to a 50% reduction in Bcl-2 expression whereas single modality treatment had little bearing on the expression of this antiapoptotic gene. Conclusions: Overall, these results reveal that (a) CTL killing can be enhanced by combining multiagent chemotherapy and radiation and (b) combination treatment enhanced or sensitized HNSCC to the perforin pathway, perhaps by down-regulating Bcl-2 expression. These studies thus form the rational basis for clinical trials of immunotherapy concomitant with the current standard of care of HNSCC.

Synergistic antitumor activity of immune strategies combined with radiation.

Since its discovery more than a hundred years ago, radiation has been used to treat cancer. In recent decades, advances in radiation technology have expanded the role and value of radiation in imaging and treating many forms of cancer. Currently, there is a growing interest in combining radiation with other modalities, such as immunotherapy, to treat a broad range of malignancies. This article reviews the use of standard and novel combinations of radiation therapy and immunotherapy to eradicate tumor cells. The combination of radiation therapy and immunotherapy holds particular promise as a strategy for cancer therapeutics for a variety of reasons. First, there is evidence that immunotherapy is most beneficial when employed early in the disease process and in combination with standard therapies. In addition, 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. Finally, 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 cross-priming and presentation of tumor antigens to the immune system, thereby potentiating antitumor responses.

Intratumoral delivery of vector mediated IL-2 in combination with vaccine results in enhanced T cell avidity and anti-tumor activity

Systemic IL-2 is currently employed in the therapy of several tumor types, but at the price of often severe toxicities. Local vector mediated delivery of IL-2 at the tumor site may enhance local effector cell activity while reducing toxicity. To examine this, a model using CEA-transgenic mice bearing established CEA expressing tumors was employed. The vaccine regimen was a s.c. prime vaccination with recombinant vaccinia (rV) expressing transgenes for CEA and a triad of costimulatory molecules (TRICOM) followed by i.t. boosting with rF-CEA/TRICOM. The addition of intratumoral (i.t.) delivery of IL-2 via a recombinant fowlpox (rF) IL-2 vector greatly enhanced anti-tumor activity of a recombinant vaccine, resulting in complete tumor regression in 70–80% of mice. The anti-tumor activity was shown to be dependent on CD8+ cells and NK1.1+. Cellular immune assays revealed that the addition of rF-IL-2 to the vaccination therapy enhanced CEA-specific tetramer+ cell numbers, cytokine release and CTL lysis of CEA+ targets. Moreover, tumor-bearing mice vaccinated with the CEA/TRICOM displayed an antigen cascade, i.e., CD8+ T cell responses to two other antigens expressed on the tumor and not the vaccine: wild-type p53 and endogenous retroviral antigen gp70. Mice receiving rF-IL-2 during vaccination demonstrated higher avidity CEA-specific, as well as higher avidity gp70-specific, CD8+ T cells when compared with mice vaccinated without rF-IL-2. These studies demonstrate for the first time that the level and avidity of antigen specific CTL, as well as the therapeutic outcome can be improved with the use of i.t. rF-IL-2 with vaccine regimens.

Abstract 1676: Chemotherapy-induced immunogenic modulation of tumor cells enhances killing by cytotoxic T lymphocytes and is distinct from immunogenic cell death.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Certain chemotherapeutic regimens trigger cancer cell death while inducing dendritic cell maturation and subsequent immune responses. However, chemotherapy-induced immunogenic cell death (ICD) has thus far been restricted to select agents. In contrast, several chemotherapeutic drugs modulate antitumor immune responses, despite not inducing classic ICD. In addition, in many cases tumor cells do not die after treatment. Here, using docetaxel, one of the most widely used cancer chemotherapeutic agents, as a model, we examined phenotypic and functional consequences of tumor cells that do not die from immunogenic cell death. Docetaxel treatment of tumor cells did not induce ATP or HMGB1 secretion, or cell death. However, calreticulin exposure was observed in all cell lines examined after chemotherapy treatment. Killing by CEA, MUC-1, or PSA-specific CD8+ CTLs was significantly enhanced after docetaxel treatment. This killing was associated with increases in components of antigen-processing machinery, and mediated largely by calreticulin membrane translocation, as determined by functional knockdown of calreticulin, PERK, or calreticulin-blocking peptide. A docetaxel-resistant cell line was selected (MDR-1+, CD133+) by continuous exposure to docetaxel. These cells, while resistant to direct cytostatic effects of docetaxel, were not resistant to the chemomodulatory effects that resulted in enhancement of CTL killing. Here, we provide an operational definition of “immunogenic modulation,” where exposure of tumor cells to nonlethal/sublethal doses of chemotherapy alters tumor phenotype to render the tumor more sensitive to CTL killing. These observations are distinct and complementary to immunogenic cell death and highlight a mechanism whereby chemotherapy can be used in combination with immunotherapy. Citation Format: James W. Hodge, Charlie T. Garnett, Benedetto Farsaci, Claudia Palena, Kwong-Yok Tsang, Soldano Ferrone, Sofia R. Gameiro. Chemotherapy-induced immunogenic modulation of tumor cells enhances killing by cytotoxic T lymphocytes and is distinct from immunogenic cell death. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1676. doi:10.1158/1538-7445.AM2013-1676