Induction Of Antitumor Immune Responses Research Articles

Decreasing of primary tumor and factors associated with poor prognosis, together with anti-tumor immune response generation with a Gallotannin-rich Caesalpinia spinosa fraction in a highly metastatic murine breast cancer model.

Decreasing of primary tumor and factors associated with poor prognosis, together with anti-tumor immune response generation with a Gallotannin-rich Caesalpinia spinosa fraction in a highly metastatic murine breast cancer model.

Vγ9Vδ2-T cells as antigen presenting cells for iNKT cell based cancer immunotherapy

CD1d-restricted invariant natural killer T cells (iNKT) constitute an important immunoregulatory T-cell subset involved in the induction of antitumor immune responses. Here, we provide a view on the recent observation that Vγ9Vδ2-T cells, through trogocytosis of CD1d-containing membrane fragments, have the capacity to act as antigen presenting cells for iNKT.

Antigen delivery to CD11c+CD8- dendritic cells induces protective immune responses against experimental melanoma in mice in vivo.

Dendritic cells (DCs) are central modulators of immune responses and, therefore, interesting target cells for the induction of antitumor immune responses. Ag delivery to select DC subpopulations via targeting Abs to DC inhibitory receptor 2 (DCIR2, clone 33D1) or to DEC205 was shown to direct Ags specifically to CD11c(+)CD8(-) or CD11c(+)CD8(+) DCs, respectively, in vivo. In contrast to the increasing knowledge about the induction of immune responses by efficiently cross-presenting CD11c(+)CD8(+) DCs, little is known about the functional role of Ag-presenting CD11c(+)CD8(-) DCs with regard to the initiation of protective immune responses. In this study, we demonstrate that Ag targeting to the CD11c(+)CD8(-) DC subpopulation in the presence of stimulating anti-CD40 Ab and TLR3 ligand polyinosinic-polycytidylic acid induces protective responses against rapidly growing tumor cells in naive animals under preventive and therapeutic treatment regimens in vivo. Of note, this immunization protocol induced a mixed Th1/Th2-driven immune response, irrespective of which DC subpopulation initially presented the Ag. Our results provide important information about the role of CD11c(+)CD8(-) DCs, which have been considered to be less efficient at cross-presenting Ags, in the induction of protective antitumor immune responses.

Monocyte-derived dendritic cells are critical for the induction of anti-tumor immune responses (TUM4P.932)

Abstract The DC subsets that are required for the induction of effective anti-tumor immune responses and the success of immunotherapy are unknown. We used mouse models to compare different immune-activating agents for their impact on tumor growth, tumor-specific T cells, cytokine production and DC activation. Treatments with poly I:C or a combination of monososdium-urate crystals (MSU) + Mycobacterium smegmatis delayed growth of B16 melanoma and 4T1 mammary carcinoma tumors, whereas LPS, M. smegmatis or MSU alone were ineffective. Effective treatments required both CD8+ and NK1.1+ cells, and increased CD8+ T cell priming, tumor-infiltration by effector cells and effector cytokine production. In addition, only the successful treatments induced the appearance of a population of monocyte-derived DC in tumor-draining lymph nodes. Recent experiments revealed that immunotherapy was required for the differentiation of blood monocytes into DC in the lymph node, and that these monocyte-derived DC were both necessary and sufficient for successful immunotherapy of B16 melanoma tumors. Further experiments are required to clarify the precise function of this DC population. We conclude that the activation of existing DC subsets is not sufficient for the induction of anti-tumor immunity, whereas newly recruited inflammatory DC are critical mediators of the successful activation of anti-tumour immune responses.

Current status of cancer immunotherapy

To prove clinical benefits of cancer vaccine is currently difficult, except for one phase III trial has documented improved overall survival with the vaccine, Sipuleucel-T, although induction of anti-tumor immune responses through cancer vaccine is theoretically promising and would be straightforward. In contrast, immune checkpoint blockade with anti-CTLA4 mAb and anti-PD-1 mAb has demonstrated clear evidence of objective responses including improved overall survival and tumor shrinkage, driving renewed enthusiasm for cancer immunotherapy in multiple cancer types. In addition, there is a promising novel cancer immunotherapy, CAR therapy-a personalized treatment that involves genetically modifying a patient's T-cells to make them target tumor cells. We are now facing new era of cancer immunotherapy.

Oncolytic viruses and their application to cancer immunotherapy.

Oncolytic viruses (OV) selectively replicate and kill cancer cells and spread within the tumor, while not harming normal tissue. In addition to this direct oncolytic activity, OVs are also very effective at inducing immune responses to themselves and to the infected tumor cells. OVs encompass a broad diversity of DNA and RNA viruses that are naturally cancer selective or can be genetically engineered. OVs provide a diverse platform for immunotherapy; they act as in situ vaccines and can be armed with immunomodulatory transgenes or combined with other immunotherapies. However, the interactions of OVs with the immune system may affect therapeutic outcomes in opposing fashions: negatively by limiting virus replication and/or spread, or positively by inducing antitumor immune responses. Many aspects of the OV-tumor/host interaction are important in delineating the effectiveness of therapy: (i) innate immune responses and the degree of inflammation induced; (ii) types of virus-induced cell death; (iii) inherent tumor physiology, such as infiltrating and resident immune cells, vascularity/hypoxia, lymphatics, and stromal architecture; and (iv) tumor cell phenotype, including alterations in IFN signaling, oncogenic pathways, cell surface immune markers [MHC, costimulatory, and natural killer (NK) receptors], and the expression of immunosuppressive factors. Recent clinical trials with a variety of OVs, especially those expressing granulocyte macrophage colony-stimulating factor (GM-CSF), have demonstrated efficacy and induction of antitumor immune responses in the absence of significant toxicity. Manipulating the balance between antivirus and antitumor responses, often involving overlapping immune pathways, will be critical to the clinical success of OVs.

CD40 ligand and tdTomato-armed vaccinia virus for induction of antitumor immune response and tumor imaging

Oncolytic vaccinia virus is an attractive platform for immunotherapy. Oncolysis releases tumor antigens and provides co-stimulatory danger signals. However, arming the virus can improve efficacy further. CD40 ligand (CD40L, CD154) can induce apoptosis of tumor cells and it also triggers several immune mechanisms. One of these is a T-helper type 1 (Th1) response that leads to activation of cytotoxic T-cells and reduction of immune suppression. Therefore, we constructed an oncolytic vaccinia virus expressing hCD40L (vvdd-hCD40L-tdTomato), which in addition features a cDNA expressing the tdTomato fluorochrome for detection of virus, potentially important for biosafety evaluation. We show effective expression of functional CD40L both in vitro and in vivo. In a xenograft model of bladder carcinoma sensitive to CD40L treatment, we show that growth of tumors was significantly inhibited by the oncolysis and apoptosis following both intravenous and intratumoral administration. In a CD40-negative model, CD40L expression did not add potency to vaccinia oncolysis. Tumors treated with vvdd-mCD40L-tdtomato showed enhanced efficacy in a syngenic mouse model and induced recruitment of antigen-presenting cells and lymphocytes at the tumor site. In summary, oncolytic vaccinia virus coding for CD40L mediates multiple antitumor effects including oncolysis, apoptosis and induction of Th1 type T-cell responses.

Immunological Mechanisms of Low and Ultra-Low Dose Cancer Chemotherapy

Traditionally, anticancer chemotherapy has been generally considered to be strongly immunosuppressive. However, increasing evidence suggests that certain chemotherapeutic agents rely on the induction of antitumor immune responses, in both experimental animal models and patients with cancer. Many of these chemotherapeutic agents exert immunogenic effects via the induction and release of immunostimulatory "danger" signals from dying cancerous cells when used in low doses. New data suggests that several common chemotherapeutic agents may also display direct stimulating effects on immune cells even when applied in ultra-low concentrations (chemoimmunomodulation). Importantly, it is becoming clear that both immune effector cells and immune regulatory cells can be targeted by various chemotherapeutic agents to produce favorable antitumor immune responses. Therefore, utilizing cancer drugs to enhance host antitumor immunity should be considered a feasible therapeutic approach; and recent characterization of the immunomodulatory mechanisms of anticancer chemotherapy using both new and traditional cytotoxic agents suggests that combinations of these approaches with "classical" immunomodulatory agents could lead to a viable new therapeutic paradigm for the treatment of cancer.

Induction of Anti-Tumor Immune Responses by Peptide Receptor Radionuclide Therapy with 177Lu-DOTATATE in a Murine Model of a Human Neuroendocrine Tumor

Peptide receptor radionuclide therapy (PRRT) is a relatively new mode of internally targeted radiotherapy currently in clinical trials. In PRRT, ionizing radioisotopes conjugated to somatostatin analogues are targeted to neuroendocrine tumors (NETs) via somatostatin receptors. Despite promising clinical results, very little is known about the mechanism of tumor control. By using NCI-H727 cells in an in vivo murine xenograft model of human NETs, we showed that 177Lu-DOTATATE PRRT led to increased infiltration of CD86+ antigen presenting cells into tumor tissue. We also found that following treatment with PRRT, there was significantly increased tumor infiltration by CD49b+/FasL+ NK cells potentially capable of tumor killing. Further investigation into the immunomodulatory effects of PRRT will be essential in improving treatment efficacy.

Zinc supplementation is required for the cytotoxic and immunogenic effects of chemotherapy in chemoresistant p53-functionally deficient cells

Optimal tumor eradication often results from the death of malignant cells, as induced by chemotherapeutic agents, coupled to the induction of antitumor immune responses. However, cancer cells frequently become resistant to the cytotoxic activity of chemotherapy. The aim of the present study was to evaluate whether zinc dichloride (ZnCl2), which was known to re-establish the chemosensitivity of cancer cells by reactivating p53, promotes immunogenic instances of cell death. We found that ZnCl2, in combination with chemotherapeutic agents such as cisplatin and adriamycin (ADR), favors the apoptotic demise of chemoresistant cells, while cisplatin and ADR alone fail to do so. The co-culture of immature dendritic cells (DCs) with cancer cells succumbing to the co-administration of chemotherapy and ZnCl2 led to DC activation, as indicated by the upregulation of the activation markers CD83 and CD86. In part, such process depended on cell death, as it was limited (but not abrogated) by the pan-caspase inhibitor Z-VAD-fmk. Moreover, DC activation relied on the ZnCl2-induced exposure of calreticulin (CRT) on the surface of cancer cells, correlating with the phosphorylation of eukaryotic translation initiation factor 2α (eIF2α), a marker of endoplasmic reticulum stress. The siRNA-mediated knockdown of CRT as well as the inhibition of CRT exposure with brefeldin A strongly impaired DC maturation, indicating CRT translocation as induced by that ZnCl2 is a key event in this setting. Altogether, these results suggest that ZnCl2, has the potential to enhance the therapeutic effects of antineoplastic agents not only by improving their cytotoxic activity but also by promoting CRT exposure.

IL-18-based combinatorial adjuvants promote the intranodal production of CCL19 by NK cells and dendritic cells of cancer patients

The effective accumulation and interaction of mature dendritic cells (DCs) and naïve T cells within lymph nodes (LNs), which are driven by the CCR7-CCL19/CCL21 chemokine axis, are critical for the induction of adaptive T-cell immunity. Human natural killer (NK) cells activated by interleukin (IL)-18 exhibit a unique ‘helper’ activity in promoting productive DC-T cell interactions, inducing DC maturation and shifting DC-primed T-cell responses toward a TH1 polarization. Here, we demonstrate that such IL-18-activated ‘helper’ NK cells uniquely stimulate DCs to produce high levels of CCL19 through tumor necrosis factor α (TNFα) and interferon γ (IFNγ), a process that relies on secondary NK-cell activation by additional inflammatory signals including IFNα, IL-15, IL-12 and IL-2. DCs activated by helper NK cells not only promote the efficient CCR7-mediated recruitment of naïve CD8+ T cells, but also stimulate their expansion and expression of granzyme B. Using an ex vivo explant culture system based on LNs isolated from colorectal cancer patients, we found that CCL19 is upregulated in human tumor-associated lymphoid tissues treated with helper NK cell-stimulating factors. Our findings demonstrate the ability of 2 signal-activated helper NK cells to promote the production of the DC- and naïve/memory T cell-attracting chemokine CCL19 in LNs, and provide a rationale for the therapeutic application of IL-18-containing ‘combinatorial adjuvants’ to facilitate the induction of antitumor immune responses.

Increased Numbers of Monocyte-Derived Dendritic Cells during Successful Tumor Immunotherapy with Immune-Activating Agents

Local treatment with selected TLR ligands or bacteria such as bacillus Calmette-Guérin increases antitumor immune responses and delays tumor growth. It is thought that these treatments may act by activating tumor-associated dendritic cells (DCs), thereby supporting the induction of antitumor immune responses. However, common parameters of successful immune activation have not been identified. We used mouse models to compare treatments with different immune-activating agents for the ability to delay tumor growth, improve priming of tumor-specific T cells, and induce early cytokine production and DC activation. Treatment with polyinosinic-polycytidylic acid or a combination of monosodium urate crystals and Mycobacterium smegmatis was effective at delaying the growth of s.c. B16 melanomas, orthotopic 4T1 mammary carcinomas, and reducing 4T1 lung metastases. In contrast, LPS, monosodium urate crystals, or M. smegmatis alone had no activity. Effective treatments required both NK1.1(+) and CD8(+) cells, and resulted in increased T cell priming and the infiltration of NK cells and CD8(+) T cells in tumors. Unexpectedly, both effective and ineffective treatments increased DC numbers and the expression of costimulatory molecules in the tumor-draining lymph node. However, only effective treatments induced the rapid appearance of a population of monocyte-derived DCs in the draining lymph node, early release of IL-12p70 and IFN-γ, and low IL-10 in the serum. These results suggest that the activation of existing DC subsets is not sufficient for the induction of antitumor immune responses, whereas early induction of Th1 cytokines and monocyte-derived DCs are features of successful activation of antitumor immunity.

Injection site and regulatory T cells influence durable vaccine-induced tumor immunity to an over-expressed self tumor associated antigen

Tumor protein D52 (D52) is constitutively expressed in healthy tissues and overexpressed in multiple cancers, including (but not limited to) breast, prostate and ovarian carcinomas. Although the normal functions of D52 are unknown, it is clear that increased D52 expression levels not only stimulate cell proliferation and metastasis, but also correlate with poor prognosis in a subset of breast cancer patients. The murine orthologs of D52 (mD52) shares 86% identity with its human counterpart (hD52) and mirrors hD52 expression patterns. The forced overexpression of mD52 induces anchorage-independent growth in vitro and promotes tumor formation as well as spontaneous metastasis in vivo. We have previously reported that the intramuscular administration of recombinant mD52 elicits immune responses capable of rejecting a challenge with tumor cells and preventing spontaneous metastasis only in 50% of mice. We hypothesized that mechanisms of peripheral tolerance dampen immune responses against mD52, thus limiting the protective effects of vaccination. To test this hypothesis, mice were depleted of CD25+ regulatory T cells (Tregs) and subcutaneously immunized with mD52 prior to a tumor challenge. The subcutaneous immunization failed to induce protective antitumor immunity unless accompanied by Treg depletion, which resulted in a rate of protection of 70% as compared with <10% achieved in immunized Treg-repleted mice. The depletion of CD25+ Tregs did not inhibit the induction of immunological memory, since mice rejected a second tumor challenge administered weeks later. These data indicate that the induction of antitumor immune responses and immunologic memory by an mD52-based subcutaneous vaccination requires the depletion of CD25+ Tregs.

Requirement of Tumor-Associated Antigen-Specific CD4 + T Cells for an Efficient Dendritic Cell Vaccine in Antitumor Immunotherapy

Evaluation of: Aarntzen EH, De Vries IJ, Lesterhuis WJ et al. Targeting CD4(+) T-helper cells improves the induction of antitumor responses in dendritic cell-based vaccination. Cancer Res. 73(1), 19-29 (2012). The induction of antitumor immune responses in patients is one of the most sought-after goals in cancer treatment. The proposed clinical approach is to use autologous mature dendritic cells (DCs) loaded with class I peptides from tumor-associated antigens (TAAs), as DCs are the most efficient immune cells to generate strong and specific cytotoxic CD8(+) T-lymphocyte (CTL) responses. To optimize DC-based cancer vaccines, Aarntzen et al. evaluated the necessity to stimulate TAA-specific CD4(+) T-helper cells to reinforce antitumor CTL responses. They demonstrated that intranodal injection of DCs pulsed with class I- and II-restricted TAA epitopes increases TAA-specific CTL responses and induces better clinical responses in stage III/IV melanoma patients than the use of DCs pulsed with class I-restricted TAA epitopes alone. This study highlights the interest of concomitant stimulation of TAA-specific CD4(+) and CD8(+) T cells for DC-based antitumor immunotherapy.

Abstract 1253: Improvement of the potency of the dendritic cell-based vaccine immunotherapy through local inhibition of TGF-β in tumor-draining lymph nodes.

Abstract The dendritic cell (DC) -based vaccine immunotherapy has been a promising anti-cancer immunotherapy, but has been unable to elicit anti-tumor immune responses enough to eradicate the tumor in patients with advanced cancer. In order to develop the potent DC-based vaccine immunotherapy, it should be required to focus on the unique environment implicated in the induction of anti-tumor immune responses. Transforming growth factor-β (TGF-β), an immunosuppressive cytokine, is produced in the tumor microenvironment, and flows into tumor-draining lymph nodes (TDLs), primary priming sites for generation of anti-tumor immune responses. In TDLs, TGF-β plays a critical role in suppressing the induction of anti-tumor immune responses. In this study, we focused on TGF-β-mediated immunosuppression in TDLs, and examined whether local inhibition of TGF-β in TDLs could improve the potency of the DC-based vaccine immunotherapy in tumor-bearing mouse model. C57BL/6 mice bearing Lewis lung carcinoma (LLC1) subcutaneously were vaccinated with DCs loading LLC1-derived antigen. In order to inhibit TGF-β in TDLs, those mice were administered the plasmid DNA encoding the extracellular domain of TGF-β type II receptor fused to the human IgG heavy chain(TGFR DNA) near the established tumor intramuscularly. Soluble TGF-β type II receptor secreted from TGFR DNA-transfected cells is expected to function to attenuate TGF-β level in TDLs. After this combination therapy, anti-tumor immune responses elicited in those mice were evaluated. As results, the level of TGF-β in TDLs was decreased by administrations of TGFR DNA near the established tumor. The attenuation of TGF-β level in TDLs by TGFR DNA was able to suppress the proliferative activity of Foxp3+ regulatory T cells in TDLs. Regarding the induction of effector cells in TDLs, tumor antigen-specific CD8+ cells producing interferon-gamma were significantly increased by this combination therapy. Next, we evaluated the association between the local inhibition of TGF-β in TDLs and systemic anti-tumor immune responses. Tumor antigen-specific cytotoxic responses as well as natural killer activities were significantly enhanced through the local inhibition of TGF-β in TDLs, leading to effective suppression of tumor growth. Such potent anti-tumor immune responses were not achieved in mice that had been administered DC-based vaccine alone. Improvement of the induction of anti-tumor immune responses in TDLs by the local inhibition of TGF-β contributed to enhancement of systemic anti-tumor immune responses. In conclusion, inhibition of TGF-β-mediated immunosuppression in TDLs can enhance the potency of DC-based vaccine immunotherapy. This animal model provides for a novel rationale with DC-based vaccine immunotherapy. Citation Format: Koji Teramoto, Yasuhiko Ohshio, Takuya Fujita, Jun Hanaoka, Yataro Daigo. Improvement of the potency of the dendritic cell-based vaccine immunotherapy through local inhibition of TGF-β in tumor-draining lymph nodes. [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 1253. doi:10.1158/1538-7445.AM2013-1253

Immunotherapy for Gastrointestinal Malignancies

Gastrointestinal (GI) cancers are the most common human tumors encountered worldwide. The majority of GI cancers are unresectable at the time of diagnosis, and in the subset of patients undergoing resection, few are cured. There is only a modest improvement in survival with the addition of modalities such as chemotherapy and radiation therapy. Due to an increasing global cancer burden, it is imperative to integrate alternative strategies to improve outcomes. It is well known that cancers possess diverse strategies to evade immune detection and destruction. This has led to the incorporation of various immunotherapeutic strategies, which enable reprogramming of the immune system to allow effective recognition and killing of GI tumors. A review was conducted of the results of published clinical trials employing immunotherapy for esophageal, gastroesophageal, gastric, hepatocellular, pancreatic, and colorectal cancers. Monoclonal antibody therapy has come to the forefront in the past decade for the treatment of colorectal cancer. Immunotherapeutic successes in solid cancers such as melanoma and prostate cancer have led to the active investigation of immunotherapy for GI malignancies, with some promising results. To date, monoclonal antibody therapy is the only immunotherapy approved by the US Food and Drug Administration for GI cancers. Initial trials validating new immunotherapeutic approaches, including vaccination-based and adoptive cell therapy strategies, for GI malignancies have demonstrated safety and the induction of antitumor immune responses. Therefore, immunotherapy is at the forefront of neoadjuvant as well as adjuvant therapies for the treatment and eradication of GI malignancies.

CCL2 is critical for immunosuppression to promote cancer metastasis

We previously found that cancer metastasis is accelerated by immunosuppression during Snail-induced epithelial-to-mesenchymal transition (EMT). However, the molecular mechanism still remained unclear. Here, we demonstrate that CCL2 is a critical determinant for both tumor metastasis and immunosuppression induced by Snail(+) tumor cells. CCL2 is significantly upregulated in various human tumor cells accompanied by Snail expression induced by snail transduction or TGFβ treatment. The Snail(+) tumor-derived CCL2 amplifies EMT events in other cells including Snail(-) tumor cells and epithelial cells within tumor microenvironment. CCL2 secondarily induces Lipocalin 2 (LCN2) in the Snail(+) tumor cells in an autocrine manner. CCL2 and LCN2 cooperatively generate immunoregulatory dendritic cells (DCreg) having suppressive activity accompanied by lowered expression of costimulatory molecules such as HLA-DR but increased expression of immunosuppressive molecules such as PD-L1 in human PBMCs. The CCL2/LCN2-induced DCreg cells subsequently induce immunosuppressive CD4(+)FOXP3(+) Treg cells, and finally impair tumor-specific CTL induction. In murine established tumor model, however, CCL2 blockade utilizing the specific siRNA or neutralizing mAb significantly inhibits Snail(+) tumor growth and metastasis following systemic induction of anti-tumor immune responses in host. These results suggest that CCL2 is more than a chemoattractant factor that is the significant effector molecule responsible for immune evasion of Snail(+) tumor cells. CCL2 would be an attractive target for treatment to eliminate cancer cells via amelioration of tumor metastasis and immunosuppression.

Regulatory T-cell Modulation Using Cyclophosphamide in Vaccine Approaches: A Current Perspective

Regulatory T cells (Treg) have become an important player in regulating anticancer immune responses. In fact, published studies describe a correlation between tumor-infiltrating Tregs and poor prognosis. Once called "suppressor T cells," these T cells evaded isolation because of a lack of known markers that distinguished them from other T cells. However, the biology of these T cells is currently a major focus of immunologic research. Markers have since been discovered that identify these T cells and provide insights into how these T cells are regulated. Despite these advances, much needs to be learned about the subsets of Tregs and their specific roles in regulating immune responses. In addition, specific agents that target Tregs are currently unavailable. Cyclophosphamide has emerged as a clinically feasible agent that can suppress Tregs and allow more effective induction of antitumor immune responses. This review focuses on the use of cyclophosphamide in targeting Tregs to augment cancer vaccine approaches. However, these principles can also be applied to other immunotherapy strategies.

1099 Induction of Anti-tumor Immune Responses by Ablation of the Primary Tumor With Pulsed Electric Currents

1099 Induction of Anti-tumor Immune Responses by Ablation of the Primary Tumor With Pulsed Electric Currents

Oncolytic Viruses for Induction of Anti-Tumor Immunity

Oncolytic virotherapy is an evolving but, as yet, unrealized treatment option for cancer. This approach harnesses the cancer-restricted replicative activity of engineered viruses to achieve tumor cell kill. Tumors that are resistant to chemotherapy or radiotherapy can be susceptible to viral oncolysis because of distinct cell kill mechanisms. There is now compelling evidence that collateral induction of anti-tumor immune responses contributes substantially to viral antitumor activities. In addition to the expected anti-viral immune clearance, the "danger" signal created by virus-infected cells can generate immune co-stimulation known to override immune suppression and reverse tolerance within the tumor microenvironment. Our recent findings indicate that immune activation augments the clinical outcomes of oncolytic virotherapy. Strikingly similar and robust clinical response rates ( > 25%) were observed among advanced cancer patients following intratumoral treatments with adenoviral (AdΔ24) and herpes simplex (JS1/34.5-/47) constructs armed with an integrated granulocyte-macrophage colony-stimulating factor (GMCSF) payload. Both agents produced regressions in injected as well as distant, uninjected lesions, demonstrating systemic effectiveness. We discuss the innate and adaptive immune activating events that may contribute to these clinical outcomes, and examine systemic delivery strategies to tilt the immunological balance from viral clearance to tumor elimination.