Immunologic approaches to the treatment of human cancer based on a guinea pig model

Summary Local immunotherapy is a form of cancer treatment where exogenous antigen is introduced into the area of the tumor. Under favorable circumstances, the perfused tumor regresses, systemic tumor-specific transplantation immunity is augmented, and distant microscopic metastases regress. Successful local immunotherapy requires an immunologically competent host, small tumor burden, and tumor located usually in the skin. A wide variety of biologic agents are capable of promoting local immunotherapy. BCG has been most widely studied. The antitumor activity of two different preparations of the Tice substrain of BCG were compared. No significant differences in antitumor activity were found. Alternative approaches to intralesional injection were sought. Intradermal injection of BCG adjacent to dermal tumors, prior to surgery, led to eradication of axillary metastases and to the development of tumor-specific transplantation immunity.Successful local BCG immunotherapy is a by-product of the host response to BCG infection. Involved are lymphocytes specifically sensitized to mycobacterial antigens, lymphocyte mediators, and macrophages which develop the capacity to kill tumor cells. Tumor-cell killing may be mediated by exocytosis of macrophage lysosomes into tumor cells. Complete and permanent tumor eradication probably requires the development of tumor-specific transplantation immunity mediated by sensitized lymphocytes. Local infection of the tumor may augment the development of this tumor-specific immunity.     

Preexisting antitumor immunity augments the antitumor effects of chemotherapy

Efficacy of cancer chemotherapy is generally believed to be the result of direct drug killing of tumor cells. However, increased tumor cell killing does not always lead to improved efficacy. Herein, we demonstrate that the status of antitumor immunity at the time of chemotherapy treatment is a critical factor affecting the therapeutic outcome in that tumor-bearing mice that possess preexisting antitumor immunity respond to chemotherapy much better than those that do not. Enhancing antitumor immunity before or at the time of chemotherapy-induced antigen release increases subsequent response to chemotherapy significantly. By in vitro and in vivo measurements of antitumor immunity, we found a close correlation between the intensity of antitumor immunity activated by chemotherapy and the efficacy of treatment. Immune intervention with interleukin-12 during the early phase of chemotherapy-induced immune activation greatly amplifies the antitumor response, often resulting in complete tumor eradication not only at the chemo-treated local site, but also systemically. These findings provide additional evidence for an immune-mediated antitumor response to chemotherapy. Further, our results show that timely immune modification of chemotherapy-activated antitumor immunity can result in enhanced antitumor-immune response and complete tumor eradication.     

Activation of dendritic cells that cross-present tumor-derived antigen licenses CD8+ CTL to cause tumor eradication

The fate of naive CD8(+) T cells is determined by the environment in which they encounter MHC class I presented peptide Ags. The manner in which tumor Ags are presented is a longstanding matter of debate. Ag presentation might be mediated by tumor cells in tumor draining lymph nodes or via cross-presentation by professional APC. Either pathway is insufficient to elicit protective antitumor immunity. We now demonstrate using a syngeneic mouse tumor model, expressing an Ag derived from the early region 1A of human adenovirus type 5, that the inadequate nature of the antitumor CTL response is not due to direct Ag presentation by the tumor cells, but results from presentation of tumor-derived Ag by nonactivated CD11c(+) APC. Although this event results in division of naive CTL in tumor draining lymph nodes, it does not establish a productive immune response. Treatment of tumor-bearing mice with dendritic cell-stimulating agonistic anti-CD40 mAb resulted in systemic efflux of CTL with robust effector function capable to eradicate established tumors. For efficacy of anti-CD40 treatment, CD40 ligation of host APC is required because adoptive transfer of CD40-proficient tumor-specific TCR transgenic CTL into CD40-deficient tumor-bearing mice did not lead to productive antitumor immunity after CD40 triggering in vivo. CpG and detoxified LPS (MPL) acted similarly as agonistic anti-CD40 mAb with respect to CD8(+) CTL efflux and tumor eradication. Together these results indicate that dendritic cells, depending on their activation state, orchestrate the outcome of CTL-mediated immunity against tumors, leading either to an ineffective immune response or potent antitumor immunity.     

Spontaneous elicitation of potent antitumor immunity and eradication of established tumors by administration of DNA encoding soluble transforming growth factor-β II receptor without active antigen-sensitization

Since immunity is generally suppressed by immunoregulatory factors, such as transforming growth factor-beta (TGF-β), interleukin (IL)-10, and vascular endothelial growth factor (VEGF), produced by tumor cells or stromal cells surrounding tumor cells, various kinds of cancer immunotherapy mostly fail to elicit potent antitumor immunity. Herein, we tested whether neutralization of TGF-β can elicit strong antitumor immune responses and tumor regression in tumor-bearing mice. A plasmid DNA, pcDNA-sTGFβR/huIg, encoding a fusion protein consisting of the extracellular domain of TGF-β type II receptor (TGFβRII) and the Fc portion of human IgG heavy chain, was injected through different routes into B6 mice carrying established tumors of E.G7 cells, which consist of the poorly immunogenic tumor cells EL4, transfected with the ovalbumin (OVA) gene. The frequency of OVA-specific cytotoxic T lymphocytes (CTL), in the treated mice. increased resulting in the tumor eradication and relapse-free survival in around 70% of the E.G7-bearing mice. In contrast, administration of mock DNA into E.G7-bearing mice did not elicit tumor-specific immune responses. Therefore, administration of DNA encoding TGFβRII allowed tumor-bearing hosts to elicit sufficiently potent antitumor immune responses without requirement of further active antigen-immunization. This strategy seems to be applicable to clinical therapy against cancer, because it is low-cost, safe, and easy to manipulate.     

Characterization of defective CD4-CD8- T cells in murine tumors generated independent of antigen specificity

Immune-based therapy confers limited benefits to hosts bearing late-stage tumors. Mounting evidence points to local suppression of T cell function as the most substantial barrier to effective antitumor immunity in hosts with large tumor burdens. Despite this, events responsible for locally defective T cells and immune suppression in tumors remain unclear. We describe in this study a predominant T cell population localized within two murine tumors that is characterized by expression of apoptotic markers and TCRalphabeta/CD3, but not CD4, CD8, or NK-associated markers. These defective cells resembled double negative (DN) T cells in lpr mice, harbored defects in the expression of T cell signaling molecules, and produced the anti-inflammatory cytokine, IL-10. Conditions known to increase or decrease the accumulation of lpr DN T cells had corresponding effects on local DN tumor infiltrating lymphocyte (TIL) levels and inversely impacted host survival. Adoptive transfer into s.c. tumors demonstrated that naive CD8(+) T cells were highly susceptible to becoming DN TIL, and local supplementation of tumors with nontumor Ag-bearing MHC class I-expressing fibroblasts decreased both this susceptibility and endogenous DN TIL levels. These findings identify a major defective T cell population with suppressive potential within tumors. The data also suggest that local T cell defectiveness is controlled by the tumor environment independent of cognate Ag specificity per se. Decreasing defective DN TIL levels by increasing noncognate peptide MHC class I availability, or modulating TCR or cytokine signaling may facilitate host survival by bolstering endogenous immunity to late-stage tumors, and may help improve therapeutic tumor vaccines.     

Elimination of Metastatic Melanoma Using Gold Nanoshell-Enabled Photothermal Therapy and Adoptive T Cell Transfer

Ablative treatments such as photothermal therapy (PTT) are attractive anticancer strategies because they debulk accessible tumor sites while simultaneously priming antitumor immune responses. However, the immune response following thermal ablation is often insufficient to treat metastatic disease. Here we demonstrate that PTT induces the expression of proinflammatory cytokines and chemokines and promotes the maturation of dendritic cells within tumor-draining lymph nodes, thereby priming antitumor T cell responses. Unexpectedly, however, these immunomodulatory effects were not beneficial to overall antitumor immunity. We found that PTT promoted the infiltration of secondary tumor sites by CD11b⁺Ly-6G/C⁺ myeloid-derived suppressor cells, consequently failing to slow the growth of poorly immunogenic B16-F10 tumors and enhancing the growth of distant lung metastases. To exploit the beneficial effects of PTT activity against local tumors and on antitumor immunity whilst avoiding the adverse consequences, we adoptively transferred gp100-specific pmel T cells following PTT. The combination of local control by PTT and systemic antitumor immune reactivity provided by adoptively transferred T cells prevented primary tumor recurrence post-ablation, inhibited tumor growth at distant sites, and abrogated the outgrowth of lung metastases. Hence, the combination of PTT and systemic immunotherapy prevented the adverse effects of PTT on metastatic tumor growth and optimized overall tumor control.     

Purification of immunoprotective tumor antigens by preparative isotachophoresis

Following inoculation with 1 X 10(6) MOPC-315 tumor cells, a single injection of a very low dose of melphalan (L-PAM, L-phenylalanine mustard), 0.75 mg/kg, cured most of the mice bearing a day 11 large primary tumor (20 mm) and metastases, but failed to cure mice bearing a day 4 nonpalpable tumor. Treatment of mice bearing a nonpalpable tumor with the very low dose of drug compromised the ability of the mice to respond effectively to the same low dose of drug when the tumor became large (day 12). However, a nonpalpable tumor could be eradicated by treatment of tumor bearers with a low dose of L-PAM, if it was present concomitantly with a large tumor on the contralateral side. A high dose of L-PAM, 15 mg/kg, cured mice bearing either a nonpalpable or a large tumor. The eradication of the tumor induced by the high dose of L-PAM appeared to be due solely to the tumoricidal effect of the drug. On the other hand, the eradication of the tumor by the low dose of L-PAM also required the participation of antitumor immunity of the host, since subsequent injection of antithymocyte serum abrogated the curative effect of the drug in most mice. Mice cured by a high dose of L-PAM were not resistant to subsequent lethal tumor challenge. In contrast, mice cured by the low dose of L-PAM were able to reject a tumor challenge of 300 times the minimal lethal tumor dose. The results obtained with L-PAM therapy are similar to the results that we had previously reported with cyclophosphamide therapy. Thus, the timing of therapy with a low dose of drug for mice bearing a MOPC-315 tumor is critical for successful therapy. Moreover, the selection of a low dose rather than a high dose of drug to eradicate a large tumor offers the advantage that it results in long-lasting potent antitumor immunity as a consequence of the participation of host antitumor immunity in the eradication of the tumor.     

Host B7-1 and B7-2 costimulatory molecules contribute to the eradication of B7-1-transfected P815 tumor cells via a CD8+ T cell-dependent mechanism

B7-1 (CD80)-transfected P815 tumor cells were previously shown to elicit tumor-eradicating immunity that leads to the regression of B7-1+ P815 tumors after transient growth in normal syngeneic (DBA/2) mice. Here, we show that not only the B7-1 molecule but also the B7-2 (CD86) molecule contributed to the eradication of B7-1+ P815 tumors. The B7-1 molecule that contributed to the eradication of B7-1+ P815 tumors was expressed not only on the tumor cells but also on host APCs, including MAC-1+ cells. The B7-2 molecule that contributed to the eradication of B7-1+ P815 tumors was expressed only on host APCs, such as B220+ cells, and not on the tumor cells. In spite of the fact that B7-expressing host APCs contributed to the eradication of B7-1+ P815 tumors, only CD8+ T cells without help from CD4+ T cells were important for tumor eradication. Taken together, these findings indicate that in addition to the ability of B7-1-transfected tumor cells to stimulate CD8+ T cell-mediated tumor-eradicating immunity directly, such tumor cells can also stimulate CD8+ T cell-mediated tumor-eradicating immunity indirectly as a result of cross-priming through B7-expressing host APCs.     

Combinational adenovirus-mediated gene therapy and dendritic cell vaccine in combating well-established tumors

Recent developments in tumor immunology and biotechnology have made cancer gene therapy and immunotherapy feasible. The current efforts for cancer gene therapy mainly focus on using immunogenes, chemogenes and tumor suppressor genes. Central to all these therapies is the development of efficient vectors for gene therapy. By far, adenovirus （AdV）-mediated gene therapy is one of the most promising approaches, as has confirmed by studies relating to animal tumor models and clinical trials. Dendritic cells （DCs） are highly efficient, specialized antigen-presenting cells, and DC- based tumor vaccines are regarded as having much potential in cancer immunotherapy. Vaccination with DCs pulsed with tumor peptides, lysates, or RNA, or loaded with apoptotic/necrotic tumor cells, or engineered to express certain cytokines or chemokines could induce significant antitumor cytotoxic T lymphocyte （CTL） responses and antitumor immunity. Although both AdV-mediated gene therapy and DC vaccine can both stimulate antitumor immune responses, their therapeutic efficiency has been limited to generation of prophylactic antitumor immunity against re-challenge with the parental tumor cells or to growth inhibition of small tumors. However, this approach has been unsuccessful in combating well-established tumors in animal models. Therefore, a major strategic goal of current cancer immunotherapy has become the development of novel therapeutic strategies that can combat well-established tumors, thus resembling real clinical practice since a good proportion of cancer patients generally present with significant disease. In this paper, we review the recent progress in AdV-mediated cancer gene therapy and DC-based cancer vaccines, and discuss combined immunotherapy including gene therapy and DC vaccines. We underscore the fact that combined therapy may have some advantages in combating well-established tumors vis-a-vis either modality administered as a monotherapy.     

Treatment of disseminated leukemia with cyclophosphamide and immune cells: tumor immunity reflects long-term persistence of tumor-specific donor T cells

B6 mice bearing disseminated syngeneic FBL leukemia can be cured by treatment on day 5 with 180 mg/kg cyclophosphamide and 2 x 10(7) adoptively transferred syngeneic immune spleen cells. Complete tumor eradication in this model requires more than 30 days and is dependent upon the transfer of specifically immune T cells. To evaluate the relative contributions of host and donor T cells to tumor elimination and the maintenance of tumor immunity, donor cells obtained from Thy congenic mice were used for adoptive transfer. Thus, host and donor T cells could be readily distinguished by the expression of either Thy-1.2 or Thy-1.1 antigen. The results demonstrated that the majority of immunologically competent T cells present in hosts cured by adoptive therapy were of host origin. A small population of donor T cells, however, persisted long after transfer. At day 60, a time point shortly after tumor eradication had been completed, 5% of splenic T cells were of donor origin, and by day 120 this percentage had decreased to less than 2%. Functional studies performed at both time points revealed that this small number of residual donor T cells contained the subpopulation of tumor-reactive T cells present in the host. Thus, host T cells did not make a substantial contribution to the expression of the anti-tumor response and presumably have little role in either tumor eradication or the long-term maintenance of tumor immunity.     

Induction of antitumor immunity after cure of pulmonary metastases, using staphylococcal enterotoxin B and bispecific antibody

The combination of staphylococcal enterotoxin B (SEB) and anti-p97 x anti-CD3 bispecific antibody (bsAb) cures 60%-80% of mice with established pulmonary metastases of the syngeneic p97+ murine melanoma, CL62. We investigated the ability of cured mice to generate protective antitumor immunity. In tumor rechallenge experiments, CL62-cured mice developed protective immunity against rechallenge with CL62. The majority of mice also rejected the p97-negative parental cell line, K1735, indicating an immune response to tumor antigens common to both cell lines that were not bsAb-targeted. A significant humoral response developed against p97 antigen, but not against other antigens common to both CL62 and K1735. That the majority of cured mice nevertheless rejected K1735 suggests that tumor immunity is not antibody-dependent. Evidence of cellular immunity was obtained from the results of delayed-type hypersensitivity, proliferation and cytotoxicity assays, which revealed the presence of tumor-specific memory in bsAb-treated, CL62-cured mice. CD8+ T cells from cured, but not control mice were able to lyse tumor; however, memory CD4 cells had no cytolytic function. In vivo, however, both CD4 and CD8 T cells were required for effective protective immunity. These studies demonstrate that treatment with SEB and bsAb not only confers passive immune effects of tumor eradication, but also actively promotes the generation of a host antitumor immune response.     

Vesicular stomatitis virus sensitizes immunologically cold tumors to checkpoint blockade by inducing pyroptosis

BackgroundTraditionally, vesicular stomatitis virus (VSV) and other oncolytic viruses (OVs) are thought to kill tumors by inducing apoptosis. However, cell apoptosis leads to immune quiescence, which is incompatible with the ability of OVs to activate the antitumor immune microenvironment. Thus, studying OVs-mediated oncolytic mechanisms is of great importance for the clinical application of OVs.MethodsWe examined the pyroptosis in tumor cells and tissues by morphological observation, Lactate Dehydrogenase (LDH) assay, frozen section observation, and western-blotting techniques. The critical role of GSDME in VSV-induced pyroptosis was confirmed by CRISPR/Cas9 technique. VSV virotherapy-recruited cytotoxic lymphocytes in the tumors were examined by flow cytometry assay. VSV-activated antitumor immunity was further enhanced by the co-administration with anti-PD-1 antibody.ResultsHere, we observed that VSV was able to trigger tumor pyroptosis through Gasdermin E (GSDME) in tumor cells, human tumor samples, and tumor-bearing mouse models. Importantly, the effectiveness of VSV-based virotherapy is highly dependent on GSDME, as depletion of GSDME not only reverses VSV-induced tumor-suppressive effects but also diminishes the ability of VSV to activate antitumor immunity. Notably, VSV treatment makes immunologically ‘cold’ tumors more sensitive to checkpoint blockade.ConclusionsOncolytic VSV induces tumor cell pyroptosis by activating GSDME. GSDME is critical in recruiting cytotoxic T lymphocytes in the context of VSV therapy, which can switch immunologically ‘cold’ tumors into ‘hot’ and enhance immune checkpoint therapy efficacy.     

Combined alpha tumor necrosis factor gene therapy and engineered dendritic cell vaccine in combating well-established tumors

BACKGROUND: Although current immunotherapeutic strategies including adenovirus (AdV)-mediated gene therapy and dendritic cell (DC) vaccine can all stimulate antitumor cytotoxic T lymphocyte (CLT) responses, their therapeutic efficiency has still been limited to generation of prophylactic antitumor immunity against re-challenge with the parental tumor cells or growth inhibition of small tumors in vivo. However, it is the well-established tumors in animal models that mimic clinical patients with existing tumor burdens. Alpha tumor necrosis factor (TNF-alpha) is a multifunctional and immunoregulatory cytokine that induces antitumor activity and activates immune cells such as DCs and T cells. We hypothesized that a combined immunotherapy including gene therapy and DC vaccine would have some advantages over each modality administered as a monotherapy. METHODS: We investigated the antitumor immunotherapeutic efficiency of gene therapy by intratumoral injection of AdVTNF-alpha and DC vaccine using subcutaneous injection of TNF-alpha-gene-engineered DC(TNF-alpha) cells, and further developed a combined AdV-mediated TNF-alpha-gene therapy and TNF-alpha-gene-engineered DC(TNF-alpha) vaccine in combating well-established MO4 tumors expressing the ovalbumin (OVA) gene in an animal model. RESULTS: Our data show that vaccination of DC(TNF-alpha) cells pulsed with the OVA I peptide can (i) stimulate type 1 immune response with enhanced antitumor CTL activities, (ii) induce protective immunity against challenge of 5 x 10(5) MO4 tumor cells, and (iii) reduce growth of the small (3-4 mm in diameter), but not large, established MO4 tumors (6-8 mm in diameter). Our data also show that AdVTNF-alpha-mediated gene therapy can completely eradicate small tumors in 6 out of 8 (75%) mice due to the extensive tumor necrosis formation, but not the large tumors (0%). Interestingly, a combined AdVTNF-alpha-mediated gene therapy and TNF-alpha-gene-engineered DC(TNF-alpha) vaccine is able to cure 3 out of 8 (38%) mice bearing large MO4 tumors, indicating that the combined immunotherapy strategy is much more efficient in combating well-established tumors than monotherapy of either gene therapy or DC vaccine alone. CONCLUSIONS: This novel combined immunotherapy may become a tool of considerable conceptual interest in the implementation of future clinical objectives.     

Virology- and immunology-based gene therapy for cancer

Current strategies for cancer gene therapy consist mainly of direct inhibition of tumor cell growth and activation of systemic host defense mechanisms. Conventional chemotherapy and radiotherapy, even considered to be temporally suppressing tumor growth, suppress immune responses; therefore, we examined potential clinical feasibility of virus-mediated tumor destruction, which can rather enhance immunity. We showed that human tumors were more susceptible to adenoviruses (Ad) in which the E1A expression was controlled by a putative tumor promoter than normal cells, and that a replication of the Ad was greater in tumor cells than in normal cells. We also demonstrated that the intratumoral injection of the Ad bearing a tumor promoter inhibited the subsequent tumor growth in vivo. The E1A expression was detected in the tumors injected with the Ad but not in non-tumorous tissues of the same mice. The Ad modified to show the regulated E1A expression is thereby oncolytic in nature. Antitumor immune responses are initiated after the acquisition of putative tumor antigen(s) by dendritic cells (DCs); therefore, enhanced antigen presentation is a crucial step for the early phase of cell-mediated immunity. Destruction of tumors can release the tumor antigens and DCs come to recognize them thereafter. We found that the stimulation of Fas expressed on DCs with Fas ligand (FasL) did not induce apoptosis of DCs but rather enhanced the antigen presentation. Activation of DCs induced production of a number of cytokines, and we showed that the interleukin-12 family secreted from tumors could induce systemic antitumor immunity. We presume that the administration of oncolytic Ad, which can destroy local tumors and subsequently make the putative tumor antigen(s) released from the tumors, stimulation of DCs with the Fas/FasL signal pathway and secretion of DCs-derived cytokines coordinately produce synergistic antitumor effects and that a combinatory application of these procedures can be a possible therapeutic strategy for cancer treatment.This article is a symposium paper from the Annual Meeting of the “International Society for Cell and Gene Therapy of Cancer” held in Shenzhen, China, on 9–11 December 2005.     

Cytokine-gene-modified tumor vaccination intensified by a streptococcal preparation OK-432

Vaccinations with tumor cells engineered to express certain cytokines have been demonstrated to induce potent and specific antitumor immunity. In our previous report, we carried out a comparative study on the ability of cytokine-gene-modified tumor vaccines to induce host immune responses, and found that irradiated tumor cells, genetically modified to secrete granulocyte/macrophagecolony-stimulating factor (GM-CSF tumor vaccine), were the most potent stimulators of systemic antitumor immunity. In this report, using the experimental tumor models in which the GM-CSF tumor vaccine was less effective in immunopotentiation, we found that the combined use of a biological response modifier (BRM) OK-432 remarkably enhanced the antitumor activity induced by the GM-CSF tumor vaccine. These data indicate the possible role of a BRM such as OK-432 to intensify further the specific tumor vaccination therapy.     

Antitumor immunity and cellular cancer therapies

The identification of tumor specific antigens has provided important advance in tumor immunology. It is now established that specific cytotoxic T lymphocytes (CTL) and natural killer cells infiltrate tumor tissues and are effector cells able to control tumor growth. However, such a natural antitumor immunity has limited effects in cancer patients. Failure of host defenses against tumor is consecutive to several mechanisms which are becoming targets to design new immunotherapeutic approaches. CTL are critical components of the immune response to human tumors and induction of strong CTL responses is the goal of most current vaccine strategies. Effectiveness of cytokine therapy, cancer vaccines and injection of cells improving cellular immunity have been established in tumor grafted murine models. Clinical trials are underway. To day, interest is particularly focused on cell therapy: injected cells are either "ready to use" effector cells (lymphocytes) or antigen presenting cells able to induce a protective immune reaction in vivo (dendritic cells). The challenge ahead lie in the careful optimization of the most promising strategies in clinical situation.     

Monitoring photodynamic therapy of solid tumors online by BOLD-contrast MRI

Antivascular photodynamic therapy (PDT) of tumors with palladium-bacteriopheophorbide (TOOKAD) relies on in situ photosensitization of the circulating drug by local generation of cytotoxic reactive oxygen species, which leads to rapid vascular occlusion, stasis, necrosis and tumor eradication. Intravascular production of reactive oxygen species is associated with photoconsumption of O(2) and consequent evolution of paramagnetic deoxyhemoglobin. In this study we evaluate the use of blood oxygenation level-dependent (BOLD) contrast magnetic resonance imaging (MRI) for real-time monitoring of PDT efficacy. Using a solid tumor model, we show that TOOKAD-PDT generates appreciable attenuation (25-40%) of the magnetic resonance signal, solely at the illuminated tumor site. This phenomenon is independent of, though augmented by, ensuing changes in blood flow. These results were validated by immunohistochemistry and intravital microscopy. The concept of photosensitized BOLD-contrast MRI may have intraoperative applications in interactive guidance and monitoring of antivascular cancer therapy, PDT treatment of macular degeneration, interventional cardiology and possibly other biomedical disciplines.     

The deubiquitinase OTUD1 enhances iron transport and potentiates host antitumor immunity

Although iron is required for cell proliferation, iron‐dependent programmed cell death serves as a critical barrier to tumor growth and metastasis. Emerging evidence suggests that iron‐mediated lipid oxidation also facilitates immune eradication of cancer. However, the regulatory mechanisms of iron metabolism in cancer remain unclear. Here we identify OTUD1 as the deubiquitinase of iron‐responsive element‐binding protein 2 (IREB2), selectively reduced in colorectal cancer. Clinically, downregulation of OTUD1 is highly correlated with poor outcome of cancer. Mechanistically, OTUD1 promotes transferrin receptor protein 1 (TFRC)‐mediated iron transportation through deubiquitinating and stabilizing IREB2, leading to increased ROS generation and ferroptosis. Moreover, the presence of OTUD1 promotes the release of damage‐associated molecular patterns (DAMPs), which in turn recruits the leukocytes and strengthens host immune response. Reciprocally, depletion of OTUD1 limits tumor‐reactive T‐cell accumulation and exacerbates colon cancer progression. Our data demonstrate that OTUD1 plays a stimulatory role in iron transportation and highlight the importance of OTUD1‐IREB2‐TFRC signaling axis in host antitumor immunity.     

Therapeutic efficacy of tumor-targeted IL2 in LTα−/− mice depends on conditioned T cells

An effective immunological eradication of tumors by the adaptive immune system depends on T cell priming, expansion of specific T cells and their effector function. It has been shown that either step may be impaired in the tumor-bearing host, and several strategies have been used to improve antitumor immune responses. In this regard, tumor-targeted IL2 therapy leads to the destruction of established melanoma metastases in fully immune competent mice as previously demonstrated. This effect has been attributed, but never directly confirmed, to the boost of antigen-experienced T cells. To this end, we demonstrate the absence of any antitumor effect of targeted IL2 in mice characterized by an impaired priming of T cell responses. Notably, in these animals tumor-targeted IL2 therapy induced tumor regression only after adoptive transfer of tumor-conditioned splenocytes. A detailed analysis revealed that T cells present within the transferred splenocytes were actively participating in the immune response as these were clonally expanded after targeted IL2 therapy. In summary, we demonstrate here that in LTα^−/− mice lacking sufficient numbers of tumor-specific T cells only the passive transfer of such cells prior to therapy restores the efficacy of tumor-targeted IL2 therapy. Thus, the antitumor effect of tumor-targeted IL2 is indeed based on the boost of pre-existing T cell responses.     

Immune checkpoint blockade opens a new way to cancer immunotherapy

Among the main promising systems to triggering therapeutic antitumor immunity is the blockade of immune checkpoints. Immune checkpoint pathways regulate the control and eradication of infections, malignancies, and resistance against a host of autoantigens. Initiation point of the immune response is T cells, which have a critical role in this pathway. As several immune checkpoints are initiated by ligand–receptor interactions, they can be freely blocked by antibodies or modulated by recombinant forms of ligands or receptors. Antibodies against cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) were the first immunotherapeutics that achieved the US Food and Drug Administration approval. Preliminary clinical results with the blockers of additional immune checkpoint proteins, such as programmed cell death protein 1 (PD-1) indicate extensive and different chances to boost antitumor immunity with the objective of conferring permanent clinical effects. This study provides an overview of the immune checkpoint pathways, including CTLA-4, PD-1, lymphocyte activation gene 3, T-cell immunoglobulin and mucin domain 3, B7-H3, and diacylglycerol kinase α and implications of their inhibition in the cancer therapy.