Tumor antigen cross-presentation and the dendritic cell: Where it all begins?

Dendritic cells (DCs) are professional antigen-presenting cells (APCs) that are critical for the generation of effective cytotoxic T lymphocyte (CTL) responses; however, their function and phenotype are often defective or altered in tumor-bearing hosts, which may limit their capacity to mount an effective tumor-specific CTL response. In particular, the manner in which exogenous tumor antigens are acquired, processed, and cross-presented to CD8 T cells by DCs in tumor-bearing hosts is not well understood, but may have a profound effect on antitumor immunity. In this paper, we have examined the role of DCs in the cross-presentation of tumor antigen in terms of their subset, function, migration, and location with the intention of examining the early processes that contribute to the development of an ineffective anti-tumor immune response

Tumor-infiltrating dendritic cells exhibit defective cross-presentation of tumor antigens, but is reversed by chemotherapy

Cross-presentation defines the unique capacity of an APC to present exogenous Ag via MHC class I molecules to CD8+ T cells. DCs are specialized cross-presenting cells and as such have a critical role in antitumor immunity. DCs are routinely found within the tumor microenvironment, but their capacity for endogenous or therapeutically enhanced cross-presentation is not well characterized. In this study, we examined the tumor and lymph node DC cross-presentation of a nominal marker tumor Ag, HA, expressed by the murine mesothelioma tumor AB1-HA. We found that tumors were infiltrated by predominantly CD11b+ DCs with a semimature phenotype that could not cross-present tumor Ag, and therefore, were unable to induce tumor-specific T-cell activation or proliferation. Although tumor-infiltrating DCs were able to take, process, and cross-present exogenous cell-bound and soluble Ags, this was significantly impaired relative to lymph node DCs. Importantly, however, systemic chemotherapy using gemcitabine reversed the defect in Ag cross-presentation of tumor DCs. These data demonstrate that DC cross-presentation within the tumor microenvironment is defective, but can be reversed by chemotherapy. These results have important implications for anticancer therapy, particularly regarding the use of immunotherapy in conjunction with cytotoxic chemotherapy

Cranking the immunologic engine with chemotherapy: Using context to drive tumor antigen cross-presentation towards useful antitumor immunity

This review shows how tumor antigen cross-presentation is affected by the major therapeutic modalities including chemotherapy, radiotherapy, and surgery. We argue that this process could affect the way that a tumor works as its own cellular vaccine, and that it is differentially modulated by the choice of treatment

Loss of antigen cross-presentation after complete tumor resection is associated with the generation of protective tumor-specific CD8+ T-cell immunity

An incomplete understanding on the effect of surgery on tumor-specific immunity continues to hamper efforts to combine surgery with immunotherapy in the clinic. Herein, we describe the impact of tumor resection on the tumor-specific T-cell response, showing that complete tumor resection is associated with (1) a decline in the amount of cross-presented tumor antigens, (2) a decline of cytolytic tumor-specific CD8+ T cell activity, and (3) the development of systemic CD8+ T cell-mediated protective immunity. Our findings are consistent with a model whereby tumor resection releases antitumor CD8+ T cells from chronic antigen exposure, allowing a gradual differentiation toward functional antitumor memory T cells. This process depends on sentinel lymph nodes, as their removal at the time of surgery was associated with a strong negative effect on survival. We conclude that complete tumor resection provides a unique environment that boosts protective immunological memory and might provide a powerful platform for immunotherapy. Our findings also carry important implications for the design and timing of post-surgery immunotherapeutic regimens

Decoding dangerous death: how cytotoxic chemotherapy invokes inflammation, immunity or nothing at all

Chemotherapy and immunotherapy can be either synergistic or antagonistic modalities in the treatment of cancer. Cytotoxic chemotherapy not only affects the tumor but also targets dividing lymphocytes, the very cells that are required to develop an immune response. For this reason, chemo- and immunotherapy have been seen as antagonistic. However, cell death can be immunogenic and the way in which chemotherapeutic drug kills a tumor cell is likely to be an important determinant of how that dying cell interacts with the immune system and whether the interaction will lead to an immune response. When a cell dies as the result of infection, the immune system responds rapidly and the system of Toll-like receptors (TLR) plays a key role in this process. In this review, we will briefly summarize the intracellular signaling pathways that link TLR ligation with immune activation and we will address the questions where and how TLRs recognize their targets

Restoration of defective cross-presentation in tumors by gemcitabine

Tumor antigen cross-presentation by dendritic cells (DCs) to specific CD8(+) T cells is central to antitumor immunity. Although highly efficient in draining lymph nodes, it is defective within the tumor site itself. Importantly, an immunogenic chemotherapy, gemcitabine, reverses this defect, allowing the potential re-stimulation of cytotoxic T lymphocytes within tumor sites

Tumor cells, rather than dendritic cells, deliver antigen to the lymph node for cross-presentation

It is widely accepted that generation of tumor specific CD8+ T-cell responses occur via cross-priming; however the source of tumor antigen for this event is unknown. We examined the source and form of tumor antigen required for cross-presentation in the local lymph node (LN) using a syngeneic mouse tumor model expressing a marker antigen. We found that cross-presentation of this model tumor antigen in the LN is dependent on continuous traffic of antigen from the tumor site, but without any detectable migration of tumor resident dendritic cells (DCs). Instead, small numbers of tumor cells metastasize to local LNs where they are exposed to a localized CTL attack, resulting in delivery of tumor antigen into the cross-presentation pathway

Intratumoral poly-N-acetyl glucosamine-based polymer matrix provokes a prolonged local inflammatory response that, when combined with IL-2, induces regression of malignant mesothelioma in a murine model

The authors have previously shown that cytokines delivered directly into malignant mesothelioma (MM) tumors can retard tumor growth and mediate tumor regression under certain conditions. In this report the authors compared the efficacy of serial intratumoral injections of three cytokines, GM-CSF, IL-12, and IL-2, to their sustained release using a single injection in a poly-N-acetyl glucosamine gel. IL-2 combined with the polymer gel gave optimal antitumor results when MM tumors were accessible as either subcutaneous deposits or as masses spread throughout the peritoneal cavity. The gel acted not only as a slow-release cytokine depot but also as a trigger for inflammation and recruited several immune cell types to the gel/tumor interface; when combined with IL-2 (but not with GM-CSF or IL-12), it acted as a selective reservoir for infiltrating CD8+ T cells. Hence, the IL-2/gel may provide a microenvironment that allows intratumoral T cells to proliferate and retain their cytolytic functions as they encounter their cognate antigens expressed by tumor cells

Agonistic anti-CD40 antibody therapy is effective against postoperative cancer recurrence and metastasis in a murine tumor model

Postresection recurrences of cancer arising from occult tumor deposits, either local or metastatic, represent major causes of death in patients with operable solid tumors. Thus, new therapies are required that complement existing treatments to eradicate these occult deposits. Agonistic anti-CD40 antibody is one of the most powerful new cancer immunotherapies, enhancing immune priming of effector CD8 T cells by dendritic cells, leading to increased antitumor activity. We investigated the use of anti-CD40 antibody for the treatment of postoperative recurrence and metastasis, with regional lymphadenectomy, in a murine model of cancer. Subcutaneous AB1-HA mesothelioma tumors were induced in BALB/c mice. Established tumors were surgically excised on day 16, with or without sentinel lymph node removal. On the day of surgery, animals were rechallenged with AB1-HA tumor cells at the surgical site (local recurrence) or the opposite flank (metastasis). Postoperative tumors were treated with anti-CD40 (FGK45) on emergence, delivered either intratumorally, peritumorally, or systemically. Local or systemic anti-CD40 treatment slowed postsurgical metastatic growth relative to untreated controls (P=0.020) and improved survival from metastasis. Anti-CD40 also retarded the growth of local recurrences (P=0.004) and improved survival from recurrence. Sentinel lymph node dissection did not impair efficacy (P>0.05). This study demonstrates that anti-CD40 therapy, given either locally or systemically, may be a powerful and readily translatable adjuvant to cancer surgery, including in cases where regional lymphadenectomy is indicated

CD8α+ DC are not the sole subset cross-presenting cell-associated tumor antigens from a solid tumor

One of the clear paradoxes in tumor immunology is the fact that cross-presentation of cell-associated tumor antigens to CD8+ T cells is efficient, yet CTL generation is weak, and tumors continue to grow. We examined, for the first time whether this may be due to alterations in the phenotype or function of cross-presenting DC using a solid tumor model expressing a membrane bound neo-antigen (hemagglutinin, HA). Tumor antigen was constitutively cross-presented in the tumor-draining LN throughout tumor progression by CD11c+ DC. Further analysis revealed that both CD8α+ and CD8α− DC subsets, but not plasmacytoid DC, were effective at cross-presenting HA tumor antigen. The proportions of DC subsets in the tumor-draining LN were equivalent to those seen in the LN of naïve mice; however, a significant increase in the expression of the potential inhibitory B7 molecule, B7-DC, was noted and appeared to be restricted to the CD8α– DC subset. Therefore LN resident CD8α+ DC are not the sole DC subset capable of cross-presenting cell-associated tumor antigens. Migratory tumor DC subsets with altered co-stimulatory receptor expression may contribute to induction and regulation of tumor-specific responses