Immunomodulation of the melanoma sentinel lymph node: a novel adjuvant therapeutic option

Langerhans Cells in Sentinel Lymph Nodes from Melanoma Patients

BACKGROUND

Langerhans cells (LCs) are professional Dendritic Cells (DCs) involved in immunoregulatory functions. At the skin level, LCs are immature. In response to tissue injuries, they migrate to regional Lymph Nodes (LNs), reaching a full maturation state. Then, they become effective antigen-presenting cells (APCs) that induce anti-cancer responses. Notably, melanoma patients present several DC alterations in the Sentinel Lymph Node (SLN), where primary antitumoral immunity is generated. LCs are the most represented DCs subset in melanoma SLNs and are expected to play a key role in the anti-melanoma response. With this paper, we aim to review the current knowledge and future perspectives regarding LCs and melanoma.

METHODS

A systematic review was carried out according to the PRISMA statement using the PubMed (MEDLINE) library from January 2004 to January 2024, searching for original studies discussing LC in melanoma.

RESULTS

The final synthesis included 15 articles. Several papers revealed significant LCs-melanoma interactions.

CONCLUSIONS

Melanoma immune escape mechanisms include SLN LC alterations, favoring LN metastasis arrival/homing and melanoma proliferation. The SLN LCs of melanoma patients are defective but not irreversibly, and their function may be restored by appropriate stimuli. Thus, LCs represent a promising target for future immunotherapeutic strategies and cancer vaccines.

Targeting C-type lectin receptors: a high-carbohydrate diet for dendritic cells to improve cancer vaccines

There is a growing understanding of why certain patients do or do not respond to checkpoint inhibition therapy. This opens new opportunities to reconsider and redevelop vaccine strategies to prime an anticancer immune response. Combination of such vaccines with checkpoint inhibitors will both provide the fuel and release the brake for an efficient anticancer response. Here, we discuss vaccine strategies that use C-type lectin receptor (CLR) targeting of APCs, such as dendritic cells and macrophages. APCs are a necessity for the priming of antigen-specific cytotoxic and helper T cells. Because CLRs are natural carbohydrate-recognition receptors highly expressed by multiple subsets of APCs and involved in uptake and processing of Ags for presentation, these receptors seem particularly interesting for targeting purposes.

Local delivery of CpG-B and GM-CSF induces concerted activation of effector and regulatory T cells in the human melanoma sentinel lymph node

Impaired immune effector functions in the melanoma sentinel lymph node (SLN) may allow for early metastatic events. In an effort to determine the optimal way to strengthen immune defenses, 28 clinical stage I-II melanoma patients were randomized in a 3-arm Phase II study to receive, prior to excision and sampling of the SLN, i.d. injections of saline or low-dose CpG-B (CpG), alone or combined with GM-CSF (GM), around the melanoma excision site. We previously described the combined administration of these DC-targeting agents to result in activation and recruitment of potentially cross-presenting BDCA3(+) DCs to the SLN. In this report we describe the effects on effector and regulatory T and NK cell subsets. Local low-dose CpG administration resulted in lower CD4/CD8 ratios, Th1 skewing, increased frequencies of melanoma-specific CD8(+) T cells and possible recruitment of effector NK cells, irrespective of GM co-administration. These immune-potentiating effects were counterbalanced by increased IL-10 production by T cells and significantly higher levels of FoxP3 and CTLA4 in regulatory T cells (Tregs) with correspondingly higher suppressive activity in the SLN. Notably, CpG ± GM-administered patients showed significantly lower numbers of SLN metastases (saline: 4/9, CpG + GM: 1/9, CpG: 0/10, p = 0.04). These findings indicate that i.d. delivery of low-dose CpG ± GM potentially arms the SLN of early-stage melanoma patients against metastatic spread, but that antitumor efficacy may be further boosted by counteracting the collateral activation of Tregs.

Induction of dendritic cell maturation in the skin microenvironment by soluble factors derived from colon carcinoma

Autologous tumor cell-based vaccines provide a wide range of tumor antigens and personalized neo-epitopes based on individual tumors' unique antigenic mutanome signatures. However, tumor-derived factors may hamper in situ maturation of dendritic cells (DC) and thus interfere with the generation of effective anti-tumor immunity. As the skin is a preferred site for tumor vaccine delivery, we investigated the influence of primary colon carcinoma-derived soluble factors on the maturation state of migrating DC in a human skin explant model. Primary tumor-derived supernatants (TDSN) enhanced the phenotypic maturation state of skin-emigrated DC, resulting in an increased T-cell stimulatory ability in an allogeneic mixed leukocyte response. In case of monocyte-derived DC a similar TDSN-induced maturation induction was found to entirely depend on cyclooxygenase (COX)-regulated prostaglandins. In contrast, the increase in skin-emigrated DC maturation was completely prostaglandin-independent, as evidenced by the inability of the COX inhibitor indomethacin to abrogate this TDSN-induced effect. Although TDSN conditioning affected a drop in IL-12p70 release by the skin-emigrated DC and induced a predominant Th17/Th22 transcriptional profile in subsequently stimulated T-cells, Th cell subset differentiation, as assessed by intracellular cytokine expression upon polyclonal priming and re-stimulation, was not affected. Comparative analysis of phenotypic and transcriptional profiles suggests that the observed maturational effects in skin-derived DC may have been induced by tumor-derived GM-CSF. In conclusion, soluble factors derived from whole-cell colon tumor vaccines will not negatively impact DC migration and maturation in human skin, but rather induce DC maturation that will facilitate the priming of a poly-functional Th cell response.

The dermis as a portal for dendritic cell-targeted immunotherapy of cutaneous melanoma

Complete surgical excision at an early stage remains the only curative treatment for cutaneous melanoma with few available adjuvant therapy options. Nevertheless, melanoma is a relatively immunogenic tumor type and particularly amenable to immunotherapeutic approaches. A dense network of cutaneous dendritic cells (DC) may account for the reported efficacy of vaccination through the skin and provide an attractive target for the immunotherapy of melanoma. Several phenotypically distinct DC subsets are discernable in the skin, among others, epidermal Langerhans cells and dermal DC. Upon appropriate activation both subsets can efficiently migrate to melanoma-draining lymph nodes (LN) to prime T cell-mediated responses. Unfortunately, from an early stage, melanoma development is characterized by strong immune suppression, facilitating unchecked tumor growth and spread. Particularly the primary tumor site and the first-line tumor-draining LN, the so-called sentinel LN, bear the brunt of this melanoma-induced immune suppression-and these are exactly the sites where anti-melanoma effector T cell responses should be primed by DC in order to prevent early metastasis. Through local immunopotentiation or through DC-targeted vaccination, the dermis may be utilized as a portal to activate DC and kick-start or boost effective T cell-mediated anti-melanoma immunity, even in the face of this immune suppression.

4-1BB-mediated expansion affords superior detection of in vivo primed effector memory CD8+ T cells from melanoma sentinel lymph nodes

We have been studying the re-activation of tumor-associated antigen (TAA)-specific CD8(+) T cells in sentinel lymph nodes (SLN) of melanoma patients upon intradermal administration of the CpG-B oligodeoxynucleotide PF-3512676. To facilitate functional testing of T cells from small SLN samples, high-efficiency polyclonal T cell expansion is required. In this study, SLN cells were expanded via classic methodologies with plate- or bead-bound anti-CD3/CD28 antibodies and with the K562/CD32/4-1BBL artificial APC system (K32/4-1BBL aAPC) and analyzed for responsiveness to common recall or TAA-derived peptides. K32/4-1BBL-expanded T cell populations contained significantly more effector/memory CD8(+) T cells. Moreover, recall and melanoma antigen-specific CD8(+) T cells were more frequently detected in K32/4-1BBL-expanded samples as compared with anti-CD3/CD28-expanded samples. We conclude that K32/4-1BBL aAPC are superior to anti-CD3/CD28 antibodies for the expansion of in vivo-primed specific CD8(+) T cells and that their use facilitates the sensitive monitoring of functional anti-tumor T cell immunity in SLN.

Identifying tumor antigens in endocrine malignancies

Tumor antigens are surface molecules that are mostly cancer specific, often overexpressed and recognized by the immune system. Therefore, identifying tumor antigens is of key importance for developing new immunotherapies for incurable cancers. For endocrine malignancies, several different tumor-associated antigens have been described, including polypeptide hormones and/or vesicle-associated antigens in Th1-mediated autoimmune diseases. Other antigens have been identified by screening tumor DNA libraries. Furthermore, vaccination studies in humans and animal models have revealed a tumor-antigen-specific immunity and clinical responses with reduced tumor size. Here, we provide an overview of the recent progress achieved in identifying tumor antigens and predict how this knowledge can be used in the future for developing anti-tumor vaccinations.

Therapeutic injection of C-class CpG ODN in draining lymph node area induces potent activation of immune cells and rejection of established breast cancer in mice

In order to develop novel CpG ODNs for the treatment of breast cancer, we have designed a series of CpG ODNs and evaluated their anti-tumor activity in a breast cancer mouse model. Interestingly, a C-class CpG ODN, designated as YW002, showed a vigorous activity on the inhibition of tumor growth in mice and completely cured some of the tumor-bearing mice through injection at tumor draining lymph node (TDLN) area. The expansion of immune cells in the TDLN and tumor and the generation of tumor specific immune memory were found associated with YW002-induced anti-tumor activity in mice. These results indicate that C-class CpG ODN could be developed into a medicament in a monotherapeutic regimen for the treatment of breast cancer through injection at TDLN area in clinic.

Local administration of PF-3512676 CpG-B instigates tumor-specific CD8+ T-cell reactivity in melanoma patients

PURPOSE

Impaired immune effector functions in the melanoma sentinel lymph node (SLN) may allow for early metastatic events. Local administration of PF-3512676 (formerly known as CpG 7909) has shown immunostimulatory effects of both dendritic cell and T-cell subsets in the melanoma SLN. Here, we set out to ascertain whether these PF-3512676-induced immunostimulatory effects translate into higher frequencies of melanoma-specific CD8(+) T cells.

EXPERIMENTAL DESIGN

Twenty-four stage I to III melanoma patients were randomized to preoperative local administration of either PF-3512676 or saline. CD8(+) T cells from SLN and peripheral blood were tested for reactivity by IFN-gamma ELISPOT assay against several HLA-A1/A2/A3-restricted epitopes derived from various melanoma-associated antigens (MAA) in 21 of 24 enrolled patients. Frequencies of natural killer (NK) cells and frequencies and maturation state of dendritic cell subsets in the SLN were determined by flow cytometry.

RESULTS

Melanoma-specific CD8(+) T-cell response rates against >1 MAA epitope in the SLN were 0 of 11 for the saline group versus 5 of 10 for the PF-3512676-administered group (P = 0.012). Of these 5 responding patients, 4 also had a measurable response to >1 MAA epitope in the blood. Increased frequencies in the SLN of both MAA-specific CD8(+) T cells and NK cells correlated to CpG-induced plasmacytoid dendritic cell maturation.

CONCLUSIONS

These data show an increase in melanoma-specific CD8(+) T-cell frequencies as well as an increased effector NK cell rate after a single dose of PF-3512676 and thus support the utility of local PF-3512676 administration as adjuvant treatment in early-stage melanoma to try and halt metastatic spread.

TLR9-mediated recognition of DNA

The mammalian immune system senses pathogens through pattern recognition receptors (PRRs) and responds with activation. The Toll-like receptor (TLR) family that consists of 13 receptors plays a critical role in this process. TLRmediated signaling activates immune cells and leads to an innate immune response with subsequent initiation of an adaptive immune response. Toll-like receptor 9 (TLR9) recognizes deoxyribonucleic acid (DNA) leading to cellular activation and cytokine production influencing the immune response against viruses and bacteria. The stimulation of TLR9 will be exploited for adjuvant therapy and treatment of cancer or allergy. In this review we will discuss TLR9 ligands, TLR9 expression, signaling, and the therapeutic potential of TLR9 ligands in treatment of infectious or allergic diseases and cancer.

Molecular characterization of inflammatory genes in sentinel and nonsentinel nodes in melanoma

PURPOSE

Identification of regional node metastasis is important for accurate staging and optimal treatment of early melanoma. We hypothesize that the nodal profile of immunoregulatory cytokines can confirm the identity of the first tumor-draining regional node, i.e., the sentinel node (SN) and indicate its tumor status.

EXPERIMENTAL DESIGN

RNA was extracted from freshly dissected and preserved nodal tissue of 13 tumor-negative SNs, 10 tumor-positive SNs (micrometastases <2 mm), and 11 tumor-negative non-SNs (NSN). RNA was converted into cDNA and then amplified by PCR. Expression of 96 cytokines and chemokines was assessed using cDNA microarray and compared by using hierarchical clustering.

RESULTS

Fifty-seven genes were expressed at significantly (P < 0.05) different levels in SNs and NSNs (4 genes had higher expression, and 53 genes had lower expression in SNs). Expression levels of interleukin-13 (IL-13), leptin, lymphotoxin beta receptor (LTbR), and macrophage inflammatory protein 1b (MIP1b) were significantly higher (P < 0.04, P < 0.01, P < 0.05, and P < 0.01, respectively), and expression level of IL-11Ra was lower (P < 0.03) for tumor-positive as compared with tumor-negative SN. Receiver-operator characteristics curve analyses showed that the area under the curve (AUC) for IL-13, leptin, LTbR, MIP1b, and IL-11Ra was 0.79, 0.83, 0.75, 0.81, and 0.77, respectively. The AUC for the five genes in combination was 0.973, suggesting high concordance of gene-expression profiles with SN staging.

CONCLUSIONS

SNs have a different immunoregulatory cytokine profile than NSNs. The cytokine profile of tumor-positive SNs; increased expression of IL-13, leptin, LTbR, and MIP1b and decreased expression of IL-11Ra, may provide clues to the local tumor lymph node interaction seen in the earliest steps of melanoma metastasis.

Development of TLR9 agonists for cancer therapy

In vertebrates, the TLRs are a family of specialized immune receptors that induce protective immune responses when they detect highly conserved pathogen-expressed molecules. Synthetic agonists for several TLRs, including TLR3, TLR4, TLR7, TLR8, and TLR9, have been or are being developed for the treatment of cancer. TLR9 detects the unmethylated CpG dinucleotides prevalent in bacterial and viral DNA but not in vertebrate genomes. As discussed in this Review, short synthetic oligodeoxynucleotides containing these immune stimulatory CpG motifs activate TLR9 in vitro and in vivo, inducing innate and adaptive immunity, and are currently being tested in multiple phase II and phase III human clinical trials as adjuvants to cancer vaccines and in combination with conventional chemotherapy and other therapies.

Immunobiology of the sentinel lymph node and its potential role for antitumour immunity

The sentinel lymph node (SLN) is thought to be an important lymphoid organ for protecting against metastasis and is thought to play a crucial part in provoking antitumour immunity. Because SLN biopsy is undertaken for various types of cancers, such as malignant melanoma and breast cancer, SLN mapping has become a standard procedure, thereby eliminating unnecessary lymph-node resection in patients who do not have affected nodes. The immune surveillance activities of the SLN in melanoma and breast cancer are thought to be suppressed, whereas in cancers of gastrointestinal-tract, the presence of T cells in the SLN has not been shown to suppress the host's immune function. Furthermore, cell death after primary systemic chemotherapy for solid tumours can provoke an antigen-specific immunity in the tumour, which affects tumour response to treatment and, therefore, survival in patients. This review discusses the immunobiology of the SLN and potential strategies for activation of antitumour immunity by primary systemic chemotherapy and other modalities, in terms of tumour-size reduction and survival benefit.