Th1-like Treg cells are dressed to suppress anti-tumor immunity.

Mechanisms of Th1-like Treg suppression are unknown in cancer. Two studies in Immunity by Ayala et al. and Zagorulya et al. demonstrate that Th1-like Treg cells interact with type 1 dendritic cells in tumors and draining lymph nodes to potently suppress anti-tumor immunity.

Resident memory CD8+ T cells in regional lymph nodes mediate immunity to metastatic melanoma.

The nature of the anti-tumor immune response changes as primary tumors progress and metastasize. We investigated the role of resident memory (Trm) and circulating memory (Tcirm) cells in anti-tumor responses at metastatic locations using a mouse model of melanoma-associated vitiligo. We found that the transcriptional characteristics of tumor-specific CD8+ T cells were defined by the tissue of occupancy. Parabiosis revealed that tumor-specific Trm and Tcirm compartments persisted throughout visceral organs, but Trm cells dominated lymph nodes (LNs). Single-cell RNA-sequencing profiles of Trm cells in LN and skin were distinct, and T cell clonotypes that occupied both tissues were overwhelmingly maintained as Trm in LNs. Whereas Tcirm cells prevented melanoma growth in the lungs, Trm afforded long-lived protection against melanoma seeding in LNs. Expanded Trm populations were also present in melanoma-involved LNs from patients, and their transcriptional signature predicted better survival. Thus, tumor-specific Trm cells persist in LNs, restricting metastatic cancer.

Oncogenes Feed Treg Cells without Calling CD8s to the Table.

Metabolic support for regulatory T (Treg) cells in noninflamed tumors is not well understood. In this issue of Immunity, Kumagai et. al. show how oncogene-driven fatty-acid synthesis favors Treg cells over effector T cells and how this imbalance can be overcome.

CD39 Is Expressed on Functional Effector and Tissue-resident Memory CD8+ T Cells.

The ecto-ATPase CD39 is expressed on exhausted CD8+ T cells in chronic viral infection and has been proposed as a marker of tumor-specific CD8+ T cells in cancer, but the role of CD39 in an effector and memory T cell response has not been clearly defined. We report that CD39 is expressed on Ag-specific CD8+ short-lived effector cells, while it's co-ectoenzyme, CD73, is found on memory precursor effector cells (MPECs) in vivo. Inhibition of CD39 enzymatic activity during in vitro T cell priming enhances MPEC differentiation in vivo after transfer and infection. The enriched MPEC phenotype is associated with enhanced tissue resident memory T cell (TRM cell) establishment in the brain and salivary gland following an acute intranasal viral infection, suggesting that CD39 ATPase activity plays a role in memory CD8+ T cell differentiation. We also show that CD39 is expressed on human and murine TRM cells across several nonlymphoid tissues and melanoma, whereas CD73 is expressed on both circulating and resident memory subsets in mice. In contrast to exhausted CD39+ T cells in chronic infection, CD39+ TRM cells are fully functional when stimulated ex vivo with cognate Ag, further expanding the identity of CD39 beyond a T cell exhaustion marker.

Memory CD8+ T cell responses to cancer.

Long-lived memory CD8+ T cells play important roles in tumor immunity. Studies over the past two decades have identified four subsets of memory CD8+ T cells - central, effector, stem-like, and tissue resident memory - that either circulate through blood, lymphoid and peripheral organs, or reside in tissues where cancers develop. In this article, we will review studies from both pre-clinical mouse models and human patients to summarize the phenotype, distribution and unique features of each memory subset, and highlight specific roles of each subset in anti-tumor immunity. Moreover, we will discuss how stem-cell like and resident memory CD8+ T cell subsets relate to exhausted tumor-infiltrating lymphocytes (TIL) populations. These studies reveal how memory CD8+ T cell subsets together orchestrate durable immunity to cancer.

IL-35-mediated induction of a potent regulatory T cell population.

Regulatory T cells (T(reg) cells) have a critical role in the maintenance of immunological self-tolerance. Here we show that treatment of naive human or mouse T cells with IL-35 induced a regulatory population, which we call 'iT(R)35 cells', that mediated suppression via IL-35 but not via the inhibitory cytokines IL-10 or transforming growth factor-ß (TGF-ß). We found that iT(R)35 cells did not express or require the transcription factor Foxp3, and were strongly suppressive and stable in vivo. T(reg) cells induced the generation of iT(R)35 cells in an IL-35- and IL-10-dependent manner in vitro and induced their generation in vivo under inflammatory conditions in intestines infected with Trichuris muris and within the tumor microenvironment (B16 melanoma and MC38 colorectal adenocarcinoma), where they contributed to the regulatory milieu. Thus, iT(R)35 cells constitute a key mediator of infectious tolerance and contribute to T(reg) cell-mediated tumor progression. Furthermore, iT(R)35 cells generated ex vivo might have therapeutic utility.

VISTA expression on tumor-infiltrating inflammatory cells in primary cutaneous melanoma correlates with poor disease-specific survival.

Adaptive immune responses contribute to the pathogenesis of melanoma by facilitating immune evasion. V-domain Ig suppressor of T-cell activation (VISTA) is a potent negative regulator of T-cell function and is expressed at high levels on monocytes, granulocytes, and macrophages, and at lower densities on T-cell populations within the tumor microenvironment. In this study, 85 primary melanoma specimens were selected from pathology tissue archives and immunohistochemically stained for CD3, PD-1, PD-L1, and VISTA. Pearson's correlation coefficients identified associations in expression between VISTA and myeloid infiltrate (r = 0.28, p = 0.009) and the density of PD-1+ inflammatory cells (r = 0.31, p = 0.005). The presence of VISTA was associated with a significantly worse disease-specific survival in univariate analysis (hazard ratio = 3.57, p = 0.005) and multivariate analysis (hazard ratio = 3.02, p = 0.02). Our findings show that VISTA expression is an independent negative prognostic factor in primary cutaneous melanoma and suggests its potential as an adjuvant immunotherapeutic intervention in the future.

Challenges faced when identifying patients for combination immunotherapy.

In 1996, Jim Allison demonstrated that blocking the immune regulatory molecule CTLA-4 with anit-CTLA4 antibody led to enhance tumor responses in mice. It would take an additional 15 years for human studies to confirm the potency and clinical efficacy of anti-CTLA4, ultimately leading to US FDA approval of the first checkpoint inhibitor, ipilimumab. Now with a plethora of immune-modulating agents demonstrating single agent safety and benefit across many tumor types, investigation on the optimal combination of immune-based therapies has begun in earnest. While there are many challenges, a central one is how to select which combination for which patient is the best. Here we review the current approaches that a practitioner can use to achieve this therapeutic goal.

Autoimmune vitiligo does not require the ongoing priming of naive CD8 T cells for disease progression or associated protection against melanoma.

Vitiligo is a CD8 T cell-mediated autoimmune disease that has been shown to promote the longevity of memory T cell responses to melanoma. However, mechanisms whereby melanocyte/melanoma Ag-specific T cell responses are perpetuated in the context of vitiligo are not well understood. These studies investigate the possible phenomenon of naive T cell priming in hosts with melanoma-initiated, self-perpetuating, autoimmune vitiligo. Using naive pmel (gp10025-33-specific) transgenic CD8 T cells, we demonstrate that autoimmune melanocyte destruction induces naive T cell proliferation in skin-draining lymph nodes, in an Ag-dependent fashion. These pmel T cells upregulate expression of CD44, P-selectin ligand, and granzyme B. However, they do not downregulate CD62L, nor do they acquire the ability to produce IFN-γ, indicating a lack of functional priming. Accordingly, adult thymectomized mice exhibit no reduction in the severity or kinetics of depigmentation or long-lived protection against melanoma, indicating that the continual priming of naive T cells is not required for vitiligo or its associated antitumor immunity. Despite this, depletion of CD4 T cells during the course of vitiligo rescues the priming of naive pmel T cells that are capable of producing IFN-γ and persisting as memory, suggesting an ongoing and dominant mechanism of suppression by regulatory T cells. This work reveals the complex regulation of self-reactive CD8 T cells in vitiligo and demonstrates the overall poorly immunogenic nature of this autoimmune disease setting.

Immune-mediated regression of established B16F10 melanoma by intratumoral injection of attenuated Toxoplasma gondii protects against rechallenge.

Immune recognition of tumors can limit cancer development, but antitumor immune responses are often blocked by tumor-mediated immunosuppression. Because microbes or microbial constituents are powerful adjuvants to stimulate immune responses, we evaluated whether intratumoral administration of a highly immunogenic but attenuated parasite could induce rejection of an established poorly immunogenic tumor. We treated intradermal B16F10 murine melanoma by intratumoral injection of an attenuated strain of Toxoplasma gondii (cps) that cannot replicate in vivo and therefore is not infective. The cps treatment stimulated a strong CD8(+) T cell-mediated antitumor immune response in vivo that regressed established primary melanoma. The cps monotherapy rapidly modified the tumor microenvironment, halting tumor growth, and subsequently, as tumor-reactive T cells expanded, the tumors disappeared and rarely returned. The treatment required live cps that could invade cells and also required CD8(+) T cells and NK cells, but did not require CD4(+) T cells. Furthermore, we demonstrate that IL-12, IFN-γ, and the CXCR3-stimulating cytokines are required for full treatment efficacy. The treatment developed systemic antitumor immune activity as well as antitumor immune memory and therefore might have an impact against human metastatic disease. The approach is not specific for either B16F10 or melanoma. Direct intratumoral injection of cps has efficacy against an inducible genetic melanoma model and transplantable lung and ovarian tumors, demonstrating potential for broad clinical use. The combination of efficacy, systemic antitumor immune response, and complete attenuation with no observed host toxicity demonstrates the potential value of this novel cancer therapy.

Local hyperthermia treatment of tumors induces CD8(+) T cell-mediated resistance against distal and secondary tumors.

Combinatorial use of iron oxide nanoparticles (IONPs) and an alternating magnetic field (AMF) can induce local hyperthermia in tumors in a controlled and uniform manner. Heating B16 primary tumors at 43°C for 30 min activated dendritic cells (DCs) and subsequently CD8(+) T cells in the draining lymph node (dLN) and conferred resistance against rechallenge with B16 (but not unrelated Lewis Lung carcinoma) given 7 days post hyperthermia on both the primary tumor side and the contralateral side in a CD8(+) T cell-dependent manner. Mice with heated primary tumors also resisted rechallenge given 30 days post hyperthermia. Mice with larger heated primary tumors had greater resistance to secondary tumors. No rechallenge resistance occurred when tumors were heated at 45°C. Our results demonstrate the promising potential of local hyperthermia treatment applied to identified tumors in inducing anti-tumor immune responses that reduce the risk of recurrence and metastasis. FROM THE CLINICAL EDITOR: Local heating of tumors via iron oxide NPs and an alternating magnetic field led to activation of anti-cancer CD8 T cells, which resulted in resistance against re-challenge and greater resistance to secondary tumors. Similar local heating-based strategies may become an important weapon in enhancing tumor elimination via a naturally existing but attenuated immune response.

CD39 is expressed on functional effector and tissue resident memory CD8+ T cells.

The ecto-ATPase CD39 is expressed on exhausted CD8+ T cells in chronic viral infection and has been proposed as a marker of tumor-specific CD8+ T cells in cancer, but the role of CD39 in an effector and memory T cell response has not been clearly defined. We report that CD39 is expressed on antigen-specific CD8+ short-lived effector cells (SLECs), while it's co-ecto-enzyme, CD73, is found on memory precursor effector cells (MPEC) in vivo . Inhibition of CD39 enzymatic activity during in vitro T cell priming enhances MPEC differentiation in vivo after transfer and infection. The enriched MPEC phenotype is associated with enhanced tissue resident memory (T RM ) establishment in the brain and salivary gland following an acute intranasal viral infection, suggesting that CD39 ATPase activity plays a role in memory CD8+ T cell differentiation. We also show that CD39 is expressed on human and murine T RM across several non-lymphoid tissues and melanoma, while CD73 is expressed on both circulating and resident memory subsets in mice. In contrast to exhausted CD39+ T cells in chronic infection, CD39+ T RM are fully functional when stimulated ex vivo with cognate antigen. This work further expands the identity of CD39 beyond a T cell exhaustion marker.

Stimulation of the glucocorticoid-induced TNF receptor family-related receptor on CD8 T cells induces protective and high-avidity T cell responses to tumor-specific antigens.

Treatment of tumor-bearing mice with a stimulatory Ab to glucocorticoid-induced TNFR family-related receptor (GITR) has previously been shown to elicit protective T cell responses against poorly immunogenic tumors. However, the role of GITR stimulation on CD8 T cells and the nature of tumor rejection Ags have yet to be determined. In this study, we show that a stimulatory mAb to GITR (clone DTA-1) acts directly on CD8 T cells, but not on CD4(+)CD25(+) regulatory T (T(reg)) cells, in B16 tumor-bearing mice to induce concomitant immunity against secondary B16 tumors, as well as protective memory following surgical excision of the primary tumor. Melanoma growth itself induced GITR expression on tumor-specific CD8 T cells, providing a mechanism whereby these cells may respond to stimulatory anti-GITR. Unexpectedly, in contrast to T(reg) cell depletion therapy with anti-CD4, GITR stimulation induced very weak CD8 T cell responses to melanocyte differentiation Ags expressed by the tumor, and did not induce autoimmune vitiligo. Accordingly, GITR-stimulated hosts that were primed with B16 melanoma rejected B16, but not the unrelated JBRH melanoma, indicating that tumor rejection Ags are tumor-specific rather than shared. In support of this, we show that GITR stimulation induces CD8 T cell responses to a tumor-specific Ag, and that these responses are of higher functional avidity compared with those induced by T(reg) cell depletion. We conclude that stimulation of GITR on effector CD8 T cells results in high-avidity T cell responses to tumor-specific Ags, thereby inducing potent antitumor immunity in the absence of autoimmunity.

Adenocarcinoma contains more immune tolerance regulatory t-cell lymphocytes (versus squamous carcinoma) in non-small-cell lung cancer.

BACKGROUND: Regulatory T lymphocytes (Tregs) are known to have host-immune dampening effects in many tumors and to be associated with increased tumor recurrence. Pharmacologic therapies have been developed to target these cells and hence strengthen the host's immune system. The FoxP3 gene is a marker of Tregs and can be visualized with immunohistochemistry (IHC). We investigated the presence and pattern of Tregs in non-small-cell lung tumors to determine possible therapeutic targets in lung cancer. METHODS: We selected archival samples of primary lung carcinoma and benign inflamed lung from 32 surgical resections. We created a tissue array containing duplicate cores from the N1 and N2 nodal stations from 16 of the cases along with paired benign lung and tumor. We used whole-slide analysis for the other 16 cases. We used FoxP3 IHC to visualize Tregs in all lymphoid tissue present and to assess the quantity and pattern within the tissues. RESULTS: All lymphoid tissue contains Tregs, but adenocarcinoma had significantly higher levels than both inflammatory lung controls and squamous carcinomas (p ≤ 0.008). Benign N1 lymph nodes (from patients with lung cancer) showed higher numbers of Tregs for adenocarcinoma versus squamous carcinoma. CONCLUSIONS: These findings reveal that Tregs are present in all lung tissues examined, but with significant enrichment in adenocarcinoma. This may lead to a more permissive microenvironment for adenocarcinoma and may explain aggressive patterns of tumor spread for this histology. Lung cancer patients with adenocarcinoma histology may benefit most from Treg-targeted therapy.

In the right place at the right time: tissue-resident memory T cells in immunity to cancer.

Tissue-resident memory (Trm) cells have recently emerged as essential components of the immune response to cancer. Here, we highlight new studies that demonstrate how CD8+ Trm cells are ideally suited to accumulate in tumors and associated tissues, to recognize a wide range of tumor antigens (Ags), and to persist as durable memory. We discuss compelling evidence that Trm cells maintain potent recall function and serve as principal mediators of immune checkpoint blockade (ICB) therapeutic efficacy in patients. Finally, we propose that Trm and circulating memory T-cell compartments together form a formidable barrier against metastatic cancer. These studies affirm Trm cells as potent, durable, and necessary mediators of cancer immunity.

TimiGP: Inferring cell-cell interactions and prognostic associations in the tumor immune microenvironment through gene pairs.

Determining the prognostic association of different immune cell types in the tumor microenvironment is critical for understanding cancer biology and developing new therapeutic strategies. However, this is challenging in certain cancer types, where the abundance of different immune subsets is highly correlated. In this study, we develop a computational method named TimiGP to overcome this challenge. Based on bulk gene expression and survival data, TimiGP infers cell-cell interactions that reveal the association between immune cell relative abundance and prognosis. As demonstrated in metastatic melanoma, TimiGP prioritizes immune cells critical in prognosis based on the identified cell-cell interactions. Highly consistent results are obtained by TimiGP when applied to seven independent melanoma datasets and when different cell-type marker sets are used as inputs. Additionally, TimiGP can leverage single-cell RNA sequencing data to delineate the tumor immune microenvironment at high resolutions across a wide range of cancer types.

The Effect of Lung Resection for NSCLC on Circulating Immune Cells: A Pilot Study.

This pilot study sought to evaluate the circulating levels of immune cells, particularly regulatory T-cell (Treg) subsets, before and after lung resection for non-small cell lung cancer. Twenty-five patients consented and had specimens collected. Initially, peripheral blood of 21 patients was collected for circulating immune cell studies. Two of these patients were excluded due to technical issues, leaving 19 patients for the analyses of circulating immune cells. Standard gating and high-dimensional unsupervised clustering flow cytometry analyses were performed. The blood, tumors and lymph nodes were analyzed via single-cell RNA and TCR sequencing for Treg analyses in a total of five patients (including four additional patients from the initial 21 patients). Standard gating flow cytometry revealed a transient increase in neutrophils immediately following surgery, with a variable neutrophil-lymphocyte ratio and a stable CD4-CD8 ratio. Unexpectedly, the total Treg and Treg subsets did not change with surgery with standard gating in short- or long-term follow-up. Similarly, unsupervised clustering of Tregs revealed a dominant cluster that was stable perioperatively and long-term. Two small FoxP3hi clusters slightly increased following surgery. In the longer-term follow-up, these small FoxP3hi Treg clusters were not identified, indicating that they were likely a response to surgery. Single-cell sequencing demonstrated six CD4+FoxP3+ clusters among the blood, tumors and lymph nodes. These clusters had a variable expression of FoxP3, and several were mainly, or only, present in tumor and lymph node tissue. As such, serial monitoring of circulating Tregs may be informative, but not completely reflective of the Tregs present in the tumor microenvironment.

CDDO-Methyl Ester Inhibits BRAF Inhibitor Resistance and Remodels the Myeloid Compartment in BRAF-mutant Melanoma.

Approximately 50% of advanced melanomas harbor activating BRAF V600E mutations that are sensitive to BRAF inhibition. However, the duration of the response to BRAF inhibitors (BRAFi) has been limited due to the development of acquired resistance, which is preceded by recruitment of immunosuppressive myeloid cells and regulatory T cells (T regs ). While the addition of MAPK/ERK kinase 1 inhibitors (MEKi) prolongs therapeutic response to BRAF inhibition, most patients still develop resistance. Using a Braf V600E/+ /Pten -/- graft mouse model of melanoma, we now show that the addition of the methyl ester of the synthetic triterpenoid 2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oic acid (C-Me) to the BRAFi vemurafenib analog PLX4720 at resistance significantly reduces tumor burden. Dual treatment remodels the BRAFi resistant-tumor microenvironment (TME), reducing infiltration of T regs and tumor associated macrophages (TAMs), and attenuates immunosuppressive cytokine production. For the first time, we characterize myeloid populations using scRNA-seq in BRAFi-resistant tumors and demonstrate that restoration of therapeutic response is associated with significant changes in immune-activated myeloid subset representation. Collectively, these studies suggest that C-Me inhibits acquired resistance to BRAFi. Use of C-Me in combination with other therapies may both inhibit melanoma growth and enhance therapeutic responsiveness more broadly.

Dendritic cells maintain anti-tumor immunity by positioning CD8 skin-resident memory T cells.

Tissue-resident memory (TRM) T cells are emerging as critical components of the immune response to cancer; yet, requirements for their ongoing function and maintenance remain unclear. APCs promote TRM cell differentiation and re-activation but have not been implicated in sustaining TRM cell responses. Here, we identified a novel role for dendritic cells in supporting TRM to melanoma. We showed that CD8 TRM cells remain in close proximity to dendritic cells in the skin. Depletion of CD11c+ cells results in rapid disaggregation and eventual loss of melanoma-specific TRM cells. In addition, we determined that TRM migration and/or persistence requires chemotaxis and adhesion mediated by the CXCR6/CXCL16 axis. The interaction between CXCR6-expressing TRM cells and CXCL16-expressing APCs was found to be critical for sustaining TRM cell-mediated tumor protection. These findings substantially expand our knowledge of APC functions in TRM T-cell homeostasis and longevity.

Toward a better understanding of T cells in cancer.

T cells mediate anti-tumor immune responses and are the key target of immune checkpoint therapy, but they can also promote immune tolerance. A clear understanding of the specific contributions and biology of different T cell subsets is required to fully harness the curative potential of immunotherapies. Experts discuss the state of the field and key challenges for moving forward.