Tertiary lymphoid structures in desmoplastic melanoma have increased lymphocyte density, lymphocyte proliferation, and immune cross talk with tumor when compared to non-desmoplastic melanomas

Tertiary lymphoid structures (TLS) are ectopic lymphoid structures that can arise in human cancers and are associated with improved overall survival (OS) and response to immune checkpoint blockade (ICB) in several cancers, including non-desmoplastic metastatic melanoma (NDMM). Desmoplastic melanoma (DM) has one of the highest response rates to ICB, and we previously identified that primary DM (PDM) contains TLS. Despite the association of TLS with survival and ICB response, it is unknown whether TLS or associated markers of immune activity can differ between PDM and NDMM. We hypothesized that PDM would contain higher frequencies of TLS than NDMM, that T and B-cell densities and proliferation would be greater in TLS of PDM than TLS of NDMM, and that proliferation rates of T and B-cells in PDM TLS would be concordant with those of intratumoral lymphocytes. We found that four features of TLS in PDM distinguish them from TLS in NDMM. TLS were peritumoral in NDMM but intratumoral in PDM. CD8⁺ T-cell and CD20⁺ B-cell densities and proliferative fractions were higher in PDM TLS than NDMM TLS. Additionally, the proliferative fractions of T- and B-cells were concordant between the TLS and tumor site in PDM and discordant in NDMM. Collectively, these data suggest that TLS and associated immune markers can differ across melanoma subsets and suggest that PDM TLS may be more immunologically active and have enhanced immune cell trafficking between tumor and TLS compared to NDMM.

NK cells reduce anergic T cell development in early-stage tumors by promoting myeloid cell maturation

Introduction

Studies of NK cells in tumors have primarily focused on their direct actions towards tumor cells. We evaluated the impact of NK cells on expression of homing receptor ligands on tumor vasculature, intratumoral T cell number and function, and T cell activation in tumor draining lymph node.

Methods

Using an implantable mouse model of melanoma, T cell responses and homing receptor ligand expression on the vasculature were evaluated with and without NK cells present during the early stages of the tumor response by flow cytometry.

Results

NK cells in early-stage tumors are one source of IFNγ that augments homing receptor ligand expression. More significantly, NK cell depletion resulted in increased numbers of intratumoral T cells with an anergic phenotype. Anergic T cell development in tumor draining lymph node was associated with increased T-cell receptor signaling but decreased proliferation and effector cell activity, and an incomplete maturation phenotype of antigen presenting cells. These effects of NK depletion were similar to those of blocking CD40L stimulation.

Discussion

We conclude that an important function of NK cells is to drive proper APC maturation via CD40L during responses to early-stage tumors, reducing development of anergic T cells. The reduced development of anergic T cells resulting in improved tumor control and T cell responses when NK cells were present.

Tumor necrosis factor receptor regulation of peripheral node addressin biosynthetic components in tumor endothelial cells

Tumor-associated tertiary lymphoid structures are ectopic lymphoid aggregates that have considerable morphological, cellular, and molecular similarity to secondary lymphoid organs, particularly lymph nodes. Tumor vessels expressing peripheral node addressin (PNAd) are hallmark features of these structures. Previous work from our laboratory demonstrated that PNAd is displayed on intratumoral vasculature of murine tumors, and its expression is controlled by the engagement of lymphotoxin-α₃, secreted by effector CD8 T cells, with tumor necrosis factor receptors (TNFR) on tumor endothelial cells (TEC). The goals of the present work were: 1) to identify differences in expression of genes encoding the scaffolding proteins and glycosyl transferases associated with PNAd biosynthesis in TEC and lymph node blood endothelial cells (LN BEC); and 2) to determine which of these PNAd associated components are regulated by TNFR signaling. We found that the same genes encoding scaffolding proteins and glycosyl transferases were upregulated in PNAd⁺ LN BEC and PNAd⁺ TEC relative to their PNAd^neg counterparts. The lower level of PNAd expression on TEC vs LN BEC was associated with relatively lower expression of these genes, particularly the carbohydrate sulfotransferase Chst4. Loss of PNAd on TEC in the absence of TNFR signaling was associated with lack of upregulation of these same genes. A small subset of PNAd⁺ TEC remaining in the absence of TNFR signaling showed normal upregulation of a subset of these genes, but reduced upregulation of genes encoding the scaffolding proteins podocalyxin and nepmucin, and carbohydrate sulfotransferase Chst2. Lastly, we found that checkpoint immunotherapy augmented both the fraction of TEC expressing PNAd and their surface level of this ligand. This work points to strong similarities in the regulation of PNAd expression on TEC by TNFR signaling and on LN BEC by lymphotoxin-β receptor signaling, and provides a platform for the development of novel strategies that manipulate PNAd expression on tumor vasculature as an element of cancer immunotherapy.

An activation to memory differentiation trajectory of tumor-infiltrating lymphocytes informs metastatic melanoma outcomes

There is a need for better classification and understanding of tumor-infiltrating lymphocytes (TILs). Here, we applied advanced functional genomics to interrogate 9,000 human tumors and multiple single-cell sequencing sets using benchmarked T cell states, comprehensive T cell differentiation trajectories, human and mouse vaccine responses, and other human TILs. Compared with other T cell states, enrichment of T memory/resident memory programs was observed across solid tumors. Trajectory analysis of single-cell melanoma CD8+ TILs also identified a high fraction of memory/resident memory-scoring TILs in anti-PD-1 responders, which expanded post therapy. In contrast, TILs scoring highly for early T cell activation, but not exhaustion, associated with non-response. Late/persistent, but not early activation signatures, prognosticate melanoma survival, and co-express with dendritic cell and IFN-γ response programs. These data identify an activation-like state associated to poor response and suggest successful memory conversion, above resuscitation of exhaustion, is an under-appreciated aspect of successful anti-tumoral immunity.

Characteristics of Immune Memory and Effector Activity to Cancer-Expressed MHC Class I Phosphopeptides Differ in Healthy Donors and Ovarian Cancer Patients

Elevated immunity to cancer-expressed antigens can be detected in people with no history of cancer and may contribute to cancer prevention. We have previously reported that MHC-restricted phosphopeptides are cancer-expressed antigens and targets of immune recognition. However, the extent to which this immunity reflects prior or ongoing phosphopeptide exposures was not investigated. In this study, we found that preexisting immune memory to cancer-expressed phosphopeptides was evident in most healthy donors, but the breadth among donors was highly variable. Although three phosphopeptides were recognized by most donors, suggesting exposures to common microbial/infectious agents, most of the 205 tested phosphopeptides were not recognized by peripheral blood mononuclear cells (PBMC) from any donor and the remainder were recognized by only 1 to 3 donors. In longitudinal analyses of 2 donors, effector immune response profiles suggested active reexposures to a subset of phosphopeptides. These findings suggest that the immunogens generating most phosphopeptide-specific immune memory are rare infectious agents or incipient cancer cells with distinct phosphoproteome dysregulations, and that repetitive immunogenic exposures occur in individual donors. Phosphopeptide-specific immunity in PBMCs and tumor-infiltrating lymphocytes from ovarian cancer patients was limited, regardless of whether the phosphopeptide was expressed on the tumor. However, 4 of 10 patients responded to 1 to 2 immunodominant phosphopeptides, and 1 showed an elevated effector response to a tumor-expressed phosphopeptide. As the tumors from these patients displayed many phosphopeptides, these data are consistent with lack of prior exposure or impaired ability to respond to some phosphopeptides and suggest that enhancing phosphopeptide-specific T-cell responses could be a useful approach to improve tumor immunotherapy.

Associations of immune cell homing gene signatures and infiltrates of lymphocyte subsets in human melanomas: discordance with CD163+ myeloid cell infiltrates

BACKGROUND

Immune cells in the tumor microenvironment have prognostic value. In preclinical models, recruitment and infiltration of these cells depends on immune cell homing (ICH) genes such as chemokines, cell adhesion molecules, and integrins. We hypothesized ICH ligands CXCL9-11 and CCL2-5 would be associated with intratumoral T-cells, while CXCL13 would be more associated with B-cell infiltrates.

METHODS

Samples of human melanoma were submitted for gene expression analysis and immune cells identified by immunohistochemistry. Associations between the two were evaluated with unsupervised hierarchical clustering using correlation matrices from Spearman rank tests. Univariate analysis performed Mann-Whitney tests.

RESULTS

For 119 melanoma specimens, analysis of 78 ICH genes revealed association among genes with nonspecific increase of multiple immune cell subsets: CD45⁺, CD8⁺ and CD4⁺ T-cells, CD20⁺ B-cells, CD138⁺ plasma cells, and CD56⁺ NK-cells. ICH genes most associated with these infiltrates included ITGB2, ITGAL, CCL19, CXCL13, plus receptor/ligand pairs CXCL9 and CXCL10 with CXCR3; CCL4 and CCL5 with CCR5. This top ICH gene expression signature was also associated with genes representing immune-activation and effector function. In contrast, CD163⁺ M2-macrophages was weakly associated with a different ICH gene signature.

CONCLUSION

These data do not support our hypothesis that each immune cell subset is uniquely associated with specific ICH genes. Instead, a larger set of ICH genes identifies melanomas with concordant infiltration of B-cell and T-cell lineages, while CD163⁺ M2-macrophage infiltration suggesting alternate mechanisms for their recruitment. Future studies should explore the extent ICH gene signature contributes to tertiary lymphoid structures or cross-talk between homing pathways.

Phospho-β-catenin expression in primary and metastatic melanomas and in tumor-free visceral tissues, and associations with expression of PD-L1 and PD-L2

β-catenin (βcat) is an important downstream effector in the Wnt signaling pathway and plays important roles in the development and progression of many cancers including melanoma. βcat expression is regulated by GSK-3β-mediated phosphorylation at positions 33, 37 and 41. In normal cells, phosphorylation at these sites triggers proteasomal degradation, which prevents accumulation of free cytoplasmic βcat. In cancer cells, stabilized β-catenin translocates into the nucleus, where it associates with TCF/Lef proteins to activate transcription of genes that promote tumorigenesis and metastasis, including PD-L1. It has been suggested that nuclear phospho-βcat (pβcat) staining may be diagnostically useful in differentiating primary from metastatic melanoma. Also, a pβcat peptide (residues 30-39, with only S33 phosphorylated) is naturally presented by melanoma cells as a T-cell target. We evaluated expression of pS33-βcat in primary and metastatic melanomas by immunohistochemistry and found its expression varied widely but was most commonly cytoplasmic. Nuclear staining was identified in only 18% of metastatic melanomas. Staining with antibodies to pS33-βcat and pS33/37/T41-βcat was most intense in mitotic melanoma cells; however, pS33-βcat intensity was not significantly associated with AJCC stage, tumor location, BRAF mutation status, or immune infiltrates. Yet, PD-L1 and PD-L2 expression by tumor cells were significantly higher in tumors with high pS33-βcat expression. The low rate of nuclear pS33-βcat expression suggests that pS33-βcat may have limited utility for identifying metastatic melanomas. However, high expression in dividing cells and strong associations with PD-L1 and PD-L2 expression may inform future personalized therapies for tumors with high pS33-βcat expression.

Immune mechanisms orchestrate tertiary lymphoid structures in tumors via cancer-associated fibroblasts

Tumor-associated tertiary lymphoid structures (TA-TLS) are associated with enhanced patient survival and responsiveness to cancer therapies, but the mechanisms underlying their development are unknown. We show here that TA-TLS development in murine melanoma is orchestrated by cancer-associated fibroblasts (CAF) with characteristics of lymphoid tissue organizer cells that are induced by tumor necrosis factor receptor signaling. CAF organization into reticular networks is mediated by CD8 T cells, while CAF accumulation and TA-TLS expansion depend on CXCL13-mediated recruitment of B cells expressing lymphotoxin-α1β2. Some of these elements are also overrepresented in human TA-TLS. Additionally, we demonstrate that immunotherapy induces more and larger TA-TLS that are more often organized with discrete T and B cell zones, and that TA-TLS presence, number, and size are correlated with reduced tumor size and overall response to checkpoint immunotherapy. This work provides a platform for manipulating TA-TLS development as a cancer immunotherapy strategy.

MHC-restricted phosphopeptide antigens: preclinical validation and first-in-humans clinical trial in participants with high-risk melanoma

BACKGROUND

Phosphorylated peptides presented by MHC molecules represent a new class of neoantigens expressed on cancer cells and recognized by CD8 T-cells. These peptides are promising targets for cancer immunotherapy. Previous work identified an HLA-A*0201-restricted phosphopeptide from insulin receptor substrate 2 (pIRS2) as one such target. The purpose of this study was to characterize a second phosphopeptide, from breast cancer antiestrogen resistance 3 (BCAR3), and to evaluate safety and immunogenicity of a novel immunotherapic vaccine comprising either or both of these phosphorylated peptides.

METHODS

Phosphorylated BCAR3 protein was evaluated in melanoma and breast cancer cell lines by Western blot, and recognition by T-cells specific for HLA-A*0201-restricted phosphorylated BCAR3 peptide (pBCAR3_126-134) was determined by ⁵¹Cr release assay and intracellular cytokine staining. Human tumor explants were also evaluated by mass spectrometry for presentation of pIRS2 and pBCAR3 peptides. For the clinical trial, participants with resected stage IIA-IV melanoma were vaccinated 6 times over 12 weeks with one or both peptides in incomplete Freund's adjuvant and Hiltonol (poly-ICLC). Adverse events (AEs) were coded based on National Cancer Institute (NCI) Common Terminology Criteria for Adverse Events (CTCAE) V.4.03, with provision for early study termination if dose-limiting toxicity (DLT) rates exceeded 33%. The enrollment target was 12 participants evaluable for immune response to each peptide. T-cell responses were assessed by interferon-γ ELISpot assay.

RESULTS

pBCAR3 peptides were immunogenic in vivo in mice, and in vitro in normal human donors, and T-cells specific for pBCAR3_126-134 controlled outgrowth of a tumor xenograft. The pIRS2_1097-1105 peptide was identified by mass spectrometry from human hepatocellular carcinoma tumors. In the clinical trial, 15 participants were enrolled. All had grade 1 or 2 treatment-related AEs, but there were no grade 3-4 AEs, DLTs or deaths on study. T-cell responses were induced to the pIRS2_1097-1105 peptide in 5/12 patients (42%, 90% CI 18% to 68%) and to the pBCAR3_126-134 peptide in 2/12 patients (17%, 90% CI 3% to 44%).

CONCLUSION

This study supports the safety and immunogenicity of vaccines containing the cancer-associated phosphopeptides pBCAR3_126-134 and pIRS2_1097-1105, and the data support continued development of immune therapy targeting phosphopeptides. Future studies will define ways to further enhance the magnitude and durability of phosphopeptide-specific immune responses.

TRIAL REGISTRATION NUMBER

NCT01846143.

Heterogeneity in tertiary lymphoid structure B-cells correlates with patient survival in metastatic melanoma

BACKGROUND

Tertiary lymphoid structures (TLSs) are immune aggregates in peripheral tissues that may support adaptive immune responses. Their presence has been associated with clinical response to checkpoint blockade therapy (CBT), but it is unknown whether TLS have prognostic significance independent of CBT in melanoma. We hypothesized that TLS in melanoma metastases would be associated with increased intratumoral lymphocyte infiltration, but that the intra-TLS immunological milieu would be distinct from the intratumoral immunological milieu. We also hypothesized that the presence of TLS would be associated with improved survival, and that TLS maturation or intra-TLS lymphocyte activity would also correlate with survival.

METHODS

Cutaneous melanoma metastases (CMM) from 64 patients were evaluated by multiplex immunofluorescence for the presence and maturation status of TLS. Intra-TLS lymphocyte density, proliferation and B-cell Ig somatic hypermutation (AID+) were analyzed, as were markers of T-cell exhaustion and Th1/Tc1 differentiation. Associations between TLS maturation and intra-TLS immunologic activity were assessed, as well as associations with intratumoral immune cell infiltration. Independent associations with overall survival (OS) were assessed using log-rank tests and Cox proportional hazards models.

RESULTS

TLS were identified in 30 (47%) of 64 CMM (TLS+) and were associated with increased intratumoral lymphocyte infiltration. However, proliferation of intra-TLS lymphocytes did not correlate with intratumoral lymphocyte proliferation. Most were early TLS; however, subsets of primary or secondary follicle-like TLS were also present. TLS+ lesions were associated with lower risk of tumor recurrence after metastasectomy and with improved OS in multivariate analyses (HR 0.51, p=0.04). OS was longer for TLS with low fractions of CD21+ B-cells (HR 0.29, p=0.02) and shorter for those with low AID+ fraction of B-cells (HR 2.74, p=0.03).

CONCLUSIONS

The presence of TLS in CMMs is associated with improved OS in patients treated with surgery before CBT, but TLS vary widely in maturation state, in proportions of proliferating T and B cells, and in markers of B cell function, including AID and CD21. Importantly, these features have additional prognostic significance, which suggest that some TLS may have regulatory function, while others functioning to support antigen-driven immune responses, depending on the cellular composition and activation status.

Differential Expression of CD49a and CD49b Determines Localization and Function of Tumor-Infiltrating CD8+ T Cells

CD8⁺ T-cell infiltration and effector activity in tumors are correlated with better overall survival of patients, suggesting that the ability of T cells to enter and remain in contact with tumor cells supports tumor control. CD8⁺ T cells express the collagen-binding integrins CD49a and CD49b, but little is known about their function or how their expression is regulated in the tumor microenvironment (TME). Here, we found that tumor-infiltrating CD8⁺ T cells initially expressed CD49b, gained CD49a, and then lost CD49b over the course of tumor outgrowth. This differentiation sequence was driven by antigen-independent elements in the TME, although T-cell receptor (TCR) stimulation further increased CD49a expression. Expression of exhaustion markers and CD49a associated temporally but not mechanistically. Intratumoral CD49a-expressing CD8⁺ T cells failed to upregulate TCR-dependent Nur77 expression, whereas CD69 was constitutively expressed, consistent with both a lack of productive antigen engagement and a tissue-resident memory-like phenotype. Imaging T cells in live tumor slices revealed that CD49a increased their motility, especially of those in close proximity to tumor cells, suggesting that it may interfere with T-cell recognition of tumor cells by distracting them from productive engagement, although we were not able to augment productive engagement by short-term CD49a blockade. CD49b also promoted relocalization of T cells at a greater distance from tumor cells. Thus, our results demonstrate that expression of these integrins affects T-cell trafficking and localization in tumors via distinct mechanisms, and suggests a new way in which the TME, and likely collagen, could promote tumor-infiltrating CD8⁺ T-cell dysfunction.

Insights into Tumor-Associated Tertiary Lymphoid Structures: Novel Targets for Antitumor Immunity and Cancer Immunotherapy

Tertiary lymphoid structures (TLS) are ectopic lymphoid aggregates that phenotypically resemble conventional secondary lymphoid organs and are commonly found at sites of chronic inflammation. They are also found in a wide variety of primary and metastatic human tumors. The presence of tumor-associated TLS (TA-TLS) is associated with prolonged patient survival, higher rates of disease-free survival, and a favorable response to current cancer therapies. However, the immune responses that occur in these structures, and how they contribute to improved clinical outcomes, remain incompletely understood. In addition, it is unknown how heterogeneity in TA-TLS cellular composition, structural organization, and anatomic location influences their functionality and prognostic significance. Understanding more about TA-TLS development, formation, and function may offer new therapeutic options to modulate antitumor immunity.

Immunomodulation of intracranial melanoma in response to blood-tumor barrier opening with focused ultrasound

Background: Focused ultrasound (FUS) activation of microbubbles (MBs) for blood-brain (BBB) and blood-tumor barrier (BTB) opening permits targeted therapeutic delivery. While the effects of FUS+MBs mediated BBB opening have been investigated for normal brain tissue, no such studies exist for intracranial tumors. As this technology advances into clinical immunotherapy trials, it will be crucial to understand how FUS+MBs modulates the tumor immune microenvironment. Methods and Results: Bulk RNA sequencing revealed that FUS+MBs BTB/BBB opening (1 MHz, 0.5 MPa peak-negative pressure) of intracranial B16F1cOVA tumors increases the expression of genes related to proinflammatory cytokine and chemokine signaling, pattern recognition receptor signaling, and antigen processing and presentation. Flow cytometry revealed increased maturation (i.e. CD86) of dendritic cells (DCs) in the meninges and altered antigen loading of DCs in both the tumor and meninges. For DCs in tumor draining lymph nodes, FUS+MBs had no effect on maturation and elicited only a trend towards increased presentation of tumor-derived peptide by MHC. Neither tumor endothelial cell adhesion molecule expression nor homing of activated T cells was affected by FUS+MBs. Conclusion: FUS+MBs-mediated BTB/BBB opening elicits signatures of inflammation; however, the response is mild, transient, and unlikely to elicit a systemic response independent of administration of immune adjuvants.

Evidence of ongoing immune surveillance to cancer-associated phosphopeptides in healthy individuals

Dysregulated protein phosphorylation plays a major role in cancer cell malignancy. We showed that phosphopeptides are presented by MHC-I molecules, representing a new class of cancer neoantigens. We found that healthy donors with no evident prior cancer had robust CD8+ T cell responses to a cohort of HLA-B7+ leukemia-associated phosphopeptides. Here we report that CD8+CD45RO+ T cells purified from blood of different healthy donors showed responses to 2–25% of HLA-A2+ and 0–23% of HLA-B7+ cancer-associated phosphopeptides, confirming that individuals with no evident cancer history have pre-existing phosphopeptide specific immune memory. Six of 59 HLA-A2+ phosphopeptides were “immunodominant,” with memory responses evident in the majority of analyzed donors. This suggests that these phosphopeptides result from processes common in cellular transformation or viral infection. In contrast, no immunodominant HLA-B7+ phosphopeptides were identified among the 168 analyzed, suggesting that mechanisms driving their expression in healthy donors are less common. Robust day 14 responses were observed against a small cohort of HLA-B7+ phosphopeptides in 2 donors. Responses to some of these phosphopeptides could be detected ex vivo and were evident over 3 years, suggesting they reflected chronic antigen exposures. In contrast, responses to 2 phosphopeptides evident ex vivo diminished or disappeared over 14 days in culture, suggesting a recent acute immune response composed of terminal effectors unable to persist long term. These results provide evidence of ongoing immune surveillance in healthy individuals to phosphopeptides known to be expressed on cancers.

Low immunogenicity of intracranial tumors limits immune response to brain malignancies

The presence of CD8 T cells in tumors, including melanomas, is correlated with longer survival. Cutaneous melanoma is a highly immunogenic malignancy with high rate of dissemination into central nervous system but the brain is considered immunologically privileged due to the blood-brain barrier, which limits T cell entry. To determine if brain tumors are also poorly infiltrated by T cells we evaluated intracranial (IC) and subcutaneous (SC) B16 melanomas expressing different model antigens.

CD8 T cells were present in IC tumors 7 days post tumor implantation in B16 melanomas expressing chicken ovalbumin (B16OVA) or influenza M1 protein (B16M1), but infiltrates were only 10% of those observed in SC tumors. We also observed that expression of homing receptor ligands (HRLs) known to mediate T cell infiltration was lower on IC than SC tumor-associated vasculature. Despite the fact that HRL expression decreased over time in tumors grown in both locations, T cell infiltrates increased, suggesting that HRL are not the only factor limiting T cells entry into IC tumors.

To determine whether the IC tumor infiltrate size was limited by inefficient stimulation of effectors cells, we vaccinated mice to generate fully activated effector T cells able to recognize tumor associated antigen. Vaccination normalized the infiltrate sizes in IC and SC tumors. Interestingly, this was also dependent on expression of Ag by the tumor cells. This suggests that IC tumors are not able to efficiently elicit a robust immune response, possibly due to limitations on drainage to lymph nodes, while IC tumor vasculature does not impose inherently greater limitations on the ability of T cells to enter.

Abstract B68: Pre-existing immune memory to cancer-associated phosphopeptides in healthy donors

Identifying appropriate antigens is essential to developing effective cancer vaccines. Protein phosphorylation plays a major role in signal transduction pathways that are dysregulated and contribute to the malignant phenotype of cancer cells. Our lab has shown that phosphopeptides derived from these proteins can be presented by major histocompatibility complex Class-I molecules and represent a new class of cancer-associated neoantigens. We previously reported that healthy donors without evident prior cancer had unusually robust CD8 T-cell responses to a cohort of HLA-B7+ leukemia-associated phosphopeptides, suggesting that they might be due to pre-existing phosphopeptide specific memory T cells. To test this, we evaluated CD8+CD45RO+ memory T cells purified from the blood of healthy donors. These cells showed robust responses to 2-25% of HLA-A2+ and 0-23% of HLA-B7+ cancer-associated phosphopeptides. This demonstrates that healthy individuals with no evident cancer history have pre-existing immune memory to some cancer-associated phosphopeptides. We identified 3 “immunodominant” HLA-A2 associated phosphopeptides, in that memory responses were evident to them in the majority of analyzed donors. Such immunodominance suggests that these phosphopeptides result from signaling processes that occur commonly in transformation- or viral infection-related processes. In contrast, immunodominant phosphopeptides were not evident in the context of HLA-B7. While 2 donors showed pre-existing immune memory to a large number of shared targets, other donors showed memory to only small numbers of nonoverlapping phosphopeptides. This suggests that the mechanisms driving expression of these phosphopeptide antigens among healthy donors are much less common. We also found that responses to some phosphopeptides could be detected directly ex vivo. In some cases, the phosphopeptide targets of these ex vivo responses did not stimulate responses after 2 weeks in culture. These results suggest that some phosphopeptides in some donors may be the targets of ongoing immune responses composed of effector or effector memory cells that do not persist long-term in culture. These results provide evidence of regular, ongoing immune surveillance in healthy individuals to cancer-associated phosphopeptides.

Citation Format: Amanda M. Lulu, Kara L. Cummings, Victor H. Engelhard. Pre-existing immune memory to cancer-associated phosphopeptides in healthy donors [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2018 Nov 27-30; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(4 Suppl):Abstract nr B68.

Antibiotics Drive Microbial Imbalance and Vitiligo Development in Mice

Vitiligo is impacted by environmental triggers. We studied the contribution of the microbiome in FH mice, in which depigmentation is mediated by tyrosinase-reactive T cells. The mice received oral antibiotics and were monitored for depigmentation. The microbiome was studied in fecal and skin samples using 16S rRNA analysis. The resulting T-cell distributions were evaluated. In untreated mice, pigment loss did not expand to the pelage, whereas mice in the ampicillin group were approximately 1/3 depigmented at 30 weeks. In contrast to models of autoimmunity that are less dependent on IFN-γ, ampicillin but not neomycin treatment correlated with accelerated disease and reduced bacteria in the fecal pellets. Modified cytokine patterns in the tissue and serum suggest a response that transcends the gut. Ampicillin-induced depigmentation was accompanied by gut but not skin dysbiosis, and reduced T cell numbers in both sites. Neomycin induced a redistribution of gut T cells and an accumulation of skin regulatory T cells. This treatment spurred a Bacteroides-dominated population of fecal bacteria. Reduced diversity is prominent particularly after ampicillin treatment, when the gut is dominated by Pseudomonas species. In line with current concepts relating the microbiome and the immune system, we predict that dietary measures might promote skin health and delay vitiligo onset.

The Antigen Processing and Presentation Machinery in Lymphatic Endothelial Cells

Until a few years ago, lymphatic vessels and lymphatic endothelial cells (LEC) were viewed as part of a passive conduit for lymph and immune cells to reach lymph nodes (LN). However, recent work has shown that LEC are active immunological players whose interaction with dendritic cells and T cells is of important immunomodulatory relevance. While the immunological interaction between LEC and other immune cells has taken a center stage, molecular analysis of LEC antigen processing and presentation machinery is still lagging. Herein we review the current knowledge of LEC MHC I and MHC II antigen processing and presentation pathways, Including the role of LEC in antigen phagocytosis, classical, and non-classical MHC II presentation, proteasome processing and MHC I presentation, and cross-presentation. The ultimate goal is to provide an overview of the LEC antigen processing and presentation machinery that constitutes the molecular basis for their role in MHC I and MHC II-restricted immune responses.

Comparative Transcriptomic Analysis Identifies a Range of Immunologically Related Functional Elaborations of Lymph Node Associated Lymphatic and Blood Endothelial Cells

Lymphatic and blood vessels are formed by specialized lymphatic endothelial cells (LEC) and blood endothelial cells (BEC), respectively. These endothelial populations not only form peripheral tissue vessels, but also critical supporting structures in secondary lymphoid organs, particularly the lymph node (LN). Lymph node LEC (LN-LEC) also have been shown to have important immunological functions that are not observed in LEC from tissue lymphatics. LN-LEC can maintain peripheral tolerance through direct presentation of self-antigen via MHC-I, leading to CD8 T cell deletion; and through transfer of self-antigen to dendritic cells for presentation via MHC-II, resulting in CD4 T cell anergy. LN-LEC also can capture and archive foreign antigens, transferring them to dendritic cells for maintenance of memory CD8 T cells. The molecular basis for these functional elaborations in LN-LEC remain largely unexplored, and it is also unclear whether blood endothelial cells in LN (LN-BEC) might express similar enhanced immunologic functionality. Here, we used RNA-Seq to compare the transcriptomic profiles of freshly isolated murine LEC and BEC from LN with one another and with freshly isolated LEC from the periphery (diaphragm). We show that LN-LEC, LN-BEC, and diaphragm LEC (D-LEC) are transcriptionally distinct from one another, demonstrating both lineage and tissue-specific functional specializations. Surprisingly, tissue microenvironment differences in gene expression profiles were more numerous than those determined by endothelial cell lineage specification. In this regard, both LN-localized endothelial cell populations show a variety of functional elaborations that suggest how they may function as antigen presenting cells, and also point to as yet unexplored roles in both positive and negative regulation of innate and adaptive immune responses. The present work has defined in depth gene expression differences that point to functional specializations of endothelial cell populations in different anatomical locations, but especially the LN. Beyond the analyses provided here, these data are a resource for future work to uncover mechanisms of endothelial cell functionality.

Formation and phenotypic characterization of CD49a, CD49b and CD103 expressing CD8 T cell populations in human metastatic melanoma

Integrins α1β1 (CD49a), α2β1 (CD49b) and αEβ7 (CD103) mediate retention of lymphocytes in peripheral tissues, and their expression is upregulated on tumor infiltrating lymphocytes (TIL) compared to circulating lymphocytes. Little is known about what induces expression of these retention integrins (RI) nor whether RI define subsets in the tumor microenvironment (TME) with a specific phenotype. Human metastatic melanoma-derived CD8 TIL could be grouped into five subpopulations based on RI expression patterns: RI^neg, CD49a⁺ only, CD49a⁺CD49b⁺, CD49a⁺CD103⁺, or positive for all three RI. A significantly larger fraction of the CD49a⁺ only subpopulation expressed multiple effector cytokines, whereas CD49a⁺CD103⁺ and CD49a⁺CD49b⁺ cells expressed IFNγ only. RI^neg and CD49a⁺CD49b⁺CD103⁺ CD8 TIL subsets expressed significantly less effector cytokines overall. Interestingly, however, CD49a⁺CD49b⁺CD103⁺ CD8 expressed lowest CD127, and highest levels of perforin and exhaustion markers PD-1 and Tim3, suggesting selective exhaustion rather than conversion to memory. To gain insight into RI expression induction, normal donor PBMC were cultured with T cell receptor (TCR) stimulation and/or cytokines. TCR stimulation alone induced two RI⁺ cell populations: CD49a single positive and CD49a⁺CD49b⁺ cells. TNFα and IL-2 each were capable of inducing these populations. Addition of TGFβ to TCR stimulation generated two additional populations; CD49a⁺CD49b^negCD103⁺ and CD49a⁺CD49b⁺CD103^+. Taken together, our findings identify opportunities to modulate RI expression in the TME by cytokine therapies and to generate subsets with a specific RI repertoire in the interest of augmenting immune therapies for cancer or for modulating other immune-related diseases such as autoimmune diseases.

Cellular and molecular mechanisms regulating the development of tertiary lymphoid structures in tumor

Tertiary lymphoid structures (TLS) have been described in association with several tumor types, and they are usually associated with enhanced patient survival. However, mechanisms regulating their formation remain unknown. We found that intra- and peri-tumoral TLS develop in intraperitoneal (IP) but not subcutaneously (SC) implanted tumors. These TLS are characterized by a robust accumulation of B cells, and an associated reticular network of podoplanin+ fibroblasts expressing high levels of CXCL12, CXCL13, and the B-cell survival factors BAFF and APRIL. These results suggest that IP tumor-associated fibroblasts are polarized into organizer cells that orchestrate TLS formation. We’ve previously demonstrated that CD8 T effectors induce the development of lymph node-like vasculature in IP tumors. To determine whether these cells also regulate TLS development, we evaluated IP tumors grown in Rag1−/− mice and Rag1−/− mice repleted with bulk CD8 T cells. CD8 T cells upregulated the number of podoplanin+ fibroblasts and CXCL12 expression. However, CXCL13, BAFF and APRIL expression was not dependent on CD8 T cells. Thus, the representation of podoplanin+ fibroblasts and their expression of CXCL12 is regulated by adaptive immunity, while their expression of CXCL13, BAFF and APRIL is mediated by an innate element within the IP tumor microenvironment. We also found that increasing the load of the model tumor antigen ovalbumin led to an increased formation of peri-tumoral TLS with a classical organization, on top of the non-classical intratumoral structures evident at a low antigen load. These results identify novel mechanisms regulating different elements involved in organizing tumor-associated TLS.

Cancer vaccine formulation dictates synergy with CTLA-4 and PD-L1 checkpoint blockade therapy

Anticancer vaccination is a promising approach to increase the efficacy of cytotoxic T lymphocyte-associated protein 4 (CTLA-4) and programmed death ligand 1 (PD-L1) checkpoint blockade therapies. However, the landmark FDA registration trial for anti-CTLA-4 therapy (ipilimumab) revealed a complete lack of benefit of adding vaccination with gp100 peptide formulated in incomplete Freund's adjuvant (IFA). Here, using a mouse model of melanoma, we found that gp100 vaccination induced gp100-specific effector T cells (Teffs), which dominantly forced trafficking of anti-CTLA-4-induced, non-gp100-specific Teffs away from the tumor, reducing tumor control. The inflamed vaccination site subsequently also sequestered and destroyed anti-CTLA-4-induced Teffs with specificities for tumor antigens other than gp100, reducing the antitumor efficacy of anti-CTLA-4 therapy. Mechanistically, Teffs at the vaccination site recruited inflammatory monocytes, which in turn attracted additional Teffs in a vicious cycle mediated by IFN-γ, CXCR3, ICAM-1, and CCL2, dependent on IFA formulation. In contrast, nonpersistent vaccine formulations based on dendritic cells, viral vectors, or water-soluble peptides potently synergized with checkpoint blockade of both CTLA-4 and PD-L1 and induced complete tumor regression, including in settings of primary resistance to dual checkpoint blockade. We conclude that cancer vaccine formulation can dominantly determine synergy, or lack thereof, with CTLA-4 and PD-L1 checkpoint blockade therapy for cancer.

Immune Cell Infiltration and Tertiary Lymphoid Structures as Determinants of Antitumor Immunity

Limited representation of intratumoral immune cells is a major barrier to tumor control. However, simply enhancing immune responses in tumor-draining lymph nodes or through adoptive transfer may not overcome the limited ability of tumor vasculature to support effector infiltration. An alternative is to promote a sustained immune response intratumorally. This idea has gained traction with the observation that many tumors are associated with tertiary lymphoid structures (TLS), which organizationally resemble lymph nodes. These peri- and intratumoral structures are usually, but not always, associated with positive prognoses in patients. Preclinical and clinical data support a role for TLS in modulating immunity in the tumor microenvironment. However, there appear to be varied functions of TLS, potentially based on their structure or location in relation to the tumor or the origin or location of the tumor itself. Understanding more about TLS development, composition, and function may offer new therapeutic opportunities to modulate antitumor immunity.

Differential Expression of Homing Receptor Ligands on Tumor-Associated Vasculature that Control CD8 Effector T-cell Entry

Although CD8⁺ T cells are critical for controlling tumors, how they are recruited and home to primary and metastatic lesions is incompletely understood. We characterized the homing receptor (HR) ligands on tumor vasculature to determine what drives their expression and their role in T-cell entry. The anatomic location of B16-OVA tumors affected the expression of E-selectin, MadCAM-1, and VCAM-1, whereas the HR ligands CXCL9 and ICAM-1 were expressed on the vasculature regardless of location. VCAM-1 and CXCL9 expression was induced by IFNγ-secreting adaptive immune cells. VCAM-1 and CXCL9/10 enabled CD8⁺ T-cell effectors expressing α₄β₁ integrin and CXCR3 to enter both subcutaneous and peritoneal tumors, whereas E-selectin enabled E-selectin ligand⁺ effectors to enter subcutaneous tumors. However, MadCAM-1 did not mediate α₄β₇⁺ effector entry into peritoneal tumors due to an unexpected lack of luminal expression. These data establish the relative importance of certain HRs expressed on activated effectors and certain HR ligands expressed on tumor vasculature in the effective immune control of tumors. Cancer Immunol Res; 5(12); 1062-73. ©2017 AACR.

Abstract 4609: Agenus’ next generation cancer vaccine platforms

Most cancer cells carry mutations unique to the patient’s individual tumor and shared biochemical signatures that are not present in healthy cells. Agenus has three vaccine platforms designed to treat cancers based on the unique needs of a given patient. Our vaccine platforms are designed to educate the patient’s immune system to recognize tumor-specific aberrations, or neo-antigens, and mount an anti-tumor immune response.

Agenus’ Prophage™ vaccine platform is an individualized vaccine made from the patient’s own tumor tissue. Heat shock proteins (gp-96) that naturally chaperone and bind tumor-derived peptides are extracted from the patient’s tumor and constitute the vaccine. Some of these peptides are neo-antigens. Agenus has completed Phase 2 clinical trials with Prophage™ vaccine in newly diagnosed glioblastoma (ndGBM), and has previously reported that there was improved progression-free and overall survival with Prophage™ vaccine compared to standard of care.

Agenus’ AutoSynVax™ vaccines are uniquely designed and manufactured for each patient based on NGS profiling of the patient’s tumor from a biopsy. Leveraging the Agenus Immunogenic Mutation (AIM™) workflow, we are able to generate a synthesis-ready blueprint for an optimal immunogenic and personalized neo-antigen vaccine. The AIM™ platform provides a robust and efficient approach to computational vaccinology designed to deliver a set of likely immunogenic peptides, agnostic to vaccine format, followed by generation of a format-specific blueprint ready for vaccine synthesis and manufacture. The synthesized neo-epitopes are complexed to recombinant heat shock protein 70 (HSC70) and are administered along with our QS-21 Stimulon® adjuvant. HSC70 is known to transport epitopes and play a role in displaying them to T cells.

While the first two of Agenus’ vaccine platforms are highly individualized, our PhosphoSynVax™ vaccine is an off-the-shelf vaccine format targeting a novel class of tumor neo-antigens arising from post translational modifications (PTMs). Due to dysregulated cell signaling pathways in cancer, self-peptides can be aberrantly phosphorylated, a number of which are subsequently presented on HLA molecules. Using mass-spectrometry, we have identified a library of over a thousand HLA phospholigands. Many of these are tumor specific and found in multiple patients across multiple indications, enabling pre-manufacture of PhosphoSynVax™ vaccines for ready use.

Upon testing the HSP plus synthetic peptide vaccine format in murine models, we have demonstrated effective tumor control in a therapeutic setting and also effective immune memory in a long-term prophylactic setting. Given Agenus’ diverse portfolio we have the opportunity to combine our immune education strategies with immunomodulatory antibodies to increase therapeutic efficacy.

Citation Format: Mohamed Uduman, Mithun Khattar, Bishnu Joshi, Antoine Tanne, Benjamin Morin, Armen Karapetyan, Elise Drouin, Sandra Craig, Paisley Myers, Erin Jeffery, Nicholas Wilson, Amy Yang, Victor H. Engelhard, Mark Cobbold, Donald F. Hunt, Dennis Underwood, Shiwen Lin, Mark Findeis, Jeffrey Raizer, John Goldberg, Jennifer S. Buell, Robert Stein, Daniel L. Levey, John Castle. Agenus’ next generation cancer vaccine platforms [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4609. doi:10.1158/1538-7445.AM2017-4609

Factors controlling the tolerogenic phenotype of lymphatic endothelial cells

The prevailing model of peripheral tolerance necessitates tissue-resident dendritic cells migrating to lymph nodes and cross presenting self-antigen to T cells, resulting in their deletion or anergy. Our lab has identified a novel mechanism of peripheral tolerance involving a subset of lymph node stromal cells called lymphatic endothelial cells (LEC). LEC in the lymph node induce peripheral tolerance by presenting epitopes derived from peripheral tissue antigens (PTAs) in conjunction with expression of PD-L1, leading to CD8 T cell deletion. However, PTAs and PD-L1 are not expressed on LEC in the colon or diaphragm. We performed RNAseq analysis on LEC from lymph node and diaphragm to identify differences in expression of transcription factors that might control expression of PD-L1 and PTA. We found that Spi-B is the most differentially expressed transcription factor in the lymph node compared to the diaphragm, with a fold change of over 500. Spi-B has been implicated in the development and function of medullary thymic epithelial cells, a key cell type in central tolerance. Lymph node LEC harvested from Spi-B deficient mice have a significant shift in markers associated with LEC tolerogenicity. Expression levels of PD-L1, ICAM-1, MAdCAM-1, and LTbR delineate different lymph node LEC subpopulations that vary in their ability to express PTAs and tolerize CD8 T cells. LEC from Spi-B deficient mice have decreased MAdCAM-1 expression and increased LTbR and ICAM-1 expression suggesting a population shift of non-tolerogenic lymph node LEC to tolerogenic lymph node LEC. This data suggests Spi-B may be involved in a negative feedback mechanism to limit the number of tolerogenic LEC during development.

The antigenic identity of human class I MHC phosphopeptides is critically dependent upon phosphorylation status

Dysregulated post-translational modification provides a source of altered self-antigens that can stimulate immune responses in autoimmunity, inflammation, and cancer. In recent years, phosphorylated peptides have emerged as a group of tumour-associated antigens presented by MHC molecules and recognised by T cells, and represent promising candidates for cancer immunotherapy. However, the impact of phosphorylation on the antigenic identity of phosphopeptide epitopes is unclear. Here we examined this by determining structures of MHC-bound phosphopeptides bearing canonical position 4-phosphorylations in the presence and absence of their phosphate moiety, and examining phosphopeptide recognition by the T cell receptor (TCR). Strikingly, two peptides exhibited major conformational changes upon phosphorylation, involving a similar molecular mechanism, which focussed changes on the central peptide region most critical for T cell recognition. In contrast, a third epitope displayed little conformational alteration upon phosphorylation. In addition, binding studies demonstrated TCR interaction with an MHC-bound phosphopeptide was both epitope-specific and absolutely dependent upon phosphorylation status. These results highlight the critical influence of phosphorylation on the antigenic identity of naturally processed class I MHC epitopes. In doing so they provide a molecular framework for understanding phosphopeptide-specific immune responses, and have implications for the development of phosphopeptide antigen-specific cancer immunotherapy approaches.

Abstract A031: Cancer vaccine formulation dictates synergy with CTLA-4 and PD-L1 checkpoint blockade therapy

Introduction: Therapeutic blockade of the T cell checkpoint receptors, CTLA-4 and PD-1, can cure some patients with metastatic cancer. Primary resistance to checkpoint blockade therapy is likely due to insufficient spontaneous anti-tumor immunity, and might be overcome by tumor-specific vaccination. However, the same 676-patient landmark study1 that led to FDA approval of anti-CTLA-4 for patients with melanoma showed no added benefit to anti-CTLA-4 monotherapy of concurrent vaccination with gp100 peptide in Incomplete Freund's Adjuvant (IFA), which instead significantly decreased overall response rate and disease control rate through an unknown mechanism1.

Experimental Procedure: To understand the parameters that control synergy between checkpoint blockade and anti-cancer vaccination, we modelled vaccination with gp100 peptide in IFA and anti-CTLA-4 therapy in the standard treatment model of established subcutaneous B16 melanoma2. To correct for the fact that B16 melanoma progresses so rapidly that there is no time for multiple cycles of gp100 vaccination as was given to the melanoma patients, we adoptively transferred naive TCR-transgenic pmel-1 CD8+ T cells that specifically recognize the hgp10025-33 epitope.

Results: Paralleling what was observed in patients1, gp100/IFA vaccination did not enhance, but significantly decreased, the therapeutic efficacy of anti-CTLA-4 therapy, even though we found high levels of gp100-specific pmel-1 T cells in the circulation. Anti-CTLA-4 monotherapy increased intratumoral localization of Tyrosinase-related protein-2 (TRP-2), p15E and gp100 melanoma antigen-specific CD8+ effector T cells (Teff), while gp100/IFA vaccination-induced, gp100-specific CD8+ Teff accumulated at the inflamed vaccination site. Combination of gp100/IFA vaccination and anti-CTLA-4 therapy caused TRP-2, p15E and gp100-specific Teff to similarly redistribute to the gp100/IFA vaccination site and away from the tumor site. This T cell redistribution was accompanied by reduced tumor control and was mediated by IFN-γ, CXCR3 and ICAM-1. At vaccination sites, ICAM-1 and VCAM-1 expression lacked clear association with the vasculature, and instead was abundant on SSChiCD11bhiLy6GloLy6ChiF4-80+CCR2+ (inflammatory) monocytes. Inflammatory monocytes infiltrating were accompanied by CD8+ Teff recruitment; and, conversely, when CD8+ Teff level were low so were inflammatory monocytes, indicating CCR2/CXCR3 positive feedback loop between CD8+ Teff and inflammatory monocytes resulting in their accumulation at the vaccination site, and consequent local skin inflammation. Non-persistent vaccine formulations do not induce these undesirable effects and potently synergize with anti-CTLA-4 and anti-PD-L1 checkpoint blockade, resulting in markedly increased anti-tumor activity. In a challenging setting of 7-day established tumors where dual checkpoint blockade cured only 10% of the mice, addition of non-persistent Vesicular Stomatitis Virus encoding gp100 (VSV.gp100) resulted in 67% cure (p < 0.0001, >200d). Correspondently, dual checkpoint blockade with gp100/IFA vaccination did not cure any mice.

Conclusions: Overall, our results indicate persistent vaccine formulations can fail to increase, or even diminish, the efficacy of CTLA-4 and PD-L1 checkpoint-based cancer therapy through divergent trafficking of checkpoint blockade-induced Teff to the vaccination site. Non-persistent vaccine formulations do not induce these undesirable effects and potently synergize with anti-CTLA-4 and anti-PD-L1 checkpoint blockade, resulting in markedly increased anti-tumor activity.

1. Hodi, F.S., et al. Improved survival with ipilimumab in patients with metastatic melanoma. N Engl J Med 363, 711-723 (2010).

2. Fu, T., He, Q. & Sharma, P. The ICOS/ICOSL pathway is required for optimal antitumor responses mediated by anti-CTLA-4 therapy. Cancer Res 71, 5445-5454 (2011).

Citation Format: Yared Hailemichael, Tihui Fu, Amber Woods, Jason Roszik, Kimberly S. Schluns, Victor H. Engelhard, Padmanee Sharma, Willem W. Overwijk. Cancer vaccine formulation dictates synergy with CTLA-4 and PD-L1 checkpoint blockade therapy [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr A031.

Identification and Characterization of Complex Glycosylated Peptides Presented by the MHC Class II Processing Pathway in Melanoma

The MHC class II (MHCII) processing pathway presents peptides derived from exogenous or membrane-bound proteins to CD4+ T cells. Several studies have shown that glycopeptides are necessary to modulate CD4+ T cell recognition, though glycopeptide structures in these cases are generally unknown. Here, we present a total of 93 glycopeptides from three melanoma cell lines and one matched EBV-transformed line with most found only in the melanoma cell lines. The glycosylation we detected was diverse and comprised 17 different glycoforms. We then used molecular modeling to demonstrate that complex glycopeptides are capable of binding the MHC and may interact with complementarity determining regions. Finally, we present the first evidence of disulfide-bonded peptides presented by MHCII. This is the first large scale study to sequence glyco- and disulfide bonded MHCII peptides from the surface of cancer cells and could represent a novel avenue of tumor activation and/or immunoevasion.

CD49a and CD103 expression on tumor infiltrating lymphocytes in B16-OVA tumors depends on location and is correlated with a naive phenotype

Tissue resident memory (TRM) cells are found in certain peripheral tissues long after resolution of infections that generate them. TRM formation is induced by TGFβ and has been associated with upregulation of CD49a and CD103. Interaction of CD49a and CD103 with their respective ligands is thought to allow long term persistence of TRM cells in peripheral tissues. In melanoma patients, increased expression of CD49a and CD103 has been observed on tumor infiltrating lymphocytes (TIL) compared to PBMCs. These phenotypic similarities suggest that a subset of TIL might function as TRM. However, the impact of continuous antigen presentation and/or differential TGFβ expression levels on this property of TIL is currently unknown. Here we demonstrate that, in B16-OVA melanoma tumors, CD49a and CD103 expression on CD8 TILs is upregulated compared to lymph node (LN) derived CD8 T cells from non-tumor bearing mice. Additionally, relative expression of CD49a and CD103 differs between subcutaneous and intraperitoneal tumors. The capacity of T cells to persist in tumors thus potentially changes based on tumor location, which may be dependent on TGFβ levels. In contrast to LN of non-tumor bearing mice, CD103 is expressed on 50–90% of LN CD8 T cells in tumor bearing mice. Furthermore, CD103+CD8 TILs have a more naïve phenotype, whereas CD103neg CD8 TILs mainly express memory/effector T cell markers. The opposite is observed when T cells are activated in vitro. These data suggest that CD103+CD8 T cells in tumors are largely due to a tumor induced systemic induction of CD103 on naïve T cells, rather than intratumoral TRM differentiation. The importance of CD103 in retaining naïve T cells for functional differentiation within the tumor remains to be established.

Regulation of peripheral node addressin in tumor-associated CD31+ vascular endothelial cells

Naïve T cells use peripheral node addressin (PNAd), normally found on lymph node (LN) high endothelial venules (HEV), to traffic into lymphoid organs. We previously reported that the vasculature of murine tumors expressed PNAd and CCL21, which supports infiltration and intratumoral activation of naïve T cells, in turn delaying tumor growth. PNAd expression on tumor vasculature depends on effector CD8+ T cells that secrete LTα3, which signals through TNFR on tumor-associated CD31+ endothelial cells. PNAd expression is low on tumor vasculature, suggesting that it might be regulated differently than PNAd on HEV. Using RT-qPCR, we found that most of the enzymes responsible for PNAd synthesis are expressed comparably in CD31+ cells from tumors and LN. However, the primary sulfotransferase responsible for the generation of the 6-sulfo sialyl Lewis X structure on PNAd HEV, GlcNAc6ST-2, is minimally expressed in tumors. Tumor CD31+ cells expressed equivalent levels of GlcNAc6ST-1, suggesting that it is responsible for low-level PNAd expression. Of the scaffolding proteins that make up PNAd, GlyCAM-1 was minimally expressed in tumor CD31+ cells, whereas all others were expressed comparably. To identify the components of PNAd biosynthesis in tumor CD31+ cells that are controlled by LTα3-TNFR signaling, we evaluated tumors from WT and TNFR1/2KO mice. GlyCAM-1 was the only assessed PNAd component that was ablated in TNFR1/2KO tumors. However, based on transcript levels, GlyCAM-1 accounts for only about 10% of the PNAd scaffolding proteins in tumor CD31+ cells. This suggests that TNFR signaling regulates additional PNAd biosynthetic components yet to be examined, or that it regulates one or more components at the level of protein translation.

Effector CD8 T cells use different homing receptor/ligand interactions to enter subcutaneous and intraperitoneal B16 melanoma tumors

CD8 T cell infiltration into tumors is critical for controlling cancer and relies on interactions between homing receptors (HR) on CD8 T cells and ligands on the vasculature. However, the ligands expressed on tumor vasculature, and the receptor interactions required for entry into tumors are incompletely characterized. The HR ligands VCAM-1 and E-selectin were highly expressed on the vasculature of B16-F1 melanomas expressing the strong antigen ovalbumin (B16-OVA) and growing subcutaneously but were significantly decreased compared to inflamed skin vasculature. In contrast, the vasculature of intraperitoneal tumors expressed MadCAM-1, negligible E-selectin, and lower VCAM-1. However, MadCAM-1 was not displayed on the luminal surface. B16-F1 parental tumors lacking a strong antigen, and B16-OVA tumors grown in Rag1KO animals, expressed negligible VCAM-1 and MadCAM-1, suggesting that previously infiltrating activated adaptive immune cells drove their expression. VCAM-1 and CXCL9/10 enabled entry of CD8 T cell effectors expressing α4β1+ integrin and CXCR3 into both subcutaneous and peritoneal tumors, while E-Selectin enabled entry of E-Selectin ligand+ effectors preferentially into subcutaneous tumors. MadCAM-1 did not mediate entry of α4β7+ effectors into peritoneal tumors, in keeping with its lack of luminal expression. Disrupting immunosuppression with checkpoint blockade inhibitors may increase HR ligand expression on tumor vasculature and improve CD8 T cell entry into tumors.

Immunosuppression limits CD8+ T cell entry into subcutaneous B16 melanoma

Interactions between homing receptors (HR) and ligands on the vasculature facilitate effector CD8 T cell entry into tissues. HR ligand expression on normal inflamed tissue vasculature is induced by the local release of pro-inflammatory cytokines. In tumors, however, it is likely that expression of HR ligands on tumor vasculature is suboptimal due to immunosuppression. We hypothesized that disruption of immunosuppression would increase HR ligand expression on tumor vasculature, and consequently, enhance CD8 T cell entry. B16-F1 melanoma tumor-bearing mice were treated with blocking antibodies against CTLA-4 or PD-1. HR ligand expression on tumor vasculature and CD8 T cell representation were assessed. We found that CTLA-4 or PD-1 blockade significantly increased intravascular CXCL9 expression in subcutaneous B16-F1 tumors. Unlike PD-1 blockade, CTLA-4 blockade was associated with increased E-selectin expression on tumor vasculature, which we have shown to be important for CD8 T cell entry into subcutaneous tumors. CTLA-4 blockade also enhanced CD8 T cell representation and reduced tumor size. We observed a very low percentage of PD-1+ CD8 T cells in B16-F1 tumors, which may account for the limited efficacy of PD-1 blockade. Interestingly, the percentage of intratumoral PD-1+ CD8 T cells increased post-treatment with anti-CTLA-4. Our data suggest that CTLA-4 blockade may act to enhance T cell priming in the lymph node to increase the number of CD8 T cell effectors available to infiltrate tumors. It is also possible that CTLA-4 blockade may act on CTLA-4+ intratumoral Tregs, thereby promoting reactivation of tumor-resident CD8 T cell effectors that secrete pro-inflammatory cytokines that upregulate HR ligands on tumor vasculature.

Abstract IA23: T cell trafficking in lymphoid and non-lymphoid tissues

Increased representation of CD8 T-lymphocytes in tumors, spontaneously, or after vaccination or adoptive therapy, is essential for immune mediated control of human cancers. T-cell infiltrates are a positive prognostic indicator of patient survival, and it has become clear that the patients who respond clinically to new generation immunotherapies are those in which an immunological infiltrate is already evident prior to treatment. Thus, limited representation of intratumoral T-cells is a major barrier to tumor control, distinct from the barrier created by immunosuppression. Understanding and overcoming this limitation will enable us to extend the effectiveness of many immunotherapies to a broader cross-section of cancer patients.

T cell infiltration into lymphoid and non-lymphoid tissues is controlled by homing receptors (HR) that engage corresponding ligands expressed on tissue-associated vasculature. Naïve T-cells enter LN based on expression of L-selectin and CCR7. These HR bind to peripheral node addressin (PNAd) and the chemokines CCL19/CCL21, respectively, which are expressed on specialized lymph node blood vessels called high endothelial venules (HEV). During differentiation, effector T-cells acquire the ability enter peripheral tissues, including tumors, by upregulating other selectins, integrins and chemokine receptors that bind to ligands expressed on inflamed vasculature. However, we lack a full understanding of which HR expressed by CD8 T-cell effectors control their migration into tumors, how this is influenced by expression of the corresponding ligands on tumor vasculature, and whether ligand expression changes as a result of vessel normalization. We have explored the hypothesis that CD8 T-cell effectors activated in different secondary lymphoid organs express distinct HR, which in turn control infiltration into tumors in different anatomical locations. We identified 3 major populations of primary CD8 T-cell effectors based on site of activation and HR expression pattern, and have established which HR enable infiltration of one of these populations into tumors.

While it has been assumed that all tumor-infiltrating lymphocytes are effectors that differentiate in tumor-draining LN and subsequently enter the tumor, we have shown that naïve CD8 T-cells also can directly enter tumors. These naïve cells differentiate into functional effectors in the tumor, and can promote its control. Naïve CD8 T-cell infiltration depends on L-selectin and CCR7, as in lymph nodes, and on the development of blood vessels in the tumor that express PNAd and CCL21 and resemble lymph node HEV. Similar lymph node-like vasculature has been reported in human tumors along with ectopic organized lymphoid tissue (tertiary lymphoid organs or TLO), and correlated with longer metastasis-free, disease-free, and overall survival.

Development of this vasculature in murine tumors was controlled by a novel mechanism involving effector CD8 T-cells and NK cells that secreted Lymphotoxin-α3 and IFNγ;. This suggests that early infiltration of effectors induces LN-like vasculature, which in turn supports a self-sustaining recruitment of naïve T-cells that differentiate within the tumor. In intraperitoneal but not subcutaneous tumors, this lymph node-like vasculature was also associated with organized aggregates of B-lymphocytes and gp38+ fibroblasts that resembled TLO. The differential expression of these elements in SC and IP tumors reflects differences in immunological tumor microenvironments that remain to be explored further. Nonetheless, these results establish LN-like vasculature as both a consequence of and key contributor to anti-tumor immunity based on its role in promoting T-cell infiltration.

Citation Format: Victor H. Engelhard, David Peske, Amber Woods, Nithya Srinivasan, Colin Brinkman, Andrew Ferguson. T cell trafficking in lymphoid and non-lymphoid tissues. [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy: A New Chapter; December 1-4, 2014; Orlando, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2015;3(10 Suppl):Abstract nr IA23.

Control of CD8 T-Cell Infiltration into Tumors by Vasculature and Microenvironment

CD8 T-cells are a critical brake on the initial development of tumors. In established tumors, the presence of CD8 T-cells is correlated with a positive patient prognosis, although immunosuppressive mechanisms limit their effectiveness and they are rarely curative without manipulation. Cancer immunotherapies aim to shift the balance back to dominant antitumor immunity through antibody blockade of immunosuppressive signaling pathways, vaccination, and adoptive transfer of activated or engineered T-cells. These approaches have yielded striking responses in small subsets of patients with solid tumors, most notably those with melanoma. Importantly, the subset of patients who respond to vaccination or immunosuppression blockade therapies are those with CD8 T-cells present in the tumor prior to initiating therapy. While current adoptive cell therapy approaches can be dramatically effective, they require infusion of extremely large numbers of T-cells, but the number that actually infiltrates the tumor is very small. Thus, poor representation of CD8 T-cells in tumors is a fundamental hurdle to successful immunotherapy, over and above the well-established barrier of immunosuppression. In this review, we discuss the factors that determine whether immune cells are present in tumors, with a focus on the representation of cytotoxic CD8 T-cells. We emphasize the critically important role of tumor-associated vasculature as a gateway that enables the active infiltration of both effector and naïve CD8 T-cells that exert antitumor activity. We also discuss strategies to enhance the gateway function and extend the effectiveness of immunotherapies to a broader set of cancer patients.

Effector lymphocyte-induced lymph node-like vasculature enables naive T-cell entry into tumours and enhanced anti-tumour immunity

The presence of lymph node (LN)-like vasculature in tumors, characterized by expression of peripheral node addressin and chemokine CCL21, is correlated with T-cell infiltration and positive prognosis in breast cancer and melanoma patients. However, mechanisms controlling the development of LN-like vasculature and how it might contribute to a beneficial outcome for cancer patients are unknown. Here we demonstrate that LN-like vasculature is present in murine models of melanoma and lung carcinoma. It enables infiltration by naïve T-cells that significantly delay tumor outgrowth after intratumoral activation. Development of this vasculature is controlled by a mechanism involving effector CD8 T-cells and NK cells that secrete LTα₃ and IFNγ. LN-like vasculature is also associated with organized aggregates of B-lymphocytes and gp38⁺ fibroblasts that resemble tertiary lymphoid organs that develop in models of chronic inflammation. These results establish LN-like vasculature as both a consequence of and key contributor to anti-tumor immunity.

Immune responses in a mouse model of vitiligo with spontaneous epidermal de- and repigmentation

To generate a mouse model of spontaneous epidermal depigmentation, parental h3TA2 mice, expressing both a human-derived, tyrosinase-reactive T-cell receptor on T cells and the matching HLA-A2 transgene, were crossed to keratin 14-promoter driven, stem cell factor transgenic (K14-SCF) mice with intra-epidermal melanocytes. In resulting Vitesse mice, spontaneous skin depigmentation precedes symmetrical and sharply demarcated patches of graying hair. Whereas the SCF transgene alone dictates a greater retinoic acid receptor-related orphan receptor gamma (RORγt)(+) T-cell compartment, these cells displayed markedly increased IL-17 expression within Vitesse mice. Similar to patient skin, regulatory T cells were less abundant compared with K14-SCF mice, with the exception of gradually appearing patches of repigmenting skin. The subtle repigmentation observed likely reflects resilient melanocytes that coexist with skin-infiltrating, melanocyte-reactive T cells. Similar repigmenting lesions were found in a different TCR transgenic model of vitiligo developed on an SCF transgenic background, supporting a role for SCF in repigmentation.

MHC-restricted phosphopeptides from insulin receptor substrate-2 and CDC25b offer broad-based immunotherapeutic agents for cancer

Cancer cells display novel phosphopeptides in association with MHC class I and II molecules. In this study, we evaluated two HLA-A2-restricted phosphopeptides derived from the insulin receptor substrate (IRS)-2 and the cell-cycle regulator CDC25b. These proteins are both broadly expressed in multiple malignancies and linked to cancer cell survival. Two phosphopeptides, termed pIRS-21097-1105 and pCDC25b38-46, served as targets of strong and specific CD8 T-cell memory responses in normal human donors. We cloned T-cell receptor (TCR) cDNAs from murine CD8 T-cell lines specific for either pIRS-21097-1105 or pCDC25b38-46. Expression of these TCRs in human CD8 T cells imparted high-avidity phosphopeptide-specific recognition and cytotoxic and cytokine-secreting effector activities. Using these cells, we found that endogenously processed pIRS-21097-1105 was presented on HLA-A2(+) melanomas and breast, ovarian, and colorectal carcinomas. Presentation was correlated with the level of the Ser(1100)-phosphorylated IRS-2 protein in metastatic melanoma tissues. The highest expression of this protein was evident on dividing malignant cells. Presentation of endogenously processed pCDC25b38-46 was narrower, but still evident on HLA-A2(+) melanoma, breast carcinoma, and lymphoblastoid cells. Notably, pIRS-21097-1105-specific and pCDC25b38-46-specific TCR-expressing human CD8 T cells markedly slowed tumor outgrowth in vivo. Our results define two new antigens that may be developed as immunotherapeutic agents for a broad range of HLA-A2(+) cancers.

MHC class I-associated phosphopeptides are the targets of memory-like immunity in leukemia

Deregulation of signaling pathways is a hallmark of malignant transformation. Signaling-associated phosphoproteins can be degraded to generate cancer-specific phosphopeptides that are presented by major histocompatibility complex (MHC) class I and II molecules and recognized by T cells; however, the contribution of these phosphoprotein-specific T cells to immune surveillance is unclear. We identified 95 phosphopeptides presented on the surface of primary hematological tumors and normal tissues, including 61 that were tumor-specific. Phosphopeptides were more prevalent on more aggressive and malignant samples. CD8(+) T cell lines specific for these phosphopeptides recognized and killed both leukemia cell lines and human leukocyte antigen-matched primary leukemia cells ex vivo. Notably, healthy individuals showed robust CD8(+) T cell responses against many of these phosphopeptides within the circulating memory compartment. This immunity was significantly reduced or absent in some leukemia patients. This reduction correlated with clinical outcome; however, immunity was restored after allogeneic stem cell transplantation. These results suggest that phosphopeptides may be targets of cancer immune surveillance in humans, and point to their importance for development of vaccine-based and T cell adoptive transfer immunotherapies.

Tolerogenic properties of lymphatic endothelial cells are controlled by the lymph node microenvironment

Peripheral self-tolerance eliminates lymphocytes specific for tissue-specific antigens not encountered in the thymus. Recently, we demonstrated that lymphatic endothelial cells in mice directly express peripheral tissue antigens, including tyrosinase, and induce deletion of specific CD8 T cells via Programmed Death Ligand-1 (PD-L1). Here, we demonstrate that high-level expression of peripheral tissue antigens and PD-L1 is confined to lymphatic endothelial cells in lymph nodes, as opposed to tissue (diaphragm and colon) lymphatics. Lymphatic endothelial cells in the lymph node medullary sinus express the highest levels of peripheral tissue antigens and PD-L1, and are the only subpopulation that expresses tyrosinase epitope. The representation of lymphatic endothelial cells in the medullary sinus expressing high-level PD-L1, which is necessary for normal CD8 T cell deletion kinetics, is controlled by lymphotoxin-β receptor signaling and B cells. Lymphatic endothelial cells from neonatal mice do not express high-level PD-L1 or present tyrosinase epitope. This work uncovers a critical role for the lymph node microenvironment in endowing lymphatic endothelial cells with potent tolerogenic properties.

Regulation of T-cell Tolerance by Lymphatic Endothelial Cells

Lymphatic endothelial cells are most often thought of as structural cells that form the lymphatic vasculature, which transports fluid out of peripheral tissues and transports antigens and antigen presenting cells to lymph nodes. Recently, it has been shown that lymphatic endothelial cells also dynamically respond to and influence the immune response in several ways. Here, we describe how lymphatic endothelial cells induce peripheral T-cell tolerance and how this relates to tolerance induced by other types of antigen presenting cells. Furthermore, the ability of lymphatic endothelial cells to alter immune responses under steady-state or inflammatory conditions is explored, and the therapeutic potential of bypassing lymphatic endothelial cell-induced tolerance to enhance cancer immunotherapy is discussed.

Regulatory T cells and vasectomy

CD4+ CD25+ regulatory T cells (Tregs) strongly influence the early and late autoimmune responses to meiotic germ cell antigens (MGCA) and the gonadal immunopathology in vasectomized mice. This is supported by the published and recently acquired information presented here. Within 24h of unilateral vasectomy (uni-vx) the ipsilateral epididymis undergoes epithelial cell apoptosis followed by necrosis, severe inflammation, and granuloma formation. Unexpectedly, vasectomy alone induced MGCA-specific tolerance. In contrast, uni-vx plus simultaneous Treg depletion resulted in MGCA-specific autoimmune response and bilateral autoimmune orchitis. Both tolerance and autoimmunity were strictly linked to the early epididymal injury. We now discovered that testicular autoimmunity in uni-vx mice did not occur when Treg depletion was delayed by one week. Remarkably, this delayed Treg depletion also prevented tolerance induction. Therefore, tolerance depends on a rapid de novo Treg response to MGCA exposed after vasectomy. Moreover, tolerance was blunted in mice genetically deficient in PD-1 ligand, suggesting the involvement of induced Treg. We conclude that pre-existing natural Treg prevents post-vasectomy autoimmunity, whereas vasectomy-induced Treg maintains post-vasectomy tolerance. We further discovered that vasectomized mice were still resistant to autoimmune orchitis induction for at least 12-16 months; thus, tolerance is long-lasting. Although significant sperm autoantibodies of low titers became detectable in uni-vx mice at 7 months, the antibody titers fluctuated over time, suggesting a dynamic "balance" between the autoimmune and tolerance states. Finally, we observed severe epididymal fibrosis and hypo-spermatogenesis at 12 months after uni-vx: findings of highly critical clinical significance.

Peripheral tissue homing receptors enable T cell entry into lymph nodes and affect the anatomical distribution of memory cells

Peripheral tissue homing receptors enable T cells to access inflamed nonlymphoid tissues. In this study, we show that two such molecules, E-selectin ligand and α4β1 integrin, enable activated and memory T cells to enter lymph nodes (LN) as well. This affects the quantitative and qualitative distribution of these cells among regional LN beds. CD8 memory T cells in LN that express these molecules were mostly CD62L(lo) and would normally be classified as effector memory cells. However, similar to central memory cells, they expanded upon Ag re-encounter. This led to differences in the magnitude of the recall response that depended on the route of immunization. These novel cells share properties of both central and effector memory cells and reside in LN based on previously undescribed mechanisms of entry.

Relapse or eradication of cancer is predicted by peptide-major histocompatibility complex affinity

Cancers often relapse after adoptive therapy, even though specific T cells kill cells from the same cancer efficiently in vitro. We found that tumor eradication by T cells required high affinities of the targeted peptides for major histocompatibility complex (MHC) class I. Affinities of at least 10 nM were required for relapse-free regression. Only high-affinity peptide-MHC interactions led to efficient cross-presentation of antigen, thereby stimulating cognate T cells to secrete cytokines. These findings highlight the importance of targeting peptides with high affinity for MHC class I when designing T cell-based immunotherapy.

Lymphatic endothelial cells - key players in regulation of tolerance and immunity

The lymphatic vasculature provides routes for dendritic cell and lymphocyte migration into and out of lymph nodes. Lymphatic endothelial cells (LEC) control these processes by expression of CCL21, sphingosine-1-phosphate, and adhesion molecules. LEC express MHC-I and MHC-II, but not costimulatory molecules, and present antigen on MHC-I via both direct and cross-presentation. Whether LEC present to CD4 T cells on MHC-II is unknown. Interestingly, LEC express antigens otherwise restricted to a small number of peripheral tissues in an autoimmune regulatory element-independent manner. Direct presentation of peripheral tissue antigens (PTA) to CD8 T cells results in abortive proliferation and deletion, due to both a lack of costimulation and active PD-L1 engagement. Autoimmunity develops when deletion is subverted, suggesting that LEC presentation of PTA could lead to human disease if PD-1 signaling were impaired by genetic polymorphisms, or aberrant costimulation occurred during inflammation. The expression of additional inhibitory molecules, which are not involved in LEC-mediated deletion, suggests that LEC may have additional immunoregulatory roles. LEC express receptors for several immunomodulatory molecules whose engagement alters their phenotype and function. In this review we describe the role of LEC in distinct anatomical locations in controlling immune cell trafficking, as well as their emerging role in the regulation of T cell tolerance and immunity.

Abstract 1584: MHC-restricted phosphopeptides as broad-based immunotherapeutic targets for cancer

Identification of the antigens (Ags) recognized by CD8+ T cells specific for melanoma and other types of cancer cells has been motivated by the expectation that they will serve as the basis for a therapeutic vaccine or will be useful for the stimulation of more effective CD8+ CTL for adoptive immunotherapy. Few of the currently identified Ags are derived from source proteins directly associated with transformation or metastasis, and many are self-Ags which may be subject to tolerance mechanisms. We have defined a new array of phosphorylated peptides presented by HLA-A1, -A2, -A3, -B7, -B44 and HLA-B27 that are presented on melanomas from multiple patients at >1 copy per cell and derived from source proteins associated with tumorigenesis and metastasis. We evaluated the immunogenicity of several of the HLA-A2-restricted phosphopeptide Ags in an HLA-transgenic murine model system and in vitro human T cell cultures, evaluated the presence of the phosphorylated source protein or display of the phosphorylated epitope on cancers of different histological types, and investigated the ability of phosphopeptide-specific CD8+ T cells to prevent outgrowth of cancer cells in a xenogenic model. Evaluation of metastatic melanoma tissue microarrays and cancer cell lysates demonstrated that the phosphorylated source proteins for β-catenin (Ser33-phosphorylated), Breast cancer anti-estrogen resistance −3 (BCAR3; Thr130-phosphorylated), and Insulin receptor substrate-2 (IRS2; Ser1100-phosphorylated) were broadly expressed in melanomas and other cancers but not normal tissues. In addition, these epitopes can be utilized to elicit phosphopeptide-specific T cells in both murine HLA-A2 transgenic mice in vivo and human in vitro culture. The phospho-β-catenin, phospho-IRS2 and phospho-BCAR3-specific-T cells that were generated differentiate between the phosphorylated and non-modified forms of their respective peptides and recognize the endogenously processed and presented phosphopeptide on the surface of cancer cells. Finally, adoptive transfer of these phosphopeptide-specific T cells slowed outgrowth of melanoma tumors implanted in immunodeficient NOD.SCID.IL2Rα-/- mice. Thus, we have defined a new set of post-translationally modified epitopes derived from source proteins associated with tumorigenesis and metastasis that are immunogenic and capable of slowing tumor outgrowth in a xenograft model. Based on these results, we are currently planning a clinical trial utilizing these HLA-A2-restricted phosphopeptides in melanoma patients.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1584. doi:1538-7445.AM2012-1584

Tumor masses support naive T cell infiltration, activation, and differentiation into effectors

Studies of T cell responses to tumors have focused on the draining lymph node (LN) as the site of activation. We examined the tumor mass as a potential site of activation after adoptive transfer of naive tumor-specific CD8 T cells. Activated CD8 T cells were present in tumors within 24 h of adoptive transfer and proliferation of these cells was also evident 4-5 d later in mice treated with FTY720 to prevent infiltration of cells activated in LNs. To confirm that activation of these T cells occurred in the tumor and not the tumor-draining LNs, we used mice lacking LNs. Activated and proliferating tumor-infiltrating lymphocytes were evident in these mice 24 h and 4 d after naive cell transfer. T cells activated within tumors acquired effector function that was evident both ex vivo and in vivo. Both cross-presenting antigen presenting cells within the tumor and tumor cells directly presenting antigen activated these functional CD8 effectors. We conclude that tumors support the infiltration, activation, and effector differentiation of naive CD8 T cells, despite the presence of immunosuppressive mechanisms. Thus, targeting of T cell activation to tumors may present a tool in the development of cancer immunotherapy.