Radiation and anti-PD-L1 synergize by stimulating a stem-like T cell population in the tumor-draining lymph node

Radiotherapy (RT) and anti-PD-L1 synergize to enhance local and distant (abscopal) tumor control. However, clinical results in humans have been variable. With the goal of improving clinical outcomes, we investigated the underlying synergistic mechanism focusing on a CD8+ PD-1+ Tcf-1+ stem-like T cell subset in the tumor-draining lymph node (TdLN). Using murine melanoma models, we found that RT + anti-PD-L1 induces a novel differentiation program in the TdLN stem-like population which leads to their expansion and differentiation into effector cells within the tumor. Our data indicate that optimal synergy between RT + anti-PD-L1 is dependent on the TdLN stem-like T cell population as either blockade of TdLN egress or specific stem-like T cell depletion reduced tumor control. Together, these data demonstrate a multistep stimulation of stem-like T cells following combination therapy which is initiated in the TdLN and completed in the tumor.

Early generation of a precursor CD8 T cell that can adapt to acute or chronic viral infection

Virus specific PD-1+ TCF-1+ TOX+ stem-like CD8+ T cells are essential for maintaining T cell responses during chronic infection and are also critical for PD-1 directed immunotherapy. In this study we have used the mouse model of chronic LCMV infection to examine when these virus specific stem-like CD8+ T cells are generated during the course of chronic infection and what is the role of antigen in maintaining the stem-like program. We found that these stem-like CD8+ T cells are generated early (day 5) during chronic infection and that antigen is essential for maintaining their stem-like program. This early generation of stem-like CD8+ T cells suggested that the fate commitment to this cell population was agnostic to the eventual outcome of infection and the immune system prepares a priori for a potential chronic infection. Indeed, we found that an identical virus specific stem-cell like CD8+ T cell population was also generated during acute LCMV infection but these cells were lost once the virus was cleared. To determine the fate of these early PD-1+TCF-1+TOX+ stem-like CD8+ T cells that are generated during both acute and chronic LCMV infection we set up two reciprocal adoptive transfer experiments. In the first experiment we transferred day 5 stem-like CD8+ T cells from chronically infected into acutely infected mice and examined their differentiation after viral clearance. We found that these early stem-like CD8+ T cells downregulated canonical markers of the chronic stem-like CD8+ T cells and expressed markers (CD127 and CD62L) associated with central memory CD8+ T cells. In the second experiment, we transferred day 5 stem-like cells from acutely infected mice into chronically infected mice and found that these CD8+ T cells could function like resource cells after transfer into a chronic environment by generating effector CD8+ T cells in both lymphoid and non-lymphoid tissues while also maintaining the number of stem-like CD8+ T cells. These findings provide insight into the generation and maintenance of virus specific stem-like CD8+ T cells that play a critical role in chronic viral infection. In particular, our study highlights the early generation of stem-like CD8+ T cells and their ability to adapt to either an acute or chronic infection. These findings are of broad significance since these novel stem-like CD8+ T cells play an important role in not only viral infections but also in cancer and autoimmunity.

Characteristics and anatomic location of PD-1+TCF1+ stem-like CD8 T cells in chronic viral infection and cancer

CD8 T cells play an essential role in antitumor immunity and chronic viral infections. Recent findings have delineated the differentiation pathway of CD8 T cells in accordance with the progenitor-progeny relationship of TCF1+ stem-like and Tim-3+TCF1- more differentiated T cells. Here, we investigated the characteristics of stem-like and differentiated CD8 T cells isolated from several murine tumor models and human lung cancer samples in terms of phenotypic and transcriptional features as well as their location compared to virus-specific CD8 T cells in the chronically lymphocytic choriomeningitis virus (LCMV)-infected mice. We found that CD8 tumor-infiltrating lymphocytes (TILs) in both murine and human tumors exhibited overall similar phenotypic and transcriptional characteristics compared to corresponding subsets in the spleen of chronically infected mice. Moreover, stem-like CD8 TILs exclusively responded and produced effector-like progeny CD8 T cells in vivo after antigenic restimulation, confirming their lineage relationship and the proliferative potential of stem-like CD8 TILs. Most importantly, similar to the preferential localization of PD-1+ stem-like CD8 T cells in T cell zones of the spleen during chronic LCMV infection, we found that the PD-1+ stem-like CD8 TILs in lung cancer samples are preferentially located not in the tumor parenchyma but in tertiary lymphoid structures (TLSs). The stem-like CD8 T cells are present in TLSs located within and at the periphery of the tumor, as well as in TLSs closely adjacent to the tumor parenchyma. These findings suggest that TLSs provide a protective niche to support the quiescence and maintenance of stem-like CD8 T cells in the tumor.

Immune niches in brain metastases contain TCF1+ stem-like T cells, are associated with disease control and are modulated by preoperative SRS

The CD8+ T-cell response is prognostic for survival outcomes in several tumor types. However, whether this extends to tumors in the brain, an organ with barriers to T cell entry, remains unclear. Here, we analyzed immune infiltration in 67 brain metastasis (BrM) and found high frequencies of PD1+ TCF1+ stem-like CD8+ T-cells and TCF1- effector-like cells. Importantly, the stem-like cells aggregate with antigen presenting cells in immune niches, and niches were prognostic for local disease control. Standard of care for BrM is resection followed by stereotactic radiosurgery (SRS), so to determine SRS's impact on the BrM immune response, we examined 76 BrM treated with pre-operative SRS (pSRS). pSRS acutely reduced CD8+ T cells at 3 days. However, CD8+ T cells rebounded by day 6, driven by increased frequency of effector-like cells. This suggests that the immune response in BrM can be regenerated rapidly, likely by the local TCF1+ stem-like population.

CD8+ T cell activation in cancer comprises an initial activation phase in lymph nodes followed by effector differentiation within the tumor

Improvements in tumor immunotherapies depend on better understanding of the anti-tumor T cell response. By studying human tumor-draining lymph nodes (TDLNs), we found that activated CD8⁺ T cells in TDLNs shared functional, transcriptional, and epigenetic traits with TCF1⁺ stem-like cells in the tumor. The phenotype and TCR overlap suggested that these TDLN cells were precursors to tumor-resident stem-like CD8⁺ T cells. Murine tumor models revealed that tumor-specific CD8⁺ T cells were activated in TDLNs but lacked an effector phenotype. These stem-like cells migrated into the tumor, where additional co-stimulation from antigen-presenting cells drove effector differentiation. This model of CD8⁺ T cell activation in response to cancer is different from that of canonical CD8⁺ T cell activation to acute viruses, and it proposes two stages of tumor-specific CD8⁺ T cell activation: initial activation in TDLNs and subsequent effector program acquisition within the tumor after additional co-stimulation.

Clinical outcome following checkpoint therapy in renal cell carcinoma is associated with a burst of activated CD8 T cells in blood

PURPOSE

Checkpoint therapy is now the cornerstone of treatment for patients with renal cell carcinoma (RCC) with advanced disease, but biomarkers are lacking to predict which patients will benefit. This study proposes potential immunological biomarkers that could developed for predicting therapeutic response in patients with RCC.

METHODS

Using flow cytometry, RNA sequencing, and T-cell receptor (TCR) sequencing, we investigated changes in T cells in the peripheral blood of patients with advanced RCC after receiving immunotherapy. We used immunofluorescence (IF) imaging and flow cytometry to investigate how intratumoral T cells in patients' tumors (resected months/years prior to receiving checkpoint therapy) predicted patient outcomes after immunotherapy.

RESULTS

We found that a small proportion of CD4 and CD8 T cells in the blood activate following checkpoint therapy, expressing the proliferation marker Ki67 and activation markers HLA-DR and CD38. Patients who had the highest increase in these HLA-DR +CD38+CD8 T cells after treatment had the best antitumor immune response and experienced clinical benefit. Using RNA sequencing, we found that while these cells expanded in most patients, their phenotype did not drastically change during treatment. However, when we analyzed the TCR repertoire of these HLA-DR +CD38+CD8+T cells, we found that only patients who clinically benefitted had a burst of new clonotypes enter this pool of activated cells. Finally, we found that abundant T cells in the untreated tumors predicted clinical benefit to checkpoint therapy on disease progression.

CONCLUSIONS

Together, these data suggest that having a strong pre-existing immune response and immediate peripheral T-cell activation after checkpoint therapy is a predictor of clinical benefit in patients with RCC.

CD8 T cell activation in cancer is comprised of two distinct phases

The CD8 T cell response to tumors is extremely variable with heterogenous T cell subsets, a stem-like CD8 T cell (PD1+TCF1+) that sustains the CD8 response and gives rise to a terminally differentiated (TD) cytotoxic cell (TCF1-Tim3+). Although these subsets have been described, how tumor-specific CD8 T cells are activated and differentiate in tumors are not well defined. Using a prostate cancer model that expresses the LCMV-GP (TRAMPC1-GP), we studied tumor-specific CD8 T cell activation by transferring LCMV-GP specific P14 CD8 T cells into tumor-bearing mice. We found that P14s are activated in the tumor-draining LNs (TDLNs) and acquire a stem-like phenotype. These cells migrate into the tumor as stem-like CD8 T cells and only differentiate into a TD CD8 T cell in the tumor. We found that stem-like CD8 T cells need additional co-stimulation from antigen presenting cells within the tumor to fully differentiate, even though they have been previously activated in TLDNs. Similarly, stem-like CD8s from human kidney cancer require both TCR and co-stimulatory signals to divide and differentiation ex-vivo and can differentiate when co-cultured with autologous dendritic cells. The addition of IL12 with TCR alone was not sufficient to induce differentiation, but improved differentiation when co-stimulation was present. This demonstrates the necessity of additional TCR and co-stimulation once activated stem-like CD8 T cells migrate into the tumor. Overall, these data suggest two distinct phases of CD8 T cell differentiation, the first occurs in the TDLN where they are initially activated. The second occurs in the tumor, where they require additional co-stimulation to differentiate and acquire an effector phenotype.

640 Stem-like CD4 T cells in cancer

Background

CD4 T cells can differentiate into multiple effector subsets that can mediate variable functions. In this work we aim to understand how CD4 T cells differentiate in response to tumor antigens and their respective function in the anti-tumor response.

Methods

Tumor tissue was collected from patients undergoing surgery at Emory University Hospital. Activated PD1+ CD45RA- tumor infiltrating CD4 T cells were sent for 10X single cell RNA-seq. Tumor samples were also processed for flow cytometry and ex vivo functional analyses. For in vivo studies, prostate cancer mouse model expressing the LCMV glycoprotein (TRAMPC1-GP) was used, as well as LCMV Armstrong infection.

Results

To characterize the heterogeneity of CD4 T cells infiltrating kidney tumors, we performed single cell RNAseq. We found three distinct activated (PD1+ CD45RA-) CD4 T cell populations. Two effector clusters consisting of Th1-like (EOMES+) and Treg (FOXP3+) cells, and a third cluster expressing TCF1, and genes associated with stemness and survival that did not fit defined CD4 effector lineages. We further confirmed these data by flow cytometry and found the same tumor infiltrating CD4 subsets in 100 kidney cancer patients. When placed in culture under different polarization conditions, tumor TCF1+ CD4 T cells proliferated and differentiated into the Th1-like and Treg effector populations found in the tumor, in addition to other effector lineages (Th1, Tfh) given the appropriate conditions, while the Th1-like and Treg cells underwent no proliferation or phenotype changes. These data suggests that the TCF1+ CD4s act as activated unpolarized precursors to the effector subsets in the tumor. To further test this hypothesis in vivo, we adoptively transferred tumor specific (SMARTA) CD4 T cells into mice followed by TRAMPC1-GP tumor inoculation. Transferred SMARTAs activated and first acquired a TCF1+ phenotype in the TDLN prior to predominantly differentiating into Tregs in the tumor. Given their plasticity in vitro, we asked whether TCF1+ SMARTAs primed in tumors were destined to differentiate into Tregs. To test this, we transferred 4-week activated TCF1+ SMARTAs from TDLNs of TRAMPC1-GP mice into naïve mice that were immediately infected with LCMV Armstrong. We found that the transferred SMARTAs differentiated into Th1 and Tfh cells in response to the virus, similar to the endogenous virus specific CD4 T cells.

Conclusions

Overall, this work shows that CD4 T cells remain in an activated phenotype in the tumor with the capacity to differentiate into non-suppressive effector lineages given the appropriate conditions that may benefit the anti-tumor response.

929 Dissecting intratumoral immune organization: defining the comparative cellular composition of tertiary lymphoid structures T-cell supportive antigen presenting niches in renal tumors

Background

Tumor infiltrating T-cells have a prognostic benefit in many tumor types,1–8 and we recently sought to determine whether the level of T-cell infiltration into renal tumors predicts clinical outcomes. In our recent publication,9 we showed that patients with high of CD8 T-cell infiltration have improved progression free survival (PFS). Further, we found that this T-cell response is supported by TCF1+ stem-like CD8 T-cells, which reside within dense regions of closely clustered antigen presenting cells within the tumor. Interestingly, aggregations of immune cells have also been described in other tumor types and termed ‘tertiary lymphoid structures’ (TLS), which are typically defined as B-cell-dominant aggregates, containing high endothelial venules and reactive germinal centers.10–12 Together, these findings raise several important questions, which we explore here—(1) what additional cell types comprise these niches?9 and (2) how are these niches similar to or different from TLS?

Methods

Tumor tissue was collected from patients with renal tumors undergoing surgery at Emory University Hospital. Intraoperative tumor samples were analyzed by flow cytometry, RNA sequencing, immunofluorescence, and immunohistochemistry. Immunofluorescence data was analyzed using our custom quantitative analysis pipelines, which allows for delineation of cell type and location, cell-cell distance, and density of cellular aggregation.

Results

The proportion of CD8 T-cells infiltration human renal tumors varied widely, consistent with our previous reports.9 TCF1+ stem-like CD8 T-cells were identifiable by both flow cytometry and immunofluorescence and resided in dense antigen presenting niches. Quantitative immunofluorescence revealed the location of aSMA+ fibroblasts within tumor tissue, in relation to antigen presenting niches, and in tumors with many infiltrating T-cells. Pathologist scored hematoxylin and eosin-stained slides were delineated TLS+ or TLS-. Quantitative immunofluorescence imaging analysis revealed the detailed composition of tumor infiltrating immune cell populations and the contrasting cellular organization in TLS as compared to in antigen presenting niches.

Conclusions

As we have shown CD8 T-cell infiltration to predict PFS in renal tumors and that antigen presenting niches containing stem-like cells maintain the anti-tumor T-cell response,9 it is critical to understand the additional cell types present in these niches and to understand how these niches relate to previously described phenomena of immune organization, such as TLS.10–12 This mechanistic understanding of the anti-tumor immune response represents an opportunity to inform development of enhanced prognostic tools and innovative therapeutic possibilities.

References

Azimi F, et al. Tumor-infiltrating lymphocyte grade is an independent predictor of sentinel lymph node status and survival in patients with cutaneous melanoma. J Clin Oncol 2012;30(21):2678–83. Epub 2012/06/20. doi: 10.1200/jco.2011.37.8539. PubMed PMID: 22711850.

Galon J, et al. Type, density, and location of immune cells within human colorectal tumors predict clinical outcome. Science 2006;313(5795):1960–4. Epub 2006/09/30. doi: 10.1126/science.1129139. PubMed PMID: 17008531.

Mlecnik B, et al. Integrative analyses of colorectal cancer show immunoscore is a stronger predictor of patient survival than microsatellite instability. Immunity 2016;44(3):698–711. Epub 2016/03/18. doi: 10.1016/j.immuni.2016.02.025. PubMed PMID: 26982367.

Mlecnik B, et al. Histopathologic-based prognostic factors of colorectal cancers are associated with the state of the local immune reaction. J Clin Oncol 2011;29(6):610–8. Epub 2011/01/20. doi: 10.1200/JCO.2010.30.5425. PubMed PMID: 21245428.

Pagès F, et al. Immune infiltration in human tumors: a prognostic factor that should not be ignored. Oncogene 2009;29:1093. doi: 10.1038/onc.2009.416.

Peranzoni E, et al. Macrophages impede CD8 T cells from reaching tumor cells and limit the efficacy of anti-PD-1 treatment. Proceedings of the National Academy of Sciences of the United States of America 2018;115(17):E4041–E50. Epub 2018/04/11. doi: 10.1073/pnas.1720948115. PubMed PMID: 29632196.

Savas P, et al. Single-cell profiling of breast cancer T cells reveals a tissue-resident memory subset associated with improved prognosis. Nat Med 2018;24(7):986–93. Epub 2018/06/27. doi: 10.1038/s41591-018-0078-7. PubMed PMID: 29942092.

Tosolini M, et al. Clinical impact of different classes of infiltrating T cytotoxic and helper cells (Th1, th2, treg, th17) in patients with colorectal cancer. Cancer Res 2011;71(4):1263–71. Epub 2011/02/10. doi: 10.1158/0008-5472.Can-10-2907. PubMed PMID: 21303976.

Jansen CS, et al. An intra-tumoral niche maintains and differentiates stem-like CD8 T cells. Nature 2019;576(7787):465–70. doi: 10.1038/s41586-019-1836-5.

Dieu-Nosjean MC, et al. Tertiary lymphoid structures in cancer and beyond. Trends Immunol 2014;35(11):571–80. Epub 2014/12/03. doi: 10.1016/j.it.2014.09.006. PubMed PMID: 25443495.

Goc J, et al. Characteristics of tertiary lymphoid structures in primary cancers. Oncoimmunology 2013;2(12):e26836. Epub 2014/02/06. doi: 10.4161/onci.26836. PubMed PMID: 24498556; PMCID: PMC3912008.

Sautes-Fridman C, et al. Tertiary lymphoid structures in the era of cancer immunotherapy. Nature reviews Cancer 2019;19(6):307–25. Epub 2019/05/17. doi: 10.1038/s41568-019-0144-6. PubMed PMID: 31092904.

Ethics Approval

Samples are collected under an approved IRB protocol (The Urological Satellite Specimen Bank at Emory University, IRB00055316). All patients provided informed consent.

Consent

Samples are collected under an approved IRB protocol (The Urological Satellite Specimen Bank at Emory University, IRB00055316). All patients provided informed consent.

658 CD8 T cell activation in cancer is comprised of two distinct phases

Background

CD8 T cell are a crucial part of the immune response to tumors, with CD8 infiltration predicting disease progression in numerous cancer types. Recently two subsets of CD8 T cells that respond to tumors have been described, a stem-like (TCF1+) CD8 T cell that can give rise to a more cytotoxic terminally differentiated (TD) (TCF1-Tim3+) CD8 T cell. In this study we aimed to understand the origin of stem-like TCF1+ CD8 T cells within tumors.

Methods

Human patient TDLN and tumor samples from kidney and prostate cancer were processed after resection and used for flow cytometry, RNA-seq, TCR-seq and whole genome DNA methylation analysis. We also used a prostate cancer mouse model that expresses the LCMV GP protein (TRAMPC1-LCMV-GP) to track tumor-specific CD8 T cells in both TDLNs and tumors.

Results

We studied human prostate and kidney cancer tumor-draining lymph nodes (TDLN) and found that CD8 T cells are activated but fail to acquire an effector phenotype within the TDLN. Instead, they share functional, transcriptional, and epigenetic traits with stem-like cells in the tumor. We also found that activated CD8 T cells from TDLNs shared TCR overlap with both CD8 subsets within tumors. This suggests that these activated cells are a precursor to the stem-like CD8 T cells in tumors. To further test this hypothesis, we used our TRAMPC1-LCMV-GP tumor model to study tumor-specific CD8 T cell activation. We found that CD8 T cells are activated in TDLNs but fail to acquire an effector program. These cells then establish the stem-like CD8s within tumor where they require additional co-stimulation from antigen presenting cells to differentiate into TCF1- TD CD8 T cells. This is strikingly different from canonical CD8 T cell activation to acute viruses, where the effector program is acquired immediately. We also showed that human stem-like CD8 T cells require co-stimulation and TCR stimulation to divide and differentiate into terminally differentiated CD8s in-vitro, and DCs from autologous tumors can also induce this differentiation.

Conclusions

Overall this work shows a model of CD8 T cell activation in response to tumors that has two distinct phases. The first occurs in the TDLN where CD8 T cells are initially activated, the second occurs in the tumor where CD8 T cells acquire an effector function after additional co-stimulation. This model of T cell differentiation adds to our understanding of basic CD8 T cell biology and has important implications to improve our current immunotherapies.

CD8 T cell differentiation in cancer is comprised of two distinct phases

A crucial part of the immune response to tumors are CD8 T cells, with CD8 infiltration predicting disease progression in many cancers. Recent work has shown two subsets of CD8 T cells that respond to tumors, one a stem-like CD8 T cell (TCF1+) that can give rise to a more cytotoxic terminally differentiated cell (TCF1−). To understand the CD8 T cell response to tumors it is important to study how tumor-specific CD8 T cells activate and differentiate. To study this we have made a prostate cancer model which expresses the LCMV glycoprotein (GP) and acts as a tumor-specific antigen. This model allows us to transfer LCMV GP specific P14 CD8 T cells into TRAMPC1-GP bearing mice to study how tumor-specific CD8 T cells activate. These studies have shown that tumor-specific CD8 T cells are activated in tumor draining lymph nodes (TDLN), where they retain an activated undifferentiated phenotype, upregulating CD44, PD1, while maintaining TCF1. These tumor-specific CD8 T cells only differentiate (TCF1−) once they have migrated into the tumor. This model can also be seen in human prostate cancer, with CD8 T cells in TDLNs retaining an activated undifferentiated phenotype (PD1+CD45RA-TCF1+). To determine if these cells are related to the CD8s within the tumor we have shown TCR overlap between the activated CD8s T cells in human prostate TDLNs and the CD8 T cell subsets within the tumor. These data suggest a two-step differentiation process for tumor-specific CD8 T cells where they are activated in TDLNs and differentiate further only in the tumor. This model of two distinct phases of CD8 T cell differentiation adds to the basic understanding of the immune response to cancer.

Organized immune cell interactions within tumors sustain a productive T-cell response

Tumor-infiltrating CD8 T cells are associated with improved patient survival and response to immunotherapy in various cancers. Persistent antigen leads to CD8 T-cell exhaustion, where proliferation/self-renewal and killing are divided within distinct subsets of CD8 T cells in the tumor. CD8 T-cell responses in chronic antigen settings must be maintained for long periods of time, suggesting that mechanisms that regulate chronic CD8 T-cell responses may differ from those in acute settings. Currently, factors that regulate the maintenance of stem-like CD8 T cells in the tumor or their differentiation into terminally differentiated cells are unknown. In this review, we discuss the role of dendritic cells in the activation and differentiation of CD8 T-cell subsets within secondary lymphoid tissue and tumors. In addition, we examine changes in CD4 T-cell differentiation in response to chronic antigens and consider how subset-specific mechanisms could assist the stem-like and terminally differentiated CD8 T-cell subsets. Finally, we highlight how tumor-infiltrating CD4 T cells and dendritic cells interact with CD8 T cells within organized lymphoid-like areas in the tumor and propose a CD8 T-cell differentiation model that requires the collaboration of CD4 T cells and dendritic cells. These organized interactions coordinate the anti-tumor response and control disease progression by mechanisms that regulate CD8 T-cell differentiation, which permit the maintenance of an effective balance of stem-like and terminally differentiated CD8 T cells.

CD4 T cell phenotypes differentially modulate the CD8 T cell response in kidney cancer

CD8 T cell infiltration can independently predict survival and response to immunotherapy in kidney cancer patients. Given the importance of the CD8 T cell response in cancer, it is crucial to understand what signals promote their infiltration and support the maintenance of the anti-tumor response. The proportion of tumor infiltrating CD8 T cells, as measured by flow cytometry, was found to significantly correlate (R = 0.8, p<0.0001) with tumor infiltrating CD4 T cells in 160 renal cell carcinoma patients, suggesting that CD4 T cells may promote the tumor-specific CD8 T cell response. We hypothesize that the phenotype of tumor infiltrating CD4 T cells affects CD8 T cell differentiation and may contribute to the efficiency of the anti-tumor response. We performed flow cytometry analysis on a subset of kidney cancer patients to further characterize the CD4 populations in the tumor tissue. T-regulatory cells (Treg), defined by their master transcription factor FOXP3, accounted for 15.5 ± 7.2 % of the tumor infiltrating CD4 T cells. Importantly, the Treg population negatively correlated with CD8 differentiation and expression of effector-like molecules. Additionally, we found a Th1-like population expressing high levels of EOMES and GZMK that have previously been associated with cytolytic capacities. In conclusion, we found various subsets of CD4 T cells in the tumor that may differentially modulate CD8 T cell function and influence the anti-tumor response.

Tumor-specific CD8 T cell activation in draining lymph nodes supports the anti-tumor CD8 T cell response

CD8 T cells are a critical part of the immune response to tumors, with CD8 T cell infiltration predicting disease progression in many types of cancer. Recent work in CD8 T cell immunology described how CD8 T cells respond to chronic diseases, finding two subsets of CD8 T cells within tumors. One is a stem-like CD8 T cell and the other is a terminally differentiated CD8 T cell with cytotoxic capabilities. Determining how tumor-specific CD8 T cells activate and differentiate is critical to understanding why some tumors are highly infiltrated. To study how tumor-specific CD8 T cells are activated, I have made a prostate cancer model that expresses the viral LCMV glycoprotein (GP) which acts as a tumor-specific antigen. We have used this model to study tumor-specific CD8 T cell activation by adoptively transferring LCMV GP specific TCR transgenic P14 CD8 T cells into TRAMPC1-LCMV-GP bearing mice. We have found when tumor-specific CD8 T cells are activated in the tumor-draining lymph node they acquire an undifferentiated but activated program, upregulating CD44, PD1 but retaining high TCF1 and CD62L expression. These undifferentiated activated CD8 T cells do not acquire a typical effector program that is seen in an acute viral infection such as LCMV Armstrong, yet they are able to migrate to the tumor to establish the anti-tumor response. In conclusion, tumor-specific CD8 T cells do not acquire an effector program after activation and instead gain an undifferentiated activated phenotype. These data suggest that tumor-specific CD8 T cells are activated in the TDLN and differentiate to become the stem-like CD8 T cells within the tumor, establishing the anti-tumor CD8 response.

Immunological Complexity of the Prostate Cancer Microenvironment Influences the Response to Immunotherapy

Prostate cancer is one of the most common cancers in men and a leading cause of cancer-related death. Recent advances in the treatment of advanced prostate cancer, including the use of more potent and selective inhibitors of the androgen signaling pathway, have provided significant clinical benefit for men with metastatic castration-resistant prostate cancer (mCRPC). However, most patients develop progressive lethal disease, highlighting the need for more effective treatments. One such approach is immunotherapy, which harness the power of the patient's immune system to identify and destroy cancer cells through the activation of cytotoxic CD8 T cells specific for tumor antigens. Although immunotherapy, particularly checkpoint blockade, can induce significant clinical responses in patients with solid tumors or hematological malignancies, minimal efficacy has been observed in men with mCRPC. In the current review, we discuss our current understanding of the immunological complexity of the immunosuppressive prostate cancer microenvironment, preclinical models of prostate cancer, and recent advances in immunotherapy clinical trials to improve outcomes for men with mCRPC.

An intra-tumoral niche maintains and differentiates stem-like CD8 T cells

Tumour-infiltrating lymphocytes are associated with a survival benefit in several tumour types and with the response to immunotherapy^1-8. However, the reason some tumours have high CD8 T cell infiltration while others do not remains unclear. Here we investigate the requirements for maintaining a CD8 T cell response against human cancer. We find that CD8 T cells within tumours consist of distinct populations of terminally differentiated and stem-like cells. On proliferation, stem-like CD8 T cells give rise to more terminally differentiated, effector-molecule-expressing daughter cells. For many T cells to infiltrate the tumour, it is critical that this effector differentiation process occur. In addition, we show that these stem-like T cells reside in dense antigen-presenting-cell niches within the tumour, and that tumours that fail to form these structures are not extensively infiltrated by T cells. Patients with progressive disease lack these immune niches, suggesting that niche breakdown may be a key mechanism of immune escape.

Abstract 2700: CD8 T-cell infiltration into renal tumors requires a supportive antigen-presenting niche

Background: Tumor infiltrating immune cells have a clear prognostic benefit in many tumor types. Immune variables have independently improved prognostication in various cancer types, with tumor-infiltrating lymphocytes (TILs) more accurately predicting patient survival than currently employed methods. This has been shown using the Immuno-score, which predicts disease progression in colorectal cancer based on CD8 T cell infiltration. Many recent studies have also highlighted similar observations in other cancers, including breast cancer, lung cancer, and melanoma. These observations raise the question of whether the level of CD8 T cell infiltration into renal cell tumors may also predict patient survival, and more fundamentally, why some patients may mount a strong immune response to their tumors and others do not.

Methods: Tumor tissue was collected from 68 renal cell carcinoma (RCC) patients undergoing surgery at Emory University Hospital. Patients had a minimum follow up time of 24 months. Intraoperative tumor samples were processed and analyzed by flow cytometry and immunofluorescence.

Results: The proportion of CD8 TILs, measured by flow cytometry, was found to vary widely in RCC patients. This CD8 T cell response is independent of standard risk assessment tools, tumor size, pathology, and patient demographics. Significantly, an increasing percent of tumor CD8 T cells is associated with improved cancer-specific survival in these patients, and this association is particularly strong in a small cohort of stage III patients.

The phenotype and functional capacity of TILs were examined, and presence of a stem-like CD8 T cell—that can proliferate and differentiate—was required to generate a strong anti-tumor Tcell response. When this stem-like T cell is lost, there is a poor anti-tumor immune response and patients experience progressive disease. Flow cytometry analysis revealed that the number of dendritic cells in the tumor correlates with T cell infiltration, and immunofluorescence image analysis showed that stem-like T cells reside in areas of high antigen-presenting cell density. Tumors with poor T cell infiltration lack APC density, suggesting that an antigen presenting niche is required for a strong T cell response.

Conclusions: Measuring CD8 T cell infiltration in RCC predicts cancer-specific survival, particularly in patients with advanced disease. As this patient population is one for whom improved prognostication is a critical clinical goal, this study represents an opportunity to inform future prognostic measures and to direct reduction or intensification of therapy.

The T cell response was found to be maintained by a population of cells, which harbor both proliferative and differentiation capacity. These stem-like cells require a supportive niche inside the tumor in order to persist, and without this support, the T cell response collapses, resulting in disease progression.

Citation Format: Caroline S. Jansen, Nataliya Prokhnevska, Viraj A. Master, Jennifer W. Carlisle, Mehmet A. Bilen, Adriana M. Reyes, Haydn T. Kissick. CD8 T-cell infiltration into renal tumors requires a supportive antigen-presenting niche [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2700.

The requirement for immune infiltration and organization in the tumor microenvironment for successful immunotherapy in prostate cancer

Immunotherapy-particularly immune checkpoint blockade-has seen great success in many tumor types. However, checkpoint-based therapies have not demonstrated high levels of success in prostate cancer, and there is much to be learned from both the successes and failures of these treatments. Here we review the evidence that composition of infiltrating immune cells in the tumor microenvironment is fundamental to the response to immunotherapy. Additionally, we discuss the emerging idea that the organization of these immune cells may also be crucial to this response. In prostate cancer, the composition and organization of the tumor immune microenvironment are preeminent topics of discussion and areas of important future investigation.

Immunologic profile and prognostic significance of tumor-infiltrating lymphocytes in renal cell carcinoma

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Background: Renal cell carcinoma (RCC) has been shown to be a genetically and morphologically heterogeneous cancer. As studies show the significance of tumor-infiltrating lymphocytes (TIL) in cancer, it is critical to examine how the phenotype of TILs manifests in RCC. Such analysis may help explain the role of the immune landscape in developing resistance and its contribution to the high treatment failure observed in immunotherapy for RCC. This study compares the immune phenotype of primary tumors, venous tumor thrombi (VTT), and metastases, as well as multiple sites within primary tumors, and investigates whether inter- and intra-tumoral immune heterogeneity is present in RCC. The association of TIL levels and clinical prognosis will also be assessed and compared with current RCC prognostic scores. Methods: Our cohort included 15 VTT and 6 metastases (3 adrenal, 2 bone, 1 liver) with 20 matched primary tumors, as well as 25 non-metastatic primary tumors. The RCC tissue was collected and digested into single cell suspensions. Suspensions were stained for TIL surface markers and processed using flow cytometry. The data was analyzed to capture %CD8+ and %CD4+ in total tumor. The %CD28+ and %PD1+ of CD8+ cells were measured to describe the co-stimulatory and co-inhibitory receptor expression, respectively. Clinical data was obtained to calculate the Mayo Stage, Size, Grade, and Necrosis (SSIGN) and UCLA Integrated Staging System (UISS) scores for each patient and to evaluate recurrence. Results: Immunologic concordance was observed in all measured parameters (%CD8+, %CD4+, %CD28+, and %PD1+) for primary tumors and VTT, for primary tumors and their metastases, and for different sites within 10 primary tumors. In our overall cohort, %CD8+ was found to be inversely associated with recurrence (p = 0.02). Furthermore, %CD8+ was not significantly associated with patient Mayo SSIGN and UISS scores. Conclusions: Despite the genetic and morphologic heterogeneity seen in RCC, immunologic concordance was observed for both inter- and intra-tumoral analysis. The association between %CD8+ and recurrence presents a novel and objective immune-based prognostic factor for RCC, independent of Mayo SSIGN and UISS scores.