Understanding and overcoming resistance to immunotherapy in genitourinary cancers

The introduction of novel immunotherapies has significantly transformed the treatment landscape of genitourinary (GU) cancers, even becoming the standard of care in some settings. One such type of immunotherapy, immune checkpoint inhibitors (ICIs) like nivolumab, ipilimumab, pembrolizumab, and atezolizumab play a pivotal role by disturbing signaling pathways that limit the immune system's ability to fight tumor cells. Despite the profound impact of these treatments, not all tumors are responsive. Recent research efforts have been focused on understanding how cancer cells manage to evade the immune response and identifying the possible mechanisms behind resistance to immunotherapy. In response, ICIs are being combined with other treatments to reduce resistance and attack cancer cells through multiple cellular pathways. Additionally, novel, targeted strategies are currently being investigated to develop innovative methods of overcoming resistance and treatment failure. This article presents a comprehensive overview of the mechanisms of immunotherapy resistance in GU cancers as currently described in the literature. It explores studies that have identified genetic markers, cytokines, and proteins that may predict resistance or response to immunotherapy. Additionally, we review current efforts to overcome this resistance, which include combination ICIs and sequential therapies, novel insights into the host immune profile, and new targeted therapies. Various approaches that combine immunotherapy with chemotherapy, targeted therapy, vaccines, and radiation have been studied in an effort to more effectively overcome resistance to immunotherapy. While each of these combination therapies has shown some efficacy in clinical trials, a deeper understanding of the immune system's role underscores the potential of novel targeted therapies as a particularly promising area of current research. Currently, several targeted agents are in development, along with the identification of key immune mediators involved in immunotherapy resistance. Further research is necessary to identify predictors of response.

Established and emerging biomarkers of immunotherapy in renal cell carcinoma

Immunotherapies, such as immune checkpoint inhibitors, have heralded impressive progress for patient care in renal cell carcinoma (RCC). Despite this success, some patients' disease fails to respond, and other patients experience significant side effects. Thus, development of biomarkers is needed to ensure that patients can be selected to maximize benefit from immunotherapies. Improving clinicians' ability to predict which patients will respond to immunotherapy and which are most at risk of adverse events - namely through clinical biomarkers - is indispensable for patient safety and therapeutic efficacy. Accordingly, an evolving suite of therapeutic biomarkers continues to be investigated. This review discusses biomarkers for immunotherapy in RCC, highlighting current practices and emerging innovations, aiming to contribute to improved outcomes for patients with RCC.

Impact of immunotherapy time-of-day infusion on survival and immunologic correlates in patients with metastatic renal cell carcinoma: a multicenter cohort analysis

BACKGROUND

Recent studies have demonstrated that earlier time-of-day infusion of immune checkpoint inhibitors (ICIs) is associated with longer progression-free survival (PFS) and overall survival (OS) among patients with metastatic melanoma and non-small cell lung cancer. These data are in line with growing preclinical evidence that the adaptive immune response may be more effectively stimulated earlier in the day. We sought to determine the impact of time-of-day ICI infusions on outcomes among patients with metastatic renal cell carcinoma (mRCC).

METHODS

The treatment records of all patients with stage IV RCC who began ICI therapy within a multicenter academic hospital system between 2015 and 2020 were reviewed. The associations between the proportion of ICI infusions administered prior to noon (denoting morning infusions) and PFS and OS were evaluated using univariate and multivariable Cox proportional hazards regression.

RESULTS

In this study, 201 patients with mRCC (28% women) received ICIs and were followed over a median of 18 months (IQR 5-30). The median age at the time of ICI initiation was 63 years (IQR 56-70). 101 patients (50%) received ≥20% of their ICI infusions prior to noon (Group A) and 100 patients (50%) received <20% of infusions prior to noon (Group B). Across the two comparison groups, initial ICI agents consisted of nivolumab (58%), nivolumab plus ipilimumab (34%), and pembrolizumab (8%). On univariate analysis, patients in Group A had longer PFS and OS compared with those in Group B (PFS HR 0.67, 95% CI 0.48 to 0.94, Punivar=0.020; OS HR 0.57, 95% CI 0.34 to 0.95, Punivar=0.033). These significant findings persisted following multivariable adjustment for age, sex, performance status, International Metastatic RCC Database Consortium risk score, pretreatment lactate dehydrogenase, histology, and presence of bone, brain, and liver metastases (PFS HR 0.70, 95% CI 0.50 to 0.98, Pmultivar=0.040; OS HR 0.57, 95% CI 0.33 to 0.98, Pmultivar=0.043).

CONCLUSIONS

Patients with mRCC may benefit from earlier time-of-day receipt of ICIs. Our findings are consistent with established mechanisms of chrono-immunology, as well as with preceding analogous studies in melanoma and lung cancer. Additional prospective randomized trials are warranted.

Localized high-risk prostate cancer harbors an androgen receptor low subpopulation susceptible to HER2 inhibition

Patients diagnosed with localized high-risk prostate cancer have higher rates of recurrence, and the introduction of neoadjuvant intensive hormonal therapies seeks to treat occult micrometastatic disease by their addition to definitive treatment. Sufficient profiling of baseline disease has remained a challenge in enabling the in-depth assessment of phenotypes associated with exceptional vs. poor pathologic responses after treatment. In this study, we report comprehensive and integrative gene expression profiling of 37 locally advanced prostate tumors prior to six months of androgen deprivation therapy (ADT) plus the androgen receptor (AR) inhibitor enzalutamide prior to radical prostatectomy. A robust transcriptional program associated with HER2 activity was positively associated with poor outcome and opposed AR activity, even after adjusting for common genomic alterations in prostate cancer including PTEN loss and expression of the TMPRSS2:ERG fusion. Patients experiencing exceptional pathologic responses demonstrated lower levels of HER2 and phospho-HER2 by immunohistochemistry of biopsy tissues. The inverse correlation of AR and HER2 activity was found to be a universal feature of all aggressive prostate tumors, validated by transcriptional profiling an external cohort of 121 patients and immunostaining of tumors from 84 additional patients. Importantly, the AR activity-low, HER2 activity-high cells that resist ADT are a pre-existing subset of cells that can be targeted by HER2 inhibition alone or in combination with enzalutamide. In summary, we show that prostate tumors adopt an AR activity-low prior to antiandrogen exposure that can be exploited by treatment with HER2 inhibitors.

Cutaneous T-cell lymphoma with CNS involvement: a case series and review of the literature

Cutaneous T-cell lymphoma (CTCL) is a rare hematologic malignancy that traditionally presents with cutaneous lesions, though metastases are not uncommon in progressive disease. We describe four cases of CTCL with central nervous system (CNS) involvement, detailing the history, pathological characteristics, treatment response, and progression. Median time from initial diagnosis to CNS metastasis was ∼5.4 years (range 3.4-15.5 years) and survival after metastasis was ∼160 days (range 19 days-4.4 years). No patients achieved long-term (>5 years) survival, though some displayed varying degrees of remission following CNS-directed therapy. We conclude that clinicians must be attentive to the development of CNS metastases in patients with CTCL. The growing body of literature on such cases will inform evolving therapeutic guidelines on this rare CTCL complication.

Physician-scientist trainees with parenting responsibilities need financial and childcare support

Physician–scientists who become parents during their long period of training need additional funding and support for lactation, childcare and healthcare, to ensure an equitable workforce.

Case Report: Exceptional response to nivolumab plus cabozantinib in a patient with extrarenal clear cell renal cell carcinoma

Extrarenal clear cell renal cell carcinoma (eccRCC) is a rare type of RCC that arises in areas other than the kidney. Given its rarity, consensus guidelines for optimal treatment of eccRCC have not been established, and the literature is lacking any reports of patient response to systemic therapy and any reports of administration of immunotherapy to patients with ecRCC. Here, we present the case of a patient in their 60s with eccRCC arising in the spleen. The patient underwent splenic resection and then received systemic therapy, due to disease recurrence, with a combination of immunotherapy (IO) and tyrosine kinase inhibitor targeted therapy (VEGF-TKI). The patient had an excellent and durable response to this therapeutic regimen with minimal adverse effects, completing 2 years of therapy of nivolumab and cabozantinib. At the time of this report, the disease remains stable. This case demonstrates that combination therapy with IO+VEGF-TKI represents a reasonable and well-tolerated treatment option with activity in eccRCC and reveals interesting correlative data, including nests of stem-like CD8+T-cell infiltration in tumor tissue, which provide important biological context to this patient's exceptional therapeutic response.

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.

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.

Case Report: Exceptional Response to Nivolumab Plus Ipilimumab in a Young Woman With TFE3-SFPQ Fusion Translocation-Associated Renal Cell Carcinoma

Translocation-associated renal cell carcinoma (tRCC) is a rare, aggressive malignancy that primarily affects children and young adults. There is no clear consensus on the most effective treatment for tRCC and there are no biomarkers of response to treatments in these patients. We present a case of a 23 year-old female with metastatic tRCC to the lungs who was started on treatment with nivolumab and ipilimumab. She had a complete radiographic response to treatment and has been progression-free for over 18 months. Immunofluorescence imaging performed on the baseline primary tumor sample showed significant intratumoral immune infiltration. Importantly, these cells are present in niches characterized by TCF1+ CD8+ T cells. Histopathologic investigation showed the presence of lymphocytes in the fibrovascular septae and foci of lymphovascular invasion. Furthermore, lymphovascular invasion and intratumor niches with TCF1+ CD8+ T cells may predict a favorable response to treatment with nivolumab and ipilimumab. These findings have significant clinical relevance given that immune checkpoint inhibitors are approved for several malignancies and predictive biomarkers for response to treatment are lacking. Importantly, the identification of these TCF1+ CD8+ T cells may guide treatment for patients with tRCC, which is a rare malignancy without a consensus first-line treatment option.

A Subset of Localized Prostate Cancer Displays an Immunogenic Phenotype Associated with Losses of Key Tumor Suppressor Genes

PURPOSE

A subset of primary prostate cancer expresses programmed death-ligand 1 (PD-L1), but whether they have a unique tumor immune microenvironment or genomic features is unclear.

EXPERIMENTAL DESIGN

We selected PD-L1-positive high-grade and/or high-risk primary prostate cancer, characterized tumor-infiltrating lymphocytes with multiplex immunofluorescence, and identified genomic alterations in immunogenic and nonimmunogenic tumor foci.

RESULTS

One quarter of aggressive localized prostate cancer cases (29/115) had tumor PD-L1 expression more than 5%. This correlated with increased density of CD8⁺ T cells, a large fraction coexpressing PD-1, versus absent PD-1 expression on sparse CD8 T cells in unselected cases. Most CD8⁺PD-1⁺ cells did not express terminal exhaustion markers (TIM3 or LAG3), while a subset expressed TCF1. Consistent with these CD8⁺PD-1⁺TCF1⁺ cells being progenitors, they were found in antigen-presenting cell niches in close proximity to MHC-II⁺ cells. CD8 T-cell density in immunogenic prostate cancer and renal cell carcinoma (RCC) was nearly identical. Shallow RB1 and BRCA2 losses, and deep deletions of CHD1, were prevalent, the latter being strongly associated with a dendritic cell gene set in The Cancer Genome Atlas. Tumor mutation burden was variable; neither high microsatellite instability nor CDK12 alterations were present.

CONCLUSIONS

A subset of localized prostate cancer is immunogenic, manifested by PD-L1 expression and CD8⁺ T-cell content comparable with RCC. The CD8⁺ T cells include effector cells and exhausted progenitor cells, which may be expanded by immune checkpoint inhibitors (ICI). Genomic losses of RB1, BRCA2, and CHD1 may be drivers of this phenotype. These findings indicate that immunotherapies may be effective in biomarker-selected subpopulations of patients with localized prostate cancer.

Abstract PO-041: An immunologic niche of antigen presenting cells and stem-like CD8+ T-cells is present in non-small cell lung cancer brain metastases

Background: Non-small cell lung cancer (NSCLC) patients with brain metastases have a very poor prognosis. The first line treatments for NSCLC brain metastases are typically surgery and pre- or post-operative stereotactic radiosurgery (SRS) or SRS alone. However, subsequent intra-cranial failure and death is common. Importantly, we have previously shown that a unique immune niche in genitourinary malignancies correlates with the risk for disease recurrence. Accordingly, here we investigated whether this immune niche was present in brain metastases, whether it correlated with patient outcomes, and whether it was modulated by SRS. Methods: Formalin fixed paraffin embedded brain metastases were stained by immunofluorescence for CD8, PD-1, TCF-1, MHC-II and DAPI. Following successful image acquisition using fluorescent whole slide scanning, we used a custom quantitative analysis pipeline to measure the cellularity, relative cellular locations, local cellular density, and marker staining intensity. Results: We identified immune niches consisting of both stem-like TCF-1+ CD8+ T-cells and antigen presenting cells (MHC-II+) in brain metastases. TCF-1+ CD8+ T-cells were found at in areas of higher MHC-II+ cell density than the TCF-1 CD8+negative T-cells. The amount of tumor issue occupied by immune niches correlated with TCF1+ CD8+ T-cell infiltration, as well as with total CD8+ T-cell and MHC-II+ cell infiltration. Importantly, we found that higher MHC-II+ cell density correlated with longer overall survival in this cohort of patients. Additionally, we found this immune niche is preserved following pre-operative SRS. Conclusions: Our study is the first to demonstrate stem-like CD8+ T-cells in brain metastases and that these cells form an immune niche similar to those described extra-cranial tumor sites. Additionally, we report that the immune niche is preserved following SRS, which is highly clinically relevant to the use of combinatorial strategies between SRS and checkpoint blockade.

Citation Format: Caroline S. Jansen, Luke del Balzo, Roshan Prabhu, Suzanna Logan, Prasanthi Chappa, Kirtesh Patel, Scott Wilkinson, Ross Lake, Hui-Kuo G. Shu, Jim Zhong, Vishal Dhere, Jeffrey Olson, Adam G. Sowalsky, Mohammad K. Khan, Haydn T. Kissick, Zachary S. Buchwald. An immunologic niche of antigen presenting cells and stem-like CD8+ T-cells is present in non-small cell lung cancer brain metastases [abstract]. In: Proceedings of the AACR Virtual Special Conference on Radiation Science and Medicine; 2021 Mar 2-3. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(8_Suppl):Abstract nr PO-041.

Neoadjuvant Cabozantinib in an Unresectable Locally Advanced Renal Cell Carcinoma Patient Leads to Downsizing of Tumor Enabling Surgical Resection: A Case Report

Introduction

Cabozantinib (XL-184) is a small molecule inhibitor of the tyrosine kinases c-Met, AXL, and VEGFR2 that has been shown to reduce tumor growth, metastasis, and angiogenesis. After the promising results from the METEOR and CABOSUN trials, cabozantinib was approved for use in the first- and second-line setting in patients with advanced RCC. Previously, targeted therapies have been used in the neoadjuvant setting for tumor size reduction and facilitating nephrectomies. The increased response rates with cabozantinib in metastatic renal cell carcinoma (mRCC), along with the other neoadjuvant TKI data, strongly support an expanded role for cabozantinib in the neoadjuvant setting.

Case Description

We report on a 59-year-old gentleman presenting with an unresectable 21.7 cm left renal cell carcinoma (RCC) with extension to soft tissue and muscles of the thoracic cage, psoas muscle, posterior abdominal wall, tail of pancreas, splenic flexure of colon, and inferior margin of spleen. Presurgical, neoadjuvant systemic therapy with cabozantinib was initiated for 11 months in total. Initially after 2 months of cabozantinib, magnetic resonance imaging (MRI) revealed a significant reduction (44.2%) in tumor diameter from 21.7 to 12.1 cm with decreased extension into adjacent structures. After 11 months total of cabozantinib, the corresponding MRI showed grossly stable size of the tumor and significant resolution of invasion of adjacent structures. After washout of cabozantinib, radical resection, including nephrectomy, was successfully performed without any major complications, either intra-operative or perioperative. Negative margins were achieved.

Conclusions

This is a report of neoadjuvant cabozantinib downsizing a tumor and enabling surgical resection in this patient with locally advanced RCC. Our findings demonstrate that neoadjuvant cabozantinib to facilitate subsequent surgical resection may be a feasible option for patients presenting with unresectable RCC.

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&lt;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.

The immunosuppressive phenotype of tumor-infiltrating neutrophils is associated with obesity in kidney cancer patients

Infiltrating tumor neutrophils and myeloid-derived suppressor cells represent major populations in the tumor microenvironment that contribute to tumor progression. However, the phenotype of circulating and tumor-associated neutrophils, and the impact of cancer patients' metabolic state on neutrophil function need further characterization. Here we show that in kidney cancer patients, circulating neutrophils display an altered immature-like phenotype, and an activated/primed metabolic state. Circulating immature-like neutrophils acquire an activated phenotype upon migration into the tumor tissue, characterized by high expression of the immunosuppressive enzyme arginase-1, and active granule release. Interestingly, obesity and adipose tissue distribution were significantly associated with this activated phenotype of neutrophils, including the release of arginase-1 in the tumor tissue. These results provide a possible functional relationship between the metabolic status of the patients and disease progression, through an active immunosuppressive role of neutrophils within the kidney tumor microenvironment.

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.

Role of the Gut Microbiota of Children in Diarrhea Due to the Protozoan Parasite Entamoeba histolytica

Background. An estimated 1 million children die each year before their fifth birthday from diarrhea. Previous population-based surveys of pediatric diarrheal diseases have identified the protozoan parasite Entamoeba histolytica, the etiological agent of amebiasis, as one of the causes of moderate-to-severe diarrhea in sub-Saharan Africa and South Asia.

Methods. We prospectively studied the natural history of E. histolytica colonization and diarrhea among infants in an urban slum of Dhaka, Bangladesh.

Results. Approximately 80% of children were infected with E. histolytica by the age of 2 years. Fecal anti-galactose/N-acetylgalactosamine lectin immunoglobulin A was associated with protection from reinfection, while a high parasite burden and expansion of the Prevotella copri level was associated with diarrhea.

Conclusions. E. histolytica infection was prevalent in this population, with most infections asymptomatic and diarrhea associated with both the amount of parasite and the composition of the microbiota.