Despite the clinical success of immunotherapy, long-lasting benefit remains restricted to a subset of patients. Tumor metabolic adaptation is emerging as a key factor limiting immunotherapy efficacy. We previously found that glycolysis-low tumor variants, compared to the parental glycolytic tumors, better respond to neoadjuvant CTLA-4 immune checkpoint blockade (ICB) therapy. Here, we investigated new rational modalities to restore immune sensitivity of glycolytic tumors by studying how lowering the tumor-cell glycolytic capacity reshapes the tumor microenvironment (TME) to favor long-lasting systemic anti-tumor responses upon immunotherapy. We found that lowering glycolysis in cancer cells through LDHA-knock down (KD) results in TME displaying normalized vasculature, reduced angiogenic markers, increased high endothelial venules (HEVs), and enhanced recirculation of CD8 + T cells both in and out of the tumor. By leveraging public transcriptomic data sets from human solid cancers, we confirmed that glycolysis positively correlates with neo-angiogenesis and inversely correlates with features of vascular normalization and immune cytolytic activity. Moreover, a tumor signature that incorporates glycolysis- and angiogenesis-related genes as positive features, and normal vasculature, HEV, and immune cytolytic activity genes as negative features predicted poor outcomes better than the individual features across most human solid tumor types in the TCGA. To determine the therapeutic implication of these interrelated processes, we asked if targeting the vasculature would restore immunotherapy responses in glycolytic tumors. We found that combining low-dose anti-VEGFR2 with CTLA-4 blockade induces tumor regressions and protection from metastases in glycolytic tumors. These therapeutic effects were associated with vasculature normalization and increased abundance of HEVs and concentrations of lymphangiogenic factors in the TME of glycolytic tumors. Moreover, anti-VEGFR2 with anti-CTLA-4 restored recirculation of anti-tumor CD8 + T cells in and out of the TME in glycolytic tumors, with specific increases in intratumoral recruitment and activation of cytolytic CD62L⁺CD44⁺CD8⁺ T cells expressing VEGFR2 and low levels of CTLA-4, suggesting potential novel direct synergistic effects of anti-VEGFR2 and anti-CTLA-4 on CD8 + T cells. Conversely, this combination opposed the beneficial immune and vascular TME features of LDHA-KD tumors, indicating tumor-metabolic-dependent effects. Accordingly, we found that standard combined regimens of anti-VEGF and ICB therapy improve survival with respect to ICB alone in patients with glycolysis-high but not glycolysis-low tumors. Together, these findings indicate that tumor cell glycolysis "primes" the TME for aberrant vascular architecture and T-cell exclusion, and that modulating the tumor vasculature can unravel these mechanisms restoring immune responsiveness. This suggests that tailoring anti-angiogenic and immunotherapy combinations to the tumor glycolytic state and associated vasculature profiles may restore immune surveillance and overcome therapy resistance.

Abstract Due to the rising use of androgen deprivation therapy (ADT) and AR signaling inhibitors (ARSIs), metastatic castration-resistant prostate cancer is expanding and although it is known that its subtypes provide predictive utility, their individual tumor-immune microenvironments are woefully underexplored mechanistically. Careful investigation of these subtypes of mCRPC may provide insights into therapeutic resistance beyond mCRPC. Using both publicly available and in-house single-cell RNA-sequencing and spatial transcriptomics datasets, we have characterized mCRPC cells and their accompanying tumor-immune microenvironment using established marker genes and verified their identity using inferred copy-number variation status. Firstly, we have explored metabolic profiles of the various cell-types in our samples by calculating scores based on transcription of genes involved in metabolic processes. We have performed ligand-receptor pair analysis to predict which cell types are interacting and through which inflammatory and metabolic axes these interactions are occurring. Finally, we have demonstrated interaction feasibility by measuring distance in space via our spatial transcriptomics data. Our preliminary results indicate that these subtypes have significantly different metabolic profiles. Additionally, the immune cells near to these different subtypes have shown differential immunosuppressive programs and metabolic reprogramming. These findings suggest the potential role of tumor metabolic forces in the induction of an immunosuppressive tumor microenvironment and point to a promising utility of metabolic perturbations in mCRPC as a neoadjuvant to enhance response to immune checkpoint blockade (ICB). This work highlights novel lenses in which to analyze tumors in the hopes of suggesting combination therapies that may overcome treatment obstacles. Citation Format: Tonatiuh A. Gonzalez, Anisha Tehim, Inna Serganova, Roberta Zappasodi, Ekta Khurana. Metabolic dependence of prostate cancer subtypes and its association with the tumor-immune microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 7434.

PURPOSE:Glucocorticoid-induced tumor necrosis factor receptor-related protein (GITR) agonism in T cells may potentiate antitumor immune responses to immune checkpoint blockade therapy. This first-in-human, phase I/II dose escalation/expansion study assessed INCAGN01876, a humanized GITR-targeting agonistic mAb, for advanced solid tumors (NCT02697591). PATIENTS AND METHODS:Dose was escalated by 0.03 to 20 mg/kg every 2 weeks; flat doses of 400 mg every 4 weeks and 300 mg every 2 weeks were also evaluated. The primary objective was safety/tolerability; secondary objectives were pharmacokinetics and preliminary efficacy; and exploratory objectives were immunogenicity, GITR occupancy, and immune biomarker assessment. RESULTS:Among 100 patients enrolled [prior anti-PD-1/PD-L1 therapy, 47%; most common tumors: colorectal (19%) and melanoma (14%)], 2% had one dose-limiting toxicity (grade 4 hypoxia and grade 3 pleurisy). The MTD was not reached. Treatment-related adverse events (TRAE) occurred in 69% of patients, most frequently fatigue (17%) and pruritus (14%); 10% had grade ≥3 TRAEs, most commonly fatigue (3%); and 23% reported immune-related adverse events, most frequently generalized pruritus and generalized rash (7% each). Doses ≥5 mg/kg every 2 weeks resulted in full receptor occupancy at trough. INCAGN01876 elicited changes in immune parameters in some patients, including variable peripheral regulatory T-cell depletion and cytokine upregulation. Two patients achieved confirmed partial responses: one with appendiceal mucinous carcinoma and another with melanoma previously treated with pembrolizumab and glembatumumab; 36% of patients had disease control. CONCLUSIONS:INCAGN01876 was generally well tolerated; fatigue was the most frequent TRAE. INCAGN01876 elicited transient and variable regulatory T-cell depletion and limited antitumor activity. Future studies will explore combinatorial approaches.

Baseline demographics and characteristics.

Epstein-Barr virus (EBV) infection is implicated in the pathogenesis of a significant subset of human lymphomas. EBV+ tumors exhibit distinct latency programs: latency I (expressing only EBNA1) is minimally immunogenic, whereas latency II/III expresses additional viral antigens (e.g., LMP1/2 and EBNA2/3) that are recognised by EBV-specific cytotoxic T cells (EBV-CTLs). Consequently, allogeneic EBV-CTLs are effective cellular therapy in latency II/III tumors but are largely ineffective against latency I tumors such as EBV+ Burkitt lymphoma (BL) and subsets of diffuse large B-cell lymphoma (DLBCL). We previously showed that DNMT1 inhibition with decitabine (DCB) can partially induce latency II/III gene expression in latency I BL, sensitizing tumors to EBV-CTLs. One limitation of DNMT1 inhibition is that the induction of latency II/III is only observed in a subset of cells. Here, we investigated the epigenetic mechanisms underlying resistance to latency conversion in EBV+ tumours. To understand the transcriptional programs limiting latency conversion, we performed RNA-sequencing on EBV+ BL cells that are sensitive vs. resistant to DCB-induced latency conversion. Transcription factor enrichment analysis revealed SP140, a chromatin reader linked to the repressive mark H3K27me3, as enriched in DCB-resistant cells. To examine whether SP140 is responsible for the resistance to DCB-induced latency conversion, we examined the effect of the SP140 inhibitor, GSK761 on viral latency with or without DCB in latency I EBV+ BL cells (Kem I). When combined with DCB, GSK761 significantly increased the proportion of cells converting to latency II/III cells compared to either drug alone (EBNA2+/LMP1+ cells after treatment with DCB vs DCB+GSK761: 15.4% vs 52.2% adj-p<0.0001). Enhanced latency conversion with DCB+GSK761 was also observed in latency I EBV+ DLBCL cells (Val). Given SP140's role in regulating H3K27me3, we next performed ChIP-qPCR to determine if H3K27me3 at key viral promoters of latency (Cp and LMP1p) could be mediating latency restriction. We observed elevated H3K27me3 in resistant vs. sensitive Kem I cells at Cp (2-fold; adj-p=0.0009) and LMP1p (2.45-fold; adj-p=0.0086). The elevation in H3K27me3 at Cp and LMP1p was confirmed in an additional BL cell line (Rael) and in DLBCL (Val). Based on this, we evaluated the EZH2 inhibitor, tazemetostat (TAZ), which reduces H3K27me3. Combined treatment with DCB+TAZ increased EBNA2+ LMP1+ cells compared to DCB alone (DCB vs DCB+TAZ: 15.4% vs 38.7% adj-p<0.0001) in Kem I cells. Increased latency conversion with the combination was also observed in DLBCL (Val). The addition of both GSK761 and TAZ to DCB did not further enhance latency conversion, suggesting SP140 promotes resistance via H3K27me3. Given the efficacy of combined DNMT1 and EZH2 inbition in vitro, we evaluated the combination in vivo in BL xenografts. Mice were engrafted with Kem I and then treated with either DCB, TAZ, or the combination. At day 15, tumors were evaluated for latency profiling by flow cytometry. Combined treatment with DCB+TAZ significantly increased the proportion of LMP1-expressing tumor cells in comparison to DCB alone (adj-p≤0.0001). We next evaluated if enhanced latency conversion improves T-cell mediated killing of BL by allogeneic EBV-CTLs. EBV-CTLs were generated using partially HLA-matched allogeneic peripheral blood mononuclear cells exposed to an EBV peptide mix including latent antigens. EBV-CTLs were co-cultured with BL cells pre-treated with DCB, TAZ, or the combination. T cells exposed to BL pretreated with the combination of DCB and TAZ showed a 1.46-fold increase in IFNg production compared to those exposed to DCB only treated BL (p=0.0032), indicating enhanced tumor immunogenicity.Together, these findings identify SP140 and H3K27me3 as key epigenetic barriers to latency conversion in EBV+ latency I lymphomas. Dual inhibition of DNMT1 and EZH2 enhances expression of immunogenic viral antigens, improving tumor susceptibility to EBV-CTLs. This strategy offers a promising approach for treating otherwise immune-refractory EBV+ lymphomas.

Patient disposition. aTwo patients completed treatment [0.3 mg/kg every 2 weeks (Q2W) and 300 mg Q2W, respectively]. The death in the 300-mg Q2W cohort was coded as dyspnea secondary to disease progression. Reasons for patient ineligibility included meeting the following exclusion criteria: (i) laboratory and medical history parameters not within the protocol-defined range (39%; 17/44 patients); (ii) any condition that would, in the investigator’s judgment, interfere with full participation in the study (including administration of the study drug and attending required study visits), pose a significant risk to the subject, or interfere with the interpretation of study data (16%; 7/44 patients); (iii) known active central nervous system metastases and/or carcinomatous meningitis (14%; 6/44 patients); and (iv) evidence of hepatitis B virus (HBV) or hepatitis C virus (HCV) infection or risk of reactivation (positive testing for HBV DNA and/or HCV RNA; 11%; 5/44 patients) and not meeting the following inclusion criteria: willingness to provide a written informed consent form (7%; 3/44 patients) and having Eastern Cooperative Oncology Group performance status of 0 or 1 (5%; 2/44 patients). FAS, full analysis set.

A, Frequencies of Tregs. B, Changes in central memory (CM) and EM CD4+ T cells.

A, INCAGN01876 mean (±SE) concentration–time profiles after the first dose and at steady state. B, Relationship between serum concentrations of INCAGN01876 and GITR receptor occupancy. C, Percentage of INCAGN01876 receptor occupancy vs. time. The average receptor occupancy per cohort is depicted (± SD). PK analysis includes patients with ADA-negative status at the respective visit; first visit/steady state: 0.03 mg/kg, n = 4/n = 0; 0.1 mg/kg, n = 4/n = 0; 0.3 mg/kg, n = 3/n = 1; 1 mg/kg, n = 3/n = 1; 3 mg/kg, n = 15/n = 5; 5 mg/kg, n = 16/n = 5; 10 mg/kg, n = 14/n = 4; 20 mg/kg, n = 3/n = 0; 300 mg, n = 21/n = 7; and 400 mg, n = 9/n = 3. RO, receptor occupancy.

T cell exhaustion is a major barrier to effective cancer immunotherapy. Although immune checkpoint blockade can reinvigorate exhausted T cells, not all patients achieve long-term responses, partly due to the refractory nature of terminally exhausted T cells. Beyond persistent antigen stimulation, the environmental drivers of exhaustion remain to be thoroughly characterized. Here we identify CD47 upregulation in tumor-infiltrating exhausted CD8+ T cells in both human and murine tumors. We reveal a novel role for the extracellular matrix protein thrombospondin-1 (TSP-1) in engaging CD47 on T cells to promote exhaustion. This interaction activates calcineurin–NFAT signaling, inducing upregulation of TOX and expression of inhibitory receptors, and impairing effector function during tumor progression. Importantly, disrupting the TSP-1–CD47 axis prevents T cell exhaustion and enhances tumor control. Our findings identify a novel pathway promoting T cell dysfunction and suggest that targeting the TSP-1–CD47 axis is a promising strategy to enhance T cell immunity and immunotherapy efficacy. Merghoub, Wolchok and colleagues reveal a role of the extracellular matrix protein thrombospondin-1 (TSP-1) and CD47 in promoting T cell exhaustion during tumor progression in mice and humans.

Cancer immunotherapy approaches aim to instruct the immune system to eliminate tumor cells. Immune checkpoint blockade (ICB) therapies, such as anti-CTLA-4 and anti-PD-1, have significantly advanced the field, and other immunotherapeutic modalities are constantly being developed and tested in pre-clinical and clinical studies. One of the most important outcomes of cancer immunotherapy is efficient elimination of tumor cells by cytotoxic CD8+ T cells. Thus, accurate measurement of tumor cell sensitivity to T-cell-mediated killing is crucial for improving treatment development. This paper presents a flow cytometry-based protocol to assess antigen-specific CD8+ T-cell cytotoxicity using ovalbumin (OVA)-specific CD8+ T cells from OT-1 TCR transgenic mice and OVA-presenting tumor cell lines (either transduced with OVA or pulsed with a class-I-MHC-restricted OVA-derived peptide). This method minimizes contribution from non-antigen-mediated killing into readouts by incorporating non-target cells (not expressing/presenting-OVA cells) into co-cultures. The procedure also allows for the evaluation of T-cell-mediated cytotoxicity under various conditions and enables concurrent immunophenotyping of effector T cells and target tumor cells if desired. The protocol can be easily customized, offers advantages over methods that rely on luciferase-expressing tumor cell lines and provides versatility in detecting multiple parameters, making it a useful and valuable tool for advancing cancer immunotherapy research.

Abstract Several patients do not benefit from anti-cancer immunotherapies due to resistance for metabolic adaptation and fitness of tumor cells. Highly glycolytic tumor cells outcompete effector T cells for glucose in the tumor microenvironment (TME), impairing T cell function. High levels of lactate dehydrogenase (LDH) correlate with poor prognosis in cancer patients undergoing immunotherapies, inducing aberrant angiogenesis by activating HIF-1α and VEGF expression in endothelial cells (ECs), underscoring a biological interplay between tumor metabolism and neo-angiogenesis that can impact anti-tumor immunity. Main vasculature cells – ECs and pericytes (PCs) – may serve as antigen-presenting cells (APC), influencing T cell responses. While these findings point to a joint metabolic and immune regulation of the vasculature:T-cell crosstalk in the TME, we currently lack a precise understanding of the mechanisms linking tumor metabolism, aberrant angiogenesis, and anti-tumor T-cell responses, and how cell-based therapy may be influence by these factors. We have compared and contrasted vasculature and immune cells phenotypes by high-dimensional flow cytometry in established tumor models representing three major metabolic states by perturbing the two main cellular hubs for producing energy (aerobic glycolysis, by LDHA knock-down; oxidative phosphorylation, by depleting mitochondria as in Rho0 cells) compared to control tumors (NC). We functionally tested the impact of intratumor T cell recruitment according to these phenotypes, by adoptive cell transfer (ACT) therapy using T cells from donor mice immunized with matched-tumor injected i.v. in RAG2 KO mice bearing metabolically-defective tumor (KD or Rho0) and control tumor (NC) in contralateral mammary fat pad. We found that glycolysis-low tumors (LDH-A KD) show a better vasculature with reduced proportions of angiogenic activated PCs (cluster1: NG2+PDGFRbneg) and increased frequencies of “stabilizing” PCs (cluster 2: NG2negPDGFRb+, which counteract the formation of leaky vessels), compared to NC. However, KD tumors also display a reduction in MECA-79+ high endothelial venules. Moreover, LDHA-KD vs. NC tumors displayed ECs and cluster 2 PCs with greater expression of MHCI and decreased expression of FAS-L, and more EC expressing MHCII or PD-L1. In addition, the immune infiltrate of KD tumors is characterized by increased amounts of T effector cells and lower amounts of Gr1-low myeloid derived suppressor cells (MDSCs). The changes in vascularization phenotype have been confirmed in RAG2 KO mice bearing bilateral tumor variants model. ACT in these mice bearing bilateral 4T1-NC and -KD tumors resulted in greater biodistribution of T cells in the KD tumors, showing decreasing tumor growth. Vasculature features correspond to greater intratumor T-cell trafficking, indicating a mechanistic link between tumor glycolysis, aberrant angiogenesis, and T-cell exclusion. This would aim to elucidate the mechanisms through which these processes are connected for developing more efficacious T-cell-targeted therapies. Citation Format: Giorgia Colombo, Jee Hye Kang, Inna Serganova, Roberta Zappasodi. Interplay between tumor metabolism, vasculature, and T-cell infiltration in anti-tumor immunity [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor Immunology and Immunotherapy; 2024 Oct 18-21; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2024;12(10 Suppl):Abstract nr B049.

Abstract Background Diffuse large B cell lymphoma (DLBCL) is the most frequent subtype of non-Hodgkin lymphomas (B-NHLs). B-NHLs respond poorly to currently available immune checkpoint blockade (ICB) therapies, such as anti-PD-1 or anti-CTLA-4 + anti-PD-1 combination and the reason for this is unknown. New genetic classifications of DLBCL have been recently proposed, providing rationale for studying ICB resistance mechanisms according to these novel molecular DLBCL subtypes. Methods Genetic aberration involving Bcl2 and EZH2 are commonly found in follicular lymphoma (FL) and DLBCL in patients. Here, we used mouse models of EZH2/Bcl2-mutant (EZB) lymphoma, constitutively expressing Bcl-2 and EZH2Y641F mutation in germinal center B (GCB) cells (Cg1-Cre; Rosa26LSL.BCL2.IRES.GFP; EZH2Y641F), including a genetically engineered mouse model (GEMM) which spontaneously develops diseases resembling FL and wild type mice transplanted with a GEMM-derived EZB cell line resembling DLBCL lymphoma. Mice were treated with ICB therapy alone or in combination with the EZH2 inhibitor, tazemetostat (TAZ). Immune and lymphoma cells from spleens and lymph nodes were analyzed by flow cytometry and immunofluorescence staining of tissue sections. These parameters were correlated with tumor progression by bioluminescence imaging, MRI, and overall survival. Results We found that TAZ alone or in combination with anti-CTLA-4 moderately decreased tumor burden but did not significantly improve survival of EZB GEMM mice. This was associated with increased frequencies of CXCR5+ CD8+ T cells in spleen and lymph nodes. We then evaluated the effect of dual anti-CTLA-4 + anti-PD-1 ICB therapy to target the additional immune checkpoint, PD-1. In EZB GEMM mice, at 150 days post-treatment, anti-CTLA-4 + anti-PD-1 therapy with or without TAZ extended survival, compared to single agents (71.4% vs 42.6%). Of note, tumor burden irrespective of treatment positively correlated with frequencies of CXCR5+Bcl6+CD4+ T follicular helper cells and MHC-I/II+CD86+ normal B cells, suggesting ongoing immune reaction. Interestingly, mice receiving TAZ + ICB had lower tumor burden and highest percentages of NK cells. In the more aggressive transplantable EZB-DLBCL model, anti-CTLA-4 + anti-PD-1 combination led to complete tumor regressions, extending survival, and inducing anti-tumor immunological memory. Combination-treated tumors had greater proportions of CXCR5+GzmB+CD8+ T cells and greater CXCR5 expression levels on conventional T cells compared to monotherapy or control tumors. Anti-PD-1 or ICB combination increased the proportion of Ly6c+ lymphoma cells, suggesting diversion to plasmablast phenotype. Conclusions Our results indicate that CXCR5+ T-cell:B cells interactions may be implicated in EZH2-driven lymphomas, with different outcomes depending on the disease stage (FL vs. DLBCL). Ongoing work is focused on the mechanistic role of increasing access of cytolytic immune cells to lymphoma niches via CXCR5 and promoting lymphoma cell reprogramming in the responses of EZB lymphoma to ICB therapy. Citation Format: Alexey V Sarapulov, Serganova Inna, Ryan Bucktrout, Yusuke Isshiki, Anthony Santella, Marc-Anthony Rodriguez, Sanjukta Chakraborty, Solene Brunschvig, Santhosha Vardhana, Claudio Tripodo, Ari Melnick, Wendy Beguelin, Roberta Zappasodi. Mechanisms of action of immune checkpoint blockade therapy in EZH2/Bcl2-mutant B-cell lymphomas [abstract]. In: Proceedings of the Fourth AACR International Meeting on Advances in Malignant Lymphoma: Maximizing the Basic-Translational Interface for Clinical Application; 2024 Jun 19-22; Philadelphia, PA. Philadelphia (PA): AACR; Blood Cancer Discov 2024;5(3_Suppl):Abstract nr PO-040.

Despite regulating overlapping gene enhancers and pathways, CREBBP and KMT2D mutations recurrently co-occur in germinal center (GC) B cell-derived lymphomas, suggesting potential oncogenic cooperation. Herein, we report that combined haploinsufficiency of Crebbp and Kmt2d induces a more severe mouse lymphoma phenotype (vs either allele alone) and unexpectedly confers an immune evasive microenvironment manifesting as CD8+ T-cell exhaustion and reduced infiltration. This is linked to profound repression of immune synapse genes that mediate crosstalk with T-cells, resulting in aberrant GC B cell fate decisions. From the epigenetic perspective, we observe interaction and mutually dependent binding and function of CREBBP and KMT2D on chromatin. Their combined deficiency preferentially impairs activation of immune synapse-responsive super-enhancers, pointing to a particular dependency for both co-activators at these specialized regulatory elements. Together, our data provide an example where chromatin modifier mutations cooperatively shape and induce an immune-evasive microenvironment to facilitate lymphomagenesis. CREBBP and KMT2D mutations frequently co-occur in B cell lymphomas with unclear significance. Here the authors show that they cooperate to skew B cell fate decisions and induce a CD8-depleted immune-evasive microenvironment to facilitate lymphomagenesis.

Abstract Background: Immune checkpoint inhibitors (ICIs) offer new treatment possibilities for women with triple-negative breast cancer (TNBC) – one of the most challenging breast cancer subtypes. The PD-1 inhibitor pembrolizumab (pembro; Keytruda®) is approved in metastatic TNBC (mTNBC) patients with PD-L1(+) tumors, and for neoadjuvant treatment (NAT) in stage II/III TNBC [1, 2]. Residual cancer burden (RCB) after NAT is highly prognostic, with pathologic complete response (pCR, RCB 0) anticipating long-term survival [3]. In mTNBC, pembro plus chemotherapy in the 1st-line improves progression free survival (PFS), but durable responses are rare. Optimizing ICI use in TNBC thus remains an unmet need, and defining easily assessable markers of response is crucial. Neutrophil-to-lymphocyte ratio (NLR) and platelet-to-lymphocyte ratio (PLR) are peripheral blood surrogates of tumor inflammation and have prognostic and predictive value in TNBC [4-8]. Elevated NLR (≥ 5) and PLR (≥ 200) correlate with worse outcomes upon ICIs in melanoma and non-small-cell lung cancer [9, 11-14]; however, this has not been studied in breast cancer [9, 10]. We evaluated the relationship of baseline NLR and PLR with pembro responses in TNBC patients. Methods: We retrospectively reviewed data from TNBC patients who completed pembro between 10/2/20 - 6/1/23 at Weill Cornell. Patients on NAT who did not complete treatment were excluded. RCB score (pCR/0, 1, 2, 3) was calculated from surgical resection pathology reports using the MD Anderson RCB Calculator [15, 16]. Baseline laboratory data were obtained from clinical records. Associations between NLR and PLR with RCB levels were examined using the non-parametric Kruskal-Wallis test (if >2 levels), the Wilcoxon rank sum test (if 2 levels), or the Spearman’s rank correlation. NLR and PLR were also correlated with PFS (measured from pembro start date to date of progression) in metastatic patients. PFS data for metastatic patients without interval imaging since pembro initiation were censored at the date of data analysis, and PFS was not calculated for patients who received only 1 cycle of pembro. Results: We identified 63 eligible patients: 24 were excluded due to lack of TNBC diagnosis (n=20), or because they only received adjuvant pembro (n=4). Of the 39 remaining patients, 5 did not complete NAT and 2 had missing data, leaving 32 evaluable patients (17 in the NAT cohort and 15 in the mTNBC cohort). Overall, the median age was 51 years, and 16% were Hispanic, 11% Asian, 57% non-Hispanic, 24% Black, and 65% Non-Black. Neoadjuvant cohort: The pCR rate was 30%. Patients with both NLR ≥ 5 and PLR ≥ 200, had a pCR rate of 0%; in patients with NLR < 5 or PLR < 200, pCR rate was 43%. Median NLR in pCR vs. non-pCR groups was 1.91 [IQR: 1.72- 2.73] vs. 2.44 [IQR: 1.97- 5.24] (p=0.3), with trends towards significance when NLR was compared between RCB levels >1 (2.67; IQR: 2.05, 6.49) vs. RCB levels ≤1 (1.91; IQR: 1.63, 2.58) (p=0.14). Mean PLR was higher in patients with RCB 2-3 (409) compared to those with pCR or RCB 1 (167) (p=0.146). Metastatic cohort: The overall mean PFS was 7.8 months. Visceral metastases were seen in 80% of patients (17% liver, 33% brain). In patients with brain mets, baseline NLR and PLR were higher than in the overall cohort (NLR, 4.86 vs. 2.78; PLR, 429 vs. 186). Conclusions: Our study is the first to evaluate NLR and PLR as response biomarkers in TNBC patients receiving pembro and is the first report of our real-world data of TNBC patients on pembro. In our neoadjuvant cohort, higher baseline NLR and PLR correlated with higher RCB levels, with a trend towards statistical significance. Further investigation and correlation of NLR and PLR with tumor microenvironment features will help to clarify these relationships. Citation Format: Ashley Schreier, Roberta Zappasodi, Inna Serganova, Laura Munoz Arcos, Xi Kathy Zhou, Massimo Cristofanilli, Eleni Andreopolu. Predictive value of neutrophil-to-lymphocyte and platelet-to-lymphocyte ratios in patients with triple negative breast cancer treated with pembrolizumab [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-25-04.