Abstract HER2-01: HER2-01 Clinical and Molecular Characteristics of HER2-low/zero Early Stage Triple-Negative Breast Cancer

Background: In the metastatic setting, low HER2 expression is associated with clinical benefit from trastuzumab deruxtecan, a HER2-targeting antibody drug conjugates. However, little is known about the biological significance of low HER2 expression in patients with early stage triple-negative breast cancer (TNBC) receiving neoadjuvant therapy (NAT). Methods: Out of 595 patients with stage I-III TNBC enrolled on the prospective ARTEMIS trial (NCT02276443) from 2015-2021, we identified 367 patients with available HER2 immunohistochemistry (IHC) results on pre-NAT tumor tissue (HER2-zero: n=218; HER2-low [IHC 1+, 2+]: n=149). All patients were treated with anthracycline-based NAT. In cases where sufficient pre-NAT tumor tissue were available, additional IHC and/or RNAseq were performed. Differential gene expression (DGE) and pathway analysis were performed using DEseq2. Gene set enrichment analysis (GSEA) was performed using the Hallmark gene sets. Deconvolution analyses were performed using CIBERSORT. We controlled for multiple hypothesis using a false discovery rate (FDR) threshold with the Benjamini-Hochberg method, accepting as significant genes with at least a 2-fold change and < 5% FDR. Results: Table 1 summarizes baseline clinicopathological features of the 367 patients. Compared to HER2-zero tumors, HER2-low tumors were less likely of metaplastic histology (p=0.001), associated with lower Ki67 (p=0.017) and were more likely to be androgen receptor (AR)-positive (p=0.01). There were no significant differences in tumor-infiltrating lymphocytes (TILs) infiltration and PD-L1 expression between HER2-zero and HER2-low tumors. Among the 226 patients with sufficient pre-NAT tissue for RNAseq, DGE analyses demonstrated upregulation of genes involved in fatty acid metabolism (ACSM1) and steroid hormone metabolism (DHRS2, UGT2B28) in HER2-low tumors compared with HER2-zero tumors. Deconvolution analyses revealed no significant differences between predicted proportions of immune cell subpopulations between HER2-low and HER2-zero tumors. Although rates of pCR were not significantly different between patients with HER2-zero (46%) and HER2-low tumors (40%) (p=0.34), non-pCR in patients with HER2-low tumors was associated with increased expression of EREG, which encodes an EGFR ligand, while non-pCR in patients with HER2-zero tumors was associated with downregulation in genes involved in immune response pathways. GSEA further identified the Hallmark allograft rejection (FDR q=0.001), interferon gamma response (FDR q=0.002), and interferon alpha response pathways (FDR q=0.007) as the 3 most significantly downregulated pathways in HER2-zero tumors from patients experiencing a non-pCR relative to HER2-zero tumors from patients experiencing a pCR. Conclusion: In early stage TNBC, low HER2 expression is associated with increased AR expression and upregulation of genes associated with fatty acid and steroid hormone metabolism. Gene expression analyses suggest that drivers of resistance to NAT differ between HER2-low and HER2-zero tumors. Biological differences between HER2-zero and HER2-low tumors exist and may influence future personalized treatment for patients with early stage TNBC.

Citation Format: Clinton Yam, Ziyi Li, Anil Korkut, Wencai Ma, Elisabeth Kong, Holly A. Hill, Hussein Abbas, Sausan Abouharb, Beatriz Adrada, Banu K. Arun, Carlos H. Barcenas, Ajit Bisen, Daniel Booser, Aman Buzdar, Rosalind Candelaria, Junjie Chen, Alyson Clayborn, Senthil Damodaran, Qingqing Ding, Haven Garber, Gabriel N. Hortobagyi, Kelly K. Hunt, Nuhad K. Ibrahim, Adaeze Iheme, Meghan S. Karuturi, Kimberly Koenig, Rachel M. Layman, Jangsoon Lee, Jennifer K. Litton, Melissa Mitchell, Giancarlo Moscol, Jason Mouabbi, Rashmi K. Murthy, Oluchi Oke, Paula Pohlmann, David Ramirez, Elizabeth Ravenberg, Sadia Saleem, Mediget Teshome, Vicente Valero, Jason White, Madison Williams, Wendy Woodward, Chasity Yajima, Naoto T. Ueno, Ken Chen, Gaiane Rauch, Lei Huo, Debu Tripathy. HER2-01 Clinical and Molecular Characteristics of HER2-low/zero Early Stage Triple-Negative Breast Cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr HER2-01.

Tumor Immune Microenvironment Changes by Multiplex Immunofluorescence Staining in a Pilot Study of Neoadjuvant Talazoparib for Early-Stage Breast Cancer Patients with a Hereditary BRCA Mutation

PURPOSE

The immunological profile of early-stage breast cancer treated with neoadjuvant PARP inhibitors has not been described. The aim of this study was to delineate the changes in the tumor immune microenvironment (TiME) induced by talazoparib.

PATIENTS AND METHODS

Patients with operable germline BRCA1/2 pathogenic variant (gBRCA1/2+) breast cancer were enrolled in a feasibility study of neoadjuvant talazoparib. Thirteen patients who received 8 weeks of neoadjuvant talazoparib were available for analysis, including 11 paired pre- and post-talazoparib core biopsies. Treatment-related changes in tumor-infiltrating lymphocytes were examined and immune cell phenotypes and their spatial distribution in the TiME were identified and quantified by multiplex immunofluorescence using a panel of 6 biomarkers (CD3, CD8, CD68, PD-1, PD-L1, and CK).

RESULTS

Neoadjuvant talazoparib significantly increased infiltrating intratumoral and stromal T-cell and cytotoxic T-cell density. There was no difference in PD-1 or PD-L1 immune cell phenotypes in the pre- and post-talazoparib specimens and PD-L1 expression in tumor cells was rare in this cohort. Spatial analysis demonstrated that pre-talazoparib interactions between macrophages and T cells may correlate with pathologic complete response.

CONCLUSIONS

This is the first study with phenotyping to characterize the immune response to neoadjuvant talazoparib in patients with gBRCA1/2+ breast cancer. These findings support an emerging role for PARP inhibitors in enhancing tumor immunogenicity. Further investigation of combinatorial strategies is warranted with agents that exploit the immunomodulatory effects of PARP inhibitors on the TiME.

Immune Phenotype and Response to Neoadjuvant Therapy in Triple-Negative Breast Cancer

PURPOSE

Increasing tumor-infiltrating lymphocytes (TIL) is associated with higher rates of pathologic complete response (pCR) to neoadjuvant therapy (NAT) in patients with triple-negative breast cancer (TNBC). However, the presence of TILs does not consistently predict pCR, therefore, the current study was undertaken to more fully characterize the immune cell response and its association with pCR.

EXPERIMENTAL DESIGN

We obtained pretreatment core-needle biopsies from 105 patients with stage I-III TNBC enrolled in ARTEMIS (NCT02276443) who received NAT from Oct 22, 2015 through July 24, 2018. The tumor-immune microenvironment was comprehensively profiled by performing T-cell receptor (TCR) sequencing, programmed death-ligand 1 (PD-L1) IHC, multiplex immunofluorescence, and RNA sequencing on pretreatment tumor samples. The primary endpoint was pathologic response to NAT.

RESULTS

The pCR rate was 40% (42/105). Higher TCR clonality (median = 0.2 vs. 0.1, P = 0.03), PD-L1 positivity (OR: 2.91, P = 0.020), higher CD3⁺:CD68⁺ ratio (median = 14.70 vs. 8.20, P = 0.0128), and closer spatial proximity of T cells to tumor cells (median = 19.26 vs. 21.94 μm, P = 0.0169) were associated with pCR. In a multivariable model, closer spatial proximity of T cells to tumor cells and PD-L1 expression enhanced prediction of pCR when considered in conjunction with clinical stage.

CONCLUSIONS

In patients receiving NAT for TNBC, deep immune profiling through detailed phenotypic characterization and spatial analysis can improve prediction of pCR in patients receiving NAT for TNBC when considered with traditional clinical parameters.

The incidence and impact of brain metastasis in patients with hereditary BRCA1/2 mutated invasive breast cancer in a prospectively followed cohort

1096

Background: Previous reports suggest the incidence of brain metastasis is higher in patients with hereditary BRCA1 mutations compared to BRCA1 noncarriers among breast cancer patients who develop recurrent disease. PARP inhibitors are now standard therapies for metastatic breast cancer patients with germline BRCA1 or BRCA2 mutations ( gBRCA1/2) based on their efficacy in treating systemic disease. However, as management of systemic disease improves, a concern is that patients with hereditary BRCA mutations may experience higher rates of disease progression in the CNS. We aimed to estimate the incidence of brain metastasis in breast cancer patients with gBRCA1/2 using a prospectively maintained gBRCA database and to assess the impact of brain metastasis on survival. Methods: To determine incidence, we queried a prospectively maintained electronic database that included patients referred to the MDACC genetics department and who underwent gBRCA1/2 testing. We identified patients with stage I-III invasive breast cancer who were treated between 2000-2017 and assessed for disease recurrence and brain metastasis. To expand our cohort for descriptive characteristics (separate from the incidence analysis), we queried the Breast Medical Oncology database for patients with brain metastasis who had undergone BRCA1/2 testing outside the genetics department or at outside institutions. Results: Of 474 patients with Stage I-III breast cancer and gBRCA1, 77 (16.2%) developed distant metastasis (median f/u: 9.1 years). Of these patients, 34/77 (44.2%) developed brain metastasis. In comparison, 42 of 318 (13.2%) of gBRCA2 patients with Stage I-III breast cancer developed distant recurrence (median f/u: 8.4 years), and 7/42 (16.7%) experienced brain metastasis. In gBRCA1 patients with brain metastasis, 45/48 (83.8%) had triple negative disease, and the median time from diagnosis to brain metastasis was 2.45 years. The brain was among the initial sites of disease recurrence in 24/48 (50%) of gBRCA1 patients. For gBRCA1 patients with distantly recurrent disease, median OS from diagnosis was 3.19 years for patients with brain metastasis vs. 5.37 years for patients without brain mets (HR 0.54; 95% CI 0.34 to 0.85; P = 0.0082). Conclusions: Brain metastasis is frequent among breast cancer patients with recurrent disease and hereditary BRCA1 mutations. Development and testing of agents with intracranial activity is critical for improving long-term outcomes in gBRCA1 patients with metastatic breast cancer.

Immune phenotype and response to neoadjuvant systemic therapy (NAST) in triple negative breast cancer (TNBC)

509

Background: In TNBC patients (pts) receiving NAST, increasing tumor infiltrating lymphocytes (TILs) is associated with higher pathologic complete response (pCR) rates. However, since the presence of TIL do not consistently predict pCR, the current study was undertaken to more fully characterize the immune cell response and its association with pCR. Methods: T cell receptor (TCR) sequencing, PD-L1 immunohistochemistry and multiplex immunofluorescence were performed on prospectively collected pre-NAST tumor samples from 98 pts with stage I-III TNBC enrolled in ARTEMIS (NCT: 02276443). TCR clonality was calculated using Shannon’s entropy. PD-L1+ was defined as ≥1% immune cell staining. Response to NAST was defined using the residual cancer burden (RCB) index. Associations between TCR clonality, immune phenotype, and response were examined with the Wilcoxon rank sum test, Spearman’s rank correlation and multivariable logistic regression using stepwise elimination (threshold p > 0.2), as appropriate. Results: The pCR rate was 39% (38/98). pCR was associated with higher TCR clonality (median = 0.2 [in pts with pCR] vs 0.1 [in pts with residual disease], p = 0.05). Notably, the association between pCR and higher TCR clonality was observed in pts with ≥5% TIL (n = 61; p = 0.05) but not in pts with < 5% TIL (n = 37; p = 0.87). Among pts with ≥5% TIL, TCR clonality emerged as the only independent predictor of response in a multivariable model of tumor immune characteristics (odds ratio/0.1 increase in TCR clonality: 3.0, p = 0.021). PD-L1+ status was associated with higher TCR clonality (median = 0.2 [in PD-L1+] vs 0.1 [in PD-L1-], p = 0.004). Higher TCR clonality was associated with higher CD3+ (rho = 0.32, p = 0.0018) and CD3+CD8+ (rho = 0.33, p = 0.0013) infiltration but lower expression of PD-1 on CD3+ (rho = -0.24, p = 0.021) and CD3+CD8+ cells (rho = -0.21, p = 0.037). Conclusions: In TNBC, a more clonal T cell population is associated with an immunologically active microenvironment (higher CD3+ and CD3/8+ T cell; lower PD-1+CD3+ and PD-1+CD3/8+ T cell; PD-L1+) and favorable response to NAST, especially in pts with ≥5% TIL, suggesting a role for deep immune phenotyping in further refining the predictive value of TILs.

Abstract P2-16-09: Residual cancer burden in patients with early stage triple negative breast cancer who progress on anthracycline-based neoadjuvant chemotherapy in an ongoing clinical trial (ARTEMIS)

BACKGROUND: Current treatment for early stage triple negative breast cancer (TNBC) includes neoadjuvant systemic chemotherapy (NAST), which is used to assess disease biology and the need for adjuvant treatment in case of residual disease at the time of surgery, also known as residual cancer burden (RCB). Patients with TNBC who experience RCB-0 (pathologic complete response [pCR]) or RCB-I after NAST have an excellent prognosis whereas patients with significant residual disease (RCB-II or RCB-III) are at a high risk of relapse. Standard NAST for TNBC achieves pCR in 30-50% of cases. NAST typically consists of anthracycline-based chemotherapy followed or preceded by a taxane +/- carboplatin. Disease progression (PD) is uncommon in TNBC patients receiving NAST and little is known regarding outcomes in patients who have PD during the initial phase of NAST. METHODS: Total 316 TNBC patients were evaluated from two prospectively accrued clinical trials of NAST (NCT02276443 and NCT01334021). The ARTEMIS trial (NCT02276443) aims to improve pCR rates by adding targeted therapy to chemotherapy as the second phase of NAST for those patients who do not experience at least a 70% volumetric reduction after 4 cycles of doxorubicin/cyclophosphamide (AC). Unique histopathologic features including % stromal tumor-infiltrating lymphocytes (sTIL), presence of mesenchymal histology (high vimentin expression by IHC), and androgen receptor expression are used to guide second phase therapy. RESULTS: 31 TNBC patients had PD while receiving AC as the first phase of NAST (10%; 95% CI= 6.69-13.31%). 9 of 31 patients proceeded to standard chemotherapy and all had RCB II/III disease. 22 of 31 patients were enrolled to targeted therapy trials. 6 were treated with the EGFR inhibitor panitumumab + carboplatin/paclitaxel, 9 with atezolizumab + nab-paclitaxel, and 7 with everolimus, bevacizumab, and liposomal doxorubicin (DAE). Of these 22 patients, 3 (13.6%) had pCR/RCB-0, 1 (4.5%) RCB-I and 18 (81.8%) had RCB II/III. All 4 patients who experienced RCB-0/I had T2N0 disease at diagnosis. 2 had sTIL &lt; 5% and 2 patients had 70% sTIL. CONCLUSION: PD is uncommon while receiving NAST. Patients with TNBC and progression on initial NAST with AC are unlikely to achieve pCR or RCB-I status despite subsequent standard chemotherapy. Combination chemotherapy with targeted therapy on clinical trial resulted in a numerically higher rate of pCR+RCB-I (18%) as salvage therapy, but this was not statistically significant and requires confirmation in larger trials.

Citation Format: Haven Garber, Gaiane Rauch, Beatriz Adrada, Rosalind Candelaria, Elizabeth Mittendorf, Alastair Thompson, Jennifer Litton, Senthil Damodaran, Bora Lim, Banu Arun, Naoto Ueno, Vicente Valero, Nuhad Ibrahim, Rashmi Murthy, Debu Tripathy, Helen Piwnica-Worms, Fraser Symmans, Lei Huo, Stacy Moulder. Residual cancer burden in patients with early stage triple negative breast cancer who progress on anthracycline-based neoadjuvant chemotherapy in an ongoing clinical trial (ARTEMIS) [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P2-16-09.

Stochastic cancer-immune coevolution: Implications for cancer incidence and immunotherapeutic efficacy

e14023

Background: Despite recent progress, robust treatment strategies that lead to durable remission are still lacking for many cancer types. This disease is difficult to treat owing in part to the complexity introduced by a heterogeneous population of cancer cells capable of evolving mechanisms of resistance to traditional therapy. Nonetheless, the discovery and continued optimization of T-cell immunotherapy has revolutionized the treatment of many cancers. This treatment strategy stands out from other approaches in its unique ability to co-evolve alongside an evading tumor. While promising, such therapies are also complex. For example, allogeneic stem cell transplantation leverages a donor-derived T-cell repertoire to treat patients with refractory hematologic malignancies and relies upon a delicate balance between desirable anti-tumor effects and potentially life-threatening graft-versus-host-disease. Currently, the decision to utilize this therapy and others like it is largely influenced by prior empirical evidence. Thus, there is great need for quantitative models of the cancer-immune interaction to generate testable predictions of treatment outcome, which could then be validated prior to T-cell immunotherapy administration. Methods: We develop a foundational mathematical model to investigate the properties of stochastic tumor-immune co-evolution using applied stochastic process theory and probabilistic analysis. We use this model to predict the effects of reduced immunity, T-cell diversity, and thymic turnover rates on cancer incidence, and compare model simulations to cancer evolutionary data. Results: We predict that changes in T-cell diversity, and to a lesser degree thymic turnover, increase the chance of tumor progression. When applied to experimental data, we demonstrate that the observations are consistent with co-evolution between an indolent cancer population and the adaptive immune system prior to clinical disease. Conclusions: Our results provide a fundamental framework for analyzing the interaction dynamics of an evolving threat like cancer and the adaptive immune system in order to better understand and predict immunotherapeutic efficacy.

Brain metastasis in patients with hereditary BRCA-mutated invasive breast cancer

1074

Background: In the past six months, two poly(ADP-ribose) polymerase (PARP) inhibitors have been approved for the treatment of patients with metastatic breast cancer and germline pathogenic variants in BRCA1 or BRCA2 ( gBRCA). In addition, recent data from the IMpassion 130 trial lends support for the role of immunotherapy in a subset of patients with triple negative breast cancer (TNBC). Approximately 60% of patients with gBRCA1 have TNBC. There is evidence that both PARP inhibitors and checkpoint inhibitors cross the blood-brain barrier and both classes of agents have entered clinical trials for patients with brain metastases in other tumor types. We studied the clinical course of breast cancer patients with gBRCA and brain metastasis at our institution to inform clinical trial design for this group of patients with poor outcomes. Methods: Patients with stage I to III invasive breast cancer, gBRCA, and eventual development of brain metastasis were identified from clinical databases. Data analyzed included breast cancer subtype and stage at diagnosis, treatment, time to distant recurrence and to discovery of brain metastasis, and overall survival from time of development of brain metastasis. Results: Patients in our cohort (n = 24, to date) were diagnosed at a young age (median age 39) and primarily had TNBC (21/24, 87.5%) with infiltrating ductal carcinoma histology. Nineteen patients had gBRCA1 and 4 patients had gBRCA2. All but 1 patient received anthracycline-based chemotherapy in the neoadjuvant/adjuvant setting. Median time to distant metastasis was 2 years (range: 0.8 – 15) and the brain was the first site of recurrence in 5 of 24 (21%) patients. Median time from diagnosis to development of brain metastasis was 2.6 years (range: 1.2 – 19) and most patients (18/25, 72%) had multiple brain metastases discovered on the initial brain MRI. Median overall survival (OS) was 3.7 years (range: 1.8 – 24) and median OS from the time of brain metastasis was 7 months (range: 1 month – 13 years). Conclusions: Breast cancer patients with germline pathogenic variants in BRCA1/2 who develop brain metastasis have a dismal prognosis. These patients may benefit from an agent with intracranial activity at the time of first distant recurrence.

Tumor immune microenvironment (TiME) changes by multiplex IF staining in a pilot study of neoadjuvant talazoparib for early-stage breast cancer patients with a BRCA mutation

585

Background: We previously reported a median tumor volume loss of 88% (range 30-98%) in 13 patients with early stage BRCA1/2 mutant breast cancer treated on a neoadjuvant trial of the PARP inhibitor talazoparib. The effects of PARP inhibition on immune aspects of the TiME in early-stage breast cancer has not been well described. The goal of this study was to evaluate the TiME in pre and post-treatment core biopsies from enrolled patients. Methods: Eleven paired core biopsies were available for examination. Tumor infiltrating lymphocytes (TILs) were quantified by H&E stained slides by a central pathologist. Specimens were assessed by multiplex immunofluorescence (mIF) using a panel of 6 biomarkers (PD-1, PD-L1, CD3, CD8, CD68 and CK) with the Opal 7-color Kit in LEICA BOND auto stainer, Vectra automated quantitative pathology imaging system and inForm software (PerkinElmer). Results: In the analyzed core biopsies, there was an increase in TILs evaluated by H&E in post-treatment compared to baseline (mean 36 vs 11%). By mIF there was an increase in CD3+ T cell and CD3+CD8+ cytotoxic T cell density in post-treatment samples compared to baseline, summarized in table. PD-L1 expression in tumor cells was rare in the cohort. There was no difference in CD3+PD-1+ or CD3+CD8+ PD-1+ lymphocytes in pre and post-treatment specimens. There was also no differences in macrophages (CD68+). Evaluation of immune phenotype and imaging response will be presented in the final analysis. Conclusions: This is the first study phenotyping the immune response to neoadjuvant talazoparib in BRCA-mutant breast cancer patients. In this small cohort, intratumoral and stromal CD3+ T cells and CD3+CD8+ cytotoxic T cells increased after two months of talazoparib. Clinical trial information: NCT02282345. [Table: see text]

Survivin TCR transgenic mice develop T cell lymphoblastic lymphoma (48.25)

Survivin has been considered a potential tumor antigen due to high expression in most cancers and limited expression in normal tissues. To explore the potential for survivin reactive TCRs to mediate antitumor effects in mice, we generated several founders of TCR transgenic mice with specificity for the H-2b restricted immunodominant epitope of survivin. In transgenic mice, survivin reactive T cells were predominantly CD8+ and mediated specific immune reactivity toward survivin peptide pulsed targets. Some antitumor reactivity was observed, but it was not potent, and the survivin reactive transgenic T cells were unable to mediate objective tumor regression of survivin bearing tumors in vivo. Spontaneous T cell acute lymphoblastic leukemia (T-ALL) was observed at 4-6 months of age in offspring of all 3 founders and was found in both survivin TCR+Rag+/- and survivin TCR+Rag-/- mice. Flow cytometry demonstrated that these lymphoblastic cells were CD3+ and survivin TCR+, and were variably CD8+ or CD4-/CD8-. Analysis of alpha gene rearrangements revealed oligoclonality but the cell were malignant, grew continuously in vitro and induced tumors in C57BL/6 recipients. The occurrence of T-ALL in 3 founders suggests that the transgene itself, rather than insertional mutagenesis, is causative. We postulate that self-reactive TCR serves as an oncogene if expressed early during thymopoiesis. TCR signaling may cooperate with NOTCH activation and/or other events to generate the malignancy.

Survivin: A Potential Target of Adoptive Immunotherapy for Pediatric Sarcomas (101.19)

Cell based immunity is driven by CD8+ cytotoxic T cells bearing TCR that recognize specific tumor-associated peptides bound to class I MHC molecules. Survivin, an inhibitor of apoptosis protein (IAP), is a tumor-associated antigen that is widely expressed in nearly all human cancer cells and undetectable in most normal tissues. Although there is evidence for cytotoxic T cell responses against survivin in patients, tolerance to self antigens can be a limiting factor in generating highly avid T cells capable of killing tumor cells. An alternate approach involves peptide immunization of HLA-A2 transgenic mice that express the human class I HLA-A2 molecule, which could in principle generate more highly avid TCRs to human antigens. In this study, we vaccinated A2 transgenic mice with a modified survivin epitope, Surv96M (LMLGEFLKL) and successfully generated CD8+ CTL clones that react against Survivin96-104 and a human pancreatic cancer line. The α- and β- chains for the TCR of reactive CTLs were cloned and inserted into an retrovirus vector incorporating 2A linker peptides between coding sequences of α- and β- chains of TCRs against survivin. Transduction of survivin specific TCR retrovirus constructs into human PBMCs yielded up to 70% TCR redirected lymphocytes and specific effector function as measured by IFNgamma release following co-culture with peptide-pulsed targets and one A2+ pediatric osteosarcoma line. Ongoing work is underway to increase the TCR affinity to potency.