Abstract P2-11-23: Evaluation of T-cell infiltrating lymphocytes vs. Th2 in triple negative breast cancers (TNBC)
Authors: Brousse Susie , Godey Florence , Laffont Elodie , Tas Patrick , Campillo-Gimenez Boris , Lavoué Vincent , Gallo Matthieu Le 
Published: March 2023

Abstract
Purpose. Triple-negative breast cancers (TNBC) are defined as negative for hormonal receptors and human epidermal growth factor receptors 2 and account for 15% of breast cancers. TNBC carry the worst prognosis mainly because of their high proliferation index and the absence of efficient targeted therapies due to their molecular heterogeneity, even though some promising options are emerging. Besides, they do share a very high and distinct tumor-infiltrating lymphocytes (TILs) infiltration. Amongst TILs, CD8+ cytotoxic and CD4+ helper T-cells (TC) proved to be markers of a good outcome. However, pathologists routinely quantify overall TILs density only. Anti-PD-1/PD-L1 immunotherapies recently became available for immunosuppressive TNBC. Unfortunately, neither PD-1/PD-L1 expression nor TILs quantification is able to predict patients’ responses accurately. Thus, we aimed at precisely characterizing TILs sub-populations and evaluating their prognostic significance before their predictive one. Methods. We selected 91 patients at the time of surgery before any adjuvant therapy from January 2013 to December 2018 in Rennes, France. TNBC tumors went through TILs quantification on hematoxylin and eosin slides by a trained pathologist and immune microenvironment characterization using flow cytometry. We then compared the prognostic value of immune microenvironment subpopulations vs total TILs count. Results. TNBCs contained a mean of 22.8±25.9% TILs, including CD4+ TC (14.1%) mainly made of Th2 (11.7%), CD8+ TC (11.1%), and myeloid cells (8.4%) such as antigen presenting cells (APC). TILs groups and percentages were correlated with the abundance of these cellular subpopulations (p≤0.004). TILs percentage was predictive of overall survival (OS), while high APC infiltration was of relapse-free survival (RFS) in univariate analyses (p=0.044 & p≤0.030 respectively). Only Th2 infiltration was predictive of both RFS and OS in univariate (p=0.009 & p=0.008 respectively) and multivariate analyses (p=0.002 & p=0.010 respectively). When considering the different Th populations, only Th2 was a better predictive factor of survival than total leukocytes. Discussion. The development of immune therapies aiming at unlocking the anti-tumor immune response has revealed the desperate need to better characterize the tumor immune infiltrate. TILs quantification by pathologists is the only parameter routinely measured so far but it must be standardized since variability can affect their correlation with pCR. In our study, and contrary to most previous ones, stromal TILs were not significantly associated with RFS and OS. Thus, the characterization of TILs subtypes is critical since they can have either a pro- or an anti-tumorigenic function. Thus, we counteracted the limitations of TILs pathological quantification by finely characterizing the immune infiltrate using flow cytometry. Th2 infiltrate was the most frequent, as previously reported, and counterintuitively, was associated with a favorable prognostic value. This is rarely shown as Th2 infiltration is frequently reported to favor pro-tumorigenic immune tolerance. This proves that a more refined characterization of the intra-tumoral immune landscape is essential to derive interesting therapeutic perspectives, either by recapacitating Th2 response or by targeting their interaction with other immune subsets, like fibroblasts, macrophages, dendritic cells, or eosinophils and IgE. Finally, immunotherapies modulating Th2 response could also be used around the time of surgery that has been proved to induce immunomodulation. Conclusion. The characterization of TILs composition is essential to better understand the potential antitumoral functions of these cells and to substantially improve the associated prognostic and predictive values.
Citation Format: Susie Brousse, Florence Godey, Elodie Laffont, Patrick Tas, Boris Campillo-Gimenez, Vincent Lavoué, Matthieu Le Gallo. Evaluation of T-cell infiltrating lymphocytes vs. Th2 in triple negative breast cancers (TNBC) [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 P2-11-23.