The immune landscape of breast cancer

The immune landscape of breast cancer

At the University of Turku, Maija Hollmén, PhD, is helping to elucidate the significance of macrophage-expressed Clever-1 in defining the immune cell composition in human breast cancer.

The immune cell composition of tumours is a strong predictor of disease outcome, particularly breast cancer, and therapy response to drugs re-activating anti-tumour T cell responses.1 However, to date there are no definitive biomarkers to predict treatment response to immune checkpoint blockage apart from a patient’s microsatellite instability status. Mostly this is due to lack of understanding on the underlying pathways and cells that contribute to the efficacy or refractoriness to a given treatment.

Therefore, understanding the heterogeneity and regulation of immune cell infiltration into tumours, and defining immunotherapy responders from non-responders, would dramatically improve current patient care, clinical trial design and future drug development.

Essentially, the identification of responsive patients would be economically more sustainable and save non-responders from ineffective treatments accompanied by severe side effects.

Breast cancer, a heterogenous entity

Notably, breast cancer is one of the cancer types that shows very modest responses to immune checkpoint blockage therapies. This can be, at least partly, attributed to the low mutational burden found in the majority of breast cancer patients whose tumours are commonly driven by overactive hormone signalling or amplification of growth responses (HER2+). Triple-negative breast cancers (TNBC), however, seem to be more responsive to immunotherapy, albeit not reaching similar response rates as in melanoma and lung cancer.

The presence of immune cells within both HER2+ and TNBC has been reported to be especially relevant since tumours with high immune cell number show better responses to HER2-targeted therapies and chemotherapy, respectively. It is important to note that a high immune cell count does not necessarily indicate better outcome since the type of inflammation can dramatically influence tumour progression, adding an extra layer of complexity to the management of cancer. In fact, the crosstalk between immune cells and cancer cells can lead to different outcomes depending on the molecular characteristics of the tumour. We have previously demonstrated that human macrophages gain anti-tumoral properties under the influence of hormone receptor positive breast cancer cells, whereas the more aggressive triple-negative subtype promotes the differentiation of tumour-supporting macrophages.2,3

A barrier preventing therapy response

In light of the current knowledge of predictive and prognostic markers, macrophages are major contributors of resistance formation and effective suppressors of anti-tumour immune responses. Among the molecules that contribute to the undesired functions of tumour-associated macrophages is Clever-1, a scavenger receptor that reduces the ability of macrophages to present antigen and secrete pro-inflammatory cytokines, leading to ineffective activation of antigen-specific T cell responses. These effects are considerably important in breast cancer since macrophages can constitute as much as half of the tumour mass, making them and the molecules they express elusive targets for novel anticancer treatments. In support of effective macrophage-targeted therapies, a broader understanding of macrophage heterogeneity in association with other immune cells and their relation to different breast cancer subtypes is needed.

Our research – Breast Cancer Biomarkers of Immunosuppression (BCBI)

Our goal is to elucidate the significance of macrophage-expressed Clever-1 in defining the immune cell composition in human breast cancer and to understand why breast cancers are poor responders to immune checkpoint blockage despite a relatively high abundance of T cell infiltration. In addition, we evaluate the possibility of probing the immune molecular landscape of solid tumours via blood sampling (liquid biopsy) using Clever-1 as an immunosuppressive biomarker.

For this we collect blood, plasma, healthy breast tissue and tumour tissue from 200 newly diagnosed treatment naïve breast cancer patients with a tumour nodule exceeding 2cm in diameter who are undergoing breast ablation surgery at Turku University Hospital, Finland, in collaboration with Dr Ilkka Koskivuo (Department of Plastic Surgery) and Dr Pia Boström (Department of Pathology). Since commonly used methods for assessing immune cells in tumours are limited to a few analytes per sample, we take advantage of mass cytometry (CyTOF), allowing us to interrogate more than 40 analytes at a single-cell resolution and enable systemic identification of complex cellular populations using high-dimensional analyses. Additionally, we model Clever-1 dependent regulation of immune cell activation using an ex vivo tumour organoid platform where BCBI tissues are cultured in the presence of Clever-1 targeting antibodies. The responses to anti-Clever-1 treatment are measured by cytokine release (multiplex and ELISA) as well as by changes in immune cell phenotype by immunohistochemical evaluation before and after treatment.

Immunoprofiling human responses to anti-Clever-1 therapy

The knowledge collected in the BCBI project will be applied to the molecular characterisation of treatment response in patients participating in the MATINS (Macrophage Antibody to FP-1305 To INhibit immune Suppression) first-in-human open label Phase I/II adaptive clinical trial (sponsored by Faron Pharmaceuticals). The eligible patients to receive the humanised monoclonal anti-Clever-1 antibody (FP-1305) in MATINS have cutaneous melanoma, hepatobiliary, pancreatic, ovarian or colorectal cancer. These cancer types were selected based on pre-screening of archived tumour material and observed to contain the highest amount of Clever-1 positive macrophages.

Overall, the development of Clever-1 as a companion diagnostic and prognostic biomarker would be highly useful for personalised therapy, and the results of this project are expected to promote anti-Clever-1 therapy into clinical use for those suffering from refractory, untreatable solid tumours. By combining anti-Clever-1 with clinically used treatments we could more effectively convert immunologically ignorant tumours into inflamed ones and help the remaining 80% of cancer patients who do not respond to immune checkpoint blockage.


  1. Galluzzi L, Chan TA, Kroemer G, Wolchok JD, López-Soto A. The hallmarks of successful anticancer immunotherapy. Sci Transl Med 2018;10
  2. Hollmén M, Roudnicky F, Karaman S, Detmar M. Characterization of macrophage – cancer cell crosstalk in estrogen receptor positive and triple-negative breast cancer. Sci Rep 2015;5:9188
  3. Hollmén M, Karaman S, Schwager S, Lisibach A, Christiansen AJ, Maksimow M, et al. G-CSF regulates macrophage phenotype and associates with poor overall survival in human triple-negative breast cancer. Oncoimmunology 2016;5:e1115177


Maija Hollmén, PhD
Group Leader, Academy Research Fellow, Adjunct Professor of
Tumour Immunology
MediCity Research Laboratory Institute of Biomedicine
University of Turku
+358 50 514 2893
Tweet @maijahollmen/@HollmenMaija


This article will appear in issue 7 of Health Europa Quarterly, which will be published in November 2018.

Subscribe to our newsletter


Please enter your comment!
Please enter your name here