Isolation and characterization of tumor infiltrating lymphocytes in primary human breast cancer

Introduction: Priming the immune system against tumor cells in breast cancer (BC) has recently become a major issue in developing personalized therapeutic strategies. Although the immunogenicity of BC is considered to be limited recent partial success of checkpoint-inhibitors emphasize the potential of immunotherapy in BC. Previous studies confirm the prognostic value of tumor infiltrating lymphocytes (TIL's) in BC, particularly in aggressive or metastatic forms, however the therapeutic significance of TIL's in BC is still poorly investigated.

Methods: We established a method generating single cell suspensions of living TIL's and cancer cells of primary human tumor tissues isolated under sterile conditions after surgical intervention. We studied the tumor infiltrating immunocytes (TII) isolated from therapy naïve primary human BC tissues using a multicolor FACS analysis and antigen dependent cell isolation.

Results: We identified two different tumor modalities: 1) high TIL count, 2) low/very low TIL count (> 15% vs. < 5% [% of TIL's per 100 BC cells]). The distribution of TII's showed a predominant infiltration through CD3^high T-lymphocytes (66 ± 14% [% of CD45^high TII]) with a mean CD4/DC8 ratio of 3,4, along with CD19^high B-lymphocytes (8 ± 7%) and CD33^high myeloid cells (13 ± 10%). Concerning the TII distribution no significant difference was found between high vs. low TIL count samples.

Conclusions: Generation of single cell suspension enables a detailed characterization of TIL's along with primary tumor cells to study the biological behavior and immunological nature of BC and allows further investigations through establishing xeno-models to study the potential of TIL's in BC in vivo.