178P - Dynamics of breast cancer T cell repertoire during neoadjuvant chemotherapy / immunotherapy.

Background

The immunogenicity of breast cancer (BC) determines the efficacy of treatment with immune checkpoint inhibitors (ICI), but it remains difficult to assess.

Methods

We analyzed the T cell repertoire (TCR) in 7 patients from B-IMMUNE trial exploring a neoadjuvant treatment with paclitaxel (week 1-12) and epirubicin / cyclophosphamide combined with durvalumab (week 13-24) on locally advanced luminal B HER2(-) or TN BC. Paired blood / tumor samples were collected before treatment, at week 12 and 24. The TCR repertoire was assessed by NGS targeted to TCRβ genes using an absolute quantitative bias-controlled approach. Paired tumor and blood TCR repertoire were compared in 5000 TCRβ sequenced molecules randomly selected. A tumor-enriched T-cell clonotype (TE-TC) was defined as a clonotype at least 50x more abundant in tumor than in blood (Fisher's test = p < 10^-6). The spatial localization of TE-TCs in tumors was determined using a TCR-targeted custom adaptation of the 10x visium spatial transcriptomics method.

Results

TE-TC could be explained by an anti-tumor T-cell response and be a sign of tumor immunogenicity. They were tested before treatment in 7/7 patients and monitored at weeks 12 and 24 in 5/7. Overall, 101 TE-TCs were identified: 34 before treatment, 26 at week 12 and 41 at week 24 (respectively 2 to 9, 1 to 10 and 2 to 20 per patient). Of the 34 TE-TCs before treatment, 10 (29%) remained enriched in the tumor at week 12 and/or W24. Among the 41 TE-TCs detected at week 24, 31 (75%) were not detected before. The tumor spatial distribution of TE-TCs prior to treatment was assessed by spatial transcriptomic (50 μm resolution) in 4/7 patients. TE-TCs were detected in 3/4 patients in a minority of spatial spots (0.3 to 3%). For one patient, the spatial analysis was also assessed after 12 weeks of treatment. TE-TCs were detected in 10% of spatial spots with a predominant TE-TC that emerged during treatment and appears to be associated with Granzyme B and PD-1 expression in spatial clusters.

Conclusions

Before treatment, variable quantities of T cell clonotypes are highly enriched in locally advanced BC compared to blood, and new ones are enriched during neoadjuvant/ICI treatment. The influence of these clonotypes on tumor response needs to be studied.

Clinical trial identification

NCT03356860.

Legal entity responsible for the study

GHdC.

Funding

Seqalis.

Disclosure

J. Carrasco: Non-Financial Interests, Personal, Advisory Role: Seqalis. All other authors have declared no conflicts of interest.