Circulating CD8+ T-cell repertoires reveal the biological characteristics of tumors and clinical responses to chemotherapy in breast cancer patients

Abstract

Purpose: CD8⁺ T cells are primarily cytotoxic cells that provide immunological protection against malignant cells. Considerable evidence suggests that the T-cell repertoire is closely associated with the host immune response and the development of cancer. In this study, we explored the characteristics of the circulating CD8⁺ T-cell repertoire and their potential value in predicting the clinical response of breast cancer patients to chemotherapy.

Experimental design: We applied a high-throughput TCR β-chain sequencing method to characterize the CD8⁺ T-cell repertoire of the peripheral blood from 26 breast cancer patients. In addition, changes in the circulating CD8⁺ T-cell repertoire during chemotherapy were analyzed.

Results: We found that the HEC ratios of the CD8⁺ T-cell repertoires from HER2⁺ breast cancer patients were significantly higher than those of HER2^- patients, suggesting that the HER2 protein is released into circulation where it is targeted by CD8⁺ T cells. Several Vβ and CDR3 motifs preferentially used in HER2⁺ patients were identified. Besides, we found that the circulating CD8⁺ T-cell repertoires evolved during chemotherapy and correlated with patient clinical responses to chemotherapy. Increased CD8⁺ T-cell repertoire heterogeneity during chemotherapy was associated with a better clinical response.

Conclusions: Although functional studies of clonally expanded CD8⁺ T-cell populations are clearly required, our results suggest that the circulating CD8⁺ T-cell repertoire reflects the characteristics of the tumor-associated biomolecules released into the blood and correlates with the clinical responses of the patients to chemotherapy which might assist in making treatment decisions.

Keywords: Breast cancer; CD8+ T-cell repertoire; Clinical response; HER2 expression status.

Fig. 1

Comparison of Vβ gene usage and the HEC ratios in blood samples from different patient subgroups. a Vβ gene usage in blood samples from 26 patients. * Vβ gene usage frequencies in HER⁺ patients were significantly higher than those of HER⁻ patients. b Jβ gene usage in blood samples from 26 patients. c Variance analysis of the HEC ratios in blood samples from patients with different TNM stages. d Variance analysis of the HEC ratios in blood samples from patients with different biological subtypes. e Variance analysis of HEC ratios comparing the HER⁺ and HER⁻ patient subgroups. f Variance analysis of HEC ratios comparing the response and non-response subgroups. g Variance analysis of HEC ratios comparing HER2⁺ patients in the response and non-response subgroups. The bar indicates the median value

Fig. 2

Comparison of the amino acid sequences of 8 CDR3 motifs preferentially used in HER2⁺ patients. Each logo consists of stacks of symbols, with one stack for each amino acid in the sequence. The overall height of the stack indicates the degree of sequence conservation at that position, while the height of the symbols within the stack indicates the relative frequency of each amino acid at that position. The width of the stack is proportional to the fraction of valid symbols at that position. (Positions with many gaps have thin stacks.) The CDR3 sequences within the motifs are listed below the stacks. *Amino acid is missing

Fig. 3

Usage patterns of Vβ gene families in blood samples before chemotherapy and after the indicated cycle of chemotherapy from seven patients. The clinical responses after the indicated chemotherapy cycle are shown below

Fig. 4

Good clinical response during chemotherapy correlates with increased pairwise distance of circulating CD8⁺ TCR repertoires before and after the indicated chemotherapy cycle. The pairwise distance was recorded at the indicated chemotherapy cycle for seven patients. The clinical responses after the indicated chemotherapy cycle are shown above. ↓ indicates clinical confirmation of PR; ↑ indicates clinical confirmation of SD

Fig. 5

Representative computed tomography images of tumors from breast cancer patient 7. The white arrows in the CT images indicate the locations of the tumor lesions. The size of the primary lesion decreased during chemotherapy, but metastasis was observed during the 6th cycle of chemotherapy