Frequency of tumor-reactive T cells in the blood of breast cancer patients and healthy donors.

As cancer immunotherapy gains importance, the determination of a patient’s ability to react to his/her tumor is unquestionable. Though the presence of T cells that recognize specific tumor antigens is well established, the total frequency of tumor-reactive T cells in humans is difficult to assess, especially due to the lack of broad analysis techniques. Here, we describe a strategy that allows this determination using T-cell proliferation induced by tumor cell-lysate pulsed dendritic cells as the readout. The frequency of tumor-specific T cells was determined, in healthy donors and cancer patients, by challenging multiple wells containing a defined number of T cells with autologous monocyte-derived dendritic cells loaded with tumor lysates and assessing the wells with T-cell proliferation by CFSE dilution. It was possible to find CD4+ and CD8+ T cells specific for the lysate of the breast cancer cell lines MCF-7 (luminal), SK-BR-3 (Her2 subtype) and MDA-MB-231 (triple-negative) in the blood of most healthy donors. All healthy donors tested had tumor cell lines-reactive T cells for at least one of the cell lines, some, not only in the naive, but also in the memory compartment. Patients had higher frequencies of reactive T cells and, unexpectedly, this was not correlated to the frequency of tumor-reactive infiltrating T cells. The method showed here seems to be a robust and powerful strategy to evaluate the T-cell response against cancer, that has already helped to unveil some important aspects about the breast tumor-reactive T cell repertoire in humans, and opens the possibility of tracking T-cell repertoire changes along disease progression. Financial support: FAPESP (2014/25988-1). Citation Format: Mariana P. Pinho, Thiago A. Patente, Elizabeth A. Flatow, Jose Alexandre M. Barbuto. Frequency of tumor-reactive T cells in the blood of breast cancer patients and healthy donors [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2018 Nov 27-30; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(4 Suppl):Abstract nr B80.