Updated project metadata. Three breast cancer cell lines were co-cultured with T cells isolated from normal donors, in 3: 1 ratio. As controls, the breast cancer cells were cultured without T cells for three days. All cell cultures were washed three times with PBS to remove T cells before they were scraped and collected in 1.5 mL Eppendorf tubes. Three additional washing steps with PBS were applied. After removing the supernatant, the cell pellets were immediately snap-frozen on dry-ice and stored in -80 °C until the time of preparation. After thawing the samples, they were prepared and measured on nano LC.