LAUSR

T cell proliferation is routinely identified in vitro using tracking dyes or through detecting intracellular upregulation of the nuclear protein, Ki‐67. However, labeling with tracking dyes is cumbersome, associated with cellular toxicity, while Ki‐67 cannot be used to identify and isolate viable T cells, and both techniques are incompatible with MACS technology. Here, we introduce a simple tool to identify and isolate in vitro T cell expansion that is tracking dye‐independent and allows for sorting of viable T cells. We show that CD71, a transferrin receptor, and CD98, a heterodimer glycoprotein involved in both integrin signaling and amino‐acid transport, are both highly upregulated on proliferating T cells upon in vitro stimulation, and that CD71 expression is maximal on the more recent progeny T cells, while CD98 upregulation remains stable across different generations of progeny T cells. Moreover, we demonstrate that the upregulation of CD71 and CD98 identifies CFSElow T cells and provides further proof of the antigen‐specificity of T cells identified by CD71 and CD98 dual upregulation based on tetramer staining. We further show that CD71 can be used to enrich for in vitro expanding T cells using MACS technology. In conclusion, we show that CD71 and CD98 can be used to identify and isolate expanded T cells following in vitro stimulation and that CD71 is an MACS‐compatible alternative to tracking dyes or Ki‐67 detection. © 2019 International Society for Advancement of Cytometry