CD28 and cancer: After 12 days of culture, consistent with numerous in vitro Vδ2 T cell expansion protocols for cancer therapy [14, 40, 41, 42, 43, 44, 45], we assessed the proliferation and cytokine production capacity of Vδ2 T cells by flow cytometry upon anti‐CD3 and anti‐CD28 restimulation (Figure 1C–F and Figure S1A).