Blimp 1

To examine the effect of IL-15 and IL-15_TRANS at the protein level, primary T cells for each condition were harvested 2 days following IL-2, IL-15, or IL-15_TRANS treatment. Antibodies used were as follows: pSTAT5 (611964, BD Biosciences), STAT5 (sc-482X, Santa Cruz), Bcl-6 (561520, BD Biosciences), pSTAT4 (5267S, Cell Signaling), STAT4 (sc-486X, Santa Cruz), Blimp-1 (A01647-40, Genscript), GAPDH (sc-25778, Santa Cruz), β-Actin (A00730-40, Genscript). Further details regarding the clone and/or dilution of antibodies used can be found in Supplementary Table S2).

An equal number of cells were collected and subjected to immunoblot analysis to determine protein expression levels of Bcl-6 (BD Biosciences, 561520, dilution 1:500), Blimp-1 (Genscript, A01647, dilution 1:500), STAT5 (Santa Cruz, sc-835, dilution 1:5,000), phospho-STAT5 (pY694, BD Biosciences, 611964, dilution 1:5,000) and V5-tagged proteins (Invitrogen, R960-25, dilution 1:5,000). In brief, separation of lysates by SDS–polyacrylamide gel electrophoresis was followed by immunoblot analysis. GAPDH (Santa Cruz, sc-25778, dilution 1:2,500) or β-actin (Genscript, A00730, dilution 1:10,000) expression was monitored to ensure equal protein loading. Additional information for antibodies can be found in Supplementary Table 3 and uncropped versions of all immunoblots are provided in Supplementary Fig. 5.