library_construction_protocol: Spleens were dissociated and filtered through 100-μm cell strainer. Flow cytometry and cell sorting were performed on the Cytek Aurora (Cytek Biosciences) and Aria II cytometers (BD Biosciences), respectively. Before cell sorting, NK cells were enriched by incubating whole splenocytes with the following antibodies at 20 μg/ml against CD3ε (17A2), CD4 (GK1.5), CD8 (2.43), Ter119 (TER-119), CD19 (1D3), Ly6G (1A8) (BioXCell) followed by magnetic depletion using goat anti-rat beads (QIAGEN). For scRNA-seq enriched splenocytes were then stained with surface markers to identify Ly49H+ NK cells (CD3/TCRb/CD19- NK1.1+ CD49b+ Ly49H+) and sorted based on congenic markers (CD45.1 and CD45.2) to identify WT and Tcf19−/− cells with > 95% purity. Ly49H+ NK cells (CD3/TCRb/CD19− NK1.1+ CD49b+ Ly49H+) from either WT or Tcf19-/- NK cells were sorted from spleens of MCMV-infected WT:Tcf19-/- adoptive transfer mice as described from day 0, 2, 4 and 7 PI, and stained with barcoded antibodies (Total-Seq B, Biolegend). After hash-staining, WT and Tcf19-/- Ly49H+ NK cells were mixed at 1:1 ratio for each time point. The single-cell RNA-seq from these pooled FACS-sorted cell suspensions was then performed on Chromium instrument (10X genomics) following the user guide manual for 3′ v3.1. In brief, FACS-sorted cells were washed once with PBS containing 1% bovine serum albumin (BSA) and resuspended in PBS containing 1% BSA to a final concentration of 700–1,300 cells per μl. The viability of cells was above 80%, as confirmed with 0.2% (w/v) trypan blue staining (Countess II). Cells were captured in droplets. Following reverse transcription and cell barcoding in droplets, emulsions were broken, and cDNA purified using Dynabeads MyOne SILANE followed by PCR amplification per manual instruction. Samples were multiplexed together on one lane of 10X Chromium (using Hash Tag Oligonucleotides - HTO) following a previously published protocol. Final libraries were sequenced on Illumina NovaSeq S4 platform (R1 – 28 cycles, i7 – 8 cycles, R2 – 90 cycles). The cell-gene count matrix was constructed using the Sequence Quality Control (SEQC) package.