Splenic single cell suspensions were enriched for NK cells by use of an NK cell-specific magnisort negative selection kit. The enriched fraction was stained in 50 µl containing FACS antibiodies, Fc block and the mouse cell surface protein antibody panel (TotalSeq-A, BioLegend). Cell hashing was performed by adding 1 µl of diluted hashtag oligos (HTO) to each biological replicate for identification purposes upon sequencing. Initially, biological replicates were sorted separately but pooled in the next step according to the total number of sorted cells.  On day 1,5 post-infection, a total of 190 000 and 65 000 cells were sorted from mock infected and MCMV infected samples, respectively. On day 4,5 post-infection, a total of 78 000 cells were sorted. Half of these numbers represented sorted NK cells (live,CD3-,CD19-,NK1.1+,CD49b+), the other half sorted non-NK cells (live,NK1.1+,CD49b+). Congenic markers (CD45.1 and CD45.2) were used to distinguish sorted WT (CD45.1.2+) and DKO (CD45.2+) cells. Sorted single-cell suspensions were resuspended at an estimated final concentration of 1000 cells/µl and loaded on a Chromium GemCode Single Cell Instrument (10x Genomics) to generate single-cell gel beads-in-emulsion (GEM). The scRNA-Seq libraries were prepared using the GemCode Single Cell 3' Gel Bead and Library kit, version NextGEM 3.1 (10x Genomics) according to the manufacturer's instructions with the addition of amplification primer (3 nM, 5'CCTTGGCACCCGAGAATT*C*C) during cDNA amplification to enrich the TotalSeq-A cell surface protein oligos. Size selection with SPRIselect Reagent Kit (Beckman Coulter) was used to separate amplified cDNA molecules for 3' gene expression and cell surface protein construction. TotalSeq-A protein library construction including sample index PCR using Illumina's Truseq Small RNA primer sets and SPRIselect size selection was performed according to the manufacturer's instructions. The cDNA content of pre-fragmentation and post-sample index PCR samples was analyzed using the 2100 BioAnalyzer (Agilent). Sequencing libraries were loaded on an Illumina NovaSeq flow cell at VIB Nucleomics core with sequencing settings according to the recommendations of 10x Genomics, pooled in a 70:20:10 ratio for the combined 3' gene expression, cell surface protein samples and HashTag-Oligo (HTO) data, respectively. OTHER: CITE-seq (Cellular Indexing of Transcriptomes and Epitopes by sequencing)