Delivery of chimeric antigen receptors (CARs) to T cells is usually mediated by lentiviral vectors (LVs), which can have broad tropism or be T cell targeted. To better understand the molecular events during CAR T cell generation, T cell transduction with four different LVs is followed by single-cell multi-omics analysis, distinguishing between transduced T cells and T cells with vector signal but no CAR. We find that only a fraction of the T cells that encounter vectors convert into CAR T cells. Single-cell transcriptome data reveal that interferon-stimulated genes are upregulated in non-transduced cells, whereas extracellular signal-regulated kinase (ERK)2 phosphatases are upregulated in CAR T cells. This expression pattern is evident in CAR T cells from healthy donors and patients. The role of the mitogen-activated protein kinase (MAPK)/ERK pathway in CAR T cell generation is confirmed by chemical inhibitors. These data provide molecular insights into T cell transduction with implications for improving CAR T cell generation.