In the TRANSCEND NHL 001 study, 53% of patients with relapsed/refractory large B-cell lymphoma (LBCL) treated with lisocabtagene maraleucel (liso-cel) achieved a complete response (CR). To determine characteristics of patients who did and did not achieve a CR, we examined the tumor biology and microenvironment from lymph node tumor biopsies. LBCL biopsies from liso-cel–treated patients were taken pre-treatment and ~11 days post-treatment for RNA sequencing (RNA-seq) and multiplex immunofluorescence. We analyzed gene expression data from the pre-treatment biopsies (n = 78) to identify gene sets enriched in patients who achieved a CR to those with progressive disease (PD). Pre-treatment biopsies from month-3 CR patients displayed higher expression levels of T-cell and stroma-associated genes, and lower expression of cell cycle genes. To interpret whether LBCL samples were “follicular lymphoma (FL)–like,” we constructed an independent gene expression signature and found that patients with a higher “FL-like” gene expression score had longer progression-free survival (PFS). Cell of origin was not associated with response or PFS, but double-hit gene expression was associated with shorter PFS. The day 11 post-treatment samples (RNAseq, n = 73; multiplex immunofluorescence, n = 53) had higher levels of chimeric antigen receptor (CAR) T-cell densities and CAR gene expression, general immune infiltration, and immune activation in patients with CR. Further, the majority of T cells in the day 11 samples were endogenous. Gene expression signatures in liso-cel–treated patients with LBCL can inform the development of combination therapies and next-generation CAR T-cell therapies.