Background: Clinical studies of liso-cel show low incidences of severe CRS and NEs. Pts with high tumor burden and inflammation are at higher risk of CRS and NEs (Borrega, Hemasphere 2019). Here, we characterize the presenting symptoms, timing, and management of CRS and NEs in pts with R/R LBCL treated with liso-cel in TRANSCEND NHL 001 (NCT02631044). A deeper understanding of CRS/NEs after liso-cel treatment may help clinicians identify and manage these toxicities. Methods: Pts with R/R LBCL and ≥2 lines of therapy received liso-cel after lymphodepletion (LD) with fludarabine and cyclophosphamide. Bridging therapy was allowed for pts with PET-positive disease before LD (Abramson, ASH 2019 #241). Investigators were educated on prospectively identifying liso-cel–related NEs and CRS, which were collected and graded per NCI CTCAE v4.03 (NEs) or 2014 Lee criteria (CRS). Timing and severity of individual CRS/NE symptoms and interventions were also collected. Results: The analysis included 269 pts (median age, 63 y): 38% had sum of perpendicular diameters ≥50 cm² or lactate dehydrogenase ≥500 U/L, and 59% received bridging therapy. CRS and NEs had delayed onset (median, 5 and 9 d, respectively) and a low incidence of grade (Gr) ≥3 events (CRS 2%; NE 10%). CRS occurred before NEs in most pts and was Gr 1/2 at onset in all but 2 pts (Table). The most common CRS symptoms were pyrexia (40%), hypotension (20%), and tachycardia (18%). Overall, 20% of pts received tocilizumab and/or corticosteroids for CRS (10% tocilizumab only; 2% corticosteroids only; 8% both); 3% received vasopressors. The most common NE symptoms were confusional state (11%), tremor (9%), and aphasia (8%); most were low grade. A total of 17% of pts received tocilizumab and/or corticosteroids for NEs (13% corticosteroids only; < 1% tocilizumab only; 3% both); < 1% received vasopressors. Overall, 4% of pts were admitted to the ICU for CRS and/or NEs. Additional analyses on timing of intervention and type/severity of initial symptoms will be presented. Conclusions: In pts with high-risk, aggressive R/R LBCL, liso-cel treatment was associated with a low incidence of severe CRS/NEs, late onset of mostly low-grade events at presentation, and low use of tocilizumab/corticosteroids. Clinical trial information: NCT02631044.