Bridging RT (bRT) may be used as a strategy for disease control in patients with relapsed/refractory aggressive B cell lymphoma treated with anti-CD19-directed chimeric antigen receptor T-cell therapy (CART). The correlation of treatment-related lymphopenia with adverse outcomes in patients has been widely documented in several malignancies. Here, we assessed lymphocyte kinetics during bRT and impact on clinical outcome. After IRB-approval, records were retrospectively reviewed for adults with DLBCL who received bRT for axicabtagene ciloleucel 11/2017-12/2022. Clinical/treatment characteristics, lab values, and outcomes were extracted. ALC Δ RT was computed by subtracting pre-RT ALC from post-RT ALC count. Survival was modeled using Kaplan-Meier for events distributed over time, or binary logistic regression for disease response. Fisher's Exact Test or Mann-Whitney U methods were used. Forty patients met inclusion criteria. Fourteen (35%) received bRT with systemic therapy. Thirty-two (80%) patients received bRT that started post-leukapheresis. bRT was delivered with a median dose of 30 Gy (range: 4-46) in 10 fractions (range: 2-23). Twenty-three patients (57.5%) had CR at 30 days post-CART infusion. Nine had PR (22.5%), and 8 patients (20%) had PD or SD. Median PFS was 8.9 months and median OS was 22 months. The pre-RT ALC mean ± SD was 0.74 ± 0.49 K/µL, and post-RT was 0.43 ± 0.35 K/µL. The absolute ALC Δ RT was 0.31 ± 0.43 K/µL, and ratio post-RT/pre-RT was 0.74 ± 0.64. Stratifying by receipt of bRT alone or with systemic therapy, there was no statistically significant difference in ALC count post-RT (chemoRT: 0.33 ± 0.23 vs. RT: 0.48 ± 0.4, p = 0.2), but there was a lower ALC count pre-RT in the chemoRT group (0.5 ± 0.3 vs. 0.87 ± 0.52 for RT alone, p = 0.02). Post-RT ALC was not significantly associated with CR/PR vs. PD/SD, or with DSS, PFS, or OS. A greater drop in ALC Δ RT trended towards association with improved 90-day response (p = 0.066), without correlation with DSS, OS, or response at 30 days. Median dose per fraction was lower among patients that got pre-leukapheresis RT (2.25 vs. 2.5, p = 0.04), but total dose of bRT or number of fractions was not significantly different. Otherwise, the groups were similar in terms of stage, disease bulk, or comprehensive vs. focal bRT. The average decrease in ALC post-RT for patients who received bRT prior to apheresis was 0.215 K/µL, compared to 0.268 K/µL for patients who received bRT post-apheresis (p = 0.75). Treatment with pre-leukapheresis bRT or ALC Δ RT among these patients were not associated with worse DFS, PFS, or OS (p>0.15). Post-bRT ALC and reduction in ALC during bRT is not associated with worse treatment response or survival outcomes after CAR-T cell treatment in aggressive B cell lymphoma. Pre-leukapheresis bRT did not appear to substantially impact ALC, and ALC Δ RT among these patients were not associated with worse outcomes.