T-cell counts in peripheral blood at leukapheresis predict responses to subsequent CAR-T cell therapy

Prediction of responses to chimeric antigen receptor (CAR)-T cell therapies is essential to maximize their therapeutic efficacy for diffuse large B-cell lymphoma (DLBCL). While several tumor-intrinsic risk factors of resistance and/or early relapse have been identified, clinically useful markers that determine potential activity of CAR-T cells have not been fully investigated. T-cell property at the time of leukapheresis may serve as such a marker. Therefore, we evaluated the clinical impact of CD3⁺ cell count in peripheral blood at leukapheresis on clinical outcomes of CAR-T cell therapy. In total, 44 patients with relapsed or refractory (r/r) DLBCL who received tisagenlecleucel at Kyoto University Hospital were included. According to CD3⁺ cell counts, patients were categorized into CD3^LOW and CD3^HIGH groups with a threshold of 553/μL, based on receiver operating characteristic curve analysis. 1-year progression-free survival was significantly higher in the CD3^HIGH group than the CD3^LOW group (68.3% vs. 17.3%; adjusted hazard ratio [aHR], 0.37; p = 0.042). Overall survival was also superior in the CD3^HIGH group (aHR, 0.24; p = 0.043). Moreover, higher CD3⁺ cell counts at leukapheresis were associated with significantly higher lymphocyte counts in peripheral blood at day 7 after CAR-T cell infusion (median 860 vs. 420/μL, P = 0.021), suggesting more extensive expansion of infused CAR-T cells in vivo. In conclusion, we demonstrated that the CD3⁺ cell count at leukapheresis predicts both expansion of CAR-T cells after infusion and outcomes of CAR-T cell therapy, and are useful for building comprehensive therapeutic strategies at the time of leukapheresis.