A Novel Autologous CAR-T Therapy, YTB323, with Preserved T-cell Stemness Shows Enhanced CAR T-cell Efficacy in Preclinical and Early Clinical Development

CAR T-cell product quality and stemness (T_stem) are major determinants of in vivo expansion, efficacy, and clinical response. Prolonged ex vivo culturing is known to deplete T_stem, affecting clinical outcome. YTB323, a novel autologous CD19-directed CAR T-cell therapy expressing the same validated CAR as tisagenlecleucel, is manufactured using a next-generation platform in <2 days. Here, we report the preclinical development and preliminary clinical data of YTB323 in adults with relapsed/refractory diffuse large B-cell lymphoma (r/r DLBCL; NCT03960840). In preclini-cal mouse models, YTB323 exhibited enhanced in vivo expansion and antitumor activity at lower doses than traditionally manufactured CAR T cells. Clinically, at doses 25-fold lower than tisagenlecleucel, YTB323 showed (i) promising overall safety [cytokine release syndrome (any grade, 35%; grade ≥3, 6%), neurotoxicity (any grade, 25%; grade ≥3, 6%)]; (ii) overall response rates of 75% and 80% for DL1 and DL2, respectively; (iii) comparable CAR T-cell expansion; and (iv) preservation of T-cell phenotype. Current data support the continued development of YTB323 for r/r DLBCL. SIGNIFICANCE: Traditional CAR T-cell manufacturing requires extended ex vivo cell culture, reducing naive and stem cell memory T-cell populations and diminishing antitumor activity. YTB323, which expresses the same validated CAR as tisagenlecleucel, can be manufactured in <2 days while retaining T-cell stemness and enhancing clinical activity at a 25-fold lower dose.