biostudies-literatureBlanco BCarlos III Health InstituteSpanish Ministry of Science and Innovation under a Ramon y Cajal grantCatSalut, Fundació La CaixaPortuguese Foundation for Science and TechnologyISCIIIEuropean Research CouncilSpanish Ministry of Science and InnovationComunidad Autónoma de MadridSpanish Association Against CancerCRIS Cancer Foundation498-511https://www.ebi.ac.uk/biostudies/studies/S-EPMC7612571biostudies-literatureUnknown10(4)Chimeric antigen receptor (CAR)-modified T cells have revolutionized the treatment of CD19-positive hematologic malignancies. Although anti-CD19 CAR-engineered autologous T cells can induce remission in patients with B-cell acute lymphoblastic leukemia, a large subset relapse, most of them with CD19-positive disease. Therefore, new therapeutic strategies are clearly needed. Here, we report a comprehensive study comparing engineered T cells either expressing a second-generation anti-CD19 CAR (CAR-T19) or secreting a CD19/CD3-targeting bispecific T-cell engager antibody (STAb-T19). We found that STAb-T19 cells are more effective than CAR-T19 cells at inducing cytotoxicity, avoiding leukemia escape in vitro, and preventing relapse in vivo. We observed that leukemia escape in vitro is associated with rapid and drastic CAR-induced internalization of CD19 that is coupled with lysosome-mediated degradation, leading to the emergence of transiently CD19-negative leukemic cells that evade the immune response of engineered CAR-T19 cells. In contrast, engineered STAb-T19 cells induce the formation of canonical immunologic synapses and prevent the CD19 downmodulation observed in anti-CD19 CAR-mediated interactions. Although both strategies show similar efficacy in short-term mouse models, there is a significant difference in a long-term patient-derived xenograft mouse model, where STAb-T19 cells efficiently eradicated leukemia cells, but leukemia relapsed after CAR-T19 therapy. Our findings suggest that the absence of CD19 downmodulation in the STAb-T19 strategy, coupled with the continued antibody secretion, allows an efficient recruitment of the endogenous T-cell pool, resulting in fast and effective elimination of cancer cells that may prevent CD19-positive relapses frequently associated with CAR-T19 therapies.Cancer immunology researchOvercoming CAR-Mediated CD19 Downmodulation and Leukemia Relapse with T Lymphocytes Secreting Anti-CD19 T-cell Engagers.PMC7612571811220SAF2017-89437-PFCRIS-IFI-2018CP042702SFRH/BD/136574/2018SAF-2019-108160-RPIE13/33AECC CICPF18030TORIPI20/01030AECC 19084CoG-2014-646903646903PI19/00132PID2020-117323RB-100RTC-2017-5944-1PI13/676PEJD-2018- PRE/BMD-8314PoC-2018-811220PI16/00357PI20/00822PI18/775PDC2021-121711-100SAF2016-75656-PPRE2018-083445CM20/00004957466PID2019-105623RB-I00PICI14/122FCRIS-IFI-2020RYC2018-024442-IDTS20/00089Rubio-Perez LRamirez-Fernandez APaz-Artal EFuentes PHarwood SLTapia-Galisteo ASanz LBetriu SLykkemark SArgemi-Muntadas LBlanco BMenendez PMorales PDominguez-Alonso CJuan MGutierrez-Aguera FDiez-Alonso LAlvarez-Vallina LAguilar-Sopena OToribio MLJimenez-Reinoso AMarzal BCompte MZanetti SRRoda-Navarro PBueno CErce-Llamazares ACastella MSegura-Tudela ANeves MGuedan SfalseOvercoming CAR-Mediated CD19 Downmodulation and Leukemia Relapse with T Lymphocytes Secreting Anti-CD19 T-cell Engagers.Chimeric antigen receptor (CAR)-modified T cells have revolutionized the treatment of CD19-positive hematologic malignancies. Although anti-CD19 CAR-engineered autologous T cells can induce remission in patients with B-cell acute lymphoblastic leukemia, a large subset relapse, most of them with CD19-positive disease. Therefore, new therapeutic strategies are clearly needed. Here, we report a comprehensive study comparing engineered T cells either expressing a second-generation anti-CD19 CAR (CAR-T19) or secreting a CD19/CD3-targeting bispecific T-cell engager antibody (STAb-T19). We found that STAb-T19 cells are more effective than CAR-T19 cells at inducing cytotoxicity, avoiding leukemia escape in vitro, and preventing relapse in vivo. We observed that leukemia escape in vitro is associated with rapid and drastic CAR-induced internalization of CD19 that is coupled with lysosome-mediated degradation, leading to the emergence of transiently CD19-negative leukemic cells that evade the immune response of engineered CAR-T19 cells. In contrast, engineered STAb-T19 cells induce the formation of canonical immunologic synapses and prevent the CD19 downmodulation observed in anti-CD19 CAR-mediated interactions. Although both strategies show similar efficacy in short-term mouse models, there is a significant difference in a long-term patient-derived xenograft mouse model, where STAb-T19 cells efficiently eradicated leukemia cells, but leukemia relapsed after CAR-T19 therapy. Our findings suggest that the absence of CD19 downmodulation in the STAb-T19 strategy, coupled with the continued antibody secretion, allows an efficient recruitment of the endogenous T-cell pool, resulting in fast and effective elimination of cancer cells that may prevent CD19-positive relapses frequently associated with CAR-T19 therapies.2022-01-01T00:00:00Z2022 Apr2026-06-21T03:09:56.373Z2025-04-05T18:23:20.984ZS-EPMC76125713536204310.1158/2326-6066.CIR-21-0853