In vivo CAR T-cell engineering in B-cell malignancies: A systematic review of emerging clinical and translational evidence.

e14512 Background: Autologous ex vivo CAR T-cell therapies have transformed outcomes in relapsed/refractory (R/R) B-cell malignancies, producing durable remissions in diffuse large B-cell lymphoma (DLBCL), high-grade B-cell lymphoma (HGBCL), and multiple myeloma (MM), but remain limited by leukapheresis needs, protracted manufacturing times, lymphodepleting chemotherapy, and high cost. In vivo CAR T can overcome these barriers by delivering CAR-encoding payloads directly to endogenous T cells via lipid nanoparticles (LNPs), lentiviral vectors, or fusogenic viral particles, enabling CAR T-cell generation inside the patient. Methods: We performed a literature search of peer-reviewed publications, conference proceedings (ASH, ASCO, EHA), and registered clinical trials (2018–2025) evaluating in vivo CAR T. Identified platforms included KLN-1010 (in vivo anti-BCMA CAR), INT2104 (CD20 CAR), Umoja CD22 CAR, Capstan CD8-targeted LNP CD19 CAR, and Orna circular RNA CD19 CAR systems. Endpoints included CAR expression, B-cell aplasia, MRD negativity, objective response rate (ORR), CRS, ICANS, and CAR persistence. Results: First-in-human in vivo CAR T trial (KLN-1010) enrolled heavily pretreated R/R MM patients and administered a single IV dose of a lentiviral anti-BCMA CAR vector without lymphodepletion. All treated patients achieved MRD negativity at 1 month, including one complete response and three partial responses, with in vivo CAR T expansion and persistence comparable to ex vivo BCMA CAR T therapies. Grade ≥3 CRS occurred in 50% of patients, with no ICANS. Early-phase clinical programs for CD20- and CD22-directed in vivo CAR T therapies have initiated enrollment in aggressive B-cell lymphomas after CD19 CAR T failure. Preliminary data demonstrate successful in vivo CAR transduction, circulating CAR T expansion, and rapid B-cell aplasia. CD8-targeted LNP delivery of CD19 CAR mRNA induced efficient in vivo T-cell engineering with complete B-cell depletion and eradication of human DLBCL xenografts. In non-human primates, targeted LNP systems produced deep, rapid, and sustained B-cell depletion without uncontrolled immune activation. Circular RNA-based CAR platforms achieved durable CD19 CAR expression, B-cell depletion, and lymphoma regression. Conclusions: In vivo CAR T engineering has now demonstrated clinical proof-of-concept with deep molecular responses, robust in vivo CAR expansion, and manageable toxicity. Translational and preclinical CD19-, CD20-, and CD22-directed platforms show potent activity in aggressive lymphoma models, supporting direct applicability to DLBCL and HGBCL. Compared with ex vivo CAR T, in vivo systems offer elimination of leukapheresis, no manufacturing delays, outpatient feasibility, repeat dosing, and substantially reduced cost, potentially enabling earlier-line and broader access to CAR-T–level therapy.