A first-in-disease phase 1 trial suggests an off-the-shelf T-cell engager can achieve deep B-cell depletion and sustained improvements in SLE without the complexity of CAR T-cell therapy.
A bispecific antibody that redirects patients’ own T cells against CD19-positive B cells has produced encouraging 12-month results in patients with active systemic lupus erythematosus.
The finding has raised the prospect of a more accessible approach to the “immune reset” seen with CAR T-cell therapy.
The first-in-disease phase 1 trial of A-319, published in Nature Medicine, included 12 women with active SLE who received the CD3×CD19 bispecific T-cell engager intravenously over four weeks and were followed for up to 52 weeks.
The primary endpoint was safety and tolerability, with efficacy outcomes exploratory.
The researchers said the approach could potentially overcome some of the barriers to CAR T-cell therapy, which required lymphodepleting chemotherapy, individualised cell manufacturing, and specialised infrastructure.
A-319 is an “off-the-shelf” therapy designed to recruit endogenous T cells to kill CD19-expressing B cells. Participants received priming doses of 0.05μg/kg during the first week, followed by doses of 0.3, 0.6, or 1.2μg/kg three times weekly for another three weeks.
The treatment produced rapid and dose-dependent B-cell depletion. Mean peripheral B-cell counts fell by around 80% within six hours of the first infusion, and complete depletion was achieved by day 28 in the two higher-dose cohorts.
Clinical improvements were also seen over follow-up. Among the 10 patients evaluable at 12 months, eight achieved Lupus Low Disease Activity State and six met the Definition of Remission in SLE criteria.
Mean SLEDAI-2K scores fell from 13.1 at baseline to 3.2 at six months and 1.7 at 12 months, while daily glucocorticoid use fell by 67%.
Renal outcomes provided another encouraging signal. Four of seven patients with proteinuria at baseline had normalised proteinuria by 12 months. Two patients with class III+V lupus nephritis who underwent repeat kidney biopsies showed marked histological improvement, including depletion of CD19/CD20-positive B cells, reduced immune-complex deposition and lower NIH activity indices.
The researchers stressed, however, that efficacy was exploratory and could not be attributed solely to A-319. Background immunosuppression was largely continued after treatment and adjusted in some patients during follow-up, unlike published CAR T studies in which immunosuppressive drugs are generally stopped before lymphodepletion.
Safety findings were broadly reassuring for an early-phase study. There were no treatment-related serious adverse events or deaths, and no grade 3 or higher cytokine release syndrome or immune effector cell-associated neurotoxicity syndrome. Cytokine release syndrome occurred in all participants but was grade 1 in 11 of 12.
Infections occurred in seven participants and were mostly mild respiratory infections. All patients developed grade 3 or higher lymphopenia during treatment, attributed to rapid B-cell depletion and transient redistribution of T cells, but T-cell numbers recovered rapidly.
“The safety profile observed in our cohort was consistent with published experience for A-319 in B cell malignancies and with the broader class of CD3-engaging antibodies,” the researchers wrote.
“CRS occurred in all patients but was predominantly grade 1, with no grade 3 or higher CRS, no ICANS and no IEC-HS. This pattern aligns with oncology experience in which CRS severity correlates with target antigen burden and other patient-specific factors.
“Notably, hematologic toxicity was limited: cytopenias were uncommon and mild, and infections were largely low grade. This contrasts with CD19 CAR T-cell therapy, where lymphodepleting chemotherapy contributes to profound cytopenias and necessitates prolonged antimicrobial prophylaxis until immune reconstitution.
“Together, these findings suggest that CD19×CD3 TCEs can be delivered without lymphodepletion while maintaining a manageable inflammatory toxicity profile, a feature that may expand feasibility and reduce resource utilization in autoimmune indications.
“Future studies should directly compare infection risk, hypogammaglobulinemia requiring immunoglobulin replacement and patient-reported outcomes across TCE-based and CAR T-based strategies.”
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The researchers noted that one of the most striking findings came from single-cell RNA sequencing. As B cells returned after treatment, the repertoire shifted towards naive rather than memory B cells, while inflammatory interferon signatures were suppressed across B-cell, T-cell and myeloid compartments. The molecular changes closely resembled those previously reported following CD19 CAR T-cell therapy in SLE.
The researchers said this suggested A-319 may achieve an immune reset extending beyond simple depletion of circulating B cells, while avoiding lymphodepleting chemotherapy and bespoke cell manufacturing.
But they cautioned against drawing firm conclusions from the results. The trial was small, single-centre, open-label, and uncontrolled, follow-up was limited to 12 months, and concomitant immunosuppression and substantial corticosteroid exposure could have influenced both clinical and molecular findings.
“In summary, these phase 1 data demonstrate the safety and feasibility of a CD3×CD19 TCE in active SLE, achieving deep B cell depletion and broad multi-lineage immune reprogramming with predominantly low-grade CRS and limited cytopenias,” the researchers concluded.
“As deep B cell depletion in autoimmune disease rapidly expands beyond autologous CD19 CAR T-cells to include lymphodepletion-free, allogeneic and in vivo CAR T and CAR NK approaches, randomized controlled trials with standardised background immunosuppression, longer follow-up and biomarker-integrated designs will be essential to define the therapeutic index, optimal dosing and comparative effectiveness of TCE therapy among CD19-directed immune-reset strategies for autoimmune rheumatic disease.”
