Directly Isolated Allogeneic Virus-Specific T Cells in Progressive Multifocal Leukoencephalopathy.

Importance: Progressive multifocal leukoencephalopathy (PML) is a life-threatening viral infection with no approved antiviral treatment. Objective: To determine whether restoring the compromised immune system of patients with PML with directly isolated allogeneic virus-specific (DIAVIS) T cells is a promising therapeutic strategy, especially if other curative options are absent. Design, Setting, and Participants: A retrospective case series of patients with PML who were treated with DIAVIS T cells was conducted between March 2020 and February 2022. T cells were isolated from healthy donors within 24 hours and targeted against the BK polyomavirus. Patients with PML were treated monocentrically. Eligibility for treatment with DIAVIS T cells was assessed for patients with confirmed PML, and exclusion criteria included stable PML disease and previous treatment with natalizumab. Exposure: Fresh DIAVIS T cells were administered with a maximum dose of 2 × 104 CD3+ cells/kg body weight. Remaining T cells were cryopreserved in divided doses and administered in additional treatments approximately 2 and 6 weeks later. Main Outcomes and Measures: Primary outcome measures were clinical response and survival of patients, compared with the outcomes of a historical reference group of PML cases receiving best supportive treatment (BST) and with recently published real-world data of patients with PML who were treated with immune checkpoint inhibition. Results: The study cohort consisted of 28 patients (median [IQR] age, 60 [51-72] years; 20 male [71.4%]). Twenty-two patients (79%) treated with DIAVIS T cells showed response, resulting in significant clinical stabilization or improvement and a reduction in viral load. Six individuals (21%) were classified as nonresponders, deteriorated rapidly, and died, as did 2 other patients during a 12-month follow-up. Older age was the only predictor of a poor treatment response. Survival analysis revealed better 12-month survival rates (hazard ratio, 0.42; 95% CI, 0.24-0.73; P =.02) from diagnosis for patients treated with DIAVIS T cells (18 of 26 [69%]; 12-mo survival rate, 69%) compared with historical controls with BST (57 of 113 [50%]; 12-mo survival rate, including censored data, 45%). Conclusion and Relevance: This case series of DIAVIS T-cell therapy in PML provides first class IV evidence suggesting efficacy to reduce mortality and improve functional outcome. Further prospective studies are required to confirm these results.