Experimental cell therapy delivers encouraging results for patients with rare, potentially fatal brain infection

UT MD Anderson Research News July 10, 2026

• No approved treatments exist for progressive multifocal leukoencephalopathy (PML), a serious neurological condition caused by the JC virus (JCV) 

• Up to 70% of adults carry the JCV symptom-free, but the virus can reactivate with diseases or conditions that weaken the immune system

• A UT MD Anderson-developed virus-specific T cell therapy produced rapid responses and strong overall survival  

HOUSTON, JULY 10, 2026 ― In the largest study of its kind, a virus-specific T cell therapy developed by researchers at The University of Texas MD Anderson Cancer Center achieved a response in more than half of treated patients with a rare and often deadly neurological condition caused by viral infection.

Findings from the Phase 2 study were published in Clinical Infectious Diseases. The investigational, off-the-shelf virus-specific T cells achieved an overall response rate of 56.8% in 37 patients with progressive multifocal leukoencephalopathy (PML), including 43.2% achieving complete viral clearance with stabilization or improvement of neurological symptoms. Patients responded quickly – typically within 23 days – and the one-year overall survival rate for all treated patients was 61.1%. Patients who responded after their first infusion experienced a one-year survival rate of 93.3%.

“For decades, physicians have had no approved treatment to offer patients with PML, and this disease has long represented one of the greatest unmet needs in neuroinfectious medicine," said corresponding author Katy Rezvani, M.D., Ph.D., vice president and head of the Institute for Cell Therapy Discovery & Innovation, and professor of Stem Cell Transplantation and Cellular Therapy, whose team developed the virus-specific T cell platform. “Seeing rapid viral clearance and meaningful clinical responses in more than half of treated patients is extremely encouraging as we try to identify a potential standard treatment.”

What is PML and why are new treatments needed? 

PML is a rare and deadly neurological disease that develops when the normally dormant JC virus (JCV) reactivates in people with severely weakened immune systems. More than half of adults acquire the JC virus in childhood or early adulthood and will never experience symptoms. However, the virus can become active in immune-compromised individuals, such as patients with cancer.

PML symptoms may include cognitive decline, speech difficulties, vision problems, weakness, balance disturbances and progressive neurological deterioration. In individuals with conditions such as blood cancer, HIV/AIDS, organ transplants, autoimmune diseases or treatment-related immunosuppression, the virus can reactivate and attack the brain’s white matter. This can lead to severe neurological disability or death, with mortality rates ranging from 50% to 80%. 

There currently are no established treatments for PML, so new therapeutic options are urgently needed. 

How does this virus-specific T cell therapy work? 

The researchers used a bank of cryopreserved T cells from healthy donors that recognize the BK virus, which shares certain features with the JCV. Therefore, these BK virus-specific T cells can recognize and attack JCV-infected cells. 

The virus-specific T cell therapy provides patients with the necessary virus-fighting immune cells that they often lack due to their suppressed immune system. Unlike patient-specific cellular therapies that may require weeks or months to manufacture, the cells in this study were immediately available off-the-shelf for treatment and delivered through an infusion similar to other cell therapies. 

What are additional key findings from this study?

These findings build directly on earlier UT MD Anderson research published in the New England Journal of Medicine, which first demonstrated the potential of BK virus-specific T cells in a small group of patients with PML and provided the foundation for the current Phase 2 study. 

The study also found that patients with lower JCV levels before treatment were more likely to respond, suggesting that earlier intervention may improve outcomes. Greater immune compatibility between donor T cells and recipients also was linked to better responses and survival. Importantly, responses appeared to be durable. Patients who responded to therapy did not develop recurrent PML during follow-up, and there was no evidence of disease relapse after achieving a response.

Among the 37 study participants, 23 had underlying hematologic malignancies, a particularly high-risk group in which PML can carry mortality rates exceeding 90% within two months of diagnosis. Responses also were observed in patients who developed PML after CAR T cell therapy or transplantation, as well as in individuals with HIV/AIDS and autoimmune diseases treated with immunosuppressive therapies, highlighting the broader potential of this off-the-shelf approach across diverse causes of severe immune suppression.

"Many of the patients enrolled in this trial were among the highest-risk individuals we see," Rezvani said. "The fact that responses were durable and observed across patients with different underlying causes of immune suppression highlights the broad potential of this approach." 

Researchers believe the results warrant further studies and support the development of BK-virus-specific T cell therapy as a potential standard treatment for PML. The clinical trial remains open and continues to enroll patients with PML.

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This research was supported by UT MD Anderson institutional funds. For a full list of collaborating authors, disclosures and funding sources, see the full paper in Clinical Infectious Diseases.