Resolution of PML after Treatment with Virus-Specific T Cells and HCT

Dr. Justin Abbatemarco talks with Dr. Irene Cortese about recent advances in the treatment of progressive multifocal leukoencephalopathy (PML), focusing on immune-based therapies like virus-specific T cells and immune checkpoint inhibitors. 

Read the related article in The New England Journal of Medicine. 

Disclosures can be found at Neurology.org. 

Show transcript: 

Dr. José Merino:
This is José Merino, editor-in-chief of the Neurology Family of Journals. The Neurology Podcast provides practical information to neurologists and other clinicians to help them provide better care for their patients. Thanks for listening, and have a great week.

Dr. Justin Abbatemarco:
Hello and welcome. This is Justin Abbatemarco with the Cleveland Clinic here with Irene Cortese to discuss an update on progressive multifocal leukoencephalopathy treatment in light of a New England Journal of Medicine correspondence, Resolution of PML After Treatment with Virus-Specific T Cells and HCT. Irene directs the Experimental Immunotherapeutics Unit at NINDS. Hello and welcome.

Dr. Irene Cortese:
Hi, thank you for the invitation to join you today.

Dr. Justin Abbatemarco:
It's a pleasure to have you on and to talk about this expanding space in rare disease. And maybe if we could start off, can we just take an overview on how PML usually presents and why does it remain so difficult to treat?

Dr. Irene Cortese:
PML, or progressive multifocal leukoencephalopathy, is an opportunistic infection of the brain that is caused by the JC virus. And most of us carry this virus lifelong and without any symptoms, and it really only causes disease when the immune system is significantly compromised and loses the ability to keep it in check. And so when that happens, the virus can gain the ability to infect oligodendrocytes, and this can lead to the rapidly progressive demyelinating infection called PML.
These lesions that develop in PML are typically located in the white matter, and they are most often multifocal. And this leads to the clinical manifestation of a combination of cortical and subcortical symptoms that evolve over weeks to months. And, unfortunately, if immune competence can't be restored quickly, then the disease is fatal within just a few months. And so that's really the core of the problem here, is that there is no effective direct antiviral treatment. And the only thing that works is restoring the immune system ability to control it, but that's often very difficult to do. When it's even possible, it's frequently just not even fast enough.
And so you can see this even in situations where you'd think that we'd have an advantage, for example, in HIV-associated PML, where we do have effective antiretroviral therapy. Even there, restoring immune competence can sometimes just take too long relative to how quickly PML progresses.
And so on top of all that, PML is really quite rare and is also remarkably heterogeneous because it can occur in very different patient populations from HIV to hematological malignancy to genetic immune deficiencies. And this rarity and heterogeneity really make both the diagnosis difficult and also treatment development quite difficult.

Dr. Justin Abbatemarco:
It's such a interesting story, and these different backgrounds really present different challenges. But at these last few years, this has been a success story in some way because we've seen so much effort and research into this rare disease space, which is encouraging. We mentioned this at the top, but there are immune checkpoint inhibitors that have at least been trialed for this T cell exhaustion to see if we can boost the immune system, and then more recently with your work around allogeneic-specific T cells to help clear the infection. What have you taken away from those updates?

Dr. Irene Cortese:
The biggest takeaway is that these two approaches, checkpoint inhibitors and Virus-Specific T Cells, have really transformed the way that we think about PML. So for decades, our only option was really to try to reverse the underlying immune suppressive condition and just hope that the immune system caught up in time. And now we have these two active strategies to try to speed this process up.
Importantly, both these strategies have validated the same core hypothesis that even without a direct antiviral agent, we can improve PML outcomes by restoring effective antiviral immunity. And that said, each of these approaches has real limitations. So first of all, they don't work in all patients. And we have best estimates of success rates somewhere in the 50 to 60% range overall. With checkpoint inhibitors, the fundamental issue is that you're trying to unleash an immune response that has to already be there in some latent or exhausted form.
For example, in patients with very advanced immune compromise where the T-cell compartment is essentially absent, there's just nothing left to invigorate, and so checkpoint blockade is really unlikely to help. And even when they do work, there is a real risk of exacerbating underlying autoimmune disease as well as the risk of leading to immune reconstitution inflammatory syndrome, or IRIS, where inflammation in the central nervous system of this immune system waking up and attacking the infection can actually lead to severe morbidity and even death in some patients.
Virus-Specific T Cells have a whole different set of limitations. These are mostly practical and logistical at this point. Access is really the big one because there are only a handful of centers worldwide that can manufacture Virus-Specific T Cells. And so this just isn't something you can easily do everywhere or quickly. An