Prof G what happens to MS disease activity if you stimulate T-cells?
About 2 years ago I attended a grand round during which a patient with a history of RRMS had had a catastrophic relapse after receiving ipilimumab for metastatic melanoma. The patient has a massive brain stem relapse and her MRI showed multiple Gd-enhancing lesions with several pseudotumoral lesions. She was in a bad way. Interestingly, this case was not unique as a very similar case had been published. In addition, there are series of other examples of ipilimumab and other immune checkpoint inhibitors exacerbating and/or triggering autoimmune diseases including an MS-like disease. I say MS-like because we don’t know for sure if these cases will turn out to have classic MS on biopsy, or at post-mortem, to prove they have definite MS according to a conventional definition of the disease.
Ipilimumab belongs to the class of drugs called ‘checkpoint inhibitors’ that are designed to remove one of the immunological brakes that control T-cell activation. Ipilimumab is one of many T-cell stimulants that have revolutionised the care of patients with various different cancers. Ipilimumab is a very smart drug it blocks CTLA-4, a cell surface molecule on T cells, which normally blocks or downregulates T cell activation when it binds to CD80 and CD86 on antigen-presenting cells. Ipilimumab enhances the anti-tumoral response while increasing the likelihood of autoimmunity.
So what has this really got to do with MS? Well, these cases are telling us in a not so subtle way that by stimulating T-cells we can exacerbate MS. In other words, T-cells are probably still active in established MS. What this experiment is not telling us is which population of T-cells is the culprit as CD4+, CD8+ and T-regulatory cells express CTLA-4 and are hence affected by Ipilimumab. Nor is it telling us about the APC side, which APC is stimulating the T-cells. Is it the B-cell, the macrophage/microglia or another APC?
The moral of this story is that it takes two to tango; the T-cell and its APC. The question is which APC is the preferred partner for the T-cell in MS. Based on the evidence the B-cell seems to be the dominant partner, but who knows in the presence of peripheral B-cell depletion other less dominant partners may take to the floor.
Gettings et al. Severe relapse in a multiple sclerosis patient associated with ipilimumab treatment of melanoma. Mult Scler. 2015 Apr;21(5):670.