What do you do when you get recurrent disease activity on cladribine?
I am repeatedly being asked what to do about disease activity in patients treated with cladribine. The following is my suggestions on how to approach this thorny issue.
As you know disease activity on immune reconstitution therapies (IRTs) don’t necessarily mean you failed or are failing the therapy. Disease activity could be an indication to retreat with an additional course. Interpreting when and what to do depends on when the disease activity emerges and how severe it is.
If you have a relapse after the first course (cycles 1 & 2) of cladribine I would hold fast and have the second course. There is no reason why someone who has disease activity in year 1 post-cladribine won’t necessarily respond to the second course. There is, however, one proviso here. With alemtuzumab, another IRT, rare patients get rebound activity, over and above baseline activity, around months 7-9 post the first course of alemtuzumab infusions. Why this happens we don’t know. We have not observed this with cladribine yet, but it could theoretically happen. In this situation, the disease activity is so severe that most of these patients are offered alternative treatments, in particular, anti-CD20 therapies (rituximab or ocrelizumab), mitoxantrone, cyclophosphamide or HSCT.
When we see recurrent disease activity in year 1 post-alemtuzumab we have often brought forward the second course of alemtuzumab. I see no reason why we wouldn’t consider this with cladribine as well, provided the total lymphocyte counts have recovered to above 800/mm3.
Post-course 2 – year 2
If disease activity occurs in year 2 this is not good news. This would indicate that the patient has not responded to cladribine and would be an indication to switch therapeutic strategies.
Post-course 2 – year 3 & 4
If you have disease activity in years 3 & 4 the timeframe covered by the current cladribine label you are not meant to retreat with cladribine. However, this makes no sense to me. IRT works by depletion and reconstitution. In some people, the two cycles of depletion with cladribine may not be sufficient to deplete the autoreactive pool and hence MS disease activity resurfaces. I personally think there is no reason why a further course of cladribine should not be offered alongside other DMTs in this situation. This is exactly how we use alemtuzumab in this situation; the difference being alemtuzumab is now licensed to be used in this way. Clearly there is an evidence gap around cladribine and hopefully, this will be filled as real-life data sets emerge in the future.
Post-course 2 – after 4 years
Similar to the above I see no reason why a further course of cladribine should not be offered alongside other DMTs in this situation. This is how we use alemtuzumab and other IRTs. I am aware of one patient in the US has had 7 courses of intravenous cladribine over a period of 21 years.
Cladribine has a variable treatment effect on the total lymphocyte counts. There are biochemical reasons why this may occur. I see in the future adapting the dose of cladribine we use to achieve an optimal level of lymphocyte depletion. This makes sense.
I also see cladribine being used as induction therapy, i.e. after an initial course of cladribine, we will be following it with maintenance therapy. Based on the memory B-cell hypothesis BTKi (Bruton’s Tyrosine Kinase inhibitor) or teriflunomide (antiproliferative/antiviral) makes the most sense at present.
I would love to do a trial of an IRT followed by maintenance therapy. Any takers? Any funders? In terms of safety and cost, I would go off-label and test rituximab followed by leflunomide vs. rituximab as an IRT.
The following is a visual summary of some of the information above.