The results, drawn from a retrospective analysis, provide support for clinical trials to rest longer re-infusion intervals.
The study appeared online Jan. 21 in the journal Multiple Sclerosis and Related Disorders, presented by lead author Mahmoud AbdelRazek, MD, at the annual meeting held by the Americas Committee for Treatment and Research in Multiple Sclerosis (ACTRIMS).
Both drugs were approved based on clinical trials that investigated 6-month doses, but previous studies have suggested depletion can last longer, including a range of 9-26 months in the case of rituximab.
The initial rationale for monitoring B cell depletion was to prevent a relapse by re-infusing a patient if B cells levels rise, but the researchers noted a pattern of sustained depletion, especially in patients who had a delayed infusion for some reason – they often still had low B cell counts at the time of the next drug infusion. “That became not an unusual finding,” said Dr. AbdelRazek in an interview. He is an instructor of neurology at Harvard Medical School.
Patients also found the delay appealing, in part because they often felt unwell in the days following an infusion, and delays could mean fewer infections and other adverse effects. “Most of my patients I’ve discussed this with would be very appreciative of that delay,” said Dr. AbdelRazek. “There’s obviously an economic benefit as well,” said Dr. AbdelRazek.
The final answer?
The retrospective nature of the study is a key weakness, and the rationale to delay infusions based on continuing B cell depletion assumes that B cell depletion is in fact the mechanism of action for countering MS. “That is a critical question,” said Mark Gudesblatt, MD, who was asked to comment on the study. But if that is indeed the way the drugs work, then it would make sense to identify patients who repopulate B cells more slowly and tailor drug regimens. “It’s not one size fits all and blindly just re-dosing. The upsides are good: You come in less frequently for dosing, the cost to payers is less. But the bad is, maybe there are other markers. This is the putative mechanism, but what we believe may not be the final answer. There may be more to the story,” said Dr. Gutesblatt, who is Medical Director at South Shore Neurologic Associates, Patchogue, New York.
Dr. AbdelRazek also noted the study’s limitation. “I think a clinical trial is going to be warranted to really have this translated into clinical practice,” he said. His group is planning to conduct just such a trial, pending confirmation of a funding source.
B cell depletion beyond 6 months
The researchers analyzed data from 178 patients with MS and 10 patients with NMOSD who received ocrelizumab (n = 111) or rituximab (n = 53), or both (n = 24) at two Harvard Medical School teaching hospitals between 2010 and 2020. The data included 800 infusions and 1,054 CD19 measurements.
The researchers defined B cell depletion as an absolute count of 20 cells/uL or less, a B cell percentage of 2% or less, or if B cells were 5% or less of total lymphocytes.
Among the patient population, B cell depletion that met all 3 criteria occurred as long as 13.8 months after an initial ocrelizumab infusion cycle, and 22.8 months after second or more cycles of ocrelizumab. Following rituximab, the researchers noted B cell depletions. Following 500 mg of rituximab, B cell depletion defined by the first, second, or third criteria occurred as far out as 22.3, 26.2, and 28.5 months. For 1,000 mg doses of rituximab, B cell depletion occurred as long as 18.3, 18.3, and 29.1 months after a dose.
Examining 90 B cell measurements conducted at least 8 months after an ocrelizumab infusion, 50% were depleted by the first definition and 54% by the second definition. At 13 months, the figures were 58% and 62% among 26 B-cell measurements. Eight months or more after rituximab, 113 B-cell measurements showed rates of 43% and 52% B-cell depletion by the first two criteria.
Dr. AbdelRazek and Dr. Gudesblatt have no relevant financial disclosures.