Characterizing absolute lymphocyte count profiles in dimethyl fumarate-treated patients with MS: Patient management considerations.

BACKGROUND: Delayed-release dimethyl fumarate (DMF), indicated for the treatment of patients with relapsing-remitting multiple sclerosis (MS), is a disease-modifying therapy with potential immunomodulatory and neuroprotective effects. In clinical trials, DMF was associated with reduced white blood cell and absolute lymphocyte counts. Current US prescribing information recommends obtaining a complete blood count, including absolute lymphocyte count (ALC), before initiating and during DMF treatment.
METHODS: We conducted an integrated analysis of phase 2b/3/long-term extension studies of DMF in MS (N = 2,470) to characterize ALC profiles.
RESULTS: Mean ALCs decreased by 30% during the first year and then plateaued, remaining above the lower limit of normal (LLN). Among patients treated ≥6 months (N = 2,099), 2.2% experienced ALCs <500 mm3 persisting ≥6 months. ALCs remained ≥LLN in 84% and 76% of patients during the first 6 and 12 months, respectively; of these, 0.1% and 0%, respectively, developed ALCs <500 mm3 persisting ≥6 months at any time. Evidence of ALC improvement following DMF discontinuation was observed. DMF efficacy was not substantially different in patients with and without lymphopenia.
CONCLUSION: Lymphocyte monitoring provides effective means for early identification of patients at risk for developing severe, prolonged lymphopenia.

Current management strategies for relapsing-remitting multiple sclerosis (RRMS) are focused on prevention of new disease activity via disease-modifying therapies (DMTs).[1,2] Delayed-release dimethyl fumarate (DMF; also known as gastro-resistant DMF) is a DMT with potential immunomodulatory and neuroprotective effects.[3,4] DMF is indicated for the treatment of patients with RRMS.[5] In clinical trials, DMF was associated with flushing and gastrointestinal events as well as reduced white blood cell (WBC) and absolute lymphocyte counts (ALCs).[6,7] Current US prescribing information recommends obtaining a complete blood count, including ALC, before initiating and during DMF treatment and considering treatment interruption in patients with ALCs <500 mm3 persisting >6 months[5] to minimize the risk of developing severe, prolonged lymphopenia and its potential complications. We conducted an integrated analysis of data from phase 2b and 3 studies of DMF to characterize ALC profiles and to examine efficacy in DMF-treated patients with and without lymphopenia.

METHODS

Standard protocol approvals, registrations, and patient consents

This analysis is based on data from 1 phase 2b study (NCT00168701), 2 pivotal phase 3 studies (DEFINE [NCT00420212]; CONFIRM [NCT00451451]), and an ongoing long-term extension of DEFINE/CONFIRM (ENDORSE [NCT00835770]). Each study was approved by central and local ethics committees and conducted in accordance with the International Conference on Harmonisation Guidelines for Good Clinical Practice and the Declaration of Helsinki. All patients provided written informed consent.

Study design and treatment

The study designs have been described in detail previously[6-9]; a brief summary is provided here.

The phase 2b study and DEFINE/CONFIRM were multicenter, randomized, double-blind, placebo-controlled, parallel-group trials of DMF monotherapy in RRMS. The 12-month phase 2b study included a 6-month placebo-controlled period (part 1) and a 6-month uncontrolled safety extension (part 2). During part 1, patients were randomized equally to DMF 120 mg once daily, 120 mg tid, 240 mg tid, or placebo.

In the 2-year DEFINE/CONFIRM studies, patients were randomized equally to DMF 240 mg bid, 240 mg tid, or matching placebo. CONFIRM also included a glatiramer acetate (GA) reference comparator arm (not reported here).

ENDORSE is an ongoing multicenter, parallel-group, dose-blinded extension of DEFINE/CONFIRM with up to 8 additional years of follow-up. Patients who received DMF 240 mg bid or tid for up to 2 years in the parent studies remained on the same dosage in ENDORSE. Patients who received placebo (DEFINE and CONFIRM) or GA (CONFIRM) in the parent studies were randomized equally to DMF 240 mg bid or tid.

Patients

Key patient inclusion criteria for all studies included age 18–55 years, RRMS diagnosis (McDonald criteria[10]), and an Expanded Disability Status Scale (EDSS) score of 0–5.0. Key exclusion criteria were relapse within 50 days before randomization, treatment with corticosteroids within 30 (phase 2b study) or 50 (DEFINE and CONFIRM) days before randomization, and prior treatment with potent immunosuppressant agents/procedures or MS therapies within predefined washout periods. Exclusion criteria included prespecified abnormal laboratory parameters, including WBC count <3,500/mm3 or eosinophils >700/mm3.

Hematology

Blood was collected every 4 weeks in the phase 2b study. In DEFINE and CONFIRM, blood was collected every 4 weeks for the first 3 months and every 12 weeks thereafter, and within 1 month after study withdrawal or completion if a patient did not continue in the extension. Blood was collected every 12 weeks in ENDORSE.

Hematology assessments included hemoglobin, hematocrit, red blood cell count, WBC count (with differential), and platelet count. ALCs were graded according to the Common Terminology Criteria for Adverse Events (CTCAE v4.0) as follows: grade 0 (≥lower limit of normal [LLN] [≥910 mm3]); grade 1 (<LLN to ≥800 mm3); grade 2 (<800–500 mm3); grade 3 (<500–200 mm3); and grade 4 (<200 mm3).[11]

Statistical analysis

For the analysis of ALCs, the data from all patients exposed to DMF in DEFINE, CONFIRM, ENDORSE, and the phase 2b study, including the 6-month safety extension phase, were pooled to identify all patients with low ALC values on DMF treatment. The data cutoff for this interim report was May 14, 2014; the minimum ENDORSE study follow-up for those patients remaining on study was approximately 3 years.

Because the efficacy evaluation was based on annualized relapse rate (ARR) at 2 years vs placebo, only data from DEFINE and CONFIRM were included. The ARR was analyzed in each ALC subgroup (all ALC ≥LLN vs ≥1 ALC <LLN) using a negative binomial regression model adjusted for baseline EDSS score, age, region, study, and number of relapses in the 12 months before study entry. Because there were no cases of ALC <LLN in the placebo group, each of the DMF ALC subgroups was compared with the entire placebo group in the ARR analysis. The ALC subgroup definition used in this analysis (≥LLN throughout and ≥1 ALC <LLN) allowed an adequate sample size in each subgroup for a reliable estimate of ARR reduction vs placebo.

RESULTS

The safety population comprised 2,513 patients with RRMS, including 1,136 patients treated with DMF 240 mg bid, 1,249 treated with DMF 240 mg tid, and 128 treated with lower doses of DMF. Mean (SD) time on study treatment was 3.1 (2.2) years (total of 7,250.0 cumulative patient-years); 74%, 55%, 29%, and 1% of patients were on study treatment for ≥1, 3, 5, and 7 years, respectively (table e-1 at Neurology.org/cp). A total of 2,470 patients (98.3%) had any post-baseline ALC (median [range] follow-up: 39.0 [0.0–90.5] months).

Mean WBC counts and ALCs throughout time with continuing DMF treatment

Mean baseline ALCs were similar across the DMF treatment arms: 1,870/mm3 with lower doses of DMF, 1,980/mm3 with 240 mg bid, and 1,990/mm3 with 240 mg tid. Mean ALCs decreased by approximately 30% during the first year of treatment and then plateaued, remaining above LLN (910 mm3) throughout the observation period (figure 1A).

Figure 1.

Mean ALCs (±SE) throughout time

(A) Patients treated with lower doses of DMFa, DMF 240 mg bid, or DMF 240 mg tid. (B) Patients with ALCs <500 mm3 persisting ≥6 months vs all other patients. ALC = absolute lymphocyte count; BL = baseline; DMF = dimethyl fumarate; LLN = lower limit of normal. aDMF, delayed-release DMF (also known as gastro-resistant DMF). bBaseline (week 0) n includes all patients for whom a baseline ALC value was available. cMean ALCs throughout time are presented out to approximately 5 years (week 240), as this is the minimum follow-up for patients remaining on study in ENDORSE.

Incidence of CTCAE grade 0–4 lymphopenia

In most patients in the safety population (61%; 1,533/2,513), ALCs were within normal limits at all visits (CTCAE grade 0). The incidence of worst post-baseline CTCAE grade 1 and 2 lymphopenia was 9% (236/2,513) and 21% (528/2,513), respectively. A further 7% (n = 171/2,513) experienced CTCAE grade 3 lymphopenia and <1% (n = 2/2,513) experienced CTCAE grade 4 lymphopenia.

ALC profiles

Among patients treated for ≥6 months (N = 2,099), 47 (2.2%) experienced ALCs <500 mm3 that persisted for ≥6 months. For these patients, ALCs generally remained <500 mm3 with continued therapy. ALCs remained ≥LLN in 84% of patients (2,083/2,470) during the first 6 months and in 76% (1,876/2,470) during the first year; of these patients, 0.1% (3/2,083) and 0% (0/1,876), respectively, developed ALCs <500 mm3 persisting for ≥6 months at any time (table 1). The percentages of patients with all ALCs ≥800 or ≥500 mm3 during the first 6 months or during the first year of treatment who developed ALCs <500 mm3 persisting for ≥6 months at any time were similarly low (0%–1.5%). However, for patients with ≥1 ALC <800 mm3 during the first 6 months or first year of treatment, the proportion who developed ALC <500 mm3 persisting for ≥6 months was higher (15% and 11%, respectively). For patients with ≥1 ALC <500 mm3 during the first 6 months or first year of treatment, the percentage of patients who developed ALCs <500 mm3 persisting for ≥6 months at any time was considerably higher (42% and 51%, respectively) (table 1).

Table 1.

Proportion of patients who subsequently developed ALCs <500 mm3 persisting ≥6 months at any time (up to 7 years after initiating treatment) according to ALCs within the first 6 months or 1 year of DMFa treatment

Time course of mean ALC changes in patients with ALCs <500 mm3 persisting ≥6 months

Mean ALCs in patients with ALCs <500 mm3 persisting for ≥6 months showed a faster decline than those in counterparts without ALCs <500 mm3 persisting for ≥6 months (figure 1B), decreasing to 650 mm3 by week 24 and to 480 mm3 by week 48.

Recovery of ALCs post discontinuation of DMF treatment

Among the 47 patients with ALCs <500 mm3 for ≥6 months, 9 discontinued or completed the study and had limited posttreatment data, as shown in figure 2. Of these 9 patients, 8 had ALCs ≥1 month after their final dose. All of these patients generally showed ALC increases following their final DMF dose. The remaining 38 patients with ALCs <500 mm3 for ≥6 months remained on treatment at the time of this analysis (May 14, 2014).

Figure 2.

ALCs following treatment discontinuation in 9 patients with ALCs <500 mm3 for at least 6 months

ALC = absolute lymphocyte count; DMF = dimethyl fumarate; LLN = lower limit of normal. aDMF, delayed-release DMF (also known as gastro-resistant DMF).

Efficacy in patients with and without lymphopenia (

In DEFINE and CONFIRM, the reduction in ARR at 2 years in patients treated with DMF 240 mg bid vs placebo was not substantially different in patients with lymphopenia (≥1 ALC <LLN) compared to those without lymphopenia (all ALCs ≥LLN) (rate ratio [95% confidence interval] vs placebo: 0.472 [0.364–0.611] and 0.547 [0.441–0.679], respectively), figure 3.

Figure 3.

ARR reduction at 2 years in patients with and without lymphopenia in DEFINE and CONFIRM

Results represent ARR reductions in patients in the DMF bid group with lymphopenia (at least 1 ALC 2.0), baseline age (<40 vs ≥40 years), region, and number of relapses in the 1 year before study entry.

Results represent ARR reductions in patients in the DMF bid group with lymphopenia (at least 1 ALC <LLN) or without lymphopenia (all ALCs ≥LLN) compared with all patients in the placebo group (pooled analysis of DEFINE and CONFIRM). ALC = absolute lymphocyte count; ARR = annualized relapse rate; CI = confidence interval; DMF = dimethyl fumarate; EDSS = Expanded Disability Status Scale; LLN = lower limit of normal. aDMF, delayed-release DMF (also known as gastro-resistant DMF). bBased on negative binomial regression, adjusted for baseline EDSS score (≤2.0 vs >2.0), baseline age (<40 vs ≥40 years), region, and number of relapses in the 1 year before study entry.

General safety

As identified in this interim analysis, lymphopenia in DMF-treated patients was not associated with an overall increased risk of serious infections, including opportunistic infections. The incidence of serious infection was low (83/2,513; 3%). Also, there was no apparent relationship between increased incidence of serious infection and increased lymphopenia grade. Serious infections were reported in 3% (n = 43), 6% (n = 13), and 4% (n = 22) of patients with CTCAE grade 0, 1, or 2 lymphopenia, respectively, and in 3% (n = 5) with CTCAE grade 3 or 4 lymphopenia. The most common infections were abdominal and gastrointestinal (n = 20), urinary tract (n = 14), and upper respiratory tract (n = 10), and all occurred with an incidence of <1% in the patient population overall. Subsequent to the data cutoff for this interim report, a case of progressive multifocal leukoencephalopathy (PML) in a patient treated with DMF 240 mg tid was reported in the setting of severe, prolonged lymphopenia (approximately <500 mm3 for 3.5 years). Details of this case are reported separately.[12]

DISCUSSION

A key objective of this analysis was to provide practical considerations for the management of DMF-treated patients with MS by characterizing ALC profiles and examining efficacy in patients with and without lymphopenia. ALC profiles were generally stable throughout time. Mean ALCs decreased by approximately 30% in DMF-treated patients during the first year of treatment and then plateaued, remaining above the LLN throughout the observation period. Among patients treated with DMF for ≥6 months, few (2.2%) experienced ALCs <500 mm3 persisting for ≥6 months, and subsequent ALCs of these patients generally remained <500 mm3. This suggests that ALC <500 mm3 persisting for ≥6 months was an early predictor for those patients at risk of developing severe, prolonged lymphopenia. Our results indicate that patients with ALCs ≥LLN for the first 6 months and first year on DMF treatment are unlikely to have ALC <500 mm3 persisting for ≥6 months. Thus, lymphocyte monitoring provides an effective means for early identification of patients at risk for subsequently developing severe, prolonged lymphopenia.

Recent labeling changes in the United States include a recommendation to consider interruption of DMF in patients with ALCs <500 mm3 persisting >6 months to minimize the risk of subsequently developing severe, prolonged lymphopenia and its potential complications.[5] Similar labeling changes are pending in the European Union. Although data are limited and based on a small number of patients (n = 9), the current interim data provide preliminary evidence for ALC improvement following DMF discontinuation in patients with an ALC <500 mm3 persisting for ≥6 months. To further study the recovery profile in patients with decreases in lymphocyte counts who are considered at risk for severe and prolonged lymphopenia, a recent ENDORSE protocol amendment stipulated that study treatment must be temporarily withheld if a patient's ALC is <500 mm3 for >6 months. If the ALC remains <500 mm3 for 24 weeks after the last dose, study treatment must be permanently discontinued. It is anticipated that this protocol amendment will enable further evaluation of lymphocyte count recovery after temporary withholding or permanent discontinuation of DMF in patients who develop ALCs <500 mm3 persisting for >6 months.

As of August 31, 2015, more than 170,000 patients have been treated with DMF worldwide, representing more than 170,000 patient-years of exposure. Of these patients, 3,887 received DMF in clinical trials, which equates to 8,640 patient-years of exposure (clinical trial exposure data as of April 15, 2015). In this analysis, the overall incidence of serious infections was low, and there was no apparent correlation between the incidence of infection and CTCAE grade ALC (patients with CTCAE grade 3 or 4 ALC did not experience a higher incidence of serious infection than patients with CTCAE grade 0 or 1 ALC). Subsequent to the data cutoff for this interim report (May 2014), a fatal case of PML was reported in a 54-year-old patient with MS treated with delayed-release DMF 240 mg tid in the setting of severe, prolonged lymphopenia (approximately <500 mm3 for 3.5 years).[12] In addition, rare cases of PML occurred in the postmarketing setting in the presence of prolonged lymphopenia. Specifically, 2 cases occurred in the presence of severe and prolonged lymphopenia (approximately <500 mm3 persisting for >6 months) and 1 case occurred in the presence of moderate and prolonged lymphopenia (nadir 600 mm3 for >6 months) (Biogen data on file). Aside from rare cases of PML, there is no overall increased risk for serious infections, including other opportunistic infections.[13] Rare cases of PML have also been reported with other fumarates[14-16]; however, it is important to note that Fumaderm is a distinct product with different active ingredients and that compounded fumarates are unregulated products that may contain different active ingredients. These products have different pharmacokinetic and pharmacodynamic profiles and may have a differential effect on lymphocytes (Biogen data on file)[17]; however, one salient feature of these cases is prolonged lymphopenia, as the majority of these cases shared this characteristic. Periodic monitoring of ALCs to identify patients who may have developed severe, prolonged lymphopenia is therefore recommended (as per the label for DMF). Furthermore, health care providers should assess the benefit and risk of continued DMF treatment in patients who experience moderate lymphopenia persisting for >6 months.

Immune cell changes are an important component in MS pathophysiology, as the immune system plays a central role in myelin and nervous cell destruction and lesion development.[18,19] The beneficial effects of immunomodulatory and immunosuppressive therapies on MS disease activity provide further support to this theory. Herein, we noted similar DMF therapeutic efficacy (ARR reduction) in patients with and without lymphopenia, suggesting that lymphopenia is not a primary mechanism for the therapeutic effects of DMF.

Our findings are supported by independent research findings in the real-world setting. In a retrospective chart review evaluating effects of DMF on lymphocytes in patients with MS (n = 221) prescribed DMF over a 2-year period, grade 3 lymphopenia was reported in approximately 5% of patients.[20] DMF-induced lymphopenia also did not predict clinical response in that study. A second retrospective chart review (n = 159) reported an incidence of DMF-associated lymphopenia (all grades) of 45% (41% grade 1/2, 4% grade 3), consistent with that observed in clinical trials; the mean ALC nadir (1,220 mm3) was within normal limits and occurred at a mean of 10.5 months.[21]

The underlying mechanism of DMF-induced lymphopenia is not well understood. DMF-dependent lymphocyte reduction has not been observed in any preclinical species, including chronic primate studies, indicating that this phenomenon is specific to human biology. This restriction to humans is a major hindrance to identification and characterization of the underlying molecular mechanisms of lymphopenia. Preliminary findings suggest that DMF affects several lymphocyte populations, most notably CD4+ and CD8+ cells, potentially eliciting a greater reduction in the latter.[22,23] However, despite these preliminary findings, the role of lymphocyte subsets in the action of DMF is unknown. Further research is ongoing to determine the link between DMF and lymphopenia, including its effect on lymphocyte subsets and the mechanisms responsible for these effects.

The results of this integrated analysis suggest the overall benefit–risk of DMF remains favorable. ALC profiles in DMF-treated patients with RRMS were generally stable throughout time. ALC <500 mm3 persisting for ≥6 months appeared to be an early predictor for the development of severe, prolonged lymphopenia in a small number of DMF-treated patients; however, there was no evidence suggesting an association between the rate of serious infections and incidence of lymphopenia. Comparable therapeutic efficacy in patients with and without lymphopenia suggests that lymphopenia is not a primary mechanism of action of DMF.