B-Lymphocyte Depletion in Myalgic Encephalopathy/ Chronic Fatigue Syndrome. An Open-Label Phase II Study with Rituximab Maintenance Treatment

Abstract

Background: Myalgic Encephalopathy/Chronic Fatigue Syndrome (ME/CFS) is a disease of unknown etiology. We previously reported a pilot case series followed by a small, randomized, placebo-controlled phase II study, suggesting that B-cell depletion using the monoclonal anti-CD20 antibody rituximab can yield clinical benefit in ME/CFS.

Methods: In this single-center, open-label, one-armed phase II study (NCT01156909), 29 patients were included for treatment with rituximab (500 mg/m2) two infusions two weeks apart, followed by maintenance rituximab infusions after 3, 6, 10 and 15 months, and with follow-up for 36 months.

Findings: Major or moderate responses, predefined as lasting improvements in self-reported Fatigue score, were detected in 18 out of 29 patients (intention to treat). Clinically significant responses were seen in 18 out of 28 patients (64%) receiving rituximab maintenance treatment. For these 18 patients, the mean response durations within the 156 weeks study period were 105 weeks in 14 major responders, and 69 weeks in four moderate responders. At end of follow-up (36 months), 11 out of 18 responding patients were still in ongoing clinical remission. For major responders, the mean lag time from first rituximab infusion until start of clinical response was 23 weeks (range 8-66). Among the nine patients from the placebo group in the previous randomized study with no significant improvement during 12 months follow-up after saline infusions, six achieved a clinical response before 12 months after rituximab maintenance infusions in the present study. Two patients had an allergic reaction to rituximab and two had an episode of uncomplicated late-onset neutropenia. Eight patients experienced one or more transient symptom flares after rituximab infusions. There was no unexpected toxicity.

Conclusion: In a subgroup of ME/CFS patients, prolonged B-cell depletion with rituximab maintenance infusions was associated with sustained clinical responses. The observed patterns of delayed responses and relapse after B-cell depletion and regeneration, a three times higher disease prevalence in women than in men, and a previously demonstrated increase in B-cell lymphoma risk for elderly ME/CFS patients, suggest that ME/CFS may be a variant of an autoimmune disease.

Trial registration: ClinicalTrials.gov NCT01156909.

Fig 1. Consort 2010 Flow Diagram for the KTS-2-2010 study.

Consort Flow Diagram for the KTS-2-2010 study, with enrollment, allocation to induction and maintenance rituximab treatment, and follow-up showing number of patients who withdrew from study before 36 months.

Fig 2. Self-reported Fatigue scores for 28 patients receiving rituximab induction and maintenance treatment.

Fatigue score was recorded every second week, always compared to baseline, as the mean of four fatigue-related symptoms (scale 0–6; 3: no change from baseline; 4, 5, 6: slight, moderate, major improvement, respectively; 2, 1, 0: slight, moderate, major worsening, respectively). Panel A shows Fatigue scores for the time intervals 0–6, 6–12, 12–18, 18–24, 24–30 and 30–36 months, with means and 95% CI for each time interval. In panel B the corresponding Fatigue scores are shown for each time interval during follow-up, divided between 18 patients with clinically significant responses, and 10 patients with either marginal response (n = 1) or no response (n = 9). Out of 10 patients with no clinically significant response, one patient withdrew from study after 12 months, and four patients after 24–26 months follow-up. Out of 18 patients with clinically significant responses, one withdrew from study after 24 months due to a diagnosis of T2N0 breast cancer, two moderate responders withdrew after 25 and 32 months, respectively, and one major responder withdrew after 32 months.

Fig 3. Clinical response durations after rituximab maintenance therapy, within 36 months follow-up.

In panel A, response durations within the three years (156 weeks) follow-up are shown, for 14 major responders and four moderate responders. In panel B, time points for start of clinical responses are shown, for major and moderate responders. In both panels A and B, the 11 red dots denote patients with still ongoing clinical response at 156 weeks (end of study), while the 7 black squares denote patients experiencing partial or full relapse during the 36 months follow-up period. The overall response criterion was a Fatigue score ≥ 4.5 for a minimum of six consecutive weeks, which must include at least one recording of Fatigue score > 5.0 during the response period. Single response periods and the sum of response periods during follow-up were recorded as response duration.

Fig 4. Historic comparison of Fatigue scores for nine patients given placebo in KTS-1-2008, and rituximab maintenance in KTS-2-2010.

Nine patients from the placebo group in the previous randomized KTS-1-2008 study were included in the present KTS-2-2010 study with rituximab induction and maintenance treatment. The mean Fatigue scores for consecutive 3-months intervals, until 12 months follow-up, were compared using General Linear Model (GLM) for repeated measures. Four time intervals with mean Fatigue scores in each were included in the comparison. Main effect for the interaction between time and intervention group (rituximab maintenance versus the patient’s own “historic” placebo) was assessed.

Fig 5. SF-36 questionnaire, raw scores.

SF-36 (Norwegian ver. 1.2) forms were recorded at baseline and at 3, 6, 10, 15, 20, 24, 30 and 36 months. SF-36 raw scores (mean, SEM) are shown for 27 patients, for the subdimensions Physical function (panel A), Bodily pain (panel C), Vitality (panel E), Social function (panel G) and Mental health (panel I). In panels B, D, F, H and J are shown the corresponding SF-36 raw scores separately for 13 major responders, four moderate responders, and 10 patients with no clinical significant response (one marginal responder and nine non-responders). One pilot patient (major responder, withdrew from study after 32 months) did not fill in SF-36 forms. One included patient did not receive induction rituximab infusions due to an allergic reaction to the first infusion, and did not fill in SF-36 forms. One major responder was withdrawn from study after 24 months due to being diagnosed with a T2N0 breast cancer. Out of four moderate responders, one withdrew from the study after 25 months, and one after 32 months. Out of 10 patients with no clinically significant response one withdrew from study after 12 months, and four patients after approximately 24 months follow-up.

Fig 6. Function level and “SF-36mean5”.

Mean values of SF-36 raw scores for the five subdimensions Physical function (PF), Bodily pain (BP), Vitality (V), Social function (SF) and General health (GH) are shown (denoted “SF-36mean5”, scale 0–100), at baseline and at 3, 6, 10, 15, 20, 24, 30 and 36 months follow-up. SF-36mean5 scores for each time point during follow-up were compared to baseline scores. P-values were calculated using Repeated Measures One-way ANOVA, with Dunnett’s multiple comparison adjustments, and are indicated at the top of each panel. ns: not significant; **: p<0.01; ***: p<0.001; ****: p<0.0001. To be able to analyze for differences at each time point relative to baseline, a missing value at a time point for a patient was replaced with value interpolated between the previous and next values during follow-up for that patient (but not replaced in the plot). Panel A shows “SF-36mean5” (raw) scores for 27 patients in this study. One pilot patient did not fill in SF-36 forms. In addition 22/243 (9.1%) data were missing, including for patients out of study before end of follow-up, as explained in M&M. Panel C shows “SF-36mean5” scores for 17 patients with clinically significant response (data from pilot 2, and in addition 10/153 (6.5%) data were missing). Panel E shows “SF-36mean5” scores for 10 patients with no clinically significant response during follow-up (12/90 (13.3%) data were missing). Panels B, D and F show self-reported Function levels (according to a form with examples, see S3 Fig), at baseline and at 15, 24 and 36 months. In panel B for 28 patients included in the KTS-2-2010 study, in panel D for 18 patients with clinically significant responses, and in panel F for 10 patients without clinically significant responses. In panels B and D, two moderate responders registered their Function level at 32 and 33 months (instead of 36 months), respectively. Panel G shows a correlation plot between “SF-36mean5” raw scores and self-reported Function levels (both with scale 0–100), with pooled data from baseline and at 15, 24 and 36 months follow-up. Panel H shows a Bland-Altman plot for difference (“SF-36mean5”—Function level) versus average.

Fig 7. CD19+ B-lymphocytes in peripheral blood during follow-up.

B-lymphocyte numbers from immunophenotyping of peripheral blood during follow-up are shown, at baseline and 3, 6, 12, 15, 20, 24, 30 and 36 months follow-up. The red dots represent mean value at each time point, for patients with either major or moderate clinical response (n = 16). The blue squares denote the mean values for patients with no significant response (n = 10). The value zero for B-lymphocytes in peripheral blood was substituted by 0.1 (to enable plotting on the log scale). B-lymphocyte counts x 10⁶/L (normal range 110–449). The error bars denote mean ± 95% CI. B-cell data during follow-up were not available for the two pilot patients (both major responders). According to an amendment, seven patients received further rituximab infusions in addition to the six infusions stated in the initial protocol. Two major responders received five and four rituximab additional rituximab infusions, respectively. Four moderate responders received five, four, three and three additional rituximab infusions. One non-responder received two additional rituximab infusions.