Extremely high titer of anti-human chimeric antibody following re-treatment with rituximab in a patient with active systemic lupus erythematosus

K. Saito, M. Nawata, S. Iwata, M. Tokunaga and Y. Tanaka

The First Department of Internal Medicine, University of Occupational and Environmental Health, School of Medicine, 1–1 Iseigaoka, Yahatanishi-ku, Kitakyushu 807-8555, Japan

Correspondence to: Y. Tanaka, The First Department of Internal Medicine, School of Medicine, University of Occupational and Environmental Health, 1–1 Iseigaoka, Yahatanishi, Kitakyushu 807-8555, Japan. E-mail: tanaka{at}med.uoeh-u.ac.jp

SIR, In a recent issue and elsewhere [1, 2] we reported five cases of life-threatening refractory systemic lupus erythematosus (SLE). In May 2004, one of the patients had a flare-up after 18 months’ remission and infusion of rituximab was employed again. However, it did not reduce disease activity because of the development of anti-human chimeric antibody (HACA) against rituximab. There is growing evidence for the efficacy of rituximab in refractory SLE [1–5]. However, prevention of production of HACA could become important for successful treatment of SLE with rituximab. Little is known about HACA in SLE at present. We present our case in detail and also describe the characteristic features associated with the development of HACA in autoimmune disease.

A 35-yr-old woman was diagnosed with SLE in 1991 and had been treated since then with repeated steroid pulses, intravenous cyclophosphamide infusion and cyclosporin A. However, her level of consciousness deteriorated to stupor because of involvement of the central nervous system (CNS), with an extremely high titer of anti-dsDNA antibody in June 2002 despite intensive conventional therapies. Finally, a decision was made to treat the patient with the anti-CD20 monoclonal antibody rituximab, which is known to be highly effective against in vivo B-cell depletion, based on the consideration that the serious status of CNS lupus was mainly due to autoantibodies from activated B lymphocytes. Just 2-weekly infusions of rituximab (375/m2 of body surface area) resulted in dramatic recovery from her catastrophic status, and the patient became fully alert with significant improvement of proteinuria being noted at day 30. In addition, anti-dsDNA antibody and complement levels returned to normal at day 90. It is noteworthy that the above improvement of clinical signs, symptoms and laboratory findings remained normal and the SLEDAI (SLE disease activity index) was less than 2 points even after tapering of betamethasone. The above treatment allowed the patient to go back to her job within 6 months of her life-threatening status.

After about an 18-month remission, SLE flare-up occurred in July 2004 with a rise in anti-dsDNA antibody titer, hypocomplementaemia, lymphocytopenia and high positivity of CD19 cells (21.7% of white blood cells) and CD20 (25.4%). After the infusion of rituximab, almost all CD20 molecules on B cells are consistently saturated with rituximab without any internalization. Therefore we also observed CD19, which is also exclusively expressed on B cells, to evaluate the depletion of B cells. Although 2-weekly infusion of 375/m2 of body surface area of rituximab was administered, it did not resolve disease activity and anti-dsDNA antibody progressively increased to 1244 IU/ml as shown in Fig. 1. The severity of proteinuria worsened to 2 g/day and more than 4% CD19-positive lymphocytes were still noted after rituximab infusion, while CD20-positive cells were detected only 10 days after the second infusion of rituximab. We considered the possible development of HACA against rituximab and examined the blood concentration of rituximab and HACA. The blood concentration of rituximab was lower than the detectable level (0.1 µg/ml) on 21, 28 and 35 days after initial infusion as well as just before the rituximab infusions. Furthermore, an extremely high titre of HACA against rituximab was detected even just after rituximab infusion.


Figure 1
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FIG. 1. Clinical course and response to treatment with rituximab. Rituximab was administrated at 375 mg/m2 body surface area twice weekly at the indicated hatched arrows, together with 1 mg of betamethasone. Top graph: anti-dsDNA antibody (open circles) and human anti-chimeric antibody (HACA; closed circles) examined by enzyme-linked immunosorbent assay. Bottom graph: expression of CD19 (open circles) and CD20 (closed circles) on peripheral lymphocytes as determined by flow cytometric assay.

 
Rituximab is a genetically engineered chimeric murine variable regions/human IgG1 anti-CD20 monoclonal antibody [6]. Recent studies have shown that rituximab is effective for SLE as well as haematological malignancies [1–5]. Regarding the mechanism of action of rituximab in SLE, we provided evidence that rituximab not only reduces B-cell numbers by in vivo deletion but down-regulates co-stimulatory molecules on B cells, resulting in disturbed T-cell activation [1]. Reduction in both the quantity and quality of B cells suggests that rituximab could improve the disease course in patients with refractory SLE.

Recent studies have reported detection of an autoantibody against rituximab following such treatment [5], and that the detection rate was significantly higher in SLE than in lymphoma patients [5, 7]. Specifically, high-titre HACAs were detected in six of 17 SLE patients [5] but in only one of 166 lymphoma patients [7]. These results suggest that human–mouse chimeric antibodies may be more immunogenic in autoimmune disease, especially in SLE, because of the highly activated B-lymphocyte status.

High titres of HACA in SLE were reported to be associated with disease activity, reduced B-cell depletion, low levels of rituximab and loss of efficacy of rituximab at 2 months after the initial infusion [5]. With regard to the present case, although HACA was not detected just before rituximab infusion, the titre at 3 weeks after the first infusion was one order higher than that reported in a previous paper [5]. Furthermore, serum rituximab could not be detected even at 14 days after the second infusion. These findings suggest prompt development of HACA on the background of extremely high disease activity (SLEDAI = 21 points), resulting in neutralization of rituximab and abolition of the therapeutic effect of rituximab in our patient.

The issue of drug-related antigenicity is not unique to rituximab. In a 26-week phase II study of infliximab, which is also a mouse–human chimeric antibody used to block tumour necrosis factor-{alpha}, 21% of rheumatoid arthritis patients treated with standard-dose infliximab (3 mg/kg) developed infliximab-specific HACA. Concomitant therapy with low-dose weekly methotrexate significantly diminished the incidence of HACA [8]. In a more recent cohort study of patients with Crohn's disease treated with serial infusions of infliximab, concomitant immunosuppressive therapy led to a lower incidence of HACA and a more prolonged duration of response. Pre-medication with intravenous hydrocortisone significantly reduced HACA levels but did not eliminate HACA production or infusion reactions [9]. In this regard, Sandborn [10] proposed that one optimization strategy is the use of immunosuppressive therapy for a clinically relevant period of time with azathioprine for 2–3 months or methotrexate for 1.5–2 months prior to initiating infliximab. However, our patient was also on azathioprine prior to the infusion of rituximab to prevent HACA production, but it resulted in severe granulocytopenia, necessitating discontinuation of the medication.

However, rituximab maintenance therapy is also reported to successfully control SLE. In one such study, two patients were treated with rituximab (375 mg/m2 x 4, repeated at weekly intervals) followed by maintenance therapy with rituximab 375 mg/m2 every 3 months. At 30 months after the commencement of rituximab therapy, both patients were free of symptoms [4]. Thus, repeated treatment with rituximab seems to induce persistent suppression of B-cell function and reduce the likelihood of development of HACA.

In conclusion, SLE is a representative autoimmune disease characterized by polyclonal activation of B lymphocytes and production of diverse autoantibodies. The frequency of HACA production among SLE patients appears to be high compared with patients with haematological malignancies or other autoimmune diseases. Since the development of HACA results in the negation of a strong weapon against refractory SLE, we must pay attention to the possible development of HACA, especially in the case of re-treatment with rituximab. Concomitant treatment with immunosuppressants or repeated maintenance therapy seems to be a useful strategy to prevent production of HACA. We have to establish a practical strategy to prevent the development of HACA in SLE.

The authors have declared no conflicts of interest.

References

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Accepted 14 July 2005





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