Ofatumumab in the treatment of low-grade non-Hodgkin's lymphomas and chronic lymphocytic leukemia

Complement System: a Neglected Pathway in Immunotherapy

Approved for the treatment of autoimmune diseases, hematological malignancies, and solid cancers, several monoclonal antibodies (mAb) make use of complement in their mechanism of action. Such an assessment is based on comprehensive investigations that used mouse models, in vitro studies, and analyses from patients at initiation (basal level to highlight deficiencies) and after treatment initiation (mAb impact on complement), which have further provided key insights into the importance of the complement activation and/or complement deficiencies in mAb activity. Accordingly, new approaches can now be developed with the final objective of increasing the clinical efficacy of mAb. These improvements include (i) the concurrent administration of fresh frozen plasma during mAb therapy; (ii) mAb modifications such as immunoglobulin G subclass switching, Fc mutation, or IgG hexamerization to improve the fixation and activation of C1q; (iii) optimization of the target recognition to induce a higher complement-dependent cytotoxicity (CDC) and/or complement-dependant cellular cytotoxicity (CDCC); and (iv) the control of soluble and cellular complement inhibitors.

Clinical aspects of malt lymphomas

Extranodal marginal zone lymphoma of the mucosa-associated lymphoid tissue (MALT) is an indolent lymphoma arising in extranodal sites. Several infectious agents and autoimmune disorders have been implicated in its pathogenesis. The stomach represents the most common and best-studied organ involved by MALT lymphoma and its development is strongly associated with Helicobacter pylori (Hp) infection. MALT lymphomas are characterized by an indolent clinical course and excellent survival in most cases, independently of the treatment delivered. Recent progress in the knowledge of the etiology and the cellular and molecular pathological events related to MALT lymphomas allowed us to improve our clinical understanding of this disease entity and to better define treatment strategies.

Ofatumumab, the first human anti-CD20 monoclonal antibody for the treatment of B cell hematologic malignancies

Ofatumumab is the first human anti-CD20 monoclonal antibody to be approved for patients in the United States and the European Union. Ofatumumab received accelerated approval from the U.S. Food and Drug Administration in October 2009 and was granted a conditional marketing authorization by the European Medicines Agency in April 2010 for the treatment of patients with chronic lymphocytic leukemia (CLL) refractory to fludarabine and alemtuzumab, based on interim results of a pivotal phase 2 trial. Preliminary positive results for ofatumumab in combination with chemotherapy in patients with CLL are currently being confirmed in larger randomized trials in both the frontline setting and the relapsed/refractory setting. Ofatumumab has also shown potential in treating B cell non-Hodgkin's lymphoma, such as follicular lymphoma (FL), diffuse large B cell lymphoma (DLBCL), and Waldenström's macroglobulinemia. Additional trials are ongoing to confirm activity of ofatumumab as monotherapy and in combination with chemotherapy in patients with FL or DLBCL.

Single-agent rituximab in treatment-refractory or poor prognosis patients with chronic lymphocytic leukemia

OBJECTIVE

Rituximab in combination with fludarabine and cyclophosphamide has significantly improved outcomes for patients with chronic lymphocytic leukemia (CLL) and an improvement in overall survival has recently been shown for the first time in the history of CLL treatment. However, the chemotherapy portion of this regimen may be unsuitable for elderly patients or those with significant comorbidities. We investigated the safety and tolerability of single-agent rituximab in 23 consecutive patients presenting with CLL at a single institution.

RESEARCH DESIGN AND METHODS

Patients received eight cycles of weekly rituximab (375 mg/m(2) initially). Patients progressing on rituximab treatment could receive up to five further courses of single-agent rituximab in escalating doses up to 3 gm/m(2) per dose. Previously untreated and previously treated patients, including those refractory to fludarabine, were eligible for the study.

RESULTS

Single-agent rituximab was efficacious, even in patients with treatment-refractory or poor-prognosis CLL. The overall response rate was 90.9% with a CR rate of 63.6%. The median PFS was 28.5 months, and median duration of response was 26 months. Responses were seen regardless of prior treatment including in patients refractory to fludarabine. Especially encouraging results were seen in patients receiving rituximab maintenance therapy who had a median duration of response substantially longer than those who did not receive maintenance (35 months vs. 14 months, respectively).

CONCLUSIONS

Rituximab was well tolerated with no unexpected adverse events even at the highest dose. These results indicate that single-agent rituximab is effective and has a place in the treatment of CLL.