Monoclonal Antibodies in the Treatment of Non-Hodgkin’s Lymphoma

Antibody-based therapeutic approaches have had a significant impact in the treatment of non-Hodgkin’s lymphoma (NHL). Rituximab’s development as an anti-CD20 antibody heralded a new era in treatment approaches for NHL. While rituximab was first shown to be effective in the treatment of relapsed follicular lymphoma, it is now standard monotherapy for front-line treatment of follicular lymphoma, and is also used in conjunction with chemotherapy for other indolent, intermediate and aggressive B-cell lymphomas. The development of rituximab has led to intense interest in this type of therapeutic approach and to development and approval of the radioimmunoconjugates of rituximab, ⁹⁰Y-ibritumomab tiuxetan and ¹³¹I-tositumomab, which have added to the repertoire of treatments for relapsed follicular lymphoma and increased interest in developing other conjugated antibodies. Since rituximab is a chimeric antibody, there is a need to develop fully humanised antibodies, such as IMMU-106 (hA20), in order to minimise infusion reactions and eliminate the development of human antibodies against the drug.

Further clinical evaluation of antibodies has been based largely on our knowledge of antigen expression on the surface of lymphoma cells and has led to the development of antibodies against CD22 (unconjugated epratuzumab and calicheamicin conjugated CMC-544 [inotuzumab ozogamicin]), CD80 (galiximab), CD52 (alemtuzumab), CD2 (MEDI-507 [siplizumab]), CD30 (SGN-30 and MDX-060 [iratumumab]), and CD40 (SGN-40). Furthermore, the VEGF (vascular endothelial growth factor) inhibitor bevacizumab, which was first approved for the treatment of colon cancer is currently under investigation in NHL, and agonists rather than antibodies to TRAIL (tumour necrosis factor-related apoptosis-inducing ligand) [rApo2L/TRAIL, HGS-ETRl{mapatumumab}, HGS-ETR2] are currently being investigated as treatments for both advanced solid tumours and NHL. Knowledge of the ability of cancer cells to become resistant to a targeted therapy by activating an alternative pathway to evade apoptosis has driven studies that combine antibodies such as epratuzumab plus rituximab (ER) or ER plus chemotherapy with CHOP (cyclophosphamide, doxorubicin, vincristine, and prednisone) [ER-CHOP], inotuzumab ozogamicin plus rituximab, alemtuzumab plus CHOP (CHOP-C), bevacizumab plus rituximab, and now the combination of rApo2L/TRAIL plus rituximab.

As a result of the expansion of research in this area, several treatment-specific adverse effects have been noted, including infusion-related reactions for rituximab, myelosuppression secondary to 90Y-ibritumomab tiuxetan and ¹³¹I-tositumomab, and immunosuppression leading to infectious complications for alemtuzumab. Also, soluble forms of the antigens (sCD30) are now being investigated as potential mechanisms of resistance to antibody treatments by binding the antibody before the drug can bind to the lymphoma cell. In addition, it has also become apparent that these antibodies often have a dose-dependent half-life (rituximab) or long half-lives of up to 2–3 weeks (epratuzumab and galiximab) with a consequent delay to a response, thus influencing how long we should wait for a response before declaring an antibody to be ineffective.

Antibody-based therapeutic approaches have already had a profound impact on the treatment of NHL, and it is almost certain that, as their clinical development progresses, we will continue to refine the optimum methods of incorporating these drugs in NHL treatment in order to offer our patients the best clinical benefits.