The results, corresponding to mid-stage Phase II clinical trials, were presented at last week's Annual European Congress of Rheumatology in Barcelona and reported positively on the efficacy and safety of the drug in RA.
The experimental drug is also in Phase I/II trials as an agent for lymphatic cancer (LC), follicular non-Hodgkins's lymphoma (NHL) and chronic lymphocytic leukaemia (CLL), the most common form of adult leukaemia.
The drug is a fully human monoclonal antibody (mAb) targeted at the CD20 molecule in the membrane of B-cells, which are the immunological cells most commonly involved in autoimmune diseases and certain types of lymphatic cancer.
As such it is a direct competitor to Roche's MabThera/Rituxan (rituximab), which made sales of $3.9bn (€2.9bn) in 2006. However, according to analysts, ofatumumab's results do not show any improvement in efficacy compared to Roche's drug.
MabThera has been in the EU market since 2004 and in the US since 2002 as a single-agent treatment for relapsed or refractory indolent NHL, and also for the treatment of aggressive NHL in combination with chemotherapy.
In 2006, Roche also received marketing approval in the EU and in the US for indications in arthritis.
Genmab and GSK hope that their experimental drug will make the difference because ofatumumab, as a fully humanised mAb, is less likely to cause side effects than Roche's chimeric mouse-human mAb, and also be less likely to stimulate an immune response that can limit its efficacy.
Genmab said that the drug is due to initiate Phase III trials in RA by the end of 2007, which will shed light on the safety and efficacy profile of the new drug.
In the oncology setting, the development of ofatumumab was described at a GSK oncology seminar yesterday. It was announced that Phase II studies of ofatumumab in previously untreated follicular NHL and refractory CLL patients have been recently initiated.
GSK and Genmab expect to initiate randomised Phase III studies of ofatumumab in CCL and follicular NHL in the first half of 2008. Under these circumstances, the drug could potentially enter the market in 2008 first for the treatment of CLL and subsequently for rituximab-refractory follicular NHL.
"We are pleased to begin this study of ofatumumab for front line treatment of follicular NHL," said Lisa Drakeman, chief executive officer of Genmab, "which we hope may be more effective than currently available treatment."
Genmab also plans to expand the ofatumumab program into new cancer indications with clinical studies in diffuse large B-cell lymphoma (DLBCL) by the end of 2007.
In the autoimmune disease setting, Genmab also intends to expand the development program with initiation of a Phase II study in relapsing remitting multiple sclerosis (RRMS) in the first quarter of 2008.
Genmab has said in the past that the drug could generate well over $2bn in annual sales in a variety of indications. The global mAbs market is expected to triple in size to $30bn by 2010.
GSK, within its expansion of the company's biopharmaceutical pipeline, bought global rights to ofatumumab in deal worth up to $2.1bn last December.
Analysts have said they doubt rheumatoid arthritis will become a major market for ofatumumab, they rather see its main potential in erythematosus Hodgkin's lymphoma and other autoimmune diseases such as lupus.
