Celgene is one of two companies discussing whether to bid for Human Genome Sciences, which seeks an alternative to a hostile offer by British drugmaker GlaxoSmithKline, a source familiar with the situation said.

Conventional wisdom among investors has been that Human Genome was unlikely to find another bidder, as Glaxo reaps 50% of the profit from the lupus drug Benlysta, to which Glaxo and Human Genome share the rights.

Human Genome has so far refused Glaxo's $13 per share, or $2.6 billion offer as too low and Wall Street analysts (surveyed by Reuters in May) had predicted that bid would need to be raised to about $15 per share to succeed.

According to a source familiar with the situation, two companies are in discussions with Human Genome, aside from Glaxo, with Celgene probably in the pole position should it decide to bid.

The source, who spoke on condition of anonymity because the person was not authorized to speak to the media, did not identify the second bidder but said it would most likely be a merger-of-equals scenario. The deadline for bids is July 16.

A Celgene spokesman declined to comment on the company's acquisition-related activity. Representatives for Human Genome were not immediately available for comment.

Celgene, based in Summit, New Jersey, is one of the world's biggest biotechnology companies and makes the blood cancer drugs Revlimid and Vidaza. It is also developing a pipeline of drugs to treat autoimmune conditions such as rheumatoid arthritis and lupus, a disease in which the immune system attacks the patient's own body.

Last year Human Genome and Glaxo won approval for Benlysta, the first new treatment for lupus in 50 years. But the drug's launch proved disappointing and Human Genome's shares fell from a high above $25 to a low of $6.51 in December. Glaxo made its offer a few months later, prompting Human Genome to launch an auction with the help of Credit Suisse and Goldman Sachs.

Board fight looms

Glaxo, in turn, is considering whether to seek to replace the entire board of Human Genome, and has lined up candidates who have agreed to be nominees, once the outcome of the auction process is known, a separate source familiar with the situation told Reuters earlier this week.

The takeover battle marks a turning point in the long-standing partnership between the two drugmakers. Glaxo and Human Genome are also developing a heart disease drug, darapladib, that, if successful, could generate more than $1 billion in sales.

Celgene has long been one of biotechnology's most reliable growth stocks, with a market value of nearly $29 billion, largely built on the success of its multiple myeloma treatments Thalomid and Revlimid.

While there is no certainty Celgene will make a bid for Human Genome, Benlysta would appear to fit into its wheelhouse. Celgene has two drugs in mid-stage trials for two types of lupus that mainly affect the skin.

About 10% of people with cutaneous lupus later develop systemic lupus, for which Benlysta is approved. Currently, cutaneous lupus is treated with a variety of ointments and, increasingly, with Celgene's own drug Thalomid.