A raft of City firms have landed roles advising pharmaceutical giants Pfizer and GlaxoSmithKline (GSK) on a joint venture that will see the creation of a new HIV and AIDS treatment company.

Allen & Overy (A&O), Slaughter and May, Clifford Chance (CC), Jones Day and Morgan Lewis & Bockius have all won instructions on the deal, which will see the drug companies merge their treatment companies into one entity.

Slaughters was instructed by GSK as lead counsel, fielding a team led by M&A partners David Johnson and Simon Nicholls.

Johnson and Nicholls provided corporate advice, alongside intellectual property (IP) partner Susie Middlemiss, tax partner Steve Edge, competition partner Bertrand Louveaux, and employment partner Sandeep Maudgil.

A&O took the lead role advising Pfizer on the transaction, with a team led by corporate partners Ian Stanley and Anna Buscall. IP advice was given by partners Colleen Keck and Jim Ford.

The firm worked alongside Pfizer in-house counsel David Reid and Andrew Muratore on the deal.

Pfizer also turned to CC, Jones Day and Morgan Lewis for advice on the agreement, which will place 11 new AIDS and HIV treatment products on the market.

CC's European competition and regulation chief Tony Reeves advised Pfizer on UK and EU antitrust issues, while Morgan Lewis Washington antitrust partner Clay Everett provided US antitrust advice. Jones Day Washington partner Andrew Eisenberg advised on tax issues.

Under the agreement GSK will initially hold an 85% equity interest in the new company, while Pfizer will hold a 15%.

Stanley said: "This joint venture combines the strengths and abilities both companies have in the HIV area, and the new company will accomplish more than each company can on its own. This type of collaboration is an indicator of things to come and is a truly groundbreaking transaction."