NEW YORK (AP) — GlaxoSmithKline PLC and Nabi Biopharmaceuticals said Monday they will work together to develop vaccines to help smokers give up the habit, in a deal that could be worth more than $500 million. Nabi is developing a vaccine called NicVAX, which is intended to train the immune system to make antibodies that will attach themselves to nicotine. With the antibodies stuck to them, the nicotine molecules will not be able to reach the brain. The companies say that will block the pleasurable effects of nicotine. In the deal, Nabi will get $40 million upfront and complete testing of NicVAX. GlaxoSmithKline, which is based in London, will also start developing a second-generation version of the vaccine. Nabi, of Rockville, Md., is running one late-stage clinical study of NicVAX and plans to start another one. If testing is successful, GlaxoSmithKline will be responsible for getting the vaccine approved by regulators, and will market the drug if it is approved. Nabi could receive milestone payments for successful testing, regulatory approval and sales targets, as well as royalties of more than 10 percent on sales. The companies said those payments could reach more than $500 million. The deal is expected to close in the first quarter of 2010. The companies said there are about 1.2 billion smokers in the world, and smoking causes 5.4 million deaths per year.