is also home to a secondary office of Google's AdWords program—the company's primary revenue stream. The recent surge in companies operating in Ann Arbor has led to a decrease in its office and flex space vacancy rates. As of December 31, 2012, the total market vacancy rate for office and flex space is 11.80%, a 1.40% decrease in vacancy from one year previous, and the lowest overall vacancy level since 2003. The office vacancy rate decreased to 10.65% in 2012 from 12.08% in 2011, while the flex vacancy rate decreased slightly more, with a drop from 16.50% to 15.02%. As of 2022, Ann Arbor is home to more than twenty video game and XR studios of varying sizes. The city plays host to a regional chapter of the International Game Developers Association (IGDA) which hosts monthly meetups, presentations, and educational events. Pfizer, once the city's second-largest employer, operated a large pharmaceutical research facility on the northeast side of Ann Arbor. On January 22, 2007, Pfizer announced it would close operations in Ann Arbor by the end of 2008. The facility was previously operated by Warner-Lambert and, before that, Parke-Davis. In December 2008, the University of Michigan Board of Regents approved the purchase of the facilities, and the university anticipates hiring 2,000 researchers and staff during the next 10 years. It is now known as North Campus Research Complex. The city is the home of other research and engineering centers, including those of Lotus Engineering, General Dynamics and the National Oceanic and Atmospheric Administration (NOAA). Other research centers sited in the city are the United States Environmental Protection Agency's National Vehicle and Fuel Emissions Laboratory and the Toyota Technical Center. The city is also home to National Sanitation Foundation International (NSF International), the nonprofit non-governmental organization that develops generally accepted standards for a variety of public health related industries and subject areas. Borders Books, started in Ann Arbor, was opened by brothers Tom and Louis Borders in 1971 with a stock of used books. The Borders chain was based in the city, as was its flagship store until it closed in September 2011. Domino's Pizza's headquarters is near Ann Arbor on Domino's Farms, a Frank Lloyd Wright-inspired complex just northeast of the city. Another Ann Arbor-based company is Zingerman's Delicatessen, which serves sandwiches and has developed businesses under a variety of brand names. Zingerman's has grown into a family of companies