Affiliated Computer Services Inc. (ACS) has leased 22,552 square feet at HarborSouth Tower at 100 Hancock St. in Quincy.

ACS, which offers business process outsourcing support in finance, human resources, information technology, transaction processing and customer care, will occupy space on the 10th floor of the building.

The lease was signed at the end of the fourth quarter and marks the largest new lease of 2009 in the Braintree/Quincy submarket, according to a statement.

ACS joins MFS Investment Management, which signed a 41,480-square-foot lease at the property in March 2008, as the second major tenant to relocate to HarborSouth Tower from Boston in the past two years. ACS will begin its occupancy in the spring.

"Although these are challenging times in the leasing business, when a requirement presents itself, HarborSouth Tower distinguishes itself as superior product that meets the needs of sophisticated tenants like ACS and MFS," said Tod Brainard, principal at Griffith Properties LLC.

The CBRE team of Nat Kessler, first vice president, and Ogden White, senior vice president/partner, represented Griffith Properties in the transaction. ACS was represented by Jones Lang LaSalles’s Jason Cameron, assistant vice president, and Sean Lynch, associate vice president, in conjunction with the firm’s Texas office.