The Administrative Core will be responsible for providing scientific administration and coordination, fiscal oversight and administrative support for this PPG. The Administrative Core will coordinate PPG scientific group meetings among investigators at Harvard Medical School, and Massachusetts General Hospital. The Administrative Core will also design, implement and maintain a PPG website to facilitate effective communications among internal and external collaborators and the public. In addition, the Administrative Core will arrange an annual PPG meeting for investigators and the members of the Internal and External Adivisory Committees in Boston. Administratively, this Core will coordinate annual progress reports and renewal of sub-contract agreements, and will liaison between the grants offices of the various institutions and the Harvard Medical School Sponsored Programs Administration office. Ulrich H. von Andrian and Harvard Medical School, are responsible for this application and for the collaborative research activities described.