Two useful guidance documents were recently issued by FDA: 1) a final ICH guidance on Development and Manufacture of Drug Substances: http://www.fda.gov/downloads/Drugs/GuidanceComplianceRegulatoryInformation/Guidances/UCM261078.pdf and 2) a draft FDA guidance on Immunogencity Assessment for Therapeutic Protein Products: http://www.fda.gov/downloads/Drugs/GuidanceComplianceRegulatoryInformation/Guidances/UCM338856.pdf