{"data":{"id":"us/21-cfr-866.3336","jurisdiction":"us","citation":"21 CFR 866.3336","heading":"John Cunningham Virus serological reagents.","body":"(a) Identification. John Cunningham Virus serological reagents are devices that consist of antigens and antisera used in serological assays to identify antibodies to John Cunningham Virus in serum and plasma. The identification aids in the risk stratification for the development of progressive multifocal leukoencephalopathy in multiple sclerosis and Crohn's disease patients undergoing natalizumab therapy. These devices are for adjunctive use, in the context of other clinical risk factors for the development of progressive multifocal leukoencephalopathy.\n(b) Classification. Class II (special controls). The special control for this device is the FDA guideline document entitled “Class II Special Controls Guideline: John Cunningham Virus Serological Reagents.” For availability of the guideline document, see § 866.1(e).","path":["Title 21—Food and Drugs","CHAPTER I—FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES","SUBCHAPTER H—MEDICAL DEVICES","PART 866—IMMUNOLOGY AND MICROBIOLOGY DEVICES","Subpart D—Serological Reagents"],"source_url":"https://www.ecfr.gov/api/versioner/v1/full/2026-08-25/title-21.xml","current_through":"2026-08-25","vintage":"","retrieved_at":"2026-08-27T02:24:47Z","sha256":"e5756429a0625777a04cb6c876f1381ce8d3d80abe365ac5497fe8b776b972f6","source_id":"us-cfr","stale":true,"prev":"us/21-cfr-866.3332","next":"us/21-cfr-866.3340"},"notice":"GroundRules: Original legal text. Not legal advice."}