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Walker BD, Flexner C, Birch-Limberger K, Fisher L, Paradis TJ, Aldovini A, Young R, Moss B, Schooley RT.Walker BD, et al.Proc Natl Acad Sci U S A. 1989 Dec;86(23):9514-8. doi: 10.1073/pnas.86.23.9514.Proc Natl Acad Sci U S A. 1989.PMID: 2480604Free PMC article.