Dr Klein, a New Orleans native, received much of his education in Texas attending the University of Texas at Austin for undergraduate education and received his medical degree from the University of Texas Medical Branch at Galveston, the original medical campus in the University of Texas System. He served a residency in Internal Medicine at Kansas University Medical Center and completed a fellowship in Adult Nephrology at the University of Louisville and subsequently earned a PhD in Microbiology and Immunology from the University of Louisville. He is Professor of Medicine. He currently holds the James Graham Brown Foundation Endowed Chair in Proteomics at the University of Louisville School of Medicine and serves as Interim Executive Vice-President for Research and Innovation. His laboratory has received federal research grant funding from the National Institutes of Health, Veterans Administration, or Department of Energy continuously for more than 35 years. In 2013 he was appointed the Vice-Dean for Research at the University of Louisville School of Medicine. He has authored over 290 peer-reviewed papers and is known in the kidney research community for introducing proteomic analysis to kidney research and subsequently as a co-discoverer of several target antigens in autoimmune kidney disease including the PLA₂ receptor in primary membranous nephropathy.