Immune Reconstitution/Immunocompetence in Recipients of Kidney Plus Hematopoietic Stem/Facilitating Cell Transplants Joseph R. Leventhal, 1 Mary J. Elliott, 2 Esma S. Yolcu, 2 Larry D. Bozulic, 3 David J. Tollerud, 2,3 James M. Mathew, 1 Iwona Konieczna, 1 Michael G. Ison, 1 John Galvin, 1 Jayesh Mehta, 1 Mark D. Badder, 2 Michael M. I. Abecassis, 1 Joshua Miller, 1 Lorenzo Gallon, 1 and Suzanne T. Ildstad 2,3 Nineteen subjects have more than 18 months' follow-up in a phase IIb tolerance protocol in HLA–mismatched re- cipients of living donor kidney plus facilitating cell enriched hematopoietic stem cell allografts (FCRx). Reduced in- tensity conditioning preceded a kidney allograft, followed the next day by FCRx. Twelve have achieved stable donor chimerism and have been successfully taken off immunosuppression (IS). We prospectively evaluated im- mune reconstitution and immunocompetence. Return of CD4 + and CD8 + T central and effector memory cell pop- ulations was rapid. T-cell receptor (TCR) Excision Circle analysis showed a significant proportion of chimeric cells produced were being produced de novo. The TCR repertoires posttransplant in chimeric subjects were nearly as diverse as pretransplant donors and recipients, and were comparable to subjects with transient chimerism who underwent autologous reconstitution. Subjects with persistent chimerism developed few serious infections when off IS. The majority of infectious complications occurred while subjects were still on conventional IS. BK viruria and viremia resolved after cessation of IS and no tissue-invasive cytomegalovirus infections occurred. Notably, al- though 2 of 4 transiently or nonchimeric subjects experienced recurrence of their underlying autoimmune disor- ders, none of the chimeric subjects have, suggesting that self-tolerance is induced in addition to tolerance to alloantigen. No persistently chimeric subject has developed donor-specific antibody, and renal function has remained within normal limits. Patients were successfully vaccinated per The American Society for Blood and Mar- row Transplantation guidelines without loss of chimerism or rejection. Memory for hepatitis vaccination persisted after transplantation. Chimeric subjects generated immune responses to pneumococcal vaccine. These data sug- gest that immune reconstitution and immunocompetence are maintained in persistently chimeric subjects. (Transplantation 2015;99: 288–298) S olid organ transplant recipients require life-long immu- nosuppressive agents to maintain graft acceptance. This is associated with a number of toxicities, including renal dys- function, metabolic abnormalities, opportunistic infection, and malignancies. 1-3 Approaches to induce tolerance remain a major focus of research. We recently reported a reduced-intensity nonmyeloablative conditioning approach to establish high levels of donor chime- rism without graft-versus-host disease (GVHD) or engraftment Received 14 August 2014. Revision requested 13 November 2014. Accepted 14 November 2014. 1 Comprehensive Transplant Center, Northwestern Memorial Hospital, Chicago, IL. 2 Institute for Cellular Therapeutics, University of Louisville, Louisville, KY. 3 Regenerex, LLC, Louisville, KY. S.T.I. has equity interest in and is the CEO of Regenerex, LLC, a start-up biotech company. D.J.T. is an officer of Regenerex, LLC. L.D.B. and M.D.B. are employees of Regenerex, LLC. In September 2013, the company entered into a global licensing and research collaboration agreement with Novartis for the development of FCRx. J. R.L. receives grant support from Regenerex, LLC and Novartis. He is on an advisory board of Astellas. M.G.I. received grant or research support, paid to Northwestern University Feinberg School of Medicine, from Cellex, Crucell, GlaxoSmithKlein and NexBio; he is a paid consultant to Genentech/Roche, Crucell, Alios and Abbott; and he is a paid member of a Data and Safety Monitor Board for Biota and NexBio. All other authors have no conflict of interest to declare.Trial registry: FDA-IDE 13947-ClinicalTrials.gov Identifier: NCT00497926J.R.L. participated in man- uscript preparation, data analysis, and clinical conduct of study. M.J.E. participated in immunophenotyping assays and data analyses. E.S.Y. partic- ipated in review and analysis of immunophenotyping, data analysis, and man- uscript preparation. L.D.B. participated in data analysis and preparation of FCRx. D.J.T. participated in data analysis and manuscript preparation. J.M. M. participated in data analysis and manuscript preparation. I.K. participated in TREC analysis and data interpretation. M.G.I. participated in infectious dis- ease testing and management. J.G. participated in clinical trial patient man- agement. J.M. participated in clinical trial patient management. M.D.B. participated in immunophenotypingstudies and analyses. M.M.I.A. participated in study design and data analysis. J.M. participated in study design and data analysis. L.G. participated in con- duct of clinical trial and review of patient data. S.T.I. participated in study design, manuscript preparation, and data analysis. Correspondence: Suzanne T. Ildstad, MD, 570 South Preston St, Suite 404, Louisville, KY 40202-1760. (suzanne.ildstad@regenerex.com) Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved. ISSN: 0041-1337/15/9902-288 DOI: 10.1097/TP.0000000000000605 Original Clinical Science 288 www.transplantjournal.com Transplantation ■ February 2015 ■ Volume 99 ■ Number 2 Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.