Abstract: We would like to thank Drs Northrup and Goldstein [1Northrup W.F. Goldstein S. Potential benefits of antigen reduction in heart valve allografts (letter).Ann Thorac Surg. 2010; 90: 357Abstract Full Text Full Text PDF PubMed Scopus (1) Google Scholar] for their interest in our work [2Feingold B. Wearden P.D. Morell V.O. Galvis D. Galambos C. Expression of A and B blood group antigens on cryopreserved homografts.Ann Thorac Surg. 2009; 87: 211-214Abstract Full Text Full Text PDF PubMed Scopus (12) Google Scholar], and we appreciate the editor for giving us the opportunity to reply. We disagree with Drs Northrup and Goldstein's assertion that our findings of A and B blood group antigen expression on human cryopreserved pulmonary homografts simply reaffirm those of others. The cited works of Kadner and colleagues [3Kadner A. Chen R.H. Mitchell R.N. Adams D.H. Lack of ABH-antigen expression on human cardiac valves.J Heart Valve Dis. 2000; 9: 512-516PubMed Google Scholar, 4Kadner A. Chen R.H. Mitchell R.N. Adams D.H. Homograft crossmatching is unnecessary due to the absence of blood group antigens.Ann Thorac Surg. 2001; 71: S349-S352Abstract Full Text Full Text PDF PubMed Scopus (31) Google Scholar] reported expression of blood group antigens in the context of a preserved microvasculature endothelium on freshly explanted “myocardial tissue” and cryopreserved “septal myocardial tissue.” They also reported intact endothelium without blood group antigen expression on freshly harvested human cardiac valve leaflets and no blood group antigen expression nor intact endothelium on cryopreserved valve leaflets. In addition, we found no report in the literature detailing the expression of blood group antigens on homograft conduit (vessel) microvasculature. Thus, our findings of blood group A and B antigen expression and preservation of cryopreserved homograft conduit microvasculature (vasa vasorum) endothelium are indeed unique. We do agree with Dr Jacobs, who wrote the invited comment on our article [5Jacobs M.L. Invited commentary.Ann Thorac Surg. 2009; 87: 214-215Abstract Full Text Full Text PDF PubMed Scopus (2) Google Scholar], and with Drs Northrup and Goldstein that an optimal tissue-based implant would lack immunogenicity. Putting aside the issue of whether an immune response to blood group and/or major histocompatibility complex antigens expressed on the homograft microvasculature affects homograft longevity, a significant proportion of children with homograft exposure ultimately require heart transplantation. Many are highly allosensitized, which poses a significant barrier to transplantation [6Feingold B. Olesnevich P.J. Girnita A. et al.Survival in allosensitized children after listing for cardiac transplantation.J Heart Lung Transplant. 2007; 26: 565-571Abstract Full Text Full Text PDF PubMed Scopus (72) Google Scholar, 7Holt D.B. Lublin D.M. Phelan D.L. et al.Mortality and morbidity in pre-sensitized pediatric heart transplant recipients with a positive donor crossmatch utilizing perioperative plasmapheresis and cytolytic therapy.J Heart Lung Transplant. 2007; 26: 876-882Abstract Full Text Full Text PDF PubMed Scopus (80) Google Scholar, 8Pollock-BarZiv S.M. den Hollander N. Ngan B.-Y. Kantor P. McCrindle B. Dipchand A.I. Pediatric heart transplantation in human leukocyte antigen sensitized patients: evolving management and assessment of intermediate-term outcomes in a high-risk population.Circulation. 2007; 116: I172-I178Crossref PubMed Scopus (77) Google Scholar]. This problem is likely to grow during the next 10 to 20 years as the initial waves of patients who have been surgical successes in staged single-ventricle palliation reach adolescence or young adulthood and present with end-stage ventricular dysfunction. Although data showing decreased antigen expression on and low panel reactive antibody response to decellularized homografts are encouraging [9Elkins R.C. Dawson P.E. Goldstein S. Walsh S.P. Black K.S. Decellularized human valve allografts.Ann Thorac Surg. 2001; 71: S428-S432Abstract Full Text Full Text PDF PubMed Scopus (188) Google Scholar], analysis with modern, highly sensitive alloantibody detection techniques (eg, Luminex; Luminex Corp, Austin, TX) would be most indicative of whether or not decellularized homograft is immunogenic. Potential Benefits of Antigen Reduction in Heart Valve AllograftsThe Annals of Thoracic SurgeryVol. 90Issue 1PreviewThe publication by Feingold and colleagues [1] concerning the expression of blood group antigens in cryopreserved allografts confirms the findings of Kadner and colleagues [2] in aortic and mitral allografts that was published earlier than the referenced citation [3]. Both groups conclude that (1) the microvascular endothelial cells of human heart valve conduits and myocardium express blood group antigens, whereas luminal endothelium does not, and (2) cryopreservation preserves the microvascular endothelial cells. Full-Text PDF