Todd J. Grazia

Rosiglitazone promotes development of a novel adipocyte population from bone marrow-derived circulating progenitor cells.

Obesity and weight gain are characterized by increased adipose tissue mass due to an increase in the size of individual adipocytes and the generation of new adipocytes. New adipocytes are believed to arise from resident adipose tissue preadipocytes and mesenchymal progenitor cells. However, it is possible that progenitor cells from other tissues, in particular BM, could also contribute to development of new adipocytes in adipose tissue. We tested this hypothesis by transplanting whole BM cells from GFP-expressing transgenic mice into wild-type C57BL/6 mice and subjecting them to a high-fat diet or treatment with the thiazolidinedione (TZD) rosiglitazone (ROSI) for several weeks. Histological examination of adipose tissue or FACS of adipocytes revealed the presence of GFP(+) multilocular (ML) adipocytes, whose number was significantly increased by ROSI treatment or high-fat feeding. These ML adipocytes expressed adiponectin, perilipin, fatty acid-binding protein (FABP), leptin, C/EBPalpha, and PPARgamma but not uncoupling protein-1 (UCP-1), the CD45 hematopoietic lineage marker, or the CDllb monocyte marker. They also exhibited increased mitochondrial content. Appearance of GFP(+) ML adipocytes was contemporaneous with an increase in circulating levels of mesenchymal and hematopoietic progenitor cells in ROSI-treated animals. We conclude that TZDs and high-fat feeding promote the trafficking of BM-derived circulating progenitor cells to adipose tissue and their differentiation into ML adipocytes.

Following Universal Prophylaxis with Intravenous Ganciclovir and Cytomegalovirus Immune Globulin, Valganciclovir is Safe and Effective for Prevention of CMV Infection Following Lung Transplantation

We prospectively determined the safety and efficacy of valganciclovir for prevention of cytomegalovirus (CMV) in at‐risk (donor positive/recipient negative [D+/R−] or R+) lung transplant recipients. We also determined the length of prophylaxis required to significantly decrease both CMV infection and disease. Consecutive lung transplant recipients surviving >30 days (n = 90) received combination prophylaxis with intravenous (i.v.) ganciclovir (GCV) 5 mg/kg/day and cytomegalovirus immune globulin (CMV‐IVIG) followed by valganciclovir (450 mg twice‐daily) to complete 180, 270 or 365 days of prophylaxis. This group was compared to a historical group (n = 140) who received high‐dose oral acyclovir following i.v. GCV and CMV‐IVIG. CMV disease was significantly lower in patients receiving valganciclovir compared to acyclovir (2.2% vs. 20%; p < 0.0001). Freedom from CMV infection and disease was significantly greater (p < 0.02) in patients receiving 180, 270 or 365 days of prophylaxis (90%, 95% and 90%, respectively) compared to those receiving 100–179 days (64%) or <100 days (59%). No patient receiving valganciclovir died during the study. Following prophylaxis with i.v. GCV and CMV‐IVIG, valganciclovir is safe and effective for prevention of CMV infection and disease in at‐risk lung transplant recipients. The required length of prophylaxis was at least 180 days.

Impact of rituximab-associated B-cell defects on West Nile virus meningoencephalitis in solid organ transplant recipients

Levi ME, Quan D, Ho JT, Kleinschmidt‐DeMasters BK, Tyler KL, Grazia TJ. Impact of rituximab‐associated B‐cell defects on West Nile virus meningoencephalitis in solid organ transplant recipients.
Clin Transplant 2009 DOI: 10.1111/j.1399‐0012.2009.01044.x
© 2009 John Wiley & Sons A/S.

A Two-Step Model of Acute CD4 T-Cell Mediated Cardiac Allograft Rejection

CD4 T cells are both necessary and sufficient to mediate acute cardiac allograft rejection in mice. This process requires “direct” engagement of donor MHC class II molecules. That is, acute rejection by CD4+ T cells requires target MHC class II expression by the donor and not by the host. However, it is unclear whether CD4+ T cell rejection requires MHC class II expression on donor hemopoietic cells, nonhemopoietic cells, or both. To address this issue, bone marrow transplantation in mice was used to generate chimeric heart donors in which MHC class II was expressed either on somatic or on hemopoietic cells. We report that direct recognition of hemopoietic and nonhemopoietic cells are individually rate limiting for CD4+ T cell-mediated rejection in vivo. Importantly, active immunization with MHC class II+ APCs triggered acute rejection of hearts expressing MHC class II only on the somatic compartment. Thus, donor somatic cells, including endothelial cells, are not sufficient to initiate acute rejection; but they are necessary as targets of direct alloreactive CD4 T cells. Taken together, results support a two-stage model in which donor passenger leukocytes are required to activate the CD4 response while direct interaction with the somatic compartment is necessary for the efferent phase of acute graft rejection.

Lobar torsion complicating bilateral lung transplantation

We report a case of left lower lobe torsion in a patient who had undergone bilateral lung transplantation for alpha(1)-antitrypsin deficiency. The patient experienced acute pulmonary hypertension and hypoxemia on post-operative Day 3 and the chest X-ray showed bilateral alveolar infiltrates and a new focal consolidation of the left lower lobe. Fiberoptic bronchoscopy showed complete obstruction of the left lower lobe bronchus and abnormal rotation of the left upper lobe bronchus suggesting torsion, which was confirmed by pulmonary angiography and ultimately at thoracotomy. The possibility of acute lobar torsion should be considered in lung transplant recipients who demonstrate evidence of acute respiratory insufficiency in the early post-operative period.

Acute cardiac allograft rejection by directly cytotoxic CD4 T cells: parallel requirements for Fas and perforin.

Background. CD4 T cells can suffice as effector cells to mediate primary acute cardiac allograft rejection. Although CD4 T cells can readily kill appropriate target cells in vitro, the corresponding role of such cytolytic activity for mediating allograft rejection in vivo is unknown. Therefore, we determined whether the cytolytic effector molecules perforin (PFP) and/or FasL (CD95L) were necessary for CD4 T cell-mediated rejection in vivo. Methods. Wild-type C3H(H-2k) or Fas (CD95)-deficient C3Hlpr (H-2k) hearts were transplanted into immune-deficient C57B6rag−/− (H-2b) mice. Then, recipients were reconstituted with naïve purified CD4 T cells from wild-type, PFP-deficient, or FasL (gld)-deficient T-cell donors. Results. In vitro, alloreactive CD4 T cells were competent to lyse donor major histocompatibility complex class II+ target cells, largely by a Fas-dependent mechanism. In vivo, the individual disruption of donor Fas expression (lpr) or CD4 T-cell-derived PFP had no significant impact on acute rejection. However, FasL-deficient (gld) CD4 T cells demonstrated delayed allograft rejection. Importantly, the simultaneous removal of both donor Fas expression and CD4 T-cell PFP completely abrogated acute rejection, despite the persistence of CD4 T cells within the graft. Conclusions. Results demonstrate that the direct rejection of cardiac allografts by CD4 effector T cells requires the alternative contribution of graft Fas expression and T cell PFP expression. To our knowledge, this is the first demonstration that cytolytic activity by CD4 T cells can play an obligate role for primary acute allograft rejection in vivo.

Late-onset cytomegalovirus (CMV) in lung transplant recipients: can CMV serostatus guide the duration of prophylaxis?

Evidence supports the use of 12 months of cytomegalovirus prophylaxis in all at‐risk lung transplants; whether cytomegalovirus serostatus can be used to further optimize this duration remains to be determined. The purpose of this retrospective study was to determine if cytomegalovirus serostatus of both donor and recipient were associated with late‐onset cytomegalovirus. The primary outcome was the proportion of lung transplants that developed cytomegalovirus infection or disease during the 180‐day period following 6 months of prophylaxis in each at‐risk serotype. Two hundred forty‐four consecutive lung transplants were evaluated, 131 were included. The proportion of recipients with cytomegalovirus differed significantly between serotypes (20 of 41 [48.8%] D+/R‐ vs. 19 of 56 [33.9%] D+/R+ vs. 2 of 34 [5.9%] D‐/R+; p < 0.001). In a multivariate model, older age (odds ratio [OR], 1.05, 95% confidence interval [CI] 1.004–1.099; p = 0.03) and D+/R‐ serostatus (OR, 3.83; 95% CI 1.674–8.770; p = 0.002) were associated with cytomegalovirus. Among R+ lung transplants, D‐ serostatus was associated with the absence of cytomegalovirus (OR, 0.12; 95% CI 0.0263–0.563; p = 0.007). These findings suggest that in the valganciclovir era, cytomegalovirus serostatus of both donor and recipient may identify lung transplants at heightened risk for late‐onset cytomegalovirus.

Cutting Edge: Roles for Batf3-Dependent APCs in the Rejection of Minor Histocompatibility Antigen–Mismatched Grafts

In transplantation, a major obstacle for graft acceptance in MHC-matched individuals is the mismatch of minor histocompatibility Ags. Minor histocompatibility Ags are peptides derived from polymorphic proteins that can be presented by APCs on MHC molecules. The APC subtype uniquely responsible for the rejection of minor Ag–mismatched grafts has not yet been identified. In this study, we examined graft rejection in three mouse models: 1) mismatch of male-specific minor Ags, 2) mismatch of minor Ags distinct from male-specific minor Ags, and 3) skin transplant. This study demonstrates that in the absence of pathogen-associated molecular patterns, Batf3-dependent dendritic cells elicit the rejection of cells and grafts expressing mismatched minor Ags. The implication of our findings in clinical transplantation may be significant, as minor Ag reactivity has been implicated in the pathogenesis of multiple allograft tissues.

Ectopic expression of Fas Ligand on cardiomyocytes renders cardiac allografts resistant to CD4(+) T-cell mediated rejection.

Fas Ligand limits inflammatory injury and permits allograft survival by inducing apoptosis of Fas-bearing lymphocytes. Previous studies have shown that the CD4(+) T-cell is both sufficient and required for murine cardiac allograft rejection. Here, utilizing a transgenic mouse that over-expresses Fas Ligand specifically on cardiomyocytes as heart donors, we sought to determine if Fas Ligand on graft parenchymal cells could resist CD4(+) T-cell mediated rejection. When transplanted into fully immunocompetent BALB/c recipients Fas Ligand transgenic hearts were acutely rejected. However, when transplanted into CD4(+) T-cell reconstituted BALB/c-rag(-/-) recipients, Fas Ligand hearts demonstrated long-term survival. These results indicate that Fas Ligand over-expression on cardiomyocytes can indeed resist CD4(+) T-cell mediated cardiac rejection and suggests contact dependence between Fas Ligand expressing graft parenchymal cells and the effector CD4(+) T-cells.

Four Decades of Vascularized Heterotopic Cardiac Transplantation in the Mouse

ABSTRACT Since the first clinical heart transplant in 1967, there has been a heightened need to understand immune and inflammatory responses to “foreign” tissues. Research efforts in those early days were based on species that would now be considered “large” and were typically out-bred individuals. While this closely mirrors the clinical scenario, where genetic mismatches of donors and recipients can only be minimized in the selection process, these were not ideal models for studying the complexities and nuances of the immune system. Even when the rat was considered the standard model those early endeavors were limited by a small number of rat strains. The mouse model has provided us with an overwhelming array of strains, knockouts, knockins and transgenics that allow us to investigate the many layers of the innate and adaptive immune systems leading to a much greater understanding of immune responses. Fully vascularized heterotopic cardiac transplantation in the mouse has now been with us for four decades; the original papers describing this technique being published by Corry in 1973. In the subsequent 40 years, this technique has been used by many laboratories, including our own, and has become a powerful tool for the investigation of transplant immunity and ischemia reperfusion injury. Given the modern availability of mouse strains and mouse-related reagents, our current understanding of transplant immunity undoubtedly would not exist without such a technique.