Murine Heterotopic Heart Transplant Technique

It is now over forty years since this technique was first reported by Corry, Wynn and Russell. Although it took some years for other labs to become ...

University of Colorado Denver

Supplementation of cultured human pulmonary arterial endothelial cells (PAEC) with sn-1-O-hexadecylglycerol (HG) resulted in an approximately twofold increase in cellular levels of plasmalogens, a subclass of phospholipids known to have antioxidant properties; this was due, primarily, to a fourfold increase in the choline plasmalogens. Exposure of unsupplemented human PAEC to hypoxia (PO(2) = 20-25 mmHg) caused an increase in cellular reactive oxygen species (ROS) over a period of 5 days with a coincident decrease in viability. In contrast, HG-supplemented cells survived for at least 2 wk under these conditions with no evidence of increased ROS. Hypoxia resulted in a selective increase in the turnover of the plasmalogen plasmenylethanolamine. Human PAEC with elevated plasmalogen levels were also more resistant to H(2)O(2), hyperoxia, and the superoxide generator plumbagin. This protection was seemingly specific to cellular stresses in which significant ROS were generated because the sensitivity to lethal heat shock or glucose deprivation was not altered in HG-treated human PAEC. HG, by itself, was not sufficient for protection; HG supplementation of bovine PAEC had no effect upon plasmalogen levels and did not rescue these cells from the cytotoxic effects of hypoxia. This is the initial demonstration that plasmalogen content can be substantially enhanced in a normal cell. These data also demonstrate that HG can protect cells during hypoxia and other ROS-mediated stress, likely due to the resulting increase in these antioxidant phospholipids.

Increasing plasmalogen levels protects human endothelial cells during hypoxia.

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.

Lobar torsion complicating bilateral lung transplantation.

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.

A two-step model of acute CD4 T-cell mediated cardiac allograft rejection.

Various studies indicate the requirements for tolerance induction may vary between different transplanted tissues and organs. Consequently, we compared the efficacy of anti-leukocyte function-associated antigen-1 (LFA-1)/anti-intercellular adhesion molecule-1 (ICAM-1) monoclonal antibody therapy for facilitating cardiac vs islet long-term allograft acceptance in mice.

Perturbation of leukocyte function-associated antigen-1/intercellular adhesion molecule-1 results in differential outcomes in cardiac vs islet allograft survival.

Acute cardiac allograft rejection requires host, but not donor, expression of B7-1/B7-2 costimulatory molecules. However, acute cardiac rejection requires direct antigen presentation by donor-derived antigen presenting cells to CD4 T-cells and does not require indirect antigen presentation to CD4 T-cells. Given this discrepancy in the literature and that the consequence of allograft exposure in B7-deficient mice is unknown; the goal of the study was to examine the antidonor status of allografted B7-1/B7-2-deficient hosts.

Spontaneous allograft tolerance in B7-deficient mice independent of preexisting endogenous CD4+CD25+ regulatory T-cells.

Evidence suggests that West Nile virus (WNV) neuroinvasive disease occurs more frequently in both solid organ and human stem cell transplant recipients. The effect of concomitant anti-B-cell therapy with rituximab, a CD20(+) monoclonal antibody, on WNV infection in this population, however, has not been reported. We describe a case of a patient with alpha-1-antitrypsin deficiency who underwent single lung transplantation in 2005 and was maintained on tacrolimus, cytoxan and prednisone. More recently, she had received two courses of rituximab for recurrent A2-A3 grade rejection with concomitant capillaritis and presented six months later with rapid, fulminant WNV meningoencephalitis. Her diagnosis was made by cerebrospinal fluid (CSF) PCR but serum and CSF WNV IgM and IgG remained negative. She received WNV-specific hyperimmune globulin (Omr-Ig-Am) through a compassionate protocol. She experienced a rapidly progressive and devastating neurological course despite treatment and died three wk after onset of her symptoms. Autopsy revealed extensive meningoencephalomyelitis.

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

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.

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

Previous studies have shown that acute CD4 T-cell-mediated cardiac allograft rejection requires donor major histocompatibility complex (MHC) Class II expression and can be independent of "indirect" antigen presentation. However, other studies suggested that indirect antigen presentation to CD4 T cells may play a primary role in cellular xenograft immunity. Thus, the relative roles of direct/indirect CD4 T cell reactivity against cardiac xenografts are unclear. In this study we set out to determine the role for indirect CD4 T cell reactivity in cardiac xenograft rejection.

CD4 T cells mediate cardiac xenograft rejection via host MHC Class II.

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.

Four decades of vascularized heterotopic cardiac transplantation in the mouse.

Previous reports using cell-based methods (CDC-AHG) suggest that the presence of pre-transplant HLA Class I and II antibodies are associated with worse survival following lung transplantation. Similarly, antibodies to major histocompatibility complex Class I chain-related gene A (MICA) have been associated with increased graft failure following kidney transplantation. Using highly sensitive solid phase assays, we sought to determine whether the pre-transplant presence of antibodies to MICA or HLA Class I or II predicted short or long-term lung allograft function. Pre-transplant sera screened for antibodies to MICA by Labscreen Single Antigen format and HLA by Luminex (n = 192) revealed antibody presence in 31 (16.1%) and 70 (36.4%) patients, respectively. HLA antibody presence correlated with increased bronchiolitis Obliterans syndrome (BOS)-1 development at 3 years [32.9% (23/70) vs. 18.9% (23/122), p = 0.03] while MICA antibodies correlated with BOS-2 development [32.3% (10/31) vs. 14.9% (24/161), p = 0.02]. The presence of HLA or MICA antibodies correlated with BOS-1 development [32.5% (26/81) vs.18.0% (20/111), p = 0.02] and BOS-2 [24.7% (20/81) vs. 12.6% (14/111), p = 0.02] at 3 years. We found no correlation between antibody presence and episodes of acute cellular rejection or overall survival. We conclude that the presence of pre-transplant HLA or MICA antibodies is associated with earlier BOS onset following lung transplantation.

Pre-transplant presence of antibodies to MICA and HLA class I or II are associated with an earlier onset of bronchiolitis obliterans syndrome in lung transplant recipients.

Todd J. Grazia

Colorado Center for Transplantation Care,
Research and Education and Division of Pulmonary Sciences and Critical Care Medicine,
Colorado Center for Transplantation Care, Research and Education and Division of Pulmonary Sciences and Critical Care Medicine

University of Colorado Denver

Murine Heterotopic Heart Transplant Technique