The role of donor CD4 T lymphocyte chimerism in lung transplant recipients

Abstract Long-term outcomes for lung transplantation remain disappointing; as many as 50% of lung transplant recipients develop progressive Bronchiolitis Obliterans Syndrome (BOS) by 5 years after transplant. In the last decade, several experimental and clinical studies have demonstrated that cellular and humoral autoimmune responses to ‘self’ antigens may play a causative role in the onset of BOS. Work from our research group has highlighted a novel mechanism for triggering autoimmunity following transplantation. In a murine model of chronic heart rejection, transplant-induced autoimmunity - characterised by production of class-switched anti-nuclear effector autoantibody responses was dependent upon provision of help from donor CD4 T cells that were passengers within the graft. However, the fate of the donor passenger CD4 T cells in clinical organ transplantation is unclear. To assess whether a similar mechanism may occur in human transplant recipients, I have studied the presence and the impact of passenger donor CD4 T cells on the development of humoral auto- and alloimmune responses in a prospective cohort of primary lung transplant recipients (n=21). The development of autoantibody and, in particular, the specificity of target autoantigens was also evaluated in a lung transplant patients with either established grade 2-3 BOS (n=10), or without BOS (n=10). My work suggests that the presence of donor CD4 T cell chimerism in the peripheral blood of lung transplant recipients is a uniform phenomenon. Donor CD4 T lymphocytes were consistently detected in the recipients’ peripheral blood during the first post-operative month; however, the number of detectable donor CD4 T cells fluctuated over time, and varied between individual lung transplant recipients. In a follow-up period of one year after transplantation, three distinct patterns of donor CD4 T cell chimerism were observed: short (donor CD4 T cells detectable for up to six weeks after transplantation, n=13), intermediate (donor CD4 T cells detectable between three to six months after transplantation, n=3) and long-lasting chimerism (donor CD4 T cells detectable for more than six months after transplantation, n=5). Surprisingly, the degree of HLA mismatching and the predicted NK cell alloreactivity did not correlate with the longevity of donor CD4 T cell chimerism, and did not influence the development of BOS. Furthermore, transcriptomic analysis of the donor CD4 T cell population consisted of a heterogenous mixture of different CD4 T cell sub-types, with no consistent pattern evident in patients with short and long lasting donor CD4 T cell chimerism. The assessment of the humoral autoimmune responses revealed unexpected findings. Anti-nuclear IgG autoantibody levels were greater in the recipients’ sera before the transplant, when compared to sera sampled at one and 12 months after transplantation, but the titre of pre-transplant anti-nuclear autoantibody did not correlate with the subsequent development of BOS. Similar findings were observed in the retrospective cohort of 24 lung and 18 heart and lung transplant recipients. Assessment of the repertoire of pretransplant autoantibody did however suggest that a unique set of autoantigens were targeted in those patients that subsequently developed BOS. The involvement of donor CD4 T cell in the development of transplant-induced autoimmunity and augmentation of humoral alloimmunity was not confirmed in human lung transplant recipients and the role of donor CD4 T chimerism remains unclear. However, solid organ transplant recipients are subjected to highly potent T-cell depleting immunosuppressive drugs that can alter the number and function of T cells. This may obviate the impact of donor CD4 T cell chimerism in the development of transplant-induced autoimmunity. Understanding the clinical relevance of the autoantibody repertoire present at the time of transplant may, however, hold potential in identifying recipients with predisposition to develop BOS, and may therefore possibly provide a window of opportunity for targeted immunosuppression.This thesis was supported by The British Heart Foundation, Non-Clinical PhD Studentship Grant (RG088); Papworth Hospital research grant (to Dr Jasvir Papmar) and Addenbrooke’s Charitable Trust (to Mr Gavin J. Pettigrew)

Prolongation of allograft survival by passenger donor regulatory T cells.

Tissue resident lymphocytes are present within many organs, and are presumably transferred at transplantation, but their impact on host immunity is unclear. Here, we examine whether transferred donor natural regulatory CD4 T cells (nT-regs) inhibit host alloimmunity and prolong allograft survival. Transfer of donor-strain lymphocytes was first assessed by identifying circulating donor-derived CD4 T cells in 21 consecutive human lung transplant recipients, with 3 patterns of chimerism apparent: transient, intermediate, and persistent (detectable for up to 6 weeks, 6 months, and beyond 1 year, respectively). The potential for transfer of donor nT-regs was then confirmed by analysis of leukocyte filters recovered from ex vivo normothermic perfusion circuits of human kidneys retrieved for transplantation. Finally, in a murine model of cardiac allograft vasculopathy, depletion of donor CD4 nT-regs before organ recovery resulted in markedly accelerated heart allograft rejection and augmented host effector antibody responses. Conversely, adoptive transfer or purified donor-strain nT-regs inhibited host humoral immunity and prolonged allograft survival, and more effectively so than following administration of recipient nT-regs. In summary, following transplantation, passenger donor-strain nT-regs can inhibit host adaptive immune responses and prolong allograft survival. Isolated donor-derived nT-regs may hold potential as a cellular therapy to improve transplant outcomes.This work was supported by a British Heart Foundation project grant, the NIHR Cambridge Biomedical Research Centre and the NIHR Blood and Transplant Research Unit in Organ Donation and Transplantation at the University of Cambridge in collaboration with Newcastle University and Royal Papworth Hospital in partnership with NHS Blood and Transplant (NHSBT). The views expressed are those of the authors and not necessarily those of the NHS, the NIHR, the Department of Health or NHSBT. IGH was supported by a Wellcome Trust Clinical Research Training Fellowships and Raymond and Beverly Sackler Scholarships. IGH received additional support from an Addenbrooke’s Charitable Trust Clinical Research Fellowship. RM was supported by a European Society of Organ Transplantation Junior Basic Science Grant. JHS was supported by a Gates PhD Fellowship

Impact of donor mismatches at individual HLA-A, -B, -C, -DR, and -DQ loci on the development of HLA-specific antibodies in patients listed for repeat renal transplantation.

We have analyzed the relationship between donor mismatches at each HLA locus and development of HLA locus-specific antibodies in patients listed for repeat transplantation. HLA antibody screening was undertaken using single-antigen beads in 131 kidney transplant recipients returning to the transplant waiting list following first graft failure. The number of HLA mismatches and the calculated reaction frequency of antibody reactivity against 10,000 consecutive deceased organ donors were determined for each HLA locus. Two-thirds of patients awaiting repeat transplantation were sensitized (calculated reaction frequency over 15%) and half were highly sensitized (calculated reaction frequency of 85% and greater). Antibody levels peaked after re-listing for repeat transplantation, were independent of graft nephrectomy and were associated with length of time on the waiting list (odds ratio 8.4) and with maintenance on dual immunosuppression (odds ratio 0.2). Sensitization was independently associated with increasing number of donor HLA mismatches (odds ratio 1.4). All mismatched HLA loci contributed to the development of HLA locus-specific antibodies (HLA-A: odds ratio 3.2, HLA-B: odds ratio 3.4, HLA-C: odds ratio 2.5, HLA-DRB1: odds ratio 3.5, HLA-DRB3/4/5: odds ratio 3.9, and HLA-DQ: odds ratio 3.0 (all significant)). Thus, the risk of allosensitization following failure of a first renal transplant increases incrementally with the number of mismatches at all HLA loci assessed. Maintenance of re-listed patients on dual immunosuppression was associated with a reduced risk of sensitization