Patterns of De Novo Allo B Cells and Antibody Formation in Chronic Cardiac Allograft Rejection After Alemtuzumab Treatment

Abstract

Even though the etiology of chronic rejection (CR) is multifactorial, donor specific antibody (DSA) is considered to have a causal effect on CR development. Currently the antibody-mediated mechanisms during CR are poorly understood due to lack of proper animal models and tools. In a clinical setting, we previously demonstrated that induction therapy by lymphocyte depletion, using alemtuzumab (anti-human CD52), is associated with an increased incidence of serum alloantibody, C4d deposition and antibody-mediated rejection in human patients. In this study, the effects of T cell depletion in the development of antibody-mediated rejection were examined using human CD52 transgenic (CD52Tg) mice treated with alemtuzumab. Fully mismatched cardiac allografts were transplanted into alemtuzumab treated CD52Tg mice and showed no acute rejection while untreated recipients acutely rejected their grafts. However, approximately half of long-term recipients showed increased degree of vasculopathy, fibrosis and perivascular C3d depositions at posttransplant day 100. The development of CR correlated with DSA and C3d deposition in the graft. Using novel tracking tools to monitor donor-specific B cells, alloreactive B cells were shown to increase in accordance with DSA detection. The current animal model could provide a means of testing strategies to understand mechanisms and developing therapeutic approaches to prevent chronic rejection.

HMGB1 Is Involved in Chronic Rejection of Cardiac Allograft via Promoting Inflammatory-Like mDCs

“…The circulating donor-specific alloantibody (DSA) level in recipient serum (1:32 dilution) was evaluated by the flow cross-match technique described previously (29), using donor splenocytes as targeting cells. More details can be seen in the Supplementary Materials and Methods.…”

Lymphodepletional Strategies in Transplantation

“…Despite complete T-cell repopulation by 10 weeks, treated animals showed no evidence of acute rejection, and showed excellent graft survival and function for more than 200 days. Half of the alemtuzumab recipients, however, showed alloantibody production and antibody-mediated chronic rejection (Kwun et al 2012b). Furthermore, alloantibody-producing animals had increased allospecific B cells found in their spleens, as well as ongoing germinal center reactions represented by CD38-alloreactive B cells.…”

“…Because mature B-cell depletion with CD20 mAb will not be sufficient to prevent acute and chronic allograft rejection, new therapies such as CD19 mAb and the next generation of proteasome inhibitors may offer a new approach for depleting both B cells and plasma cells. For testing these agents to investigate their mechanisms, proper animal models will be needed due to constraints in strain and species specifics (Kwun et al 2012b). …”

“…Although little is known on the direct role of Tcell depletion on Tfh cells, our preclinical and clinical studies have reported increased humoral responses and de novo alloantibody production after T-cell depletion (Barth et al 2006;Page et al 2012;Kwun et al 2012b). Tfh cells are known to express high levels of IL-21, which is required for cognate B-cell help and germinal center (GC) formation (Silver and Hunter 2008).…”

Lessons and Limits of Mouse Models

“…Thus, the report by Kwun et al (2012) of a chronic cardiac allograft rejection model in mice after alemtuzumab (antihuman CD52 mAb) is noteworthy. Induction therapy with alemtuzumab in human kidney transplant recipients has been associated with increased incidence of serum alloantibody, C4d deposition, and antibody-mediated rejection.…”