728 Repopulating T cells and alpha1-antitrypsin therapy synergize to remove the immunological barrier to successful islet xenotransplantation
Wednesday November 18, 2015 from 11:00 to 12:30
Plenary Room 1

Boris M Baranovski, Israel

Ph.D Candidate

Clinical Biochemistry and Pharmacology

Ben-Gurion University of the Negev


Repopulating T cells and alpha1-antitrypsin therapy synergize to remove the immunological barrier to successful islet xenotransplantation

Boris Baranovski1, David E Ochayon1, Peleg Rider1, Omer Nisim1, Eli C Lewis1.

1Clinical Biochemistry and Pharmacology, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel

Introduction. The balance between regulatory T cells and memory T cells is detrimental to xenograft survival. After temporary T cell depletion, T cells repopulate secondary immune organs in a profile that is, to some degree, distinct from the original repertoire prior to depletion, yet falls short of acheving xenograft tolerance. Human α1-antitrypsin (AAT) is an anti-inflammatory and immunomodulatory molecule. AAT allows undeterred purified T cell responses and downplays the levels of local proinflammatory cytokines, two parameters that are critical for Treg expansion. Monotherapy with AAT induces islet allograft tolerance, but fails to induce both skin allograft tolerance and islet xenograft tolerance. However, in combination with temporary T cell depletion, AAT significantly promotes rat-to-mouse islet xenograft acceptance. The mechanism behind this intriguing synergy is unknown.
Aim. To establish the mechanism of synergy between AAT and temporary T cell depletion in promoting a xenograft-favorable immune profile.
. Concordant islet xenotransplantation was performed together with temporary T cell depletion using either anti-CD4 or anti-CD8–depleting antibodies; rat islets were grafted into either non-depleted mice, depleted mice and AAT-treated depleted mice. T cell repopulation profile was determined in the circulation at specific time-points. Skin allotransplantation was performed to examine whether the synergy also addresses excessive antigenic load. In order to study repopulating T cells in draining lymph nodes, hind-limb skin grafts were performed, followed by T cell subtyping in the inguinal lymph nodes.
Results. Islet xenograft survival. Non-depleted mice rejected grafts on day 15.3 (mean, n=6); CD4-depleted mice rejected on day 26.4 (n=5), and CD8-depeleted mice on day 15.5 (n=6). None displayed graft survival that exceeded day 35. In the AAT group, 40% of CD4-depleted mice and, unexpectedly, 67% of CD8-depleted mice displayed graft function after day 35. Skin allograft survival. The group of untreated mice rejected grafts on day 11 (mean, n=5), T cell depleted group on day 13.8 (n=5) and AAT group on day 9.5 (n=4). None displayed graft survival beyond day 25. However, 4 out of 7 mice treated by both AAT and T cell depletion displayed skin graft survival that exceeded day 25 (30, 38, 67 and >100). T cell repopulation profile. All non-grafted mice displayed slow repopulation of CD8+ T cells, regardless of AAT treatment. However, CD4+ T cell repopulation was significantly more rapid in the AAT group, and the composition of the returning cells included markedly elevated foxp3+ Tregs and significantly lower levels of CD44HI memory T cells. A consistent regulatory trend was established in the draining lymph nodes of AAT-treated skin-grafted mice.
Conclusion. Human AAT therapy synergizes with temporal T cell depletion by indirectly modifying repopulating CD4+ T cells towards a profile that is memory T cell-poor and Treg-rich. AAT also addresses antigenic load, an important barrier in the xenoimmune response. Combination of the two clinically-available approaches should be further challenged in a discordant model, and adoptive T cell transfer should be examined for transferable graft protection; a molecular bone-marrow profiling is to afford some insight into the factors that govern this favorable outcome, toward establishing this novel therapeutic approach for the prevention of islet xenograft rejection in an immune competent host.

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