LATE BREAKING I

P. Dutta¹, M. Dart², A. David³, S.M. Schumacher¹, W.J. Burlingham^4
1Surgery, University of Wisconsin-Madison, Madison/UNITED STATES OF AMERICA, ²Surgery - Division Of Transplantation, University of Wisconsin, Madison/UNITED STATES OF AMERICA, ³Surgery, University of Wisconsin-Madison, Madison/WI/UNITED STATES OF AMERICA, ⁴Surgery, University of Wisconsin, Madison/WI/UNITED STATES OF AMERICA

Body: Introduction: Exposure to non-inherited maternal antigens (NIMA) in fetal and neonatal life of an F1 backcross (BDF1female x B6 male) mouse can result in lifelong tolerance to allografts expressing the NIMA (H2^d) in some (50%), but not all offspring. We discovered previously that NIMA-specificregulatory CD4 T cells were directly correlated with level of maternal microchimerism (MMc), indicating a causative link between the two. Whether high levels of Tregs and MMc could be used to predictsuccessful graft outcome is unknown. Hypothesis: Pretransplant levels of NIMA-specific regulatory T cells will predict subsequent NIMA-specific tolerance to allografts. Methods: Six-week old F1 backcross males were bled and H2^bxd heterozygous vs. H2^bxb homozygous offspring were determined by flow cytometry typing of PBMC.H2^bxb homozygotes were immunized with tetanus toxoid (TT). Two weeks later, hemisplenectomy was performed to obtain splenocytes from NIMA^d-exposed mice. Indirect delayed typehypersensitivity (DTH) assays were performed by transfer of splenocytes into a naïve B6 mouse footpad to measure bystander suppression of recall TT response in presence of maternal (BDF1)antigens, a measurement of NIMA-specific regulatory T cells. After a week, DBA/2 hearts expressing NIMA (H2^d) were transplanted in the abdominal cavity of the offspring. Results: Splenocytes from 15 NIMA^d-exposed offspring were tested. Ten were negative for suppression, while 5 suppressed recall TT response in presence of maternal antigens to avarying degree (20-55%) indicating the presence of NIMA-specific T regulatory cells. Out of the latter 5 offspring, 4 have beating DBA/2 hearts (f/u d 71, d18, d 12, d12 post transplant) as of thetime of writing and only one has rejected the heart (d.11). In contrast, all 10 of the NIMA^d-exposed “non-regulator”offspring rejected DBA/2 hearts by day 9-11 post transplant.BDF1 skin graft prolongation was also only observed in pre-transplant regulators, not in non-regulators. Conclusion: While f/u time is still short, the finding of a predictivecorrelation between DTH suppression of TT recall response in presence of maternal antigens and NIMA-specific tolerance suggests that one may predict NIMA-specific tolerance before transplantation. Iftranslated to human solid organ transplantation, this will allow us to prescreen recipients of a living related donor kidney allograft for enrollment in tolerance trials.

Disclosure: All authors have declared no conflicts of interest.