F.145. Induction of Donor-Specific AllograftTolerance By Donor-Derived Exosomes andShort-Term Immunosuppression.Maria Cristina Cuturi, Helene Peche, Karine Renaudin,Gaelle Beriou. U643, Inserm ITERT, Nantes, France.

The use of immunosuppressive drugs in human transplan-tation has increased graft survival. However, this results arebalanced by the occurrence of opportunistic infections andcancer as a result of non-specific immunesuppression andalso that in a high percentage of transplant recipients, thesedrugs do not prevent chronic rejection. One major aim intransplantation research is therefore the induction of donor-specific tolerance, which would enable a reduction in long-term, non-specific immunosuppression. The presentation ofdonor MHC antigens before transplantation has been previ-ously shown to modulate acute rejection. Exosomes secret-ed by dendritic cells are enriched in MHC class I and class IImolecules and can be used as a source of donor MHCantigens. When injected prior to transplantation, exosomesare able to significantly prolong heart allograft survival.Dendritic cells have been shown to play an important role inallograft response. It has been also shown that n theimmature state, (tolerogenic) DC can suppress T-cellresponses. Maintenance of DC in an immature state aftertransplantation, is important to ensure presentation ofalloantigens in a tolerogenic fashion. In this study, we usedLF 15-0195 (LF), a new desoxypergualin analog that hasrecently been reported to prevent DC maturation in vivo.We demonstrate that donor derived-exosomes administeredafter transplantation are able to prolong heart allograftsurvival in a donor-specific manner. Interestingly, thecombination of donor derived-exosomes with a short-termtreatment with LF has striking synergistic effects andinduces donor-specific heart allograft tolerance withoutsigns of chronic rejection. These results are very encourag-ing and provide new approaches for protocols of induction oftolerance based in the presentation of donor MHC antigensto be tested in clinical trials.

doi:10.1016/j.clim.2006.04.185

F.146. Inflammation and Graft Rejection in CD200R1KO Mice.Reg Gorczynski, Ivo Boudakov. Transplant Research, Univer-sity Health Network, Toronto, ON, Canada.

WE and others reported that interactions between therealtively ubiquitously expressed molecule, CD200, and oneof the members of the CD200R family, CD200R1, results indelivery of signals which suppress both inflammation andgraft rejection. We have generated a BL/6 mouse withdeletion of the exons encoding the extracellular domains ofCD200R1. When spleen lymphocytes were examined, byFACS analysis and real-time PCR, neither mRNA nor cellsurface protein for CD200R1 was detected, unlike littermate(wild-type, (wt) controls). Spleen cells from KO and wt micewere cultured with/without stimulation by LPS or allogeneic(C3H) spleen cells. Culture supernatants were assayed byELISA for spontaneous or induced production of a number of

inflammatory cytokines. In addition, cells from all cultureswere assayed at 5 days for development of CTL specific forC3H targets. Elevated spontaneous production of IL-1, TNFaand IL-6 was seen with cells of KO mice, with even moreenhanced production (relative to controls) following stimu-lation. CTL induction was similarly increased. When cultureswere initiated in the presence of exogenous CD200Fc asimmunosuppressant, only cells from wt mice showedevidence for suppression (see Figure). Finally, we examinedthe effect of exogenous CD200Fc on skin allograft rejection(C3H) in KO and wt mice. There was a trend to fasterrejection in untreated KO mice, with no effect of infusion ofCD200Fc. In contrast, graft rejection was suppressed byCD200Fc in wt mice, as was allosensitization (CTL assayswith spleen cells from grafted mice). We conclude thatCD200R1 is an important molecule in delivery of anti-inflammatory and immunosuppressivce signals followingengagement of CD200.

doi:10.1016/j.clim.2006.04.186

F.147. Antibodies to HLA Defined By Single AntigenTests: Correlation with Assays Using Cells and withClinical Endpoints.Karen Nelson, Paul Warner, Danny Youngs. Immunogenetics,Puget Sound Blood Center, Seattle, WA.

Candidates waiting for a kidney transplant who haveantibodies (Ab) to HLA wait longer for a compatible donorthan those without allosensitization. Identification of thespecificities of their Ab to HLA facilitates crossmatchoutcome prediction. This may allow allocation of donororgans over broader geographical areas thereby increasingthe odds of finding a compatible donor. Assays employingsingle HLA antigens provide increased specificity; butantigen concentration and gain or loss of epitopes may leadto false assignments. This study correlated assigned specifi-cities, i.e. unacceptable antigens(UA), for HLA-A, B, C, DR,and DQ with crossmatch (XM) outcome. In addition, theseassays identified Ab to HLA-DP that correlated with XM andtransplant outcome. Allosensitized renal transplant candi-dates had Ab to HLA characterized with flow cytometry-based single antigen assays. XM performed in the followingyear were evaluated; CDC crossmatches were from regionaltrays. XM with donors lacking UA were predicted to benegative. Prediction was highly accurate as shown. Discor-dant CDC XM showed false positive XM due to technical error.Five candidates showed allele-specific Ab. Ab to HLA-C notassigned as UA were associated with positive Flow T XM.Discordant B-cell XM identified Ab to HLA-DP associated withpositive B-cell crossmatch. Transplants with HLA-DP UA asthe only mismatch experienced multiple severe humoralrejection events. These data show that single HLA assaysidentify UA that accurately predict negative XM. Identifica-tion of Ab to HLA-DP and to HLA alleles aids in interpreting XMwith well-matched donors and in assigning risk to thosetransplants.

doi:10.1016/j.clim.2006.04.187

AbstractsS102