The toxicity of chronic immunosuppressive agents required for organ transplant maintenance has prompted investigators to pursue approaches to induce immune tolerance. We developed an approach using a bioengineered mobilized cellular product enriched for hematopoietic stem cells (HSC) and tolerogenic CD8+/TCR− graft facilitating cells (FC) combined with nonmyeloablative conditioning that allows engraftment, durable chimerism, and tolerance induction in highly mismatched related and unrelated donor-recipient pairs. Eight recipients of HLA-mismatched kidney and FC/HSC transplants underwent conditioning with fludarabine, 200 cGy total body irradiation, and cyclophosphamide followed by post-transplant immunosuppression with tacrolimus and mycophenolate mofetil. Subjects ranged in age from 29 to 56 years. HLA match ranged from 5 of 6 related to 1 of 6 unrelated. The absolute neutrophil counts nadired approximately one week after transplant, with recovery by two weeks. Multilineage chimerism at one month was 6% to 100%. The conditioning was well tolerated with outpatient management after postoperative day two. Two subjects exhibited transient chimerism and have been reduced to low-dose tacrolimus monotherapy. One subject developed viral sepsis two months after transplant and experienced renal artery thrombosis. Five subjects have durable chimerism, with immunocompetence and donor-specific tolerance by in vitro proliferative assays and were successfully weaned off all immunosuppression one year after transplant. None of the recipients produced anti-donor antibody or exhibited engraftment syndrome or graft-versus-host disease. These results suggest that manipulation of a mobilized stem cell graft and nonmyeloablative conditioning represents a safe, practical, and reproducible means of inducing durable chimerism and donor-specific tolerance in solid organ transplant recipients.

The presence of donor-specific HLA antibodies before or after transplantation may have different implications based on the antibody strength. Yet, current approaches do not provide information regarding the true antibody strength as defined by antigen-antibody dissociation rate. To assess currently available methods, we compared between neat mean fluorescence intensity (MFI) values, C1q MFI values, ethylenediaminetetraacetic acid (EDTA)-treated samples, as well as titration studies and peak MFI values of over 7000 Luminex-based single-antigen HLA antibody data points. Our results indicate that neat MFI values do not always accurately depict antibody strength. We further showed that EDTA treatment (6%) does not always remove all inhibitory factors compared with C1q or titration studies. In this study of patients presenting with multiple antibody specificities, a prozone effect was observed in 71% of the cohort (usually not affecting all antibody specificities within a single serum sample, though). Similar to titration studies, the C1q assay was able to address the issue of potential inhibition; however, its limitation is its low sensitivity and inability to detect the presence of weak antibodies. Titration studies are the only method among the approaches used in this study to provide information suggesting antigen-antibody dissociation rates and are, therefore, likely to provide better indication of true antibody strength.Abbreviations: AMR, antibody-mediated rejection; DSA, donor-specific antibody; EDTA, ethylenediaminetetraacetic acid; MFI, mean fluorescence intensity; SAB, single antigen beads; SPA, solid phase assays

There is considerable interest in therapeutic transfer of regulatory T cells (Tregs) for controlling aberrant immune responses. Initial clinical trials have shown the safety of Tregs in hematopoietic stem cell transplant recipients and subjects with juvenile diabetes. Our hypothesis is that infusion(s) of Tregs may induce transplant tolerance thus avoiding long-term use of toxic immunosuppressive agents that cause increased morbidity/mortality. Towards testing our hypothesis, we conducted a phase I dose escalation safety trial infusing billions of ex vivo expanded recipient polyclonal Tregs into living donor kidney transplant recipients. Despite variability in recipient’s renal disease, our expansion protocol produced Tregs which met all release criteria, expressing >98% CD4+CD25+ with <1% CD8+ and CD19+ contamination. Our product displayed >80% FOXP3 expression with stable demethylation in the FOXP3 promoter. Functionally, expanded Tregs potently suppressed allogeneic responses and induced the generation of new Tregs in the recipient’s allo-responders in vitro. Within recipients, expanded Tregs amplified circulating Treg levels in a sustained manner. Clinically, all doses of Treg therapy tested were safe with no adverse infusion related side effects, infections or rejection events up to two years post-transplant. This study provides the necessary safety data to advance Treg cell therapy to phase II efficacy trials.

This study examined alemtuzumab (anti-CD 52, Campath-1H) and basiliximab (anti-CD 25, Simulect) as induction immunosuppression in kidney transplantation.We used a single-center, nonrandomized, retrospective, sequential study design to evaluate outcomes in kidney transplant recipients given either alemtuzumab (n = 123) or basiliximab (n = 155) induction in combination with a prednisone-free maintenance protocol using tacrolimus and mycophenolate mofetil. KaplanMeier analyses of long-term patient and graft survivals and rejection rates were determined according to induction agent, donor source and recipient ethnicity. Secondary endpoints included the quality of renal allograft function and the etiology of infectious complications.Overall long-term patient and graft survival rates did not significantly differ between patients treated with alemtuzumab and basiliximab. A lower rate of early (<3 months) rejection was observed in the alemtuzumab (4.1%) versus the basiliximab (11.6%) group, but the rates for both groups were equivalent at 1 year. Patient and kidney survival and rejection rates were nearly identical between Caucasians and African Americans that received alemtuzumab. Quality of renal function and incidence of infectious complications were similar in the two groups.Alemtuzumab induction therapy was similar in efficacy to basiliximab in a prednisone-free maintenance immunosuppressive protocol for an ethnically diverse population of kidney transplant recipients.

Nineteen subjects have more than 18 months' follow-up in a phase IIb tolerance protocol in HLA-mismatched recipients of living donor kidney plus facilitating cell enriched hematopoietic stem cell allografts (FCRx). Reduced intensity conditioning preceded a kidney allograft, followed the next day by FCRx. Twelve have achieved stable donor chimerism and have been successfully taken off immunosuppression (IS). We prospectively evaluated immune reconstitution and immunocompetence. Return of CD4 and CD8 T central and effector memory cell populations was rapid. T-cell receptor (TCR) Excision Circle analysis showed a significant proportion of chimeric cells produced were being produced de novo. The TCR repertoires posttransplant in chimeric subjects were nearly as diverse as pretransplant donors and recipients, and were comparable to subjects with transient chimerism who underwent autologous reconstitution. Subjects with persistent chimerism developed few serious infections when off IS. The majority of infectious complications occurred while subjects were still on conventional IS. BK viruria and viremia resolved after cessation of IS and no tissue-invasive cytomegalovirus infections occurred. Notably, although 2 of 4 transiently or nonchimeric subjects experienced recurrence of their underlying autoimmune disorders, none of the chimeric subjects have, suggesting that self-tolerance is induced in addition to tolerance to alloantigen. No persistently chimeric subject has developed donor-specific antibody, and renal function has remained within normal limits. Patients were successfully vaccinated per The American Society for Blood and Marrow Transplantation guidelines without loss of chimerism or rejection. Memory for hepatitis vaccination persisted after transplantation. Chimeric subjects generated immune responses to pneumococcal vaccine. These data suggest that immune reconstitution and immunocompetence are maintained in persistently chimeric subjects.