Donor bone marrow transplantation: chimerism and tolerance

Clinical Operational Tolerance and Immunosuppression Minimization in Kidney Transplantation: Where Do We Stand?

BACKGROUND

The 20th century represents a breakthrough in the transplantation era, since the first kidney transplantation between identical twins was performed. This was the first case of tolerance, since the recipient did not need immunosuppression. However, as transplantation became possible, an immunosuppression-free status became the ultimate goal, since the first tolerance case was a clear exception from the hard reality nowadays represented by rejection.

METHODS

A plethora of studies was described over the past decades to understand the molecular mechanisms responsible for rejection. This review focuses on the most relevant studies found in the literature where renal tolerance cases are claimed. Contrasting, and at the same time, encouraging outcomes are herein discussed and a glimpse on the main renal biomarkers analyzed in this field is provided.

RESULTS

The activation of the immune system has been shown to play a central role in organ failure, but also it seems to induce a tolerance status when an allograft is performed, despite tolerance is still rare to register. Although there are still overwhelming challenges to overcome and various immune pathways remain arcane; the immunosuppression minimization might be more attainable than previously believed.

CONCLUSION

. Multiple biomarkers and tolerance mechanisms suspected to be involved in renal transplantation have been investigated to understand their real role, with still no clear answers on the topic. Thus, the actual knowledge provided necessarily leads to more in-depth investigations, although many questions in the past have been answered, there are still many issues on renal tolerance that need to be addressed.

Inducción de tolerancia inmunológica: alotrasplantes compuestos vascularizados y trasplantes de órgano sólido

Introducción. La inducción de tolerancia inmunológica solucionaría los problemas asociados con la inmunosupresión de por vida, necesaria para evitar el rechazo de aloinjertos.Objetivos. Revisar aspectos inmunológicos, modelos clínicos utilizados y resultados obtenidos en la tolerancia y comparar los resultados obtenidos con trasplante de órgano sólido y alotrasplante compuesto vascularizado.Materiales y métodos. Se realizó una búsqueda en la base de datos PubMed que arrojó 299 resultados; se revisaron las bibliografías de los artículos y se consultaron las referencias pertinentes. Al final se seleccionaron 83 artículos.Resultados. Existen mecanismos centrales y periféricos para mantener la tolerancia a antígenos propios; en la práctica clínica, la tolerancia central ha sido más utilizada, esto se ha hecho mediante estrategias que utilizan trasplante conjunto de medula ósea. Varios ensayos clínicos, la mayoría en pacientes con trasplante renal, han mostrado resultados prometedores pero inconsistentes.Conclusiones. En trasplantes renales fue posible suspender de forma exitosa la inmunosupresión, mientras que en trasplantes de mano se logró disminuirla considerablemente. El quimerismo inmunológico parece ser indispensable para el desarrollo de tolerancia a aloinjertos, por lo que es necesario desarrollar protocolos para inducir quimerismo mixto persistente.

Novel Immune Check-Point Regulators in Tolerance Maintenance

The great success of anti-cytotoxic lymphocyte antigen 4 (CTLA4) and anti-programed cell death protein 1 (PD1) in cancer treatment has encouraged more effort in harnessing the immune response through immunomodulatory molecules in various diseases. The immunoglobulin (Ig) super family comprises the majority of immunomodulatory molecules. Discovery of novel Ig super family members has brought novel insights into the function of different immune cells in tolerance maintenance. In this review, we discuss the function of newly identified B7 family molecules, B7-H4 and V-domain Ig Suppressor of T cell Activation (VISTA), and the butyrophilin/butyrophilin-like family members. We discuss the current stages of immunomodulatory molecules in clinical trials of organ transplantation. The potential of engaging the novel Ig superfamily members in tolerance maintenance is also discussed. We conclude with the challenges remaining to manipulate these molecules in the immune response.

Regulatory T-cell subset analysis and profile of interleukin (IL)-10, IL-17 and interferon-gamma cytokine-producing cells in kidney allograft recipients with donor cells infusion

BACKGROUND

This pilot study aimed to assess whether the perioperative infusion of donor bone marrow cells (DBMC) in renal allograft recipients can affect the appearance of peripheral regulatory T-cell subsets and the profile of cytokine-producing cells [interferon-gamma (IFN-γ), interleukin (IL)-17 and IL-10] 2 years after transplantation.

METHODS

Fresh blood samples were collected from 14 kidney recipients who received infusion and from 13 kidney recipients without infusion who served as controls at the end of the second post-transplantation year. Initially the percentages of CD4(+)CD25(+)FoxP3(+) T cells and CD3(+)CD8(+)CD28(-) T cells were quantified using flowcytometry. Thereafter, the frequencies of IL-10-, IL-17- and IFN-γ-producing cells were determined separately using the ELISPOT technique with peptides corresponding to mismatched donor HLA-DR molecules and phytohemagglutinin (PHA).

RESULTS

The mean numbers of IFN-γ- and IL-17-producing cells in response to PHA were lower in infused patients than in controls (P = 0.02 and P = 0.18, respectively); however, an increased frequency of IL-10-producing cells was observed compared to controls (P = 0.07). Furthermore, the ratio of IL-10/IFN-γ-producing cells was significantly higher in the DBMC-infused group versus controls (P = 0.01). There was a negative correlation between the percentage of CD3(+)CD8(+)CD28(-)T cells and IL-17-producing cells in the infused group (r = -0.539, P = 0.04). The mean levels and the frequency of microchimerism within the first post-transplantation year were also significantly higher in infused patients than in controls (P = 0.007 and P = 0.001, respectively).

CONCLUSION

Our findings suggest that DBMC infusion could partially stimulate the regulatory mechanisms against alloimmune responses in kidney allograft recipients

Upper-extremity transplantation using a cell-based protocol to minimize immunosuppression

OBJECTIVE

To minimize maintenance immunosuppression in upper-extremity transplantation to favor the risk-benefit balance of this procedure.

BACKGROUND

Despite favorable outcomes, broad clinical application of reconstructive transplantation is limited by the risks and side effects of multidrug immunosuppression. We present our experience with upper-extremity transplantation under a novel, donor bone marrow (BM) cell-based treatment protocol ("Pittsburgh protocol").

METHODS

Between March 2009 and September 2010, 5 patients received a bilateral hand (n = 2), a bilateral hand/forearm (n = 1), or a unilateral (n = 2) hand transplant. Patients were treated with alemtuzumab and methylprednisolone for induction, followed by tacrolimus monotherapy. On day 14, patients received an infusion of donor BM cells isolated from 9 vertebral bodies. Comprehensive follow-up included functional evaluation, imaging, and immunomonitoring.

RESULTS

All patients are maintained on tacrolimus monotherapy with trough levels ranging between 4 and 12 ng/mL. Skin rejections were infrequent and reversible. Patients demonstrated sustained improvements in motor function and sensory return correlating with time after transplantation and level of amputation. Side effects included transient increase in serum creatinine, hyperglycemia managed with oral hypoglycemics, minor wound infection, and hyperuricemia but no infections. Immunomonitoring revealed transient moderate levels of donor-specific antibodies, adequate immunocompetence, and no peripheral blood chimerism. Imaging demonstrated patent vessels with only mild luminal narrowing/occlusion in 1 case. Protocol skin biopsies showed absent or minimal perivascular cellular infiltrates.

CONCLUSIONS

Our data suggest that this BM cell-based treatment protocol is safe, is well tolerated, and allows upper-extremity transplantation using low-dose tacrolimus monotherapy.

Donor-derived peripheral mononuclear cell DNA is associated with stable kidney allograft function: a randomized controlled trial

A large body of literature has documented an inconsistent relationship of peripheral donor cell chimerism with alloimmune tolerance following kidney transplantation. We revisit this association with assays capable of quantifying cellular microchimerism with 150-1500-fold greater sensitivity than previously utilized allo-antibody based flow cytometric approaches. Forty renal transplant patients, 20 with concurrent donor bone marrow infusion (DBMI) and 20 control participants without infusion were prospectively monitored for peripheral blood microchimerism using donor polymorphism-specific quantitative real-time PCR. Thirty-eight patients were evaluated for microchimerism, 19 in each group. The frequency of testing positive for (95% vs. 58%, p = 0.02) and mean concentrations of microchimerism (115 ± 66 vs. 13 ± 3 donor genomes/million recipient genomes, p = 0.007), respectively, were higher in infused patients compared with controls. Thirty-one patients maintained stable graft function; 17 in the DBMI group vs. 14 in controls. Patients with stable graft function in the DBMI group compared with control patients harbored microchimerism more frequently (94 vs. 50%, p = 0.01) and at higher concentrations (123 ± 67 vs. 11 ± 4, p = 0.007), respectively. Significant correlation between dose of infused cells and microchimerism levels was found post-transplant (p = 0.01). Using very sensitive assays, our findings demonstrate associations between the presence and quantity of microchimerism with stable graft function in infused patients.

Immunologic aspects and rejection in solid organ versus reconstructive transplantation

The immunosuppressive medications developed over the past 3 decades have paved the way for solid organ transplantation to become the treatment of choice for end-stage organ failure. At the end of the century, composite tissue transplantation in humans was performed with success using the same immunosuppressive medications and therapeutic principles. A decade later, experience from >100 cases of reconstructive transplantation have increased the knowledge, changed the view, and affected the therapeutic principles in this novel field. We herein portray the evolution of this novel type of transplant with particular reference to immunologic aspects, particularly differences between reconstructive and solid organ transplantation.

Clinical operational tolerance after renal transplantation: current status and future challenges

In solid organ transplantation, the achievement of an immunosuppression (IS)-free state [also referred to as clinical operational tolerance (COT)] represents the ultimate goal. Although COT is feasible and safe in selected cases after liver transplantation, it is an exceptional finding after other types of solid organ transplantation. In the field of renal transplantation (RT), approximately 100 cases of COT have been reported to date, mainly in patients who were not compliant with their immunosuppressive regimens or in individuals who had previously received a bone marrow transplant for hematological disorders. On the basis of promising results obtained in animal models, several tolerogenic protocols have been attempted in humans, but most have failed to achieve robust and stable COT after RT. Molecule-based regimens have been largely ineffective, whereas cell-based regimens have provided some encouraging results. In these latter regimens, apart from standard IS, patients usually receive perioperative infusion of donor bone marrow-derived stem cells, which are able to interact with the immune cells of the host and mitigate their response to engraftment. Unfortunately, most renal transplant patients who developed acute rejection-occurring either during the weaning protocol or after complete withdrawal of IS-eventually lost their grafts. Currently, the immune monitoring necessary for predicting the presence and persistence of donor-specific unresponsiveness is not available. Overall, the present review will provide a conceptual framework for COT and conclude that stable and robust COT after RT remains an elusive goal and that the different strategies attempted to date are not yet reproducibly safe or effective.

Portal venous donor-specific transfusion in conjunction with sirolimus prolongs renal allograft survival in nonhuman primates

Pretransplant exposure to donor antigen is known to modulate recipient alloimmunity, and frequently results in sensitization. However, donor-specific transfusion (DST) can have a protolerant effect that is dependent on route, dose and coadministered immunosuppression. Rodent studies have shown in some strain combinations that portal venous (PV) DST alone can induce tolerance, and uncontrolled clinical use of PVDST has been reported. In order to determine if pretransplant PVDST has a clinically relevant salutary effect, we studied it and the influence of concomitant immunosuppression in rhesus monkeys undergoing renal allotransplantation. Animals received PVDST with unfractionated bone marrow and/or tacrolimus or sirolimus 1 week prior to transplantation. Graft survival was assessed without any posttransplant immunosuppression. PVDST alone or in combination with tacrolimus was ineffective. However, PVDST in combination with sirolimus significantly prolonged renal allograft survival to a mean of 24 days. Preoperative sirolimus alone had no effect, and peripheral DST with sirolimus prolonged graft survival in 2/4 animals, but resulted in accelerated rejection in 2/4 animals. These data demonstrate that PVDST in combination with sirolimus delays rejection in a modest but measurable way in a rigorous model. It may thus be a preferable method for donor antigen administration.

Expansion of effector memory TCR Vbeta4+ CD8+ T cells is associated with latent infection-mediated resistance to transplantation tolerance

Therapies that control largely T cell-dependent allograft rejection in humans also possess the undesirable effect of impairing T cell function, leaving transplant recipients susceptible to opportunistic viruses. Prime among these opportunists are the ubiquitous herpesviruses. To date, studies are lacking that address the effect of viruses that establish a true latent state on allograft tolerance or the effect of tolerance protocols on the immune control of latent viruses. By using a mixed chimerism-based tolerance-induction protocol, we found that mice undergoing latent infection with gammaHV68, a murine gamma-herpesvirus closely related to human gamma-herpesviruses such as EBV and Kaposi's sarcoma-associated herpesvirus, significantly resist tolerance to allografts. Limiting the degree of virus reactivation or innate immune response did not reconstitute chimerism in latently infected mice. However, gammaHV68-infected mice showed increased frequency of CD8+ T cell alloreactivity and, interestingly, expansion of virus-induced, alloreactive, "effector/effector memory" TCR Vbeta4+CD8+ T cells driven by the gammaHV68-M1 gene was associated with resistance to tolerance induction in studies using gammaHV68-M1 mutant virus. These results define the viral gene and immune cell types involved in latent infection-mediated resistance to allograft tolerance and underscore the influence of latent herpesviruses on allograft survival.

Sequence-specific analysis of microchimerism by real-time quantitative polymerase chain reaction in same-sex nonhuman primates after islet and bone marrow transplantation

BACKGROUND

Accurate and sensitive detection of microchimerism in nonhuman primates (NHPs) after hematopoietic cell transplantation is essential for monitoring cell engraftment, for evaluating the success of transplant protocols, and for expanding the utility of NHP in transplantation studies. Because limited sequences are available for NHP major histocompatibility complex polymorphic loci, methods that can accurately determine low levels of donor cells in recipients with same-sex bone marrow transplantation are essential.

METHODS

Thirty-seven pairs of primers, 16 from monkey and 21 from human, were screened with cynomolgus DNA samples. Real-time quantitative polymerase chain reaction was developed for accurately determining low levels of donor-specific DNA in the peripheral blood of islet/bone marrow transplant recipients of same sex cynomolgus monkeys.

RESULTS

A total of six sets of primer and Taqman(R) probe combinations were included in this study, which are the most informative primer and probe sets ever reported for cynomolgus monkeys. Three pairs of primers were chosen from exon 2 of the Macaca DRB1 gene and another three pairs were chosen from human HLA DRB1 and DRB3 loci. Three of the six primer-probe sets were also found to work well for baboon (Papio hamadryas) and rhesus monkeys (Macaca mulatta). Sensitivity of the assay ranged from 0.03% to 0.1%, depending on the primer-probe set and donor-recipient pair. The methods are reproducible with relatively low standard error and coefficient of variation.

CONCLUSIONS

This method is an informative, practical and sensitive method for the determination of donor-specific cells in the peripheral blood of NHP recipients of bone marrow transplant.

Inhibition of NF-kappa B during human dendritic cell differentiation generates anergy and regulatory T-cell activity for one but not two human leukocyte antigen DR mismatches

We examined the in vitro inhibition of human monocyte-derived dendritic cells (DC) maturation via NF-kappaB blockade on T-cell allostimulation, cytokine production, and regulatory T-cell generation. DC were generated from CD14+ monocytes isolated from peripheral blood using GM-CSF and IL-4 for differentiation and TNF-alpha, IL-1beta, and PGE2 as maturational stimuli with or without the NF-kappaB inhibitors, BAY 11-7082 (BAY-DC) or Aspirin (ASA-DC). Stimulator and responder cells were one versus two HLA-DR mismatched in direct versus indirect presentation assays. Both BAY-DC and ASA-DC expressed high levels of HLA-DR and CD86 but always expressed less CD40 compared with controls. Some experiments showed slightly lower levels of CD80. Both BAY- and ASA-allogeneic DC and autologous alloantigen pulsed DC were weaker stimulators of T cells (by MLR) compared with controls, and there was reduced IL-2 and IFN-gamma production by T cells stimulated with BAY-DC or ASA-DC (by ELISPOT) (more marked results were always observed with ASA-treated DC). In addition, NF-kappaB blockade of DC maturation caused the generation of T cells with regulatory function (T regs) but only when T cells were stimulated by either allogeneic (direct presentation) or alloantigen pulsed autologous DC (indirect presentation) with one HLA-DR mismatch and not with two HLA-DR mismatches (either direct or indirect presentation). However, the T regs generated from these ASA-DC showed similar FoxP3 mRNA expression to those from nontreated DC. Extension of this study to human organ transplantation suggests potential therapies using one DR-matched NF-kappaB blocked DC to help generate clinical tolerance.

Applications of bilateral vascularized femoral bone marrow transplantation for chimerism induction across the major histocompatibility (MHC) barrier: part II

Bilateral vascularized bone marrow transplant (VBMT) model was designed to induce chimerism across the major histocompatibility (MHC) barrier under combined alphabeta T-cell receptor monoclonal antibody and cyclosporine A (alphabeta-TCRmAb/CsA) protocol. Seventeen transplants were performed between BN(RT1) donors and Lewis(RTI) recipients. Group I, isograft controls; Group II, allografts rejection controls; Group III, allografts under 7-day protocol of alphabeta-TCRmAb/CsA. Donor bilateral femoral bones were bilaterally anastomosed to the abdominal aorta and inferior vena cava of recipient. At day 7 posttransplantation, all bone flaps were viable. Groups I and III survived without signs of rejection. In Group III, peak level of chimerism in peripheral blood was evaluated at day 21 (24.2%), at day 63 declined to 1.5%, and was maintained at this level thereafter. Donor-derived cells were present in the bone marrow of recipients at 28.2% at day 21 posttransplant. Histology confirmed viability of bone marrow cells in isograft during the entire follow-up and up to 35 days in treatment Group III. Bilateral VBMT induced donor-specific chimerism across the MHC barrier under the immunomodulatory protocol of alphabeta-TCRmAb/CsA.

Blood group chimerism

PURPOSE OF REVIEW

With improved methods for detecting chimeras and growing numbers of stem cell transplantations, blood group and other forms of chimerism are observed with increasing frequency. This review will focus on the state of science and new insights into the multifaceted subject of blood group chimerism.

RECENT FINDINGS

Recognition that the immune system tolerates chimeric cells under certain conditions has led to efforts to elucidate related immune-modulating processes. The chimeric state following transplantation of hematopoietic stem cells, as well as after solid organ transplantation, is of special interest. Also, chimerism is considered to be a potential trigger for certain autoimmune diseases. Natural chimerism is more frequent than previously recognized. Using improved laboratory techniques, investigators can often trace chimeric tissues to their origin. New therapeutic strategies have been applied after stem cell transplantation depending on the chimeric state. Also, recent research has resulted in methods for determining chimerism in maternal peripheral blood that reflect fetal blood type and certain congenital diseases.

SUMMARY

The subject of human chimerism has evolved from a curiosity of nature to an important field of research and, potentially, holds the key to advancing our understanding of the fundamental mechanisms of immune tolerance.

Modeling CTLA4-linked autoimmunity with RNA interference in mice

The CTLA4 gene is important for T lymphocyte-mediated immunoregulation and has been associated with several autoimmune diseases, in particular, type 1 diabetes. To model the impact of natural genetic variants of CTLA4, we constructed RNA interference (RNAi) "knockdown" mice through lentiviral transgenesis. Variegation of expression was observed in founders but proved surmountable because it reflected parental imprinting, with derepression by transmission from male lentigenics. Unlike the indiscriminate multiorgan autoimmune phenotype of the corresponding knockout mice, Ctla4 knockdown animals had a disease primarily focused on the pancreas, with rapid progression to diabetes. As with the human disease, the knockdown phenotype was tempered by genetic-modifier loci. RNAi should be more pertinent than gene ablation in modeling disease pathogenesis linked to a gene-dosage variation.

The concept of “partial” clinical tolerance

The status of "partial" tolerance to organ allografts versus the status of complete tolerance is the main topic of this paper. Progress made in immunosuppression, particularly by use of various lymphocyte depleting agents for "induction therapy", seems to favor the subsequent development of T cells with suppressor/regulatory properties. The effective deletion of alloreactive T helper and cytotoxic cells in conjunction with the expansion of antigen-specific suppressor (CD8 + CD28 - FOXP3+) and regulatory (CD4 + CD25+ FOXP3+) T cells creates a milieu in which the graft is well tolerated under an "umbrella" of low dosage immunosuppression. The most effective induction treatment is Campath-1H, although ATGAM at high dosage is also widely used. Total lymphoid irradiation (TLI) is another very effective pretreatment strategy in spite of the risks which are associated with it. The induction of "partial" tolerance is a step in the right direction for exploring strategies that may lead to the induction of complete tolerance. It is safe for the patients and can prolong significantly the function of the graft, preventing the onset of chronic rejection.