Intrathymic deletion of alloreactive T cells in mixed bone marrow chimeras prepared with a nonmyeloablative conditioning regimen

Mechanisms involved in the establishment of tolerance through costimulatory blockade and BMT: lack of requirement for CD40L-mediated signaling for tolerance or deletion of donor-reactive CD4+ cells

We have previously shown that high levels of multiline-age mixed hematopoietic chimerism and systemic T-cell tolerance can be achieved in mice without myeloablation through the use of anti-CD40L and costimulatory blockade alone (plus CTLA4Ig) or with recipient CD8 depletion and allogeneic bone marrow transplantation. Chimeric mice permanently accept donor skin grafts (> 100 days), and rapidly reject third-party grafts. The mechanisms by which costimulatory blockade facilitates the engraftment of allogeneic hematopoietic cells have not been defined. To further understand the in vivo mechanisms by which the administration of anti-CD40L mAb facilitates the engraftment of donor bone marrow and rapidly tolerizes CD4+ T cells, we analyzed the establishment of chimerism and tolerance in CD40L -/- mice. We demonstrate here that anti-CD40L mAb treatment is required only to prevent CD40L/CD40 interactions, and that no signal to the T cell through CD40L is necessary for the induction of CD4+ tolerance. Peripheral deletion of donor-reactive CD4+ T cells occurs rapidly in CD40L -/- mice receiving bone marrow transplantation (BMT), indicating that this deletion in the presence of anti-CD40L is not due to targeting of activated CD4+ cells by the antibody. Complete CD4+ cell tolerance is observed by both skin graft acceptance and in vitro assays before deletion is complete, indicating that additional mechanisms play a role in inducing CD4+ T-cell tolerance as the result of BMT in the presence of CD40/CD40L blockade.

Reducing transplant toxicity

Conventional myeloablative allogeneic hematopoietic cell transplantation produces considerable morbidity and mortality. These generally limit this treatment to patients in good medical condition who are younger than 55 years of age. T-cell-mediated graft-versus-tumor effects play a key role in the elimination of malignancy after allografting. Several investigators have sought to reduce regimen-related toxicities while optimizing graft-versus-tumor effects. Strategies can be broadly classified as (1) reduced-intensity regimens that retain some toxicity, and (2) minimally myelosuppressive regimens that rely on immunosuppression for allogeneic engraftment and resultant graft-versus-tumor effects. Although follow-up has been short, preliminary results are encouraging. Current challenges include defining a regimen that will facilitate full donor engraftment while minimizing toxicities and graft-versus-host disease. If long-term efficacy is demonstrated, such strategies will expand the options for patients who would not qualify for conventional allogeneic transplants.

Indefinite allograft survival mediated by donor bone marrow is dependent on the presence of a functional CD95 (Fas) gene in recipients

It is well documented that donor bone marrow in combination with peri-transplant anti-thymocyte globulin (ATG) administration induces transplantation tolerance in a variety of animal models. Our previous work showed that the ability of donor marrow to induce tolerance was dependent on the presence of CD95 ligand (Fas-ligand) on the donor cells. In this study we investigate whether CD95 (Fas) on the recipient cells is required. By comparing skin allograft survival times between wild-type C57BL/6 ATG-treated recipients and C57BL/6(lpr/lpr) ATG-treated recipients (which do not have a functional CD95 gene), we show that donor bone marrow could induce indefinite transplant survival (median survival time >200 days) only in recipients with a functional CD95 gene. Thus, we conclude that the CD95 ligand-CD95 apoptotic pathway plays a major role in donor bone marrow-induced transplantation tolerance.

Alloantigen-induced specific immunological unresponsiveness

When the immune system encounters alloantigen it can respond in any one of a number of different ways. The choice that is made will take into account factors such as where, when and how the contact with the alloantigen takes place, as well as the environmental conditions that prevail at the time the alloantigen is encountered. Alloantigen administration before transplantation either alone or in combination with therapeutic agents that modulate the functional activity of the responding leucocytes can be a powerful way of inducing specific unresponsiveness to alloantigens in vivo. The molecular mechanisms that influence the way the outcome of the immune response to alloantigen develops, either activation or unresponsiveness to the triggering antigen, hold the key to our ability to manipulate the immune system effectively by exposing it to donor antigen for therapeutic purposes. This review will focus on alloantigen-induced immunological unresponsiveness and how insights into the mechanisms of unresponsiveness have driven the development of novel tolerance-induction strategies that show promise for translation into the clinic in the future.

Mixed chimerism

Induction of mixed chimerism has the potential to overcome the current limitations of transplantation, namely chronic rejection, complications of immunosuppressive therapy and the need for xenografts to overcome the current shortage of allogeneic organs. Successful achievement of mixed chimerism had been shown to tolerize T cells, B cells and possibly natural killer cells, the lymphocyte subsets that pose major barriers to allogeneic and xenogeneic transplants. Current understanding of the mechanisms involved in tolerization of each cell type is reviewed. Considerable advances have been made in reducing the potential toxicity of conditioning regimens required for the induction of mixed chimerism in rodent models, and translation of these strategies to large animal models and in a patient are important advances toward more widespread clinical application of the mixed chimerism approach for tolerance induction.

Transplantation tolerance induced by mixed chimerism

Although short- and long-term results after organ transplantation have improved considerably in recent years, morbidity and mortality rates in graft recipients remain high. The induction of lifelong donor-specific tolerance would dramatically improve outcome after organ transplantation. Although many tolerance protocols have been successful in rodent studies, most of these approaches have failed when attempted in large animals or humans. Robust tolerance, in contrast, has been demonstrated with mixed chimerism regimens not only in rodents but also in large animal models, including non-human primates. Furthermore, mixed chimerism protocols have been developed that would be feasible in cadaveric, and thus in thoracic, transplantation. The induction of mixed hematopoietic chimerism is therefore an attractive experimental approach for development of clinical tolerance protocols. One of the obstacles to widespread clinical application of this concept is the remaining toxicity of the host conditioning. Recent advances, however, have led to substantially milder protocols that could become clinically acceptable in the foreseeable future. This article provides a short overview of the basic mechanisms by which immunologic tolerance may be induced, describes the concept of mixed chimerism as a promising approach for clinical tolerance induction, and reviews recent progress in developing clinically feasible mixed chimerism protocols.

Allogeneic hematopoietic stem-cell transplantation after nonmyeloablative preparative regimens: impact of pretransplantation and posttransplantation factors on outcome

PURPOSE

To analyze the impact of pre- and posttransplantation factors on the outcome of allogeneic transplantation after nonmyeloablative conditioning regimens.

PATIENTS AND METHODS

Ninety-two allogeneic transplantations after nonmyeloablative preparative regimens were reported to the Société Française de Greffe de Moelle Registry registry. Initial diagnoses were lymphoid diseases (n = 22), myeloma (n = 14), acute leukemia and myelodysplasia (n = 41), chronic myelogenous leukemia (n = 12), and solid tumors (n = 3). Forty-six patients had previously received a transplant, and 49 had progressive disease before transplantation. Three types of conditioning regimens were used with fludarabine or antithymocyte globulins. Eighty-nine patients underwent transplantation, 60 from peripheral-blood progenitor cells. Eighty-six patients received graft-versus-host disease (GHVD) prophylaxis for a median duration of 53 days.

RESULTS

Seventy-nine patients engrafted, with 40 complete and 21 mixed chimerisms. The acute GHVD rate at 3 months was 50% +/- 11%. Fifty-two patients achieved complete remission and 12, partial remission. At 18 months after transplantation, the overall survival (OS) and the transplant-related mortality (TRM) were 32% +/- 12% and 38% +/- 14%, respectively. Initial diagnosis and disease status before transplantation significantly influenced survival. Age and GHVD prophylaxis type significantly influenced TRM. We also showed an impact of GHVD prophylaxis duration on OS and TRM. In multivariate analysis, three factors remained of prognostic value on OS: initial diagnosis, disease status at transplantation, and GHVD prophylaxis duration.

CONCLUSION

This series shows encouraging results from nonmyeloablative conditioning regimens before allotransplantation and demonstrates the impact of some pre- and posttransplantation factors on outcome after transplantation.

Mixed chimerism and transplantation tolerance

Achieving transplantation tolerance is an important goal in the effort to reduce long-term morbidity and mortality in organ transplant recipients. Robust, lifelong, donor-specific tolerance can be reliably achieved by induction of mixed chimerism in various animal models. To date, the clinical application of these proto-cols has been impeded partly by the potential toxicity of the required host conditioning regimens and the lack of successful studies in large animals. This article reviews the progress achieved in recent years in developing considerably milder conditioning protocols in rodents, and in extending some of these models to achieve permanent mixed chimerism and tolerance in large animals. Advances in the induction of xenogeneic tolerance through mixed chimerism are also discussed.

Nonmyeloablative hematopoietic cell transplantation

The myeloablative doses of chemotherapy and radiation used with conventional allogeneic hematopoietic cell transplantation produce considerable morbidity and mortality that generally limit this treatment to patients younger than 55 years of age and in good general medical condition. It has become clear that T-cell-mediated graft-versus-tumor effects play an important role in the elimination of malignant disease after allotransplants. Several investigators have sought to reduce regimen-related toxicities while optimizing graft-versus-tumor effects. Strategies can be broadly categorized as reduced-intensity regimens that retain some toxicities and require hospitalization, and minimally myelosuppressive regimens that rely on immunosuppression for allogeneic engraftment and resultant graft-versus-tumor effects. The latter approach can be performed in the ambulatory care setting. Preliminary results are encouraging. If long-term efficacy is demonstrated, such strategies would expand treatment options for patients who would otherwise be excluded from receiving conventional allografts.

CD4 T cell-mediated alloresistance to fully MHC-mismatched allogeneic bone marrow engraftment is dependent on CD40-CD40 ligand interactions, and lasting T cell tolerance is induced by bone marrow transplantation with initial blockade of this pathway

Costimulatory blockade can be used to promote allogeneic marrow engraftment and tolerance induction, but on its own is not 100% reliable. We sought to determine whether one or the other of the CD4 or CD8 T cell subsets of the recipient was primarily responsible for resistance to allogeneic marrow engraftment in mice receiving costimulatory blockade, and to use this information to develop a more reliable, minimal conditioning regimen for induction of mixed chimerism and transplantation tolerance. We demonstrate that a single anti-CD40 ligand mAb treatment is sufficient to completely overcome CD4 cell-mediated resistance to allogeneic marrow engraftment and rapidly induce CD4 cell tolerance, but does not reliably overcome CD8 CTL-mediated alloresistance. The data suggest that costimulation, which activates alloreactive CTL, is insufficient to activate alloreactive CD4 cells when the CD40 pathway is blocked. The addition of host CD8 T cell depletion to anti-CD40 ligand treatment reliably allows the induction of mixed chimerism and donor-specific skin graft tolerance in 3 Gy-irradiated mice receiving fully MHC-mismatched bone marrow grafts. Thus, despite the existence of multiple costimulatory pathways and pathways of APC activation, our studies demonstrate an absolute dependence on CD40-mediated events for CD4 cell-mediated rejection of allogeneic marrow. Exposure to donor bone marrow allows rapid tolerization of alloreactive CD4 cells when the CD40 pathway is blocked, leading to permanent marrow engraftment and intrathymic tolerization of T cells that develop subsequently.

Both gamma delta T cells and NK cells inhibit the engraftment of xenogeneic rat bone marrow cells and the induction of xenograft tolerance in mice

In murine allogeneic bone marrow transplantation recipients, treatment of the hosts with a nonmyeloablative regimen, including depleting anti-CD4 and anti-CD8 mAbs, allows establishment of long-term mixed chimerism and donor-specific tolerance. However, in the xenogeneic rat-to-mouse combination, additional anti-Thy1.2 and anti-NK1.1 mAbs are required. We have now attempted to identify the xenoresistant mouse cell populations that are targeted by anti-NK1.1 and anti-Thy1.2 mAbs. C57BL/6 (B6) wild-type, B6 TCRbeta(-/-), and B6 TCRdelta(-/-) mice received anti-CD4 and anti-CD8 mAbs, followed by 3 Gy of whole body irradiation, 7 Gy of thymic irradiation, and transplantation of T cell-depleted rat bone marrow cells. Anti-NK1.1 and anti-Thy1.2 mAbs were additionally administered to some groups. Increased rat chimerism was observed in TCRdelta(-/-) mice treated with anti-CD4, anti-CD8, and anti-NK1.1 mAbs compared with similarly treated TCRbeta(-/-) mice. In TCRbeta(-/-) mice, but not in TCR delta(-/-) mice, donor chimerism was increased by treatment with anti-Thy1.2 mAb, indicating that CD4(-)CD8(-)TCRgammadelta(+)Thy1. 2(+)NK1.1(-) cells (gammadelta T cells) are involved in the rejection of rat marrow. In addition, chimerism was enhanced in both TCRbeta(-/-) and TCRdelta(-/-) mice treated with anti-CD4, anti-CD8, and anti-Thy1.2 mAbs by the addition of anti-NK1.1 mAb to the conditioning regimen. Donor-specific skin graft prolongation was enhanced by anti-Thy1.2 and anti-NK1.1 mAbs in TCRdelta(-/-) mice. Therefore, in addition to CD4 and CD8 T cells, gammadelta T cells and NK cells play a role in resisting engraftment of rat marrow and the induction of xenograft tolerance in mice.

A novel application of cyclosporine A in nonmyeloablative pretransplant host conditioning for allogeneic BMT

The treatment of mice with anti-CD4 and anti-CD8 monoclonal antibodies (mAbs) on day −5, plus 3 Gy whole body irradiation (WBI) and 7 Gy thymic irradiation (TI) on day 0, allows fully major-histocompatibility-complex–mismatched allogeneic bone marrow engraftment and the induction of immunologic tolerance. TI is required in this model to overcome alloreactivity and possibly to make “space” in the recipient thymus so that lasting central tolerance can be achieved. In addition to suppressing mature T cells in the periphery, Cyclosporine A (CYA) and glucocorticoids have a powerful influence on the thymus. In this study, we evaluated whether the administration of CYA to recipient mice for 12 days prior to bone marrow transplant (BMT), of glucocorticosteroids on the day of BMT, or a combination of both, could create space and overcome alloresistance in the thymus by specifically depleting immature and mature thymocytes prior to BMT. High levels of multilineage donor hematopoietic repopulation and specific transplantation tolerance were achieved in mice treated from days −15 to −3 with CYA (20 mg/kg/d subcutaneously), anti-CD4/CD8 mAbs on day −5, followed by 3 Gy WBI and 15 × 106 allogeneic bone marrow cells on day 0. Vβ analysis suggested a central deletional tolerance mechanism. The same treatment without CYA pretreatment allowed only transient chimerism, without tolerance. Corticosteroid treatment abolished the engraftment-promoting and tolerance-inducing effects of CYA. These results demonstrate a novel pretransplantation-only application of CYA, which facilitates allogeneic marrow engraftment with minimal conditioning, by creating thymic space and/or overcoming intrathymic alloresistance.

A novel application of cyclosporine A in nonmyeloablative pretransplant host conditioning for allogeneic BMT

The treatment of mice with anti-CD4 and anti-CD8 monoclonal antibodies (mAbs) on day −5, plus 3 Gy whole body irradiation (WBI) and 7 Gy thymic irradiation (TI) on day 0, allows fully major-histocompatibility-complex–mismatched allogeneic bone marrow engraftment and the induction of immunologic tolerance. TI is required in this model to overcome alloreactivity and possibly to make “space” in the recipient thymus so that lasting central tolerance can be achieved. In addition to suppressing mature T cells in the periphery, Cyclosporine A (CYA) and glucocorticoids have a powerful influence on the thymus. In this study, we evaluated whether the administration of CYA to recipient mice for 12 days prior to bone marrow transplant (BMT), of glucocorticosteroids on the day of BMT, or a combination of both, could create space and overcome alloresistance in the thymus by specifically depleting immature and mature thymocytes prior to BMT. High levels of multilineage donor hematopoietic repopulation and specific transplantation tolerance were achieved in mice treated from days −15 to −3 with CYA (20 mg/kg/d subcutaneously), anti-CD4/CD8 mAbs on day −5, followed by 3 Gy WBI and 15 × 106 allogeneic bone marrow cells on day 0. Vβ analysis suggested a central deletional tolerance mechanism. The same treatment without CYA pretreatment allowed only transient chimerism, without tolerance. Corticosteroid treatment abolished the engraftment-promoting and tolerance-inducing effects of CYA. These results demonstrate a novel pretransplantation-only application of CYA, which facilitates allogeneic marrow engraftment with minimal conditioning, by creating thymic space and/or overcoming intrathymic alloresistance.

Adoptive immunotherapy in canine mixed chimeras after nonmyeloablative hematopoietic cell transplantation

Development of nontoxic and nonmyeloablative regimens for allogeneic hematopoietic stem-cell transplantation will decrease transplantation-related mortality caused by regimen-related toxic effects. In pursuit of this goal, a dog model of stable mixed hematopoietic chimerism was established in which leukocyte-antigen–identical litter mates are given sublethal total-body irradiation (2 Gy) before stem-cell transplantation and immunosuppression with mycophenolate mofetil and cyclosporine afterward. In the current study, we examined whether donor lymphocyte infusion (DLI) could be used as adoptive immunotherapy to convert mixed to complete donor chimerism. First, 8 mixed chimeras were given unmodified DLI between day 36 and day 414 after stem-cell transplantation. After a 10- to 47-week follow-up period, there were no significant changes in the percentage of donor engraftment. Next, we immunized the donor to the minor histocompatibility antigens (mHA) of the recipient by means of repeated skin grafting. Lymphocytes from the mHA-sensitized donor were infused between day 201 and day 651 after transplantation. All 8 recipients of mHA-sensitized DLI had conversion to greater than 98% donor chimerism within 2 to 12 weeks of the infusion. Complications from mHA-sensitized DLI included graft-versus-host disease in 2 dogs and marrow aplasia in 1. These results showed that the low-dose transplant regimen establishes immune tolerance, and mHA-sensitized DLI is required to break tolerance, thereby converting mixed to complete donor chimerism. We propose that mixed chimerism established after nonmyeloablative allogeneic stem-cell transplantation provides a platform for adoptive immunotherapy that has clinical potential in the treatment of patients with malignant diseases.

Adoptive immunotherapy in canine mixed chimeras after nonmyeloablative hematopoietic cell transplantation

Development of nontoxic and nonmyeloablative regimens for allogeneic hematopoietic stem-cell transplantation will decrease transplantation-related mortality caused by regimen-related toxic effects. In pursuit of this goal, a dog model of stable mixed hematopoietic chimerism was established in which leukocyte-antigen–identical litter mates are given sublethal total-body irradiation (2 Gy) before stem-cell transplantation and immunosuppression with mycophenolate mofetil and cyclosporine afterward. In the current study, we examined whether donor lymphocyte infusion (DLI) could be used as adoptive immunotherapy to convert mixed to complete donor chimerism. First, 8 mixed chimeras were given unmodified DLI between day 36 and day 414 after stem-cell transplantation. After a 10- to 47-week follow-up period, there were no significant changes in the percentage of donor engraftment. Next, we immunized the donor to the minor histocompatibility antigens (mHA) of the recipient by means of repeated skin grafting. Lymphocytes from the mHA-sensitized donor were infused between day 201 and day 651 after transplantation. All 8 recipients of mHA-sensitized DLI had conversion to greater than 98% donor chimerism within 2 to 12 weeks of the infusion. Complications from mHA-sensitized DLI included graft-versus-host disease in 2 dogs and marrow aplasia in 1. These results showed that the low-dose transplant regimen establishes immune tolerance, and mHA-sensitized DLI is required to break tolerance, thereby converting mixed to complete donor chimerism. We propose that mixed chimerism established after nonmyeloablative allogeneic stem-cell transplantation provides a platform for adoptive immunotherapy that has clinical potential in the treatment of patients with malignant diseases.

Nonmyeloablative stem cell transplants

Allogeneic stem cell transplantation (SCT) is a curative procedure in a number of hematologic malignancies, but its efficacy is limited by its toxicity, much of which is consequent upon the myeloablative conditioning regimens currently used. The recent demonstration that an immunologically mediated graft-versus-leukemia effect plays a central role in delivering the anti-leukemic effect of an allograft has led to a fundamental reevaluation of the role of conditioning therapy in allogeneic transplantation. Recent animal studies have demonstrated that stem cell engraftment can occur using conditioning regimens that are minimally myelotoxic. This has prompted the development of less toxic nonmyeloablative conditioning protocols, the goal of which is to achieve donor stem cell engraftment allowing the graft-versus-tumor effect of the allograft to be exploited as the primary anti-leukemic strategy. Preliminary results using such nonmyeloablative clinical protocols confirm that durable engraftment of allogeneic stem cells can be achieved with a marked reduction in the immediate toxicity of transplantation. The extent to which this radically different transplant strategy allows the delivery of a sustained anti-leukemic effect is unclear at present, but it is likely that this approach will make an important contribution to allogeneic SCT in the future.

Stable Mixed Hematopoietic Chimerism in Dogs Given Donor Antigen, CTLA4Ig, and 100 cGy Total Body Irradiation Before and Pharmacologic Immunosuppression After Marrow Transplant

Stable mixed chimerism can be established in dogs given a sublethal dose of 200 cGy total body irradiation (TBI) before and immunosuppression with mycophenolate mofetil (MMF) and cyclosporine (CSP) for 28 and 35 days, respectively, after dog leukocyte antigen-identical marrow transplantation. Most likely, the role of pretransplant TBI was to provide host immunosuppression, since stable mixed chimerism was also achieved in MMF/CSP-treated dogs when 450 cGy irradiation, targeted to cervical, thoracic, and upper abdominal lymph nodes, was substituted for TBI. When TBI was reduced from 200 to 100 cGy, all grafts were rejected within 3 to 12 weeks. Here, we asked whether stable engraftment after 100 cGy TBI could be accomplished by first reducing the intensity of host immune responsiveness with help of the fusion peptide CTLA4Ig, which blocks T-cell costimulation through the B7-CD28 signal pathway. Accordingly, recipient T cells were activated with intravenous (IV) injections of 106 donor peripheral blood mononuclear cells (PBMC)/kg per day on days −7 to −1 before 100 cGy TBI, with concurrent administration of CTLA4Ig 4 mg/kg/d IV. All 7 dogs so treated showed initial mixed chimerism. Two rejected their allografts after 8 and 20 weeks, respectively, and survived with autologous marrow recovery; 1 mixed chimera was unevaluable because of death at 3 weeks from intussusception; and 4 showed persisting mixed chimerism, including unirradiated marrow and lymph node spaces, for now more than 46 to 70 weeks after transplant. Data support the hypothesis that stable marrow allografts can be established by combining nonmyeloablative pretransplant host immunosuppression with posttransplant host and donor cell immunosuppression using MMF/CSP.

Allogeneic hematopoietic transplantation as adoptive immunotherapy. Induction of graft-versus-malignancy as primary therapy

An immune-mediated graft-versus-malignancy effect is important to prevent relapse after allogeneic bone marrow transplant for a range of hematologic malignancies and potentially some solid tumors. Graft-versus-leukemia (GVL) effects as seen in response to donor lymphocyte infusions have been most prominent against indolent malignancies including chronic myelogenous leukemia, chronic lymphocytic leukemia, and low-grade lymphoma. Acute myelogenous leukemia and multiple myeloma may also respond. An alternative strategy for allogeneic transplantation is to avoid the toxicity of high-dose chemoradiotherapy and use a relatively nontoxic, nonablative preparative regimen to achieve engraftment, allowing subsequent infusion of additional donor lymphocytes to mediate GVL. Fludarabine-based nonablative chemotherapy agents, using standard dose combinations, produce moderate myelosuppression but are sufficiently immunosuppressive to allow engraftment of an allogeneic hematopoietic transplant and generation of graft-versus-malignancy effects.

Combined histocompatibility leukocyte antigen-matched donor bone marrow and renal transplantation for multiple myeloma with end stage renal disease: the induction of allograft tolerance through mixed lymphohematopoietic chimerism

BACKGROUND

Experimental and clinical evidence has demonstrated that the establishment of allogeneic chimerism after bone marrow transplantation may provide donor-specific tolerance for solid organ allografts.

METHODS

Based on the preliminary results of a clinical trial using nonmyeloablative preparative therapy for the induction of mixed lymphohematopoietic chimerism, we treated a 55-year-old woman with end stage renal disease secondary to multiple myeloma with a combined histocompatibility leukocyte antigen-matched bone marrow and renal transplant after conditioning with cyclophosphamide, antithymocyte globulin, and thymic irradiation.

RESULTS

The posttransplant course was notable for early normalization of renal function, the absence of acute graft-versus-host disease, and the establishment of mixed lymphohematopoietic chimerism. Cyclosporine, which was the only posttransplant immunosuppressive therapy, was tapered and discontinued on day +73 posttransplant. No rejection episodes occurred, and renal function remains normal on day + 170 posttransplant (14 weeks after discontinuing cyclosporine). Although there is presently no evidence of donor hematopoiesis, there is evidence of an ongoing antitumor response with a recent staging evaluation showing no measurable urine kappa light chains. The patient remains clinically well and is off all immunosuppressive therapy.

CONCLUSION

This is the first report of the deliberate induction of mixed lymphohematopoietic chimerism after a nonmyeloablative preparative regimen to treat a hematological malignancy and to provide allotolerance for a solid organ transplant.