Review of "minitransplantation": nonmyeloablative allogeneic hematopoietic stem cell transplantation

Phase 2 clinical trial of rapamycin-resistant donor CD4+ Th2/Th1 (T-Rapa) cells after low-intensity allogeneic hematopoietic cell transplantation

In experimental models, ex vivo induced T-cell rapamycin resistance occurred independent of T helper 1 (Th1)/T helper 2 (Th2) differentiation and yielded allogeneic CD4(+) T cells of increased in vivo efficacy that facilitated engraftment and permitted graft-versus-tumor effects while minimizing graft-versus-host disease (GVHD). To translate these findings, we performed a phase 2 multicenter clinical trial of rapamycin-resistant donor CD4(+) Th2/Th1 (T-Rapa) cells after allogeneic-matched sibling donor hematopoietic cell transplantation (HCT) for therapy of refractory hematologic malignancy. T-Rapa cell products, which expressed a balanced Th2/Th1 phenotype, were administered as a preemptive donor lymphocyte infusion at day 14 post-HCT. After T-Rapa cell infusion, mixed donor/host chimerism rapidly converted, and there was preferential immune reconstitution with donor CD4(+) Th2 and Th1 cells relative to regulatory T cells and CD8(+) T cells. The cumulative incidence probability of acute GVHD was 20% and 40% at days 100 and 180 post-HCT, respectively. There was no transplant-related mortality. Eighteen of 40 patients (45%) remain in sustained complete remission (range of follow-up: 42-84 months). These results demonstrate the safety of this low-intensity transplant approach and the feasibility of subsequent randomized studies to compare T-Rapa cell-based therapy with standard transplantation regimens.

Two days of antithymocyte globulin are associated with a reduced incidence of acute and chronic graft-versus-host disease in reduced-intensity conditioning transplantation for hematologic diseases

BACKGROUND

The optimal combination of fludarabine, busulfan, and antithymocyte globulin (ATG) for reduced-intensity conditioning (RIC) transplantation has not been established. ATG plays a pivotal role in the prevention of graft-versus-host disease (GvHD), but it is associated with a higher relapse rate and an elevated incidence of infections when high doses are used.

METHODS

The authors retrospectively compared 2 different doses of ATG combined with fludarabine and busulfan in 229 adult patients who underwent transplantation at their institution. ATG was administered over 1 day (FBA1) or over 2 days (FBA2) at a daily dose of 2.5 mg/kg.

RESULTS

There were 124 patients in the FBA2 cohort and 105 patients in the FBA2 cohorts. Patients in the FBA2 cohort were older and more frequently underwent transplantation from an unrelated donor; 93% of patients in the FBA2 cohort received intravenous busulfan versus only 5% in the FBA1 cohort. The incidence of grade 2 through 4 acute GvHD was 23% in the FBA2 cohort versus 42% in the FBA1 cohort (P = .002); the incidence of grade 3 through 4 acute GvHD was 10% versus 23%, respectively (P = .006); and the incidence of chronic GvHD was 35% versus 69%, respectively (P < .0001). The 2-year rates of overall survival, nonrelapse mortality, and relapse/progression for the FBA1 and FBA2 cohorts were 65% versus 67%, respectively (P = .99), 20% versus 19%, respectively (P = .61), and 30% versus 19%, respectively (P = .09). The results were confirmed in multivariate analysis.

CONCLUSIONS

The use of ATG at a dose of 5 mg/kg was correlated significantly with reduced incidence and severity of GvHD without impairing disease control. Taken together, the current results suggest that this conditioning represents a step forward in the optimization of RIC.

Pentostatin plus cyclophosphamide safely and effectively prevents immunotoxin immunogenicity in murine hosts

PURPOSE

The success of immunotoxin therapy of cancer is limited by host production of neutralizing antibodies, which are directed toward the Pseudomonas exotoxin A (PE) component. In this proof-of-principle study using a well-established murine model, we hypothesized that a newly developed immune depletion regimen consisting of pentostatin plus cyclophosphamide would abrogate anti-immunotoxin reactivity.

EXPERIMENTAL DESIGN

BALB/c hosts were injected weekly with recombinant immunotoxin (RIT) SS1P, which is an antimesothelin Fv antibody fragment genetically fused to a 38 kDa portion of PE, and has been evaluated in clinical trials. Experimental cohorts received induction chemotherapy consisting of pentostatin (P) plus cyclophosphamide (C) prior to initial RIT exposure; some cohorts received further maintenance PC therapy of varying intensity just prior to each weekly RIT challenge. Cohorts were monitored for T, B, myeloid cell depletion, and for total anti-SS1P antibody (Ab) formation.

RESULTS

Controls uniformly developed anti-SS1P Ab after the third RIT exposure. Induction PC therapy reduced the frequency of hosts with anti-SS1P Ab. Abrogation of antibody generation was improved by maintenance PC therapy: nearly 100% of recipients of intensive PC maintenance were free of anti-SS1P Ab after 9 weekly RIT doses. The most effective PC regimen yielded the greatest degree of host B-cell depletion, moderate T-cell depletion, and minimal myeloid cell depletion.

CONCLUSIONS

Induction and maintenance PC chemotherapy safely prevented anti-immunotoxin antibody formation with uniform efficacy. These data suggest that immunotoxin therapy might be used in combination with pentostatin plus cyclophosphamide chemotherapy to improve the targeted therapy of cancer.

The pentostatin plus cyclophosphamide nonmyeloablative regimen induces durable host T cell functional deficits and prevents murine marrow allograft rejection

We describe a novel animal model of nonmyeloablative bone marrow transplantation (BMT) using the purine analog pentostatin. Other cohorts of mice received another purine analog, fludarabine, which we and others have previously evaluated in nonmyeloablative murine models. We evaluated pentostatin for its ability to (1) operate synergistically with cyclophosphamide to induce host T cell depletion; (2) induce host T cell suppression, as defined by modulation of cytokine secretion in vitro and abrogation of host-versus-graft reactivity in vivo; (3) constrain host T cell recovery post-therapy; and (4) prevent the rejection of T cell-depleted, fully major histocompatibility complex-mismatched bone marrow allografts. Relative to single-agent regimens, combination regimens with pentostatin and cyclophosphamide (PC) and with fludarabine and cyclophosphamide (FC) worked synergistically to deplete host CD4(+) and CD8(+) T cells. PC and FC regimens were developed that yielded similar levels of host T cell and myeloid cell depletion. In the setting of these generally comparable states of host T cell and myeloid cell depletion, the PC regimen was found to be highly immunosuppressive, as evidenced by a reduced host T cell capacity to secrete interleukin-2 and interferon-γ in vitro, to mediate host-versus-graft reactivity in vivo, and to recover numerically and functionally during a 2-week observation period after chemotherapy. Finally, using B6 hosts treated with the 14-day chemotherapy regimens, the PC regimen more consistently prevented the rejection of BALB/c T cell-depleted allografts compared with the FC regimen (rate of alloengraftment, 14/15 [93%] of PC-treated recipients vs 8/14 [57%] of FC-treated recipients; P < .05); similar results were observed using an 8-day conditioning regimen. These data suggest that host T cell suppression, distinct from T cell depletion, may be a critical determinant of engraftment after purine analog-based regimens and also may be preferentially attained by the use of pentostatin.

Derivation and characterization of canine embryonic stem cell lines with in vitro and in vivo differentiation potential

Embryonic stem cells (ESCs) represent permanent cell lines that can be maintained in an undifferentiated state. In an environment that induces differentiation, they form derivatives of the three embryonic germ layers: mesoderm, ectoderm, and endoderm. These characteristics give ESCs great potential for both basic research and clinical applications in the areas of regenerative medicine and tissue engineering. The establishment of ESCs from large animals that model human diseases is of significant importance. We describe the derivation of permanent canine cell lines from preimplantation-stage embryos. Similar to human ESCs, canine ESCs expressed OCT3/4, NANOG, SOX2, SSEA-3, SSEA-4, TRA-1-60, TRA-1-81, and alkaline phosphatase, whereas they expressed very low levels of SSEA-1. They maintained a normal karyotype and morphology typical of undifferentiated ESCs after multiple in vitro passages and rounds of cryopreservation. Plating cells in the absence of a feeder layer, either in attachment or suspension culture, resulted in the formation of embryoid bodies and their differentiation to multiple cell types. In vivo, canine ESCs gave rise to teratomas comprising cell types of all three embryonic germ layers. These cells represent the first pluripotent canine ESC lines with both in vitro and in vivo differentiation potential and offer the exciting possibility of testing the efficacy and safety of ESC-based therapies in large animal models of human disease.

Low-dose parenteral busulfan provides an extended window for the infusion of hematopoietic stem cells in murine hosts

OBJECTIVE

Myeloablative total body irradiation (TBI) in the setting of autologous transplantation of genetically modified hematopoietic stem cells (HSC) is associated with substantial toxicity. Nonmyeloablative doses of TBI are less toxic, but result in low-level engraftment of genetically modified HSCs. As an alternative to TBI, escalating doses of parenteral busulfan were tested for their hematologic toxicity, their ability to promote donor leukocyte engraftment, and the time window for such engraftment.

MATERIALS AND METHODS

Hematologic toxicity of busulfan was assessed in C57BL6 mice after single nonmyeloablative doses of intraperitoneal busulfan ranging from 1 to 40 mg/kg by serial complete blood counts monitored up to 40 days. The level of donor engraftment attainable after nonmyeloablative busulfan was determined by infusion of 20 million congenic murine bone marrow nucleated cells (BMNC) following 5 to 40 mg/kg of busulfan. To determine the effects of delayed HSC infusions, BMNCs were infused 1, 10, 15, and 20 days after a single dose of 10 mg/kg of busulfan.

RESULTS

Busulfan doses from 1 to 40 mg/kg produced hematologic toxicity that was most pronounced in the 2nd to 3rd week. In transplantation experiments, dose-dependent donor leukocyte engraftment was attained with levels >70% after only 20 mg/kg of busulfan. Similar levels of engraftment were achieved even when infusion of BMNCs was delayed up to 20 days after busulfan injection.

CONCLUSION

Nonmyeloablative parenteral busulfan produced transient myelosuppressive effects, clinically relevant levels of engraftment, and an extended time window for HSC infusion in murine hosts.

Outpatient allografting using non-myeloablative conditioning: the Mexican experience

A group of 132 patients with both malignant and nonmalignant conditions was allografted using the 'Mexican' method of non-ablative conditioning. The conditioning was delivered on an outpatient basis and the procedure was planned to be conducted on outpatients in all cases. While 103 patients (78%) were able to complete the procedure totally as outpatients, 29 (22%) were hospitalized because of fever, mucositis or acute graft-versus-host disease. In a multivariate analysis, although differences were not statistically significant, it was found that the patients who were allografted as outpatients had higher levels of hemoglobin (12 versus 11.8 g/dl), higher platelet counts (248 versus 191 x 10(9)/l), lower white blood cell counts (11.7 versus 12.4 x 10(9)/l), higher Karnofsky scale scores (100 versus 90%) and lower creatinine levels (0.9 versus 0.93 mg/dl). A total of 86% of the patients with normal values for these variables could be allografted as outpatients, whereas only 67% of those with abnormal values completed the entire procedure as outpatients. It is concluded that allografting can be accomplished totally on an outpatient basis using the 'Mexican' reduced intensity-conditioning regimen.

Extramedullary Leukemic Relapses following Hematopoietic Stem Cell Transplantation with Nonmyeloablative Conditioning

Of a group of 149 patients who underwent allogeneic stem cell transplantation using the "Mexican approach", a nonablative preparative regimen, 49 individuals developed bone marrow relapse, and 8 patients developed extramedullary relapse (EMR). All EMR cases presented in patients who received allografts for myeloid malignancies. In contrast, bone marrow relapses presented in patients with myeloid or lymphoid malignancies. EMR presented 60 to 1010 days after the allograft and appeared in 3 cases as subcutaneous nodules in different parts of the body, in the vertebrae in 3 cases, and in the kidney and the breast in 1 case each. One patient had both subcutaneous nodules and epididymis EMR. When EMR was noted, acute graft-versus-host disease (GVHD) had presented in 4 patients, and limited forms of chronic GVHD were present in 3 patients. All but 1 of the patients were full chimeras when the EMR ensued, and the EMR preceded an overt hematologic relapse in all but 1 of the patients. Patients who experienced an overt hematologic relapse died 20 to 180 days (median, 40 days) after the EMR. The only individual alive 240 days after relapse shows no evidence of a full-blown hematologic relapse. An EMR after allogeneic hematopoietic stem cell transplantation usually has a bad prognosis and presents mainly in individuals with high-risk malignancies.

Hematologic aspects of myeloablative therapy and bone marrow transplantation

The transplantation of bone marrow cells or isolated hematopoietic stem cells from the bone marrow or peripheral blood is a widely utilized form of therapy for patients with incurable diseases of the hematopoietic and immune systems. Successful engraftment of the transplanted stem cells in an adequately prepared recipient normally leads to bone marrow reconstitution over a period of several weeks, accompanied by more gradual reconstitution of the immune system. Since the recipient is profoundly ill during the initial treatment period, laboratory data is critical for monitoring engraftment, detecting residual/recurrent disease, and identifying problems that may delay bone marrow reconstitution or lead to other medical complications. Accurate blood cell counts are imperative, and most bone marrow transplantation patients undergo periodic monitoring with bone marrow aspirates and biopsies with cytogenetic, molecular, and multiparametric flow cytometric studies. The potential complications of bone marrow transplantation include engraftment failure and delayed engraftment, infection, residual bone marrow disease, acute and chronic graft versus host disease, myelofibrosis, therapy-related acute leukemia, post-transplant lympho-proliferative disorders, and toxic myelopathy.

Immune restoration following hematopoietic stem cell transplantation: an evolving target

Hematopoietic stem cell transplantation (HSCT) is the definitive cure for many malignant and nonmalignant diseases. However, delays in immune reconstitution (IR) following HSCT significantly limit the success of transplantation and increase the risk for infection and disease relapse in the transplant recipient. Therefore, ways to measure and to manipulate immune recovery following HSCT are emerging and their success depends directly upon an enhanced understanding for the underlying mechanisms responsible for reconstituted immunity and hematopoiesis. Recent discoveries in the activation, function, and regulation of dendritic cell (DC), natural killer (NK) cell, and T-lymphocyte subtypes have been critical in developing immunotherapies used to prevent graft-versus-host disease and to enhance graft-versus-leukemia. For example, regulatory T cells that induce tolerance and NK receptor-tumor ligand disparities that result in tumor lysis are being used to minimize GVHD and tumor burden, respectively. Furthermore, expansion and modulation of immune effector cells are being used to augment hematopoietic and immune recovery and to decrease transplant-related toxicity in the transplant recipient. Specifically, DC expansion and incorporation into antitumor and anti-microbial vaccines is fast approaching application into clinical trials. This paper will review our current understanding for IR following HSCT and the novel ways in which to restore immune function and decrease transplant-related toxicity in the transplant recipient.

Breaking dogmata to help patients: non-myeloablative haematopoietic stem cell transplantation

Various dogmata have been broken as a consequence of the evolution of knowledge in the area of allogeneic haematopoietic stem cell (HSC) transplantation. The following is now clear: for the successful engraftment of allogeneic HSC, bone marrow ablation of the recipient is not required; HSCs create their own space through graft-versus-host reactions; several malignancies can be eradicated by the graft-versus-tumour effect; HSC allografting can be conducted on an out-patient basis; HSC allografting can be done in aged or debilitated individuals; HSC allografting can be achieved without transfusion of blood products; and the costs of the allografting procedures can be substantially diminished. Despite the fact that HSC allografting with reduced intensity conditioning may be related to several disadvantages, such as mixed chimaerism and relapse of the malignancy, breaking these dogmata has resulted in availability of HSC allografting to a larger number of individuals worldwide, thus offering true curative therapeutic options to patients who otherwise would not qualify to be given these opportunities.

Chimerism studies in HLA-identical nonmyeloablative hematopoietic stem cell transplantation point to the donor CD8(+) T-cell count on day + 14 as a predictor of acute graft-versus-host disease

Chimerism analysis of hematopoietic cells has emerged as an essential tool in nonmyeloablative hematopoietic stem cell transplantation. We have investigated the development of donor chimerism in granulocytes and CD4(+) and CD8(+) T cells in blood and bone marrow of 24 patients with hematologic malignancies who received HLA-identical sibling peripheral blood stem cell grafts after conditioning with fludarabine and 2 Gy of total body irradiation. The T-cell chimerism of blood and bone marrow was tightly correlated. Complete donor chimerism was reached earlier in the granulocytes than in the T cells. Mixed T-cell chimerism was common at the time of onset of acute graft-versus-host disease (aGVHD), and both CD4(+) and CD8(+) donor T-cell chimerism increased with the occurrence of aGVHD grades II to IV (P =.0002 and P =.019, respectively). The rate of disappearance of recipient CD8(+) T cells was faster in patients with aGVHD grades II to IV than in patients without clinically significant aGVHD (P =.016). This observation indicates a role of graft-versus-lymphohematopoietic tissue reactions in creating complete donor T-cell chimerism. A donor CD8(+) T-cell count above the median on day +14 increased the risk of subsequent development of aGVHD grades II to IV (P =.003).

Significance of one human leukocyte antigen mismatch on outcome of nonmyeloablative allogeneic stem cell transplantation from related donors using the Mexican schedule

Using the Mexican approach to conduct nonablative stem cell transplantation (NST), we have prospectively performed 58 allografts in individuals with various malignant and nonmalignant hematological diseases using sibling donors, either HLA identical (6/6) or compatible, with one mismatch (5/6). When comparing allografts obtained from HLA identical (n=40) or compatible (n=18) siblings, respectively, the overall median survival was found to be 33 vs 8 months (P<0.01), the 52-month survival was 47 vs 38% (P>0.2), the prevalence of acute graft-versus-host disease (GVHD) 57 vs 38%, that of chronic GVHD 25 vs 11% and the relapse rate 45 vs 55%. The two patients who failed to engraft were both 5/6 matches. Probably stemming from the low number of patients, and despite a trend toward worse results in patients allografted from HLA compatible (5/6) siblings, most differences in outcome were not significant. It seems that NST can be offered to individuals with either an HLA identical or a compatible sibling donor.

Kinetics of in vivo elimination of suicide gene-expressing T cells affects engraftment, graft-versus-host disease, and graft-versus-leukemia after allogeneic bone marrow transplantation

Suicide gene therapy is one approach being evaluated for the control of graft-vs-host disease (GVHD) after allogeneic bone marrow transplantation (BMT). We recently constructed a novel chimeric suicide gene in which the entire coding region of HSV thymidine kinase (HSV-tk) was fused in-frame to the extracellular and transmembrane domains of human CD34 (DeltaCD34-tk). DeltaCD34-tk is an attractive candidate as a suicide gene in man because of the ensured expression of HSV-tk in all selected cells and the ability to rapidly and efficiently purify gene-modified cells using clinically approved CD34 immunoselection techniques. In this study we assessed the efficacy of the DeltaCD34-tk suicide gene in the absence of extended ex vivo manipulation by generating transgenic animals that express DeltaCD34-tk in the peripheral and thymic T cell compartments using the CD2 locus control region. We found that DeltaCD34-tk-expressing T cells could be purified to near homogeneity by CD34 immunoselection and selectively eliminated ex vivo and in vivo when exposed to low concentrations of GCV. The optimal time to administer GCV after allogeneic BMT with DeltaCD34-tk-expressing transgenic T cells was dependent on the intensity of the conditioning regimen, the leukemic status of the recipient, and the dose and timing of T cell infusion. Importantly, we used a controlled graft-vs-host reaction to promote alloengraftment in sublethally irradiated mice and provide a graft-vs-leukemia effect in recipients administered a delayed infusion of DeltaCD34-tk-expressing T cells. This murine model demonstrates the potential usefulness of DeltaCD34-tk-expressing T cells to control GVHD, promote alloengraftment, and provide a graft-vs-leukemia effect in man.

Non-myeloablative bone marrow transplantation

As a result of the evolution of knowledge in the area of allogeneic hematopoietic stem cells (HSC) transplantation, several dogmata have been broken. We now have the following information: a) successful engraftment if allogeneic HSC bone marrow ablation of the recipient is not required; b) HSC create their own space through graft-vs.-host reactions; c) several malignancies are eradicated by the graft-vs.-tumor effect; d) allografting can be conducted on an out-patient basis; e) allografting can be done in aged or debilitated individuals; f) allografting can be achieved without transfusion of blood products, and g) costs of the allografting procedures can be substantially diminished. Breaking all these dogmata has resulted in availability of HSC allografting to a larger number of individuals, thus offering true curative therapeutic options to patients who otherwise would not qualify to receive these opportunities.

The Mexican schedule to conduct allogeneic stem cell transplantation is related to a low risk of cytomegalovirus reactivation and disease

The prevalence of cytomegalovirus (CMV) reactivation and disease after non-myeloablative stem cell transplantation is largely unknown. Using fludarabine combined with alemtuzumab or antithymocyte globulin in the conditioning regimen, some authors have found increased prevalences of CMV disease, whereas other authors using different schedules have observed decreased prevalences. In a group of 17 individuals allografted using the Mexican conditioning regimen, which employs fludarabine, cyclophosphamide, and busulfan, we assessed CMV reactivation, morbidity, and mortality. Before transplant, IgG anti-CMV antibodies were found in 11 patients and in 10 donors; in 8 cases, both donor and patient had IgG anti-CMV antibodies. In only one case (6%) was CMV mRNA identified 30 days after the allograft during grade IV acute graft-versus-host disease. CMV reactivation, disease, and mortality were very low using our non-myeloablative stem cell transplantation schedule, which has been shown to be useful for allografting with minimal toxicity and reduced costs.

Treosulfan and fludarabine: a new toxicity-reduced conditioning regimen for allogeneic hematopoietic stem cell transplantation

New conditioning regimens are being explored to reduce toxicity and enable allogeneic bone marrow transplantation in patients not eligible for conventional transplantation. We have investigated treosulfan, an alkylating agent, with the aim of developing an efficient and reliable but less-toxic conditioning regimen. A series of 30 patients who were not eligible for standard conditioning therapy received transplants from HLA-matched related (n = 14) or unrelated (n = 16) donors after administration of treosulfan 10 g/m2 intravenously daily for 3 days and fludarabine 30 mg/m2 intravenously daily for 5 days. Patients receiving grafts from unrelated donors also were given rabbit antithymocyte globulin 10 mg/kg intravenously daily for 3 days. All patients achieved prompt neutrophil and platelet recovery. Extramedullary toxicity was generally mild with Common Toxicity Criteria (CTC) grade 3 or 4 attributable to the conditioning seen only with transaminases. Complete donor chimerism was achieved by 90% of the patients. Acute graft-versus-host disease (GVHD) grade III or IV developed in 14% of the patients and chronic GVHD in 39%. An estimated overall survival rate of 73% and an event-free survival rate of 49% have been reached after a median of 22 months (range, 7.4-33.4 months). In summary, the combination of treosulfan and fludarabine is a safe and efficient conditioning regimen.