Effect of total body irradiation dose escalation on outcome following T-cell-depleted allogeneic bone marrow transplantation

Electron FLASH radiotherapy in vivo studies. A systematic review

FLASH-radiotherapy delivers a radiation beam a thousand times faster compared to conventional radiotherapy, reducing radiation damage in healthy tissues with an equivalent tumor response. Although not completely understood, this radiobiological phenomenon has been proved in several animal models with a spectrum of all kinds of particles currently used in contemporary radiotherapy, especially electrons. However, all the research teams have performed FLASH preclinical studies using industrial linear accelerator or LINAC commonly employed in conventional radiotherapy and modified for the delivery of ultra-high-dose-rate (UHDRs). Unfortunately, the delivering and measuring of UHDR beams have been proved not to be completely reliable with such devices. Concerns arise regarding the accuracy of beam monitoring and dosimetry systems. Additionally, this LINAC totally lacks an integrated and dedicated Treatment Planning System (TPS) able to evaluate the internal dose distribution in the case of in vivo experiments. Finally, these devices cannot modify dose-time parameters of the beam relevant to the flash effect, such as average dose rate; dose per pulse; and instantaneous dose rate. This aspect also precludes the exploration of the quantitative relationship with biological phenomena. The dependence on these parameters need to be further investigated. A promising advancement is represented by a new generation of electron LINAC that has successfully overcome some of these technological challenges. In this review, we aim to provide a comprehensive summary of the existing literature on in vivo experiments using electron FLASH radiotherapy and explore the promising clinical perspectives associated with this technology.

ACR-ARS Practice Parameter for the Performance of Total Body Irradiation

OBJECTIVES

This practice parameter was revised collaboratively by the American College of Radiology (ACR) and the American Radium Society (ARS). This practice parameter provides updated reference literature regarding both clinical-based conventional total body irradiation and evolving volumetric modulated total body irradiation.

METHODS

This practice parameter was developed according to the process described under the heading The Process for Developing ACR Practice Parameters and Technical Standards on the ACR website ( https://www.acr.org/Clinical-Resources/Practice-Parameters-and-Technical-Standards ) by the Committee on Practice Parameters-Radiation Oncology of the ACR Commission on Radiation Oncology in collaboration with the ARS.

RESULTS

This practice parameter provides a comprehensive update to the reference literature regarding conventional total body irradiation and modulated total body irradiation. Dependence on dose rate remains an active area of ongoing investigation in both the conventional setting (where instantaneous dose rate can be varied) and in more modern rotational techniques, in which average dose rate is the relevant variable. The role of imaging during patient setup and the role of inhomogeneity corrections due to computer-based treatment planning systems are included as evolving areas of clinical interest notably surrounding the overall dose inhomogeneity. There is increasing emphasis on the importance of evaluating mean lung dose as it relates to toxicity during high-dose total body irradiation regimens.

CONCLUSIONS

This practice parameter can be used as an effective tool in designing and evaluating a total body irradiation program that successfully incorporates the close interaction and coordination among the radiation oncologists, medical physicists, dosimetrists, nurses, and radiation therapists.

GVHD-free, relapse-free survival provides novel clues for optimizing allogeneic-HSCT for adult T-cell leukemia/lymphoma

The outcome of allogeneic hematopoietic stem cell transplantation (allo-HSCT) for adult T-cell leukemia/lymphoma (ATL) is still unsatisfactory. To illustrate the advantages and disadvantages of each donor source, we performed a nationwide retrospective study of graft-versus-host disease (GVHD)-free, relapse-free survival (GRFS) of patients with allo-HSCT-treated ATL. One-year GRFS did not significantly differ between patients who received related bone marrow transplantation (R-BMT; 26%, n = 117), related peripheral blood stem cell transplantation (R-PBSCT; 22%, n = 225), unrelated bone marrow transplantation (UR-BMT; 26%, n = 619), and cord blood transplantation (CBT; 21%, n = 359; p = 0.09). This was attributable to a low incidence of systemically-treated chronic GVHD after CBT (9% at 1 year) and reduced non-GVHD/relapse mortality after R-PBSCT (9% at 1 year). Among patients transplanted in complete remission (CR), 1-year overall survival after CBT (52%, n = 132) was not inferior to that after R-BMT (55%, n = 51), R-PBSCT (57%, n = 79), and UR-BMT (58%, n = 280; p = 0.15), and relapse rates were equivalent among the four sources (p = 0.19). Our results suggest that all donor sources are feasible for CR patients and that GRFS provides important clues toward optimizing allo-HSCT for ATL.

Once-a-day fractionated total-body irradiation: A regimen tailored to local logistics in allogeneic stem cell transplantation for acute lymphoblastic leukemia

Aim

The objective of the study was to estimate the cumulative incidence (CI) of relapse, relapse-free survival (RFS) and overall survival (OS) in ALL patients after a once-a-day fractionated TBI (F-TBI) regimen with 9.9 Gy. The secondary objectives were evaluation of short and long-term toxicity and non-relapse mortality (NRM).

Background

Total body irradiation (TBI), as a part of the conditioning regimen before allogeneic stem cell transplantation (ASCT) for acute lymphoblastic leukemia (ALL), allows disease control by eradicating residual blast cells in the transplant recipient.

Materials and methods

Retrospective study conducted in patients with ALL who received between March 2003 and December 2013 a conditioning regimen with F-TBI and chemotherapy. Irradiation was delivered with 3.3 Gy once-a-day for three consecutive days.

Results

Eighty-seven patients were included. The median age was 19 years (range: 5-49 years). The 3-year CI of relapse was 30%. The estimated 3-year RFS and OS were 54% and 58%, respectively. Cumulative incidence of acute graft-versus-host disease (aGVHD) grade II-IV and chronic GVHD (cGVHD) was 31% and 40%, respectively. Interstitial pneumonitis was observed in 2 patients. The 3-year CI of NRM was 16%. In multivariate analysis, cGVHD was associated with a lower CI of relapse (RR = 0.26, 95% CI: 0.07-0.95, p = 0.04). High-risk cytogenetics was associated with a lower RFS (RR = 2, 95 CI: 1.04-3.84, p = 0.03). Grade II-IV aGVHD was an independent predictor of higher CI of NRM (RR = 6.7, 95% CI: 1.4-31.7, p = 0.02).

Conclusions

Once-a-day F-TBI regimen is effective, safe and practical in patients who underwent ASCT for ALL.

Organ sparing of linac-based targeted marrow irradiation over total body irradiation

PURPOSE

Targeted marrow irradiation (TMI) is an alternative conditioning regimen to total body irradiation (TBI) before bone marrow transplantation in hematologic malignancies. Intensity-modulation methods of external beam radiation therapy are intended to permit significant organ sparing while maintaining adequate target coverage, improving the therapeutic ratio. This study directly compares the dose distributions to targets and organs at risk from TMI and TBI, both modalities conducted by general-use medical linacs at our institution.

METHODS

TMI treatments were planned for 10 patients using multi-isocentric feathered volumetric arc therapy (VMAT) plans, delivered by 6 MV photon beams of Elekta Synergy linacs. The computed tomography (CT) datasets used to obtain these plans were also used to generate dose distributions of TBI treatments given in the AP/PA extended-field method. We compared dose distributions normalized to the same prescription for both plan types. The generalized equivalent uniform dose (gEUD) of Niemierko for organs and target volumes was used to quantify effective whole structure dose and dose savings.

RESULTS

For the clinical target volume (CTV), no significant differences were found in mean dose or gEUD, although the radical dose homogeneity index (minimum dose divided by maximum dose) was 31.7% lower (P = 0.002) and the standard deviation of dose was 28.0% greater (P = 0.027) in the TMI plans than in the TBI plans. For the TMI plans, gEUD to the lungs, brain, kidneys, and liver was significantly lower (P < 0.001) by 47.8%, 33.3%, 55.4%, and 51.0%, respectively.

CONCLUSION

TMI is capable of maintaining CTV coverage as compared to that achieved in TBI, while significantly sparing organs at risk. Improvement on sparing organs at risk permits a higher prescribed dose to the target or the maximum number of times marrow conditioning may be delivered to a patient while maintaining similar typical tissue complication rates.

Comparison of High Doses of Total Body Irradiation in Myeloablative Conditioning before Hematopoietic Cell Transplantation

Malignancy relapse is the most common cause of treatment failure among recipients of hematopoietic cell transplantation (HCT). Conditioning dose intensity can reduce disease relapse but is offset by toxicities. Improvements in radiotherapy techniques and supportive care may translate to better outcomes with higher irradiation doses in the modern era. This study compares outcomes of recipients of increasing doses of high-dose total body irradiation (TBI) divided into intermediate high dose (IH; 13-13.75 Gy) and high dose (HD; 14 Gy) with standard dose (SD; 12 Gy) with cyclophosphamide. A total of 2721 patients ages 18 to 60 years with hematologic malignancies receiving HCT from 2001 to 2013 were included. Cumulative incidences of nonrelapse mortality (NRM) at 5 years were 28% (95% confidence interval [CI], 25% to 30%), 32% (95% CI, 29% to 36%), and 34% (95% CI, 28% to 39%) for SD, IH, and HD, respectively (P = .02). Patients receiving IH-TBI had a 25% higher risk of NRM compared with those receiving SD-TBI (12 Gy) (P = .007). Corresponding cumulative incidences of relapse were 36% (95% CI, 34% to 38%), 32% (95% CI, 29% to 36%), and 26% (95% CI, 21% to 31%; P = .001). Hazard ratios for mortality compared with SD were 1.06 (95% CI, .94 to 1.19; P = .36) for IH and .89 (95% CI, .76 to 1.05; P = .17) for HD. The study demonstrates that despite improvements in supportive care, myeloablative conditioning using higher doses of TBI (with cyclophosphamide) leads to worse NRM and offers no survival benefit over SD, despite reducing disease relapse.

Total Body Irradiation without Chemotherapy as Conditioning for an Allogeneic Hematopoietic Cell Transplantation for Adult Acute Myeloid Leukemia

Current therapies for acute myeloid leukemia (AML), failing induction, are rarely effective. We report our experience in 4 patients with AML who received 16 Gy TBI prior to allogeneic hematopoietic cell transplantation (alloHCT), between June 2010 and May 2011. Patients were 20 to 55 years of age, 2 with relapsed disease and 2 with AML failing induction. An HLA-matched graft from related or unrelated donor was infused on day 0. All but one, who received a CD34⁺-selected graft, received methotrexate and tacrolimus +/- antithymocyte globulin, as GVHD prophylaxis. The other patient received tacrolimus alone. Neutrophil and platelet engraftment occurred at a median of 18 and 14 days, respectively. Patients were discharged at a median of 28 days. There were no unexpected toxicities in the first 30 days. One patient had cytomegalovirus (CMV) viremia and anorexia, at two months. One patient had grade 2 acute GVHD of the skin. One patient developed chronic GVHD of the eyes, mouth, skin, joints, and lung at 4 months. Two patients died from relapse of their leukemia at days 65 and 125. Two patients remain in remission beyond day 1500. 16 Gy TBI followed by an alloHCT for AML, failing induction, is feasible and tolerable.

Effect of electron contamination on in vivo dosimetry for lung block shielding during TBI

Our institution performs in vivo verification measurement for each of our total body irradiation (TBI) patients with optically stimulated luminescent dosimeters (OSLD). The lung block verification measurements were commonly higher than expected. The aim of this work is to understand this discrepancy and improve the accuracy of these lung block verification measurements. Initially, the thickness of the lung block was increased to provide adequate lung sparing. Further tests revealed the increase was due to electron contamination dose emanating from the lung block. The thickness of the bolus material covering the OSLD behind the lung block was increased to offset the electron contamination. In addition, the distance from the lung block to the dosimeter was evaluated for its effect on the OSLD reading and found to be clinically insignificant over the range of variability in our clinic. The results show that the improved TBI treatment technique provides for better accuracy of measured dose in vivo and consistency of patient setup.

PACS number(s): 87.53.Bn, 87.53.Kn, 87.55.N‐, 87.55.Qr

Outcomes of acute leukemia patients transplanted with naive T cell-depleted stem cell grafts

BACKGROUND

Graft-versus-host disease (GVHD) is a major cause of morbidity and mortality following allogeneic hematopoietic stem cell transplantation (HCT). In mice, naive T cells (TN) cause more severe GVHD than memory T cells (TM). We hypothesized that selective depletion of TN from human allogeneic peripheral blood stem cell (PBSC) grafts would reduce GVHD and provide sufficient numbers of hematopoietic stem cells and TM to permit hematopoietic engraftment and the transfer of pathogen-specific T cells from donor to recipient, respectively.

METHODS

In a single-arm clinical trial, we transplanted 35 patients with high-risk leukemia with TN-depleted PBSC grafts following conditioning with total body irradiation, thiotepa, and fludarabine. GVHD prophylactic management was with tacrolimus immunosuppression alone. Subjects received CD34-selected PBSCs and a defined dose of TM purged of CD45RA+ TN. Primary and secondary objectives included engraftment, acute and chronic GVHD, and immune reconstitution.

RESULTS

All recipients of TN-depleted PBSCs engrafted. The incidence of acute GVHD was not reduced; however, GVHD in these patients was universally corticosteroid responsive. Chronic GVHD was remarkably infrequent (9%; median follow-up 932 days) compared with historical rates of approximately 50% with T cell-replete grafts. TM in the graft resulted in rapid T cell recovery and transfer of protective virus-specific immunity. Excessive rates of infection or relapse did not occur and overall survival was 78% at 2 years.

CONCLUSION

Depletion of TN from stem cell allografts reduces the incidence of chronic GVHD, while preserving the transfer of functional T cell memory.

TRIAL REGISTRATION

ClinicalTrials.gov (NCT 00914940).

Composite end point of graft-versus-host disease-free, relapse-free survival after allogeneic hematopoietic cell transplantation

The success of allogeneic hematopoietic cell transplantation (HCT) is typically assessed as individual complications, including graft-versus-host disease (GVHD), relapse, or death, yet no one factor can completely characterize cure without ongoing morbidity. We examined a novel composite end point of GVHD-free/relapse-free survival (GRFS) in which events include grade 3-4 acute GVHD, systemic therapy-requiring chronic GVHD, relapse, or death in the first post-HCT year. In 907 consecutive University of Minnesota allogeneic HCT recipients (2000-2012), 1-year GRFS was 31% (95% confidence interval [CI] 28-34). Regression analyses showed age, disease risk, and donor type significantly influencing GRFS. Adults age 21+ had 2-fold worse GRFS vs children; GRFS did not differ beyond age 21. Adjusted for conditioning intensity, stem cell source, disease risk, age, and transplant year, HLA-matched sibling donor marrow resulted in the best GRFS (51%, 95% CI 46-66), whereas HLA-matched sibling donor peripheral blood stem cells were significantly worse (25%, 95% CI 20-30, P = .01). GRFS after umbilical cord blood transplants and marrow from matched unrelated donors were similar (31%, 95% CI 27-35 and 32%, 95% CI 22-42, respectively). Because GRFS measures freedom from ongoing morbidity and represents ideal HCT recovery, GRFS has value as a novel end point for benchmarking new therapies.

A meta-analysis of patients receiving allogeneic or autologous hematopoietic stem cell transplant in mycosis fungoides and Sézary syndrome

The survival outlook in advanced mycosis fungoides (MF) is poor. Autologous and allogeneic stem cell transplants (SCT) have been shown, in small case series and case reports, to have the potential for long-term remission or to alter disease course. Allogeneic SCT is thought to have a curative potential secondary to a graft-versus-lymphoma (GVL) effect. A patient-level meta-analysis was performed to compare the outcome of allogeneic versus autologous SCT in patients with MF/Sézary syndrome (SS) using 39 cases from the literature. There were a total of 20 allogeneic and 19 autologous transplant cases. The gender, age, and stage distribution was similar between the transplant groups. The allogeneic group received significantly more systemic therapies prior to transplant (P < .0005) and had longer follow-up after transplant. Overall survival (OS) results showed a more favorable outcome of patients who received allogeneic SCT (P = .027). Event-free survival (EFS) demonstrated a more durable response in patients who received allogeneic SCT (P = .002). In the allogeneic group, the majority (70%) of patients experienced persistent graft-versus-host disease (GVHD), mostly with mild to moderate severity, and 2 of 4 deaths were related to GVHD. Meanwhile, the majority of the deaths (8 of 10) in the autologous group were because of progressive disease. These results support the belief that allogeneic SCT offers a better survival and disease-free outcome versus autologous SCT in MF/SS, likely because of a GVL effect.

Transplantation from matched siblings using once-daily intravenous busulfan/fludarabine with thymoglobulin: a myeloablative regimen with low nonrelapse mortality in all but older patients with high-risk disease

Two hundred patients received hematopoietic stem cell transplantation (HSCT) from matched sibling donors (MSD) after myeloablative conditioning including fludarabine (Flu) and once-daily intravenous busulfan (Bu). Thymoglobulin (TG) was added to methotexate (MTX) and cyclosporine (CsA) as graft-versus-host disease (GVHD) prophylaxis. For low-risk (acute leukemia CR1/CR2, CML CP1) patients projected 5-year nonrelapse mortality (NRM) and overall survival (OS) were 4% and 76% for those <or=45 years old (n = 54) and 6% and 83% for those >45 (n = 31). For high-risk (HR) patients NRM was 6% versus 27% (18% at 1 year) (P = .04) and OS 64% versus 37% (P = .47) in younger (n = 40) and older (n = 75) patients, respectively. To correct for imbalance in HR diagnoses each of 17 younger HR patients were matched with 2 older HR (OHR) patients by diagnosis and details of stage, and thereafter for other risk factors. For the younger HR and OHR patients, respectively, OS was 70% versus 37% (P = .02) and NRM 0 versus 34% (P = .02). When outcomes of OHR patients were compared with the other 3 groups combined NRM was 27% versus 5%, respectively (P = .002). Incidence of acute graft-versus-host disease (aGVHD) grade II-IV, aGVHD grade III-IV, and chronic GVHD (cGVHD) was 23% versus 10% (P = .02), 4% versus 2% (P = ns), and 66% versus 41% (P = .001), respectively. Nine of 14 nonrelapse deaths in the OHR group were related to GVHD or its treatment compared with 3 of 6 in all others (P value for GVHD related death = .01). Multivariate analysis of OS and DFS correcting for potentially confounding pretransplant factors identified only the OHR patients as having significantly increased risk (relative risk [RR] 3.32, confidence interval [CI] 1.71-6.47, P < .0001, and RR 3.32, CI 1.71-6.43, P < .0001, respectively). The effect of age on NRM is only apparent in HR patients, and is not explained by heterogeneity in diagnoses. Older HR patients experience more GVHD and more GVHD-related death than others, but NRM is no higher than reported with many nonmyeloablative regimens.

Allogeneic transplantation for adult acute leukemia in first and second remission with a novel regimen incorporating daily intravenous busulfan, fludarabine, 400 CGY total-body irradiation, and thymoglobulin

A myeloablative conditioning regimen incorporating daily intravenous busulfan, fludarabine, and 400 cGy total-body irradiation was given before allogeneic stem cell transplantation (SCT) to 64 adults with acute leukemia in first and second remission. Graft-versus-host disease (GVHD) prophylaxis included methotrexate, cyclosporine A, and rabbit antithymocyte globulin (Thymoglobulin). For 31 matched related (MRD) and 33 alternate donor (AD) SCT the incidence of acute GVHD grade II-IV was 11% +/- 6% versus 35% +/- 9% (P = .047), acute GVHD grade III-IV was 0% versus 10% +/- 6% (P = .09), and chronic GVHD was 40% +/- 9% versus 66% +/- 9% (P = NS), respectively. Overall transplant-related mortality (TRM) was 3% +/- 2%. Projected disease-free (DFS) and overall survival (OS) at 3 years for acute myelogenous leukemia (AML) (n = 36) are the same at 83% +/- 6%, and for acute lymphoblastic leukemia (ALL) (n = 28) are 65% +/- 10% and 78% +/- 8%, respectively. For MRD SCT DFS is 77% +/- 9%, OS 87% +/- 6%, for AD SCT the respective figures are 71% +/- 8% and 74% +/- 8%. OS and DFS in patients without and with high-risk features are 100% versus 71% +/- 7% (P = .007) and 88% +/- 8% versus 68% +/- 7% (P = .04), respectively. This combination appears relatively well tolerated, gives equivalent final outcomes from MRD and AD, and may be a reasonable alternative to conventional myeloablative regimens.

Influence of Radiation Dose Rate and Lung Dose on Interstitial Pneumonitis after Fractionated Total Body Irradiation: Acute Parotitis May Predict Interstitial Pneumonitis

This study evaluated patients for the influence of the dose rate and lung dose of fractionated total body irradiation (TBI) in preparation for allogeneic bone marrow transplantation (BMT) on the subsequent development of interstitial pneumonitis (IP). Sixty-six patients at our institute were treated with TBI followed by BMT. All of the patients received a total TBI dose of 12 Gy given in 6 fractions over 3 days and were divided into 3 groups according to the radiation dose rate and lung dose: group A, lung dose of 8 Gy (n = 18); group B, lung dose of 12 Gy at 8 cGy/min (n = 25); and group C, lung dose of 12 Gy at 19 cGy/min (n = 23). The overall survival rate, the cumulative incidence of relapse, and the cumulative incidence of IP were evaluated in relation to various potential indicators of future IP. There were no significant differences in survival and relapse rates between patient group A and combined groups B and C. Clinically significant IP occurred in 13 patients. The cumulative incidence of IP was significantly higher in patients who developed acute parotitis as indicated by either an elevation in the serum amylase level or parotid pain of grade 1 to 2. There was no difference in IP incidence among groups A, B, and C. There was no significant difference in IP incidence between lung dose values of 8 Gy (with lung shielding) and 12 Gy (without lung shielding) and between dose rate values of 8 cGy/min and 19 cGy/ min, at least when TBI was given in 6 fractions. The presence of acute parotitis during or just after TBI may be a predictor of IP.

Thiotepa and fractionated TBI conditioning prior to allogeneic stem cell transplantation for advanced hematologic malignancies: a phase II single institution trial

Relapse of hematologic malignancies after allogeneic stem cell transplantation remains a common problem, in particular for patients who have advanced disease at the time of transplantation. Thiotepa has excellent antileukemic and immunosuppressive activity, and could therefore be a useful drug in the conditioning regimen for patients with advanced hematologic neoplasms. We retrospectively analyzed toxicity, engraftment and survival data of 41 patients who received a conditioning regimen of thiotepa (600 mg/m2) and hyperfractionated TBI (10 Gy) prior to matched related (n = 25) or matched unrelated (n = 16) allogeneic stem cell transplantation. The mean age at transplantation was 37.8 years (range 20-59), all but five patients had advanced hematologic malignancies at the time of transplantation. GVHD prophylaxis was with standard cyclosporine and methotrexate. Engraftment was excellent, but the regimen was associated with a high incidence of grade III renal (41%) and hepatic (15%) toxicity, and high transplant-related mortality (44% at day +90). The 3-year event-free survival was 13% and overall survival 14%. We conclude that this regimen requires modification to reduce toxicity.

A new minimally ablative stem cell transplantation procedure in high-risk patients not eligible for nonmyeloablative allogeneic bone marrow transplantation

Nonmyeloblative stem cell transplantation (NST, SCT) aims to induce host-versus-graft tolerance for subsequent immunotherapy of underlying disease with alloreactive donor lymphocytes, focusing on well-tolerated conditioning suitable for elderly individuals or for other risk factors. However, there is a subset of high-risk patients who cannot tolerate NST. A new protocol consisting of fludarabine 30 mg/m(2) x 6 days (days -8 to -2), very-low-dose busulfan (2 mg/kg x 2 days, days -6 to -5), without anti thymocyte globulin (ATG), was employed in 11 high-risk patients aged 26-58 years. Graft-versus-host-disease (GVHD) prophylaxis consisted of low-dose and short-course cyclosporine-A (CSA) alone. One patient died during the nadir due to pulmonary complications. Other patients showed rapid three-lineage engraftment, without complete aplasia; 6/10 patients did not require platelet transfusion and 8/10 had full donor chimerism without transient mixed chimerism. Owing to intentional selection of highly poor-risk patients, overall mortality was high and only one patient survived. Acute GVHD (>/=grade I) occurred in 8/10 evaluable patients, 5/8 while off CSA; 5/8 developed grade III-IV acute GVHD. It appears that our modified, minimally ablative stem cell transplantation (MST) may be used for high-risk patients in need of allo-SCT. Furthermore, although the MST conditioning is not myeloablative, it results in myeloablation of the host hematopoietic system, mediated by alloreactive lymphocytes.

New approaches to hematopoietic cell transplantation in oncology

The use of high-dose chemotherapy followed by autologous HCT and the use of allogeneic HCT in children and adolescents with high-risk ALL, AML, and NBL has successfully improved outcomes. For other diseases, however, the role of HCT in treatment remains a subject of further research. The availability of HCT was significantly expanded by developing alternative graft sources that currently include BM, peripheral blood, and UCB from autologous and allogeneic related or unrelated donors. Progress in autologous HCT has been achieved by the identification of more effective and less toxic preparative regimens and by ex vivo purging of stem cell products. In allogeneic HCT, graft-versus-leukemia or graft-versus-tumor effects are being exploited increasingly to lower relapse rates. In addition, immunomodulation to promote tolerance, as well as allogeneic antitumor reactions have been achieved by antibody therapy, cytokine therapy, or cell-based immunotherapy. Future improvements are likely, as evidenced by promising preliminary results in the development of stem cell collection techniques, in vitro stem cell expansion, and purging techniques of stem cell grafts. The development of less intensive or nonmyeloablative preparative regimens may further reduce regimen-related morbidity and mortality Specific immunotherapy may facilitate tolerance induction in mismatched allogeneic HCT and support allogeneic HCT in the setting of donor-host HLA disparity. Ultimately, advances in cytokine therapy, tumor-specific vaccines, and gene therapy may decrease or even eradicate recurrence of the malignant disease after HCT.