Chronic graft-versus-host disease: Unresolved complication or ancient history?

Chronic graft-vs.-host disease (GVHD) is associated with morbidity, mortality, impaired quality of life, prolonged immunosuppressive (IS) therapy, and infection risk after allogeneic hematopoietic cell transplantation (HCT). Major strides have occurred in the understanding of chronic GVHD biology, NIH Consensus meetings have refined rigorous approaches to diagnosis, staging and response criteria, major interventional trials have established standard benchmarks for treatment outcome, and three agents to date have been FDA-approved for treating steroid-refractory chronic GVHD. Promising results from several recent trials have led some but not others to conclude that the risk of developing chronic GVHD is sufficiently low to by-and-large be considered a major post-HCT complication of the past. We propose that it is time to critically examine the results of contemporary GVHD prophylaxis regimens and discuss the state-of-the-science and associated controversies in spectrum of conclusions reached as to the risk of chronic GVHD. With these data, the current chronic GVHD incidence can be most precisely determined, and the present and future burden of chronic GVHD-affected patients be accurately modeled. Through review of existing evidence, we highlight unresolved needs and opportunities to refine best GVHD prophylaxis or preemptive therapy approaches, optimize established chronic GVHD therapy, and make the argument that support of preclinical and clinical research is critical in improving patient outcomes.

The α-emitter astatine-211 targeted to CD38 can eradicate multiple myeloma in a disseminated disease model.

Minimal residual disease (MRD) has become an increasingly prevalent and important entity in multiple myeloma (MM). Despite deepening responses to frontline therapy, roughly 75% of MM patients never become MRD-negative to ≤10-5, which is concerning because MRD-negative status predicts significantly longer survival. MM is highly heterogeneous, and MRD persistence may reflect survival of isolated single cells and small clusters of treatment-resistant subclones. Virtually all MM clones are exquisitely sensitive to radiation, and the α-emitter astatine-211 (211At) deposits prodigious energy within 3 cell diameters, which is ideal for eliminating MRD if effectively targeted. CD38 is a proven MM target, and we conjugated 211At to an anti-CD38 monoclonal antibody to create an 211At-CD38 therapy. When examined in a bulky xenograft model of MM, single-dose 211At-CD38 at 15 to 45 µCi at least doubled median survival of mice relative to untreated controls (P < .003), but no mice achieved complete remission and all died within 75 days. In contrast, in a disseminated disease model designed to reflect low-burden MRD, 3 studies demonstrated that single-dose 211At-CD38 at 24 to 45 µCi produced sustained remission and long-term survival (>150 days) for 50% to 80% of mice, where all untreated mice died in 20 to 55 days (P < .0001). Treatment toxicities were transient and minimal. These data suggest that 211At-CD38 offers the potential to eliminate residual MM cell clones in low-disease-burden settings, including MRD. We are optimistic that, in a planned clinical trial, addition of 211At-CD38 to an autologous stem cell transplant (ASCT) conditioning regimen may improve ASCT outcomes for MM patients.

CD38-bispecific antibody pretargeted radioimmunotherapy for multiple myeloma and other B-cell malignancies.

Pretargeted radioimmunotherapy (PRIT) has demonstrated remarkable efficacy targeting tumor antigens, but immunogenicity and endogenous biotin blocking may limit clinical translation. We describe a new PRIT approach for the treatment of multiple myeloma (MM) and other B-cell malignancies, for which we developed an anti-CD38-bispecific fusion protein that eliminates endogenous biotin interference and immunogenic elements. In murine xenograft models of MM and non-Hodgkin lymphoma (NHL), the CD38-bispecific construct demonstrated excellent blood clearance and tumor targeting. Dosimetry calculations showed a tumor-absorbed dose of 43.8 Gy per millicurie injected dose of 90Y, with tumor-to-normal organ dose ratios of 7:1 for liver and 15:1 for lung and kidney. In therapy studies, CD38-bispecific PRIT resulted in 100% complete remissions by day 12 in MM and NHL xenograft models, ultimately curing 80% of mice at optimal doses. In direct comparisons, efficacy of the CD38 bispecific proved equal or superior to streptavidin (SA)-biotin-based CD38-SA PRIT. Each approach cured at least 75% of mice at the highest radiation dose tested (1200 µCi), whereas at 600- and 1000-µCi doses, the bispecific outperformed the SA approach, curing 35% more mice overall (P < .004). The high efficacy of bispecific PRIT, combined with its reduced risk of immunogenicity and endogenous biotin interference, make the CD38 bispecific an attractive candidate for clinical translation. Critically, CD38 PRIT may benefit patients with unresponsive, high-risk disease because refractory disease typically retains radiation sensitivity. We posit that PRIT might not only prolong survival, but possibly cure MM and treatment-refractory NHL patients.

A phase II trial evaluating the efficacy of high-dose Radioiodinated Tositumomab (Anti-CD20) antibody, etoposide and cyclophosphamide followed by autologous transplantation, for high-risk relapsed or refractory non-hodgkin lymphoma.

Radiation is the most effective treatment for localized lymphoma, but treatment of multifocal disease is limited by toxicity. Radioimmunotherapy (RIT) delivers tumoricidal radiation to multifocal sites, further augmenting response by dose-escalation. This phase II trial evaluated high-dose RIT and chemotherapy prior to autologous stem-cell transplant (ASCT) for high-risk, relapsed or refractory (R/R) B-cell non-Hodgkin lymphoma (NHL). The primary endpoint was progression free survival (PFS). Secondary endpoints were overall survival (OS), toxicity, and tolerability. Patients age < 60 years with R/R NHL expressing CD20 were eligible. Mantle cell lymphoma (MCL) patients could proceed to transplant in first remission. Patients received I-131-tositumomab delivered at ≤25Gy to critical normal organs, followed by etoposide, cyclophosphamide and ASCT. A group of 107 patients were treated including aggressive lymphoma (N = 29), indolent lymphoma (N = 45), and MCL (N = 33). After a median follow-up of 10.1 years, the 10-year PFS for the aggressive, indolent, and MCL groups were 62%, 64%, 43% respectively. The 10-year OS for the aggressive, indolent, and MCL groups were 61%, 71%, 48% respectively. Toxicities were similar to standard conditioning regimens and non-relapse mortality at 100 days was 2.8%. Late myeloid malignancies were seen in 6% of patients. High-dose I-131-tositumomab, etoposide and cyclophosphamide followed by ASCT appeared feasible, safe, and effective in treating NHL, with estimated PFS at 10-years of 43%-64%. In light of novel cellular therapies for R/R NHL, high-dose RIT-containing regimens yield comparable efficacy and safety and could be prospectively compared.

Hematopoietic Cell Transplantation in Myelodysplastic Syndromes after Treatment with Hypomethylating Agents.

The prognosis of patients with myelodysplastic syndromes (MDS) after failure of hypomethylating agent (HMA) therapy is poor. Allogeneic hematopoietic cell transplantation (HCT) can be effective in curing patients who have failed therapy with HMA. However, published results have not addressed the outcomes with HCT in this setting. We identified 125 MDS patients who had been treated with HMA and underwent subsequent HCT. Among these, 68 were considered HMA failures and 57 responders. Failure was defined as progression to higher grade MDS or acute myeloid leukemia, lack of hematologic improvement after at least 4 HMA cycles, or loss of response after initial improvement. Response was defined as showing at least hematologic improvement. Outcomes were compared using Cox regression. Overall, 73 of 125 HMA-treated patients (58%) had died by the time of last contact. Median follow-up of survivors, measured from HCT, was 41.9 months (range, 2.7 to 98.5). The estimated probability of relapse at 3 years was 56.6% and 34.2% among failing and responding patients, respectively (hazard ratio [HR], 2.1; 95% confidence interval [CI], 1.2 to 3.66; P < .01). The estimated probability of relapse-free survival at 3 years was 23.8% and 42% in failing and responding patients, respectively (HR for relapse/death, 1.88; 95% CI, 1.19 to 2.95; P < .01). The risk of nonrelapse mortality was similar for both groups (HR, 1.12; 95% CI, .52 to 2.39; P = .77). Failure of treatment with HMA was associated with higher risk of post-HCT relapse than observed in patients responding to HMA. Prospective trials are needed to evaluate the efficacy of novel conditioning regimens and post-HCT maintenance strategies in patients who have failed HMA pre-HCT.

Astatine-211 conjugated to an anti-CD20 monoclonal antibody eradicates disseminated B-cell lymphoma in a mouse model.

α-Emitting radionuclides deposit a large amount of energy within a few cell diameters and may be particularly effective for radioimmunotherapy targeting minimal residual disease (MRD). To evaluate this hypothesis, (211)At-labeled 1F5 monoclonal antibody (mAb) (anti-CD20) was studied in both bulky lymphoma tumor xenograft and MRD animal models. Superior treatment responses to (211)At-labeled 1F5 mAb were evident in the MRD setting. Lymphoma xenograft tumor-bearing animals treated with doses of up to 48 µCi of (211)At-labeled anti-CD20 mAb ([(211)At]1F5-B10) experienced modest responses (0% cures but two- to threefold prolongation of survival compared with negative controls). In contrast, 70% of animals in the MRD lymphoma model demonstrated complete eradication of disease when treated with (211)At-B10-1F5 at a radiation dose that was less than one-third (15 µCi) of the highest dose given to xenograft animals. Tumor progression among untreated control animals in both models was uniformly lethal. After 130 days, no significant renal or hepatic toxicity was observed in the cured animals receiving 15 µCi of [(211)At]1F5-B10. These findings suggest that α-emitters are highly efficacious in MRD settings, where isolated cells and small tumor clusters prevail.

Minimal Identifiable Disease and the Role of Conditioning Intensity in Hematopoietic Cell Transplantation for Myelodysplastic Syndrome and Acute Myelogenous Leukemia Evolving from Myelodysplastic Syndrome.

Allogeneic hematopoietic cell transplantation (HCT) is the only known treatment with curative potential for myelodysplastic syndrome, but relapse is a major cause of failure. We studied results in 289 patients transplanted between June 2004 and December 2013. Minimal identifiable disease (MID) markers pre-HCT were determined by multiparameter flow cytometry (MFC) and cytogenetics on marrow aspirates. The impact of MID on outcome after low- and high-intensity conditioning HCT was determined. Among 287 assessable patients, 68 (23.7%) had more than 5% marrow blasts at HCT; 219 patients were in morphologic remission but 154 (53.7%) were MID positive, whereas 65 (22.6%) were MID negative. The impact of MID on outcome was significantly different between patients who received low-intensity conditioning and patients who received a high-intensity regimen. The impact of conditioning intensity differed across the various MID categories. In particular, the risk of overall mortality was higher with low-intensity than with high-intensity regimens for patients who were positive for MID by cytogenetics regardless of positivity by MFC (HR, 1.67 if MFC positive/cytogenetics positive, HR, 7.23 if MFC negative/cytogenetics positive). On the other hand, patients who were MID negative by both MFC and cytogenetics had similar risks of mortality with low- and high-intensity regimens (HR, .99). The main factor responsible for mortality after low-intensity conditioning in MID-positive patients was relapse. The presence of MID should be considered when deciding on conditioning intensity because it identifies subgroups of patients who may benefit from high- or low-intensity conditioning.

Pretransplant comorbidities predict severity of acute graft-versus-host disease and subsequent mortality.

Whether the hematopoietic cell transplantation comorbidity index (HCT-CI) can provide prognostic information about development of acute graft-versus-host disease (GVHD) and subsequent mortality is unknown. Five institutions contributed information on 2985 patients given human leukocyte antigen-matched grafts to address this question. Proportional hazards models were used to estimate the hazards of acute GVHD and post-GVHD mortality after adjustment for known risk variables. Higher HCT-CI scores predicted increased risk of grades 3 to 4 acute GVHD (P < .0001 and c-statistic of 0.64), and tests of interaction suggested that this association was consistent among different conditioning intensities, donor types, and stem cell sources. Probabilities of grades 3 to 4 GVHD were 13%, 18%, and 24% for HCT-CI risk groups of 0, 1 to 4, and ≥5. The HCT-CI was statistically significantly associated with mortality rates following diagnosis of grade 2 (hazard ratio [HR] = 1.24; P < .0001) or grades 3 to 4 acute GVHD (HR = 1.19; P < .0001). Patients with HCT-CI scores of ≥3 who developed grades 3 to 4 acute GVHD had a 2.63-fold higher risk of mortality than those with scores of 0 to 2 and did not develop acute GVHD. Thus, pretransplant comorbidities are associated with the development and severity of acute GVHD and with post-GVHD mortality. The HCT-CI could be useful in designing trials for GVHD prevention and could inform expectations for GVHD treatment trials.

HLA-C expression levels define permissible mismatches in hematopoietic cell transplantation.

Life-threatening graft-versus-host disease (GVHD) limits the use of HLA-C-mismatched unrelated donors in transplantation. Clinicians lack criteria for donor selection when HLA-C-mismatched donors are a patient's only option for cure. We examined the role for HLA-C expression levels to identify permissible HLA-C mismatches. The median fluorescence intensity, a proxy of HLA-C expression, was assigned to each HLA-C allotype in 1975 patients and their HLA-C-mismatched unrelated transplant donors. The association of outcome with the level of expression of patients' and donors' HLA-C allotypes was evaluated in multivariable models. Increasing expression level of the patient's mismatched HLA-C allotype was associated with increased risks of grades III to IV acute GVHD, nonrelapse mortality, and mortality. Increasing expression level among HLA-C mismatches with residue 116 or residue 77/80 mismatching was associated with increased nonrelapse mortality. The immunogenicity of HLA-C mismatches in unrelated donor transplantation is influenced by the expression level of the patient's mismatched HLA-C allotype. HLA-C expression levels provide new information on mismatches that should be avoided and extend understanding of HLA-C-mediated immune responses in human disease.

High-dose CD20-targeted radioimmunotherapy-based autologous transplantation improves outcomes for persistent mantle cell lymphoma.

Autologous stem cell transplant (ASCT) can improve outcomes for mantle cell lymphoma (MCL) patients, yet relapses are frequent. We hypothesized that high-dose anti-CD20 radioimmunotherapy (RIT)-based conditioning could improve results in this setting. We thus assessed 162 consecutive patients with MCL at our centre undergoing ASCT following high-dose RIT-based (n = 61) or standard (n = 101) conditioning. RIT patients were less likely to be in first remission (48% vs. 72%; P = 0·002), be in complete remission (CR) (26% vs. 61%; P < 0·001) and have chemosensitive disease (84% vs. 96%; P = 0·006). RIT-based conditioning was associated with a reduced risk of treatment failure [hazard ratio (HR) 0·40; P = 0·001] and mortality (HR 0·49; P = 0·01) after adjusting for these imbalances. This difference increased as disease status worsened (from CR to partial remission to stable/progressive disease), with respective HRs of 1·14, 0·53 and 0·04 for mortality, and 0·66, 0·36 and 0·14 for treatment failure. RIT-based conditioning appears to improve outcome following ASCT for MCL patients unable to achieve CR after controlling for imbalances in important risk factors. These data support the further study of RIT and radiation-based strategies in a risk-adapted approach to ASCT for persistent MCL.

The helix-loop-helix transcription factor TWIST is dysregulated in myelodysplastic syndromes.

Patients with low-grade myelodysplastic syndromes (MDS) show high levels of tumor necrosis factor α (TNFα) and up-regulation of apoptosis in the marrow. In contrast, marrow cells in advanced MDS are typically resistant to TNFα-induced apoptosis but are rendered apoptosis-sensitive on coculture with stroma. The present studies show that CD34(+) marrow cells in advanced MDS express high levels of TWIST, a basic helix-loop-helix transcription factor that opposes p53 function. TWIST levels correlated with disease stage (advanced > low grade; P = .01). Coculture with HS5 stroma resulted in down-regulation of TWIST and increased apoptosis in response to TNFα in CD34(+) cells from advanced MDS; the same effect was achieved by TWIST-specific RNA interference in CD34(+) cells. In primary MDS marrow stroma TWIST expression was lower than in healthy controls; suppression of TWIST in stroma interfered with induction of apoptosis sensitivity in cocultured CD34(+) cells. Stroma cells so modified expressed reduced levels of intercellular adhesion molecule-1 (ICAM1; CD54); blockade of ICAM1 in unmodified stroma was associated with reduced apoptosis in cocultured CD34(+) MDS marrow cells. These data suggest role for dysregulation of TWIST in the pathophysiology of MDS. Conceivably, TWIST or components in the signaling pathway could serve as therapeutic targets for patients with MDS.

Allogeneic hematopoietic cell transplantation for hematologic malignancy: relative risks and benefits of double umbilical cord blood.

Effectiveness of double umbilical cord blood (dUCB) grafts relative to conventional marrow and mobilized peripheral blood from related and unrelated donors has yet to be established. We studied 536 patients at the Fred Hutchinson Cancer Research Center and University of Minnesota with malignant disease who underwent transplantation with an human leukocyte antigen (HLA)-matched related donor (MRD, n = 204), HLA allele-matched unrelated donor (MUD, n = 152) or 1-antigen-mismatched unrelated adult donor (MMUD, n = 52) or 4-6/6 HLA matched dUCB (n = 128) graft after myeloablative conditioning. Leukemia-free survival at 5 years was similar for each donor type (dUCB 51% [95% confidence interval (CI), 41%-59%]; MRD 33% [95% CI, 26%-41%]; MUD 48% [40%-56%]; MMUD 38% [95% CI, 25%-51%]). The risk of relapse was lower in recipients of dUCB (15%, 95% CI, 9%-22%) compared with MRD (43%, 95% CI, 35%-52%), MUD (37%, 95% CI, 29%-46%) and MMUD (35%, 95% CI, 21%-48%), yet nonrelapse mortality was higher for dUCB (34%, 95% CI, 25%-42%), MRD (24% (95% CI, 17%-39%), and MUD (14%, 95% CI, 9%-20%). We conclude that leukemia-free survival after dUCB transplantation is comparable with that observed after MRD and MUD transplantation. For patients without an available HLA matched donor, the use of 2 partially HLA-matched UCB units is a suitable alternative.

Naive T-Cell Depletion to Prevent Chronic Graft-Versus-Host Disease.

PURPOSE: Graft-versus-host disease (GVHD) causes morbidity and mortality following allogeneic hematopoietic cell transplantation. Naive T cells (TN) cause severe GVHD in murine models. We evaluated chronic GVHD (cGVHD) and other outcomes in three phase II clinical trials of TN-depletion of peripheral blood stem-cell (PBSC) grafts. METHODS: One hundred thirty-eight patients with acute leukemia received TN-depleted PBSC from HLA-matched related or unrelated donors following conditioning with high- or intermediate-dose total-body irradiation and chemotherapy. GVHD prophylaxis was with tacrolimus, with or without methotrexate or mycophenolate mofetil. Subjects received CD34-selected PBSC and a defined dose of memory T cells depleted of TN. Median follow-up was 4 years. The primary outcome of the analysis of cumulative data from the three trials was cGVHD. RESULTS: cGVHD was very infrequent and mild (3-year cumulative incidence total, 7% [95% CI, 2 to 11]; moderate, 1% [95% CI, 0 to 2]; severe, 0%). Grade III and IV acute GVHD (aGVHD) occurred in 4% (95% CI, 1 to 8) and 0%, respectively. The cumulative incidence of grade II aGVHD, which was mostly stage 1 upper gastrointestinal GVHD, was 71% (95% CI, 64 to 79). Recipients of matched related donor and matched unrelated donor grafts had similar rates of grade III aGVHD (5% [95% CI, 0 to 9] and 4% [95% CI, 0 to 9]) and cGVHD (7% [95% CI, 2 to 13] and 6% [95% CI, 0 to 12]). Overall survival, cGVHD-free, relapse-free survival, relapse, and nonrelapse mortality were, respectively, 77% (95% CI, 71 to 85), 68% (95% CI, 61 to 76), 23% (95% CI, 16 to 30), and 8% (95% CI, 3 to 13) at 3 years. CONCLUSION: Depletion of TN from PBSC allografts results in very low incidences of severe acute and any cGVHD, without apparent excess risks of relapse or nonrelapse mortality, distinguishing this novel graft engineering strategy from other hematopoietic cell transplantation approaches.

Megadose 90Y-ibritumomab tiuxetan prior to allogeneic transplantation is effective for aggressive large B-cell lymphoma.

Allogeneic hematopoietic cell transplantation (allo-HCT) can be curative for relapsed or refractory B-cell lymphomas (BCLs), although outcomes are worse in aggressive disease, and most patients will still experience relapse. Radioimmunotherapy using 90Y-ibritumomab tiuxetan can induce disease control across lymphoma subtypes in a dose-dependent fashion. We hypothesized that megadoses of 90Y-ibritumomab tiuxetan with reduced-intensity conditioning could safely produce deeper remissions in aggressive BCL further maintained with the immunologic effect of allo-HCT. In this phase 2 study, CD20+ BCL patients received outpatient 90Y-ibritumomab tiuxetan (1.5 mCi/kg; maximum, 120 mCi), fludarabine, and then 2 Gy total body irradiation before HLA-matched allo-HCT. Twenty patients were enrolled after a median of 4.5 prior lines of therapy, including 14 with prior autologous transplant and 4 with prior anti-CD19 chimeric T-cellular therapy. A median 90Y-ibritumomab tiuxetan activity of 113.6 mCi (range, 71.2-129.2 mCi) was administered, delivering a median of 552 cGy to the liver (range, 499-2411 cGy). The estimated 1- and 5-year progression-free survival was 55% (95% confidence interval [CI], 31-73) and 50% (95% CI, 27-69) with a median progression-free survival of 1.57 years. The estimated 1- and 5-year overall survival was 80% (95% CI, 54-92) and 63% (95% CI, 38-81) with a median overall survival of 6.45 years. Sixteen patients (80%) experienced grade 3 or higher toxicities, although nonrelapse mortality was 10% at 1 year. No patients developed secondary acute myeloid leukemia/myelodysplastic syndrome. Megadose 90Y-ibritumomab tiuxetan, fludarabine, and low-dose total body irradiation followed by an HLA-matched allo-HCT was feasible, safe, and effective in treating aggressive BCL, exceeding the prespecified end point while producing nonhematologic toxicities comparable to those of standard reduced-intensity conditioning regimens.

A phase I/II study of chemotherapy followed by donor lymphocyte infusion plus interleukin-2 for relapsed acute leukemia after allogeneic hematopoietic cell transplantation.

The efficacy of donor lymphocyte infusion (DLI) for treatment of relapsed acute leukemia after allogeneic hematopoietic cell transplantation is limited. We hypothesized that interleukin-2 (IL-2) combined with DLI after chemotherapy might augment graft-versus-leukemia effects. To identify a safe and effective IL-2 regimen, a phase I/II study of DLI plus IL-2 therapy was performed for such patients. After chemotherapy, 17 patients received DLI (1 × 10(8) CD3/kg for patients with related donors, and 0.1 × 10(8) CD3/kg for those with unrelated donors) and an escalating dose of induction IL-2 (1.0, 2.0, or 3.0 × 10(6) IU/m(2)/day representing levels I [n = 7], Ia [n = 9], and II [n = 1]) for 5 days followed by maintenance (1.0 × 10(6) IU/m(2)/day) for 10 days as a continuous intravenous infusion. Unacceptable IL-2-related toxicities developed in 1 patient at level I, 2 at level Ia, and 1 at level II. Grades III-IV acute graft-versus-host disease (aGVHD) developed in 5 patients, and extensive chronic GVHD (cGVHD) developed in 8. Eight patients had a complete remission after chemotherapy prior to DLI, and 2 additional patients had a complete remission after DLI plus IL-2 therapy. In conclusion, the maximal tolerated induction dose of IL-2 combined with DLI appears to be 1.0 × 10(6) IU/m(2)/day. IL-2 administration after DLI might increase the incidence of cGVHD.

Allogeneic haematopoietic cell transplantation for myelofibrosis in 30 patients 60-78 years of age.

We analysed the results of haematopoietic cell transplantation (HCT) in 30 patients aged 60-78 (median 65) years, with primary myelofibrosis or myelofibrosis evolving from antecedent polycythaemia vera or essential thrombocythaemia. Donors were human leucocyte antigen (HLA)-identical siblings (N = 15) or unrelated individuals (N = 15). Various conditioning regimens were used, ranging from very low intensity (fludarabine plus 2 Gy total body irradiation) to high dose (busulfan plus cyclophosphamide). Stem cell sources were granulocyte colony-stimulating factor mobilized peripheral blood progenitor cells in 29 patients and marrow in one patient. Sustained engraftment was documented in 27 of 30 patients. Day -100 mortality was 13%. With a median follow-up of 22 (range 0·5 - 69) months, 3-year overall survival and progression-free survival were 45% and 40%, respectively. Currently, 13 patients are surviving. Seven patients died with disease progression at 0·5 -22 months, and 10 patients died from other causes at 1·5 -37.5 months after HCT. While the selection of older patients for transplantation was probably biased, the present results are encouraging. Motivated older patients with myelofibrosis without substantial comorbid conditions should be offered the option of allogeneic HCT.

A comparative analysis of conventional and pretargeted radioimmunotherapy of B-cell lymphomas by targeting CD20, CD22, and HLA-DR singly and in combinations.

Relapsed B-cell lymphomas are currently incurable with conventional chemotherapy and radiation treatments. Radiolabeled antibodies directed against B-cell surface antigens have emerged as effective and safe therapies for relapsed lymphomas. We therefore investigated the potential utility of both directly radiolabeled 1F5 (anti-CD20), HD39 (anti-CD22), and Lym-1 (anti-DR) antibodies (Abs) and of pretargeted radioimmunotherapy (RIT) using Ab-streptavidin (SA) conjugates, followed by an N-acetylgalactosamine dendrimeric clearing agent and radiometal-labeled DOTA-biotin, for treatment of lymphomas in mouse models using Ramos, Raji, and FL-18 human lymphoma xenografts. This study demonstrates the marked superiority of pretargeted RIT for each of the antigenic targets with more complete tumor regressions and longer mouse survival compared with conventional one-step RIT. The Ab-SA conjugate yielding the best tumor regression and progression-free survival after pretargeted RIT varied depending upon the lymphoma cell line used, with 1F5 Ab-SA and Lym-1 Ab-SA conjugates yielding the most promising results overall. Contrary to expectations, the best rates of mouse survival were obtained using optimal single Ab-SA conjugates rather than combinations of conjugates targeting different antigens. We hypothesize that clinical implementation of pretargeted RIT methods will provide a meaningful prolongation of survival for patients with relapsed lymphomas compared with currently available treatment strategies.

Allogeneic hematopoietic cell transplantation after conditioning with 131I-anti-CD45 antibody plus fludarabine and low-dose total body irradiation for elderly patients with advanced acute myeloid leukemia or high-risk myelodysplastic syndrome.

We conducted a study to estimate the maximum tolerated dose (MTD) of (131)I-anti-CD45 antibody (Ab; BC8) that can be combined with a standard reduced-intensity conditioning regimen before allogeneic hematopoietic cell transplantation. Fifty-eight patients older than 50 years with advanced acute myeloid leukemia (AML) or high-risk myelodysplastic syndrome (MDS) were treated with (131)I-BC8 Ab and fludarabine plus 2 Gy total body irradiation. Eighty-six percent of patients had AML or MDS with greater than 5% marrow blasts at the time of transplantation. Treatment produced a complete remission in all patients, and all had 100% donor-derived CD3(+) and CD33(+) cells in the blood by day 28 after the transplantation. The MTD of (131)I-BC8 Ab delivered to liver was estimated to be 24 Gy. Seven patients (12%) died of nonrelapse causes by day 100. The estimated probability of recurrent malignancy at 1 year is 40%, and the 1-year survival estimate is 41%. These results show that CD45-targeted radiotherapy can be safely combined with a reduced-intensity conditioning regimen to yield encouraging overall survival for older, high-risk patients with AML or MDS. This study was registered at www.clinicaltrials.gov as #NCT00008177.