Unrelated donor allogeneic hematopoietic cell transplantation is underused as a curative therapy in eligible patients from the United States

Targeting CD45 by gene-edited CAR T cells for leukemia eradication and hematopoietic stem cell transplantation preconditioning

Hematopoietic stem cell transplantation (HSCT) is widely used to treat patients with life-threatening hematologic and immune system disorders. Current nontargeted chemo-/radiotherapy conditioning regimens cause tissue injury and induce an array of immediate and delayed adverse effects, limiting the application of this life-saving treatment. The growing demand to replace canonical conditioning regimens has led to the development of alternative approaches, such as antibody-drug conjugates, naked antibodies, and CAR T cells. Here, we introduce a preconditioning strategy targeting CD45 on hematopoietic cells with CAR45 T cells. To avoid fratricide of CD45 CAR T cells, genomic disruption of the CD45 gene was performed on human CD45 CAR T cells in combination with the signaling kinase inhibitor dasatinib. CD45Δ CAR45 T cells showed high cytotoxicity in vitro and depletion of tumor cells in vivo. These cells were effective in elimination of human hematopoietic cells engrafted in humanized immunodeficient mice by transfusion with human blood-derived hematopoietic stem cells (HSCs). Similarly, CD45Δ CAR45 natural killer (NK) cells exhibited potent cytotoxicity toward tumor cell lines and human hematopoietic cells in vitro. Thus, we provide the proof of concept for the generation and preclinical efficacy of fratricide-resistant CAR45 T and NK cells directed against CD45-expressing tumors and hematopoietic cells.

Prospective analysis to determine barriers to allogeneic hematopoietic cell transplantation in patients with acute leukemia

Allogeneic hematopoietic cell transplantation (allo-HCT) is a potentially curative treatment for patients with acute leukemia. Despite this, studies have shown that only a minority of patients ultimately proceed to allo-HCT. The primary objective of this prospective, observational study was to identify the rate of allo-HCT in patients for whom it was recommended, and reasons why patients deemed appropriate and eligible for HCT did not subsequently undergo transplant. Between April 2016 and April 2021, adult patients with newly diagnosed or relapsed/refractory acute leukemia were enrolled at the time of induction/reinduction therapy. Initial transplantation workup and allo-HCT recommendations were made during the early phase of induction/reinduction. Of the 307 enrolled patients, allo-HCT was recommended to 85% (n = 259), of whom 66% (n = 170) underwent transplant. Donor sources comprised 54% human leukocyte antigen (HLA)-matched unrelated donors, 20% HLA-matched sibling donors and HLA-mismatched graft sources with 15% umbilical cord blood units, 8% HLA-mismatched unrelated donors, and 4% HLA-haploidentical donors. The most common reason for transplant disqualification in the 89 patients in whom it was initially recommended was persistent/relapsed disease (70%), followed by early patient death (10%). In this prospective study, we report a high allo-HCT rate, which may be due to early transplant referral and workup. The main allo-HCT barrier was disease control, followed by early patient death. With the increasing availability of HLA-mismatched graft sources, the lack of donor availability was not a transplant barrier. Further development of novel transplant strategies for patients not achieving remission and improvements in induction regimens could result in increased allo-HCT utilization.

Trends in Allogeneic Hematopoietic Cell Transplantation Utilization and Estimated Unmet Need Among Medicare Beneficiaries with Acute Myelogenous Leukemia

Allogeneic hematopoietic cell transplantation (alloHCT) is a resource-intensive procedure and the sole potentially curative treatment available for patients with acute myelogenous leukemia (AML). Although Medicare coverage may help address a major financial barrier to accessing alloHCT, there remains an unmet need for alloHCT owing to sociodemographic disparities. This study examined trends and factors associated with the utilization of alloHCT and the estimated unmet need for alloHCT among Medicare beneficiaries with AML. This retrospective cohort study included patients (age 65 to 74 years) with a diagnosis of AML identified in Medicare claims data from 2010 through 2016. To study trends in utilization, transplantation rates were calculated as the number of patients who underwent alloHCT within 180 days and 1 year of diagnosis (numerator) divided by the total number of patients with AML within each diagnosis year (denominator). A multivariable logistic regression was used to identify factors associated with the likelihood of undergoing alloHCT within 1 year of diagnosis. Two approaches were applied to estimate the unmet need for alloHCT. The first approach used claims data to identify the potential need for alloHCT among patients who achieved complete remission for at least 90 days. The second approach used established National Marrow Donor Program (NMDP) methodology, which considers estimates of risk level, response to treatment, comorbidity, and early mortality, to identify the potential and unmet need for alloHCT. The overall estimated need and unmet need from 2010 to 2015 and over different time periods were evaluated for both approaches. The alloHCT rate within 180 days of diagnosis increased from 8% in 2010 to 15.8% in 2016 (P < .001), and the 1-year alloHCT rate also increased over time, from 11.9% in 2010 to 20.0% in 2015 (P < .001). The likelihood of undergoing alloHCT within 1 year of diagnosis was associated with diagnosis year, age, race, geographic region, Elixhauser Comorbidity Index, and population-level median household income. Between 2010 and 2015, the claims data approach estimated a lower potential need for alloHCT compared with the NMDP methodology estimate (27% versus 36%); both approaches estimated that 43% to 44% of patients with a potential need for alloHCT had an unmet treatment need. Despite the differences in estimated potential need between the 2 approaches, both showed a sustained unmet need but with a downward trend over time. Our data show that utilization of alloHCT has increased over time among Medicare beneficiaries with AML. Two approaches of need analysis were conducted for validation of estimated need and unmet need for alloHCT using claim-identified remission status, given the lack of cytogenetics and molecular information in claims data. Both approaches to estimating the unmet need for alloHCT found a downward trend over time; however, there are differences in utilization of alloHCT by age, race, geographic region, comorbidity, and socioeconomic status, indicating disparities in access to alloHCT among Medicare beneficiaries with AML. This suggests the need for policy efforts, research, and continued education to improve access to alloHCT and to close the gap between the actual utilization of alloHCT and the unmet need.

Antibody based conditioning for allogeneic hematopoietic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a curative therapeutic option for many patients with hematological malignancies and nonmalignant hematopoietic disorders. To achieve stable engraftment of donor hematopoietic stem cells (HSCs), recipient HSC deletion is needed to create space for incoming donor HSCs and donor HSCs must escape immune rejection by the recipient. Conventional allo-HSCT requires high dose of irradiation and/or chemotherapy to produce sufficient host stem cell and immune system ablation to permit donor HSC engraftment. However, these procedures also result in nonspecific tissue injury that can cause short- and long-term adverse effects as well as incite and amplify graft-versus-host-disease (GVHD). The delivery of targeted radiotherapy to hematopoietic tissues with the use of a radioimmunoconjugate (ROIC) as a part of transplant preparative regimen has shown clinical benefits. ROIC clinical data provide evidence for decreased relapse without increased transplant-related mortality by delivering higher targeted radiation to sites of malignancy than when given in a nontargeted fashion. An alternative approach to allo-HSCT has been developed and tested in preclinical mouse models in which nonmyeloablative preconditioning with low dose of the alkylating agent (busulfan) or lower systemic dose of irradiation combined with co-stimulatory pathway blockade (CTLA4-Ig, anti-CD40L monoclonal antibody) and/or immunosuppressive drugs have been used. Under these conditions, mixed chimerism and transplantation tolerance to fully MHC mismatched donor marrow was observed. Recently, several novel proof-of-concept antibody-mediated preconditioning methods have been developed that can selectively target hematopoietic stem and immune cells with minimal overall toxicity. Antibody-drug-conjugate (ADC) combined with reduced intensity conditioning or high dose ADC as single dose monotherapy have shown promise for allo-HSCT in preclinical models. The purpose of the current review is to discuss the literature exploring antibody-based conditioning that includes native antibody, radiolabeled antibody conjugates, and ADC for allo-HSCT.

A CD45-targeted antibody-drug conjugate successfully conditions for allogeneic hematopoietic stem cell transplantation in mice

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a potentially curative treatment of patients with nonmalignant or malignant blood disorders. Its success has been limited by graft-versus-host disease (GVHD). Current systemic nontargeted conditioning regimens mediate tissue injury and potentially incite and amplify GVHD, limiting the use of this potentially curative treatment beyond malignant disorders. Minimizing systemic nontargeted conditioning while achieving alloengraftment without global immune suppression is highly desirable. Antibody-drug-conjugates (ADCs) targeting hematopoietic cells can specifically deplete host stem and immune cells and enable alloengraftment. We report an anti-mouse CD45-targeted-ADC (CD45-ADC) that facilitates stable murine multilineage donor cell engraftment. Conditioning with CD45-ADC (3 mg/kg) was effective as a single agent in both congenic and minor-mismatch transplant models resulting in full donor chimerism comparable to lethal total body irradiation (TBI). In an MHC-disparate allo-HSCT model, pretransplant CD45-ADC (3 mg/kg) combined with low-dose TBI (150 cGy) and a short course of costimulatory blockade with anti-CD40 ligand antibody enabled 89% of recipients to achieve stable alloengraftment (mean value: 72%). When CD45-ADC was combined with pretransplant TBI (50 cGy) and posttransplant rapamycin, cyclophosphamide (Cytoxan), or a JAK inhibitor, 90% to 100% of recipients achieved stable chimerism (mean: 77%, 59%, 78%, respectively). At a higher dose (5 mg/kg), CD45-ADC as a single agent was sufficient for rapid, high-level multilineage chimerism sustained through the 22 weeks observation period. Therefore, CD45-ADC has the potential utility to confer the benefit of fully myeloablative conditioning but with substantially reduced toxicity when given as a single agent or at lower doses in conjunction with reduced-intensity conditioning.

Cardiovascular disease and its management in children and adults undergoing hematopoietic stem cell transplantation

Hematopoietic stem cell transplantation (HSCT) is a potentially curative treatment for many malignancies, hemoglobinopathies, metabolic diseases, bone marrow failure syndromes, and primary immune deficiencies. Despite the significant improvement in survival afforded by HSCT, the therapy is associated with major short and long-term morbidity and mortality. Cardiovascular complications such as cardiomyopathy, arrhythmias, pulmonary hypertension, and pericardial effusions are increasingly recognized as potential outcomes following HSCT. The incidence of cardiac complications is related to various factors such as age, co-morbid medical conditions, whether patients received cardiotoxic chemotherapy prior to HSCT, the type of HSCT (autologous versus allogeneic), and the specific conditioning regimen. Thus, the cardiovascular evaluation has become a core component of the pre-transplant assessment, however, the practice differs from center to center as national guidelines and contemporary high-quality studies are lacking. We review the incidence of cardiotoxicity in pediatric and adult HSCT, potential mechanisms of injury, and effects on long-term outcomes. We also discuss the possible therapeutic approaches when disease arises, as well as the indications and need for surveillance before, during, and after transplantation.

Addressing Knowledge Gaps in Acute Myeloid Leukemia to Improve Referral for Hematopoietic Cell Transplantation Consultation

BACKGROUND

Outcomes after hematopoietic cell transplantation (HCT) for acute myeloid leukemia (AML) are better when HCT is performed during first complete remission (CR1). This study aimed to identify and address knowledge gaps that affect the timely referral of patients for HCT consultation.

METHODS

A mixed-methods educational needs assessment included a national survey and focus groups consisting of hematologists/oncologists. An educational intervention of 3 webinars addressed identified knowledge gaps.

RESULTS

A total of 150 hematologists/oncologists were recruited for the survey, of whom 20 participated in focus groups. Physicians in practice 0 to 10 years were 4.2 times more likely to refer for HCT consultation in CR1 than those with >10 years in practice (P=.0027). Physicians seeing ≤10 patients with AML in the past year were 3.7 times more likely to refer for HCT consultation in CR1 than those seeing >10 patients (P=.0028). Knowledge gaps included (1) improper classification of molecular/cytogenetic results for risk stratification, (2) lack of understanding that disease stage impacts outcomes, and (3) use of chronologic age alone for referral decision-making. Combined attendance for the webinars was 1,098 clinicians; >74% of participants indicated that they would apply the knowledge they gained in clinical practice. Trends were observed toward improvement in identifying favorable-risk AML, from 48% to 60% (n=85; P=.12); improvement in identifying 2 poor-risk cytogenetic/molecular abnormalities, with the percentage of respondents indicating chromosome 7 deletion increasing from 51% to 70% (n=53; P=.05) and that of respondents indicating TP53 mutation increasing from 42% to 62% (n=62; P=.03); and improvement in identifying which patients with AML aged >60 years were most likely to benefit from HCT based on cytogenetic/molecular features, with the percentage of correct responses increasing from 66% to 81% (n=62; P=.07).

CONCLUSIONS

The webinars met the educational needs of learners and improved knowledge gaps. This study provided novel insights into the learning needs of clinicians who care for patients with AML and a roadmap for future educational interventions.

The MarrowMiner: A Novel Minimally Invasive and Effective Device for the Harvest of Bone Marrow

Bone marrow (BM) is a rich source of hematopoietic stem cells (HSCs), mesenchymal stem cells (MSCs), and other important stem/progenitor cells. It is the traditional source of cells used in hematopoietic cell transplantation, which is a proven curative treatment for many blood and immune diseases. BM-derived cells have also been shown to have other diverse clinical uses and are increasingly being used in orthopedic medicine, regenerative medicine, and gene therapy applications. Traditional methods for harvesting BM are crude, tedious, time-consuming, and expensive, requiring multiple bone punctures under general anesthesia with serial small-volume aspirates often diluted with peripheral blood. The MarrowMiner (MM) is a novel device designed for rapid and minimally invasive BM harvest. Here we show the safety and efficacy of the MM in both preclinical and clinical settings. In a large-animal porcine model, the MM enabled effective BM collection with similar total nucleated cell collection and increased colony formation compared with standard methods. The MM was subsequently evaluated in a clinical study showing effective and complication-free anterior and posterior BM collection of 20 patients under only local anesthesia or light sedation. Increased total nucleated and mononucleated cell collection was achieved with the MM compared with standard methods in the same patients. Importantly, stem cell content was high with trends toward increased HSC, MSC, and endothelial progenitor cells with similar T cell content. Given the MM is a novel device approved by the US Food and Drug Administration, enabling safe, effective, and minimally invasive harvest of BM, we anticipate rapid adoption for various applications.

Selective hematopoietic stem cell ablation using CD117-antibody-drug-conjugates enables safe and effective transplantation with immunity preservation

Hematopoietic stem cell transplantation (HSCT) is a curative therapy for blood and immune diseases with potential for many settings beyond current standard-of-care. Broad HSCT application is currently precluded largely due to morbidity and mortality associated with genotoxic irradiation or chemotherapy conditioning. Here we show that a single dose of a CD117-antibody-drug-conjugate (CD117-ADC) to saporin leads to > 99% depletion of host HSCs, enabling rapid and efficient donor hematopoietic cell engraftment. Importantly, CD117-ADC selectively targets hematopoietic stem cells yet does not cause clinically significant side-effects. Blood counts and immune cell function are preserved following CD117-ADC treatment, with effective responses by recipients to both viral and fungal challenges. These results suggest that CD117-ADC-mediated HSCT pre-treatment could serve as a non-myeloablative conditioning strategy for the treatment of a wide range of non-malignant and malignant diseases, and might be especially suited to gene therapy and gene editing settings in which preservation of immunity is desired.

Hematopoietic stem cell (HSC) transplantation is a desirable treatment for many non-malignant and malignant diseases, but its use requires preconditioning of recipients with irradiation or chemotherapy that often induces high toxicity. Here the authors show that antibody-drug-conjugate to CD117, a HSC marker, allows specific and efficient preconditioning for HSC therapy.

Biologic vs physiologic age in the transplant candidate

Hematopoietic cell transplantation (HCT) remains a cornerstone of treatment of many hematologic malignancies but transplant-associated morbidity and mortality limit application to older patients. Biologic or chronologic age barriers to HCT have fallen, because patients in their 8th decade of life comprise the group with the greatest rise in transplant use over the past decade. Evaluating physiologic age or general health in older transplant candidates requires a systematic approach inclusive of functional and comorbidity assessment, which typically is accomplished through geriatric assessment (GA). GA incorporates measures of comorbidity, function, nutrition, social support, and other health-related domains to better describe physiologic age. Older allogeneic transplant patients have a surprisingly high prevalence of vulnerabilities by GA prior to transplant, and significant comorbidity or functional limitations heighten the risks of transplant-related mortality. Ultimately, incorporation of physiologic age can improve estimates of nondisease life expectancy, prognostic survival after HCT, and inform HCT candidacy. Future research on the optimal tools to characterize physiologic age and appropriate interventions in the context of transplant are needed.

The prognostic value of serum C-reactive protein, ferritin, and albumin prior to allogeneic transplantation for acute myeloid leukemia and myelodysplastic syndromes

We sought to confirm the prognostic importance of simple clinically available biomarkers of C-reactive protein, serum albumin, and ferritin prior to allogeneic hematopoietic cell transplantation. The study population consisted of 784 adults with acute myeloid leukemia in remission or myelodysplastic syndromes undergoing unrelated donor transplant reported to the Center for International Blood and Marrow Transplant Research. C-reactive protein and ferritin were centrally quantified by ELISA from cryopreserved plasma whereas each center provided pre-transplant albumin. In multivariate analysis, transplant-related mortality was associated with the pre-specified thresholds of C-reactive protein more than 10 mg/L (P=0.008) and albumin less than 3.5 g/dL (P=0.01) but not ferritin more than 2500 ng/mL. Only low albumin independently influenced overall mortality. Optimal thresholds affecting transplant-related mortality were defined as: C-reactive protein more than 3.67 mg/L, log(ferritin), and albumin less than 3.4 g/dL. A 3-level biomarker risk group based on these values separated risks of transplant-related mortality: low risk (reference), intermediate (HR=1.66, P=0.015), and high risk (HR=2.7, P<0.001). One-year survival was 74%, 67% and 56% for low-, intermediate- and high-risk groups. Routinely available pre-transplant biomarkers independently risk-stratify for transplant-related mortality and survival.

Estimating demand and unmet need for allogeneic hematopoietic cell transplantation in the United States using geographic information systems

PURPOSE

Allogeneic hematopoietic cell transplantation (HCT) is an increasingly used therapy for many patients with hematologic malignancies and other marrow failure or immune system disorders. The purpose of this study was to quantify and visualize both the demand and unmet need for HCT.

METHODS

HCT use for 2012 was described using the Center for International Blood and Marrow Transplant Research registry. Potential demand for HCT was calculated using 2012 SEER data and published literature for HCT-treatable conditions. Point locations of transplant centers were geocoded using geographic information system (GIS) software; Thiessen polygons were created to establish adult (age 20 to 74 years) and pediatric (age 0 to 19 years) market areas. Market-area population estimates were calculated using 2012 population estimates by age aggregated by census block.

RESULTS

US market areas for HCTs were identified separately for transplant centers treating adult (n = 62) and pediatric patients (n = 52). Overall HCT demand among adults was 16,096, with an unmet need for HCTs of 10,276 patients. For pediatric patients, the total demand was 4,561, with an unmet need of 3,213 potential recipients. Evaluation of adult and pediatric market areas indicated that the largest unmet needs tended to be in areas with large populations.

CONCLUSION

Market-area maps and statistics developed using GIS will help communicate the unmet need for HCT, inform policy, and assist transplant centers in planning for the anticipated growth in HCT use.

Therapy-related myelodysplastic syndrome/acute leukemia after multiple myeloma in the era of novel agents

Survival for patients with multiple myeloma has increased. Both melphalan and lenalidomide are associated with subsequent development of myelodysplasia. We reviewed the cases of all patients with multiple myeloma who had subsequent development of myelodysplastic syndrome (MDS) or acute non-lymphoblastic leukemia (ANLL) during a 12-year period in three centers. Of 55 patients identified, two received only lenalidomide before myelodysplasia developed. The median time between the diagnoses of multiple myeloma and MDS/ANLL was 52.7 months. Median survival after the diagnosis of MDS or ANLL was 6.7 months. Treatment of MDS comprised allogeneic stem cell transplant in eight patients (median survival, 219 days; one patient alive at 624 days) and a hypomethylating agent in 21 patients (response of stable or better in five patients). Myelodysplasia remains a devastating complication of therapy for multiple myeloma, with short survival and poor response rates to available modalities.

Allogeneic hematopoietic cell transplantation for myelodysplastic syndromes: lingering uncertainties and emerging possibilities

The landscape of transplantation in myelodysplastic syndrome (MDS) has evolved rapidly in the last decade, driven mostly by advances in patient selection through better risk stratification, increasing age of allogeneic recipients, introduction of reduced-intensity conditioning regimens, increased availability of unrelated donors, new donor sources, and improvements in transplant technology and supportive care. Despite these advances, several issues, mostly centering on approaches to improve post-transplant survival while minimizing transplant-related mortality, continue to present significant challenges. Advances in understanding the molecular pathogenesis of MDS have made it feasible to construct clinically useful risk models that integrate prognostic genes with conventional risk parameters for better selection of patients likely to benefit from hematopoietic cell transplantation. Simultaneous research efforts in several areas, including comorbidity assessment, novel preparative regimens, optimal pretransplant cytoreductive strategy, and post-transplantation therapies, are expected to improve long-term disease-free survival and quality of life.