Reduced intensity haplo plus single cord transplant compared to double cord transplant: improved engraftment and graft-versus-host disease-free, relapse-free survival

Transplant for non-malignant disorders: an International Society for Cell & Gene Therapy Stem Cell Engineering Committee report on the role of alternative donors, stem cell sources and graft engineering

Hematopoietic stem cell transplantation (HSCT) is curative for many non-malignant disorders. As HSCT and supportive care technologies improve, this life-saving treatment may be offered to more and more patients. With the development of new preparative regimens, expanded alternative donor availability, and graft manipulation techniques, there are many options when choosing the best regimen for patients. Herein the authors review transplant considerations, transplant goals, conditioning regimens, donor choice, and graft manipulation strategies for patients with non-malignant disorders undergoing HSCT.

Haplo-Peripheral Blood Stem Cell Plus Cord Blood Grafts for Hematologic Malignancies Might Lead to Lower Relapse Compared with Haplo-Peripheral Blood Stem Cell Plus Bone Marrow Grafts

To compare the outcomes between peripheral blood stem cell (PBSC)+cord blood and PBSC+bone marrow (BM) grafts in the setting of haploidentical donor (HID) transplantation, 110 patients were enrolled in this retrospective study, including 54 recipients of haplo-PBSC+cord transplants and 56 recipients of haplo-PBSC+BM transplants. Chimerism analyses revealed that by day 30 post-transplantation, 94.3% of surviving patients in the haplo-PBSC+cord group had achieved full haploidentical chimerism and 5.7% had <10% cord chimerism, whereas 100% of surviving patients in the haplo-PBSC+BM group had achieved full donor chimerism. The cumulative incidence of platelet engraftment at 30 days was 92.6% in the haplo-PBSC+cord group versus 89.3% in the haplo-PBSC+BM group (P =.024), that of grade II-IV acute graft-versus-host disease (GVHD) at 100 days was 31.5% versus 48.2% (P =.060), and 1-year relapse was 13.0% versus 25.0% (P =.027), nonrelapse mortality was 9.3% versus 12.5% (P =.76), disease-free survival (DFS) was 77.7% versus 62.5% (P =.028), and overall survival (OS) was 81.4% versus 69.6% (P =.046). Multivariate analysis identified haplo-PBSC+cord transplantation as a protective factor for relapse (hazard ratio [HR], .31; P =.007), DFS (HR, .40; P =.007), and OS (HR, .44; P =.016). Overall, haplo-PBSC+cord transplantation led to faster platelet engraftment, lower relapse, and superior DFS and OS compared with haplo-PBSC+BM transplantation and thus might be a better transplant mode in the setting of HID transplantation.

Predictors of Covid-19 Vaccination Response After In-Vivo T-Cell–Depleted Stem Cell Transplantation

Covid-19 vaccination is recommended in allogeneic transplant recipients, but many questions remain regarding its efficacy. Here we studied serologic responses in 145 patients who had undergone allogeneic transplantation using in vivo T-cell depletion. Median age was 57 (range 21-79) at transplantation and 61 (range 24-80) at vaccination. Sixty-nine percent were Caucasian. One third each received transplants from HLA-identical related (MRD), adult unrelated (MUD), or haploidentical-cord blood donors. Graft-versus-host disease (GVHD) prophylaxis involved in-vivo T-cell depletion using alemtuzumab for MRD or MUD transplants and anti-thymocyte globulin for haplo-cord transplants. Patients were vaccinated between January 2021 and January 2022, an average of 31 months (range 3-111 months) after transplantation. Sixty-one percent received the BNT162b2 (bioNtech/Pfizer) vaccine, 34% received mRNA-1273 (Moderna), and 5% received JNJ-78436735 (Johnson & Johnson). After the initial vaccinations (2 doses for BNT162b2 and mRNA-1273, 1 dose for JNJ-7843673), 124 of the 145 (85%) patients had a detectable SARS-CoV-2 spike protein (S) antibody, and 21 (15%) did not respond. Ninety-nine (68%) had high-level responses (≥100 binding antibody units [BAU]/mL)m and 25 (17%) had a low-level response (<100 BAU/mL). In multivariable analysis, lymphocyte count less than 1 × 10⁹/ mL, having chronic GVHD, and being vaccinated in the first year after transplantation emerged as independent predictors for poor response. Neither donor source nor prior exposure to rituximab was predictive of antibody response. SARS-CoV-2 vaccination induced generally high response rates in recipients of allogeneic transplants including recipients of umbilical cord blood transplants and after in-vivo T cell depletion. Responses are less robust in those vaccinated in the first year after transplantation, those with low lymphocyte counts, and those with chronic GVHD.

The wider perspective: cord blood banks and their future prospects

Over the past three decades, cord blood transplantation (CBT) has established its role as an alternative allograft stem cell source. But the future of stored CB units should be to extend their use in updated transplant approaches and develop new CB applications. Thus, CBT will require a coordinated, multicentric, review of transplantation methods and an upgrade and realignment of banking resources and operations. Significant improvements have already been proposed to support the clinical perspective including definition of the cellular threshold for engraftment, development of transplantation methods for adult patients, engraftment acceleration with single cell expansion and homing technologies, personalised protocols to improve efficacy, use of adoptive cell therapy to mitigate delayed immune reconstitution, and further enhancement of the graft-versus-leukaemia effect using advanced therapies. The role of CB banks in improving transplantation results are also critical by optimizing the collection, processing, storage and characterization of CB units, and improving reproducibility, efficiency and cost of banking. But future developments beyond transplantation are needed. This implies the extension from transplantation banks to banks that support cell therapy, regenerative medicine and specialized transfusion medicine. This new "CB banking 2.0" concept will require promotion of international scientific and technical collaborations between bank specialists, clinical investigators and transplant physicians.

Hematopoietic Stem Cell Transplantation in T Cell and Natural Killer Cell Lymphomas: Update on Recent Advances

Mature T and natural killer (NK) cell non-Hodgkin lymphoma (T-NHL) has a poor prognosis. Data from existing retrospective and prospective studies have suggested that high-dose chemotherapy followed by autologous hematopoietic cell transplantation (auto-HCT) may improve the survival in patients with chemosensitive disease, either in the upfront or salvage setting. Auto-HCT is currently recommended to be used as frontline consolidation in peripheral T cell lymphoma not otherwise specified, angioimmunoblastic T cell lymphoma, anaplastic large cell lymphoma-anaplastic lymphoma kinase negative, NK/T cell (disseminated), and enteropathy-associated T cell lymphoma. However, about one-third of patients never reach transplantation because of early relapse or refractory disease. Allogeneic hematopoietic cell transplantation (allo-HCT), via its immunologic graft-versus-lymphoma effect, has been used to salvage patients with relapsed or refractory disease, resulting in long-term disease-free survival in a fraction of patients. However, the higher risk of transplant-related mortality due to regimen-related toxicities, graft-versus-host disease, and post-transplant infectious complications continues to limit the mainstream adoption of allo-HCT for this disease. Despite that, allo-HCT has been incorporated as part of the frontline treatment for aggressive subtypes of T-NHL, such as γδ T cell lymphoma and aggressive NK cell leukemia. Recent attempts to incorporate novel targeted T cell directed therapies into the treatment pathway of T-NHL may enhance treatment response and enable more patients to reach transplant, offering an alternative means of treating this disease.

Physioxia enhances T-cell development ex vivo from human hematopoietic stem and progenitor cells

Understanding physiologic T-cell development from hematopoietic stem (HSCs) and progenitor cells (HPCs) is essential for development of improved hematopoietic cell transplantation (HCT) and emerging T-cell therapies. Factors in the thymic niche, including Notch 1 receptor ligand, guide HSCs and HPCs through T-cell development in vitro. We report that physiologically relevant oxygen concentration (5% O₂ , physioxia), an important environmental thymic factor, promotes differentiation of cord blood CD34+ cells into progenitor T (proT) cells in serum-free and feeder-free culture system. This effect is enhanced by a potent reducing and antioxidant agent, ascorbic acid. Human CD34+ cell-derived proT cells in suspension cultures maturate into CD3+ T cells in an artificial thymic organoid (ATO) culture system more efficiently when maintained under physioxia, compared to ambient air. Low oxygen tension acts as a positive regulator of HSC commitment and HPC differentiation toward proT cells in the feeder-free culture system and for further maturation into T cells in the ATO. Culturing HSCs/HPCs in physioxia is an enhanced method of effective progenitor T and mature T-cell production ex vivo and may be of future use for HCT and T-cell immunotherapies.

Umbilical cord blood: The promise and the uncertainty

Unfortunately, many patients referred for hematopoietic cell transplant will not have a fully matched related donor, and finding matched unrelated donors through the registry may be difficult, especially if the recipient is not of Northern European descent [N Engl J Med 2014;371:339‐348]. Umbilical cord blood (UCB) has been an available graft source for hematopoietic cell transplant for more than 30 years, since the first UCB transplant was performed in the late 1980s [N Engl J Med 1989;321:1174‐1178]. UCB is readily available, has low immunogenicity, and does not require as strict of human leukocyte antigen (HLA) matching compared to other graft sources [N Engl J Med 2004;351:2265‐2275]. According to data from the Center for International Blood and Marrow Transplant Research (CIBMTR), an estimated 500 patients in the US will have received a UCB transplant in 2018. Since 2014, haploidentical transplants have surpassed UCB transplants performed in the United States (CIBMTR Summary Slides, 2018, available at https://www.cibmtr.org). Increased use of haploidentical transplants has brought to light concerns about UCB transplants, including delayed engraftment and graft failure, increased nonrelapse mortality, increased infection risk, and UCB acquisition costs [Lancet Oncol 2010;11:653‐660; Biol Blood Marrow Transplant 2019;1456‐1464]. These concerns will need to be addressed for UCB to remain a viable option as a graft source for hematopoietic cell transplant. Other promising therapeutic benefits for UCB, in addition to hematopoietic cell transplant, is its use in regenerative medicine and immune modulation, which is currently being evaluated in ongoing clinical trials.

Cord blood transplants supported by unrelated donor CD34+ progenitor cells

Alternative donor transplantation with the haplo-cord platform allows the use of a lower-dose single umbilical cord blood unit (CBU) by co-infusion of third-party CD34⁺-selected cells from a haploidentical relative, which provides early transient engraftment while awaiting durable CBU engraftment. In our experience, ~15% of patients lack a suitable haploidentical donor. Here we report 26 patients who underwent haplo-cord transplant using CD34⁺-selected partially matched unrelated donor grafts. Twenty-four were conditioned with fludarabine/melphalan +/- low-dose TBI (n = 16). Twenty-five received ATG and all received posttransplant tacrolimus and mycophenolate mofetil. Median time to neutrophil and platelet recovery was 11 and 18 days. CBU engraftment, with CD33 and CD3 >5% cord chimerism in the myeloid/lymphoid compartment by day +60, occurred in 20 of 24 patients (83%). Incidence of grade 2-4 acute graft-versus-host disease (GVHD) was 27% at day +100, and chronic GVHD was 4% at 1 year. Overall survival at 1 year was 54%. For patients in need of an alternative transplant who lack a haploidentical donor, haplo-cord transplantation using CD34⁺-selected partially matched unrelated donor grafts results in rapid engraftment with no increased rate of cord graft failure or GVHD.

Combination of HLA-Matched Sibling Allogeneic Hematopoietic Stem Cell Transplantation With Unrelated Cord Blood Unit in Patients Aged 35 to 50 Years With Severe Aplastic Anemia: Preliminary Summary of a Single-Arm Trial

This study reports a single-arm trial in the interim phase in 4 patients with median age of 40.5 years who have undergone combined HLA-matched sibling donor (MSD) stem cell graft and an unrelated cord blood (UCB) unit for the treatment of severe aplastic anemia (SAA). The median time was 10 days for neutrophil engraftment (9-18 days) and 17 days for platelets (12-24 days). Median follow-up of 22 months (ranging from 16 to 29 months) showed survival of the 4 patients with complete hematological response. Acute graft-vs-host disease (GVHD) (grade II) occurred only in 1 patient, yet chronic GVHD was free. One patient showed a pattern of transient MSD graft followed by dominant UCB chimerism, and another 1 achieved mixed chimerism in the first 6 months after allogeneic hematopoietic stem cell transplantation (allo-HSCT) then evolved to a stable MSD graft. The other 2 patients sustained a full MSD graft during the post-HSCT period. Nevertheless, none of the patients developed primary and secondary graft failure up to the final follow-up. Although this is a small cohort, the dual transplantation combining HLA-matched sibling allogeneic hematopoietic stem cell transplantation with unrelated cord blood unit may deserve further exploration for treatment of SAA patients aged 35 to 50 years old.

Haploidentical vs haplo-cord transplant in adults under 60 years receiving fludarabine and melphalan conditioning

Haplo-identical transplant with posttransplant cyclophosphamide (haplo) and umbilical cord blood transplant supported by third-party CD34 cells (haplo-cord) are competing approaches to alternative donor transplant. We compared, in adults younger than age 60 years, the outcomes of 170 haplo at 1 institution with that of 137 haplo-cord at 2 other institutions. All received reduced intensity conditioning with fludarabine and melphalan ± total body irradiation. GVHD prophylaxis for haplo consisted of cyclophosphamide, tacrolimus, and mycophenolate, whereas haplo-cord received antithymocyte globulin, tacrolimus, and mycophenolate. Haplo transplant used mostly bone marrow, and peripheral blood stem cells were used in haplo-cord transplants. Haplo-cord were older and had more advanced disease. Haplo-cord hastened median time to neutrophil (11 vs 18 days, P = .001) and platelet recovery (22 vs 25 days, P = .03). At 4 years, overall survival (OS) was 50% for haplo-cord vs 49% for haplo. Progression-free survival (PFS) was 40% for haplo-cord vs 45% for haplo. In multivariate analysis, the disease risk index was significant for OS (hazard ratio, 1.8; 95% confidence interval, 1.48-2.17; P = .00) and PFS. Total body irradiation was associated with decreased recurrence and improved PFS, age >40 with increased nonrelapse mortality. The type of transplant had no effect on OS, PFS, relapse, or nonrelapse mortality. Cumulative incidence of grade 2-4 acute graft-versus-host disease (GVHD) by day 100 was 16% after haplo-cord vs 33% after haplo (P < .0001), but grade 3-4 GVHD was similar. Chronic GVHD at 1 year was 4% after haplo-cord vs 16% after haplo (P < .0001). Haplo or haplo-cord results in similar and encouraging outcomes. Haplo-cord is associated with more rapid neutrophil and platelet recovery and lower acute and chronic GVHD. Institutional review board authorization for this retrospective study was obtained at each institution. Some patients participated in trials registered at www.clinicaltrials.gov as #NCT01810588 and NCT01050946.

Influence of Donor Type (Sibling versus Matched Unrelated Donor versus Haploidentical Donor) on Outcomes after Clofarabine-Based Reduced-Intensity Conditioning Allograft for Myeloid Malignancies

Clofarabine-based reduced-intensity conditioning (RIC) regimens are well-established schedules for allograft in patients with myeloid malignancies. A retrospective study was conducted including all adults allografted in our department with such a regimen and disease with the aim to assess whether or not the donor type (matched sibling [MSD], matched unrelated [MUD], or haploidentical [haplo]) impacted outcomes. Between October 2009 and February 2018, 118 patients met the inclusion criteria. Thirty-six, 55, and 27 patients received a graft from an MSD, MUD, or haplo donor, respectively. Peripheral blood stem cells (PBSCs) were the source of graft for all patients. The median age of the entire cohort was 62 years (range, 20 to 73), and the median follow-up was 31 months (range, 4.5 to 106). All patients engrafted except 1 haplo recipient. Neutrophils (>.5 × 10⁹/L) and platelets (50 × 10⁹/L) recoveries were significantly delayed in the haplo group (P = .0003 and P < .0001) compared with MSD and MUD. Acute grades II to IV or III to IV graft-versus-host disease (GVHD) incidences were similar between the 3 groups as well as the incidence of moderate or severe chronic GVHD. Also, similar 2-year overall survival (OS; 64.7% versus 73.9% versus 60.2%, P = .39), disease-free survival (DFS; 57.7% versus 70.9% versus and 53.6%, P = .1), and GVHD relapse-free survival (37.9% versus 54.3% versus 38.9%, P = .23) were observed between MSD versus MUD versus haplo groups. The same was true when considering only acute myeloid leukemia (AML) cases. In multivariate analysis the type of donor remained independent of outcomes in this series, whereas myelodysplastic syndrome (versus AML), high disease risk index, and older donor (≥50 years) were associated with lower OS and DFS. These data suggest that haplo donors are an acceptable alternative for patients receiving a clofarabine-based RIC PBSC allograft for myeloid malignancies who lack an MSD or a MUD.

Bortezomib and Immune Globulin Have Limited Effects on Donor-Specific HLA Antibodies in Haploidentical Cord Blood Stem Cell Transplantation: Detrimental Effect of Persistent Haploidentical Donor-Specific HLA Antibodies

Donor-specific HLA antibodies (DSAs) have been associated with an increased risk of graft failure. To decrease DSA levels and reduce the risk of graft failure in haploidentical cord blood transplantation recipients, we studied the effect of bortezomib (BTZ) and i.v. immune globulin (IVIG) pretransplantation. Between 2012 and 2016, 14 patients with a DSA level >2000 mean fluorescence intensity (MFI) to 1 or more mismatched HLA alleles of haploidentical donors, cord blood donors, or both were treated with BTZ and IVIG. Fourteen patients received a median of 4 doses (range, 2 to 8 doses) of BTZ 1.3 mg/m² and a median total IVIG of 2 g/kg before transplantation. Only 2 of 14 patients attained a reduction in MFI to <2000 with this combination. After additional IVIG (n = 8), rituximab (n = 4), and/or plasmapheresis (n = 11), 12 of 14 patients were desensitized to a DSA level <2000 MFI at the time of engraftment. All obtained initial hematopoietic reconstitution, and no DSA rebound phenomenon was observed. Responders with DSA MFI <2000 to the haploidentical donor by transplantation engrafted at a rate comparable to that of historical controls, whereas engraftment in nonresponders took 3 times as long. BTZ and IVIG alone do not appear sufficient to rapidly induce DSA desensitization, and persistent DSAs to a haploidentical donor lead to delayed count recovery. Our data suggest that additional pretreatment with BTZ and IVIG in combination with the conditioning regimen may help abrogate the rebound phenomenon observed with plasmapheresis.

Allogeneic transplantation for relapsed and refractory Hodgkin lymphoma: long-term outcomes and graft-versus-host disease-free/relapse-free survival

This monocentric retrospective study included 70 consecutive relapsed/refractory Hodgkin lymphoma (RR-HL) patients receiving reduced-intensity allogeneic stem cell transplantation (alloSCT). We evaluated overall and progression-free survival (OS, PFS), graft-versus host disease/relapse-free survival (GFRS), and chronic GVHD-free OS (cGVHD-free OS) defined as OS without moderate-to-severe cGVHD. Patients had a median age of 33 years (range, 18-60 years), 23% had refractory disease (SD/PD). Donors were HLA identical (39%), unrelated (30%), or haploidentical (31%). Median follow-up was 6.2 years. Five-year OS was 59% and PFS was 49%. NRM was 16% at 1 year. 44% of patients had cGVHD, and 14% moderate-to-severe cGVHD at last follow-up. GFRS and cGVHD-free OS were 26 and 48% at 5 years. In multivariate analysis, resistant disease at alloSCT impacted survival and GFRS. In conclusion, disease response before alloSCT impacts survival and GFRS. GVHD outcomes may help comparing the long-term effects of the new salvage treatments that bridge patients to alloSCT.

CRISPR/Cas9-Based Cellular Engineering for Targeted Gene Overexpression

Gene and cellular therapies hold tremendous promise as agents for treating genetic disorders. However, the effective delivery of genes, particularly large ones, and expression at therapeutic levels can be challenging in cells of clinical relevance. To address this engineering hurdle, we sought to employ the clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 system to insert powerful regulatory elements upstream of an endogenous gene. We achieved robust activation of the COL7A1 gene in primary human umbilical cord blood CD34⁺ hematopoietic stem cells and peripheral blood T-cells. CD34⁺ cells retained their colony forming potential and, in a second engineering step, we disrupted the T-cell receptor complex in T-cells. These cellular populations are of high translational impact due to their engraftment potential, broad circulatory properties, and favorable immune profile that supports delivery to multiple recipients. This study demonstrates the feasibility of targeted knock in of a ubiquitous chromatin opening element, promoter, and marker gene that doubles as a suicide gene for precision gene activation. This system merges the specificity of gene editing with the high level, sustained gene expression achieved with gene therapy vectors. We predict that this design concept will be highly transferrable to most genes in multiple model systems representing a facile cellular engineering platform for promoting gene expression.

Reduced-Intensity Allogeneic Transplant for Acute Myeloid Leukemia and Myelodysplastic Syndrome Using Combined CD34-Selected Haploidentical Graft and a Single Umbilical Cord Unit Compared with Matched Unrelated Donor Stem Cells in Older Adults

Haplo/cord transplantation combines an umbilical cord blood (UCB) graft with CD34-selected haploidentical cells and results in rapid hematopoietic recovery followed by durable UCB engraftment. We compared outcomes of transplants in older patients with acute myeloid leukemia (AML) or high-risk myelodysplastic syndromes (MDS) who received either HLA-matched unrelated donor (MUD) cells or haplo/cord grafts. Between 2007 and 2013, 109 adults ages 50 and older underwent similar reduced-intensity conditioning with fludarabine and melphalan and antibody-mediated T cell depletion for AML (n = 83) or high-risk MDS (n = 26) followed by either a MUD (n = 68) or haplo/cord (n = 41) graft. Patient characteristics were similar for each graft source except for more minority patients receiving a haplo/cord transplant (P = .01). One half of the AML patients were not in remission. Two-year progression-free survival (PFS), overall survival (OS), and graft-versus-host disease-free relapse-free survival were 38%, 48%, and 32.1% for MUD and 33%, 48%, and 33.8% for haplo/cord transplants (P = .62 for PFS; P = .97 for OS; P= .84), respectively. Acute grades II to IV and chronic graft-versus-host-disease rates did not differ at 19.5% and 4.9% in haplo/cord compared with 25% and 7.4% after MUD (P = .53 and P = .62, respectively). Multivariate analysis confirmed no significant differences in transplant outcomes by donor type. Haplo/cord reduced-intensity transplantation achieves similar outcomes relative to MUD in older AML and MDS patients, making this a promising option for those without matched donors.

Combined Haploidentical and Umbilical Cord Blood Allogeneic Stem Cell Transplantation for High-Risk Lymphoma and Chronic Lymphoblastic Leukemia

Limited studies have reported on outcomes for lymphoid malignancy patients receiving alternative donor allogeneic stem cell transplants. We have previously described combining CD34-selected haploidentical grafts with umbilical cord blood (haplo-cord) to accelerate neutrophil and platelet engraftment. Here, we examine the outcome of patients with lymphoid malignancies undergoing haplo-cord transplantation at the University of Chicago and Weill Cornell Medical College. We analyzed 42 lymphoma and chronic lymphoblastic leukemia (CLL) patients who underwent haplo-cord allogeneic stem cell transplantation. Patients underwent transplant for Hodgkin lymphoma (n = 9, 21%), CLL (n = 5, 12%) and non-Hodgkin lymphomas (n = 28, 67%), including 13 T cell lymphomas. Twenty-four patients (52%) had 3 or more lines of therapies. Six (14%) and 1 (2%) patients had prior autologous and allogeneic stem cell transplant, respectively. At the time of transplant 12 patients (29%) were in complete remission, 18 had chemotherapy-sensitive disease, and 12 patients had chemotherapy-resistant disease. Seven (17%), 11 (26%), and 24 (57%) patients had low, intermediate, and high disease risk index before transplant. Comorbidity index was evenly distributed among 3 groups, with 13 (31%), 14 (33%), and 15 (36%) patients scoring 0, 1 to 2, and ≥3. Median age for the cohort was 49 years (range, 23 to 71). All patients received fludarabine/melphalan/antithymocyte globulin conditioning regimen and post-transplant graft-versus-host disease (GVHD) prophylaxis with tacrolimus and mycophenolate mofetil. The median time to neutrophil engraftment was 11 days (range, 9 to 60) and to platelet engraftment 19.5 days (range, 11 to 88). Cumulative incidence of nonrelapse mortality was 11.6% at 100 days and 19 % at one year. Cumulative incidence of relapse was 9.3% at 100 days and 19% at one year. With a median follow-up of survivors of 42 months, the 3-year rates of GVHD relapse free survival, progression-free survival, and overall survival were 53%, 62%, and 65%, respectively, for these patients. Only 8% of the survivors had chronic GVHD. In conclusion, haplo-cord transplantation offers a transplant alternative for patients with recurrent or refractory lymphoid malignancies who lack matching donors. Both neutrophil and platelet count recovery is rapid, nonrelapse mortality is limited, excellent disease control can be achieved, and the incidence of chronic GVHD is limited. Thus, haplo-cord achieves high rates of engraftment and encouraging results.

Clinical Studies in Hematologic Microtransplantation

The anti-tumor effects of allogeneic hematopoietic stem cell transplantation depend upon engraftment of donor cells followed by a graft-versus-tumor (GVT) effect. However, pre-clinical and clinical studies have established that under certain circumstances, anti-tumor responses can occur despite the absence of high levels of durable donor cell engraftment. Tumor response with little or no donor engraftment has been termed "microtransplantation." It has been hard to define conditions leading to tumor responses without donor cell persistence in humans because the degree of engraftment depends very heavily upon many patient-specific factors, including immune status and degree of prior therapy. Likewise, it is unknown to what degree donor chimerism in the blood or tissue is required for an anti-tumor effect under conditions of microtransplantation. In this review, we summarize some key studies supporting the concept of microtransplantation and emphasize the importance of recent large studies of microtransplantation in patients with acute myelogenous leukemia (AML). These AML studies provide the first evidence of the efficacy of microtransplantation as a therapeutic strategy and lay the foundation for additional pre-clinical studies and clinical trials that will refine the understanding of the mechanisms involved and guide its further development as a treatment modality.

Single umbilical cord blood with or without CD34+ cells from a third-party donor in adults with leukemia

We retrospectively compared the clinical outcomes of adults with acute leukemia who received single-unit umbilical cord blood (UCB) transplantation (sUCBT) (n = 135) or stem cell transplant using coinfusion of a UCB graft with CD34⁺ cells from a third-party donor (Haplo-Cord) (n = 72) at different institutions within the Grupo Español de Trasplante Hematopoyético. In multivariable analysis, patients in the Haplo-Cord group showed more rapid neutrophil (hazard ratio [HR], 2.3; 95% confidence interval [CI], 1.5-3.3; P < .001) and platelet recovery (HR, 1.6; 95% CI, 1.2-2.3; P = .015) and lower incidence of chronic graft-versus-host disease (GVHD) (relative risk, 0.5; 95% CI, 0.3-0.8; P = .01). Nonrelapse mortality, relapse, disease-free survival (DFS), and GVHD/relapse-free survival were similar in the 2 groups. Regarding disease-specific outcomes, DFS in both acute myeloid leukemia (AML) and acute lymphoblastic leukemia patients was not significantly different; however, a significantly higher relapse rate was found in patients with AML treated with Haplo-Cord (HR, 2.3; 95% CI, 1-5.4; P = .04). Our study confirms that Haplo-Cord was an effective strategy to accelerate neutrophil and platelet recovery and shows that, in the context of specific treatment platforms, sUCBT and Haplo-Cord offer similar long-term outcomes.

Novel strategies for improving hematopoietic reconstruction after allogeneic hematopoietic stem cell transplantation or intensive chemotherapy

INTRODUCTION

High-dose conditioning regimens for allogeneic hematopoietic cell transplantation (allo-HCT) as well as intensive poly-chemotherapy for acute myeloid leukemia (AML) induce prolonged periods of neutropenia. The duration of the neutropenia is particularly long following umbilical cord blood transplantation (UCBT). Areas covered: After briefly reviewing the impact of hematopoietic growth factors administration to hasten hematologic reconstitution after allo-HCT or intensive AML chemotherapy, this article summarizes recent approaches that have been investigated to prompt hematologic reconstruction after UCBT or intensive AML chemotherapy. Expert opinion: In the allo-HCT setting, administration of G-CSF or GM-CSF shortened the duration of the neutropenia but failed to decrease infection-related mortality or to improve survival. Novel approaches to hasten hematological reconstruction after UCBT such as double UCBT with expansion of one of the 2 UCB units with Notch ligand, mesenchymal stromal cells, nicotinamide, or StemRegenin 1, co-transplanting a single UCB unit with HLA-haploidentical CD34+ cells, or increasing UCB HSC homing to marrow niches via direct intra bone UCB administration, pulse treatment with dmPGE2 or enforced fucosylation are promising and deserve further investigations in prospective phase III studies. In the AML setting, G-CSF or GM-CSF administration after intensive chemotherapy decreased the duration of the neutropenia without improving survival.

Strategies before, during, and after hematopoietic cell transplantation to improve T-cell immune reconstitution

T-cell immune reconstitution (IR) after allogeneic hematopoietic cell transplantation (allo-HCT) is highly variable between patients and may take several months to even years. Patients with delayed or unbalanced T-cell IR have a higher probability of developing transplantation-related morbidity, mortality, and relapse of disease. Hence, there is a need for strategies to better predict and improve IR to reduce these limitations of allo-HCT. In this review, we provide an update of current and in-near-future clinically relevant strategies before, during, and after transplantation to achieve successful T-cell IR. Potent strategies are choosing the right HCT source (eg, donor-recipient matching, cell dose, graft manipulation), individualized conditioning and serotherapy (eg, antithymocyte globulin), nutritional status, exercise, home care, modulation of microbiota, enhancing homeostatic peripheral expansion, promoting thymopoiesis, and the use of adjuvant-targeted cellular immunotherapies. Strategies to prevent graft-versus-host disease are important as well because this complication and the subsequent need for immunosuppression affects T-cell IR and function. These options aim for personalized precision transplantation, where allo-HCT therapy is designed to boost a well-balanced T-cell IR and limit complications in individual patients, resulting in overall lower morbidity and higher survival chances.

Haploidentical cord transplantation-The best of both worlds

Haploidentical (haplo)-cord transplantation combines infusion of an umbilical cord blood (UCB) unit with CD34-selected cells usually from human leukocyte antigen (HLA) mismatched donors. Initial rapid count recovery from the haplo-hematopoietic progenitors, is gradually replaced by durable engraftment from UCB progenitors. UCB grafts used for haplo-cord are smaller, but better matched than those required for single or double UCB stem cell transplant (SCT). More than 200 patients with hematological malignancies have been transplanted. Median age was 54 years (range 17-74) and 77 were over age 60. One-year survival was 64% for patients with intermediate- and low-risk disease, with no deaths beyond 2 years. In high-risk disease, 1-year survival was 44%. In a comparison with patients undergoing double UCB SCT, haplo-cord transplant resulted in faster hematopoietic recovery, lower rates of acute and chronic graft-versus-host disease (GVHD), lower rates of disease recurrence, and improved GVHD- and relapse-free survival (GRFS). Excellent results were also reported for patients with aplastic anemia where 18 of 21 patients had sustained cord blood engraftment. Rates of GVHD and of disease recurrence after haplo-cord are encouraging. However, in the approximately 10% of patients with failure of the UCB graft disease recurrence is high, supporting the important role of UCB-mediated graft-versus-leukemia (GVL). Ongoing efforts are aimed at identifying determinants of UCB engraftment, at reducing rates of disease recurrence in high risk patients and at optimizing dose and schedule of ATG -necessary to avoid early haplo-graft rejection, but also contributing to early post-transplant immunocompromise. For those lacking haploidentical donors, unrelated donors have been successfully utilized.

Cord blood chimerism and relapse after haplo-cord transplantation

Haplo-cord stem cell transplantation combines the infusion of CD34 selected hematopoietic progenitors from a haplo-identical donor with an umbilical cord blood (UCB) graft from an unrelated donor and allows faster count recovery, with low rates of disease recurrence and chronic graft-versus-host disease (GVHD). But the contribution of the umbilical cord blood graft to long-term transplant outcome remains unclear. We analyzed 39 recipients of haplo-cord transplants with acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS), engrafted and in remission at 2 months. Median age was 66 (18-72) and all had intermediate, high, or very-high risk disease. Less than 20% UCB chimerism in the CD33 lineage was associated with an increased rate of disease recurrence (54% versus 11% p < 0.0001) and decrease in one year progression-free (20% versus 55%, p = 0.004) and overall survival (30% versus 62%, p = 0.02). Less than 100% UCB chimerism in the CD3 lineage was associated with increase rate of disease recurrence (46% versus 12%, p = 0.007). Persistent haplo-chimerism in the CD3 lineage was associated with an increased rate of disease recurrence (40% versus 15%, p = 0.009) Chimerism did not predict for treatment related mortality. The cumulative incidence of acute GVHD by day 100 was 43%. The cumulative incidence of moderate/severe chronic GVHD was only 5%. Engraftment of the umbilical cord blood grafts provides powerful graft-versus-leukemia (GVL) effects which protect against disease recurrence and is associated with low risk of chronic GVHD. Engraftment of CD34 selected haplo-identical cells can lead to rapid development of circulating T-cells, but when these cells dominate, GVL-effects are limited and rates of disease recurrence are high.

Enhancing the efficacy of engraftment of cord blood for hematopoietic cell transplantation

Clinical cord blood (CB) hematopoietic cell transplantation (HCT) has progressed well since the initial successful CB HCT that saved the life of a young boy with Fanconi anemia. The recipient is alive and well now 28 years out since that first transplant with CB cells from his HLA-matched sister. CB HCT has now been used to treat over 35,000 patients with various malignant and non-malignant disorders mainly using HLA-matched or partially HLA-disparate allogeneic CB cells. There are advantages and disadvantages to using CB for HCT compared to other sources of transplantable hematopoietic stem (HSC) and progenitor (HPC) cells. One disadvantage of the use of CB as a source of transplantable HSC and HPC is the limited number of these cells in a single CB collected, and slower time to neutrophil, platelet and immune cell recovery. This review describes current attempts to: increase the collection of HSC/HPC from CB, enhance the homing of the infused cells, ex-vivo expand numbers of collected HSC/HPC and increase production of the infused CB cells that reach the marrow. The ultimate goal is to manipulate efficiency and efficacy for safe and economical use of single unit CB HCT.