Immune composition and its association with hematologic recovery after chemotherapeutic injury in acute myeloid leukemia.

Chemotherapy-induced bone marrow (BM) injury is a significant cause of morbidity and mortality in acute myeloid leukemia (AML). Time to hematologic recovery after standard ("7 + 3") myeloablative chemotherapy can vary considerably among patients, but the factors that drive or predict BM recovery remain incompletely understood. Here, we assessed the composition of innate and adaptive immune subsets in the regenerating BM (day 17) after induction chemotherapy and related it to hematologic recovery in AML. T cells, and in particular the CD4 central memory (CD4CM) T-cell subset, were significantly enriched in the BM after chemotherapy, suggesting the relative chemoresistance of cells providing long-term memory for systemic pathogens. In contrast, B cells and other hematopoietic subsets were depleted. Higher frequencies of the CD4CM T-cell subset were associated with delayed hematopoietic recovery, whereas a high frequency of natural killer (NK) cells was related to faster recovery of neutrophil counts. The NK/CD4CM ratio in the BM after chemotherapy was significantly associated with the time to subsequent neutrophil recovery (Spearman's ρ = -0.723, p < 0.001, false discovery rate <0.01). The data provide novel insights into adaptive immune cell recovery after injury and identify the NK/CD4CM index as a putative predictor of hematopoietic recovery in AML.

Extracellular Vesicles Derived From Adult and Fetal Bone Marrow Mesenchymal Stromal Cells Differentially Promote ex vivo Expansion of Hematopoietic Stem and Progenitor Cells.

Recently, we and others have illustrated that extracellular vesicles (EVs) have the potential to support hematopoietic stem and progenitor cell (HSPC) expansion; however, the mechanism and processes responsible for the intercellular communication by EVs are still unknown. In the current study, we investigate whether primary human bone marrow derived mesenchymal stromal cells (BMSC) EVs isolated from two different origins, fetal (fEV) and adult (aEV) tissue, can increase the relative low number of HSPCs found in umbilical cord blood (UCB) and which EV-derived components are responsible for ex vivo HSPC expansion. Interestingly, aEVs and to a lesser extent fEVs, showed supportive ex vivo expansion capacity of UCB-HSPCs. Taking advantage of the two BMSC sources with different supportive effects, we analyzed the EV cargo and investigated how gene expression is modulated in HSPCs after incubation with aEVs and fEVs. Proteomics analyses of the protein cargo composition of the supportive aEV vs. the less-supportive fEV identified 90% of the Top100 exosome proteins present in the ExoCarta database. Gene Ontology (GO) analyses illustrated that the proteins overrepresented in aEVs were annotated to oxidation-reduction process, mitochondrial ATP synthesis coupled proton transport, or protein folding. In contrast, the proteins overrepresented in fEVs were annotated to extracellular matrix organization positive regulation of cell migration or transforming growth factor beta receptor (TGFBR) signaling pathway. Small RNA sequencing identified different molecular signatures between aEVs and fEVs. Interestingly, the microRNA cluster miR-99b/let-7e/miR-125a, previously identified to increase the number of HSPCs by targeting multiple pro-apoptotic genes, was highly and significantly enriched in aEVs. Although we identified significant differences in the supportive effects of aEVs and fEVs, RNAseq analyses of the 24 h treated HSPCs indicated that a limited set of genes was differentially regulated when compared to cells that were treated with cytokines only. Together, our study provides novel insights into the complex biological role of EVs and illustrates that aEVs and fEVs differentially support ex vivo expansion capacity of UCB-HSPCs. Together opening new means for the application of EVs in the discovery of therapeutics for more efficient ex vivo HSPC expansion.

Panobinostat and decitabine prior to donor lymphocyte infusion in allogeneic stem cell transplantation.

Outcome after allogeneic hematopoietic stem cell transplantation (allo-HSCT) is adversely affected by relapse to a considerable degree. To exploit the graft-versus-leukemia effect more effectively, we assessed the feasibility of early initiation of epigenetic therapy with panobinostat and decitabine after allo-HSCT and before donor lymphocyte infusion (DLI) in poor-risk patients with acute myeloid leukemia (AML) or refractory anemia with excess blasts with International Prognostic Scoring System score ≥1.5. A total of 140 poor-risk patients with AML aged 18 to 70 years were registered, and 110 proceeded to allo-HSCT. Three dose levels were evaluated for dose-limiting toxicities, including panobinostat monotherapy 20 mg at days 1, 4, 8, and 11 of a 4-week cycle (PNB mono group) and panobinostat combined with either decitabine 20 mg/m2 (PNB/DAC20 group) or decitabine 10 mg/m2 (PNB/DAC10 group) at days 1 to 3 of every 4-week cycle. After phase 1, the study continued as phase 2, focusing on completion of protocol treatment and treatment outcome. PNB mono and PNB/DAC10 were feasible, whereas PNB/DAC20 was not related to prolonged cytopenia. Sixty of 110 patients who underwent transplantation were eligible to receive their first DLI within 115 days after allo-HSCT. Grade 3 and 4 adverse events related to panobinostat and decitabine were observed in 23 (26%) of the 87 patients, and they received epigenetic therapy. Cumulative incidence of relapse was 35% (standard error [SE] 5), and overall survival and progression-free survival at 24 months were 50% (SE 5) and 49% (SE 5). Post-allo-HSCT epigenetic therapy with panobinostat alone or in combination with low-dose decitabine is feasible and is associated with a relatively low relapse rate. The trial was registered at the European Clinical Trial Registry, https://www.clinicaltrialsregister.eu, as ECT2012-003344-74.

Identification of osteolineage cell-derived extracellular vesicle cargo implicated in hematopoietic support.

Osteolineage cell-derived extracellular vesicles (EVs) play a regulatory role in hematopoiesis and have been shown to promote the ex vivo expansion of human hematopoietic stem and progenitor cells (HSPCs). Here, we demonstrate that EVs from different human osteolineage sources do not have the same HSPC expansion promoting potential. Comparison of stimulatory and non-stimulatory osteolineage EVs by next-generation sequencing and mass spectrometry analyses revealed distinct microRNA and protein signatures identifying EV-derived candidate regulators of ex vivo HSPC expansion. Accordingly, the treatment of umbilical cord blood-derived CD34+ HSPCs with stimulatory EVs-altered HSPC transcriptome, including genes with known roles in cell proliferation. An integrative bioinformatics approach, which connects the HSPC gene expression data with the candidate cargo in stimulatory EVs, delineated the potentially targeted biological functions and pathways during hematopoietic cell expansion and development. In conclusion, our study gives novel insights into the complex biological role of EVs in osteolineage cell-HSPC crosstalk and promotes the utility of EVs and their cargo as therapeutic agents in regenerative medicine.

Peripheral Stem Cell Apheresis is Feasible Post 131Iodine-Metaiodobenzylguanidine-Therapy in High-Risk Neuroblastoma, but Results in Delayed Platelet Reconstitution.

PURPOSE: Targeted radiotherapy with 131iodine-meta-iodobenzylguanidine (131I-MIBG) is effective for neuroblastoma (NBL), although optimal scheduling during high-risk (HR) treatment is being investigated. We aimed to evaluate the feasibility of stem cell apheresis and study hematologic reconstitution after autologous stem cell transplantation (ASCT) in patients with HR-NBL treated with upfront 131I-MIBG-therapy. EXPERIMENTAL DESIGN: In two prospective multicenter cohort studies, newly diagnosed patients with HR-NBL were treated with two courses of 131I-MIBG-therapy, followed by an HR-induction protocol. Hematopoietic stem and progenitor cell (e.g., CD34+ cell) harvest yield, required number of apheresis sessions, and time to neutrophil (>0.5 × 109/L) and platelet (>20 × 109/L) reconstitution after ASCT were analyzed and compared with "chemotherapy-only"-treated patients. Moreover, harvested CD34+ cells were functionally (viability and clonogenic capacity) and phenotypically (CD33, CD41, and CD62L) tested before cryopreservation (n = 44) and/or after thawing (n = 19). RESULTS: Thirty-eight patients (47%) were treated with 131I-MIBG-therapy, 43 (53%) only with chemotherapy. Median cumulative 131I-MIBG dose/kg was 0.81 GBq (22.1 mCi). Median CD34+ cell harvest yield and apheresis days were comparable in both groups. Post ASCT, neutrophil recovery was similar (11 days vs. 10 days), whereas platelet recovery was delayed in 131I-MIBG- compared with chemotherapy-only-treated patients (29 days vs. 15 days, P = 0.037). Testing of harvested CD34+ cells revealed a reduced post-thaw viability in the 131I-MIBG-group. Moreover, the viable CD34+ population contained fewer cells expressing CD62L (L-selectin), a marker associated with rapid platelet recovery. CONCLUSIONS: Harvesting of CD34+ cells is feasible after 131I-MIBG. Platelet recovery after ASCT was delayed in 131I-MIBG-treated patients, possibly due to reinfusion of less viable and CD62L-expressing CD34+ cells, but without clinical complications. We provide evidence that peripheral stem cell apheresis is feasible after upfront 131I-MIBG-therapy in newly diagnosed patients with NBL. However, as the harvest of 131I-MIBG-treated patients contained lower viable CD34+ cell counts after thawing and platelet recovery after reinfusion was delayed, administration of 131I-MIBG after apheresis is preferred.

The feasibility and efficacy of subcutaneous plerixafor for mobilization of peripheral blood stem cells in allogeneic HLA-identical sibling donors: results of the HOVON-107 study.

BACKGROUND: Plerixafor (PFX) mobilizes CD34+ cells into circulation by disrupting the CXCR4 binding of the hematopoietic stem cell in its bone marrow niche. STUDY DESIGN AND METHODS: in the prospective HOVON-107 study (www.hovon.nl) 23 allogeneic HLA-identical sibling donors received one or two subcutaneous (sc) injections of plerixafor 0.320 mg/kg.The primary endpoint, was defined as feasibility to mobilize a minimum of 2.0 x106 CD34+ cells/kg recipient weight obtained by leukopheresis in at least 90% of the donors. RESULTS: median 3.3 x 106 CD34+ cells/kg (1.9-6.5) were collected after 1 (n=12) or 2 (n=10) sc injections of PFX. Side effects occurred in 15/23 (65%) donors: most were grade 1-2; in 5 donors grade 3 and all resolved. All grafts were directly transplanted. Compared to 10 grafts obtained with G-CSF the number of CD34+ cells was 2.4 fold lower but the percentage of phenotypically most immature CD34+ subset was higher (31% vs 15%). The total number of CD3+ cells in the graft seemed higher after PFX-mobilization, but CD4/CD 8 ratios, and frequencies of Th2, Th17 and regulatory T-cells or NK cells were comparable. All patients engrafted and no increase in incidence or severity of acute or chronic graft versus host disease was observed. CONCLUSION: stem cell mobilization with sc PFX 0.320 mg/kg in allogeneic sibling donors is feasible with limited toxicity for donors. 14 allogeneic donors were mobilized with PFX 0.320 mg intravenously according to the same protocol. Due to the limited numbers, these results are in the supplementary section.

Impaired thymopoiesis predicts for a high risk of severe infections after reduced intensity conditioning without anti-thymocyte globulin in double umbilical cord blood transplantation.

Umbilical cord blood stem cell transplantation (UCBT) is associated with retarded hematopoietic recovery and immune reconstitution and a high infection-related morbidity and mortality, especially after conditioning including anti-thymocyte globulin (ATG). However, data on immune recovery, incidence of infections, and outcome in double UCBT (dUCBT) recipients receiving an ATG-free reduced intensity conditioning (RIC) are lacking. In this study, recovery of lymphocyte subsets, thymopoiesis, and its association with severe infections and clinical outcome was assessed in a group of 55 recipients of a dUCBT ATG-free RIC regimen. T cell recovery was severely protracted in the majority of patients. However, T cell receptor excision circle TREC+ T cells were detectable in 62% of patients at 3 months post-transplantation. A total of 128 common toxicity criteria grade 3-4 infections were observed in the first year post-transplantation. Non-relapse mortality at 12 months post-transplant was 16%, of which 78% infectious mortality. One-year overall survival was 73%. Patients who failed to recover thymopoiesis at 3 months post-transplantation were at a 3.3-fold higher risk of subsequent severe grade 3-4 infections.

Autologous Dendritic Cells Pulsed with Allogeneic Tumor Cell Lysate in Mesothelioma: From Mouse to Human.

Purpose: Mesothelioma has been regarded as a nonimmunogenic tumor, which is also shown by the low response rates to treatments targeting the PD-1/PD-L1 axis. Previously, we demonstrated that autologous tumor lysate-pulsed dendritic cell (DC) immunotherapy increased T-cell response toward malignant mesothelioma. However, the use of autologous tumor material hampers implementation in large clinical trials, which might be overcome by using allogeneic tumor cell lines as tumor antigen source. The purpose of this study was to investigate whether allogeneic lysate-pulsed DC immunotherapy is effective in mice and safe in humans.Experimental Design: First, in two murine mesothelioma models, mice were treated with autologous DCs pulsed with either autologous or allogeneic tumor lysate or injected with PBS (negative control). Survival and tumor-directed T-cell responses of these mice were monitored. Results were taken forward in a first-in-human clinical trial, in which 9 patients were treated with 10, 25, or 50 million DCs per vaccination. DC vaccination consisted of autologous monocyte-derived DCs pulsed with tumor lysate from five mesothelioma cell lines.Results: In mice, allogeneic lysate-pulsed DC immunotherapy induced tumor-specific T cells and led to an increased survival, to a similar extent as DC immunotherapy with autologous tumor lysate. In the first-in-human clinical trial, no dose-limiting toxicities were established and radiographic responses were observed. Median PFS was 8.8 months [95% confidence interval (CI), 4.1-20.3] and median OS not reached (median follow-up = 22.8 months).Conclusions: DC immunotherapy with allogeneic tumor lysate is effective in mice and safe and feasible in humans. Clin Cancer Res; 24(4); 766-76. ©2017 AACR.

Multicenter study to evaluate a new enumeration method for hematopoietic stem cell collection management.

BACKGROUND: CD34 flow cytometry is the gold standard for stem cell enumeration in peripheral blood at the mobilization stage and in the final apheresis product. The new stem cell mode of the Sysmex XN Series analyzer enumerates an immature cell population in the white progenitor and pathological cell (WPC) channel, based on the cell size, internal cellular complexity, and fluorescence intensity. STUDY DESIGN AND METHODS: In this multicenter study we analyzed 147 peripheral blood samples, 22 samples during collection of stem cells, and 45 samples from the apheresis product of 18 healthy allogeneic donors and 84 autologous patients. RESULTS: In this multicenter study we demonstrate that the XN stem cell enumeration method correlates well with viable CD34+ cells determined by flow cytometry during the stem cell mobilization phase to determine apheresis start time, during apheresis for real-time monitoring and adjustment, and for quality control of the final stem cell harvest. CONCLUSION: Our data show that there is an improvement in the correlation of XN stem cells and CD34+ cells in the peripheral blood during stem cell mobilization as well as in stem cell harvests compared to SE or XE Series analyzers. The XN stem cell enumeration method has a number of advantages compared to CD34 flow cytometry: it is fast, simple, reproducible, and less expensive. CE marking for the European market has been obtained, making the stem cell count on the XN analyzer a reportable clinical variable.

Lipid-mediated Wnt protein stabilization enables serum-free culture of human organ stem cells.

Wnt signalling proteins are essential for culture of human organ stem cells in organoids, but most Wnt protein formulations are poorly active in serum-free media. Here we show that purified Wnt3a protein is ineffective because it rapidly loses activity in culture media due to its hydrophobic nature, and its solubilization requires a detergent, CHAPS (3-[(3-cholamidopropyl) dimethylammonio]-1-propanesulfonate), that interferes with stem cell self-renewal. By stabilizing the Wnt3a protein using phospholipids and cholesterol as carriers, we address both problems: Wnt activity remains stable in serum-free media, while non-toxic carriers allow the use of high Wnt concentrations. Stabilized Wnt3a supports strongly increased self-renewal of organ and embryonic stem cells and the serum-free establishment of human organoids from healthy and diseased intestine and liver. Moreover, the lipophilicity of Wnt3a protein greatly facilitates its purification. Our findings remove a major obstacle impeding clinical applications of adult stem cells and offer advantages for all cell culture uses of Wnt3a protein.

Osteoblasts secrete miRNA-containing extracellular vesicles that enhance expansion of human umbilical cord blood cells.

Osteolineage cells represent one of the critical bone marrow niche components that support maintenance of hematopoietic stem and progenitor cells (HSPCs). Recent studies demonstrate that extracellular vesicles (EVs) regulate stem cell development via horizontal transfer of bioactive cargo, including microRNAs (miRNAs). Using next-generation sequencing we show that human osteoblast-derived EVs contain highly abundant miRNAs specifically enriched in EVs, including critical regulators of hematopoietic proliferation (e.g., miR-29a). EV treatment of human umbilical cord blood-derived CD34(+) HSPCs alters the expression of candidate miRNA targets, such as HBP1, BCL2 and PTEN. Furthermore, EVs enhance proliferation of CD34(+) cells and their immature subsets in growth factor-driven ex vivo expansion cultures. Importantly, EV-expanded cells retain their differentiation capacity in vitro and successfully engraft in vivo. These discoveries reveal a novel osteoblast-derived EV-mediated mechanism for regulation of HSPC proliferation and warrant consideration of EV-miRNAs for the development of expansion strategies to treat hematological disorders.

CD4+ T-cell alloreactivity toward mismatched HLA class II alleles early after double umbilical cord blood transplantation.

Although double umbilical cord blood transplantation (dUCBT) in adult patients may be associated with less graft failure compared with single UCBT, hematopoietic recovery generally originates from a single cord blood unit (CBU). CBU predominance is still incompletely understood. We recently showed that blood CD4+ T-cell numbers rapidly increase after dUCBT, and early CD4+ T-cell chimerism predicts for graft predominance. Given the frequent HLA class II allele mismatches between CBUs in dUCBT, we hypothesized that alloreactive HLA class II-specific CD4+ T cells from the "winning" CBU may contribute to rejection of the "loser" CBU. We evaluated whether CD4+ T cells originating from the predominant (PD)-CBU would recognize HLA class II allele mismatches, expressed by the nonengrafting (NE)-CBU. Alloreactive effector CD4+ T cells toward 1 or more mismatched HLA class II alleles of the NE-CBU were detected in 11 of 11 patients, with reactivity toward 29 of 33 (88%) tested mismatches, and the strongest reactivity toward DR and DQ alleles early after dUCBT. Mismatched HLA class II allele-specific CD4+ T cells recognized primary leukemic cells when the mismatched HLA class II allele was shared between NE-CBU and patient. Our results suggest that cytotoxicity exerted by CD4+ T cells from the PD-CBU drives the rapid rejection of the NE-CBU, whose alloreactive effect might also contribute to graft-versus-leukemia.

Magnetic Resonance Detection of CD34+ Cells from Umbilical Cord Blood Using a 19F Label.

Impaired homing and delayed recovery upon hematopoietic stem cell transplantation (HSCT) with hematopoietic stem cells (HSC) derived from umbilical cord blood (UCB) is a major problem. Tracking transplanted cells in vivo will be helpful to detect impaired homing at an early stage and allows early interventions to improve engraftment and outcome after transplantation. In this study, we show sufficient intracellular labeling of UCB-derived CD34+ cells, with 19F-containing PLGA nanoparticles which were detectable with both flow cytometry and magnetic resonance spectroscopy (MRS). In addition, labeled CD34+ cells maintain their capacity to proliferate and differentiate, which is pivotal for successful engraftment after transplantation in vivo. These results set the stage for in vivo tracking experiments, through which the homing efficiency of transplanted cells can be studied.

Wnt3a protein reduces growth factor-driven expansion of human hematopoietic stem and progenitor cells in serum-free cultures.

Ex vivo expansion of hematopoietic stem and progenitor cells (HSPC) is a promising approach to improve insufficient engraftment after umbilical cord blood stem cell transplantation (UCB-SCT). Although culturing HSPC with hematopoietic cytokines results in robust proliferation, it is accompanied with extensive differentiation and loss of self-renewal capacity. Wnt signaling has been implicated in regulating HSPC fate decisions in vivo and in promoting HSPC self-renewal by inhibition of differentiation, but the effects of Wnt on the ex vivo expansion of HSPC are controversial. Here, we demonstrate that exogenous Wnt3a protein suppresses rather than promotes the expansion of UCB-derived CD34+ cells in serum free expansion cultures. The reduced expansion was also observed in cultures initiated with Lin-CD34+CD38lowCD45RA-CD90+ cells which are highly enriched in HSC and was also observed in response to activation of beta-catenin signaling by GSK3 inhibition. The presence of Wnt3a protein during the culture reduced the frequency of multilineage CFU-GEMM and the long-term repopulation ability of the expanded HSPC. These data suggest that Wnt signaling reduces expansion of human HSPC in growth factor-driven expansion cultures by promoting differentiation of HSPC.

Rapid induction of single donor chimerism after double umbilical cord blood transplantation preceded by reduced intensity conditioning: results of the HOVON 106 phase II study.

Double umbilical cord blood transplantation is increasingly applied in the treatment of adult patients with high-risk hematological malignancies and has been associated with improved engraftment as compared to that provided by single unit cord blood transplantation. The mechanism of improved engraftment is, however, still incompletely understood as only one unit survives. In this multicenter phase II study we evaluated engraftment, early chimerism, recovery of different cell lineages and transplant outcome in 53 patients who underwent double cord blood transplantation preceded by a reduced intensity conditioning regimen. Primary graft failure occurred in one patient. Engraftment was observed in 92% of patients with a median time to neutrophil recovery of 36 days (range, 15-102). Ultimate single donor chimerism was established in 94% of patients. Unit predominance occurred by day 11 after transplantation and early CD4(+) T-cell chimerism predicted for unit survival. Total nucleated cell viability was also associated with unit survival. With a median follow up of 35 months (range, 10-51), the cumulative incidence of relapse and non-relapse mortality rate at 2 years were 39% and 19%, respectively. Progressionfree survival and overall survival rates at 2 years were 42% (95% confidence interval, 28-56) and 57% (95% confidence interval, 43-70), respectively. Double umbilical cord blood transplantation preceded by a reduced intensity conditioning regimen using cyclophosphamide/fludarabine/4 Gy total body irradiation results in a high engraftment rate with low non-relapse mortality. Moreover, prediction of unit survival by early CD4(+) lymphocyte chimerism might suggest a role for CD4(+) lymphocyte mediated unit-versus-unit alloreactivity. www.trialregister.nl NTR1573.

Double umbilical cord blood transplantation: a study of early engraftment kinetics in leukocyte subsets using HLA-specific monoclonal antibodies.

Single cord blood unit (CBU) predominance is usually established within the first month after double umbilical cord blood transplantation (UCBT). However, the kinetics of engraftment of the different leukocyte subsets and the mechanism of graft predominance is largely unknown. To investigate whether a differential engraftment might reveal a specific subset that could play a key role in the mechanism of graft predominance, we studied early engraftment kinetics of different leukocyte subpopulations by flow cytometry using human monoclonal antigen-specific human leukocyte antigen antibodies, directed against mismatched human leukocyte antigen-A or -B antigens between recipient and CBUs. Twenty-two patients, who had received a double UCBT preceded by a reduced-intensity conditioning regimen, were evaluated at days +11, +18, +25, and +32 posttransplantation. Single CBU predominance in the various leukocyte subsets was established within 18 days posttransplantation. CD4+ T cells of the dominant CBU showed early peripheral blood expansion. Moreover, chimerism in CD4+ and CD8+ T cell and natural killer cell subsets at day +11 was predictive of ultimate graft predominance. These findings show that engraftment kinetics of the various leukocyte subsets vary considerably after double UCBT and may suggest an important role for CD4+ T cells in a presumed alloreactive graft-versus-graft rejection.

Peripheral stem cell harvest using regular chemotherapy schedules in childhood cancer.

Prediction of the best moment for the harvest of PBSCs after standard chemotherapy followed by filgrastim in children with cancer is difficult. We retrospectively analyzed the moment of harvesting of 152 procedures in 94 patients. The start of apheresis was guided by WBC count and CD34+ cell measurement in peripheral blood. We defined the first day of filgrastim administration, after completion of mobilizing chemotherapy, as day 1. Median time to harvest in different subgroups is as follows: neuroblastoma 11 days (range, 6-29 days), Ewing's sarcoma nine days (range, 7-15 days), brain tumor 10 days (range, 7-15 days), relapsed Wilms' tumor 16 days (range, 9-20 days), and extracranial GCT seven days (range, 6-14 days). Patients harvested after cyclophosphamide priming (time to harvest within a range of 8-9 days) were analyzed as a separate group. The optimal moment for harvesting in different types of tumors was highly variable, although most consistent in patients diagnosed with Ewing's sarcoma or brain tumors and after cyclophosphamide priming.

Keratinocyte growth factor and stem cell factor to improve thymopoiesis after autologous CD34+ cell transplantation in rhesus macaques.

Deficient thymopoiesis and retarded recovery of naive CD4(+) T cells are important determinants of insufficient immune-competence following hematopoietic stem cell transplantation (HSCT). Although keratinocyte growth factor (KGF) may protect the thymic epithelium, stem cell factor (SCF) is involved in early thymopoiesis. We evaluated whether KGF alone or combined with SCF would affect thymopoiesis and hematologic recovery following myeloablative autologous HSCT into rhesus macaques. Purpose-bred adult rhesus macaques received 10(6) autologous CD34(+)-selected mononuclear bone marrow cells (BMC)/kg after 9 Gy myeloablative conditioning. Animals were treated with phosphate-buffered saline (PBS) (n = 2), KGF alone (n = 2), or KGF combined with SCF (n = 2). KGF-treated animals showed accelerated hematologic recovery, improved thymopoiesis, and enhanced naive T-cell recovery following transplantation. Improved T cell recovery was not associated with protection against cytomegalovirus reactivation nor with improved antibody response to tetanus toxoid vaccination. Animals treated with KGF and SCF experienced severe adverse events that precluded evaluation of thymopoiesis and T cell recovery. Collectively, our data confirm that KGF may enhance thymopoiesis.