scholarly journals Complex Clonal Evolution Can Occur Following Transplantation for Transfusion Dependent Thalassaemia in the Context of Mixed Myeloid Chimerism and Reduced Conditioning Regimens

Blood ◽  
2021 ◽  
Vol 138 (Supplement 1) ◽  
pp. 2906-2906
Author(s):  
Adam Gassas ◽  
Farah O'Boyle ◽  
Shahzya Chaudhury ◽  
Toni Petterson ◽  
Kirstin Lund ◽  
...  
Keyword(s):  
Bone Marrow ◽  
T Cells ◽  
Whole Blood ◽  
Clonal Evolution ◽  
Mixed Chimerism ◽  
Progressive Reduction ◽  
Post Transplantation ◽  
Gvhd Prophylaxis ◽  
Conditioning Intensity

Abstract Haemopoietic stem cell transplantation (HSCT) is a well-established treatment modality for the cure of transfusion dependent thalassaemia (TDT) and sickle cell disease (SCD). Clonal evolution has recently been identified as a concerning event in the setting of mixed chimerism and/or ineffective haemopoiesis following conventional bone marrow transplantation and gene therapy for haemoglobinopathies. This has so far been restricted to SCD only, with the presumption that despite both conditions sharing an ineffective erythropoietic marrow compartment, there may be inflammatory and hypoxic differences enabling clonal evolution, in addition to the different exposure to hydroxycarbamide as a therapeutic agent. However, there is a need to investigate whether this may also be an occurrence in TDT. From 2011 to 2021, over a ten-year period, sixty-five consecutive paediatric patients received a sibling HSCT (n=55) or a haploidentical HSCT (n=10) for TDT in our institution. Conditioning intensity was minimised at the start of this cohort in order to limit toxicity and late effects, abandoning the use of Bu/Cy, which resulted in approximately 50% of the patients having stable mixed chimerism long-term. Sibling HSCT was conditioned with fludarabine 160 mg/m 2, treosulfan 42 g/m 2, thiotepa 10 mg/kg and ATG (Thymoglobulin) or alemtuzumab, and received GvHD prophylaxis with ciclosporin and MMF. Haploidentical HSCT was conditioned with fludarabine 150 mg/m 2, cyclophosphamide 30 mg/kg, TBI 2 or 4 Gy, and ATG 4.5 mg/kg (thiotepa 10 mg/kg added if TBI 2 Gy only) with GvHD prophylaxis provided by two doses of post-transplantation cyclophosphamide 50 mg/kg, sirolimus and MMF. All patients had pre-transplantation endogenous haemopoiesis was suppressed pre-transplantation with hypertransfusions for a minimum of 8 weeks, and/or the use of hydroxycarbamide and azathioprine. GvHD prophylaxis was provided with ciclosporin and MMF. All patients were Pesaro class I or II at the time of transplantation. The median age was 5 years (2 - 19). The median survival was 26.8 months (2.6-101.8). The OS was 93.8% and DFS was 89.2%. Three patients in this cohort developed clonal evolution in the context of myeloid mixed chimerism identified due to the development of cytopenias and transfusion dependence. All patients had a complex karyotype and it involved deletion of chromosome 7: Patient 1 had a sibling BMT at 3 years and 2 months. Day +28 chimerism was >95% in whole blood and 95% in T cells. The myeloid fraction had a progressive reduction from day +60 onwards. At 15 months post-transplantation clonal evolution was identified [18% ring sideroblasts, 46;XY, del (7) (q22 q34) [5]/46;XY [5], chimerism 13% donor in whole marrow and 41% marrow T cells. Two months later he became red cell transfusion dependence. A second BMT with busulfan based conditioning resulted in long-term cure. Patient 2 had a sibling BMT at 3 years and 8 months of age. Day +28 chimerism was 99% donor in whole blood and 99% donor in T cells. Day +161 post-transplantation he started requiring erythropoietin support to maintain him transfusion independent and on day +217 we first identified in the bone marrow the appearance of myeloid mixed chimerism (75% donor in whole marrow and 91% marrow T cells) and complex clonal evolution involving -7 and FISH identified deletion of one copy of KMT2E (7q22) and MET (7q31) detected [16/200]. The patient is under monitoring at present with a progressive reduction of the size of the abnormal clones. Patient 3 had a haplo BMT at 5 years and 8 months. Day +28 chimerism was 97% donor in whole blood and 99% donor in T cells. She developed mixed myeloid chimerism following cessation of immunosuppression on day +206: 86% donor whole blood and 99% donor in T cells. At 22 months post-BMT she started to require transfusion and a complex clonal evolution involving deletion 7 in her bone marrow when the chimerism was 42% donor whole blood and 81% donor marrow T cells. FISH identified deletion of one copy of KMT2E(7q22) and MET(7q31) detected[22/100]. She is being prepared for a second bone marrow transplant. In conclusion, complex clonal evolution also occurs post HSCT in TDT, at least in the context of reduction of conditioning intensity and development of mixed myeloid chimerism. This finding warrants further investigation and may have significant implications for the design of both conventional HSCT and gene therapy strategies. Disclosures No relevant conflicts of interest to declare.

Conditioning Intensity and T Cell Dose Determine Efficacy of CD19-Targeted T Cell-Mediated Tumor Eradication in an Immunocompetent Mouse Model of B-ALL.

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 2613-2613
Author(s):  
Marco L Davila ◽  
Christopher Kloss ◽  
Renier J Brentjens ◽  
Michel Sadelain
Keyword(s):  
Bone Marrow ◽  
T Cells ◽  
T Cell ◽  
B Cells ◽  
Mouse Model ◽  
B Cell ◽  
Immunocompetent Mouse ◽  
Cell Dose ◽  
Conditioning Intensity

Abstract Abstract 2613 Recent work by our group and others demonstrates the therapeutic potential of CD19-targeted T cells to treat patients with indolent B cell malignancies. These studies make use of T cells that are genetically engineered with chimeric antigen receptors (CARs) comprising an scFv fused to various T cell activating elements. Whereas firs-generation CARs only direct T cell activation, second-generation CARs include two signal elements, such as CD3z and CD28 signaling domains (19–28z). We and our colleagues at MSKCC are currently evaluating the safety of 19–28z-transduced T cells in patients with acute leukemia (B-ALL) in a Phase I protocol (NCT01044069). Pre-clinical studies performed to date have mostly relied on xenogeneic models utilizing immunodeficient animals, which enable the evaluation of human engineered T cells but do not recapitulate all the interactions that may affect tumor eradication by CAR-modified T cells. We have therefore developed a pre-clinical immunocompetent mouse model of B-ALL, and addressed therein the impact of conditioning and T cell dose on the eradication of leukemia by syngeneic, CAR-targeted T cells. To establish an immunocompetent mouse model of B cell leukemia, we generated a clone from the lymph node of an Eμ-myc B6 transgenic mouse. The immunophenotype and gene-expression profile of clone Eμ-ALL01 is consistent with a progenitor B cell origin. Syngeneic B6 mice inoculated with this clone develop florid acute leukemia and die approximately 2–4 weeks after injection from progressive bone marrow infiltration. We created an anti-mouse CD19 CAR comprising all murine elements, including the CD8 signal peptide, a CD19-specific single chain variable fragment, the CD8 transmembrane region, and the CD28 and CD3z signaling domains. Transduction of the murine 19–28z CAR into mouse T cells was robust and successfully retargeted the T cells to B cells. In vitro assays demonstrated that m19–28 z transduced T cells mediated effective killing of CD19-expressing target cells and the production of effector cytokines such as IFNγ and TNFα. Cyclophosphamide either alone or in combination with control syngeneic T cells is insufficient to eradicate established Eμ-ALL01 in B6 mice. However, treatment with cyclophosphamide and m19–28z-transduced T cells cured nearly all mice. Mice sacrificed six months after treatment exhibited a dramatic reduction of B cells in the bone marrow (BM), blood, and spleen. The few remaining B lineage cells found in the BM had a phenotype consistent with early pro-B cells, suggesting that endogenous reconstitution of the B cell compartment was thwarted by persisting, functional m19–28z+ T cells. Thus, T cells are retained at the site of antigen expression, which is maintained through regeneration of progenitor B cells. The persisting CD19-targeted T cells in the BM exhibited a cell surface phenotype consistent with effector and central memory cells. Using B cell aplasia as a surrogate endpoint for assessing in vivo T cell function and persistence, we evaluated how conditioning chemotherapy and T cell dose determine the level of B cell depletion induced by adoptively transferred CD19-targeted T cells. Overall, increasing the cyclophosphamide or T cell dose, increased the degree and duration of B cell depletion and the number of persisting CAR-modified T cells. Significantly, increasing the T cell dose at a set cyclophosphamide level had a lesser impact than increasing the conditioning intensity for a given T cell dose. In summary, the new Eμ-ALL01 syngeneic, immunocompetent B-ALL model we describe here is a valuable tool for modeling CD19 CAR therapies. Our results indicate that m19–28z transduced T cells are effective at eradicating B-ALL tumor cells and persist long-term, preferentially in bone marrow. Our findings further establish that conditioning intensity and T cell dose directly determine B cell elimination and long-term T cell persistence. These studies in mice will serve as an important framework to further model and perfect our studies in patients with B-ALL. Disclosures: No relevant conflicts of interest to declare.

scholarly journals A Review of Cyclophosphamide-Induced Transplantation Tolerance in Mice and Its Relationship With the HLA-Haploidentical Bone Marrow Transplantation/Post-Transplantation Cyclophosphamide Platform

2021 ◽  
Vol 12 ◽  
Author(s):  
Hisanori Mayumi
Keyword(s):  
Bone Marrow ◽  
T Cells ◽  
Bone Marrow Transplantation ◽  
Marrow Transplantation ◽  
Bone Marrow Cells ◽  
Mixed Chimerism ◽  
Post Transplantation ◽  
Clonal Deletion ◽  
Marrow Graft ◽  
Induced Tolerance

The bone marrow transplantation (BMT) between haplo-identical combinations (haploBMT) could cause unacceptable bone marrow graft rejection and graft-versus-host disease (GVHD). To cross such barriers, Johns Hopkins platform consisting of haploBMT followed by post-transplantation (PT) cyclophosphamide (Cy) has been used. Although the central mechanism of the Johns Hopkins regimen is Cy-induced tolerance with bone marrow cells (BMC) followed by Cy on days 3 and 4, the mechanisms of Cy-induced tolerance may not be well understood. Here, I review our studies in pursuing skin-tolerance from minor histocompatibility (H) antigen disparity to xenogeneic antigen disparity through fully allogeneic antigen disparity. To overcome fully allogeneic antigen barriers or xenogeneic barriers for skin grafting, pretreatment of the recipients with monoclonal antibodies (mAb) against T cells before cell injection was required. In the cells-followed-by-Cy system providing successful skin tolerance, five mechanisms were identified using the correlation between super-antigens and T-cell receptor (TCR) Vβ segments mainly in the H-2-identical murine combinations. Those consist of: 1) clonal destruction of antigen-stimulated-thus-proliferating mature T cells with Cy; 2) peripheral clonal deletion associated with immediate peripheral chimerism; 3) intrathymic clonal deletion associated with intrathymic chimerism; 4) delayed generation of suppressor T (Ts) cells; and 5) delayed generation of clonal anergy. These five mechanisms are insufficient to induce tolerance when the donor-recipient combinations are disparate in MHC antigens plus minor H antigens as is seen in haploBMT. Clonal destruction is incomplete when the antigenic disparity is too strong to establish intrathymic mixed chimerism. Although this incomplete clonal destruction leaves the less-proliferative, antigen-stimulated T cells behind, these cells may confer graft-versus-leukemia (GVL) effects after haploBMT/PTCy.

scholarly journals Effects of T cell depletion in radiation bone marrow chimeras. II. Requirement for allogeneic T cells in the reconstituting bone marrow inoculum for subsequent resistance to breaking of tolerance.

1988 ◽  
Vol 168 (2) ◽  
pp. 661-673 ◽  
Author(s):  
M Sykes ◽  
M A Sheard ◽  
D H Sachs
Keyword(s):  
Bone Marrow ◽  
T Cells ◽  
T Cell ◽  
Graft Failure ◽  
Recipient Strain ◽  
Cell Depletion ◽  
Mixed Chimerism ◽  
T Cell Depletion ◽  
Mixed Chimeras

The ability of normal recipient-type lymphocytes to break tolerance in long-term allogenic radiation chimeras has been investigated. Reconstitution of lethally irradiated mice with a mixture of syngeneic and allogeneic T cell-depleted (TCD) bone marrow (BM) has previously been shown to lead to mixed chimerism and permanent, specific tolerance to donor and host alloantigen (3-5). If allogeneic T cells are not depleted from the reconstituting inoculum, complete allogeneic chimerism results; however, no clinical evidence for GVHD is observed, presumably due to the protective effect provided by syngeneic TCD BM. This model has now been used to study the effects of allogenic T cells administered in reconstituting BM inocula on stability of long-term tolerance. We have attempted to break tolerance in long-term chimeras originally reconstituted with TCD or non-TCD BM by challenging them with inocula containing normal, nontolerant recipient strain lymphocytes. tolerance was broken with remarkable ease in recipients of mixed marrow inocula in which both original BM components were TCD. In contrast, tolerance in chimeras originally reconstituted with non-TCD allogeneic BM was not affected by such inocula. Susceptibility to loss of chimerism and tolerance was not related to initial levels of chimerism per se, but rather to T cell depletion of allogeneic BM, since chimeras reconstituted with TCD allogeneic BM alone (mean level of allogeneic chimerism 98%) were as susceptible as mixed chimeras to the tolerance-breaking effects of such inocula. The possible contribution of GVH reactivity to this resistance was investigated using an F1 into parent strain combination. In these animals, the use of non-TCD F1 BM inocula for reconstitution did not lead to resistance to the tolerance-breaking effects of recipient strain splenocytes. These results suggest that the ability of T cells in allogeneic BM inocula to confer resistance to late graft failure may be related to their graft-vs.-host reactivity, even in situations in which they do not cause clinical GVHD. These findings may have relevance to the mechanism whereby T cell depletion of allogeneic BM leads to an increased incidence of late graft failure in clinical BM transplantation situations.

Haploidentical BMT with a Post-Infusion of Stem Cells Cyclophosphamide Approach Is Feasible and Leads to a High Rate of Donor Engraftment in Haemoglobinopathies Allowing Universal Application of Transplantation

Blood ◽  
2015 ◽  
Vol 126 (23) ◽  
pp. 4317-4317 ◽  
Author(s):  
Josu de la Fuente ◽  
Farah O'Boyle ◽  
Yvonne Harrington ◽  
Anne Bradshaw ◽  
Sandra Hing ◽  
...  
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
T Cells ◽  
Whole Blood ◽  
Graft Failure ◽  
Cell Disease ◽  
Post Transplantation ◽  
Donor Pool ◽  
Haploidentical Transplantation ◽  
Post Infusion

Abstract Introduction: BMT is the only proven curative treatment available for haemoglobinopathies. However, the number of patients who can benefit is seriously restricted by the lack of HLA-matched related donors not suffering from the condition and the limited number of unrelated donors available for the ethnic groups in which these conditions are prevalent. In order to expand the donor pool, haploidentical transplantation with a post-infusion of stem cells cyclophosphamide approach has been developed for young adults, but whilst well tolerated it has resulted in relatively high rates of rejection and the need for a prolonged period of immunosuppression1. Materials (or patients) and methods: 16 consecutive related haploidentical transplants (13 for sickle cell disease and 3 for β halassaemia major) were performed at St. Mary's Hospital, London, from June 2013 to May 2015. The donor was a parent in 15 cases and a sibling in one case. The median age was 10 years of age (range 3 to 18). All patients lacked a suitable HLA-matched related donor and an unrelated search had not identified a 10/10 or 9/10 donor. Endogenous haemopoieis was suppressed with hypertransfusions, hydroxycarbamide 30 mg/kg and azathioprine 3 mg/kg for at least two months pre-transplantation. The conditioning included fludarabine 150 mg/m2, thiotepa 10 mg/kg was added, cyclophosphamide 29 mg/kg, TBI 2 Gy and ATG (Thymoglobulin) 4.5 mg/kg. GvHD prophylaxis was provided with cyclophosphamide 50 mg/kg on days +3 and +4, MMF and sirolimus. The median survival was 8.19 months post-transplantation (1.28-22.96) and half of the patients are >150 days post-transplantation and have completed all treatment. The source of stem cells was G-CSF primed bone marrow in all cases, aiming ≥8 x 108 TNC/kg [median 9.97 x 108 TNC/kg (2.35-20.5), 3.88 x 106 CD34+/kg (1.12-9.21)]. Results: All patients engrafted, though one patient subsequently suffered secondary graft failure following macrophage activation syndrome and died. The median neutrophil engraftment was 17 days (range 16 to 29). The median platelet engraftment >50 x109/L was 32 days (range 20 to 64). All 15 surviving patients are cured from the manifestations of the original disease. One patient suffered VOD following autologous rescue with limited conditioning for secondary graft failure. Infectious complications occurred at a higher rate than seen for related transplants for the same conditions at our institution. Acute GvHD ≥ grade II occurred in two patients (12.5%, skin and gut GvHD respectively) responding to treatment with MSC and one patient was treated for chronic GvHD (6.3%). The median time to cessation of immunosuppression was 124 days (108-189). All patients but one achieved ≥90% donor fraction both in whole blood and T cells at day +180, with only such patient requiring continuation of immunosuppression (day +28: 93.3% patients ≥95% donor and 6.7% patients ≥90-94% in whole blood, and 73.3% patients ≥95% donor, 13.3% patients ≥90-94%, 6.7% donor ≥50-89% and 6.7% donor <50% in T cells, n=15; day +180: 70% patients ≥95% donor, 20% patients ≥90-94% and 10% patients ≥50-89% in whole blood, and 80% patients ≥95% donor, 10% patients ≥90-94% and 10% donor <50% in T cells, n=10). Conclusion: Related haploidentical transplantation providing sufficient myelosuppression to avoid rejection is feasible, leading to outcomes which approach the results for related transplantation and allowing all patients with haemoglobinopathies requiring a transplant to benefit fromm such treatment. References: 1. Bolaños-Meade J, Fuchs EJ, Luznik L, Lanzkron SM, Gamper CJ, Jones RJ, Brodsky RA. HLA-haploidentical bone marrow transplantation with posttransplant cyclophosphamide expands the donor pool for patients with sickle cell disease. Blood. 2012 Nov 22;120(22):4285-91. Disclosures No relevant conflicts of interest to declare.

Long-Lasting Anti-Tumor Immunity Induced by the Rejection of Donor Hematopoietic Cells in Mixed Bone Marrow Chimeras.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 1319-1319
Author(s):  
Toshiki I. Saito ◽  
Megan Sykes
Keyword(s):  
Bone Marrow ◽  
T Cells ◽  
Tumor Immunity ◽  
Tumor Response ◽  
Lethal Dose ◽  
Mixed Chimerism ◽  
Spleen Cells ◽  
Tumor Challenge ◽  
Tumor Cytotoxicity

Abstract BACKGROUND Surprisingly, some patients who reject donor marrow grafts following nonmyeloablative HCT sustain remissions of advanced hematological malignancies (Br J Haematol2005, 128:351). In murine mixed chimeras prepared with nonmyeloablative conditioning, we previously showed that recipient leukocyte infusions (RLI) induced loss of donor chimerism and anti-tumor responses against host-type tumors (Blood2003, 102:2300) and that T cells in the RLI are necessary to achieve maximum anti-tumor effects (J Immunol2005, 175:665). We now examined whether or not this anti-tumor response demonstrates long-term memory. We attempted to enhance anti-tumor effects by adding exogenous IL-15, which promotes CD8 memory T cell survival. METHODS Mixed chimerism was achieved in BALB/c (H-2d) mice conditioned with depleting anti-CD4 and CD8 mAbs on Day -5, cyclophosphamide 200 mg/kg on Day -1 and 7 Gy thymic irradiation on Day 0 prior to transplantation of 25x106 B10.BR (H-2k) or B10.RIII (H-2r) bone marrow cells. Some groups received RLI (3x107 BALB/c spleen cells) seven weeks post-BMT. A20 cells (5x105) were given i.v. one week after RLI. Some groups received a secondary A20 challenge (105) 100 days after the first challenge. Some groups received 5 μg of IL-15 intraperitoneally, starting one week after RLI injection and every 12 h thereafter for a total of 10 doses. Spleen cells were isolated and anti-tumor cytotoxicity was evaluated after 5 days’ coculture with irradiated A20 cells. RESULTS We rechallenged RLI-treated long-term tumor survivors with a second lethal dose of A20 tumor cells 100 days after the first tumor challenge. One third of long-term survivors (n=20) rejected the lethal dose of A20 (median survival time [MST] 72 days). In contrast, all mice in the control group that did not previously receive RLI and received their first tumor challenge concurrently with the rechallenge group died, with MST 56 days (n=23) (p=0.02). Thus, 1/3 of long-term tumor survivors retained sufficiently strong anti-tumor immunity to reject secondary tumor. We have previously demonstrated in vitro tumor-specific cytotoxic responses 11 weeks after first tumor challenge. We now examined anti-tumor cytotoxicity at a later time point and observed such responses even 11 months after first tumor challenge in some of the tumor survivors. From these results, we speculated that memory CTL may play an important role in the anti-tumor effect of RLI. We hypothesized that exogenous IL-15 administration might enhance the anti-tumor effect of RLI, since it promotes generation and maintenance of memory T cells. Indeed, we observed increased tumor-free survival in mice that received RLI and IL-15 (n=14) compared to recipients of RLI alone (n=14) (MST 64 versus 48 days respectively, p=0.03). CONCLUSION Together, these data suggest that RLI therapy can evoke long-term anti-tumor immunity and that the anti-tumor response may be enhanced by administration of exogenous IL-15, reinforcing the potential of RLI therapy to provide a new HCT strategy lacking the risk of graft-versus-host disease.

scholarly journals Immunological and genetic kinetics from diagnosis to clinical progression in chronic lymphocytic leukemia

2021 ◽  
Vol 9 (1) ◽  
Author(s):  
Isabel Jiménez ◽  
Bárbara Tazón-Vega ◽  
Pau Abrisqueta ◽  
Juan C. Nieto ◽  
Sabela Bobillo ◽  
...  
Keyword(s):  
T Cells ◽  
Chronic Lymphocytic Leukemia ◽  
Ex Vivo ◽  
Clonal Evolution ◽  
Lymphocytic Leukemia ◽  
Clinical Progression ◽  
Molecular Changes ◽  
Main Driver ◽  
Altered Gene

Abstract Background Mechanisms driving the progression of chronic lymphocytic leukemia (CLL) from its early stages are not fully understood. The acquisition of molecular changes at the time of progression has been observed in a small fraction of patients, suggesting that CLL progression is not mainly driven by dynamic clonal evolution. In order to shed light on mechanisms that lead to CLL progression, we investigated longitudinal changes in both the genetic and immunological scenarios. Methods We performed genetic and immunological longitudinal analysis using paired primary samples from untreated CLL patients that underwent clinical progression (sampling at diagnosis and progression) and from patients with stable disease (sampling at diagnosis and at long-term asymptomatic follow-up). Results Molecular analysis showed limited and non-recurrent molecular changes at progression, indicating that clonal evolution is not the main driver of clinical progression. Our analysis of the immune kinetics found an increasingly dysfunctional CD8+ T cell compartment in progressing patients that was not observed in those patients that remained asymptomatic. Specifically, terminally exhausted effector CD8+ T cells (T-betdim/−EomeshiPD1hi) accumulated, while the the co-expression of inhibitory receptors (PD1, CD244 and CD160) increased, along with an altered gene expression profile in T cells only in those patients that progressed. In addition, malignant cells from patients at clinical progression showed enhanced capacity to induce exhaustion-related markers in CD8+ T cells ex vivo mainly through a mechanism dependent on soluble factors including IL-10. Conclusions Altogether, we demonstrate that the interaction with the immune microenvironment plays a key role in clinical progression in CLL, thereby providing a rationale for the use of early immunotherapeutic intervention.

scholarly journals Nontransplant therapy for bone marrow failure

Hematology ◽  
2016 ◽  
Vol 2016 (1) ◽  
pp. 83-89 ◽  
Author(s):  
Danielle M. Townsley ◽  
Thomas Winkler
Keyword(s):  
Bone Marrow ◽  
Aplastic Anemia ◽  
Bone Marrow Failure ◽  
Clonal Evolution ◽  
Single Agent ◽  
Telomere Attrition ◽  
Long Term Follow Up ◽  
Treatment Naïve

Abstract Nontransplant therapeutic options for acquired and constitutional aplastic anemia have significantly expanded during the last 5 years. In the future, transplant may be required less frequently. That trilineage hematologic responses could be achieved with the single agent eltrombopag in refractory aplastic anemia promotes new interest in growth factors after years of failed trials using other growth factor agents. Preliminary results adding eltrombopag to immunosuppressive therapy are promising, but long-term follow-up data evaluating clonal evolution rates are required before promoting its standard use in treatment-naive disease. Danazol, which is traditionally less preferred for treating cytopenias, is capable of preventing telomere attrition associated with hematologic responses in constitutional bone marrow failure resulting from telomere disease.

scholarly journals Myelosuppressive conditioning is required to achieve engraftment of pluripotent stem cells contained in moderate doses of syngeneic bone marrow

Blood ◽  
1994 ◽  
Vol 83 (4) ◽  
pp. 939-948 ◽  
Author(s):  
Y Tomita ◽  
DH Sachs ◽  
M Sykes
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Bone Marrow Cells ◽  
Whole Body ◽  
Mixed Chimerism ◽  
Hematopoietic Stem ◽  
Donor Cells ◽  
Donor Type ◽  
Low Levels

Abstract We have investigated the requirement for whole body irradiation (WBI) to achieve engraftment of syngeneic pluripotent hematopoietic stem cells (HSCs). Recipient B6 (H-2b; Ly-5.2) mice received various doses of WBI (0 to 3.0 Gy) and were reconstituted with 1.5 x 10(7) T-cell-depleted (TCD) bone marrow cells (BMCs) from congenic Ly-5.1 donors. Using anti-Ly-5.1 and anti-Ly-5.2 monoclonal antibodies and flow cytometry, the origins of lymphoid and myeloid cells reconstituting the animals were observed over time. Chimerism was at least initially detectable in all groups. However, between 1.5 and 3 Gy WBI was the minimum irradiation dose required to permit induction of long-term (at least 30 weeks), multilineage mixed chimerism in 100% of recipient mice. In these mice, stable reconstitution with approximately 70% to 90% donor-type lymphocytes, granulocytes, and monocytes was observed, suggesting that pluripotent HSC engraftment was achieved. About 50% of animals conditioned with 1.5 Gy WBI showed evidence for donor pluripotent HSC engraftment. Although low levels of chimerism were detected in untreated and 0.5-Gy-irradiated recipients in the early post-BM transplantation (BMT) period, donor cells disappeared completely by 12 to 20 weeks post-BMT. BM colony assays and adoptive transfers into secondary lethally irradiated recipients confirmed the absence of donor progenitors and HSCs, respectively, in the marrow of animals originally conditioned with only 0.5 Gy WBI. These results suggest that syngeneic pluripotent HSCs cannot readily engraft unless host HSCs sustain a significant level of injury, as is induced by 1.5 to 3.0 Gy WBI. We also attempted to determine the duration of the permissive period for syngeneic marrow engraftment in animals conditioned with 3 Gy WBI. Stable multilineage chimerism was uniformly established in 3-Gy-irradiated Ly-5.2 mice only when Ly-5.1 BMC were injected within 7 days of irradiation, suggesting that repair of damaged host stem cells or loss of factors stimulating engraftment may prevent syngeneic marrow engraftment after day 7.

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