Stem cell engraftment strategies

A systematic review of lifespan studies in rodents using stem cell transplantations

Organismal aging involves the progressive decline in organ function and increased susceptibility to age-associated diseases. Regardless of its origin, cellular aging is consequently reflected at the level of organ and associated systems dysfunction. Aging of stem cell populations within the body and their decreased ability to self-renew, differentiate, and regenerate damaged tissues, is a key contributor to organismal decline. Based on this, supplementing young stem cells may delay tissue aging, improve frailty and extend health and lifespan. This review investigates studies in rodents using stem cell transplantation from either mice or human donors. The aim is to consolidate available information on the efficacy of stem cell therapies in rodent models and provide insights to guide further research efforts. Out of the 21 studies included in this review, the methodology varied significantly including the lifespan measurement. To enable comparison the median lifespan was calculated using WebPlotDigitizer 4.6 if not provided by the literature. A total of 18 out of 21 studies evidenced significant lifespan extension post stem cell transplant, with 7 studies demonstrating benefits in reduced frailty and other aging complications.

Pulmonary Complications in Hematopoietic Stem Cell Transplant Recipients-A Clinician Primer

Hematopoietic stem cell transplants (HSCT) are becoming more widespread as a result of optimization of conditioning regimens and prevention of short-term complications with prophylactic antibiotics and antifungals. However, pulmonary complications post-HSCT remain a leading cause of morbidity and mortality and are a challenge to clinicians in both diagnosis and treatment. This comprehensive review provides a primer for non-pulmonary healthcare providers, synthesizing the current evidence behind common infectious and non-infectious post-transplant pulmonary complications based on time (peri-engraftment, early post-transplantation, and late post-transplantation). Utilizing the combination of timing of presentation, clinical symptoms, histopathology, and radiographic findings should increase rates of early diagnosis, treatment, and prognostication of these severe illness states.

Rescue from lethal acute radiation syndrome (ARS) with severe weight loss by secretome of intramuscularly injected human placental stromal cells

BACKGROUND

Most current cell-based regenerative therapies are based on the indirect induction of the affected tissues repair. Xenogeneic cell-based treatment with expanded human placenta stromal cells, predominantly from fetal origin (PLX-RAD cells), were shown to mitigate significantly acute radiation syndrome (ARS) following high dose irradiation in mice, with expedited regain of weight loss and haematopoietic function. The current mechanistic study explores the indirect effect of the secretome of PLX-RAD cells in the rescue of the irradiated mice.

METHODS

The mitigation of the ARS was investigated following two intramuscularly (IM) injected 2 × 10⁶ PLX-RAD cells, 1 and 5 days following 7.7 Gy irradiation. The mice survival rate and their blood or bone marrow (BM) cell counts were followed up and correlated with multiplex immunoassay of a panel of related human proteins of PLX-RAD derived secretome, as well as endogenous secretion of related mouse proteins. PLX-RAD secretome was also tested in vitro for its effect on the induction of the migration of BM progenitors.

RESULTS

A 7.7 Gy whole body mice irradiation resulted in ~25% survival by 21 days. Treatment with two IM injections of 2 × 10⁶ PLX-RAD cells on days 1 and 5 after irradiation mitigated highly significantly the subsequent lethal ARS, with survival rate increase to nearly 100% and fast regain of the initial weight loss (P < 0,0001). This was associated with a significant faster haematopoiesis recovery from day 9 onwards (P < 0.01). Nine out of the 65 human proteins tested were highly significantly elevated in the mouse circulation, peaking on days 6-9 after irradiation, relative to negligible levels in non-irradiated PLX-RAD injected mice (P < 0.01). The highly elevated proteins included human G-CSF, GRO, MCP-1, IL-6 and lL-8, reaching >500 pg/mL, while MCP-3, ENA, Eotaxin and fractalkine levels ranged between ~60-160pg/mL. The detected radiation-induced PLX-RAD secretome correlated well with the timing of the fast haematopoiesis regeneration. The radiation-induced PLX-RAD secretome seemed to reinforce the delayed high levels secretion of related mouse endogenous cytokines, including GCSF, KC, MCP-1 and IL-6. Additional supportive in vitro studies also confirmed the ability of cultured PLX-RAD secretome to induce accelerated migration of BM progenitors.

CONCLUSIONS

A well-regulated and orchestrated secretion of major pro-regenerative BM supporting secretome in high dose irradiated mice, treated with xenogeneic IM injected PLX-RAD cells, can explain the observed mitigation of ARS. This seemed to coincide with faster haematopoiesis regeneration, regain of severe weight loss and the increased survival rate. The ARS-related stress signals activating the IM injected PLX-RAD cells for the remote secretion of the relevant human proteins deserve further investigation.

Clonal dominance and transplantation dynamics in hematopoietic stem cell compartments

Hematopoietic stem cells in mammals are known to reside mostly in the bone marrow, but also transitively passage in small numbers in the blood. Experimental findings have suggested that they exist in a dynamic equilibrium, continuously migrating between these two compartments. Here we construct an individual-based mathematical model of this process, which is parametrised using existing empirical findings from mice. This approach allows us to quantify the amount of migration between the bone marrow niches and the peripheral blood. We use this model to investigate clonal hematopoiesis, which is a significant risk factor for hematologic cancers. We also analyse the engraftment of donor stem cells into non-conditioned and conditioned hosts, quantifying the impact of different treatment scenarios. The simplicity of the model permits a thorough mathematical analysis, providing deeper insights into the dynamics of both the model and of the real-world system. We predict the time taken for mutant clones to expand within a host, as well as chimerism levels that can be expected following transplantation therapy, and the probability that a preconditioned host is reconstituted by donor cells.

Clonal hematopoiesis—where mature myeloid cells in the blood deriving from a single stem cell are over-represented—is a major risk factor for overt hematologic malignancies. To quantify how likely this phenomena is, we combine existing observations with a novel stochastic model and extensive mathematical analysis. This approach allows us to observe the hidden dynamics of the hematopoietic system. We conclude that for a clone to be detectable within the lifetime of a mouse, it requires a selective advantage. I.e. the clonal expansion cannot be explained by neutral drift alone. Furthermore, we use our model to describe the dynamics of hematopoiesis after stem cell transplantation. In agreement with earlier findings, we observe that niche-space saturation decreases engraftment efficiency. We further discuss the implications of our findings for human hematopoiesis where the quantity and role of stem cells is frequently debated.

The colony-stimulating factors and cancer

The four colony-stimulating factors (CSFs) are glycoproteins that regulate the generation and some functions of infection-protective granulocytes and macrophages. Recombinant granulocyte-CSF (G-CSF) and granulocyte-macrophage-CSF (GM-CSF) have now been used to increase dangerously low white blood cell levels in many millions of cancer patients following chemotherapy. These CSFs also release haematopoietic stem cells to the peripheral blood, and these cells have now largely replaced bone marrow as more effective populations for transplantation to cancer patients who have treatment-induced bone marrow damage.

Exogenous bone marrow cells do not rescue non-irradiated mice from acute renal tubular damage caused by HgCl2, despite establishment of chimaerism and cell proliferation in bone marrow and spleen

OBJECTIVE

Various studies have shown that bone marrow stem cells can rescue mice from acute renal tubular damage under a conditioning advantage (irradiation or cisplatin treatment) favouring donor cell engraftment and regeneration; however, it is not known whether bone marrow cells (BMCs) can contribute to repair of acute tubular damage in the absence of a selection pressure for the donor cells. The aim of this study was to examine this possibility.

MATERIALS AND METHODS

Ten-week-old female mice were assigned into control non-irradiated animals having only vehicle treatment, HgCl(2)-treated non-irradiated mice, HgCl(2)-treated non-irradiated mice infused with male BMCs 1 day after HgCl(2), and vehicle-treated mice with male BMCs. Tritiated thymidine was given 1 h before animal killing.

RESULTS

Donor BMCs could not alleviate non-irradiated mice from acute tubular damage caused by HgCl(2), deduced by no reduction in serum urea nitrogen combined with negligible cell engraftment. However, donor BMCs could home to the bone marrow and spleen and display proliferative activity. This is the first report to show that despite no preparative myeloablation of recipients, engrafted donor BMCs can synthesize DNA in the bone marrow and spleen.

CONCLUSIONS

Exogenous BMCs do not rescue non-irradiated mice from acute renal tubular damage caused by HgCl(2), despite establishment of chimerism and cell proliferation in bone marrow and spleen.

Histopathology of bone marrow reconstitution after umbilical cord blood transplantation for hematological diseases

To study hematopoietic reconstitution in umbilical cord blood transplantation (CBT), bone marrow (BM) histology was investigated in 35 biopsies after bone marrow transplantation (BMT) and in 40 biopsies after CBT. BM biopsies were obtained at different times after transplantation and were evaluated for cellularity, number of megakaryocytes and CD34-positive cells, and fibrosis. In biopsies up to 29 days after BMT, cellularity was increased and megakaryocytes were observed, but at 29 days after CBT, biopsies showed severe cellular depletion and almost no megakaryocytes. In addition, fewer CD34-positive cells were observed after CBT compared to after BMT. After day 30 after CBT, hematopoietic recovery of the BM was gradually observed and after day 100 after transplantation, no essential differences were observed between BMT and CBT. Hematopoietic recovery of the BM after CBT was delayed compared to that after BMT, but engraftment of donor cells after CBT was also observed in histopathologically. To the best of the authors' knowledge this is the first histopathological description of BM reconstitution after CBT.

Morphology of the bone marrow after stem cell transplantation

In many haematological conditions the only curative option is stem cell (SCT) or bone marrow (BM) transplantation. Little information exists about BM morphology following non-ablative engraftment. During the pretransplantation period and depending on the kind of pretreatment, there may be hypoplasia, residual disease and varying degrees of fibrosis. In the post-transplantation period, after 1-3 weeks of transfusion-dependent pancytopenia, the first signs of successful engraftment are indicated by the recurrence of neutrophils, monocytes and erythrocytes in the peripheral blood. In the BM there is slow regeneration of erythropoiesis, followed by the other lineages of haematopoiesis and increase in reticulin fibres or even a resolution of fibrosis. Diagnostic problems arise when neoplastic lympho- or haematopoiesis are maintained following transplantation. Moreover, there may be a significant graft versus tumour response reaction or an already relapsing disease needing aggressive treatment. On the other hand, a conspicuous dyshaematopoiesis should not be mistaken as representing a myelodysplastic syndrome. The presence of granulomas being treatment-related or a manifestation of intercurrent granulomatous disease has to be considered. More advanced knowledge of the histological features of regenerating BM will certainly aid the recognition of relapsing disease and is needed for the adequate reporting of post-transplant alterations associated with a successful or failing engraftment.

Tolerance induction through megadose bone marrow transplantation with two-signal blockade

BACKGROUND

Induction of mixed chimerism is currently the most promising concept for clinical tolerance induction; however, the toxicity of the required host conditioning for allogeneic bone marrow transplantation (BMT) should be overcome. Therefore, we explored tolerogenic effectiveness of megadose BMT with anti-CD45RB and anti-CD154 mAb (two-signal blockade) in murine recipients without conditioning.

MATERIALS AND METHODS

Recipient B6 mice of BALB/c skin allograft received conditioning and an optimal dose (2x10(7) cells) of BMT. For a megadose BMT model, the conditioning was not performed; instead, megadose (2x10(8) cells) of BM was transplanted. The recipients were then treated with anti-CD45RB mAb and anti-CD154 mAb alone or their combination. Flow cytometry was performed to analyze the degree and distribution of donor-derived cells, peripheral deletion of Vbeta5 or Vbeta11 T cells and intrathymic presence of donor MHC class II+ cells. Induction of chimerism-based tolerance to skin allograft was further determined.

RESULTS

High levels ( approximately 23.7%) of mixed and multi-lineage chimerism-based tolerance to skin allograft were induced in the recipients (91%) treated with the optimal-dose BMT and the two-signal blockade. The megadose BMT could replace the recipient conditioning and establish low (approximately 10%) and stable multilineage chimerism. Donor-specific tolerance to skin allograft was induced in these chimeras through clonal deletion of donor-reactive cells.

CONCLUSIONS

The megadose BMT with the two-signal blockade could effectively establish mixed and multi-lineage chimerism and induce donor-specific tolerance, suggesting its potential for clinical application.

Stem cells of the alveolar epithelium

Elucidation of the biology of stem cells of the lung parenchyma could revolutionise treatment of patients with lung disorders such as cancer, acute respiratory distress syndrome, emphysema, and fibrotic lung disease. How close is this goal? Despite remarkable observations and ensuing advances, more questions than answers have been generated. Progenitors of the alveolar epithelium remain largely mysterious, so the prospect of isolating enough of these cells and delivering them effectively to cure disease remains remote. Similarly, the bone-marrow-derived cell that might most effectively engraft the lung remains unknown. If this mechanism is an important process for lung repair, why will the administration of additional cells be more effective? Finally, there is an issue of control of multipotent cells to avoid the generation of multiple teratomas, longevity of the graft, and possible immunological reactions to gene products inserted to replace a deficiency. The biology is exciting but not yet well enough understood to support therapeutic advances.

Rac2-deficient hematopoietic stem cells show defective interaction with the hematopoietic microenvironment and long-term engraftment failure

The hematopoietic-specific Rho GTPase, Rac2, regulates a variety of cellular functions including cell shape changes, motility, integrin-dependent adhesion, and apoptosis. In the study reported here, we demonstrate that wild-type (WT) hematopoietic stem cells/progenitors (HSC/P) preferentially engraft in nonablated Rac2(-/-) bone marrow. In addition, primitive Rac2(-/-) HSC/P transplanted into lethally irradiated WT recipients showed a significant competitive defect compared with WT cells. These defects appeared to be related to HSC/P-intrinsic defective microenvironment interactions, since Rac2(-/-) cells showed less adhesion to the femur bone marrow density 1 (FBMD-1) stromal cell line, a lower frequency of cobblestone area-forming cells, and lower performance in long-term marrow cultures in vitro when compared with WT cells. In contrast, primitive Rac2(-/-) hematopoietic cells exhibited normal progenitor colony formation in semisolid medium in vitro and normal proliferation in the steady state in vivo when compared with WT cells. Taken together, these data suggest that Rac2(-/-) stem/progenitor cells exhibit abnormal interaction with the hematopoietic microenvironment, which leads to defective long-term engraftment.

Cytokines and cytotoxic pathways in engraftment resistance to purified allogeneic hematopoietic stem cells

The way that allogeneic hematopoietic cells are rejected is not completely understood. Regimen-resistant populations, including natural killer (NK) cells and lymphocytes, are thought to mediate the allograft barrier. In this report, the mechanism by which recipient cell populations resist engraftment of purified allogeneic hematopoietic stem cells (HSCs) was examined in mice. To define the immunoregulatory pathways involved in allogeneic hematopoietic cell resistance, HSC transplantations were performed in immune-defective recipients. Recipients were wild-type mice treated with alpha-NK cell antibodies or knockout strain mice lacking expression of CD8, perforin, Fas ligand, or 1 of the following cytokines: tumor necrosis factor alpha, transforming growth factor beta, interferon gamma, interleukin 4, or interleukin 10. Elimination of a single cytotoxic pathway was ineffective in reducing engraftment resistance, although mice treated with a polyclonal antibody that recognizes NK-cell determinants or CD8 expression showed a profound reduction in the engraftment barrier. Posttransplantation chimerism analysis revealed regeneration of host hematopoiesis in some experimental groups. These studies show, for the first time, that elimination of selected cytokines does not alter allogeneic hematopoietic resistance. Furthermore, the chimerism data reinforce the importance of competition for HSC niches in conjunction with immune mechanisms in resistance to long-term HSC engraftment.

Targeted T-Cell Depletion or CD154 Blockade Generates Mixed Hemopoietic Chimerism and Donor-Specific Tolerance in Mice Treated with Sirolimus and Donor Bone Marrow

BACKGROUND

The administration of donor specific bone marrow (DSBM) to mice conditioned with antilymphocyte serum (ALS) and sirolimus can result in stable multilineage mixed chimerism and long-term graft survival. This study seeks to determine if either the targeted depletion of CD4 and/or CD8 pos T cells or costimulation blockade can substitute for ALS and preserve the efficacy of this regimen.

METHODS

C57BL/6 recipients of BALB/c skin allografts were treated with DSBM (150 x 10(6) cells), sirolimus (24 mg/kg intraperitonealy), and either ALS or various monoclonal antibodies (alphaCD4, alphaCD8, alphaCD154 alone or in combination). Recipient peripheral blood mononuclear cell (PBMC) depletion, donor chimerism, and deletion of donor reactive T cells were assessed using flow cytometry. The specificity of immunologic nonreactivity and the presence of immunoregulatory activity were assessed through a mixed lymphocyte reaction assay.

RESULTS

The administration of ALS, sirolimus, and DSBM resulted in sustained recipient PBMC depletion, transient chimerism, and prolonged graft survival. The substitution of an equivalent degree and duration of targeted depletion of either CD4 or CD8 pos T cells alone for ALS failed to produce chimerism or prolonged graft survival. In contrast, depletion of both CD4 and CD8 pos T cells resulted in durable multilineage chimerism, indefinite allograft acceptance (>350 days), and donor-specific tolerance to secondary skin grafts. Substitution of alphaCD154 monoclonal antibody for ALS also resulted in a state of mixed chimerism and donor specific tolerance. This tolerant state appears to be maintained at least partially through clonal deletion and suppression.

CONCLUSION

Either combined CD4 and CD8 T-cell depletion or alphaCD154 blockade can effectively substitute for ALS in producing chimerism and tolerance in this model.

Cell tracking with gadophrin-2: a bifunctional contrast agent for MR imaging, optical imaging, and fluorescence microscopy

The purpose of this study was to assess the feasibility of use of gadophrin-2 to trace intravenously injected human hematopoietic cells in athymic mice, employing magnetic resonance (MR) imaging, optical imaging (OI), and fluorescence microscopy. Mononuclear peripheral blood cells from GCSF-primed patients were labeled with gadophrin-2 (Schering AG, Berlin, Germany), a paramagnetic and fluorescent metalloporphyrin, using established transfection techniques with cationic liposomes. The labeled cells were evaluated in vitro with electron microscopy and inductively coupled plasma atomic emission spectrometry. Then, 1x10(6)-3x10(8) labeled cells were injected into 14 nude Balb/c mice and the in vivo cell distribution was evaluated with MR imaging and OI before and 4, 24, and 48 h after intravenous injection (p.i.). Five additional mice served as controls: three mice were untreated controls and two mice were investigated after injection of unlabeled cells. The contrast agent effect was determined quantitatively for MR imaging by calculating signal-to-noise-ratio (SNR) data. After completion of in vivo imaging studies, fluorescence microscopy of excised organs was performed. Intracellular cytoplasmatic uptake of gadophrin-2 was confirmed by electron microscopy. Spectrometry determined an uptake of 31.56 nmol Gd per 10(6) cells. After intravenous injection, the distribution of gadophrin-2 labeled cells in nude mice could be visualized by MR, OI, and fluorescence microscopy. At 4 h p.i., the transplanted cells mainly distributed to lung, liver, and spleen, and 24 h p.i. they also distributed to the bone marrow. Fluorescence microscopy confirmed the distribution of gadophrin-2 labeled cells to these target organs. Gadophrin-2 is suited as a bifunctional contrast agent for MR imaging, OI, and fluorescence microscopy and may be used to combine the advantages of each individual imaging modality for in vivo tracking of intravenously injected hematopoietic cells.

Tolerance induction by costimulator blockade in 100 cGy treated hosts with varying degrees of genetic disparity

Long-term multilineage allochimerism can be obtained in H2-mismatched B6.SJL to BALB/c transplants with host irradiation of 100 cGy, donor spleen cell pre-exposure and costimulator blockade with anti-CD40 ligand (CD40L) antibody. We evaluated this allochimerism approach in murine marrow transplants with different degrees of major histocompatibility complexe (MHC) mismatching; these include: (1) H2-mismatched transplant H2Kk to H2Kb, (2) full haplo-identical transplant H2Kbd to H2Kbk, (3) a partial haplo-identical transplant H2Kd to H2Kbd and (4) an MHC class II mismatch. Levels of chimerism increased up to 12 weeks and then stayed relatively stable up to 1 year after transplant. At 18 weeks post-transplant, the H2-mismatched, haplo-identical, partial haplo-identical and class II-mismatch transplants evidenced 17.9+/-4.4, 40.7+/-0.9, 25.1+/-4.19 and 33.7+/-3.5% donor chimerism, respectively. Dropping the anti-CD40 antibody treatment and spleen cells or changing the schedule of antibody to one injection, in haplo-identical or full-mismatched transplants resulted in no donor-derived chimerism. On the other hand, these still resulted in minor chimerism in class II-mismatched transplants. Lineage analysis of peripheral blood at 6 and 12 months post-transplant demonstrated a significant shift toward increased chimeric lymphocytes and decreased chimeric granulocytes in the full H2 as compared with haplo-identical or class II transplants. Transplantation with anti-CD40L antibody eliminated both graft-versus-leukemia and graft-versus-host disease (GVHD) and delayed lymphocyte infusion did not rescue animals from fatal leukemia. In conclusion, under the conditions of our tolerization regimen, a haplo transplant gives higher engraftment levels than a full H2 mismatch, and despite lower engraftment levels, a class II-mismatched transplant can be successfully accomplished with only 100 cGy and no CD40L blockade.

Cytokines and BMP-4 promote hematopoietic differentiation of human embryonic stem cells

Human embryonic stem cells (hESCs) randomly differentiate into multiple cell types during embryoid body (EB) development. To date, characterization of specific factors capable of influencing hematopoietic cell fate from hESCs remains elusive. Here, we report that the treatment of hESCs during EB development with a combination of cytokines and bone morphogenetic protein-4 (BMP-4), a ventral mesoderm inducer, strongly promotes hematopoietic differentiation. Hematopoietic progenitors of multiple lineages were generated from EBs and were found to be restricted to the population of progeny expressing cell surface CD45. Addition of BMP-4 had no statistically significant effect on hematopoietic differentiation but enabled significant enhancement in progenitor self-renewal, independent of cytokine treatment. Hematopoietic commitment was characterized as the temporal emergence of single CD45+ cells first detectable after day 10 of culture and was accompanied by expression of hematopoietic transcription factors. Despite the removal of cytokines at day 10, hematopoietic differentiation of hESCs continued, suggesting that cytokines act on hematopoietic precursors as opposed to differentiated hematopoietic cells. Our study establishes the first evidence for the role of cytokines and BMP-4 in promoting hematopoietic differentiation of hESC lines and provides an unprecedented system to study early developmental events that govern the initiation of hematopoiesis in the human.

Mechanisms of anticancer drug resistance

Chemotherapy agents are extremely important in the treatment of liquid malignancies, such as lymphoma, myeloma, and chronic lymphocytic leukemia. In addition, chemotherapy agents have proven effective in the adjuvant treatment of solid tumors, such as osteosarcoma, hemangiosarcoma, transitional cell carcinoma, and others. Unfortunately, chemotherapy resistance in these situations is the most significant cause of treatment failure. Therefore, the ability to predict, treat, or circumvent resistance is extremely likely to improve clinical outcomes. This article has reviewed the most widely investigated forms of chemotherapy resistance, such as reduced drug accumulation, increased DNA damage repair, decreased apoptosis, and others; however, new mechanisms are being found at an alarming pace. In addition, investigations to date have routinely centered on single-cell mechanisms of drug resistance, and cancer is truly a three dimensional disease. The elucidation of mechanisms surrounding (1) how tumors interact with their normal microenvironment, (2) how tumors interact in a three-dimensional environment, and (3) a better understanding of basic tumor physiology and biology may supersede in importance those previously elucidated single-cell mechanisms of chemoresistance.