Allogeneic chimerism with low-dose irradiation, antigen presensitization, and costimulator blockade in H-2 mismatched mice

We have previously shown that the keys to high-level nontoxic chimerism in syngeneic models are stem cell toxic, nonmyelotoxic host treatment as provided by 100-cGy whole-body irradiation and relatively high levels of marrow stem cells. This approach was unsuccessful in H-2 mismatched B6.SJL to BALB/c marrow transplants, but with tolerization, stable multilineage chimerism was obtained. Ten million B6.SJL spleen cells were infused intravenously into BALB/c hosts on day -10 and (MR-1) anti-CD40 ligand monoclonal antibody (mAb) injected intraperitoneally at varying levels on days -10, -7, -3, 0, and +3 and the BALB/c mice irradiated (100 cGy) and infused with 40 million B6.SJL/H-2 mismatched marrow cells on day 0. Stable multilineage chimerism at levels between 30% to 40% was achieved in the great majority of mice at 1.6 mg anti-CD40 ligand mAb per injection out to 64 weeks after transplantation, without graft-versus-host disease. The transplanted mice were also tolerant of donor B6.SJL, but not third-party CBA/J skin grafts at 8 to 9 and 39 to 43 weeks after marrow transplantation. These data provide a unique model for obtaining stable partial chimerism in H-2 mismatched mice, which can be applied to various clinical diseases of man such as sickle cell anemia, thalassemia, and autoimmune disorders

TrkA expression decreases the in vivo aggressiveness of C6 glioma cells

We stably expressed the nerve growth factor receptor trkA or a truncated trkA lacking the kinase domain (trkA delta) in a highly tumorigenic rat glioma cell line, C6. Survival of rats with large intrastriatal inocula of C6trkA cells was significantly longer than for rats bearing C6 or C6trkA delta cells. Histological studies revealed that C6trkA cells were much less invasive than C6 or C6trkA delta cells and had a greater rate of apoptosis. There was no apparent induction of differentiation of C6 cells by trkA. Therefore, unlike what is observed in neuroblastomas, trkA decreases tumorigenicity by modulating invasiveness and tumor cell death independent of inducing differentiation. This novel mechanism suggests a new therapeutic strategy for malignant gliomas

Expression of the Id family helix-loop-helix regulators during growth and development in the hematopoietic system

To better understand the molecular mechanism(s) by which growth and differentiation of the primitive hematopoietic stem cell is initiated, as well as the means by which the maturing cell can commit to development along a specific cell lineage, we elected to study the Id family of helix-loop-helix (HLH) transcriptional regulators. Some members of the HLH family are expressed in a stage-specific manner during hematopoietic development and can regulate the ability of immature hematopoietic cells to terminally differentiate. None of the four Id family genes were detected in the most primitive progenitors. Id-1 was widely expressed in proliferating bi- and unipotential progenitors, but its expression was downregulated in cells of increasing maturity; conversely, Id-2 and, to a limited extent, Id-3 gene expression increased as cells matured and lost proliferative capacity. Id-2 expression ran counter to that of Id-1 not only during maturation, but during periods of cell growth and arrest as well. This is quite distinct from the nonhematopoietic tissues, in which these two factors are coordinately expressed and suggests that Id-1 and Id-2 might be regulating very different events during hematopoiesis than they regulate in other cell types

The 30-bp Deletion Variant of Epstein-Barr Virus-Encoded Latent Membrane Protein-1 Prevails in Acute Infectious Mononucleosis

To assess the frequency of malignancy-associated 30-bp deletion variants of the latent membrane protein 1 (LMP-1) in benign conditions, a comparative sequence analysis was done using samples from 20 American children with acute infectious mononucleosis and 16 Swiss children with chronic tonsillar hyperplasia. The 30-bp deletion variant (LMP-1-del) was present in 66% of patients (12/20 with infectious mononucleosis and 12/16 with tonsillar hyperplasia). Two additional patients had a 3-bp deletion and an inframe insertion of 18 nucleotides, respectively. All but 1 isolate had numerous nonsilent point mutations. These data identify a hypervariable region within the Cterminus of LMP-1, in a domain required for maximal stimulation of NF-κB activity. These data demonstrate that LMP-1-del variants are frequent in acute infectious mononucleosis and tonsillar hyperplasia and identical to those observed in Epstein-Barr virus-associated AIDS-related lymphom

Centrosome defects and genetic instability in malignant tumors

Genetic instability is a common feature of many human cancers. This condition is frequently characterized by an abnormal number of chromosomes, although little is known about the mechanism that generates this altered genetic state. One possibility is that chromosomes are missegregated during mitosis due to the assembly of dysfunctional mitotic spindles. Because centrosomes are involved in spindle assembly, they could contribute to chromosome missegregation through the organization of aberrant spindles. As an initial test of this idea, we examined malignant tumors for centrosome abnormalities using antibodies to the centrosome protein pericentrin. We found that centrosomes in nearly all tumors and tumor-derived cell lines were atypical in shape, size, and composition and were often present in multiple copies. In addition, virtually all pericentrin-staining structures in tumor cells nucleated microtubules, and they participated in formation of disorganized mitotic spindles, upon which chromosomes were missegregated. All tumor cell lines had both centrosome defects and abnormal chromosome numbers, whereas neither was observed in nontumor cells. These results indicate that centrosome defects are a common feature of malignant tumors and suggest that they may contribute to genetic instability in cancer

Potential and distribution of transplanted hematopoietic stem cells in a nonablated mouse model

Increasingly, allogeneic and even more often autologous bone marrow transplants are being done to correct a wide variety of diseases. In addition, autologous marrow transplants potentially provide an opportune means of delivering genes in transfected, engrafting stem cells. However, despite its widespread clinical use and promising gene therapy applications, relatively little is known about the mechanisms of engraftment in marrow transplant recipients. This is especially so in the nonablated recipient setting. Our data show that purified lineage negative rhodamine 123/Hoechst 33342 dull transplanted hematopoietic stem cells engraft into the marrow of nonablated syngeneic recipients. These cells have multilineage potential, and maintain a distinct subpopulation with stem cell characteristics. The data also suggests a spatial localization of stem cell niches to the endosteal surface, with all donor cells having a high spatial affinity to this area. However, the level of stem cell engraftment observed following a transplant of stem cells was significantly lower than that expected following a transplant of the same number of unseparated marrow cells from which the purified cells were derived, suggesting the existence of a nonstem cell facilitator population, which is required in a nonablated syngeneic transplant setting

Cell cycle analysis and synchronization of pluripotent hematopoietic progenitor stem cells

Hematopoietic stem cells purified from mouse bone marrow are quiescent with less than 2% of Lin- Hoechst(low)/Rhodamine(low) (Lin- Ho(low)/Rho(low)) and 10% to 15% of Lin-/Sca+ cells in S phase. These cells enter proliferative cycle and progress through G1 and into S phase in the presence of cytokines and 5% heat-inactivated fetal calf serum (HI-FCS). Cytokine-stimulated Lin- Ho(low)/Rho(low) cells took 36 to 40 hours to complete first division and only 12 hours to complete each of 5 subsequent divisions. These cells require 16 to 18 hours to transit through G0/G1 period and 28 to 30 hours to enter into mid-S phase during the first cycle. Up to 56% of Lin- Rho(low)/Ho(low) cells are high-proliferative potential (7 factor-responsive) colony-forming cells (HPP-CFC). At isolation, HPP-CFC are quiescent, but after 28 to 30 hours of culture, greater than 60% are in S phase. Isoleucine-deprivation of Lin- Ho(low)/Rho(low) cells in S phase of first cycle reversibly blocked them from entering into second cycle. After the release from isoleucine-block, these cells exhibited a G1 period of less than 2 hours and entered into mid-S phase by 12 hours. Thus, the duration of G1 phase of the cells in second cycle is 4 to 5 times shorter than that observed in their first cycle. Similar cell cycle kinetics are observed with Lin-/Sca+ population of bone marrow cells. Stem cell factor (SCF) alone, in the presence of HI-FCS, is as effective as a cocktail of 2 to 7 cytokines in inducing quiescent Lin-/Sca+ cells to enter into proliferative cycle. Aphidicolin treatment reversibly blocked cytokine-stimulated Lin-/Sca+ cells at G1/S boundary, allowing their tight synchrony as they progress through first S phase and enter into second G1. For these cells also, SCF alone is sufficient for their progression through S phase. These studies indicate a very short G1 phase for stem cells induced to proliferate and offer experimental approaches to synchronize murine hematopoietic stem cells

Nonengraftment Haploidentical Cellular Therapy for Hematologic Malignancies

Much of the therapeutic benefit of allogeneic transplant is by a graft versus tumor effect. Further data shows that transplant engraftment is not dependant on myeloablation, instead relying on quantitative competition between donor and host cells. In the clinical setting, engraftment by competition alone is not feasible due to the need for large numbers of infused cells. Instead, low-level host irradiation has proven to be an effective engraftment strategy that is stem cell toxic but not myeloablative. The above observations served as the foundation for clinical trials utilizing allogeneic matched and haploidentical peripheral blood stem cell infusions with minimal conditioning in patients with refractory malignancies. Although engraftment was transient or not apparent, there were compelling responses in a heavily pretreated patient population that appear to result from the breaking of tumor immune tolerance by the host through the actions of IFNγ, invariant NK T cells, CD8 T cells, NK cells, or antigen presenting cells

Cells Capable of Bone Production Engraft from Whole Bone Marrow Transplants in Nonablated Mice

Allogeneic and autologous marrow transplants are routinely used to correct a wide variety of diseases. In addition, autologous marrow transplants potentially provide opportune means of delivering genes in transfected, engrafting stem cells. However, relatively little is known about the mechanisms of engraftment in transplant recipients, especially in the nonablated setting and with regard to cells not of hemopoietic origin. In particular, this includes stromal cells and progenitors of the osteoblastic lineage. We have demonstrated for the first time that a whole bone marrow transplant contains cells that engraft and become competent osteoblasts capable of producing bone matrix. This was done at the individual cell level in situ, with significant numbers of donor cells being detected by fluorescence in situ hybridization in whole femoral sections. Engrafted cells were functionally active as osteoblasts producing bone before being encapsulated within the bone lacunae and terminally differentiating into osteocytes. Transplanted cells were also detected as flattened bone lining cells on the periosteal bone surface

Cytokine-facilitated transduction leads to low-level engraftment in nonablated hosts

Using a murine bone marrow transplantation model, we evaluated the long-term engraftment of retrovirally transduced bone marrow cells in nonmyeloablated hosts. Male bone marrow was stimulated in a cocktail of interleukin-3 (IL-3), IL-6, IL-11, and stem cell factor (SCF) for 48 hours, then cocultured on the retroviral producer line MDR18.1 for an additional 24 hours. Functional transduction of hematopoietic progenitors was detected in vitro by reverse transcriptase-polymerase chain reaction (RT-PCR) amplification of multiple drug resistance 1 (MDR1) mRNA from high proliferative potential-colony forming cell (HPP-CFC) colonies. After retroviral transduction, male bone marrow cells were injected into nonablated female mice. Transplant recipients received three TAXOL (Bristol-Myers, Princeton, NJ) injections (10 mg/kg) over a 14-month period. Transplant recipient tissues were analyzed by Southern blot and fluorescence in situ hybridization for Y-chromosome-specific sequences and showed donor cell engraftment of approximately 9%. However, polymerase chain reaction amplification of DNAs from bone marrow, spleen, and peripheral blood showed no evidence of the transduced MDR1 gene. RT-PCR analysis of total bone marrow RNA showed that transcripts from the MDR1 gene were present in a fraction of the engrafted donor cells. These data show functional transfer of the MDR1 gene into nonmyeloablated murine hosts. However, the high rates of in vitro transduction into HPP-CFC, coupled with the low in vivo engraftment rate of donor cells containing the MDR1 gene, suggest that the majority of stem cells that incorporated the retroviral construct did not stably engraft in the host. Based on additional studies that indicate that ex vivo culture of bone marrow induces an engraftment defect concomitantly with progression of cells through S phase, we propose that the cell cycle transit required for proviral integration reduces or impairs the ability of transduced cells to stably engraft