Isolation and characterization of pediatric canine bone marrow CD34+ cells

In vitro investigation of canine periodontal ligament-derived mesenchymal stem cells: A possibility of promising tool for periodontal regeneration

Objectives

Recent investigations indicate that canine periodontal ligament-derived stem cells (cPDLSCs) may reveal a reliable strategy for repair of periodontal tissues via cell-based tissue engineering approaches. Due to limited research, this study aimed to demonstrate the phenotypic characterization of cPDLSc in comparison with canine bone marrow-derived mesenchymal stem cells (cBMSCs) in vitro.

Methods

Mesenchymal stem cells (MSCs) were obtained from PDL and BM of five male adult Mongrel dogs. In vitro isolation and expansion as well as biologic characterization including colony unit formation (CFU), osteogenic and adipogenic differentiation, flow cytometric analysis of CD34 and CD44, and RT-PCR of alkaline phosphatase (ALP), osteocalcin (OCN), periostin (POSTN) and S100A4 were performed. Furthermore, electron microscopy analysis was done to complement the comparative research.

Results

CFU assay revealed that colonies of cPDLSCs presented 70% confluency with a more finite lifespan than BM-MSCs, showing a significant increase in cPDLSCs. Both types of MSCs showed osteogenic and adipogenic phenotypic characterized with clusters of mineralized depositions and lipid vacuoles, respectively. Both types of MSCs expressed CD44 with limited expression of CD34. RT-PCR of cPDLSCs revealed that expression of ALP, POSTN, OCN and S100A4 genes were significantly higher than those of BMSCs. In addition, comparison of SEM and revealed that cPDLSCs expressed more extracellular collagen fibers.

Conclusions

The current study indicated that cPDLSCs show potency as a novel cellular therapy for periodontal regeneration a large animal model.

Animal Models for Preclinical Development of Allogeneic Hematopoietic Cell Transplantation

Since its inception in the 1950s, hematopoietic cell transplantation (HCT) has become a highly effective clinical treatment for malignant and nonmalignant hematological disorders. This milestone in cancer therapy was only possible through decades of intensive research using murine and canine animal models that overcame what appeared in the early days to be insurmountable obstacles. Conditioning protocols for tumor ablation and immunosuppression of the recipient using irradiation and chemotherapeutic drugs were developed in mouse and dog models as well as postgrafting immunosuppression methods essential for dependable donor cell engraftment. The random-bred canine was particularly important in defining the role of histocompatibility barriers and the development of the nonmyeloablative transplantation procedure, making HCT available to elderly patients with comorbidities. Two complications limit the success of HCT: disease relapse and graft versus host disease. Studies in both mice and dogs have made significant progress toward reducing and to some degree eliminating patient morbidity and mortality associated with both disease relapse and graft versus host disease. However, more investigation is needed to make HCT more effective, safer, and available as a treatment modality for other non-life-threatening diseases such as autoimmune disorders. Here, we focus our review on the contributions made by both the murine and canine models for the successful past and future development of HCT.

Increased numbers of peripheral blood CD34+ cells in dogs with canine atopic dermatitis

BACKGROUND

The bone marrow may be involved in human atopic diseases, as shown by the release of CD34+ cells into the peripheral blood.

HYPOTHESIS/OBJECTIVES

The aim was to determine the numbers of CD34+ cells in atopic dogs.

ANIMALS

The following three groups of dogs were studied: 27 dogs with nonfood-induced atopic dermatitis (NFICAD); 16 dogs with nonallergic inflammatory diseases; and 13 healthy control dogs.

METHODS

Dogs with NFICAD were selected after fulfilment of Favrot's criteria and exclusion of other pruritic dermatoses, including flea infestation and adverse reaction to foods. The Canine Atopic Dermatitis Extent and Severity Index (CADESI)-03 and a Visual Analog Scale (VAS) score for pruritus were used to quantify clinical signs. A phycoerythrin-conjugated anticanine CD34 antibody was used to stain peripheral blood CD34+ cells, and these were enumerated using a flow cytometer. The CD34+ cell counts were compared between groups and tested (in the NFICAD group) for correlation with the severity of clinical signs.

RESULTS

The numbers of peripheral CD34+ cells in dogs with NFICAD (median 1.7) were statistically higher than in dogs with other nonallergic inflammatory diseases (median 1.0; P = 0.01) and healthy control dogs (median 0.9; P = 0.009). In dogs with NFICAD, there was no correlation between CD34+ cell numbers and CADESI-03 scores or owner-assessed pruritus (VAS score).

CONCLUSIONS AND CLINICAL IMPORTANCE

The results of this study suggest the possible involvement of CD34+ cells in dogs with NFICAD. The role of CD34+ cells in the aetiopathogenesis of canine atopic dermatitis remains to be determined.

Células-tronco mononucleares associadas ao plasma rico em plaquetas na consolidação de falha óssea no cão. Estudo piloto

A padronização de técnicas e o teste da associação do Plasma Rico em Plaquetas (PRP) e das Células-Tronco Mononucleares (CTMs) na consolidação de falhas ósseas corticais, por meio de avaliação clínica, biomecânica, radiológica e histológica, é avaliada em um estudo piloto. Foram utilizados seis cães adultos, fêmeas, sem raça definida, pesando entre 5 e 10kg, separados por sorteio aleatório em seis tratamentos. Foi confeccionada uma falha elíptica de 1,0x0,4cm na cortical medial diafisária da tíbia direita de cada animal, sendo preenchida de acordo com o tratamento proposto. No cão I, a falha foi preenchida com solução fisiológica (SF); no II, com o PRP; no III, com a fração total das células mononucleares (FTCM); no IV, com a fração vascular estromal (FVE); no V, com o PRP associado à FTCM; no VI, com a associação PRP e FVE. Foram realizadas avaliações: clínicas, diariamente; dos graus de claudicação, semanalmente; radiológica e perimetria da coxa, antes, no pós-operatório imediato, aos 7, 14, 21 e 30 dias; biomecânica, antes do procedimento, aos 10, 20 e 30 dias; e biópsias, aos 15 e 30 dias. A FTCM obteve uma contagem e viabilidade média de 2,0x108cél. e 90%, respectivamente, enquanto a FVE obteve 3x106cél. e 50%. O PRP concentrou, em média, sete vezes o número inicial de plaquetas do sangue total, de 250.000 µl-1 plaquetas no sangue total para 1.750.000 µl-1 plaquetas no PRP. Obteve-se padronização adequada de técnicas, possibilitando o teste da associação entre as células-tronco mononucleares (CTMs) e o plasma rico em plaquetas (PRP), assim como seu uso isolado, no reparo de falhas ósseas corticais, indicando a possibilidade de a associação FTCM e PRP ser o melhor tratamento.

Foamy virus vectors for HIV gene therapy

Highly active antiretroviral therapy (HAART) has vastly improved outcomes for patients infected with HIV, yet it is a lifelong regimen that is expensive and has significant side effects. Retroviral gene therapy is a promising alternative treatment for HIV/AIDS; however, inefficient gene delivery to hematopoietic stem cells (HSCs) has so far limited the efficacy of this approach. Foamy virus (FV) vectors are derived from non-pathogenic viruses that are not endemic to the human population. FV vectors have been used to deliver HIV-inhibiting transgenes to human HSCs, and they have several advantages relative to other retroviral vectors. These include an attractive safety profile, broad tropism, a large transgene capacity, and the ability to persist in quiescent cells. In addition, the titers of FV vectors are not reduced by anti-HIV transgenes that affect the production of lentivirus (LV) vectors. Thus FV vectors are very promising for anti-HIV gene therapy. This review covers the advantages of FV vectors and describes their preclinical development for anti-HIV gene therapy.

Fração total de células mononucleares intra-articular em cães submetidos à reconstrução do ligamento cruzado

Avaliou-sea ação da fração total de células mononucleares autógenas da medula óssea (FCMO) por aplicação intra-articular, após a correção cirúrgica do ligamento cruzado rompido. Foram utilizados 20 cães, os quais sofreram desmotomia do ligamento cruzado cranial e caudal unilaterais, 21 dias antes do reparo cirúrgico. Dez animais receberam as células autógenas no momento da correção. As avaliações se deram por estudo radiográfico, exames clínicos e biópsias aos 50 e 90 dias pós-operatórios. O grupo que recebeu a FCMO apresentou crescimento ósseo intra-articular ao estudo radiográfico, contudo os 20 animais apresentaram célulasCD34 positivas em suas amostras biopsiadas, indicando haver presença de células-tronco em ambos os grupos. Conclui-se que,para o modelo experimental proposto, não se recomenda o uso da fração total de células mononucleares e que trabalhos experimentais com o uso de células-tronco nas articulações devem evitar modelos cujo foco de lesão mantenha contato direto com a medula óssea.

Large animal models for foamy virus vector gene therapy

Foamy virus (FV) vectors have shown great promise for hematopoietic stem cell (HSC) gene therapy. Their ability to efficiently deliver transgenes to multi-lineage long-term repopulating cells in large animal models suggests they will be effective for several human hematopoietic diseases. Here, we review FV vector studies in large animal models, including the use of FV vectors with the mutant O6-methylguanine-DNA methyltransferase, MGMTP140K to increase the number of genetically modified cells after transplantation. In these studies, FV vectors have mediated efficient gene transfer to polyclonal repopulating cells using short ex vivo transduction protocols designed to minimize the negative effects of ex vivo culture on stem cell engraftment. In this regard, FV vectors appear superior to gammaretroviral vectors, which require longer ex vivo culture to effect efficient transduction. FV vectors have also compared favorably with lentiviral vectors when directly compared in the dog model. FV vectors have corrected leukocyte adhesion deficiency and pyruvate kinase deficiency in the dog large animal model. FV vectors also appear safer than gammaretroviral vectors based on a reduced frequency of integrants near promoters and also near proto-oncogenes in canine repopulating cells. Together, these studies suggest that FV vectors should be highly effective for several human hematopoietic diseases, including those that will require relatively high percentages of gene-modified cells to achieve clinical benefit.

Characterization of CD34⁺ thymocytes in newborn dogs

Using two-color flow cytometry, we characterized CD34(+) cells in the newborn canine thymus. CD34(+) thymic cells comprised approximately 5% of cells recovered by thymus tissue teasing and both large and small thymocytes have been present in this population, the former being 7-12 times more frequent. All CD34(+) cells expressed the pan-leukocyte antigen CD45. The expression of CD44 profile on the large and small CD34(+) thymocytes differed: almost all large CD34(+) cells were CD44(+), while only 75% of small CD34(+) thymocytes co-expressed the CD44 antigen. We have previously described that CD172α is present on the surface of CD34(+) bone marrow cells in dogs. In the thymus, CD172α was expressed on 5-10% and less than 5% of large and small CD34(+) cells, respectively. Some CD34(+) thymocytes also co-expressed T-lineage-specific markers like CD3, CD4, CD8, TCR1 and TCR2. Their expression increased during the large-to-small thymocyte transition. Based on our findings we suggest that thymocyte progenitors enter their primary differentiation center as large CD34(+), CD44(+), CD45(+) and CD172α(+) cells. T-cell specific markers appear on their surface at early stages of differentiation. As the size of progenitors decreases with terminal primary differentiation, the CD34, CD44, and CD172α surface markers are down-regulated.

Effects of donor characteristics and ex vivo expansion on canine mesenchymal stem cell properties: implications for MSC-based therapies

Clinical trials utilizing bone marrow-derived mesenchymal stem cell (BM-MSC) therapies show promise for treating a variety of pathologic conditions. Paramount to optimization of such cell-based therapies is a thorough understanding of MSC biology. Despite the tremendous potential that exists for the clinical use of canine BM-MSCs in veterinary medicine, as well as in preclinical studies for human medicine, relatively little information exists regarding basic biological properties of the cells. In this study, we compared the importance of donor characteristics (age and harvest site) and ex vivo expansion on canine BM-MSC frequency (CFU-f) and differentiation potential. Advancing age was found to have a negative effect on CFU-f as well as osteogenic potential. Site of harvest was also found to have significant effects on MSC properties. MSCs obtained from the humerus were found at the lowest frequency and were least osteogenic compared to those harvested from the tibia, femur, and ilium. Osteogenic potential diminished significantly by the third passage. These results suggest important donor parameters and culture effects to consider in translational studies examining MSC-based regenerative medical strategies.

Morphological characterization of the progenitor blood cells in canine and feline umbilical cord

The umbilical cord blood (UCB) is an important source of hematopoietic stem cells with great deal of interest in regenerative medicine. The UCB cells have been extensively studied as an alternative to the bone marrow transplants. The challenge is to define specific methods to purify and characterize these cells in different animal species. This study is aimed at morphological characterization of progenitor cells derived from UCB highlighting relevant differences with peripheral blood of adult in dog and cats. Therefore, blood was collected from 18 dogs and 5 cats' umbilical cords from fetus in various developmental stages. The mononuclear cells were separated using the gradient of density Histopaque-1077. Characterization of CD34+ cells was performed by flow cytometric analysis and transmission electron microscopy. Granulocytes (ancestry of the basophiles, eosinophiles, and neutrophiles) and agranulocytes (represented by immature lymphocytes) were identified. We showed for the first time the ultrastructural features of cat UCB cells.

Large animal models of hematopoietic stem cell gene therapy

Large animal models have been instrumental in advancing hematopoietic stem cell (HSC) gene therapy. Here we review the advantages of large animal models, their contributions to the field of HSC gene therapy and recent progress in this field. Several properties of human HSCs including their purification, their cell-cycle characteristics, their response to cytokines and the proliferative demands placed on them after transplantation are more similar in large animal models than in mice. Progress in the development and use of retroviral vectors and ex vivo transduction protocols over the last decade has led to efficient gene transfer in both dogs and nonhuman primates. Importantly, the approaches developed in these models have translated well to the clinic. Large animals continue to be useful to evaluate the efficacy and safety of gene therapy, and dogs with hematopoietic diseases have now been cured by HSC gene therapy. Nonhuman primates allow evaluation of aspects of transplantation as well as disease-specific approaches such as AIDS (acquired immunodeficiency syndrome) gene therapy that can not be modeled well in the dog. Finally, large animal models have been used to evaluate the genotoxicity of viral vectors by comparing integration sites in hematopoietic repopulating cells and monitoring clonality after transplantation.

Isolation and characterization of canine umbilical cord blood-derived mesenchymal stem cells

Human umbilical cord blood-derived mesenchymal stem cells (MSCs) are known to possess the potential for multiple differentiations abilities in vitro and in vivo. In canine system, studying stem cell therapy is important, but so far, stem cells from canine were not identified and characterized. In this study, we successfully isolated and characterized MSCs from the canine umbilical cord and its fetal blood. Canine MSCs (cMSCs) were grown in medium containing low glucose DMEM with 20% FBS. The cMSCs have stem cells expression patterns which are concerned with MSCs surface markers by fluorescence- activated cell sorter analysis. The cMSCs had multipotent abilities. In the neuronal differentiation study, the cMSCs expressed the neuronal markers glial fibrillary acidic protein (GFAP), neuronal class III beta tubulin (Tuj-1), neurofilament M (NF160) in the basal culture media. After neuronal differentiation, the cMSCs expressed the neuronal markers Nestin, GFAP, Tuj-1, microtubule-associated protein 2, NF160. In the osteogenic & chondrogenic differentiation studies, cMSCs were stained with alizarin red and toluidine blue staining, respectively. With osteogenic differentiation, the cMSCs presented osteoblastic differentiation genes by RT-PCR. This finding also suggests that cMSCs might have the ability to differentiate multipotentially. It was concluded that isolated MSCs from canine cord blood have multipotential differentiation abilities. Therefore, it is suggested that cMSCs may represent a be a good model system for stem cell biology and could be useful as a therapeutic modality for canine incurable or intractable diseases, including spinal cord injuries in future regenerative medicine studies.

Transplantation of canine umbilical cord blood-derived mesenchymal stem cells in experimentally induced spinal cord injured dogs

This study was to determine the effects of allogenic umbilical cord blood (UCB)-derived mesenchymal stem cells (MSCs) and recombinant methionyl human granulocyte colony-stimulating factor (rmhGCSF) on a canine spinal cord injury model after balloon compression at the first lumbar vertebra. Twenty-five adult mongrel dogs were assigned to five groups according to treatment after a spinal cord injury: no treatment (CN); saline treatment (CP); rmhGCSF treatment (G); UCB-MSCs treatment (UCB-MSC); co-treatment (UCBG). The UCB-MSCs isolated from cord blood of canine fetuses were prepared as 10⁶ cells/150 µl saline. The UCB-MSCs were directly injected into the injured site of the spinal cord and rmhGCSF was administered subcutaneously 1 week after the induction of spinal cord injury. The Olby score, magnetic resonance imaging, somatosensory evoked potentials and histopathological examinations were used to evaluate the functional recovery after transplantation. The Olby scores of all groups were zero at the 0-week evaluation. At 2 week after the transplantation, the Olby scores in the groups with the UCB-MSC and UCBG were significantly higher than in the CN and CP groups. However, there were no significant differences between the UCB-MSC and UCBG groups, and between the CN and CP groups. These comparisons remained stable at 4 and 8 week after transplantation. There was significant improvement in the nerve conduction velocity based on the somatosensory evoked potentials. In addition, a distinct structural consistency of the nerve cell bodies was noted in the lesion of the spinal cord of the UCB-MSC and UCBG groups. These results suggest that transplantation of the UCB-MSCs resulted in recovery of nerve function in dogs with a spinal cord injury and may be considered as a therapeutic modality for spinal cord injury.

T cell repertoire development in XSCID dogs following nonconditioned allogeneic bone marrow transplantation

Dogs with X-linked severe combined immunodeficiency (XSCID) can be successfully treated by bone marrow transplants (BMT) resulting in full immunologic reconstitution and engraftment of both donor B and T cells without the need for pretransplant conditioning. In this study, we evaluated the T cell diversity in XSCID dogs 4 months to 10.5 years following BMT. At 4 months posttransplantation, when the number of CD45RA+ (naïve) T cells had peaked and plateaued, the T cells in the transplanted dogs showed the same complex, diverse repertoire as those of normal young adult dogs. A decline in T cell diversity became evident approximately 3.5 years posttransplant, but the proportion of Vbeta families showing a polyclonal Gaussian spectratype still predominated up to 7.5 years posttransplant. In 2 dogs evaluated at 7.5 and 10.5 years posttransplant, >75% of the Vbeta families consisted of a skewed or oligoclonal spectratype that was associated with a CD4/CD8 ratio of <0.5. The decline in the complexity of T cell diversity in the transplanted XSCID dogs is similar to that reported for XSCID patients following BMT. However, in contrast to transplanted XSCID boys who show a significant decline in their T cell diversity by 10 to 12 years following BMT, transplanted XSCID dogs maintain a polyclonal, diverse T cell repertoire through midlife.

Marking of peripheral T-lymphocytes by retroviral transduction and transplantation of CD34+ cells in a canine X-linked severe combined immunodeficiency model

A retrovirus vector containing an enhanced green fluorescent protein complimentary DNA (EGFP cDNA) was used to mark and dynamically follow vector-expressing cells in the peripheral blood of bone marrow transplanted X-linked severe combined immunodeficient dogs. CD34(+) cells isolated from young normal dogs were transduced, using a 2 day protocol, with an amphotropic retroviral vector that expressed enhanced green fluorescent protein (EGFP) and the canine common gamma chain (gammac) cDNAs. Following transplantation of the transduced cells, normal donor peripheral blood lymphocytes (PBL) appeared by 1 month post-bone marrow transplant (BMT) and rescued three of five treated dogs from their lethal immunodeficiency. PCR and flow cytometric analysis of post-BMT PBL documented the peripheral EGFP expressing cells as CD3(+) T cells, which varied from 0% to 28%. Sorting of EGFP(+) and EGFP(-) peripheral blood T cells from two dogs, followed by vector PCR analysis, showed no evidence of vector shutdown. EGFP expression in B cells or monocytes was not detected. These marking experiments demonstrate that the transduction protocol did not abolish the lymphoid engraftment capability of ex vivo transduced canine CD34(+) cells and supports the potential utility of the MSCV retroviral vector for gene transfer to XSCID affected canine hematopoietic progenitor cells (HPC).

Isolation and characterization of hematopoietic progenitor cells in canine bone marrow

For ultimate diagnoses of canine leukemia or malignant lymphoma, we sought to isolate hematopoietic progenitor cells (HPCs) from canine bone marrow (BM) using physiological phenotypes. Canine BM cells were separated by equilibrium discontinued density centrifugation, and HPCs, detected by in vitro colony formation, were significantly enriched in the relatively low density (LD) fraction. In flow cytometry, many CD34 or MHC class II expressing cells were detected in the LD fraction, but these were not significantly enriched. When the LD cells were separated, using a cell-sorting method, into cells with high affinity of wheat germ agglutinin (WGAhigh) and cells with WGAlow, almost all multipotent HPCs (MHPCs) and HPCs committed to myeloid lineage were found in the WGAhigh population. When the WGAhigh population was further stained for rhodamin 123, almost all MHPCs were included in the dull population (Rhlow), but not in the bright one (Rhhigh). Morphologically, most Rhlow cells were round, blastic cells containing a large nucleus with nucleoli and narrow cytoplasm. Based on these results, we suggest that all of the MHPCs in canine BM show the Rhlow WGAhigh LD phenotype, and may contain hematopoietic stem cells, which are the primitive HPCs.

Optimized Transduction of Canine Paediatric CD34+ Cells Using an MSCV-based Bicistronic Vector

We have used a murine MSCV-based bicistronic retroviral vector, containing the common gamma chain (gammac) and enhanced green fluorescent protein (EGFP) cDNAs, to optimize retroviral transduction of canine cells, including an adherent canine thymus fibroblast cell line, Cf2Th, as well as normal canine CD34(+) bone marrow (BM) cells. Both canine cell types were shown to express Ram-1 (the amphotropic retroviral receptor) mRNA. Supernatants containing infectious viruses were produced using both stable (PA317) and transient (Phoenix cells) amphotropic virus producer cell lines. Centrifugation (spinfection) combined with the addition of polybrene produced the highest transduction efficiencies, infecting approximately 75% of Cf2Th cells. An average of 11% of highly enriched canine CD34(+) cells could be transduced in a protocol that utilized spinfection and plates coated with the fibronectin fragment CH-296 (Retronectin). Indirect assays showed the vector-encoded canine gammac cDNA produced a gammac protein that was expressed on the cell surface of transduced cells. This strategy may result in the transduction of sufficient numbers of CD34(+) BM cells to make the treatment of canine X-linked severe combined immunodeficiency and other canine genetic diseases feasible.

Anti-bovine CD34 monoclonal antibody reveals polymorphisms within coding region of the CD34 gene

OBJECTIVE

Monoclonal antibodies (mAbs) against CD34 are widely used for purification of CD34+ hematopoietic as well as nonhematopoietic stem/progenitor cells. We produced mAbs against bovine CD34 (boCD34) to facilitate the study of hematopoiesis in cattle.

METHODS

MAbs were produced by immunizing BALB/c mice with BALB/3T3 cells transfected with boCD34 cDNA. Staining of bone marrow mononuclear cells (BMMNCs) from 10 newborn Holstein calves with the mAbs was examined by flow cytometry. The nucleotide sequence of the coding region for boCD34 in each calf was determined after amplification of the cDNA by reverse-transcription polymerase chain reaction (RT-PCR). BoCD34 fusion proteins, each representing one of the boCD34 alleles found to exist in the calves, were expressed in HeLa cells by DNA transfection, and the staining of these proteins with the mAbs was assessed.

RESULTS

One mAb, N21, stained relatively high percentages of BMMNCs from 4 calves but failed to stain those from the other calves. RT-PCR analysis revealed single-nucleotide polymorphisms within the coding region, 3 of which led to amino-acid substitutions. A CD34 mutation experiment indicated that mAb N21 bound to a boCD34 allele with tryptophan at amino acid 167 but not to that with arginine.

CONCLUSION

By using mAb N21 as an allelic cell marker, it would be feasible to detect and isolate boCD34+ cell species derived from N21+ donors in N21- recipients following allogeneic in utero transplantation; this would make cattle potentially useful as large animal models with a unique experimental advantage.

Generation and characterization of bone marrow-derived cultured canine mast cells

Disorders of mast cells, particularly mast cell tumors (MCTs), are common in dogs. There now is evidence that many of these disorders exhibit breed predilections, suggesting an underlying heritable component. In comparison to humans and mice, little is known regarding the biology of canine mast cells. To facilitate the study of mast cell biology in other species, bone marrow-derived cultured mast cells (BMCMCs) often are used because these represent a ready source of large numbers of cells. We have developed a protocol to successfully generate canine BMCMCs from purified CD34(+) cells. After 5-7 weeks of culture with recombinant canine stem cell factor (rcSCF), greater than 90% of the cell population consisted of mast cells as evidenced by staining with Wright's-Giemsa, as well as production of chymase, tryptase, IL-8 and MCP-1. These cells expressed cell surface markers typical of mast cells including Kit, Fc epsilonRI, CD44, CD45 and CD18/CD11b. The canine BMCMCs were dependent on rcSCF for survival and proliferation, and migrated in response to rcSCF gradients. Cross-linking of cell surface-bound IgE induced the release of histamine and TNFalpha. Histamine release could also be stimulated by ConA, compound 48/80, and calcium ionophore. In summary, canine BMCMCs possess phenotypic and functional properties similar to mast cells found in vivo. These cells represent a novel, valuable resource for investigating normal canine mast cell biology as well as for identifying factors that lead to mast cell dysregulation in the dog.