Myelofibrosis in the dog: three case reports

Myelofibrosis has been reported infrequently in dogs. The pathological features of three dogs with this disease are described. All three animals were presented clinically with non-regenerative anaemia. In two dogs, the neoplastic disorder was unaccompanied by other myeloproliferative disease and was characterized histologically by extensive replacement of normal bone marrow elements by proliferating reticulum cells and myeloid metaplasia of the enlarged liver and spleen. In one animal, focal myeloid metaplasia were also present in the lungs. In the third dog, myelofibrosis was accompanied by erythraemic myelosis and in this animal immature erythroid cells were present in blood, bone marrow, liver and spleen.     

Clinicopathological features and outcome for dogs with mast cell tumors and bone marrow involvement

BACKGROUND: Mast cell tumors (MCTs) with bone marrow (BM) involvement are poorly documented in dogs and are associated with a poor prognosis. Successful treatment strategies have not been described. HYPOTHESIS: Clinicopathologic findings of affected dogs are not specific. Administration of lomustine or imatinib is beneficial. ANIMALS: Fourteen dogs with MCT and BM involvement. METHODS: Clinical and laboratory evaluations were performed in each dog on admission and during follow-up. All dogs received prednisone. Additionally, 8 dogs received lomustine and 3 dogs received imatinib. Imatinib was administered if tumor-associated tyrosine kinase KIT was aberrant. RESULTS: On admission, 11 dogs had a single cutaneous nodule and 3 dogs had multiple nodules. Involvement of regional lymph nodes, liver, or spleen was observed in each dog. BM infiltration with mast cells (MCs) was observed in all dogs. On CBC, nonregenerative anemia, leukopenia, or thrombocytopenia was common. Four dogs had circulating MCs. Increased alkaline phosphatase or alanine transferase activity was observed in 12 and 10 dogs, respectively. Treatment with lomustine induced partial remission in 1 of 8 dogs. Median survival time was 43 days (range, 14-57). Dogs on imatinib experienced complete remission. Two dogs survived for 117 and 159 days, and the third was alive after 75 days. Dogs treated symptomatically did not improve and were euthanized after 1, 14, and 32 days. CONCLUSIONS AND CLINICAL IMPORTANCE: A combination of clinical and laboratory evaluation helps in identifying dogs with MCT and BM infiltration. Administration of lomustine is not helpful in affected dogs. The beneficial effect of imatinib warrants further investigation.     

Isolation and characterization of pediatric canine bone marrow CD34+ cells

Historically, the dog has been a valuable model for bone marrow transplantation studies, with many of the advances achieved in the dog being directly transferable to human clinical bone marrow transplantation protocols. In addition, dogs are also a source of many well-characterized homologues of human genetic diseases, making them an ideal large animal model in which to evaluate gene therapy protocols. It is generally accepted that progenitor cells for many human hematopoietic cell lineages reside in the CD34+ fraction of cells from bone marrow, cord blood, or peripheral blood. In addition, CD34+ cells are the current targets for human gene therapy of diseases involving the hematopoietic system. In this study, we have isolated and characterized highly enriched populations of canine CD34+ cells isolated from dogs 1 week to 3 months of age. Bone marrow isolated from 2- to 3-week-old dogs contained up to 18% CD34+ cells and this high percentage dropped sharply with age. In in vitro 6-day liquid suspension cultures, CD34+ cells harvested from 3-week-old dogs expanded almost two times more than those from 3-month-old dogs and the cells from younger dogs were also more responsive to human Flt-3 ligand (Flt3L). In culture, the percent and number of CD34+ cells from both ages of dogs dropped sharply between 2 and 4 days, although the number of CD34+ cells at day 6 of culture was higher for cells harvested from the younger dogs. CD34+ cells harvested from both ages of dogs had similar enrichment and depletion values in CFU-GM methylcellulose assays. Canine CD34+/Rho123lo cells expressed c-kit mRNA while the CD34+/Rhohi cells did not. When transplanted to a sub-lethally irradiated recipient, CD34+ cells from 1- to 3-week-old dogs gave rise to both myeloid and lymphoid lineages in the periphery. This study demonstrates that canine CD34+ bone marrow cells have similar in vitro and in vivo characteristics as human CD34+ cells. In addition, ontogeny-related functional differences reported for human CD34+ cells appear to exist in the dog as well, suggesting pediatric CD34+ cells may be better targets for gene transfer than adult bone marrow. The demonstration of similarities between canine and human CD34+ cells enhances the dog as a large, preclinical model to evaluate strategies for improving bone marrow transplantation protocols, for gene therapy protocols that target CD34+ cells, and to study the engraftment potential of various cell populations that may contain hematopoietic progenitor cell activity.     

Clinical and immunological response of lymphoma dogs following chemotherapy and irradiation

The effect of chemotherapy or chemotherapy followed by total body irradiation and autologous bone marrow transplantation on clinical status and lymphocyte function was evaluated in 79 dogs with spontaneous lymphoma. Advanced disease led to the early deaths of 28 dogs (35%), and 24 dogs (30%) administered chemotherapy had a mean survival time of 85 days (range 33–199 days). Survival for eight dogs receiving chemotherapy and BCG was comparable to that produced by chemotherapy only. Thirteen dogs administered chemotherapy followed by irradiation and autologous marrow grafts had survival times ranging from 59 to > 807 days (median 222 days) with median unmaintained clinical remission lasting 151 days. Most treated dogs experienced improvement in health, reduction in lymph node sizes and normalization of liver function. Lymphocyte reactivity to mitogens and streptolysin-O antigen by untreated and treated lymphoma dogs was depressed (P<0.05) compared to response of normal lymphocytes. Mixed leukocyte reactivity of irradiated lymphoma dogs was impaired in the first 150 days post-irradiation and returned to normal values after 150 days. Lymphocyte responses of irradiated normal dogs paralleled those seen in lymphoma dogs. Mixed leukocyte reactivity was not correlated with tumor rejection since eight of nine dogs evaluated following irradiation relapsed during a period of vigorous reactivity to allogeneic stimulating cells.     

Long-term bone marrow culture systems: normal and cyclic hematopoietic dogs.

A continuous long-term liquid culture in both a micro and macro system that incorporates bone marrow cells from normal and cyclic hematopoietic dogs is described. An adherent layer composed of fibroblasts, endothelial cells, mononuclear phagocytic cells, and fat-containing cells is essential for continuous hematopoiesis. Hematopoiesis was measured by the recovery of the nonadherent cells and the generation of committed granulocyte-monocyte progenitor cells for a period of seven weeks. Optimum growth factors include the use of horse serum, fetal bovine serum, dog serum, hydrocortisone, a 33 degrees C incubation temperature and feeding twice a week. As is true for both human and murine marrow liquid cultures, horse serum and hydrocortisone are essential for development and maintenance of fat-containing cells in the described systems. Both factors are important in hematopoiesis but their respective roles have not been defined. Normal and cyclic hematopoietic dogs bone marrow cells are comparable in their ability to establish long-term cultures. The micro-method (Linbro-well culture) gave similar results in maintaining hematopoiesis as did a macromethod (flask culture).     

Secondary myelofibrosis in three dogs

Myelofibrosis was diagnosed in 3 dogs. In each dog, there was evidence of concurrent bone marrow necrosis, suggesting that the myelofibrosis was a secondary change. This suggestion was supported by a lack of dysplastic changes in hematopoietic cells. Bone marrow necrosis in 2 of the dogs may have been the result of widespread malignancy. Reversal of the myelofibrosis in 1 dog suggested that myelofibrosis is not always a terminal disorder.     

Immunophenotypic comparison of blood and lymph node from dogs with lymphoma

Peripheral blood and lymph node tissue from 12 dogs with lymphoma was immunophenotyped. Additionally, the bone marrow was immunophenotyped in 6 dogs. The lymphomas were characterized as B-cell in 11 dogs and T-cell in 1 dog. Immunophenotypic patterns in the peripheral blood and bone marrow were variable. The trend in dogs with B-cell lymphoma was normal to increased percentage of IgG-positive cells, decreased percentage of pan-T-positive cells, decreased percentage of CD4-positive cells, and decreased CD4/CD8 ratio. Simultaneous immunophenotyping of lymph node, blood and bone marrow cannot be recommended routinely without further studies to document its value as an independent prognostic indicator. However, it is potentially useful for tumor staging and monitoring remission, especially in lymphoma patients with a leukemic phase.     

Bone marrow mastocytosis in dogs with myelosuppressive monocytic ehrlichiosis (Ehrlichia canis): a retrospective study

BACKGROUND: Bone marrow mastocytosis has been reported rarely in naturally occurring canine monocytic ehrlichiosis (CME). OBJECTIVES: The aims of the present study were to estimate the prevalence and magnitude of bone marrow mastocytosis in a case series of dogs with natural CME and to assess the association, if any, between mastocytosis and the clinical severity of the disease. METHODS: Seventy-six dogs with confirmed CME (Ehrlichia canis) were included in the study. Affected dogs were allocated into group A (n = 51) without bone marrow hypoplasia and group B (n = 25) with bone marrow hypoplasia. Twenty clinically healthy Beagles not previously exposed to E canis served as controls (group C). The main inclusion criteria for group A were documentation of normocellular to hypercellular bone marrow and complete clinical cure following a 4-week treatment with doxycycline, while those for group B were bone marrow hypoplasia and lack of response to doxycycline. Bone marrow aspirate smears from all 96 dogs were Giemsa-stained and examined for the presence of mast cells, which were calculated as a percentage of 1,000 nucleated cells (NCs). The prevalence of mastocytosis was compared among the 3 groups by the Pearson's chi-square test. RESULTS: Bone marrow mastocytosis (>0.1% of NCs) was found in 5 (20%) dogs in group B (range, 0.5-2.5% of NCs; median, 1% of NCs). One dog in each of groups A and C had 0.1% mast cells in the marrow. The prevalence of bone marrow mastocytosis in dogs in group B was significantly higher (P = .004) than in groups A and C. CONCLUSION: Bone marrow mastocytosis can be seen in a substantial number of dogs with E canis-induced myelosuppression.     

Bone changes in hypercalcemia of malignancy in dogs

Bone was collected for trabecular bone morphometry from 6 dogs with hypercalcemia of malignancy. Five of the dogs had lymphosarcoma and 1 had an anal sac apocrine gland carcinoma with vertebral metastases. Parathyroid gland weights varied around normal, with those for 1 dog being slightly low and those for another dog being moderately increased. As a group, the dogs had decreased bone volume, with increased resorption surfaces and increased numbers of osteoclasts. In 4 dogs, osteoid seams and osteoblasts were limited in extent and this distinguished them from dogs with hyperparathyroidism. Although most dogs had received corticosteroids, chemotherapy, or radiation treatment, the bone changes in these dogs were similar to 1 dog that had not received treatment. Also, the changes could not be related to uremia or renal mineralization that had developed in 2 of the dogs. Two of the dogs had somewhat greater amounts of osteoid-covered surface and slightly widened osteoid seams, ie, findings more like those of hyperparathyroidism. One of these dogs had anal sac apocrine gland carcinoma and the other had lymphosarcoma in which there was invasion of the bone cortex at the sampling site. It was concluded that bone remodeling changes do occur in hypercalcemia of malignancy and that these changes are varied and often are not those of hyperparathyroidism.     

Clinical and pathological findings in dogs following supralethal total body irradiation with and without infusion of autologous long-term marrow culture cells.

We developed a canine model for autologous bone marrow transplantation (AuBMT) with long-term marrow culture (LTMC) cells. Marrow was harvested from nine normal dogs. Harvests from dogs 2-7 were placed into 21 day LTMC. Cells in LTMC from dogs 4-7 were labelled with the neomycin phosphotransferase gene neo. Dogs were given 60Co total body irradiation (TBI) and then infused with LTMC cells: dog 1 received 500 cGy TBI and 2.08 x 10(8)/kg uncultured marrow cells. Dogs 2-7 received 600-800 cGy TBI and 0.07-0.45 x 10(8)/kg LTMC cells. Dogs 8 and 9 received 600 and 800 cGy TBI, respectively, but no infusion of marrow or LTMC cells. For all dogs, profound myelosuppression developed during week 1 and pyrexia developed during week 2. Enrofloxacin was given from one day before TBI until a peripheral neutrophil count > 1.0 x 10(9)/L was achieved, which eliminated Escherichia coli from feces. Dogs 1, 2 and 5-9 also received gentamicin and/or combination beta-lactam antibiotics. Numerous platelet transfusions were needed to control hemorrhages in all dogs except dog 1. Dog 1 achieved neutrophils > 1.0 x 10(9)/L on day 15, while dogs 2 and 5-9 achieved this count on days 33-48. Dogs 3 and 4 died on days 17 and 18, respectively, of beta-hemolytic streptococcal sepsis and hemorrhage, with no evidence of hematopoiesis at necropsy. The marker gene, neo, was documented in lymphoid and myeloid cells of dogs 5-7 up to 21 months post-AuBMT. Our studies indicate that dogs can recover following supralethal TBI and can survive the delayed engraftment associated with AuBMT using LTMC cells, if they receive intensive platelet and antimicrobial therapy. Used prophylactically for such therapy, enrofloxacin achieved selective intestinal decontamination, but did not prevent sepsis when used as the sole antimicrobial agent during myelosuppression. Furthermore, our studies indicate that infused LTMC cells, at the above doses, can contribute to hematopoietic recovery, but are not essential for recovery following TBI, and do not shorten the period of prolonged profound myelosuppression induced by TBI.     

Bone Marrow Cytological Findings in 4 Dogs and a Cat With Hemophagocytic Syndrome

Hemophagocytic syndrome or hemophagic histiocytosis was diagnosed in 4 dogs and 1 cat by evaluation of bone marrow aspirate smears. One of the dogs had a suspected infection with canine parvovirus and a confirmed infection with Salmonella spp, 2 dogs had presumptive diagnoses of myeloproliferative and lymphoproliferative disease, respectively, and 1 dog died without a diagnosis. The cat had hepatic lipidosis and lesions compatible with feline calicivirus infection. All animals had cytopenias involving 2 or more cell lines, and fragmented erythrocytes in the blood, along with mild to moderate increases in the number of macro-phages in the bone marrow. Numerous marrow macro-phages contained phagocytized hematopoietic cells. Other cytological features of the bone marrow were variable in each patient, but the degree of response in the blood was inadequate, even in those with bone marrow hyperplasia. The phagocytosis of hematopoietic elements did not appear to be caused by a primary immune disorder, but rather by the inappropriate activation of normal macrophages secondary to infectious, neoplastic, or metabolic diseases. These findings suggest that hemophagocytic syndrome may be an important factor in the development of cytopenias; the data also support the cytological evaluation of bone marrow aspirates as an aid in the diagnosis of hemophagocytic syndrome. J Vet Intern Med 1996;10:7–14. Copyright © 7996 by the American College of Veterinary Internal Medicine .     

Canine hemophagocytic histiocytic sarcoma: a proliferative disorder of CD11d+ macrophages

Histiocytic disorders of dogs include histiocytoma, localized histiocytic sarcoma (HS), disseminated HS (malignant histocytosis), and the reactive histiocytoses: cutaneous and systemic. A common element to these diseases is proliferation of dendritic cells (DC) of either Langerhans cell (epithelial DC) or interstitial DC lineage. In this report, 17 dogs with hemophagocytic HS are described. Breeds affected included Bernese Mountain Dog (6), Golden Retriever (4), Rottweiler (3), Labrador Retriever (2), a mixed-breed dog, and a Schnauzer, which were from 2.5 to 13 years old. The dogs presented with Coombs negative responsive anemia in 16/17 dogs (94%), thrombocytopenia in 15/17 dogs (88%), hypoalbuminemia in 16/17 dogs (94%), and hypocholesterolemia in 11/16 dogs (69%). All dogs died or were euthanized. The clinical course ranged from 2 to 32 weeks (mean 7.1 weeks). Diffuse splenomegaly with ill-defined masses was consistently present. Microscopic lesions were prevalent in spleen, liver, lung, and bone marrow. Metastasis occurred by insidious intravascular invasion with minimal mass formation. Histiocytes were markedly erythrophagocytic and accompanied by foci of extramedullary hemopoiesis. Cytologically, the histiocytes varied from well differentiated to atypical, with atypia more prevalent in spleen than bone marrow. These tumors arose from splenic red pulp and bone marrow macrophages, which expressed major histocompatibility complex class II and the beta2 integrin, CD11d. They had low and/or inconsistent expression of CD1 and CD11c, which are dominantly expressed by canine nonhemophagocytic HS of DC origin. Canine histiocytic proliferative diseases now encompass proliferation of all members of the myeloid histiocytic lineage: Langerhans cells, interstitial DC, and macrophages.     

Use of multigeneration-family molecular dog leukocyte antigen typing to select a hematopoietic cell transplant donor for a dog with T-cell lymphoma

CASE DESCRIPTION: A 7-year-old Golden Retriever was examined because of anorexia, lethargy, vomiting, and gradual weight loss. CLINICAL FINDINGS: Splenomegaly, pancytopenia, high serum calcium concentration, and high alkaline phosphatase activity were detected. Magnetic resonance imaging revealed an enlarged mesenteric lymph node and increased signals from the bone marrow of the ilium and vertebral bodies. Histologic examination and immunophenotyping of biopsy specimens confirmed a stage V (b) T-cell malignant lymphoma. TREATMENT AND OUTCOME: Clinical remission was attained by use of 2 chemotherapy cycles, followed by an allogeneic hematopoietic cell transplant performed at 18 weeks after diagnosis. A donor was identified by molecular dog leukocyte antigen typing methods. The patient was conditioned with 2 fractions of 4 Gy total body irradiation delivered 3 hours apart at 7 cGy/min, followed by an IV infusion of recombinant canine granulocyte colony-stimulating factor mobilized leukapheresis product and postgrafting immunosuppression with cyclosporine. Chimerism analyses revealed full donor engraftment that has been maintained for at least 58 weeks after transplant. Remission has been confirmed by normal results of serum thymidine kinase assays and the absence of peripheral blood clonal T-cell receptor gene rearrangements. CLINICAL RELEVANCE: Systemic chemotherapy induces remissions; however, most dogs succumb to disease recurrence because of multidrug resistance. Outcome of allogeneic hematopoietic cell transplantation in dogs can be excellent because of improved donor-recipient selection by use of molecular dog leukocyte antigen typing, compared with early attempts, and better prevention of graft versus host disease, better supportive care, and substitution of peripheral blood mononuclear cells for bone marrow.     

Hematologic changes associated with Adderall toxicity in a dog

A 1-year-old intact male Boxer was presented to the Texas Veterinary Medical Center for emergency treatment following suspected ingestion of a large number of tablets of Adderall, a pharmaceutical amphetamine. The dog had a temperature of 41.7 degrees C, heart rate of 192 beats per minute, and a respiratory rate of 100 breaths per minute. The dog was anxious and agitated with bilaterally dilated pupils, and shortly thereafter became recumbent and incontinent. Initial CBC results included mild leukopenia and mild thrombocytopenia. The dog was not anemic (HCT 39.9%) and had only slight polychromasia, but had 48 nucleated RBCs/100 WBC (7500/microL). Moderate numbers of neutrophils had hypersegmented nuclei and several pyknotic cells were noted. The metarubricytosis persisted for approximately 56 hours while hypersegmentation and pyknotic cells were no longer found at 8 hours after presentation. The dog received supportive care and recovered uneventfully. We hypothesized that hyperpyrexia associated with Adderall toxicity resulted in inappropriate metarubricytosis due to damaged bone marrow endothelium, and resulted in hypersegmentation and pyknosis due to damaged or accelerated aging of neutrophils in peripheral blood. Metarubricytosis has been reported previously in dogs with heat-induced illness, such as heat stroke.     

Canine leishmaniasis chemotherapy: dog's clinical condition and risk of Leishmania transmission

The aim of this study was to investigate whether treatment against canine leishmaniasis reduced the presence of Leishmania in the healthy skin of dogs, affecting the capacity of parasite transmission. A total of 37 dogs from an endemic region of leishmaniasis were studied. Thirteen symptomatic animals revealed parasites in the bone marrow and eight had also in the skin. Five of the 22 dogs that had been treated with meglumine antimoniate alone, meglumine antimoniate or trifluralin followed by allopurinol or just with allopurinol had the parasite in bone marrow but none showed Leishmania in the skin. One dog that was treated only with aminosidine was polisymptomatic and had parasites in bone marrow and skin. The different treatments used in this study did not completely eliminate the parasite allowing relapses to occur when the treatment is discontinued, but the use of meglumine antimoniate or allopurinol, alone or combined may improve dogs clinical condition and reduce or eliminate the parasite from the skin decreasing the probability of Leishmania transmission.     

A Solitary Plasmacytoma in a Dog with Progression to a Disseminated Myeloma

Solitary plasmacytomas are rare occurrences in dogs, consequently their potential for malignancy is undetermined. A solitary plasmacytoma was removed from the perianal region of a dog. The dog was clinically normal at that time, but was killed one year later as a result of hind limb stiffness and uremia. At the postmortem examination a disseminated myeloma was found, involving the vertebral column, liver, spleen, bone marrow and visceral lymph nodes.     

Effect of chronic lead exposure on the canine bone marrow

The effect of chronic oral led acetate administration on canine bone marrow was studied. Two dogs (group 1) were used as controls, 4 dogs (group 2) were given 2 mg of lead/kg of body weight daily, and 4 dogs (group 3) were given 5 mg of lead/kg daily. After a 7-day stabilizaion period, lead dosing was conducted for 91 days (13 weeks), after which half of each group was treated with calcium ethylenediaminetetraacetic acid. All dogs were then observed for another 28 days (4 weeks). Blood lead values and bone marrow cellular changes were monitored once a week during the 126 days (18 weeks) of study. Lead-dosed dogs had lower weight gains than the controls. Clinical signs of toxicosis were observed after 6 weeks in one dog in group 3. Anorexia, body weight loss, CNS depression, muscular weakness, and trembling were seen. Blood lead concentrations increased in all group 2 and 3 dogs. Lead caused increases in bone marrow segmented neutrophils and myeloid series cells, and increased myeloid:erythroid ratios. Blood lead concentrations and myeloid:erythroid ratios decreased after cessation of lead administration.     

Acquired amegakaryocytic thrombocytopenia--four cases and a literature review

Acquired amegakaryocytic thrombocytopenla was diagnosed in four dogs. Initial platelet counts in all four dogs were less than 50,000 x 10(9)/litre and initial bone marrow examinations revealed megakaryocytic hypoplasia with minimal changes in the erythroid and myeloid cell lines. Two dogs had evidence of idiopathic immune-mediated disease and two dogs had evidence of associated infectious disease. One dog had a positive antibody titre to Borrella burgdorferi, and one dog had positive titres to both Ehrlichia canis and B. burgdorferi. Treatment consisted of prednisone and cyclophosphamide for the dogs with presumptive immune-mediated disease, and prednisone and tetracycline for the dogs with positive antibody titres to the Infectious organisms. Both dogs with evidence of associated infectious disease responded to treatment. A postmortem examination did not reveal the underlying aetiology in the two dogs with presumptive idiopathic immune-mediated disease.     

Visceral leishmaniasis in the German shepherd dog. II. Pathology

Three German shepherd dogs were inoculated with Leishmania chagasi and three with Leishmania donovani and the infection was followed for 82 days. All infected dogs developed splenomegaly and lymphadenomegaly. In lymph nodes there was a reduction in lymphocyte population in paracortical areas, extensive proliferation of macrophages in paracortical areas and medullary cords, follicular hyperplasia, and increased numbers of plasma cells. The spleen had decreased numbers of lymphocytes in periarteriolar lymphoid sheaths, proliferation of macrophages in these regions, follicular hyperplasia, and enlargement of the red pulp with clusters of macrophages and plasma cells. The morphology of the tonsil was similar to the lymph nodes. Clusters of macrophages, often containing Leishmania spp, were present in liver, bone marrow, lung, and the intestines. The morphologic changes in lymph nodes and spleen were suggestive of a suppressed cell-mediated immunity and an active humoral immunity. The German shepherd dog may be a useful laboratory model for the study of immunopathologic changes in visceral leishmaniasis.     

Renal Allograft Survival in Outbred Mongrel Dogs Using Rabbit Anti-Dog Thymocyte Serum in Combination With Immunosuppressive Drug Therapy With or Without Donor Bone Marrow

Therapeutic renal transplantation in dogs is currently being investigated as a treatment for end-stage renal disease. This pilot study examines the effect of donor bone marrow (DBM) infusion and antithymocyte serum (ATS) in combination with immunosuppressive drug therapy in prolonging renal allograft survival in dogs. Seven normal outbred mongrel dogs received an unmatched renal allograft. All dogs received rabbit anti-dog thymocyte serum (RADTS), prednisone (Pr), cyclosporine-A (CsA) and azathioprine (Aza). In addition, three dogs (group 1 test) received DBM and four dogs (group 2 control) did not receive DBM. Serum CsA levels were measured throughout the study. Immunosuppressive therapy was gradually reduced with Pr, CsA, and Aza withdrawn at 200,450, and 680 days, respectively. Allograft rejection was treated with prednisolone sodium succinate. One dog in group 1 and one in group 2 died as a result of infectious canine rhinotracheitis and rejection early in the study. Renal allograft torsion occurred in one group 1 dog. The remaining four dogs survived the 2 years of the study. The dogs in group 2 (three dogs) all rejected the renal allograft after total drug withdrawal, the surviving dog in group 1 did not. This study demonstrates that RADTS, Pr, CsA, and Aza in combination can prolong renal allograft survival in mongrel dogs, whereas DBM may enhance the unresponsive state.