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A variety of immune cell activators can enhance the cytotoxic effects of monocytes/macrophages including interferon-gamma (IFN-gamma) and muramyl peptides, which are under investigation for cancer therapy in humans and dogs. Pulmonary alveolar macrophages (PAMs) in particular, are strategically located within the lung and provide a potential defense against cancer cells metastatic to the lung. For this reason, we examined the in vitro cytotoxic potential of fresh and IFN-gamma-activated PAMs from normal dogs targeted to canine malignant melanoma cells with antiganglioside monoclonal antibodies (mAbs). Antiganglioside mAbs 14.G2a (anti-GD2) and R24 (anti-GD3), both in clinical trials for human neuroectodermal tumors including melanoma, significantly enhanced the cytotoxicity of canine melanoma mediated by canine PAMs. Further, the cytotoxicity mediated by recombinant canine IFN-gamma-activated canine PAMs, in combination with anti-GD2 ganglioside mAb 14.G2a, enhanced melanoma cytotoxicity above that seen with mAb 14.G2a alone. This documentation of antibody-dependent cellular cytotoxicity mediated by activated PAMs suggests that activation and targeting of resident pulmonary immune cells be pursued as a means to control pulmonary metastases.

In 33 healthy dogs, 66 bronchoalveolar lavage samples from the right and left caudal lung lobes were analyzed for volume of return, cellularity, differential cellularity, and immunophenotypic lymphocyte subpopulations. Lavage return was 64.8% (mean) following 3 sequential 25-ml lavages, for a total lavage volume of 75 ml. With this technique, 21.1 x 10(6) cells/sample (mean) were obtained. The cellular components of bronchoalveolar lavage samples, in decreasing order of frequency, were alveolar macrophages (79.4%), lymphocytes (13.5%), eosinophils (3.6%), mast cells (2.1%), epithelial cells (0.8%), and neutrophils (0.6%). Mean alveolar lymphocyte subpopulation frequencies, determined in 18 samples, for pan T, CD4, and CD8 cells were 52, 21.9, and 17.8%, respectively, with a CD4/CD8 ratio of 1.3. Variables analyzed did not vary between right and left caudal lung lobes, nor were they affected by body weight.

The effect of human recombinant interleukin-2 (IL-2) on serum thyroid hormone concentrations in dogs was studied. Four normal adult dogs received two consecutive weekly cycles of continuous infusions of 3 x 10(6) U m-2 daily for four days per week (days 1 to 4 and 8 to 11). The serum concentrations of IL-2, thyroxine (T4) and 3, 5, 3'-triiodothyronine (T3) were measured before and on days 2, 3 and 4, and 9, 10 and 11 of the infusions. There was a significant decrease in the mean serum concentrations of T4 and T3 at all times during the infusion of IL-2; the serum T4 concentrations decreased by 50 to 75 per cent and serum T3 by 70 to 80 per cent of the pretreatment concentrations in all the dogs. No antithyroglobulin antibodies were detected in the serum of any of the dogs on days 10 and 11 of the infusions. The concentrations of circulating thyroid hormones decreased rapidly in the dogs during the infusion of IL-2, as in the euthyroid sick syndrome.

Human tumors originating from neuroectodermal cells such as malignant melanoma and neuroblastoma express high levels of disialogangliosides GD2 and GD3, making these antigens ideal for targeting by monoclonal antibodies (Mabs). The purpose of this study was to investigate expression and targeting of gangliosides on canine melanoma. Using immunohistochemical methods, we analyzed the expression of disialogangliosides GD2 and GD3 on canine oral malignant melanomas with murine Mabs 14.G2a and R24 that recognize GD2 and GD3 disialogangliosides, respectively, on human tumors. We also assessed the ability of Mab 14.G2a (and its mouse-human chimera, ch 14.18) to mediate antibody-dependent cellular cytotoxicity (ADCC) in vitro against a canine malignant melanoma cell line with human recombinant interleukin-2 (IL-2) activated canine peripheral blood lymphocytes (PBL), or canine neutrophil effector cells. Our data show that Mabs 14.G2a and R24 recognized fresh frozen canine oral melanoma. Mabs 14.G2a or ch 14.18, or IL-2, potentiated lysis of the canine malignant melanoma cell line by canine PBL. The killing effect observed using the combination of either Mab with IL-2 was additive. Mab 14.G2a mediated potent ADCC of canine melanoma by canine neutrophils. These studies indicate that disialogangliosides are expressed on fresh canine melanoma cells. Mabs reactive with these antigens can target and trigger tumor killing by multiple canine effector populations and IL-2 can potentiate these effects by canine lymphocytes. Thus, canine oral malignant melanoma, a spontaneously occurring, metastatic cancer in the dog, may be a relevant animal model to investigate combination immunotherapy using antitumor Mab and IL-2.

Interleukin-2 (IL-2) is an immunostimulatory cytokine that induces activation of peripheral blood lymphocytes (PBL) which can mediate augmented tumor cytotoxicity. Several regimens using IL-2 as treatment for metastatic melanoma and renal carcinoma have shown measurable tumor responses in 10-20% of human patients. Our overall goals are to determine the efficacy of IL-2 as an adjuvant treatment for canine tumors. In order to evaluate the possibility to extend the use of IL-2 in vivo in the dog, we examined the ability of a clinically relevant (low) dose of human recombinant IL-2 (100 units/ml) to enhance the tumoricidal properties of canine PBL in vitro. This was particularly important considering the need to establish the effects on canine PBL by IL-2 at a dose that is potentially achievable in vivo with acceptable side effects. Our data show, for the first time, the ability to separate canine natural killer (NK) cell activity from lymphokine-activated killer (LAK) cell activity (induced with a low IL-2 dose) mediated by canine PBL against two canine cell lines (CTAC and CML-10) used as targets in 4 vs. 16 hour killing assays. LAK cells generated by stimulation of canine PBL with 100 units/ml of IL-2 for 72 hours, could kill CTAC or CML-10 targets up to 11 or 18 times more efficiently, respectively, than fresh PBL in a 4 hour assay. However, the killing of efficiency of the LAK cells was only 2- to 3-fold greater than that of the fresh PBL in a 16 hour assay. This apparent reduction in the killing efficiency of the LAK cells was mostly due to increased spontaneous NK activity by the fresh PBL after 16 hours in culture; both the LAK cells and the fresh PBL (NK cells) mediated a greater overall cytotoxicity after 16 hours than they did in the 4 hour assays. These results indicate that a low dose of human recombinant IL-2 can augment tumor killing by canine PBL in vitro, and suggest that it may be feasible to examine the potential use of IL-2 as an immunotherapeutic agent in tumor-bearing dogs.

Four normal adult dogs received two consecutive weekly cycles of human recombinant interleukin-2 (IL-2) by continuous infusion for 4 days/week. The dose of IL-2 given to each dog was 3 x 10(6) units m-2 day-1. Toxicities consisted of mild vomiting, diarrhea, and lethargy to varying degrees in all the dogs. These side-effects were reversed when the treatment was discontinued. Fever, tachypnea, and weight gain were not seen. A marked lymphocytosis and eosinophilia developed in all dogs after completion of each course of IL-2 (resulting in a more than sevenfold increase in each cell type) and persisted for more than 1 month in some. Fresh peripheral blood lymphocytes (PBL) obtained during this lymphocytosis mediated enhanced in vitro lysis of a natural-killer-cell-sensitive canine tumor cell line (CTAC). The in vitro proliferative responses of these same PBL to IL-2 could be detected earlier, progressed faster, and involved more cells than PBL tested prior to IL-2 infusion. Thus, a relatively well-tolerated regime of IL-2 in dogs can induce dramatic increases in lymphocyte numbers and activation, which is associated with augmentation of their in vitro antitumor reactivity. The clinical effectiveness of this immunotherapeutic approach remains to be tested in tumor-bearing dogs where it could serve as a relevant large-animal model for immunotherapy of cancer with IL-2.

The protective effect of methimazole, a commonly used antithyroid drug, on cisplatin-induced nephrotoxicity was studied. Eight dogs received 80 mg/m2 cisplatin i.v. without saline prehydration. Dogs were randomized into two groups of four dogs each: one group received 40 mg/kg methimazole i.p. at 30 min prior to and 4 h after cisplatin delivery, and the other group received saline placebo i.p. Methimazole protected dogs against the in vivo nephrotoxicity elicited by cisplatin as evidenced by clinicopathologic and histopathologic indices. Protection was not complete, as methimazole-treated animals developed mild histopathologic renal changes. Measures of renal oxidative stress did not differ between the two groups at day 5 following cisplatin treatment. No difference was noted for serum thyroxine concentrations before or after therapy in either group; however, serum levels of 3,5,3'-triiodothyronine were significantly higher on day 5 in both groups of dogs receiving cisplatin, regardless of whether they received methimazole or not. Methimazole as used in this study was found to be well tolerated in dogs over the short term, with no significant clinical or clinicopathologic toxicity being observed. The results of this study support the additional evaluation of methimazole as a protectant against cisplatin-induced nephrotoxicity using the dog as a model.

T cells respond to peptide antigen in association with MHC products on antigen-presenting cells (APCs). A number of accessory or costimulatory molecules have been identified that also contribute to T cell activation. Several of the known accessory molecules are expressed by freshly isolated dendritic cells, a distinctive leukocyte that is the most potent APC for the initiation of primary T cell responses. These include ICAM-1 (CD54), LFA-3 (CD58), and class I and II MHC products. Dendritic cells also constitutively express the accessory ligand for CD28, B7/BB1, which has not been previously identified on circulating leukocytes freshly isolated from peripheral blood. Dendritic cell expression of both B7/BB1 and ICAM-1 (CD54) increases after binding to allogeneic T cells. Individual mAbs against several of the respective accessory T cell receptors, e.g., anti-CD2, anti-CD4, anti-CD11a, and anti-CD28, inhibit T cell proliferation in the dendritic cell-stimulated allogeneic mixed leukocyte reaction (MLR) by 40-70%. Combinations of these mAbs are synergistic in achieving near total inhibition. Other T cell-reactive mAbs, e.g., anti-CD5 and anti-CD45, are not inhibitory. Lymphokine secretion and blast transformation are similarly reduced when active accessory ligand-receptor interactions are blocked in the dendritic cell-stimulated allogeneic MLR. Dendritic cells are unusual in their comparably higher expression of accessory ligands, among which B7/BB1 can now be included. These are pertinent to the efficiency with which dendritic cells in small numbers elicit strong primary T cell proliferative and effector responses.