OBJECTIVES: Several case reports have described complete hematological remissions for patients with otherwise untreated acute myelogenous leukemia (AML) who receive hematopoietic growth factor therapy during complicating bacterial infections. This may be caused by indirect cytokine effects, but direct effects of infecting agents on the malignant cells are also possible because bacterial molecules can bind to specific receptors expressed by normal and malignant leukocytes. Lipoteichoic acid (LTA) is a cell wall component of gram-positive bacteria, and it can activate normal immunocompetent cells through binding to specific cell membrane receptors. METHODS: We investigated effects of LTA derived from Enterococcus faecalis on in vitro cultured (i) normal peripheral blood mononuclear cells (PBMC); (ii) remaining T cells derived from patients with hematologic malignancies and chemotherapy-induced leukopenia; and (iii) native human AML cells. RESULTS: Increased interleukin 1beta (IL1beta) and IL8 release by in vitro cultured normal PBMC was observed after stimulation with LTA at concentrations > or =5 microg/mL; these levels were lower than for lipopolysaccharide (LPS)-stimulated cells and LTA antagonized LPS-induced cytokine release by normal PBMC. In most cases LTA did not alter T-cell proliferation for patients with chemotherapy-induced leukopenia. The LTA effects on AML blasts were investigated for 62 consecutive patients. LTA altered either cytokine (granulocyte-macrophage colony-stimulating factor + stem cell factor + IL3)-dependent proliferation or the release of IL1beta/IL8 for 23 patients; the effects were divergent but increased proliferation/cytokine levels were most commonly observed. CONCLUSION: The LTA derived from E. faecalis can modulate the functional characteristics of normal leukocytes and native human AML blasts.
OBJECTIVES: Several case reports have described complete hematological remissions for patients with otherwise untreated acute myelogenous leukemia (AML) who receive hematopoietic growth factor therapy during complicating bacterial infections. This may be caused by indirect cytokine effects, but direct effects of infecting agents on the malignant cells are also possible because bacterial molecules can bind to specific receptors expressed by normal and malignant leukocytes. Lipoteichoic acid (LTA) is a cell wall component of gram-positive bacteria, and it can activate normal immunocompetent cells through binding to specific cell membrane receptors. METHODS: We investigated effects of LTA derived from Enterococcus faecalis on in vitro cultured (i) normal peripheral blood mononuclear cells (PBMC); (ii) remaining T cells derived from patients with hematologic malignancies and chemotherapy-induced leukopenia; and (iii) native humanAML cells. RESULTS: Increased interleukin 1beta (IL1beta) and IL8 release by in vitro cultured normal PBMC was observed after stimulation with LTA at concentrations > or =5 microg/mL; these levels were lower than for lipopolysaccharide (LPS)-stimulated cells and LTA antagonized LPS-induced cytokine release by normal PBMC. In most cases LTA did not alter T-cell proliferation for patients with chemotherapy-induced leukopenia. The LTA effects on AML blasts were investigated for 62 consecutive patients. LTA altered either cytokine (granulocyte-macrophage colony-stimulating factor + stem cell factor + IL3)-dependent proliferation or the release of IL1beta/IL8 for 23 patients; the effects were divergent but increased proliferation/cytokine levels were most commonly observed. CONCLUSION: The LTA derived from E. faecalis can modulate the functional characteristics of normal leukocytes and native humanAML blasts.