Protection of Killer Antiidiotypic Antibodies against Early Invasive Aspergillosis in a Murine Model of Allogeneic T-Cell-Depleted Bone Marrow Transplantation

Abstract

Antiidiotypic monoclonal antibodies (MAbs) representing the internal image of a yeast killer toxin (KT)have therapeutic potential against several fungal infections. The efficacy of KT MAbs against Aspergillus fumigatus was investigated in a mouse model of T-cell-depleted allogeneic bone marrow transplantation (BMT) with invasive pulmonary aspergillosis. Mice were highly susceptible to infection at 3 days post-BMT, when profound neutropenia was observed both in the periphery and in the lungs. Treatment with KT MAbs protected the mice from infection, as judged by the long-term survival and decreased pathology associated with inhibition of fungal growth and hyphal development in the lungs. In vitro, similar to polymorphonuclear neutrophils, KT MAbs significantly inhibited the hyphal development and metabolic activity of germinated Aspergillus conidia. These results indicate that mimicking the action of neutrophils could be a strategy through which KT MAbs exert therapeutic efficacy in A. fumigatus infections.Invasive fungal infections remain a major problem for bone marrow (BM) transplant (BMT) recipients (35,45). Mortality from opportunistic fungal infections exceeds 50% in most studies and has been reported to be as high as 95% in allogeneic BMT recipients with Aspergillus sp. infection, despite aggressive antifungal therapy (4).Studies in vitro and in animal models have indicated that the innate defenses are primarily responsible for the elimination of inhaled conidia from the lungs (10,13,19,38). Early fungal clearance is mediated by a dual phagocytic system involving both alveolar macrophages and recruited polymorphonuclear leukocytes capable of efficiently opposing fungal infectivity at the level of conidia or hyphal forms (37). However, the killing of phagocytosed conidia by mononuclear cells is a slow process that occurs with a low killing rate and depends on the immunocompetence of effector monocytes (19). Moreover, the finding that the conidiocidal activity of monocytes in both clinical disease and experimental chronic granulomatous disease is largely unaffected (26) reveals the unique importance of neutrophil activity against germinating conidia and hyphae in the control of aspergillosis.Human studies have shown that prolonged neutropenia is one of the most important factors predisposing to invasive aspergillosis (35,45). However, the efficacy of immunotherapies aimed at both shortening the duration of neutropenia and restoring neutrophil antifungal activity has been limited by problems associated with the transfusion therapy, including the still uncertain efficacy of colony-stimulating factors (34) and the limited persistence of the transfused cells (16). It appears that strategies aimed at keeping the infection in check until the recovery of adequate innate antifungal activity are needed for prompt handling of the fungus by the host.Recent studies have highlighted the therapeutic potential of killer antiidiotypic antibodies in several fungal infections (23). Antiidiotypes to a monoclonal antibody (MAb)...

The Contribution of the Toll-Like/IL-1 Receptor Superfamily to Innate and Adaptive Immunity to Fungal Pathogens In Vivo

“…In the case of Candida hyphae, the antifungal effector activity of PMNs from uninfected mice was significantly increased in TLR4-and TLR9-deficient mice and was impaired in MyD88-and IL-1RI-deficient mice. Because cytokine production during the infection may have an impact on the antifungal functions of PMNs, and TNF-␣ is known to selectively impair the activity of PMNs against Candida hyphae (43), the effector function of PMNs was also assessed in the presence of TNF-␣. The ability of hyphal damage was greatly reduced by TNF-␣ in TLR4-deficient PMNs and was slightly reduced in PMNs from TLR9-deficient or wild-type mice.…”

“…The number of CFUs and the percentage of CFU inhibition (mean Ϯ SE), referred to as candidacidal or conidiocidal activity, were determined as previously described (5,25). For the fungicidal activity against hyphae, a colorimetric MTT assay was used as previously described (42,43). Briefly, graded numbers of PMNs (10 6 , 5 ϫ 10 5 , and 10 5 ), either unexposed or pre-exposed for 2 h at 37°C to 10 ng/ml rTNF-␣ (R&D Systems, Space Import-Export, Milan, Italy), were added to hyphae obtained from 10 5 yeasts in 96-well, flat-bottom microtiter plates.…”

The protective role of immunoglobulins in fungal infections and inflammation

“…Killer anti-idiotypic MAb bearing the internal image of a yeast killer toxin showed protection against early invasive aspergillosis in a murine model of allogenic T-celldepleted bone marrow transplantation [150]. In addition, natural yeast KT-like antibodies with candidacidal properties were also identified in the vaginal fluid of candida infected human vaginitis patients [151].…”

Requirement for Neutralizing Antibodies to Control Bone Marrow Transplantation-Associated Persistent Viral Infection and to Reduce Immunopathology

“…Immunotherapy has been proposed recently as an alternative and effective means of pathogen control after BMT. Transfer of viral-specific CD8 ϩ T cells has been used to treat patients suffering from infection with CMV (22)(23)(24) or EBV (25,26), and Ab transfer was demonstrated to abrogate aspergillosis in an experimental model of BMT (27).…”