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Efficacy of Combined Immunostimulation and Chemotherapy in Experimental Visceral Leishmaniasis
A regimen of combined immunostimulation and chemotherapy for the elimination of Leishmania donovani amastigotes was evaluated. An in vitro experimental model utilized cultured peritoneal macrophages from C57Bl/6 mice infected with L. donovani tissue forms. Partial or complete activation of macrophages as judged by killing of tumor cells significantly enhanced the efficacy of sodium antimony gluconate (Pentostam®). The quantity of drug required for elimination of parasites from immunostimulated cells was considerably lower than that required to achieve comparable amastigote killing in thioglycolate-elicited macrophages. In contrast, amphotericin B cleared infected cells of amastigotes at comparable drug levels when tested with immunostimulated and unstimulated macrophages. Several drugs tested inhibited the conversion of amastigotes to promastigotes in vitro but were ineffective in killing of intracellular tissue forms. Allopurinol and difluoromethylornithine (DMFO) blocked amastigote conversion significantly. These drugs at high concentrations, however, exerted only minimal toxicity for amastigotes residing within macrophages. Efficacy of combined therapy was also demonstrated in vivo. Immunoenhancement of L. donovani-infected mice with Corynebacterium parvum vaccine combined with a regimen of sodium antimony gluconate was significantly more effective than was immunotherapy or drug therapy alone.