211At-AntiCD33 in NMRI nu/nu mice

SummaryThe aim of this study is to verify the in vivo stability, to determine the biodistribution and to estimate the unspecific radiotoxicity of an 211At-labelled CD33-antibody (211At-anti-CD33) in mice with a view to therapeutic application in treating leukaemia. Animals, methods: 211At was produced via the 209Bi(α,2n)211At reaction and was linked via 3-211At-succinimidyl-benzoate to the anti-CD33-antibody. The biodistribution and the in vivo stability in serum were determined after i.v.-injection in NMRI nu/nu-mice. For toxicity experiments, mice received either three times 315–650 kBq 211At-antiCD33 or unlabelled antibody and NaCl-solution respectively. Results: 211At-antiCD33 showed a characteristic biodistribution complying with the unspecific antibody retention in the reticular endothelial system. The largest proportion of radioactivity remained in blood and blood-rich tissues with a minor accumulation in the thyroid and stomach. After 21 h, > 85% of activity in serum still represented intact antibody. Mice showed no difference in unspecific toxicity of 211At-labelled antibodies over six months compared to those treated with unlabelled antibody and NaCl-solution respectively, with regard to histopathologic lesions, survival time, behaviour and haemograms. Conclusion: The radiolabelling method yielded adequate in vivo stability of 211At-antiCD33. Biodistribution with rapid elimination of free 211At via kidneys and urine complies with requirements for targeted therapy. Activity doses potentially required for treatment do not elicit radiotoxicity to normal organs in mice. Further development is required to enhance the apparent specific activity and to verify the efficacy in an adequate animal model before phase I clinical studies in leukaemia can be envisaged.

Immunocytochemical identification of leishmania and Trypanosoma cruzi amastigotes in situ with homologous and heterologous polyclonal antibodies

The unlabelled antibody peroxidase-antiperoxidase method was used to study the immunocytochemical properties of Leishmania and Trypanosoma cruzi amastigotes in situ after tissues had been submitted to different fixation procedures. Antisera were obtained from rabbits chronically infected with different strains of T. cruzi or immunized with L. mexicana amazonensis and L. braziliensis guyanensis, and were applied on 5 µm thick sections. T. cruzi antigens were well stained by the three anti-T. cruzi sera and the two anti-heis.hmama.sera at optimum dilution between 1:1,000 and 1:2,000, regardless the parasite strain. Differently, the leishmanial antigens were revealed by Leishmania sera only at low dilutions (between 1:60 -1:160), whereas the anti-T. cruzi sera, at these low dilutions, gave rather weak stainings. Although there is no clear explanation for this immunocytochemical "reverse-monodirectional" cross-reactivity between Leishmania and T. cruzi, the present results show that polyclonal antibodies agains Leishmania species, when used for immunocytochemical detection of these parasites in situ, react more strongly with T. cruzi amastigotes than with the homologous amastigotes.

Antigen production by encysted muscle larvae of Trichinella spiralis

The production of excretory-secretory antigens by encysted muscle larvae of Trichinella spiralis has been investigated immuno-histochemically using an antiserum raised by infection in rabbits and purified both before and after conjugation by ion-exchange chromatography. The specificity of the antibody for excretory-secretory products was demonstrated by the pattern of staining of live worms in vitro and the failure of the labelled antibody to stain dead, non-metabolizing worms. Using this labelled antibody, and unlabelled antibody in the immunoperoxidase system, the presence of parasite antigen-bearing cells in close proximity to encysted muscle larvae has been demonstrated. This is believed to be the first demonstration of antigen production by encysted muscle larvae in vivo. The implications of this observation to current concepts of immunity to Trichinella spiralis are discussed.