Protection tests using passively administered antibody have been carried out using 2 mouse lymphomata. The classic model (“Gorer System”) used alloantiserum which was absorbed in vivo to make it tumour specific before use. In order to provide a system suitable for our work, the model was changed by stepwise transitions to tumour specific immunoglobulin made from xenoantiserum absorbed in vitro, since such a procedure is also applicable to human patients. The time lapse used between challenge and treatment in the allo-system was generally ± 2 h but in the xeno-system could be extended to + 18 h. The xenoantisera could not be absorbed in vivo but required 3 to 5 × 103 spleens per 100 ml serum to absorb in vitro to render them tumour specific. The protective antibody was in the IgG (not IgM) fraction of serum. Maximal tumour specific antibody (measured by in vivo protection) appeared after the third injection of rabbits for one lymphoma, but after the fifth for another. The sera were not cross-reactive among 3 lymphomata tested, of which 2 were of the same H-2 genotype.
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