Immunological and pharmacological characterization of poly-DL-alanyl-modified Erwinia carotovora L-asparaginase.

The covalent attachment of poly-DL-alanine peptides to lysyl residues on the surface of Erwinia carotovora L-asparaginase has produced a modified enzyme which is much less immunogenic in mice and demonstrates 100-fold longer plasma half-life in the rhesus monkey. Immunogenic responses towards both the immunoglobulin G (IgG) and immunoglobulin E (IgE) antibody subclasses were evaluated in C57BL x DBA/2 F1 mice exposed to 250 rads of whole-body irradiation 4 hr prior to immunization with 5-diazo-4-oxynorvaline-inactivated native and modified L-asparaginase in complete Freund's adjuvant. Under these immunologically stressful conditions, the native enzyme evoked an IgE and IgG response which could be further amplified by a secondary immunization, whereas the modified enzyme evoked no IgE or IgG response even after a tertiary immunization. In experiments mimicking an intensive therapeutic schedule, whereby two groups of mice were given weekly injections of 5 to 10 units of either native or modified asparaginase for up to 14 weeks, neither enzyme form evoked a significant IgE response, and only the mice given injections of the native enzyme produced an IgG response. In a preliminary patient study, skin testing of a child who had shown an allergic reaction to the native enzyme resulted in a negative response after an intradermal injection of the modified enzyme, whereas a wheal and flare reaction was observed to both the native enzyme and a histamine control. All of these results suggest that the modified enzyme should show a definite reduction in immunological reactions associated with L-asparaginase treatment of childhood leukemia.

Sarcomas induced by injection of simian virus 40 into neonatal CFW mice.

Sarcomas were induced in CFW mice by the iv inoculation of simian virus 40 (SV40) in neonatal animals. Infection with murine malaria parasites, Plasmodium berghei yoelli, decreased the latency and increased the incidence and invasiveness of the tumors. All mice given both SV40 and P. berghei yoelli had sarcomas of the liver and spleen at 9 months of age. At 11 months of age, 70% of the SV40-inoculated mice had sarcomas of the liver indistinguishable from those in the group given both pathogens. Only 1 lung metastasis was seen in the SV40-treated group. The sarcomas contained SV40 T-antigen as revealed by the indirect immunofluorescence technique. Among adult CFW mice given iv injections of SV40, only 2 tumors were found at 11 or 12 months after virus inoculation. Both tumors were in the lungs; 1 was an adenoma and 1 was a papillary adenocarcinoma. Neither gave a positive reaction with the immunofluorescence test.