Effects of species of origin, purification levels, and formulation on insulin immunogenicity.

The immunogenicity of purified pork insulins (PPI) with and without (groups 1 and 2, respectively) trace contamination of beef insulin was contrasted with mixed beef pork insulin of lower purity (MBP, group 3) in 137 patients who had not previously been treated with insulin. Patients and physicians were blinded with regard to the species source of insulin and studies were conducted for a minimum of 1 yr. Antibody development to insulin was assessed by species-specific binding of 125I-insulin by acid charcoal extracted sera, as well as by measurement of insulin prebound to immunoglobulins by a polyethylene glycol precipitation method. NPH- and lente-treated individuals had equivalent antibody responses with regard to the rate of development of antibodies, and maximum immune responses to insulin. In all patient groups, antibody bound insulin as well as species-specific binding of 125I-insulin increased significantly over time (all P less than 0.01 for specific binding of pork and beef insulins SBP and SBB, as well as bound insulin). Maximum bound insulin and SBB as well as bound insulin and SBB over the entire course of the study were significantly greater in group 1 than in group 2 patients (both P less than 0.05). The rate of development and magnitude of antibodies' responses in both PPI-treated groups were significantly less than that seen in the MBP group (all P less than 0.01). New formation of antibeef proinsulin antibodies was seen in one patient from groups 1 and 3, but not in group 2. In all groups, insulin dose per day and fasting serum glucose concentrations increased by about 5 U/day and 10 mg/dl over 1 yr, but groups did not differ. MBP insulin used in these studies proved to be significantly less immunogenic than previously available Argentine pure beef insulin, purified by gel filtration. PPI containing even trace contamination of beef insulin was more immunogenic than PPI alone.