Human IgM monoclonal antibody 16.88: pharmacokinetics and distribution in mouse and man.

Human IgM monoclonal antibody (MAb) 16.88 recognizes an antigen strongly expressed by colon cancer tissue. We used 131I-labelled 16.88 for biodistribution and pharmacokinetic studies in nude mice bearing WiDr or NIH:OVCAR-3 xenografts. Serum half-life was 8 h. Maximum tumour uptake was between 1 and 8 h after administration and amounted to, respectively, 3% and 1% of the injected dose g-1 for WiDr and NIH:OVCAR-3 tumours. Half-lives in these tumours were approximately 24 h. Tumour to normal colon uptake ratios increased from 2.3 at 24 h to 17 at 5 days after injection. Simultaneously, pharmacokinetic studies were performed in patients with advanced colon cancer reactive with 16.88. They were injected with 5 mCi 131I-16.88 by intravenous infusion over 2 h. Serum half-life was 20 h with greater than 90% of the 131I bound to 16.88. Within 40 h 50% of the injected dose was excreted as free 131I in the urine. In one patient an accelerated clearance was found, possibly caused by pre-existing antibodies reacting with 16.88. None of the patients showed an immune response against 16.88 antibody. Immunoscintigraphy showed positive tumour localization in the majority of the patients, best visualized at later days. We conclude that 16.88 has tumour localization properties while its human origin accounts for the lack of immunogenicity.