The development of anti-interleukin-2 (IL-2) antibodies in cancer patients treated with recombinant IL-2

Serum samples from 217 cancer patients participating in phase I/II clinical trials were analysed for the development of anti-interleukin-2 (IL-2) antibodies. Patients received recombinant human IL-2 (rIL-2) by continuous intravenous infusion (c.i.v.; n = 86) or by subcutaneous (s.c.) injections (n = 131). Both patient groups developed anti-rIL-2 antibodies as detected by ELISA with similar frequencies and titres: 52% (median titre, 23) and 47% (median titre, 24), respectively. Using an IL-2-dependent T-cell proliferation assay, sera from 5 c.i.v.-treated patients (6%) and 13 s.c.-treated patients (10%) exhibited neutralising activity. Immunoabsorption studies with rIL-2-coated beads, demonstrated that in 8 of 15 patients with neutralising sera, the neutralising activity was correlated with specific anti-rIL-2 immunoglobulin. All 8 patients had received at least two cycles of rIL-2 by s.c. injections. Specific IL-2 neutralising activity affected both recombinant and natural IL-2 in all 8 patients. Development of anti-rIL-2 antibodies, irrespective of whether these exhibited neutralising activity or not, did not affect the frequency or duration of clinical responses.