Immunogenicity to three TNF-alpha blocking agents seems to vary substantially among patients with psoriatic arthritis, and the use of methotrexate appears to attenuate the presence of antidrug antibodies, according to findings from a cross-sectional study.
Although researchers have looked at the immunogenicity of TNF-alpha blockers in patients with diseases such as rheumatoid arthritis (RA), ankylosing spondylitis, psoriasis, and inflammatory bowel disease, their immunogenicity in psoriatic arthritis (PsA) patients has not been fully investigated, noted the current study’s investigators, led by Dr. Michael Zisapel of the department of rheumatology at Tel Aviv University (J. Rheumatol. 2014 Nov. 15 [doi:10.3899/jrheum.140685]).
The prevalence of antidrug antibodies (ADAb) to TNF-alpha blockers has been reported to be 20%-40% in RA, 25%-64% in ankylosing spondylitis, and about 33% in psoriasis, and evidence has shown that this is significantly reduced by the use of methotrexate, they said.
The study involved 93 patients with PsA who were taking adalimumab (n = 48), infliximab (n = 24), and etanercept (n = 21). A quarter of the patients were taking methotrexate at an average dose of 13.3 mg/week.
Overall, 77% of the patients had therapeutic drug levels. The prevalence of immunogenicity in the entire group was 33.3%, and one-fifth of patients had high concentrations of antibodies.
High levels of ADAb were found in 29% of patients taking adalimumab and 21% of the patients taking infliximab. No ADAb levels were found in patients taking etanercept.
Interestingly, the patients taking adalimumab demonstrated an immunogenicity of 54%, but only half of them (29%) showed high concentrations of antibodies.
“This finding suggests that a variety of levels might be found that might affect the significance of immunogenicity differently among patients producing ADAb,” the investigators wrote.
Fewer methotrexate-treated patients had high ADAb concentrations, compared with patients not taking methotrexate (16.7% vs. 21.7%).
A clear correlation was found between the presence of immunogenicity, lower drug levels, and decreased clinical response in PsA patients, just as other studies have found in RA and ankylosing spondylitis patients, the authors noted.
“Our results suggest that the use of methotrexate should be strongly considered in addition to monoclonal antibodies,” they said.
Limitations of their study included the small number of patients and the use of a bridging ELISA test which is reliable but considered to be less accurate than radioimmunoassay.
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