Background/Purpose: Anti-TNF-α therapy is effective for the treatment of inflammatory bowel disease (IBD). Nevertheless, over 30% of IBD patients fail to respond to anti-TNF-α therapy and approximately 60% of the patients who respond initially to the therapy will lose the response over time and will need to either dose escalation or switch to another agent to maintain response. Low serum drug levels and/or anti-drug antibody (ADA) generation may play a role for the failure and, recent data suggest monitoring of patients for serum drug and ADA levels is an important strategy for optimal patient management. Here, we report the application of the homogeneous mobility shift assay (HMSA) method for monitoring of adalimumab (ADL) and human antibodies-to-adalimumab (ATA) in serum samples from patients who lost response to ADL treatment.

Methods: Serum samples were collected from 100 patients who initially responded to ADL therapy for at least three months but were beginning to lose response. ATA and ADL levels in the serum samples were measured by ATA- and ADL-HMSA as described previously, except that in the ATA-HMSA Alexa Fluor 488 labeled ADL (ADL-488) was used as antigen and rabbit anti-ADL serum as standard. Full analytical method validation of both the ATA- and the ADL-HMSA was performed, and cut points for ADL and ATA levels were established with 100 drug-naïve healthy controls. The relationship of the ADL drug level and ATA generation in these patients was analyzed.

Results: Validation of the ATA- and ADL-HMSA revealed a lower limit of detection to be 0.026 U/mL for ATA and 0.018 µg/mL for ADL in the serum samples. The intra-assay and inter-assay precision determination yielded a coefficient of variation of less than 15%, and the accuracy of the assay is within 20% for both assays. ADL drug tolerance in ATA HMSA is up to 40 µg/ml in the test serum. Serum samples from 100 drug-naïve healthy subjects were tested to set up the cutoff point of 0.55U/mL (Mean+3.0xSD) for ATA and 0.66 µg/mL for ADL. Analysis of 100 serum samples from patients who were losing response showed that 36% of the patients had an ADL level < 3 µg/mL, of these 58.3% were ATA positive. However, only 18% of the patients (4/22) had ATA when their ADL level was over 20 µg/mL. Overall, 40% of the patient (40/100) were positive for ATA.

Conclusion: Analysis of ADL and ATA levels in non-responding IBD patients showed a high incidence of ATA generation and the ADL levels were inversely correlated with the level of ATA generation. Drug and ADA levels are important determinants of patient response to the therapy.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/influence-of-trough-serum-drug-level-and-immunogenicity-on-the-lack-of-response-to-adalimumab-therapy-in-inflammatory-bowel-disease-patients/