P119 Serum complement, B cells and T cells as markers of treatment response in those treated with adalimumab and clindamycin–rifampicin for hidradenitis suppurativa: a pilot study

Abstract B cells, plasma cells and associated increases in immunoglobulin and complement activation play important roles in the pathogenesis of hidradenitis suppurativa (HS). B cells have been identified as treatment targets for HS. Previous research by our group identified that patients with severe HS who did not respond to adalimumab had enriched complement and B-cell activation pathways at baseline (Hambly R, Gatault S, Smith CM et al. B-cell and complement signature in severe hidradenitis suppurativa that does not respond to adalimumab. Br J Dermatol 2023; 188: 52–63). The aim of this study was to identify whether easily measured blood biomarkers of B-cell activation could predict Hidradenitis Suppurativa Clinical Response in patients with HS receiving either adalimumab therapy or combination of clindamycin and rifampicin (Clin/Rif). Participants attending our HS clinic, who were commencing either Clin/Rif in combination or adalimumab, were recruited. Full blood count; C-reactive protein (CRP); immunoglobulins G, A and M; complement C3 and C4; and T-cell, natural killer (NK) cell and B-cell subsets were measured prior to treatment. When participants returned to clinic after ≥ 16 weeks on adalimumab, or after having completed 10 weeks of Clin/Rif, these tests were repeated. Fourteen patients completed 10 weeks of Clin/Rif, and 15 completed ≥ 16 weeks of adalimumab. In total, 90% were female and 10% were male. Participants in each arm were further subgrouped into nonresponders or treatment responders. Overall, 18 of 29 were total responders: 9 of 15 (60%) in the adalimumab group and 9 of 14 (64%) in the Clin/Rif group. In the Clin/Rif group, C4 was significantly higher, both pre- and post-treatment, in those who did not respond to treatment compared with those who achieved treatment response (9 of 14) (P < 0.001). In the adalimumab group, NK cells were found to increase in responders vs. nonresponders after week 16 (P = 0.02). B cells were numerically higher (P = 0.07), and responders had lower T cells at week 16 (P = 0.02). We found that platelets, lymphocytes, CRP, neutrophil–lymphocyte ratio and systemic immune–inflammation index all decreased significantly with treatment. No significant difference was found between responders and nonresponders. C4 was found to be significantly lower post-treatment than pretreatment (P = 0.02), but did not predict treatment outcome. C4 levels pretreatment predicted outcomes to Rif/Clin. We found significant changes in NK cells between adalimumab responders and nonresponders. These tests are easily performed in the outpatient setting. Our patient numbers are small. If these findings are validated in a larger cohort this would begin to allow, for the first time, the personalization of treatment for HS.