Impaired Long-Term Quantitative Cellular Response to SARS-CoV-2 Vaccine in Thiopurine-Treated IBD Patients

<b>Background</b>: Studies investigating the long-term cellular immune response to SARS-CoV-2 mRNA vaccines in patients with inflammatory bowel disease (IBD) remain limited, particularly among those receiving immunosuppressive therapy. <b>Methods</b>: We prospectively evaluated humoral and cellular immune responses at short-term (4-6 weeks) and long-term (6-12 months) time points following SARS-CoV-2 mRNA vaccination in patients with IBD receiving anti-TNF agents, thiopurines, or combination therapy. We defined the short-term response as the measurement taken 4-6 weeks after the second vaccine dose and the long-term response as the measurement taken between 6 and 12 months after the first determination. A cohort of healthy controls was included for short-term comparative analysis. <b>Results</b>: At long-term follow-up, quantitative humoral responses were reduced in patients receiving anti-TNF monotherapy. In contrast, a reduced quantitative cellular response was found in the thiopurine (median 0.7 UI/mL, <i>p</i> < 0.05) and anti-TNF combo groups (median 0.4 UI/mL, <i>p</i> < 0.01) compared to anti-TNF monotherapy (median 2.2 UI/mL). <b>Conclusions</b>: There was a robust long-term humoral and cellular response to vaccination, but a diminished quantitative cellular response in patients treated with thiopurines or combo therapy compared to anti-TNF monotherapy.