CD4+ T cells drive the immunopathogenesis of chronic beryllium disease (CBD), and their recruitment to the lung heralds the onset of granulomatous inflammation. We have shown that CD4+ Tregs control granuloma formation in an HLA-DP2 Tg model of CBD. In these mice, beryllium oxide (BeO) exposure resulted in the accumulation of 3 distinct CD4+ T cell subsets in the lung, with the majority of tissue-resident memory cells expressing FoxP3. The amount of Be regulated the number of total and antigen-specific CD4+ T cells and Tregs in the lungs of HLA-DP2 Tg mice. Depletion of Tregs increased the number of IFN-γ–producing CD4+ T cells and enhanced lung injury, while mice treated with IL-2/αIL-2 complexes had increased Tregs and reduced inflammation and Be-responsive T cells in the lung. BeO-experienced resident Tregs suppressed anti-CD3–induced proliferation of CD4+ T cells in a contact-dependent manner. CTLA-4 and ICOS blockade, as well as the addition of LPS to BeO-exposed mice, increased the effector T cell (Teff)/Treg ratio and enhanced lung injury. Collectively, these data show that the protective role of tissue-resident Tregs is dependent on quantity of Be exposure and is overcome by blocking immune regulatory molecules or additional environmental insults.