pdFVIII concentrate induces the development of T regulatory cells and a Th2 cytokine profile, whereas rFVIII induces a Th1 cytokine profile. Detection of (A) intracellular Th1 and Th2 cytokines produced by CD4⁺ T cells and (B) CD4⁺CD25⁺Foxp3⁺ T regulatory cells isolated from HBSS-, rFVIII-, or pdFVIII-treated mice. Mice were treated with 4 infusions of HBSS, 2 IU pdFVIII, or 2 IU rFVIII; 4 months later, mice were challenged with HBSS, 2 IU rFVIII, or 2 IU pdFVIII. Twenty-four hours later, CD4⁺ T cells were purified from the spleens. The Th1 cytokines IL2, IFN (3Ai-ii), Th2 cytokines IL-4, IL-5, IL-10, and TGF-β (3Biii-vi), and CD4⁺CD25⁺Foxp3⁺ expression was quantified by flow cytometry. Error bars represent the SEM for 5 mice.