Phosphodiesterase 7A-Deficient Mice Have Functional T Cells Guchen Yang, 1 Kim W. McIntyre, Robert M. Townsend, Henry H. Shen, William J. Pitts, John H. Dodd, Steven G. Nadler, Murray McKinnon, and Andrew J. Watson Phosphodiesterases (PDEs) are enzymes which hydrolyze the cyclic nucleotide second messengers, cAMP and cGMP. In leuko- cytes, PDEs are responsible for depletion of cAMP which broadly suppresses cell functions and cellular responses to many activation stimuli. PDE7A has been proposed to be essential for T lymphocyte activation based on its induction during cell activation and the suppression of proliferation and IL-2 production observed following inhibition of PDE7A expression using a PDE7A antisense oligonucleotide. These observations have led to the suggestion that selective PDE7 inhibitors could be useful in the treatment of T cell-mediated autoimmune diseases. In the present report, we have used targeted gene disruption to examine the role PDE7A plays in T cell activation. In our studies, PDE7A knockout mice (PDE7A / ) showed no deficiencies in T cell proliferation or Th1- and Th2-cytokine production driven by CD3 and CD28 costimulation. Unexpectedly, the Ab response to the T cell-dependent Ag, keyhole limpet hemocyanin, in the PDE7A / mice was found to be significantly elevated. The results from our studies strongly support the notion that PDE7A is not essential for T cell activation. The Journal of Immunology, 2003, 171: 6414 – 6420. C yclic nucleotide phosphodiesterases (PDEs) 2 catalyze the hydrolysis of second messenger purine nucleotides, 3, 5-cAMP and 3,5-cGMP, to their biologically inactive nucleotide 5-monophosphates (1). Both cAMP and cGMP play a pivotal role in regulating signaling pathways for many essential cellular functions (1–3). In the immune system, cAMP is the pri- mary regulatory cyclic nucleotide (4). It is believed that cAMP broadly suppresses the functions of immune and inflammatory cells (5– 6) and a reduction in intracellular cAMP pools is required for cells to effectively respond to extracellular stimuli. This reduc- tion is mediated principally by the action of cell-specific PDEs (4), and PDE inhibitors, such as those selective for PDE4, have been demonstrated to reinforce the cAMP constraint on activation in many immune and inflammatory cells (6 –7). This approach to sus- taining cAMP levels has proved therapeutically effective, and PDE4 inhibitors, due to their broad anti-inflammatory and bron- chodilating effects, are in late-stage clinical development for the treatment of pulmonary diseases, such as asthma and chronic ob- structive pulmonary disease (6, 8). The PDE7 family of high-affinity cAMP-specific PDEs has two members, PDE7A and PDE7B (Refs. 9 –13, see Ref. 1 for nomen- clature). PDE7A occurs as three alternative splice variants, PDE7A1, PDE7A2, and PDE7A3 (14). PDE7A1 is primarily ex- pressed in lymphoid organs, such as thymus, lymph nodes, spleen, and also peripheral blood T cells and T cell lines (10 –12). In contrast, PDE7A2 is highly expressed in skeletal muscle and heart (15) while the PDE7A3 splice variant mRNA is detected in T lymphocytes. Recombinant PDE7A3 proteins have, however, so far failed to show associated PDE enzymatic activity (14). PDE7B is expressed in a number of tissues including brain, heart, and skeletal muscle but significant expression in lymphoid organs is not observed (12–13). The T cell expression of PDE7A1 has led to the proposal that this PDE may play a broad role in regulating T cell functions. In support of this, Li et al. (16) demonstrated that PDE7A1 protein and enzymatic activity were not detectable in resting peripheral T cells but levels were induced by CD3  CD28 costimulation. These increases in the PDE7A1 protein and enzymatic activity correlated with a decrease in cAMP levels and an increase in pro- liferation and IL-2 production. In addition, a PDE7A-specific an- tisense oligonucleotide, which blocked PDE7A expression, inhibited T cell proliferation and IL-2 production in a protein kinase A-depen- dent manner. The authors inferred that PDE7A plays an essential role in T cell activation and, therefore, may be an appropriate target for therapeutic intervention in T cell-mediated diseases. In addition to PDE7A, at least five other PDEs which hydrolyze cAMP–PDE3B, PDE4A, PDE4B, PDE4D, and PDE8A–are re- ported to be present in peripheral T cells and human T cell lines (14, 17, 18). Although the relative contribution of each of these PDEs to the regulation of T cell function remains unclear, studies using selective PDE inhibitors have established that PDE4 family members, in particular PDE4B and PDE4D, regulate T cell cyto- kine production and, to a lesser extent, proliferative responses to Ags and mitogens (6). In the present study, we used mice with a targeted disruption of the PDE7A gene (PDE7A / ) to investigate the role PDE7A plays in T lymphocyte activation. Contrary to the expectation that inac- tivation of PDE7A would lead to impaired T cell activation, we found that T cell proliferative responses and secreted Th1 cytokine levels (IL-2, IFN-, TNF-) induced by CD3  CD28 costimu- lation in the PDE7A / mice were comparable to wild-type lit- termates. A clear phenotypic difference was, however, found in the in vivo Ab response to keyhole limpet hemocyanin (KLH), where the PDE7A / mice developed significantly higher mean Ab ti- ters. Our studies do not support the proposal that PDE7A plays a critical role in regulating T cell proliferation. Immunology and Inflammation Drug Discovery, Bristol-Myers Squibb Pharmaceuti- cal Research Institute, Princeton, NJ 08543 Received for publication August 13, 2003. Accepted for publication October 9, 2003. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. 1 Address correspondence and reprint requests to Dr. Guchen Yang, Bristol-Myers Squibb Pharmaceutical Research Institute, P.O. Box 4000, Princeton, NJ 08543-4000. E-mail address: guchen.yang@bms.com 2 Abbreviations used in this paper: PDE, phosphodiesterase; CBA, cytometric bead array assay; KLH, keyhole limpet hemocyanin. The Journal of Immunology Copyright © 2003 by The American Association of Immunologists, Inc. 0022-1767/03/$02.00