Matthew P. Bernard

Targeting Cyclooxygenase-2 in Hematological Malignancies: Rationale and Promise

There is much interest in the potential use of Cox-2 selective inhibitors in combination with other cancer therapeutics. Malignancies of hematopoietic and non-hematopoietic origin often have increased expression of cyclooxygenase-2 (Cox-2), a key modulator of inflammation. For example, hematological malignancies such as chronic lymphocytic leukemia, chronic myeloid leukemia, Hodgkins lymphoma, non-Hodgkins lymphoma and multiple myeloma often highly express Cox-2, which correlates with poor patient prognosis. Expression of Cox-2 enhances survival and proliferation of malignant cells, while negatively influencing anti-tumor immunity. Hematological malignancies expressing elevated levels of Cox-2 potentially avoid immune responses by producing factors that enhance angiogenesis and metastasis. Cellular immune responses regulated by natural killer cells, cytotoxic T lymphocytes, and T regulatory cells are also influenced by Cox-2 expression. Therefore, Cox-2 selective inhibitors have promising therapeutic potential in patients suffering from certain hematological malignancies.

Ibuprofen and other widely used non-steroidal anti-inflammatory drugs inhibit antibody production in human cells

The widely used non-steroidal anti-inflammatory drugs (NSAIDs) function mainly through inhibition of cyclooxygenases 1 and 2 (Cox-1 and Cox-2). Unlike Cox-1, Cox-2 is considered an inducible and pro-inflammatory enzyme. We previously reported that Cox-2 is upregulated in activated human B lymphocytes and using Cox-2 selective inhibitors that Cox-2 is required for optimal antibody synthesis. It is not known whether commonly used non-prescription and non-Cox-2 selective drugs also influence antibody synthesis. Herein, we tested a variety of Cox-1/Cox-2 non-selective NSAIDs, namely ibuprofen, tylenol, aspirin and naproxen and report that they blunt IgM and IgG synthesis in stimulated human peripheral blood mononuclear cells (PBMC). Ibuprofen had its most profound effects in inhibiting human PBMCs and purified B lymphocyte IgM and IgG synthesis when administered in the first few days after activation. As shown by viability assays, ibuprofen did not kill B cells. The implications of this research are that the use of widely available NSAIDs after infection or vaccination may lower host defense. This may be especially true for the elderly who respond poorly to vaccines and heavily use NSAIDs.

Cyclooxygenase-2 inhibition attenuates antibody responses against human papillomavirus-like particles

Vaccination to generate protective humoral immunity against infectious disease is becoming increasingly important due to emerging strains of virus, poorly immunogenic vaccines, and the threat of bioterrorism. We demonstrate that cyclooxygenase-2 (Cox-2) is crucial for optimal Ab responses to a model vaccine, human papillomavirus type 16 virus-like particles (HPV 16 VLPs). Cox-2-deficient mice produce 70% less IgG, 50% fewer Ab-secreting cells, and 10-fold less neutralizing Ab to HPV 16 VLP vaccination compared with wild-type mice. The reduction in Ab production by Cox-2−/− mice was partially due to a decrease in class switching. SC-58125, a structural analog of the Cox-2-selective inhibitor Celebrex reduced by ∼70% human memory B cell differentiation to HPV 16 VLP IgG-secreting cells. The widespread use of nonsteroidal anti-inflammatory drugs and Cox-2-selective inhibitory drugs may therefore reduce vaccine efficacy, especially when vaccines are poorly immunogenic or the target population is poorly responsive to immunization.

Peroxisome Proliferator-Activated Receptor γ Ligands Enhance Human B Cell Antibody Production and Differentiation

Protective humoral immune responses critically depend on the optimal differentiation of B cells into Ab-secreting cells. Because of the important role of Abs in fighting infections and in successful vaccination, it is imperative to identify mediators that control B cell differentiation. Activation of B cells through TLR9 by CpG-DNA induces plasma cell differentiation and Ab production. Herein, we examined the role of the peroxisome proliferator-activated receptor (PPAR)γ/RXRα pathway on human B cell differentiation. We demonstrated that activated B cells up-regulate their expression of PPARγ. We also show that nanomolar levels of natural (15-deoxy-Δ12,14-prostaglandin J2) or synthetic (rosiglitazone) PPARγ ligands enhanced B cell proliferation and significantly stimulated plasma cell differentiation and Ab production. Moreover, the addition of GW9662, a specific PPARγ antagonist, abolished these effects. Retinoid X receptor (RXR) is the binding partner for PPARγ and is required to produce an active transcriptional complex. The simultaneous addition of nanomolar concentrations of the RXRα ligand (9-cis-retinoic acid) and PPARγ ligands to CpG-activated B cells resulted in additive effects on B cell proliferation, plasma cell differentiation, and Ab production. Furthermore, PPARγ ligands alone or combined with 9-cis-retinoic acid enhanced CpG-induced expression of Cox-2 and the plasma cell transcription factor BLIMP-1. Induction of these important regulators of B cell differentiation provides a possible mechanism for the B cell-enhancing effects of PPARγ ligands. These new findings indicate that low doses of PPARγ/RXRα ligands could be used as a new type of adjuvant to stimulate Ab production.

Chronic Inhibition of Cyclooxygenase-2 Attenuates Antibody Responses against Vaccinia Infection

Generation of optimal humoral immunity to vaccination is essential to protect against devastating infectious agents such as the variola virus that causes smallpox. Vaccinia virus (VV), employed as a vaccine against smallpox, provides an important model of infection. Herein, we evaluated the importance cyclooxygenase-2 (Cox-2) in immunity to VV using Cox-2 deficient mice and Cox-2 selective inhibitory drugs. The effects of Cox-2 inhibition on antibody responses to live viruses such as vaccinia have not been previously described. Here, we used VV infection in Cox-2 deficient mice and in mice chronically treated with Cox-2 selective inhibitors and show that the frequency of VV-specific B cells was reduced, as well as the production of neutralizing IgG. VV titers were approximately 70 times higher in mice treated with a Cox-2 selective inhibitor. Interestingly, Cox-2 inhibition also reduced the frequency of IFN-gamma producing CD4(+) T helper cells, important for class switching. The significance of these results is that the chronic use of non-steroidal anti-inflammatory drugs (NSAIDs), and other drugs that inhibit Cox-2 activity or expression, blunt the ability of B cells to produce anti-viral antibodies, thereby making vaccines less effective and possibly increasing susceptibility to viral infection. These new findings support an essential role for Cox-2 in regulating humoral immunity.

Inhibition of cyclooxygenase-2 impairs the expression of essential plasma cell transcription factors and human B-lymphocyte differentiation

Cyclooxygenase (Cox) inhibitors are among the most widely used and commonly prescribed medications. Relatively little is understood about their influence on human immune responses. Herein, we discovered a novel and important mechanism whereby non‐steroidal anti‐inflammatory drugs (NSAIDs) blunt human B‐cell antibody production. We demonstrate that the Cox‐2 selective small molecule inhibitors SC‐58125 and NS‐398 attenuate the production of human antibody isotypes including immunoglobulin M (IgM), IgG1, IgG2, IgG3 and IgG4. In addition, inhibition of Cox‐2 significantly reduced the generation of CD38+ IgM+ and CD38+ IgG+ antibody‐secreting cells. Interestingly, we discovered that inhibition of Cox‐2 activity in normal human B cells severely reduced the messenger RNA and protein levels of the essential plasma cell transcription factor, Blimp‐1. These observations were mirrored in Cox‐2‐deficient mice, which had reduced CD138+ plasma cells and a near loss of Blimp‐1 expression. These new findings demonstrate a critical role for Cox‐2 in the terminal differentiation of human B lymphocytes to antibody‐secreting plasma cells. The use of NSAIDs may adversely influence the efficacy of vaccines, especially in the immunocompromised, elderly and when vaccines are weakly immunogenic.