Sex steroid ablation: an immunoregenerative strategy for immunocompromised patients

Age-related decline in thymic function is a well-described process that results in reduced T-cell development and thymic output of new naïve T cells. Thymic involution leads to reduced response to vaccines and new pathogens in otherwise healthy individuals; however, reduced thymic function is particularly detrimental in clinical scenarios where the immune system is profoundly depleted such as after chemotherapy, radiotherapy, infection and shock. Poor thymic function and restoration of immune competence has been correlated with an increased risk of opportunistic infections, tumor relapse and autoimmunity. Apart from their primary role in sex dimorphism, sex steroid levels profoundly affect the immune system in general and, in fact, age-related thymic involution has been at least partially attributed to the increase in sex steroids at puberty. Subsequently it has been demonstrated that the removal of sex steroids, or sex steroid ablation (SSA), triggers physiologic changes that ultimately lead to thymic re-growth and improved T-cell reconstitution in settings of hematopoietic stem cell transplant (HSCT). Although the cellular and molecular process underlying these regenerative effects are still poorly understood, SSA clearly represents an attractive therapeutic approach to enhance thymic function and restore immune competence in immunodeficient individuals.

Clonal B cells in Waldenström's macroglobulinemia exhibit functional features of chronic active B-cell receptor signaling

Waldenström's macroglobulinemia (WM) is a B-cell non-Hodgkin's lymphoma (B-NHL) characterized by immunoglobulin M (IgM) monoclonal gammopathy and the medullary expansion of clonal lymphoplasmacytic cells. Neoplastic transformation has been partially attributed to hyperactive MYD88 signaling, secondary to the MYD88 L265P mutation, occurring in the majority of WM patients. Nevertheless, the presence of chronic active B-cell receptor (BCR) signaling, a feature of multiple IgM+ B-NHL, remains a subject of speculation in WM. Here, we interrogated the BCR signaling capacity of primary WM cells by utilizing multiparametric phosphoflow cytometry and found heightened basal phosphorylation of BCR-related signaling proteins, and augmented phosphoresponses on surface IgM (sIgM) crosslinking, compared with normal B cells. In support of those findings we observed high sIgM expression and loss of phosphatase activity in WM cells, which could both lead to signaling potentiation in clonal cells. Finally, led by the high-signaling heterogeneity among WM samples, we generated patient-specific phosphosignatures, which subclassified patients into a ‘high' and a ‘healthy-like' signaling group, with the second corresponding to patients with a more indolent clinical phenotype. These findings support the presence of chronic active BCR signaling in WM while providing a link between differential BCR signaling utilization and distinct clinical WM subgroups.

Involvement of cPLA2 Inhibition in Dexamethasone-Induced Thymocyte Apoptosis

Various molecular mechanisms have been suggested to be involved in dexamethasone induced thymocyte apoptosis. In this study we show that pharmacological inhibition of cytoplasmic PLA2 in mouse thymocytes for 18 h with arachidonyl trifluoromethyl ketone (AACOCF3) (10 μM) and palmitoyl trifluoromethyl ketone (PACOCF3) (10 μM) induced a drastic increase of thymocyte apoptosis comparable to that observed following Dex (10−7 M) treatment, while inhibition of secretory PLA2 with p-bromophenacyl bromide (pBPB) (20 μM) did not. AACOCF3-induced thymocyte apoptosis, similarly to Dex-induced thymocyte apoptosis, was eliminated by cell pre-treatment with the PI-PLCβ inhibitor, U73122, but not by the PC-PLC inhibitor D609. These observations were corroborated by the ability of AACOCF3, like Dex, to induce a rapid and transient increase in DAG generation. In addition, AACOCF3-induced apoptosis involved the activation of the acidic sphingomyelinase (aSMase) but not of the neutral sphingomyelinase (nSMase), as evaluated by measurements of enzyme activity in cell extracts following thymocyte exposure to AACOCF3 and by the ability of monensin to inhibit AACOCF3-induced thymocyte apoptosis. In addition, the AACOCF3 apoptotic effect resulted in an early increase of ceramide levels. AACOCF3-induced thymocyte apoptosis involved the activation of caspase 3, and cell pre-treatment with a caspase 3 inhibitor prevented AACOCF3-induced apoptosis. These observations suggest that cPLA2 inhibition may have a role in Dex-induced thymocyte apoptosis and highlight the importance of cPLA2 activity in thymocyte survival.