Serine/Threonine Protein Phosphatase-Mediated Control of the Peptidoglycan Cross-Linking L,D-Transpeptidase Pathway in Enterococcus faecium

International audienceThe last step of peptidoglycan polymerization involves two families of unrelated transpeptidases that are the essential targets of ␤-lactam antibiotics. D,D-transpeptidases of the penicillin-binding protein (PBP) family are active-site serine enzymes that use pentapeptide precursors and are the main or exclusive cross-linking enzymes in nearly all bacteria. However, pepti-doglycan cross-linking is performed mainly by active-site cysteine L,D-transpeptidases that use tetrapeptides in Mycobacterium tuberculosis, Clostridium difficile, and ␤-lactam-resistant mutants of Enterococcus faecium. We have investigated reprogramming of the E. faecium peptidoglycan assembly pathway by a switch from pentapeptide to tetrapeptide precursors and bypass of PBPs by L,D-transpeptidase Ldt fm. Mutational alterations of two signal transduction systems were necessary and sufficient for activation of the L,D-transpeptidation pathway, which is essentially cryptic in wild-type strains. The first one is a classical two-component regulatory system, DdcRS, that controls the activity of Ldt fm at the substrate level. As previously described, loss of DdcS phosphatase activity leads to production of the D,D-carboxypeptidase DdcY and conversion of the pentapeptide into the tetrapeptide substrate of Ldt fm. Here we show that full bypass of PBPs by Ldt fm also requires increased Ser/Thr protein phos-phorylation resulting from impaired activity of phosphoprotein phosphatase StpA. This enzyme negatively controlled the level of protein phosphorylation both by direct dephosphorylation of target proteins and by dephosphorylation of its cognate kinase Stk. In combination with production of DdcY, increased protein phosphorylation by this eukaryotic-enzyme-like Ser/Thr protein kinase was sufficient for activation of the L,D-transpeptidation pathway in the absence of mutational alteration of pepti-doglycan synthesis enzymes

Impact of depleting therapeutic monoclonal antibodies on the host adaptive immunity: a bonus or a malus?

Clinical responses to anti-tumor monoclonal antibody (mAb) treatment have been regarded for many years only as a consequence of the ability of mAbs to destroy tumor cells by innate immune effector mechanisms. More recently, it has also been shown that anti-tumor antibodies can induce a long-lasting anti-tumor adaptive immunity, likely responsible for durable clinical responses, a phenomenon that has been termed the vaccinal effect of antibodies. However, some of these anti-tumor antibodies are directed against molecules expressed both by tumor cells and normal immune cells, in particular lymphocytes, and, hence, can also strongly affect the host adaptive immunity. In addition to a delayed recovery of target cells, lymphocyte depleting-mAb treatments can have dramatic consequences on the adaptive immune cell network, its rebound, and its functional capacities. Thus, in this review, we will not only discuss the mAb-induced vaccinal effect that has emerged from experimental preclinical studies and clinical trials but also the multifaceted impact of lymphocytes-depleting therapeutic antibodies on the host adaptive immunity. We will also discuss some of the molecular and cellular mechanisms of action whereby therapeutic mAbs induce a long-term protective anti-tumor effect and the relationship between the mAb-induced vaccinal effect and the immune response against self-antigens

Recovery of central memory and naive peripheral t cells in follicular Lymphoma patients receiving rituximab-chemotherapy based regimen

International audiencePreclinical models and clinical studies have shown that anti-CD20-based treatment has multifaceted consequences on t-cell immunity. We have performed a prospective study of peripheral t-cell compartment in FL patients, all exhibiting high tumor burden and receiving rituximab-chemotherapy-based regimen (R-CHOP). Before treatment, FL patients harbor low amounts of peripheral naive T cells, but high levels of CD4 + t eM , CD4 + t reg and CD8 + t eMRA subsets and significant amounts of CD38 + HLA-DR + activated T cells. A portion of these activated/differentiated T cells also expressed PD-1 and/or TIGIT immune checkpoints. Hierarchical clustering of phenotyping data revealed that 5/8 patients with only a partial response to R-cHop induction therapy or with disease progression segregate into a group exhibiting a highly activated/differentiated T cell profile and a markedly low proportion of naive T cells before treatment. Rituximab-based therapy induced a shift of CD4 + and CD8 + t cells toward a central memory phenotype and of CD8 + T cells to a naive phenotype. In parallel, a decrease in the number of peripheral T cells expressing both PD-1 and TIGIT was detected. These observations suggest that the standard rituximab-based therapy partially reverts the profound alterations observed in t-cell subsets in FL patients, and that blood T-cell phenotyping could provide a better understanding of the mechanisms of rituximab-based treatment. Follicular lymphoma (FL) is the second most common form of non-Hodgkin lymphoma (NHL). Its clinical course is highly variable and survival medians are 7-15 years depending on the studies. Follicular lymphoma management is characterized by a risk-adapted therapy based on the stage of the disease and the symptoms of the patients. For high tumor burden patients, treatment options could be either rituximab plus cyclophosphamide, vincristine and prednisone with (R-CHOP) or without (R-CVP) doxorubicin or other anthracyclines, or rituxi-mab plus fludarabine for patients not eligible for anthracyclines, or rituximab plus bendamustine. Experimental therapies as well as allogeneic stem cell transplantation are rather considered for relapsed and more refractory disease 1. The addition of the anti-CD20 monoclonal antibody (mAb) rituximab to chemotherapy has resulted in a higher rate of complete remission and improved survival 2. In addition, rituximab as maintenance therap