Denis Gaucher

Construction and immunogenicity of a codon-optimized Entamoeba histolytica Gal-lectin-based DNA vaccine

Invasive amebiasis caused by Entamoeba histolytica is the third leading parasitic cause of mortality, and there are no vaccines available to help control the disease. The galactose-adherence lectin (Gal-lectin) is the parasites major molecule allowing it to adhere to colonic mucin for colonization and to target cells for tissue destruction. It is immunodominant and is regarded as the most promising candidate molecule to be included in a subunit vaccine against amebiasis. In this study, we are reporting the construction of a codon-optimized DNA vaccine encoding a portion of the Gal-lectin heavy subunit that includes the carbohydrate recognition domain (CRD), and its in vivo testing in mice. The vaccine stimulated a Th1-type Gal-lectin-specific cellular immune response as well as the development of serum antibodies that recognized a recombinant portion of the heavy subunit, and that inhibited the adherence of trophozoites to target cells in vitro.

Serum from Entamoeba histolytica—Infected Gerbils Selectively Suppresses T Cell Proliferation by Inhibiting Interleukin-2 Production

Suppression of T and B cell responses during invasive amebiasis may be serum mediated. The mechanism of serum-mediated suppression of spleen cell lymphoproliferation from gerbils with amebic liver abscess was examined. Compared with uninfected gerbil serum (10%), serum samples collected at days 10, 30, and 60, but not at day 20 after infection, augmented both concanavalin A (Con A; T cell mitogen)- and lipopolysaccharide (LPS; B cell mitogen)-induced proliferation of homologous spleen cells. Only day 20 serum (>5%) inhibited Con A- but not LPS-induced proliferation of spleen cells from uninfected gerbils. The suppressive mechanism was independent of nitric oxide and prostaglandin but involved reduced interleukin (IL)-2 production. Addition of exogenous IL-2 reversed the suppressive effect of day 20 serum on Con A-stimulated proliferation. These results identify a mechanism whereby serum may contribute to transient suppression of T cell responses during Entamoeba histolytica infections.

Prospect for an Entamoeba histolytica Gal-lectin-based vaccine

Entamoeba histolytica is the aetiological agent of invasive amoebiasis, the third leading parasitic cause of mortality in the world. The disease can be easily cured by chemotherapy; however, prevention, mainly in the form of vaccination, could greatly decrease the incidence of the disease, and possibly help in its eradication. The parasites surface galactose and N‐acetyl‐d‐galactosamine‐inhibitable adherence lectin (Gal‐lectin) is highly antigenic and is the most promising subunit vaccine candidate. We have generated a Gal‐lectin‐based DNA vaccine and tested its immunogenicity in mice. Although further optimization will probably be required, this vaccine could help in the generation of an amoebiasis DNA vaccine for use in humans.

Abstract 959: FAS mutations induce therapeutic resistance in non-Hodgkin lymphomas

Lymphomas are common (1/30 Canadians), but responses to chemotherapy depend on the tumour biology. We sequenced > 300 lymphomas at diagnosis and at relapse, identified FAS as a possible tumour suppressor gene and found that mutant FAS is associated with therapeutic resistance. FAS is the death receptor that initiates the extrinsic apoptotic pathway once activated by FAS ligand (FASL). Our studies indicated that the most common FAS mutation is a dominant negative allele whose product inhibits FAS-mediated apoptosis. This allele induces resistance to doxorubicin in murine lymphoma cells transplanted into syngeneic immune competent C57BL/6 mice but, unexpectedly, the allele has no effect on chemosensitivity in cultured lymphoma lines in vitro. Because FAS signaling is initiated by FASL from neighboring cells, we asked whether chemotherapy induces FAS or FASL expression in immune cells, thereby activating apoptosis in vivo but not in vitro. Indeed, exposure to chemotherapy induced FAS in primary and malignant B cells and increased FASL in benign T cells. Thus, we hypothesize that chemotherapy may induce an anti-tumour immune response mediated by FAS-FASL interactions, and that FAS mutations cause therapeutic resistance by blocking the chemotherapy-induced immune response. We will extend this work by evaluating the role of the immune response in chemotherapy-induced lymphoma apoptosis and by identifying therapies that will target FAS mutant lymphomas. Citation Format: Nathalie Johnson, Denis Gaucher, Ryan Morin, Randy Gascoyne, Joseph Connors, Marco Marra, Jerry Pelletier, Hawley Rigsby, Koren Mann. FAS mutations induce therapeutic resistance in non-Hodgkin lymphomas. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 959. doi:10.1158/1538-7445.AM2014-959