Abstract 3995: BACH2 and PRDM1 gene expression changes in T and B cells according to age of healthy individuals and significance in chronic lymphocytic leukemia patients
Authors: Silva Pushpamali De , Chi Vu Luan Dang , Stamatopoulos Basile , Garaud Soizic , Thibaud Vincent , Duvillier Hugues , Lodewyckx Jean-Nicolas , Sibille Catherine , Willard-Gallo Karen , Bron Dominique 
Published: August 2019

Background: Aging is a risk factor for developing malignant hemopathies including chronic lymphocytic leukemia (CLL). We evaluated the relevance of BACH2 and PRDM1 gene expression in the aging of immune cells and the immunodeficiency associated with CLL.

Methods: Peripheral blood mononuclear cells were isolated from untreated CLL patients (n=41) and age-matched healthy donors (HD; n=60). T and B cells were purified (95%-99%) by magnetic isolation. BACH2, PRDM1, PD1, PDL1 and CDKN2A (p16INK4A) transcripts were quantified using RT-qPCR. ß-galactosidase activity was measured by flow cytometry. Cell apoptosis was analyzed after intracellular oxidative stress induced by etoposide treatment. ChIP-qPCR was done to find BACH2-apoptotic target genes in purified CD4+ T cells from HDs with/without etoposide treatment. Prognostic value of BACH2 and PRDM1 expression in purified CD19+ B cells was analyzed retrospectively in a cohort of CLL patients (n= 270), and correlated with clinical parameters.

Results: BACH2 expression in HDs is significantly downregulated while PRDM1 expression increased in CD4+, CD8+ T and CD19+ B cells according to age groups. BACH2 expression is further reduced in T and B cells from CLL patients compared to age-matched HDs. Also, PRDM1 is significantly upregulated in T cells from CLL patients but not in leukemic B cells. PD1 expression is significantly upregulated in T cells in the older vs younger HDs and also in CLL patients compared with age-matched HDs. High PDL1 expression is also strongly correlated with increased age in HD B cells with a further increase detected in leukemic B cells. A strong inverse correlation was observed between BACH2 and PD1 in T cells; and between BACH2 and PDL1 in B cells from HDs. We also analyzed the link between BACH2 expression and senescence markers; CDKN2A and ß-galactosidase. CDKN2A expression inversely correlated with BACH2 in CD4+, CD8+ T and CD19+ B cells. ß-galactosidase activity showed an increase compared to BACH2 deficient lymphocytes in older compared to young HDs, suggesting that BACH2 deficiency leads to the accumulation of senescent cells. A strong correlation was observed between age-related BACH2 downregulation and a decrease in CD4+ T and CD19+ B cell apoptosis after etoposide treatment. ChIP-qPCR assay confirmed that BACH2 binds to genes involved in apoptosis and after etoposide treatment, BACH2 binding was repressed. In our retrospective cohort, increased BACH2 expression was correlated with improved treatment-free survival (p=0.0352).

Conclusion: Decrease of BACH2 and increase of PRDM1, PD1 and PDL1 in T and B cells from CLL patients and aged-matched HDs, are significantly correlated with aging and could be part of immunosenescence. Involvement of BACH2 in resistance to drug-induced apoptosis of HD lymphocytes was documented and is currently investigated in the CLL cohort.

Citation Format: Pushpamali De Silva, Vu Luan Dang Chi, Basile Stamatopoulos, Soizic Garaud, Vincent Thibaud, Hugues Duvillier, Jean-Nicolas Lodewyckx, Catherine Sibille, Karen Willard-Gallo, Dominique Bron. BACH2 and PRDM1 gene expression changes in T and B cells according to age of healthy individuals and significance in chronic lymphocytic leukemia patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3995.