Venetoclax-resistant CLL cells show a highly activated and proliferative phenotype.

Venetoclax treatment has demonstrated efficacy and a safety profile in chronic lymphocytic leukemia (CLL) patients, however the emergence of resistant cells is a current complication. We and others, previously reported that the activation of CLL cells by signals that mimic microenvironment stimuli favors the upregulation of anti-apoptotic proteins from B cell lymphoma-2 (BCL-2) family that are not targeted by venetoclax, reducing malignant cell sensitivity to the drug. We here studied venetoclax-resistant CLL cells generated in vitro by autologous activated T lymphocytes, and found that they showed an aggressive phenotype characterized by increased expression of activation and proliferation markers. Moreover, surviving cells expressed high levels of B cell lymphoma-extra-large (BCL-XL) and/or myeloid cell leukemia-1 (MCL-1), and a sustained resistance to a second treatment with the drug. Interestingly, the spleen tyrosine kinase (SYK) inhibitor entospletinib, and the phosphoinositide 3-kinase delta (PI3Kδ) inhibitor idelalisib, reduced T cell activation, impaired the generation of leukemic cells with this aggressive phenotype, and were able to restore CLL sensitivity to venetoclax. Our data highlight a novel combination to overcome resistance to venetoclax in CLL.

Immunomodulatory effects of different intravenous immunoglobulin preparations in chronic lymphocytic leukemia.

Hypogammaglobulinemia is the most frequently observed immune defect in chronic lymphocytic leukemia (CLL). Although CLL patients usually have low serum levels of all isotypes (IgG, IgM and IgA), standard immunoglobulin (Ig) preparations for replacement therapy administrated to these patients contain more than 95% of IgG. Pentaglobin is an Ig preparation of intravenous application (IVIg) enriched with IgM and IgA (IVIgGMA), with the potential benefit to restore the Ig levels of all isotypes. Because IVIg preparations at high doses have well-documented anti-inflammatory and immunomodulatory effects, we aimed to evaluate the capacity of Pentaglobin and a standard IVIg preparation to affect leukemic and T cells from CLL patients. In contrast to standard IVIg, we found that IVIgGMA did not modify T cell activation and had a lower inhibitory effect on T cell proliferation. Regarding the activation of leukemic B cells through BCR, it was similarly reduced by both IVIgGMA and IVIgG. None of these IVIg preparations modified spontaneous apoptosis of T or leukemic B cells. However, the addition of IVIgGMA on in vitro cultures decreased the apoptosis of T cells induced by the BCL-2 inhibitor, venetoclax. Importantly, IVIgGMA did not impair venetoclax-induced apoptosis of leukemic B cells. Overall, our results add new data on the effects of different preparations of IVIg in CLL, and show that the IgM/IgA enriched preparation not only affects relevant mechanisms involved in CLL pathogenesis but also has a particular profile of immunomodulatory effects on T cells that deserves further investigation.