Key Points Autologous activated T cells can drive antigen-independent proliferation of CLL cells through CD40 and IL-21 signaling. An IL-21 gene induction signature, IL-21 mRNA, and protein can be found in CLL lymph node samples.

Recently, it has been described that patients with chronic lymphocytic leukemia (CLL) have increased numbers of regulatory T (T(reg)) cells. In the present study, we analysed the mechanism behind T(reg) cells expansion in CLL. Neither analysis of the T-cell receptor repertoire nor CD45 isoform expression of T(reg) cells from patients with CLL provided evidence for chronic (tumor) antigenic stimulation as a possible cause for T(reg) cells expansion in CLL. We found evidence however for increased formation of T(reg) cells via CD70 costimulation, because we observed that CD40 ligand activated CLL cells (which might be considered a model of lymph node CLL cells) strongly induced CD70-dependent formation of T(reg) cells. Reverse transcription-multiplex ligation-dependent probe amplification assay expression analysis of 34 apoptosis-regulating genes showed that in comparison with other CD4(+) T-cells, T(reg) cells from both healthy individuals (HD) and patients with CLL had a high expression of pro-apoptotic Noxa and a low expression of anti-apoptotic Bcl-2. Strikingly, Bcl-2 levels of T(reg) cells in patients with CLL were significantly higher than in HD. Finally, the different apoptotic profile resulted in differences at the functional level, because T(reg) cells from patients with CLL were more resistant to drug-induced apoptosis than T(reg) cells from HD. In conclusion, T(reg) cells in CLL may accumulate both by increased formation, facilitated by CD27-CD70 interaction in the lymph node proliferation centres, and decreased sensitivity to apoptosis because of a shifted Noxa-Bcl-2 balance.

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Sensitivity of chronic lymphocytic leukemia (CLL) cells to anti-CD20 mAbs is low and, therefore, the efficacy of monotherapy with current anti-CD20 mAbs is limited. At present, it is not known whether sensitivity of CLL cells to CD20 mAbs is modulated by microenvironmental stimuli. We have shown previously that in vitro CD40 stimulation of peripheral bloodderived CLL cells results in resistance to cytotoxic drugs. In the present study, we show that, in contrast, CD40 stimulation sensitizes CLL cells to the recently described novel type II anti-CD20 mAb GA101. Cell death occurred without crosslinking of GA101 and involved a lysosomedependent mechanism. Combining GA101 with various cytotoxic drugs resulted in additive cell death, not only in CD40-stimulated CLL cells, but also in p53-dysfunctional CLL cells. Our findings indicate that GA101 has efficacy against chemoresistant CLL, and provide a rationale for combining cytotoxic drugs with anti-CD20 mAbs. (Blood. 2011;118(19): 5178-5188) IntroductionAlthough treatment results for chronic lymphocytic leukemia (CLL) have improved considerably over the last decade, a curative drug regimen is still lacking. Similar to other B-cell malignancies such as follicular lymphoma and multiple myeloma, in CLL, the interaction of the malignant cells with their microenvironment in the lymph nodes, spleen, and possibly BM has been shown to play an important role in the biology of the disease. 1 We and others have previously shown that in vitro CD40 stimulation of CLL cells can to a certain extent mimic the lymph node environment and results in the induction of resistance of the CLL cells to cytotoxic drugs such as fludarabine, chlorambucil, bortezomib, and roscovitine. [2][3][4][5][6] These microenvironmental niches might be an important localization of minimal residual disease and form the basis for the relapses characterizing this disease. 1,[3][4][5]7,8 Moreover, after sequential treatments, selection of p53 dysfunctional clones occurs in up to 50% of patients, 9,10 which also results in chemoresistance. Therefore, there is a need for new treatments that circumvent microenvironmental chemoresistance and act independently of p53, possibly including anti-CD20 mAb-containing regimens. 11,12 However, sensitivity of CLL cells to anti-CD20 mAbs in vitro is low and monotherapy with conventional doses of the type I anti-CD20 mAb rituximab has only limited efficacy in CLL. Because of rituximab resistance or unresponsiveness, more potent anti-CD20 mAbs are currently being sought. Two types of anti-CD20 mAbs have been described. A prime difference is that, in contrast to type I anti-CD20 mAbs, type II mAbs are unable to translocate CD20 into lipid rafts or to evoke Ca 2ϩ flux. [13][14][15][16] Ofatumumab, a second-generation type I anti-CD20 mAb seems promising for the treatment of CLL, 17 although large amounts seem to be required. GA101 is a novel glycoengineered type II anti-CD20 mAb. Compared with rituximab, GA101 has enhanced direct cell death-inducing capacity and improved Ab-depende...

In vitro CD40-stimulated chronic lymphocytic leukemia (CLL) cells are resistant to cytotoxic drugs. In sharp contrast, we here show that CD40 stimulation sensitizes CLL cells to rituximabmediated cell death. This increased sensitivity is specific for anti-CD20 treatment. Rituximab-mediated death in CD40-stimulated CLL cells shows rapid kinetics (within hours), and is caspase and p53 independent, but depends on extracellular Ca 2 þ and reactive oxygen species (ROS) production. By increasing basal ROS production, CD40 stimulation sensitizes CLL cells to rituximab-mediated death. Our findings provide a rationale for combination treatment of CLL with cytotoxic drugs and anti-CD20 monoclonal antibodies.

The elimination of activated T cells is important to maintain homeostasis and avoid immunopathology. CD95 (Fas/APO-1) has been identified as a death mediator for activated T cells in vitro but the function of CD95 in death of mature T cells in vivo is still controversial. Here we show that triggering of the costimulatory TNF receptor family member CD27 sensitized T cells for CD95-induced apoptosis. CD95-deficient (lpr/lpr) T cells massively expanded and differentiated into IFN-γ-secreting effector cells in transgenic mice that constitutively express the CD27 ligand, CD70. Concomitantly, CD95-deficient CD70 transgenic mice became moribund by 4 wk of age with severe liver pathology and bone marrow failure. These findings establish that CD95 is a critical regulator of effector T cell homeostasis in chronic immune activation.

SummaryThis single‐centre retrospective observational study analysed the efficacy of retreatment with immunomodulatory agents (IMiDs) and proteasome inhibitors (PIs) after treatment with daratumumab monotherapy in patients with relapsed and/or refractory multiple myeloma (RRMM). In total 55 patients were treated with daratumumab monotherapy between 2010 and 2017. From this group 29 (53%) IMiD‐refractory patients were retreated with an IMiD after daratumumab and 6 (11%) PI‐refractory patients were retreated with a PI‐based regimen. For the IMiD‐refractory patients the overall response rate (ORR) was 52% (15/29 patients, partial response or better) upon IMiD retreatment, whereas the ORR to PI retreatment was 67% (4/6 patients) in the PI‐refractory group. The immunomodulatory effects of daratumumab may play a role in these high response rates in previously refractory patients. Due to the >6 month‐long persistence of daratumumab in the plasma the subsequent therapies can effectively be considered as combination therapy. Furthermore, the excellent tolerability of daratumumab treatment may enable patients to recover from prior lines of treatment and receive full dosing of subsequent therapies. In conclusion, a high proportion of RRMM patients benefitted from retreatment with IMiDs and PIs after daratumumab treatment. These retreatment options should therefore be explored in RRMM patients progressing on daratumumab monotherapy.

In more recent years, anti-CD20 monoclonal antibodies have become the backbone in the treatment of chronic lymphocytic leukemia (CLL). Historically, these antibodies were typically combined with chemotherapeutic agents. At present, therapeutic outcomes are significantly improving with the introduction of several novel targeted drugs to the clinical repertoire. Areas covered: In this review, we summarize the current clinical standard together with the latest developments in the field of anti-CD20 antibodies against CLL. In addition, novel promising drugs against CLL are discussed, as well as their potential for combination with anti-CD20 monoclonal antibodies. Expert opinion: At present, there are three different anti-CD20 monoclonal antibodies approved for the treatment of CLL with diverse effector mechanisms. These antibodies provide a robust foundation for combination therapy with novel molecules. Current research should be focused on reducing toxicity and reaching long-lasting remissions. There is still much to gain regarding the optimization of treatment combinations and dosing schedules for CLL. Overcoming the limitations of currently used anti-CD20 antibodies will be critical to further improve the efficacy of CLL therapy.