The PI3Kδ-Selective Inhibitor Idelalisib Minimally Interferes with Immune Effector Function Mediated by Rituximab or Obinutuzumab and Significantly Augments B Cell Depletion In Vivo.

Idelalisib is a highly selective oral inhibitor of PI3Kδ indicated for the treatment of patients with relapsed chronic lymphocytic leukemia in combination with rituximab. Despite additive clinical effects, previous studies have paradoxically demonstrated that targeted therapies potentially negatively affect anti-CD20 mAb effector mechanisms. To address these potential effects, we investigated the impact of PI3Kδ inhibition by idelalisib on the effector mechanisms of rituximab and obinutuzumab. At clinically relevant concentrations, idelalisib minimally influenced rituximab- and obinutuzumab-mediated Ab-dependent cellular cytotoxicity and phagocytosis on human lymphoma cell lines, while maintaining the superiority of obinutuzumab-mediated Ab-dependent cellular cytotoxicity. Consistent with this, idelalisib did not influence obinutuzumab-mediated B cell depletion in whole-blood B cell-depletion assays. Further, idelalisib significantly enhanced obinutuzumab-mediated direct cell death of chronic lymphocytic leukemia cells. In murine systems, in vivo inhibition of PI3Kδ minimally interfered with maximal rituximab- or obinutuzumab-mediated depletion of leukemic targets. In addition, the duration of rituximab- and obinutuzumab-mediated depletion of leukemia cells was extended by combination with PI3Kδ inhibition. Collectively, these data demonstrate that PI3Kδ inhibition does not significantly affect the effector mechanisms induced by rituximab or obinutuzumab and provides an effective in vivo therapeutic combination. Therefore, combinations of obinutuzumab and idelalisib are currently being assessed in clinical studies.

CD20-directed small modular immunopharmaceutical, TRU-015, depletes normal and malignant B cells.

PURPOSE: CD20-directed therapy with rituximab is effective in many patients with malignant lymphoma or follicular lymphoma. However, relapse frequently occurs within 1 year, and patients become increasingly refractory to retreatment. Our purpose was to produce a compact, single-chain CD20-targeting immunotherapeutic that could offer therapeutic advantages in the treatment of B-cell lymphoma. EXPERIMENTAL DESIGN: Rituximab is a chimeric antibody containing two heavy chains and two light chains. Here, we describe the properties of TRU-015, a small modular immunopharmaceutical specific for CD20, encoded by a single-chain construct containing a single-chain Fv specific for CD20 linked to human IgG1 hinge, CH2, and CH3 domains but devoid of CH1 and CL domains. RESULTS: TRU-015 mediates potent direct signaling and antibody-dependent cellular cytotoxicity but has reduced size and complement-mediated cytotoxicity activity compared with rituximab. TRU-015 is a compact dimer of 104 kDa that comigrates with albumin in size exclusion chromatography and retains a long half-life in vivo. TRU-015 induced growth arrest in multiple B lymphoma cell lines in vitro and showed effective antitumor activity against large, established subcutaneous Ramos or Daudi xenograft tumors in nude mice. TRU-015 also showed rapid, dose-dependent, and durable depletion of peripheral blood B cells following single-dose administration to nonhuman primates. CONCLUSION: These results indicate that TRU-015 may improve CD20-directed therapy by effectively depleting embedded malignant B cells and nonmalignant pathogenic B cells and do so with reduced complement activation.

In vitro engagement of CD3 and CD28 corrects T cell defects in chronic lymphocytic leukemia.

Chronic lymphocytic leukemia (CLL) is characterized by the accumulation of leukemic B cells concomitant with immunological abnormalities and depressed immune responses. The T cell abnormalities found in CLL patients are thought to increase the risk of infection and hamper immune recognition and elimination of leukemic cells. We evaluated whether providing signals through CD3 and CD28 would correct some of these T cell defects. PBMC were incubated with anti-CD3 and anti-CD28 mAbs conjugated to superparamagnetic beads for 12-14 days. This resulted in a 1400-fold increase in T cell numbers. Activated T cells expressed high levels of CD25, CD54, CD137, and CD154, and produced IFN-gamma, TNF-alpha, and GM-CSF. The mean T cell composition of cultures increased from approximately 6% to >90% and leukemic B cells decreased from a mean of approximately 85% to 0.1% or less. Leukemic B cells up-regulated expression of CD54, CD80, CD86, and CD95. Receptor up-regulation required direct cell contact with the activated T cells and could be blocked with anti-CD154 mAb, suggesting that the CD40-CD40L pathway helped mediate these effects. Poor T cell responses to allostimulation were corrected by the activation and expansion process. The skewing in the TCR repertoire returned to normal, or near normal following the culture process in eight of nine patients with abnormal TCR repertoires. Activated T cells had potent in vitro antileukemic effects in contrast to nonactivated T cells. Based upon these findings, a clinical trial has been initiated to test the potential therapeutic effects of T cells activated using this approach in patients with CLL.