Ibrutinib enhances chimeric antigen receptor T-cell engraftment and efficacy in leukemia.

Anti-CD19 chimeric antigen receptor (CAR) T-cell therapy is highly promising but requires robust T-cell expansion and engraftment. A T-cell defect in chronic lymphocytic leukemia (CLL) due to disease and/or therapy impairs ex vivo expansion and response to CAR T cells. To evaluate the effect of ibrutinib treatment on the T-cell compartment in CLL as it relates to CAR T-cell generation, we examined the phenotype and function of T cells in a cohort of CLL patients during their course of treatment with ibrutinib. We found that ≥5 cycles of ibrutinib therapy improved the expansion of CD19-directed CAR T cells (CTL019), in association with decreased expression of the immunosuppressive molecule programmed cell death 1 on T cells and of CD200 on B-CLL cells. In support of these findings, we observed that 3 CLL patients who had been treated with ibrutinib for ≥1 year at the time of T-cell collection had improved ex vivo and in vivo CTL019 expansion, which correlated positively together and with clinical response. Lastly, we show that ibrutinib exposure does not impair CAR T-cell function in vitro but does improve CAR T-cell engraftment, tumor clearance, and survival in human xenograft models of resistant acute lymphocytic leukemia and CLL when administered concurrently. Our collective findings indicate that ibrutinib enhances CAR T-cell function and suggest that clinical trials with combination therapy are warranted. Our studies demonstrate that improved T-cell function may also contribute to the efficacy of ibrutinib in CLL. These trials were registered at www.clinicaltrials.gov as #NCT01747486, #NCT01105247, and #NCT01217749.

Nature of tumor control by permanently and transiently modified GD2 chimeric antigen receptor T cells in xenograft models of neuroblastoma.

Chimeric antigen receptor (CAR) therapy has begun to demonstrate success as a novel treatment modality for hematologic malignancies. The success observed thus far has been with T cells permanently engineered to express chimeric receptors. T cells engineered using RNA electroporation represent an alternative with the potential for similar efficacy and greater safety when initially targeting novel antigens. Neuroblastoma is a common pediatric solid tumor with the potential to be targeted using immunotherapy. We performed xenograft studies in NSG mice in which we assessed the efficacy of both permanently modified and transiently modified CAR T cells directed against the neuroblastoma antigen GD2 in both local and disseminated disease models. Disease response was monitored by tumor volume measurement and histologic examination, as well as in vivo bioluminescence. RNA-modified GD2 CAR T cells mediated rapid tumor destruction when delivered locally. A single infusion of lentivirally modified GD2 CAR T cells resulted in long-term control of disseminated disease. Multiple infusions of RNA GD2 CAR T cells slowed the progression of disseminated disease and improved survival, but did not result in long-term disease control. Histologic examination revealed that the transiently modified cells were unable to significantly penetrate the tumor environment when delivered systemically, despite multiple infusions of CAR T cells. Thus, we demonstrate that RNA-modified GD2 CAR T cells can mediate effective antitumor responses in vivo, and permanently modified cells are able to control disseminated neuroblastoma in xenograft mice. Lack of long-term disease control by RNA-engineered cells resulted from an inability to penetrate the tumor microenvironment.

Thymic stromal-derived lymphopoietin induces proliferation of pre-B leukemia and antagonizes mTOR inhibitors, suggesting a role for interleukin-7Ralpha signaling.

Understanding the pathogenesis of leukemia in the context of lymphopoiesis may reveal novel therapeutic targets. Previously, we have shown that mTOR inhibitors (MTI) show activity in vitro and in preclinical models of both human and murine precursor B acute lymphoblastic leukemia (pre-B ALL), inhibiting cell proliferation and inducing apoptosis. These MTI-mediated effects can be reversed by interleukin-7 (IL-7), an important regulator of early B-cell development. This observation led us to examine the contribution of signaling via the IL-7Ralpha chain, which is shared by the receptor complexes of IL-7 and thymic stromal-derived lymphopoietin (TSLP). TSLP is closely related to IL-7 and active in lymphopoiesis, but an effect of TSLP on leukemia cells has not been described. We examined the effect of TSLP on pre-B ALL cells and their response to MTIs. Here, we show that TSLP stimulates proliferation of pre-B ALL cell lines. TSLP also partially reverses the effects of MTI on proliferation, apoptosis, and ribosomal protein S6 and 4E-BP1 phosphorylation in cell lines, with similar biological effects seen in some primary human lymphoblast samples. These data show that TSLP can promote survival of pre-B ALL cells and antagonize the effects of MTIs. These findings suggest that IL-7Ralpha chain is responsible for transducing the survival signal that overcomes MTI-mediated growth inhibition in pre-B ALL. Thus, further exploration of the IL-7Ralpha pathway may identify potential therapeutic targets in the treatment of ALL. Our data illustrate that growth-factor-mediated signaling may provide one mechanism of MTI resistance.

Rapamycin improves lymphoproliferative disease in murine autoimmune lymphoproliferative syndrome (ALPS).

Autoimmune lymphoproliferative syndrome (ALPS) is a disorder of abnormal lymphocyte survival caused by defective Fas-mediated apoptosis, leading to lymphadenopathy, hepatosplenomegaly, and an increased number of double-negative T cells (DNTs). Treatment options for patients with ALPS are limited. Rapamycin has been shown to induce apoptosis in normal and malignant lymphocytes. Since ALPS is caused by defective lymphocyte apoptosis, we hypothesized that rapamycin would be effective in treating ALPS. We tested this hypothesis using rapamycin in murine models of ALPS. We followed treatment response with serial assessment of DNTs by flow cytometry in blood and lymphoid tissue, by serial monitoring of lymph node and spleen size with ultrasonography, and by enzyme-linked immunosorbent assay (ELISA) for anti-double-stranded DNA (dsDNA) antibodies. Three-dimensional ultrasound measurements in the mice correlated to actual tissue measurements at death (r = .9648). We found a dramatic and statistically significant decrease in DNTs, lymphadenopathy, splenomegaly, and autoantibodies after only 4 weeks when comparing rapamycin-treated mice with controls. Rapamycin induced apoptosis through the intrinsic mitochondrial pathway. We compared rapamycin to mycophenolate mofetil, a second-line agent used to treat ALPS, and found rapamycin's control of lymphoproliferation was superior. We conclude that rapamycin is an effective treatment for murine ALPS and should be explored as treatment for affected humans.