Armen Mardiros

T cells expressing CD123-specific chimeric antigen receptors exhibit specific cytolytic effector functions and antitumor effects against human acute myeloid leukemia.

Induction treatments for acute myeloid leukemia (AML) have remained largely unchanged for nearly 50 years, and AML remains a disease of poor prognosis. Allogeneic hematopoietic cell transplantation can achieve cures in select patients and highlights the susceptibility of AML to donor-derived immunotherapy. The interleukin-3 receptor α chain (CD123) has been identified as a potential immunotherapeutic target because it is overexpressed in AML compared with normal hematopoietic stem cells. Therefore, we developed 2 chimeric antigen receptors (CARs) containing a CD123-specific single-chain variable fragment, in combination with a CD28 costimulatory domain and CD3-ζ signaling domain, targeting different epitopes on CD123. CD123-CAR-redirected T cells mediated potent effector activity against CD123+ cell lines as well as primary AML patient samples. CD123 CAR T cells did not eliminate granulocyte/macrophage and erythroid colony formation in vitro. Additionally, T cells obtained from patients with active AML can be modified to express CD123 CARs and are able to lyse autologous AML blasts in vitro. Finally, CD123 CAR T cells exhibited antileukemic activity in vivo against a xenogeneic model of disseminated AML. These results suggest that CD123 CAR T cells are a promising immunotherapy for the treatment of high-risk AML.

Chimeric Antigen Receptors With Mutated IgG4 Fc Spacer Avoid Fc Receptor Binding and Improve T Cell Persistence and Antitumor Efficacy

The success of adoptive therapy using chimeric antigen receptor (CAR)-expressing T cells partly depends on optimal CAR design. CARs frequently incorporate a spacer/linker region based on the constant region of either IgG1 or IgG4 to connect extracellular ligand-binding with intracellular signaling domains. Here, we evaluated the potential for the IgG4-Fc linker to result in off-target interactions with Fc gamma receptors (FcγRs). As proof-of-principle, we focused on a CD19-specific scFv-IgG4-CD28-zeta CAR and found that, in contrast to CAR-negative cells, CAR+ T cells bound soluble FcγRs in vitro and did not engraft in NSG mice. We hypothesized that mutations to avoid FcγR binding would improve CAR+ T cell engraftment and antitumor efficacy. Thus, we generated CD19-specific CARs with IgG4-Fc spacers that had either been mutated at two sites (L235E; N297Q) within the CH2 region (CD19R(EQ)) or incorporated a CH2 deletion (CD19Rch2Δ). These mutations reduced binding to soluble FcγRs without altering the ability of the CAR to mediate antigen-specific lysis. Importantly, CD19R(EQ) and CD19Rch2Δ T cells exhibited improved persistence and more potent CD19-specific antilymphoma efficacy in NSG mice. Together, these studies suggest that optimal CAR function may require the elimination of cellular FcγR interactions to improve T cell persistence and antitumor responses.

CMVpp65 Vaccine Enhances the Antitumor Efficacy of Adoptively Transferred CD19-Redirected CMV-Specific T Cells

Purpose: T cells engineered with chimeric antigen receptors (CAR) recognizing CD19 can induce complete remission of B-cell malignancies in clinical trials; however, in some disease settings, CAR therapy confers only modest clinical benefit due to attenuated persistence of CAR T cells. The purpose of this study was to enhance persistence and augment the antitumor activity of adoptively transferred CD19CAR T cells by restimulating CAR+ T cells through an endogenous cytomegalovirus (CMV)-specific T-cell receptor. Experimental Design: CMV-specific T cells from CMV seropositive healthy donors were selected after stimulation with pp65 protein and transduced with clinical-grade lentivirus expressing the CD19R:CD28:ζ/EGFRt CAR. The resultant bispecific T cells, targeting CMV and CD19, were expanded via CD19 CAR-mediated signals using CD19-expressing cells. Results: The bispecific T cells proliferated vigorously after engagement with either endogenous CMVpp65 T-cell receptors or engineered CD19 CARs, exhibiting specific cytolytic activity and IFNγ secretion. Upon adoptive transfer into immunodeficient mice bearing human lymphomas, the bispecific T cells exhibited proliferative response and enhanced antitumor activity following CMVpp65 peptide vaccine administration. Conclusions: We have redirected CMV-specific T cells to recognize and lyse tumor cells via CD19CARs, while maintaining their ability to proliferate in response to CMV antigen stimulation. These results illustrate the clinical applications of CMV vaccine to augment the antitumor activity of adoptively transferred CD19CAR T cells in patients with B-cell malignancies. Clin Cancer Res; 21(13); 2993–3002. ©2015 AACR.

T cells expressing CD123 chimeric antigen receptors for treatment of acute myeloid leukemia

Purpose of reviewThe purpose of this article is to discuss the rationale of targeting CD123 using chimeric antigen receptor (CAR) T cells for the treatment of leukemia. Recent findingsCD123 is a leukemia-associated antigen that expresses at high levels in leukemic stem cells and leukemic blasts and low level in normal hematopoietic stem/progenitor cells. Immune-based therapies targeting CD123 are being developed. Preclinical data suggest that CD123 CAR T cells exhibit potent antileukemic activity and various impacts on normal hematopoiesis. SummaryCD123 is an attractive surface target for novel antileukemic therapies. CD123 CAR T-cell-based immunotherapy is a promising treatment for patients with relapsed or refractory acute myeloid leukemia.

Intrinsically de-sialylated CD103+ CD8 T cells mediate beneficial anti-glioma immune responses

AbstractBackground Cancer vaccines reproducibly cure laboratory animals and reveal encouraging trends in brain tumor (glioma) patients. Identifying parameters governing beneficial vaccine-induced responses may lead to the improvement of glioma immunotherapies. CD103+ CD8 T cells dominate post-vaccine responses in human glioma patients for unknown reasons, but may be related to recent thymic emigrant (RTE) status. Importantly, CD8 RTE metrics correlated with beneficial immune responses in vaccinated glioma patients.MethodsWe show by flow cytometry that murine and human CD103+ CD8 T cells respond better than their CD103− counterparts to tumor peptide-MHC I (pMHC I) stimulation in vitro and to tumor antigens on gliomas in vivo.ResultsGlioma responsive T cells from mice and humans both exhibited intrinsic de-sialylation-affecting CD8 beta. Modulation of CD8 T cell sialic acid with neuraminidase and ST3Gal-II revealed de-sialylation was necessary and sufficient for promiscuous binding to and stimulation by tumor pMHC I. Moreover, de-sialylated status was required for adoptive CD8 T cells and lymphocytes to decrease GL26 glioma invasiveness and increase host survival in vivo. Finally, increased tumor ST3Gal-II expression correlated with clinical vaccine failure in a meta-analysis of high-grade glioma patients.ConclusionsTaken together, these findings suggest that de-sialylation of CD8 is required for hyper-responsiveness and beneficial anti-glioma activity by CD8 T cells. Because CD8 de-sialylation can be induced with exogenous enzymes (and appears particularly scarce on human T cells), it represents a promising target for clinical glioma vaccine improvement.

Acute myeloid leukemia therapeutics: CARs in the driver's seat.

Acute myeloid leukemia remains a difficult disease to cure and novel therapeutic approaches are needed. To this end, we developed CD123 chimeric antigen receptor (CAR) redirected T cells which exhibited potent antileukemic activity. We discuss what we learned during the development of CD123 CARs and future directions for this immunotherapy.

Comparison of naïve and central memory derived CD8+ effector cell engraftment fitness and function following adoptive transfer

abstract Human CD8+ effector T cells derived from CD45RO+CD62L+ precursors enriched for central memory (TCM) precursors retain the capacity to engraft and reconstitute functional memory upon adoptive transfer, whereas effectors derived from CD45RO+CD62L− precursors enriched for effector memory precursors do not. Here we sought to compare the engraftment fitness and function of CD8+ effector T cells derived from CD45RA+CD62L+ precursors enriched for naïve and stem cell memory precursors (TN/SCM) with that of TCM. We found that cytotoxic T cells (CTLs) derived from TCM transcribed higher levels of CD28, FOS, INFγ, Eomesodermin (Eomes), and lower levels of BCL2L11, maintained higher levels of phosphorylated AKT, and displayed enhanced sensitivity to the proliferative and anti-apoptotic effects of γ-chain cytokines compared to CTLs derived from TN/SCM. Higher frequencies of CTLs derived from TCM retained CD28 expression and upon activation secreted higher levels of IL-2. In NOD/Scid IL-2RγCnull mice, CD8+ TCM derived CTLs engrafted to higher frequencies in response to human IL-15 and mounted robust proliferative responses to an immunostimulatory vaccine. Similarly, CD8+ TCM derived CD19CAR+ CTLs exhibited superior antitumor potency following adoptive transfer compared to their CD8+ TN/SCM derived counterparts. These studies support the use of TCM enriched cell products for adoptive therapy of cancer.

Chimeric antigen receptors (CARs) incorporating mutations in the IgG4 Fc spacer region to eliminate Fc receptor recognition results in improved CAR T cell persistence and anti-tumor efficacy

Adoptive immunotherapy using T cells genetically redirected via expression of chimeric antigen receptors (CARs) is a promising approach for cancer treatment. However, this immunotherapy is dependent in part on the optimal molecular design of the CAR, which involves an extracellular ligand-binding domain connected to an intracellular signaling domain by spacer and/or transmembrane sequences. CAR designs frequently incorporate extracellular linker regions based on the immunoglobulin constant regions of either IgG1 or IgG4. In this study we evaluated the potential for the IgG4-Fc linker to result in off-target interactions between the CAR and Fc gamma receptors (FcγRs). As proof of principle, we have focused on a CD19-specific CD19scFv-IgG4-CD28-zeta CAR, and indeed found that CAR+ T cells bound to soluble FcγRs, and did not engraft in NSG mice compared to CAR-negative T cells that only expressed an EGFRt tracking marker. We hypothesized that mutations to avoid FcγR interactions would improve CAR+ T cell persistence and anti-tumor efficacy. To this end, we generated a CD19-specific CAR that has been mutated at two sites within the CH2 region (L235E; N297Q) of the IgG4 Fc spacer, here called CD19R(EQ), as well as a CD19-specific CAR that has a CH2 deletion in its IgG4 Fc spacer (CD19Rch2Δ). These mutations/deletion do not alter the functional ability of the CAR, when expressed by T cells, to mediate antigen-specific lysis of tumor cells. However, compared to T cells that express a non-mutated CAR, T cells expressing the CD19R(EQ) and CD19Rch2Δ exhibit impaired binding to recombinant soluble FcγRs. These CD19R(EQ) and CD19Rch2Δ T cells also exhibit improved engraftment in NSG mice. Indeed the engraftment levels seen with the mutated CAR were similar to that seen with CAR-negative T cells that only expressed the EGFRt tracking marker. Importantly, elimination of CAR/FcγR interactions also significantly improves CD19-specific CAR+ T cell anti-lymphoma efficacy in NSG mice. These studies provide evidence that optimal CAR function necessitates the elimination of cellular FcγR interactions in order to improve T cell persistence and anti-tumor responses.

Abstract 4979: Development of KITE-585: A fully human BCMA CAR T-cell therapy for the treatment of multiple myeloma

Background: Multiple myeloma (MM) is a usually fatal malignancy of plasma cells, with no current therapy considered curative. About 15% of patients diagnosed with MM are stratified as high risk with poor treatment outcomes and short (2-3 years) survival from diagnosis. Standard risk patients tend to live longer but undergo chronic and/or high intensity therapy and likely experience a relapsing and remitting disease pattern. Therefore, there is still a considerable unmet need for innovative therapies that improve outcomes in MM. One such approach is to use adoptive transfer of engineered autologous T cells expressing a chimeric antigen receptor (CAR) directed against malignant cells. The efficacy of CAR T cells directed against hematological malignancies, particularly CD19-expressing B cell leukemia and lymphomas, has been demonstrated in multiple clinical studies. KITE-585 was developed as a CAR T cell immunotherapy product candidate directed against B cell maturation antigen (BCMA). BCMA is nearly ubiquitously expressed on MM cells, plasma cells and subsets of mature B cells, but with limited or absent expression on other tissues. Methods: We generated >50 fully human IgGs directed against BCMA using the BCMA protein as antigen and selection criteria including affinity, cross-reactivity and poly-specificity. Following assessment of the binding of the IgGs to a MM cell line known to express BCMA, >10 IgGs were identified that met the criteria for affinity and selectivity and had a >50-fold binding over background. The 8 IgGs that demonstrated the highest specific binding were then sequence-converted to single-chain variable fragments (scFvs) and incorporated into CARs. Results: In all but one case, human T cells engineered to express these CAR constructs exhibited specific cytolytic activity against MM cell lines (NCI-H929 and MM.1s). These CAR T cells demonstrated killing efficiencies of >95% at effector:target ratios of 1:1 over a 24-hour period. Similarly antigen-specific production of inflammatory cytokines was observed in response to target cell lines in vitro. Assessment of antigen-dependent proliferation over a 5 day period revealed >80% proliferation in the 7 constructs that showed cytolytic activity in vitro. Multiple different anti-BCMA CAR constructs representing distinct epitope binding bins of BCMA were then selected for in vivo evaluation. In two disseminated tumor models of luciferase labeled NCI-H929 or MM.1s cells injected intravenously (i.v.), a single i.v. injection of anti-BCMA CAR T-cells delayed the progression of disease and significantly increased survival when compared to control treatment. Conclusions: The results of these studies highlight the potential of targeting BCMA with adoptive transfer of engineered T cells for the treatment of MM. Given these positive findings, progress towards Phase 1 clinical studies in MM patients with KITE-585 is continuing. Citation Format: Gregor B. Adams, Jun Feng, Atefah Ghogha, Armen Mardiros, Jodi Murakami, Tammy Phung, Ruben Rodriguez, Stuart Sievers, Tassja J. Spindler, Jed Wiltzius, Clare Yarka, Sean C. Yoder, Tony Polverino. Development of KITE-585: A fully human BCMA CAR T-cell therapy for the treatment of multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4979. doi:10.1158/1538-7445.AM2017-4979