Co-targeting EBV lytic as well as latent cycle antigens increases T-cell potency against lymphoma

The remarkable efficacy of Epstein-Barr virus (EBV) specific T-cells for the treatment of post-transplant lymphomas (PTLD) has not been reproduced for EBV+ malignancies outside the transplant setting. This is due in part to the heterogeneous expression and poor immunogenicity of the viral antigens expressed, namely LMPs 1 and 2, EBNA1, and BARF1 (type-2 (T2) latency). However, EBV lytic cycle proteins are also expressed in certain EBV+ malignancies, and since several EBV lytic cycle proteins are abundantly expressed, have oncogenic activity, and likely contribute to malignancy, we sought and identified viral lytic-cycle transcripts in EBV+ Hodgkin's lymphoma biopsies. This provided the rationale for broadening the target antigen-specific repertoire of EBVSTs for therapy. We stimulated healthy donors and EBV+ lymphoma patients' peripheral blood mononuclear cells (PBMCs) with both lytic and latent cycle proteins to make broad repertoire (BR)-EBVSTs). Compared to T2 Ag-specific (T2-) EBVSTs, BR-EBVSTs more rapidly cleared autologous EBV+ tumors in NSG mice and produced higher levels of pro-inflammatory cytokines that should reactivate the immunosuppressive tumor microenvironment leading to epitope spreading. Our results confirm that lytic cycle antigens are clinically relevant targets for EBV+ lymphoma and underpin the rationale for integrating BR-EBVSTs as a therapeutic approach for relapsed/refractory EBV-positive lymphoma (NCT01555892 and NCT04664179), as well as for other EBV-associated malignancies.

Eighteen-year survival after GD2-directed Chimeric Antigen Receptor-Modified Immune Effector Cell Treatment for Neuroblastoma

We report long-term outcomes up to 18 years of a clinical trial treating children with neuroblastoma with EBV-specific T lymphocytes and CD3-activated T cells - each expressing a first-generation chimeric antigen receptor targeting GD2 with barcoded transgenes to allow tracking of each population. Of 11 patients with active disease at infusion, three patients achieved a complete response that was sustained in 2, one for 8 years until lost to follow up and one for 18+ years. Of eight patients with a history of relapse or at high risk of recurrence, five are disease-free at their last follow-up between 10-14 years post-infusion. Intermittent low levels of transgene were detected during the follow up period with significantly greater persistence in those who were long-term survivors. In conclusion, patients with relapsed/refractory neuroblastoma achieved long-term disease control after receiving GD2 CAR-T cell therapy including one patient now in remission of relapsed disease for >18 years.

Structural surfaceomics reveals an AML-specific conformation of integrin β2 as a CAR T cellular therapy target

Safely expanding indications for cellular therapies has been challenging given a lack of highly cancer-specific surface markers. Here we explore the hypothesis that tumor cells express cancer-specific surface protein conformations that are invisible to standard target discovery pipelines evaluating gene or protein expression, and these conformations can be identified and immunotherapeutically targeted. We term this strategy integrating cross-linking mass spectrometry with glycoprotein surface capture 'structural surfaceomics'. As a proof of principle, we apply this technology to acute myeloid leukemia (AML), a hematologic malignancy with dismal outcomes and no known optimal immunotherapy target. We identify the activated conformation of integrin β2 as a structurally defined, widely expressed AML-specific target. We develop and characterize recombinant antibodies to this protein conformation and show that chimeric antigen receptor T cells eliminate AML cells and patient-derived xenografts without notable toxicity toward normal hematopoietic cells. Our findings validate an AML conformation-specific target antigen and demonstrate a tool kit for applying these strategies more broadly.

Constitutive Interleukin-7 Cytokine Signaling Enhances the Persistence of Epstein-Barr Virus-Specific T-Cells

The efficacy of therapeutic T-cells is limited by a lack of positive signals and excess inhibitory signaling in tumor microenvironments. We previously showed that a constitutively active IL7 receptor (C7R) enhanced the persistence, expansion, and anti-tumor activity of T-cells expressing chimeric antigen receptors (CARs), and C7R-modified GD2.CAR T-cells are currently undergoing clinical trials. To determine if the C7R could also enhance the activity of T-cells recognizing tumors via their native T-cell receptors (TCRs), we evaluated its effects in Epstein-Barr virus (EBV)-specific T-cells (EBVSTs) that have produced clinical benefits in patients with EBV-associated malignancies. EBVSTs were generated by stimulation of peripheral blood T-cells with overlapping peptide libraries spanning the EBV lymphoma antigens, LMP1, LMP2, and EBNA 1, followed by retroviral vector transduction to express the C7R. The C7R increased STAT5 signaling in EBVSTs and enhanced their expansion over 30 days of culture in the presence or absence of exogenous cytokines. C7R-EBVSTs maintained EBV antigen specificity but were dependent on TCR stimulation for continued expansion. C7R-EBVSTs produced more rapid lymphoma control in a murine xenograft model than unmodified EBVSTs and persisted for longer. The findings have led to a clinical trial, evaluating C7R-EBVSTs for the treatment of refractory or relapsed EBV-positive lymphoma (NCT04664179).

Allogeneic, off-the-shelf, SARS-CoV-2-specific T cells (ALVR109) for the treatment of COVID-19 in high-risk patients

Defects in T-cell immunity to SARS-CoV-2 have been linked to an increased risk of severe COVID-19 (even after vaccination), persistent viral shedding and the emergence of more virulent viral variants. To address this T-cell deficit, we sought to prepare and cryopreserve banks of virus-specific T cells, which would be available as a partially HLA-matched, off-the-shelf product for immediate therapeutic use. By interrogating the peripheral blood of healthy convalescent donors, we identified immunodominant and protective T-cell target antigens, and generated and characterized polyclonal virus-specific T-cell lines with activity against multiple clinically important SARS-CoV-2 variants (including 'delta' and 'omicron'). The feasibility of making and safely utilizing such virus-specific T cells clinically was assessed by administering partially HLA-matched, third-party, cryopreserved SARS-CoV-2-specific T cells (ALVR109) in combination with other antiviral agents to four individuals who were hospitalized with COVID-19. This study establishes the feasibility of preparing and delivering off-the-shelf, SARS-CoV-2-directed, virus-specific T cells to patients with COVID-19 and supports the clinical use of these products outside of the profoundly immune compromised setting (ClinicalTrials.gov number, NCT04401410).

Naive T cells inhibit the outgrowth of intractable antigen-activated memory T cells: implications for T-cell immunotherapy

BACKGROUND

The wider application of T cells targeting viral tumor-antigens via their native receptors is hampered by the failure to expand potent tumor-specific T cells from patients. Here, we examine reasons for and solutions to this failure, taking as our model the preparation of Epstein-Barr virus (EBV)-specific T cells (EBVSTs) for the treatment of EBV-positive lymphoma. EBVSTs could not be manufactured from almost one-third of patients, either because they failed to expand, or they expanded, but lacked EBV specificity. We identified an underlying cause of this problem and established a clinically feasible approach to overcome it.

METHODS

CD45RO+CD45RA- memory compartment residing antigen-specific T cells were enriched by depleting CD45RA positive (+) peripheral blood mononuclear cells (PBMCs) that include naïve T cells, among other subsets, prior to EBV antigen stimulation. We then compared the phenotype, specificity, function and T-cell receptor (TCR) Vβ repertoire of EBVSTs expanded from unfractionated whole (W)-PBMCs and CD45RA-depleted (RAD)-PBMCs on day 16. To identify the CD45RA component that inhibited EBVST outgrowth, isolated CD45RA+ subsets were added back to RAD-PBMCs followed by expansion and characterization. The in vivo potency of W-EBVSTs and RAD-EBVSTs was compared in a murine xenograft model of autologous EBV+ lymphoma.

RESULTS

Depletion of CD45RA+ PBMCs before antigen stimulation increased EBVST expansion, antigen-specificity and potency in vitro and in vivo. TCR sequencing revealed a selective outgrowth in RAD-EBVSTs of clonotypes that expanded poorly in W-EBVSTs. Inhibition of antigen-stimulated T cells by CD45RA+ PBMCs could be reproduced only by the naïve T-cell fraction, while CD45RA+ regulatory T cells, natural killer cells, stem cell memory and effector memory subsets lacked inhibitory activity. Crucially, CD45RA depletion of PBMCs from patients with lymphoma enabled the outgrowth of EBVSTs that failed to expand from W-PBMCs. This enhanced specificity extended to T cells specific for other viruses.

CONCLUSION

Our findings suggest that naïve T cells inhibit the outgrowth of antigen-stimulated memory T cells, highlighting the profound effects of intra-T-cell subset interactions. Having overcome our inability to generate EBVSTs from many patients with lymphoma, we have introduced CD45RA depletion into three clinical trials: NCT01555892 and NCT04288726 using autologous and allogeneic EBVSTs to treat lymphoma and NCT04013802 using multivirus-specific T cells to treat viral infections after hematopoietic stem cell transplantation.

Banking on virus-specific T cells to fulfill the need for off-the-shelf cell therapies

Adoptively transferred virus-specific T cells (VSTs) have shown remarkable safety and efficacy for the treatment of virus-associated diseases and malignancies in hematopoietic stem cell transplant (HSCT) recipients, for whom VSTs are derived from the HSCT donor. Autologous VSTs have also shown promise for the treatment of virus-driven malignancies outside the HSCT setting. In both cases, VSTs are manufactured as patient-specific products, and the time required for procurement, manufacture, and release testing precludes their use in acutely ill patients. Further, Good Manufacturing Practices-compliant products are expensive, and failures are common in virus-naive HSCT donors and patient-derived VSTs that are rendered anergic by immunosuppressive tumors. Hence, highly characterized, banked VSTs (B-VSTs) that can be used for multiple unrelated recipients are highly desirable. The major challenges facing B-VSTs result from the inevitable mismatches in the highly polymorphic and immunogenic human leukocyte antigens (HLA) that present internally processed antigens to the T-cell receptor, leading to the requirement for partial HLA matching between the B-VST and recipient. HLA mismatches lead to rapid rejection of allogeneic T-cell products and graft-versus-host disease induced by alloreactive T cells in the infusion product. Here, we summarize the clinical outcomes to date of trials of B-VSTs used for the treatment of viral infections and malignancies and their potential as a platform for chimeric antigen receptors targeting nonviral tumors. We will highlight the properties of VSTs that make them attractive off-the-shelf cell therapies, as well as the challenges that must be overcome before they can become mainstream.

A Practical Guide to 16S rRNA Microbiome Analysis in Musculoskeletal Disorders

Microbial taxonomic assignment based on 16S marker gene amplification requires multiple data transformations, often encompassing the use of a variety of computational platforms. Bioinformatics analysis may represent a bottleneck for researchers as many tools require programmatic access in order to implement the software. Here we describe a step-by-step approach for taxonomic assignment using QIIME2 and highlight the utility of graphical-based microbiome tools for further analysis and identification of biological relevant taxa with reference to an outcome of interest.

Multi-antigen-targeted T-cell therapy to treat patients with relapsed/refractory breast cancer

Purpose

Adoptively transferred, ex vivo expanded multi-antigen-targeted T cells (multiTAA-T) represent a new, potentially effective, and nontoxic therapeutic approach for patients with breast cancer (BC). In this first-in-human trial, we investigated the safety and clinical effects of administering multiTAA T cells targeting the tumor-expressed antigens, Survivin, NY-ESO-1, MAGE-A4, SSX2, and PRAME, to patients with relapsed/refractory/metastatic BC.

Materials and methods

MultiTAA T-cell products were generated from the peripheral blood of heavily pre-treated patients with metastatic or locally recurrent unresectable BC of all subtypes and infused at a fixed dose level of 2 × 10⁷/m². Patients received two infusions of cells 4 weeks apart and safety and clinical activity were determined. Cells were administered in an outpatient setting and without prior lymphodepleting chemotherapy.

Results

All patients had estrogen receptor/progesterone receptor positive BC, with one patient also having human epidermal growth factor receptor 2-positive. There were no treatment-related toxicities and the infusions were well tolerated. Of the 10 heavily pre-treated patients enrolled and infused with multiTAA T cells, nine had disease progression while one patient with 10 lines of prior therapies experienced prolonged (5 months) disease stabilization that was associated with the in vivo expansion and persistence of T cells directed against the targeted antigens. Furthermore, antigen spreading and the endogenous activation of T cells directed against a spectrum of non-targeted tumor antigens were observed in 7/10 patients post-multiTAA infusion.

Conclusion

MultiTAA T cells were well tolerated and induced disease stabilization in a patient with refractory BC. This was associated with in vivo T-cell expansion, persistence, and antigen spreading. Future directions of this approach may include additional strategies to enhance the therapeutic benefit of multiTAA T cells in patients with BC.

Long-term follow-up for the development of subsequent malignancies in patients treated with genetically modified IECs

Subsequent malignancies are well-documented complications in long-term follow-up of cancer patients. Recently, genetically modified immune effector (IE) cells have shown benefit in hematologic malignancies and are being evaluated in clinical trials for solid tumors. Although the short-term complications of IE cells are well described, there is limited literature summarizing long-term follow-up, including subsequent malignancies. We retrospectively reviewed data from 340 patients treated across 27 investigator-initiated pediatric and adult clinical trials at our center. All patients received IE cells genetically modified with γ-retroviral vectors to treat relapsed and/or refractory hematologic or solid malignancies. In a cumulative 1027 years of long-term follow-up, 13 patients (3.8%) developed another cancer with a total of 16 events (4 hematologic malignancies and 12 solid tumors). The 5-year cumulative incidence of a first subsequent malignancy in the recipients of genetically modified IE cells was 3.6% (95% confidence interval, 1.8% to 6.4%). For 11 of the 16 subsequent tumors, biopsies were available, and no sample was transgene positive by polymerase chain reaction. Replication-competent retrovirus testing of peripheral blood mononuclear cells was negative in the 13 patients with subsequent malignancies tested. Rates of subsequent malignancy were low and comparable to standard chemotherapy. These results suggest that the administration of IE cells genetically modified with γ retroviral vectors does not increase the risk for subsequent malignancy.

Donor-derived multiple leukemia antigen-specific T-cell therapy to prevent relapse after transplant in patients with ALL

Hematopoietic stem cell transplant (HSCT) is a curative option for patients with high-risk acute lymphoblastic leukemia (ALL), but relapse remains a major cause of treatment failure. To prevent disease relapse, we prepared and infused donor-derived multiple leukemia antigen-specific T cells (mLSTs) targeting PRAME, WT1, and survivin, which are leukemia-associated antigens frequently expressed in B- and T-ALL. Our goal was to maximize the graft-versus-leukemia effect while minimizing the risk of graft-versus-host disease (GVHD). We administered mLSTs (dose range, 0.5 × 107 to 2 × 107 cells per square meter) to 11 patients with ALL (8 pediatric, 3 adult), and observed no dose-limiting toxicity, acute GVHD or cytokine release syndrome. Six of 8 evaluable patients remained in long-term complete remission (median: 46.5 months; range, 9-51). In these individuals we detected an increased frequency of tumor-reactive T cells shortly after infusion, with activity against both targeted and nontargeted, known tumor-associated antigens, indicative of in vivo antigen spreading. By contrast, this in vivo amplification was absent in the 2 patients who experienced relapse. In summary, infusion of donor-derived mLSTs after allogeneic HSCT is feasible and safe and may contribute to disease control, as evidenced by in vivo tumor-directed T-cell expansion. Thus, this approach represents a promising strategy for preventing relapse in patients with ALL.

A Costimulatory CAR Improves TCR-based Cancer Immunotherapy

T-cell receptors (TCR) recognize intracellular and extracellular cancer antigens, allowing T cells to target many tumor antigens. To sustain proliferation and persistence, T cells require not only signaling through the TCR (signal 1), but also costimulatory (signal 2) and cytokine (signal 3) signaling. Because most cancer cells lack costimulatory molecules, TCR engagement at the tumor site results in incomplete T-cell activation and transient antitumor effects. To overcome this lack of signal 2, we genetically modified tumor-specific T cells with a costimulatory chimeric antigen receptor (CoCAR). Like classical CARs, CoCARs combine the antigen-binding domain of an antibody with costimulatory endodomains to trigger T-cell proliferation, but CoCARs lack the cytotoxic CD3ζ chain to avoid toxicity to normal tissues. We first tested a CD19-targeting CoCAR in combination with an HLA-A*02:01-restricted, survivin-specific transgenic TCR (sTCR) in serial cocultures with leukemia cells coexpressing the cognate peptide-HLA complex (signal 1) and CD19 (signal 2). The CoCAR enabled sTCR+ T cells to kill tumors over a median of four additional tumor challenges. CoCAR activity depended on CD19 but was maintained in tumors with heterogeneous CD19 expression. In a murine tumor model, sTCR+CoCAR+ T cells improved tumor control and prolonged survival compared with sTCR+ T cells. We further evaluated the CoCAR in Epstein-Barr virus-specific T cells (EBVST). CoCAR-expressing EBVSTs expanded more rapidly than nontransduced EBVSTs and delayed tumor progression in an EBV+ murine lymphoma model. Overall, we demonstrated that the CoCAR can increase the activity of T cells expressing both native and transgenic TCRs and enhance antitumor responses.

CD70-specific CAR T cells have potent activity against acute myeloid leukemia without HSC toxicity

The prognosis of patients with acute myeloid leukemia (AML) remains dismal, highlighting the need for novel innovative treatment strategies. The application of chimeric antigen receptor (CAR) T-cell therapy to patients with AML has been limited, in particular by the lack of a tumor-specific target antigen. CD70 is a promising antigen to target AML, as it is expressed on most leukemic blasts, whereas little or no expression is detectable in normal bone marrow samples. To target CD70 on AML cells, we generated a panel of CD70-CAR T cells that contained a common single-chain variable fragment (scFv) for antigen detection, but differed in size and flexibility of the extracellular spacer and in the transmembrane and the costimulatory domains. These CD70scFv CAR T cells were compared with a CAR construct that contained human CD27, the ligand of CD70 fused to the CD3ζ chain (CD27z). The structural composition of the CAR strongly influenced expression levels, viability, expansion, and cytotoxic capacities of CD70scFv-based CAR T cells, but CD27z-CAR T cells demonstrated superior proliferation and antitumor activity in vitro and in vivo, compared with all CD70scFv-CAR T cells. Although CD70-CAR T cells recognized activated virus-specific T cells (VSTs) that expressed CD70, they did not prevent colony formation by normal hematopoietic stem cells. Thus, CD70-targeted immunotherapy is a promising new treatment strategy for patients with CD70-positive AML that does not affect normal hematopoiesis but will require monitoring of virus-specific T-cell responses.

Autologous EBV-specific T cell treatment results in sustained responses in patients with advanced extranodal NK/T lymphoma: results of a multicenter study

We conducted a phase II clinical trial to develop an autologous EBV-specific T cell product (baltaleucel T) for advanced, relapsed ENKTL. Among 47 patients who provided whole blood starting material for manufacturing the product, 15 patients received a median of 4 doses of baltaleucel T. Thirty-two (68%) patients did not receive baltaleucel-T due to manufacturing failure, rapid disease progression, and death. Of the 15 patients, 10 patients had measurable disease at baseline (salvage cohort), and 5 patients had no disease at baseline assessment (adjuvant cohort). In the 15 patients, the median follow-up duration was 10.2 months (range 2.0-23.5 months), median progression-free survival (PFS) was 3.9 months, and the median overall survival (OS) was not reached. Patients in the salvage cohort achieved a 30% complete response (CR) and a 50% overall response rate (ORR). In the adjuvant cohort, disease progression was reported in three patients and two patients did not relapse during study follow-up. When we compared survival outcomes of seven responders and eight non-responders, the PFS (P = 0.001) and OS (P = 0.014) of responders proved statistically superior to that of non-responders. Baltaleucel-T was well tolerated. We have performed a phase II clinical trial of autologous EBV-specific T cell treatment (baltaleucel-T) in R/R ENKTL. Autologous EBV-specific T cells were well tolerated and demonstrated single-agent activity in R/R ENTKL.

T-Cell Therapy for Lymphoma Using Nonengineered Multiantigen-Targeted T Cells Is Safe and Produces Durable Clinical Effects

PURPOSE

Patients with relapsed lymphomas often fail salvage therapies including high-dose chemotherapy and mono-antigen-specific T-cell therapies, highlighting the need for nontoxic, novel treatments. To that end, we clinically tested an autologous T-cell product that targets multiple tumor-associated antigens (TAAs) expressed by lymphomas with the intent of treating disease and preventing immune escape.

PATIENTS AND METHODS

We expanded polyclonal T cells reactive to five TAAs: PRAME, SSX2, MAGEA4, SURVIVIN, and NY-ESO-1. Products were administered to 32 patients with Hodgkin lymphomas (n = 14) or non-Hodgkin lymphomas (n = 18) in a two-part phase I clinical trial, where the objective of the first phase was to establish the safety of targeting all five TAAs (fixed dose, 0.5 × 10⁷ cells/m²) simultaneously and the second stage was to establish the maximum tolerated dose. Patients had received a median of three prior lines of therapy and either were at high risk for relapse (adjuvant arm, n = 17) or had chemorefractory disease (n = 15) at enrollment.

RESULTS

Infusions were safe with no dose-limiting toxicities observed in either the antigen- or dose-escalation phases. Although the maximum tolerated dose was not reached, the maximum tested dose at which efficacy was observed (two infusions, 2 × 10⁷ cells/m²) was determined as the recommended phase II dose. Of the patients with chemorefractory lymphomas, two (of seven) with Hodgkin lymphomas and four (of eight) with non-Hodgkin lymphomas achieved durable complete remissions (> 3 years).

CONCLUSION

T cells targeting five TAAs and administered at doses of up to two infusions of 2 × 10⁷ cells/m² are well-tolerated by patients with lymphoma both as adjuvant and to treat chemorefractory lymphoma. Preliminary indicators of antilymphoma activity were seen in the chemorefractory cohort across both antigen- and dose-escalation phases.

Evidence review of physical distancing and partition screens to reduce healthcare acquired SARS-CoV-2

We review the evidence base for two newly introduced Infection prevention and control strategies within UK hospitals. The new standard infection control precaution of 2 metres physical distancing and the use of partition screens as a means of source control of infection for SARS-CoV-2. Following review of Ovid-MEDLINE and governmental SAGE outputs there is limited evidence to support the use of 2 metres physical distancing and partition screens within healthcare.

Protecting the Microbiota

We examine 3 different approaches to protecting the gut microbiome: highly targeted antibiotics, antibiotic destruction, and antibiotic binding. Each approach shows promise to prevent the off-target effects of antibiotics on the gut microbiome.

Anti-CD30 CAR-T Cell Therapy in Relapsed and Refractory Hodgkin Lymphoma

PURPOSE

Chimeric antigen receptor (CAR) T-cell therapy of B-cell malignancies has proved to be effective. We show how the same approach of CAR T cells specific for CD30 (CD30.CAR-Ts) can be used to treat Hodgkin lymphoma (HL).

METHODS

We conducted 2 parallel phase I/II studies (ClinicalTrials.gov identifiers: NCT02690545 and NCT02917083) at 2 independent centers involving patients with relapsed or refractory HL and administered CD30.CAR-Ts after lymphodepletion with either bendamustine alone, bendamustine and fludarabine, or cyclophosphamide and fludarabine. The primary end point was safety.

RESULTS

Forty-one patients received CD30.CAR-Ts. Treated patients had a median of 7 prior lines of therapy (range, 2-23), including brentuximab vedotin, checkpoint inhibitors, and autologous or allogeneic stem cell transplantation. The most common toxicities were grade 3 or higher hematologic adverse events. Cytokine release syndrome was observed in 10 patients, all of which were grade 1. No neurologic toxicity was observed. The overall response rate in the 32 patients with active disease who received fludarabine-based lymphodepletion was 72%, including 19 patients (59%) with complete response. With a median follow-up of 533 days, the 1-year progression-free survival and overall survival for all evaluable patients were 36% (95% CI, 21% to 51%) and 94% (95% CI, 79% to 99%), respectively. CAR-T cell expansion in vivo was cell dose dependent.

CONCLUSION

Heavily pretreated patients with relapsed or refractory HL who received fludarabine-based lymphodepletion followed by CD30.CAR-Ts had a high rate of durable responses with an excellent safety profile, highlighting the feasibility of extending CAR-T cell therapies beyond canonical B-cell malignancies.

Identification of protective T-cell antigens for smallpox vaccines

Background aims

E3L is an immediate-early protein of vaccinia virus (VV) that is detected within 0.5 h of infection, potentially before the many immune evasion genes of vaccinia can exert their protective effects. E3L is highly conserved among orthopoxviruses and hence could provide important protective T-cell epitopes that should be retained in any subunit or attenuated vaccine. We have therefore evaluated the immunogenicity of E3L in healthy VV-vaccinated donors.

Methods

Peripheral blood mononuclear cells from healthy volunteers (n = 13) who had previously received a smallpox vaccine (Dryvax) were activated and expanded using overlapping E3L peptides and their function, specificity and antiviral activity was analyzed. E3L-specific T cells were expanded from 7 of 12 (58.3%) vaccinated healthy donors. Twenty-five percent of these produced CD8+ T-cell responses and 87.5% produced CD4+ T cells. We identified epitopes restricted by HLA-B35 and HLA-DR15.

Results

E3L-specific T cells killed peptide-loaded target cells as well as vaccinia-infected cells, but only CD8+ T cells could prevent the spread of infectious virus in virus inhibition assays. The epitopes recognized by E3L-specific T cells were shared with monkeypox, and although there was a single amino acid change in the variola epitope homolog, it was recognized by vaccinia-specific T-cells.

Conclusions

It might be important to include E3L in any deletion mutant or subunit vaccine and E3L could provide a useful antigen to monitor protective immunity in humans.

Results from Melanoma Antigen Redirected Vaccine Stimulated Autologous Lymphocytes (MARVSmALo): A pilot study

e15026

Background: Despite improvements in treatment with targeted agents and immunotherapeutics metastatic melanoma still has a guarded prognosis. Many melanoma cells upregulate the disialoganglioside GD2. Early GD2 chimeric antigen receptor (CAR) T-cell studies in neuroblastoma demonstrated no toxicity but limited ability to expand in vivo. Strategies to expand these GD2.CAR T cells might improve efficacy while retaining safety. This pilot study aimed to evaluate the safety and efficacy of first generation 14g2a.zeta chimeric antigen receptor ( GD2.CAR ) transduced, activated T cells enriched for vaccine specific cytotoxic T-Lymphocytes (tvs-CTL). Methods: Patients with metastatic melanoma in which standard therapy had failed were eligible if they had recovered from effects of prior therapy, did not have rapidly progressive disease, were free of melanoma involving the CNS and did not have a contraindication to receiving Hepatitis B, Polio or DTAP vaccine. Patients received each of these vaccines prior to cell harvest, 4 days before and 28 days after autologous T cell infusion. Patient 1 was treated with 2 x 108 cell dose and patients 2 and 3 were treated with 4x108 cell dose. We used QPCR to measure transgene copy number in patients before and after infusion. Interferon-gamma enzyme linked immunospot (ELISPOT) assay was used to measure the frequencies of tetanus, pertussis, diphtheria, poliovirus and tumor antigens-specific T cells in peripheral blood. Results: GD2.CAR-tvs-CTL were manufactured and infused in 3 patients. Overall the infusions were safe. Seven low grade adverse events possibly related to study participation were reported. The first 2 patients did not demonstrate robust in vivo expansion of GD2.CAR-tvs-CTLs by QPCR and had rapid disease progression. In patient 3 a significant expansion of GD2.CAR-tvs-CTLs, i.e. 18,250 copies/ug genomic DNA was observed on day 7 and cells persisted at 159 copies/ug DNA for up to 12 months (latest measured time point). High pertussis-specific responses were also observed by INF-gamma ELISPOT in this patient starting from day 14 after the vaccination through month 12. Conclusions: We have demonstrated that GD2.CAR T cells expanded and persisted in melanoma patient for up to 12 months. The use of vaccination before blood procurement for T cell manufacture and boosting virus-specific T cell after CAR T cell infusion is a safe strategy and may have helped induced higher transgene levels in one of three patients. Clinical trial information: NCT02482532 .

T-Cell Receptor Stimulation Enhances the Expansion and Function of CD19 Chimeric Antigen Receptor-Expressing T Cells

PURPOSE

Current protocols for CD19 chimeric antigen receptor-expressing T cells (CD19.CAR-T cells) require recipients to tolerate preinfusion cytoreductive chemotherapy, and the presence of sufficient target antigen on normal or malignant B cells.

PATIENTS AND METHODS

We investigated whether additional stimulation of CD19.CAR-T cells through their native receptors can substitute for cytoreductive chemotherapy, inducing expansion and functional persistence of CD19.CAR-T even in patients in remission of B-cell acute lymphocytic leukemia. We infused a low dose of CD19.CAR-modified virus-specific T cells (CD19.CAR-VST) without prior cytoreductive chemotherapy into 8 patients after allogeneic stem cell transplant.

RESULTS

Absent virus reactivation, we saw no CD19.CAR-VST expansion. In contrast, in patients with viral reactivation, up to 30,000-fold expansion of CD19.CAR-VSTs was observed, with depletion of CD19⁺ B cells. Five patients remain in remission at 42-60+ months.

CONCLUSIONS

Dual T-cell receptor and CAR stimulation can thus potentiate effector cell expansion and CAR-target cell killing, even when infusing low numbers of effector cells without cytoreduction.

A strategy to protect off-the-shelf cell therapy products using virus-specific T-cells engineered to eliminate alloreactive T-cells

Background

The use of “off-the-shelf” cellular therapy products derived from healthy donors addresses many of the challenges associated with customized cell products. However, the potential of allogeneic cell products to produce graft-versus-host disease (GVHD), and their likely rejection by host alloreactive T-cells are major barriers to their clinical safety and efficacy. We have developed a molecule that when expressed in T-cells, can eliminate alloreactive T-cells and hence can be used to protect cell therapy products from allospecific rejection. Further, expression of this molecule in virus-specific T-cells (VSTs) should virtually eliminate the potential for recipients to develop GVHD.

Methods

To generate a molecule that can mediate killing of cognate alloreactive T-cells, we fused beta-2 microglobulin (B2M), a universal component of all human leukocyte antigen (HLA) class I molecules, to the cytolytic endodomain of the T cell receptor ζ chain, to create a chimeric HLA accessory receptor (CHAR). To determine if CHAR-modified human VSTs could eliminate alloreactive T-cells, we co-cultured them with allogeneic peripheral blood mononuclear cells (PBMC), and assessed proliferation of PBMC-derived alloreactive T-cells and the survival of CHAR-modified VSTs by flow cytometry.

Results

The CHAR was able to transport HLA molecules to the cell surface of Daudi cells, that lack HLA class I expression due to defective B2M expression, illustrating its ability to complex with human HLA class I molecules. Furthermore, VSTs expressing CHAR were protected from allospecific elimination in co-cultures with allogeneic PBMCs compared to unmodified VSTs, and mediated killing of alloreactive T-cells. Unexpectedly, CHAR-modified VSTs eliminated not only alloreactive HLA class I restricted CD8 T-cells, but also alloreactive CD4 T-cells. This beneficial effect resulted from non-specific elimination of activated T-cells. Of note, we confirmed that CHAR-modified VSTs did not affect pathogen-specific T-cells which are essential for protective immunity.

Conclusions

Human T-cells can be genetically modified to eliminate alloreactive T-cells, providing a unique strategy to protect off-the-shelf cell therapy products. Allogeneic cell therapies have already proved effective in treating viral infections in the stem cell transplant setting, and have potential in other fields such as regenerative medicine. A strategy to prevent allograft rejection would greatly increase their efficacy and commercial viability.

Electronic supplementary material

The online version of this article (10.1186/s12967-019-1988-y) contains supplementary material, which is available to authorized users.

T-cell receptor sequencing demonstrates persistence of virus-specific T cells after antiviral immunotherapy

Viral infections are a serious cause of morbidity and mortality following haematopoietic stem cell transplantation (HSCT). Adoptive cellular therapy with virus-specific T cells (VSTs) has been successful in preventing or treating targeted viruses in prior studies, but the composition of ex vivo expanded VST and the critical cell populations that mediate antiviral activity in vivo are not well defined. We utilized deep sequencing of the T-cell receptor beta chain (TCRB) in order to classify and track VST populations in 12 patients who received VSTs following HSCT to prevent or treat viral infections. TCRB sequencing was performed on sorted VST products and patient peripheral blood mononuclear cells samples. TCRB diversity was gauged using the Shannon entropy index, and repertoire similarity determined using the Morisita-Horn index. Similarity indices reflected an early change in TCRB diversity in eight patients, and TCRB clonotypes corresponding to targeted viral epitopes expanded in eight patients. TCRB repertoire diversity increased in nine patients, and correlated with cytomegalovirus (CMV) viral load following VST infusion (P = 0·0071). These findings demonstrate that allogeneic VSTs can be tracked via TCRB sequencing, and suggests that T-cell receptor repertoire diversity may be critical for the control of CMV reactivation after HSCT.

Current challenges for CAR T-cell therapy of acute myeloid leukemia

KEY IDEAS Chimeric antigen receptor (CAR) T-cell therapy has the potential to improve the dismal outcome of patients diagnosed with acute myeloid leukemia (AML). A major challenge for CAR T-cell therapy of AML patients is identifying leukemia-specific target antigens. Immune escape through down-regulation of target antigens and/or a suppressive tumor microenvironment jeopardizes the success of CAR T-cell therapy.

NK Cells Expressing a Chimeric Activating Receptor Eliminate MDSCs and Rescue Impaired CAR-T Cell Activity against Solid Tumors

Solid tumors are refractory to cellular immunotherapies in part because they contain suppressive immune effectors such as myeloid-derived suppressor cells (MDSCs) that inhibit cytotoxic lymphocytes. Strategies to reverse the suppressive tumor microenvironment (TME) should also attract and activate immune effectors with antitumor activity. To address this need, we developed gene-modified natural killer (NK) cells bearing a chimeric receptor in which the activating receptor NKG2D is fused to the cytotoxic ζ-chain of the T-cell receptor (NKG2D.ζ). NKG2D.ζ-NK cells target MDSCs, which overexpress NKG2D ligands within the TME. We examined the ability of NKG2D.ζ-NK cells to eliminate MDSCs in a xenograft TME model and improve the antitumor function of tumor-directed chimeric antigen receptor (CAR)-modified T cells. We show that NKG2D.ζ-NK cells are cytotoxic against MDSCs, but spare NKG2D ligand-expressing normal tissues. NKG2D.ζ-NK cells, but not unmodified NK cells, secrete proinflammatory cytokines and chemokines in response to MDSCs at the tumor site and improve infiltration and antitumor activity of subsequently infused CAR-T cells, even in tumors for which an immunosuppressive TME is an impediment to treatment. Unlike endogenous NKG2D, NKG2D.ζ is not susceptible to TME-mediated downmodulation and thus maintains its function even within suppressive microenvironments. As clinical confirmation, NKG2D.ζ-NK cells generated from patients with neuroblastoma killed autologous intratumoral MDSCs capable of suppressing CAR-T function. A combination therapy for solid tumors that includes both NKG2D.ζ-NK cells and CAR-T cells may improve responses over therapies based on CAR-T cells alone.

Chimeric Antigen Receptor Signaling Domains Differentially Regulate Proliferation and Native T Cell Receptor Function in Virus-Specific T Cells

The efficacy of T cells expressing chimeric antigen receptors (CARs) for solid tumors has been limited by insufficient CAR T cell expansion and persistence. The use of virus-specific T cells (VSTs) as carriers for CARs may overcome this limitation since CAR-VSTs can be boosted by viral vaccines or oncolytic viruses. However, there is limited understanding of the optimal combination of endodomains and their influence on the native T cell receptor (TCR) in VSTs. We therefore compared the function of GD2.CARs expressing the TCR zeta chain (ζ) alone or combined with endodomains from CD28 and 4-1BB in varicella zoster virus-specific (VZV) T cells. VZVSTs expressing GD2-CARs recognized VZV-derived peptides and killed GD2-expressing tumor cells. However, after repeated stimulation through their native TCR, the expansion of GD2-CAR.CD28ζ-VZVSTs was 3.3-fold greater (p < 0.001) than non-transduced VZVSTs, whereas GD2-CARζ- and GD2-CAR.41BBζ inhibited VZVST expansion (p < 0.01). Compared to control VZVSTs, GD2-CAR.ζ VZVSTs showed a greater frequency of apoptotic (p < 0.01) T cells, whereas prolonged downregulation of the native αβ TCR was observed in GD2-CAR.41BBζ VZVSTs (p < 0.001). We confirmed that CD28ζ can best maintain TCR function by expressing GD2.CARs in Epstein-Barr virus-specific T cells and CD19-CARs in VZVSTs. In response to CAR stimulation VSTs with CD28ζ endodomains also showed the greatest expansion (6 fold > GD2-CAR.41BBζ VZVSTs (p < 0.001), however anti-tumor efficacy was superior in GD2-CAR.41BBζ-VZVSTs. These findings demonstrate that CAR signaling domains can enhance or diminish the function of the native TCR and indicate that only CD28ζ may preserve the function of the native TCR in tonically signaling CAR-VSTs.

EBV/LMP-specific T cells maintain remissions of T- and B-cell EBV lymphomas after allogeneic bone marrow transplantation

Autologous T cells targeting Epstein-Barr virus (EBV) latent membrane proteins (LMPs) have shown safety and efficacy in the treatment of patients with type 2 latency EBV-associated lymphomas for whom standard therapies have failed, including high-dose chemotherapy followed by autologous stem-cell rescue. However, the safety and efficacy of allogeneic donor-derived LMP-specific T cells (LMP-Ts) have not been established for patients who have undergone allogeneic hematopoietic stem-cell transplantation (HSCT). Therefore, we evaluated the safety and efficacy of donor-derived LMP-Ts in 26 patients who had undergone allogeneic HSCT for EBV-associated natural killer/T-cell or B-cell lymphomas. Seven patients received LMP-Ts as therapy for active disease, and 19 were treated with adjuvant therapy for high-risk disease. There were no immediate infusion-related toxicities, and only 1 dose-limiting toxicity potentially related to T-cell infusion was seen. The 2-year overall survival (OS) was 68%. Additionally, patients who received T-cell therapy while in complete remission after allogeneic HSCT had a 78% OS at 2 years. Patients treated for B-cell disease (n = 10) had a 2-year OS of 80%. Patients with T-cell disease had a 2-year OS of 60%, which suggests an improvement compared with published posttransplantation 2-year OS rates of 30% to 50%. Hence, this study shows that donor-derived LMP-Ts are a safe and effective therapy to prevent relapse after transplantation in patients with B cell- or T cell-derived EBV-associated lymphoma or lymphoproliferative disorder and supports the infusion of LMP-Ts as adjuvant therapy to improve outcomes in the posttransplantation setting. These trials were registered at www.clinicaltrials.gov as #NCT00062868 and #NCT01956084.

Epstein-Barr Virus (EBV)-derived BARF1 encodes CD4- and CD8-restricted epitopes as targets for T-cell immunotherapy

BACKGROUND AIMS

EBV type II latency tumors, such as Hodgkin lymphoma (HL), Non-Hodgkin lymphoma (NHL) and nasopharyngeal carcinoma, express a limited array of EBV antigens including Epstein-Barr nuclear antigen (EBNA)1, latent membrane protein (LMP)1, LMP2, and BamH1-A right frame 1 (BARF1). Adoptive immunotherapy for these malignancies have focused on EBNA1, LMP1 and LMP2 because little is known about the cellular immune response to BARF1.

METHODS

To investigate whether BARF1 is a potential T-cell immunotherapy target, we determined the frequency of BARF1-specific T-cell responses in the peripheral blood of EBV-seropositive healthy donor and patients with EBV-positive malignancies, mapped epitopes and evaluated the effector function of ex vivo-generated BARF1-specific T-cell lines.

RESULTS

BARF1-specific T cells were present in the peripheral blood of 12/16 (75%) EBV-positive healthy donors and 13/20 (65%) patients with EBV-positive malignancies. Ex vivo expanded BARF1-specific T-cell lines contained CD4- and CD8-positive T-cell subpopulations, and we identified 23 BARF1 peptides, which encoded major histocompatibility complex class I- and/or II-restricted epitopes. Epitope mapping identified one human leukocyte antigen (HLA)-A*02-restricted epitope that was recognized by 50% of HLA-A*02, EBV-seropositive donors and one HLA-B*15(62)-restricted epitope. Exvivo expanded BARF1-specific T cells recognized and killed autologous, EBV-transformed lymphoblastoid cell lines and partially HLA-matched EBV-positive lymphoma cell lines.

DISCUSSION

BARF1 should be considered as an immunotherapy target for EBV type II (and III) latency. Targeting BARF1, in addition to EBNA1, LMP1 and LMP2, has the potential to improve the efficacy of current T-cell immunotherapy approaches for these malignancies.

In Vivo Fate and Activity of Second- versus Third-Generation CD19-Specific CAR-T Cells in B Cell Non-Hodgkin's Lymphomas

Second-generation (2G) chimeric antigen receptors (CARs) targeting CD19 are highly active against B cell malignancies, but it is unknown whether any of the costimulatory domains incorporated in the CAR have superior activity to others. Because CD28 and 4-1BB signaling activate different pathways, combining them in a single third-generation (3G) CAR may overcome the limitations of each individual costimulatory domain. We designed a clinical trial in which two autologous CD19-specific CAR-transduced T cell products (CD19.CARTs), 2G (with CD28 only) and 3G (CD28 and 4-1BB), were infused simultaneously in 16 patients with relapsed or refractory non-Hodgkin's lymphoma. 3G CD19.CARTs had superior expansion and longer persistence than 2G CD19.CARTs. This difference was most striking in the five patients with low disease burden and few circulating normal B cells, in whom 2G CD19.CARTs had limited expansion and persistence and correspondingly reduced area under the curve. Of the 11 patients with measurable disease, three achieved complete responses and three had partial responses. Cytokine release syndrome occurred in six patients but was mild, and no patient required anti-IL-6 therapy. Hence, 3G CD19.CARTs combining 4-1BB with CD28 produce superior CART expansion and may be of particular value when treating low disease burden in patients whose normal B cells are depleted by prior therapy.

Abstract 4734: Suppressive myeloid cells of the solid tumor microenvironment enhance regulatory T cell function and differentially affect CAR-T cell function

Immunotherapy with tumor-directed immune cells, such as chimeric antigen receptor-bearing T (CAR-T) cells, have shown great promise. Indeed, CAR-T cells directed against leukemia antigens such as CD19 have produced impressive complete responses even in relapsed disease patients. In contrast, CAR-T cells directed against solid tumor have produced very few durable clinical responses. This may be, in part, due to the suppressive immune microenvironment of solid tumors that inhibits the anti-tumor activity of endogenous and CAR-T cells. Myeloid-derived suppressor cells (MDSCs), regulatory T cells (Tregs) and inhibitory macrophages (M2s) are recruited by tumor-derived factors, and contribute to the immunosuppressive tumor microenvironment (TME) by secreting suppressive cytokines, expressing inhibitory ligands, and promoting tumor neovascularization. However, the contribution of each of these components to suppressing engineered cellular therapies has not been well defined. In order to design more effective cellular therapies for solid tumors, it is imperative that we understand TME-mediated immune suppression of human CAR-T cells. Therefore, the objective of this study was to evaluate the individual contribution of MDSCs, Tregs, and M2s to the suppressive TME and their ability to modulate CAR-T function. We hypothesized that MDSCs, Tregs, and M2s would inhibit GD2.CAR-T homing and proliferation at tumor sites, leading to decreased activity and tumor progression. To understand the individual contributions of these suppressive cells to inhibition of CAR-T cells, we developed a unique TME model in which human neuroblastoma tumor cells were co-inoculated subcutaneously with MDSCs, Tregs, or M2s in immunocompromised mice and then treated with GD2 neuroblastoma antigen-specific CAR-T cells. We found that while all three cell types decreased GD2.CAR-T cell-mediated tumor control in vivo, only MDSCs and M2s inhibited CAR-T homing and expansion at tumor sites. To investigate cross-talk between these suppressive cells, we assessed the phenotype and suppressive activity of MDSCs, Tregs, and M2 on autologous CAR-T cells after exposure to the other suppressive cell types. We found that the suppressive function of M2s increased by 30% after exposure to Tregs. Similarly, Treg suppressive function increased by 26% after exposure to M2s. Both M2 and Treg suppressive functions were enhanced in the presence of MDSCs. Our results suggest a potential cross-talk between suppressive cells of the TME and distinct roles in important aspects of CAR-T cell function, including homing and killing. Future studies in our lab aim to further understand the differential roles of these cells in regulating CAR-T cell function within the TME that will inform new approaches to engineer effective adoptive T-cell therapies.

Citation Format: Charlotte H. Rivas, Anna Cole, Cliona M. Rooney, Robin Parihar. Suppressive myeloid cells of the solid tumor microenvironment enhance regulatory T cell function and differentially affect CAR-T cell function [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4734.

Tonic 4-1BB Costimulation in Chimeric Antigen Receptors Impedes T Cell Survival and Is Vector-Dependent

Antigen-independent tonic signaling by chimeric antigen receptors (CARs) can increase differentiation and exhaustion of T cells, limiting their potency. Incorporating 4-1BB costimulation in CARs may enable T cells to resist this functional exhaustion; however, the potential ramifications of tonic 4-1BB signaling in CAR T cells remain unclear. Here, we found that tonic CAR-derived 4-1BB signaling can produce toxicity in T cells via continuous TRAF2-dependent activation of the nuclear factor κB (NF-κB) pathway and augmented FAS-dependent cell death. This mechanism was amplified in a non-self-inactivating gammaretroviral vector through positive feedback on the long terminal repeat (LTR) promoter, further enhancing CAR expression and tonic signaling. Attenuating CAR expression by substitution with a self-inactivating lentiviral vector minimized tonic signaling and improved T cell expansion and anti-tumor function. These studies illuminate the interaction between tonic CAR signaling and the chosen expression platform and identify inhibitory properties of the 4-1BB costimulatory domain that have direct implications for rational CAR design.

Strategies for enhancing adoptive T-cell immunotherapy against solid tumors using engineered cytokine signaling and other modalities

INTRODUCTION

Cancer therapy has been transformed by the demonstration that tumor-specific T-cells can eliminate tumor cells in a clinical setting with minimal long-term toxicity. However, significant success in the treatment of leukemia and lymphoma with T-cells using native receptors or redirected with chimeric antigen receptors (CARs) has not been recapitulated in the treatment of solid tumors. This lack of success is likely related to the paucity of costimulatory and cytokine signaling available in solid tumors, in addition to a range of inhibitory mechanisms.

AREAS COVERED

We summarize the latest developments in engineered T-cell immunotherapy, describe the limitations of these approaches in treating solid tumors, and finally highlight several strategies that may be useful in mediating solid tumor responses in the future, while also ensuring safety of engineered cells.

EXPERT OPINION

CAR-T therapies require further engineering to achieve their potential against solid tumors. Facilitating cytokine signaling in CAR T-cells appears to be essential in achieving better responses. However, the engineering of T-cells with potentially unchecked proliferation and potency raises the question of whether the simultaneous combination of enhancements will prove safe, necessitating continued advancements in regulating CAR-T activity at the tumor site and methods to safely switch off these engineered cells.

Transposon-modified antigen-specific T lymphocytes for sustained therapeutic protein delivery in vivo

A cell therapy platform permitting long-term delivery of peptide hormones in vivo would be a significant advance for patients with hormonal deficiencies. Here we report the utility of antigen-specific T lymphocytes as a regulatable peptide delivery platform for in vivo therapy. piggyBac transposon modification of murine cells with luciferase allows us to visualize T cells after adoptive transfer. Vaccination stimulates long-term T-cell engraftment, persistence, and transgene expression enabling detection of modified cells up to 300 days after adoptive transfer. We demonstrate adoptive transfer of antigen-specific T cells expressing erythropoietin (EPO) elevating the hematocrit in mice for more than 20 weeks. We extend our observations to human T cells demonstrating inducible EPO production from Epstein-Barr virus (EBV) antigen-specific T lymphocytes. Our results reveal antigen-specific T lymphocytes to be an effective delivery platform for therapeutic molecules such as EPO in vivo, with important implications for other diseases that require peptide therapy.

Tumor-Specific T-Cells Engineered to Overcome Tumor Immune Evasion Induce Clinical Responses in Patients With Relapsed Hodgkin Lymphoma

Purpose Transforming growth factor-β (TGF-β) production in the tumor microenvironment is a potent and ubiquitous tumor immune evasion mechanism that inhibits the expansion and function of tumor-directed responses; therefore, we conducted a clinical study to discover the effects of the forced expression of a dominant-negative TGF-β receptor type 2 (DNRII) on the safety, survival, and activity of infused tumor-directed T cells. Materials and Methods In a dose escalation study, eight patients with Epstein Barr virus-positive Hodgkin lymphoma received two to 12 doses of between 2 × 107 and 1.5 × 108 cells/m2 of DNRII-expressing T cells with specificity for the Epstein Barr virus-derived tumor antigens, latent membrane protein (LMP)-1 and LMP-2 (DNRII-LSTs). Lymphodepleting chemotherapy was not used before infusion. Results DNRII-LSTs were resistant to otherwise inhibitory concentrations of TGF-β in vitro and retained their tumor antigen-specific activity. After infusion, the signal from transgenic T cells in peripheral blood increased up to 100-fold as measured by quantitative polymerase chain reaction for the transgene, with a corresponding increase in the frequency of functional LMP-specific T cells. Expansion was not associated with any acute or long-term toxicity. DNRII-LSTs persisted for up to ≥ 4 years. Four of the seven evaluable patients with active disease achieved clinical responses that were complete and ongoing in two patients at > 4 years, including in one patient who achieved only a partial response to unmodified tumor-directed T cells. Conclusion TGF-β-resistant tumor-specific T cells safely expand and persist in patients with Hodgkin lymphoma without lymphodepleting chemotherapy before infusion. DNRII-LSTs can induce complete responses even in patients with resistant disease. Expression of DNRII may be useful for the many other tumors that exploit this potent immune evasion mechanism.

A New Method for Reactivating and Expanding T Cells Specific for Rhizopus oryzae

Mucormycosis is responsible for an increasing proportion of deaths after allogeneic bone marrow transplantation. Because this disease is associated with severe immunodeficiency and has shown resistance to even the newest antifungal agents, we determined the feasibility of reactivating and expanding Rhizopus oryzae-specific T cells for use as adoptive immunotherapy in transplant recipients. R. oryzae extract-pulsed monocytes were used to stimulate peripheral blood mononuclear cells from healthy donors, in the presence of different cytokine combinations. The generated R. oryzae-specific T cell products were phenotyped after the third stimulation and further characterized by the use of antibodies that block class I/II molecules, as well as pattern recognition receptors. Despite the very low frequency of R. oryzae-specific T cells of healthy donors, we found that stimulation with interleukin-2 (IL-2)/IL-7 cytokine combination could expand these rare cells. The expanded populations included 17%-83% CD4⁺ T cells that were specific for R. oryzae antigens. Besides interferon-γ (IFN-γ), these cells secreted IL-5, IL-10, IL-13, and tumor necrosis factor alpha (TNF-α), and recognized fungal antigens presented by HLA-II molecules rather than through nonspecific signaling. The method described herein is robust and reproducible, and could be used to generate adequate quantities of activated R. oryzae-specific T cells for clinical testing of safety and antifungal efficacy in patients with mucormycosis.

Abstract P3-05-07: Improving CAR T cell function by reversing the immunosuppressive tumor environment of breast cancer

Adoptive transfer of T cells redirected to tumor-associated antigens (TAAs) by expression of chimeric antigen receptors (CARs) can produce tumor responses, even in patients with resistant malignancies. To target breast cancer, we generated T cells expressing a CAR directed to the TAA mucin-1 (MUC1). T cells expressing this CAR (86±1.9%, n=5) specifically killed MUC1-expressing cells (MDA-MB-468 – 45.9±7.3%, MCF-7 – 36.8±3.6) but not MUC1(-) 293T cells (3.7±1.6% specific lysis, 20:1 E:T, n=3). Although these CAR T cells had potent anti-tumor activity against breast cancer cells, when exposed to the Th2-polarizing cytokine IL4 [which is upregulated in tumor samples (Oncomine, p&lt;0.05)] we observed a dramatic reduction in their cytolytic potential [IL2 - 45.9±7.3% vs IL4 - 11.3±3.7% specific lysis, 20:1 E:T ratio, n=4]. Thus, to protect our CAR.MUC1 T cells from the negative influences of IL4, we generated an inverted cytokine receptor (ICR) in which the IL4 receptor exodomain was fused to the IL7 receptor endodomain (4/7 ICR). Transgenic expression of this molecule in CAR.MUC1 T cells (55±4.8% double positive cells, n=5), restored the cytolytic function of CAR T cells (30.9±8.1% specific lysis, 20:1 E:T, n=3). Next, to determine the long term effects of this modification we co-cultured transgenic T cells with MUC1+ tumor cells and measured tumor and T cells numbers. In the presence of IL4, only double positive (CAR.MUC1-4/7) T cells expanded and eliminated the tumors in vitro and in vivo. However, upon tumor elimination, transgenic T cells rapidly contracted, demonstrating the antigen- and cytokine-dependence of the product. In conclusion, CAR.MUC1-4/7 T cells can effectively target breast cancer cells and retain their cytotoxic function even in the IL4-rich tumor microenvironment.

Citation Format: Bajgain P, Tawinwung S, Watanabe N, Sukumaran S, Anurathapan U, Heslop HE, Rooney CM, Brenner M, Leen AM, Vera JF. Improving CAR T cell function by reversing the immunosuppressive tumor environment of breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P3-05-07.