Tracking genetically engineered lymphocytes long-term reveals the dynamics of T cell immunological memory

T memory stem cells after allogeneic haematopoietic cell transplantation: unique long-term kinetics and influence of chronic graft-versus-host disease

T memory stem cells (TSCMs) are a subset of primitive T cells capable of both self-renewal and differentiation into all subsets of memory and effector T cells. Therefore, TSCMs may play a role in immune reconstitution and graft-versus-host disease (GVHD) in patients receiving allogeneic haematopoietic cell transplantation (HCT). We conducted a cross-sectional study to evaluate the proportions, absolute counts, phenotypes and functions of TSCMs in 152 adult patients without disease recurrence at least 12 months after undergoing HCT. CD4⁺ TSCMs were negatively correlated with number of months after transplantation in HCT patients that received cord blood transplantation, but not in patients that received bone marrow transplantation or peripheral blood stem cell transplantation. The proportions and absolute counts of CD4⁺ TSCMs and expression levels of inducible co-stimulator (ICOS) in CD8⁺ TSCMs were significantly higher in patients with mild and moderate/severe cGVHD compared to patients without cGVHD. These data suggested that, more than 12 months after allogeneic HCT, the kinetics of CD4⁺ TSCMs were dependent on the type of donor source, and further that CD4⁺ TSCMs and ICOS levels in CD8⁺ TSCMs were associated with cGVHD.

Comprehensive Characterization of a Next-Generation Antiviral T-Cell Product and Feasibility for Application in Immunosuppressed Transplant Patients

Viral infections have a major impact on morbidity and mortality of immunosuppressed solid organ transplant (SOT) patients because of missing or failure of adequate pharmacologic antiviral treatment. Adoptive antiviral T-cell therapy (AVTT), regenerating disturbed endogenous T-cell immunity, emerged as an attractive alternative approach to combat severe viral complications in immunocompromised patients. AVTT is successful in patients after hematopoietic stem cell transplantation where T-cell products (TCPs) are manufactured from healthy donors. In contrast, in the SOT setting TCPs are derived from/applied back to immunosuppressed patients. We and others demonstrated feasibility of TCP generation from SOT patients and first clinical proof-of-concept trials revealing promising data. However, the initial efficacy is frequently lost long-term, because of limited survival of transferred short-lived T-cells indicating a need for next-generation TCPs. Our recent data suggest that Rapamycin treatment during TCP manufacture, conferring partial inhibition of mTOR, might improve its composition. The aim of this study was to confirm these promising observations in a setting closer to clinical challenges and to deeply characterize the next-generation TCPs. Using cytomegalovirus (CMV) as model, our next-generation Rapamycin-treated (Rapa-)TCP showed consistently increased proportions of CD4⁺ T-cells as well as CD4⁺ and CD8⁺ central-memory T-cells (T_CM). In addition, Rapamycin sustained T-cell function despite withdrawal of Rapamycin, showed superior T-cell viability and resistance to apoptosis, stable metabolism upon activation, preferential expansion of T_CM, partial conversion of other memory T-cell subsets to T_CM and increased clonal diversity. On transcriptome level, we observed a gene expression profile denoting long-lived early memory T-cells with potent effector functions. Furthermore, we successfully applied the novel protocol for the generation of Rapa-TCPs to 19/19 SOT patients in a comparative study, irrespective of their history of CMV reactivation. Moreover, comparison of paired TCPs generated before/after transplantation did not reveal inferiority of the latter despite exposition to maintenance immunosuppression post-SOT. Our data imply that the Rapa-TCPs, exhibiting longevity and sustained T-cell memory, are a reasonable treatment option for SOT patients. Based on our success to manufacture Rapa-TCPs from SOT patients under maintenance immunosuppression, now, we seek ultimate clinical proof of efficacy in a clinical study.

CD19 CAR T cell product and disease attributes predict leukemia remission durability

BACKGROUND

Chimeric antigen receptor (CAR) T cells can induce remission in highly refractory leukemia and lymphoma subjects, yet the parameters for achieving sustained relapse-free survival are not fully delineated.

METHODS

We analyzed 43 pediatric and young adult subjects participating in a Phase I trial of defined composition CD19CAR T cells (NCT02028455). CAR T cell phenotype, function and expansion, as well as starting material T cell repertoire, were analyzed in relation to therapeutic outcome (defined as achieving complete remission within 63 days) and duration of leukemia free survival and B cell aplasia.

RESULTS

These analyses reveal that initial therapeutic failures (n = 5) were associated with attenuated CAR T cell expansion and/or rapid attrition of functional CAR effector cells following adoptive transfer. The CAR T products were similar in phenotype and function when compared to products resulting in sustained remissions. However, the initial apheresed peripheral blood T cells could be distinguished by an increased frequency of LAG-3+/TNF-αlow CD8 T cells and, following adoptive transfer, the rapid expression of exhaustion markers. For the 38 subjects who achieved an initial sustained MRD-neg remission, remission durability correlated with therapeutic products having increased frequencies of TNF-α-secreting CAR CD8+ T cells, and was dependent on a sufficiently high CD19+ antigen load at time of infusion to trigger CAR T cell proliferation.

CONCLUSION

These parameters have the potential to prospectively identify patients at risk for therapeutic failure and support the development of approaches to boost CAR T cell activation and proliferation in patients with low levels of CD19 antigen.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02028455.

FUNDING

Partial funding for this study was provided by Stand Up to Cancer & St. Baldrick's Pediatric Dream Team Translational Research Grant (SU2C-AACR-DT1113), RO1 CA136551-05, Alex Lemonade Stand Phase I/II Infrastructure Grant, Conquer Cancer Foundation Career Development Award, Washington State Life Sciences Discovery Fund, Ben Towne Foundation, William Lawrence & Blanche Hughes Foundation, and Juno Therapeutics, Inc., a Celgene Company.

Bone marrow central memory and memory stem T-cell exhaustion in AML patients relapsing after HSCT

The major cause of death after allogeneic Hematopoietic Stem Cell Transplantation (HSCT) for acute myeloid leukemia (AML) is disease relapse. We investigated the expression of Inhibitory Receptors (IR; PD-1/CTLA-4/TIM-3/LAG-3/2B4/KLRG1/GITR) on T cells infiltrating the bone marrow (BM) of 32 AML patients relapsing (median 251 days) or maintaining complete remission (CR; median 1 year) after HSCT. A higher proportion of early-differentiated Memory Stem (T_SCM) and Central Memory BM-T cells express multiple IR in relapsing patients than in CR patients. Exhausted BM-T cells at relapse display a restricted TCR repertoire, impaired effector functions and leukemia-reactive specificities. In 57 patients, early detection of severely exhausted (PD-1⁺Eomes⁺T-bet^-) BM-T_SCM predicts relapse. Accordingly, leukemia-specific T cells in patients prone to relapse display exhaustion markers, absent in patients maintaining long-term CR. These results highlight a wide, though reversible, immunological dysfunction in the BM of AML patients relapsing after HSCT and suggest new therapeutic opportunities for the disease.

Transcriptional and Epigenetic Regulation of Effector and Memory CD8 T Cell Differentiation

Immune protection and lasting memory are accomplished through the generation of phenotypically and functionally distinct CD8 T cell subsets. Understanding how these effector and memory T cells are formed is the first step in eventually manipulating the immune system for therapeutic benefit. In this review, we will summarize the current understanding of CD8 T cell differentiation upon acute infection, with a focus on the transcriptional and epigenetic regulation of cell fate decision and memory formation. Moreover, we will highlight the importance of high throughput sequencing approaches and single cell technologies in providing insight into genome-wide investigations and the heterogeneity of individual CD8 T cells.

Potential advantages of CD1-restricted T cell immunotherapy in cancer

Adoptive cell therapy (ACT) using tumor-specific "conventional" MHC-restricted T cells obtained from tumor-infiltrating lymphocytes, or derived ex vivo by either antigen-specific expansion or genetic engineering of polyclonal T cell populations, shows great promise for cancer treatment. However, the wide applicability of this therapy finds limits in the high polymorphism of MHC molecules that restricts the use in the autologous context. CD1 antigen presenting molecules are nonpolymorphic and specialized for lipid antigen presentation to T cells. They are often expressed on malignant cells and, therefore, may represent an attractive target for ACT. We provide a brief overview of the CD1-resticted T cell response in tumor immunity and we discuss the pros and cons of ACT approaches based on unconventional CD1-restricted T cells.

High-dimensional single cell analysis identifies stem-like cytotoxic CD8+ T cells infiltrating human tumors

CD8⁺ T cells infiltrating tumors are largely dysfunctional, but whether a subset maintains superior functionality remains ill defined. By high-dimensional single cell analysis of millions of CD8⁺ T cells from 53 individuals with lung cancer, we defined those subsets that are enriched in tumors compared with cancer-free tissues and blood. Besides exhausted and activated cells, we identified CXCR5⁺ TIM-3^- CD8⁺ T cells with a partial exhausted phenotype, while retaining gene networks responsible for stem-like plasticity and cytotoxicity, as revealed by single cell sequencing of the whole transcriptome. Ex vivo, CXCR5⁺ TIM-3^- CD8⁺ T cells displayed enhanced self-renewal and multipotency compared with more differentiated subsets and were largely polyfunctional. Analysis of inhibitory and costimulatory receptors revealed PD-1, TIGIT, and CD27 as possible targets of immunotherapy. We thus demonstrate a hierarchy of differentiation in the context of T cell exhaustion in human cancer similar to that of chronically infected mice, which is further shown to disappear with disease progression.

Reducing Ex Vivo Culture Improves the Antileukemic Activity of Chimeric Antigen Receptor (CAR) T Cells

The success of chimeric antigen receptor (CAR)-mediated immunotherapy in acute lymphoblastic leukemia (ALL) highlights the potential of T-cell therapies with directed cytotoxicity against specific tumor antigens. The efficacy of CAR T-cell therapy depends on the engraftment and persistence of T cells following adoptive transfer. Most protocols for T-cell engineering routinely expand T cells ex vivo for 9 to 14 days. Because the potential for engraftment and persistence is related to the state of T-cell differentiation, we hypothesized that reducing the duration of ex vivo culture would limit differentiation and enhance the efficacy of CAR T-cell therapy. We demonstrated that T cells with a CAR-targeting CD19 (CART19) exhibited less differentiation and enhanced effector function in vitro when harvested from cultures at earlier (day 3 or 5) compared with later (day 9) timepoints. We then compared the therapeutic potential of early versus late harvested CART19 in a murine xenograft model of ALL and showed that the antileukemic activity inversely correlated with ex vivo culture time: day 3 harvested cells showed robust tumor control despite using a 6-fold lower dose of CART19, whereas day 9 cells failed to control leukemia at limited cell doses. We also demonstrated the feasibility of an abbreviated culture in a large-scale current good manufacturing practice-compliant process. Limiting the interval between T-cell isolation and CAR treatment is critical for patients with rapidly progressing disease. Generating CAR T cells in less time also improves potency, which is central to the effectiveness of these therapies. Cancer Immunol Res; 6(9); 1100-9. ©2018 AACR.

Transfer of gene-corrected T cells corrects humoral and cytotoxic defects in patients with X-linked lymphoproliferative disease

BACKGROUND

X-linked lymphoproliferative disease 1 arises from mutations in the SH2D1A gene encoding SLAM-associated protein (SAP), an adaptor protein expressed in T, natural killer (NK), and NKT cells. Defects lead to abnormalities of T-cell and NK cell cytotoxicity and T cell-dependent humoral function. Clinical manifestations include hemophagocytic lymphohistiocytosis, lymphoma, and dysgammaglobulinemia. Curative treatment is limited to hematopoietic stem cell transplantation, with outcomes reliant on a good donor match.

OBJECTIVES

Because most symptoms arise from defective T-cell function, we investigated whether transfer of SAP gene-corrected T cells could reconstitute known effector cell defects.

METHODS

CD3+ lymphocytes from Sap-deficient mice were transduced with a gammaretroviral vector encoding human SAP cDNA before transfer into sublethally irradiated Sap-deficient recipients. After immunization with the T-dependent antigen 4-hydroxy-3-nitrophenylacetly chicken gammaglobulin (NP-CGG), recovery of humoral function was evaluated through germinal center formation and antigen-specific responses. To efficiently transduce CD3+ cells from patients, we generated an equivalent lentiviral SAP vector. Functional recovery was demonstrated by using in vitro cytotoxicity and T follicular helper cell function assays alongside tumor clearance in an in vivo lymphoblastoid cell line lymphoma xenograft model.

RESULTS

In Sap-deficient mice 20% to 40% engraftment of gene-modified T cells led to significant recovery of germinal center formation and NP-specific antibody responses. Gene-corrected T cells from patients demonstrated improved cytotoxicity and T follicular helper cell function in vitro. Adoptive transfer of gene-corrected cytotoxic T lymphocytes from patients reduced tumor burden to a level comparable with that seen in healthy donor cytotoxic T lymphocytes in an in vivo lymphoma model.

CONCLUSIONS

These data demonstrate that autologous T-cell gene therapy corrects SAP-dependent defects and might offer an alternative therapeutic option for patients with X-linked lymphoproliferative disease 1.

Human TSCM cell dynamics in vivo are compatible with long-lived immunological memory and stemness

Adaptive immunity relies on the generation and maintenance of memory T cells to provide protection against repeated antigen exposure. It has been hypothesised that a self-renewing population of T cells, named stem cell-like memory T (TSCM) cells, are responsible for maintaining memory. However, it is not clear if the dynamics of TSCM cells in vivo are compatible with this hypothesis. To address this issue, we investigated the dynamics of TSCM cells under physiological conditions in humans in vivo using a multidisciplinary approach that combines mathematical modelling, stable isotope labelling, telomere length analysis, and cross-sectional data from vaccine recipients. We show that, unexpectedly, the average longevity of a TSCM clone is very short (half-life < 1 year, degree of self-renewal = 430 days): far too short to constitute a stem cell population. However, we also find that the TSCM population is comprised of at least 2 kinetically distinct subpopulations that turn over at different rates. Whilst one subpopulation is rapidly replaced (half-life = 5 months) and explains the rapid average turnover of the bulk TSCM population, the half-life of the other TSCM subpopulation is approximately 9 years, consistent with the longevity of the recall response. We also show that this latter population exhibited a high degree of self-renewal, with a cell residing without dying or differentiating for 15% of our lifetime. Finally, although small, the population was not subject to excessive stochasticity. We conclude that the majority of TSCM cells are not stem cell-like but that there is a subpopulation of TSCM cells whose dynamics are compatible with their putative role in the maintenance of T cell memory.

Twenty-Five Years of Gene Therapy for ADA-SCID: From Bubble Babies to an Approved Drug

Twenty-five years have passed since first attempts of gene therapy (GT) in children affected by severe combined immunodeficiency (SCID) due to adenosine deaminase (ADA) defect, also known by the general public as bubble babies. ADA-SCID is fatal early in life if untreated. Unconditioned hematopoietic stem cell (HSC) transplant from matched sibling donor represents a curative treatment but is available for few patients. Enzyme replacement therapy can be life-saving, but its chronic use has many drawbacks. This review summarizes the history of ADA-SCID GT over the last 25 years, starting from first pioneering studies in the early 1990s using gamma-retroviral vectors, based on multiple infusions of genetically corrected autologous peripheral blood lymphocytes. HSC represented the ideal target for gene correction to guarantee production of engineered multi-lineage progeny, but it required a decade to achieve therapeutic benefit with this approach. Introduction of low-intensity conditioning represented a crucial step in achieving stable gene-corrected HSC engraftment and therapeutic levels of ADA-expressing cells. Recent clinical trials demonstrated that gamma-retroviral GT for ADA-SCID has a favorable safety profile and is effective in restoring normal purine metabolism and immune functions in patients >13 years after treatment. No abnormal clonal proliferation or leukemia development have been observed in >40 patients treated experimentally in five different centers worldwide. In 2016, the medicinal product Strimvelis™ received marketing approval in Europe for patients affected by ADA-SCID without a suitable human leukocyte antigen-matched related donor. Positive safety and efficacy results have been obtained in GT clinical trials using lentiviral vectors encoding ADA. The results obtained in last 25 years in ADA-SCID GT development fundamentally contributed to improve patients' prognosis, together with earlier diagnosis thanks to newborn screening. These advances open the way to further clinical development of GT as treatment for broader applications, from inherited diseases to cancer.

Prevention and treatment of relapse after stem cell transplantation by cellular therapies

Despite recent advances in reducing therapy-related mortality after allogeneic stem cell transplantation (alloSCT) relapse remains the major cause of treatment failure and little progress has been achieved in the last decades. At the 3rd International Workshop on Biology, Prevention, and Treatment of Relapse held in Hamburg/Germany in November 2016 international experts presented and discussed recent developments in the field. Here, the potential of cellular therapies including unspecific and specific T cells, genetically modified T cells, CAR-T cells, NK-cells, and second allografting in prevention and treatment of relapse after alloSCT are summarized.

Rapid reconstitution of CMV-specific T-cells after stem-cell transplantation

OBJECTIVE

As reconstitution of virus-specific T-cells is critical to control cytomegalovirus (CMV)-viremia following stem-cell transplantation (SCT), we characterized the dynamics in CMV-specific T-cell reconstitution after SCT.

METHODS

Cytomegalovirus-specific T-cells from 51 SCT-recipients were prospectively quantified and phenotypically characterised by intracellular cytokine-staining after specific stimulation and HLA class-I-specific pentamers using flow cytometry.

RESULTS

Cytomegalovirus-specific CD4 T-cells reconstituted after a median of 2.3 (IQR, 2.0-3.0) weeks following autografting, and 4.0 (IQR, 3.0-5.6) weeks after allografting, with CMV-specific T-cells originating from donors and/or recipients. The time for reconstitution of CMV-specific CD4 and CD8 T-cells did not differ (P = .58). Factors delaying the time to initial reconstitution of CMV-specific CD4 T-cells included a negative recipient serostatus (P = .016) and CMV-viremia (P = .026). Percentages of CMV-specific CD4 T-cells significantly increased over time and reached a plateau after 90 days (P = .043). Relative CMV-specific CD4 T-cell levels remained higher in long-term transplant recipients compared with those in controls (P < .0001). However, due to persisting lymphopenia, absolute numbers of CMV-specific T-cells were similar as in controls.

CONCLUSION

Cytomegalovirus-specific T-cells rapidly reconstitute after SCT and their percentages remain high in the long term. In the face of persistent lymphopenia, this results in similar absolute numbers of CMV-specific T-cells as in controls to ensure sufficient pathogen control.

Proceedings From the Fourth Haploidentical Stem Cell Transplantation Symposium (HAPLO2016), San Diego, California, December 1, 2016

The resurgence of haploidentical stem cell transplantation (HaploSCT) over the last decade is one of the most important advances in the field of hematopoietic stem cell transplantation (HSCT). The modified platforms of T cell depletion either ex vivo (CD34+ cell selection, "megadoses" of purified CD34+ cells, or selective depletion of T cells) or newer platforms of in vivo depletion of T cells, with either post-transplantation high-dose cyclophosphamide or intensified immune suppression, have contributed to better outcomes, with survival similar to that in HLA-matched donor transplantation. Further efforts are underway to control viral reactivation using modified T cells, improve immunologic reconstitution, and decrease the relapse rate post-transplantation using donor-derived cellular therapy products, such as genetically modified donor lymphocytes and natural killer cells. Improvements in treatment-related mortality have allowed the extension of haploidentical donor transplants to patients with hemoglobinopathies, such as thalassemia and sickle cell disease, and the possible development of platforms for immunotherapy in solid tumors. Moreover, combining HSCT from a related donor with solid organ transplantation could allow early tapering of immunosuppression in recipients of solid organ transplants and hopefully prevent organ rejection in this setting. This symposium summarizes some of the most important recent advances in HaploSCT and provides a glimpse in the future of fast growing field.

Functional, Antigen-Specific Stem Cell Memory (TSCM) CD4+ T Cells Are Induced by Human Mycobacterium tuberculosis Infection

Background

Maintenance of long-lasting immunity is thought to depend on stem cell memory T cells (TSCM), which have superior self-renewing capacity, longevity and proliferative potential compared with central memory (TCM) or effector (TEFF) T cells. Our knowledge of TSCM derives primarily from studies of virus-specific CD8+ TSCM. We aimed to determine if infection with Mycobacterium tuberculosis (M. tb), the etiological agent of tuberculosis, generates antigen-specific CD4+ TSCM and to characterize their functional ontology.

Methods

We studied T cell responses to natural M. tb infection in a longitudinal adolescent cohort of recent QuantiFERON-TB Gold (QFT) converters and three cross-sectional QFT+ adult cohorts; and to bacillus Calmette-Guerin (BCG) vaccination in infants. M. tb and/or BCG-specific CD4 T cells were detected by flow cytometry using major histocompatibility complex class II tetramers bearing Ag85, CFP-10, or ESAT-6 peptides, or by intracellular cytokine staining. Transcriptomic analyses of M. tb-specific tetramer+ CD4+ TSCM (CD45RA+ CCR7+ CD27+) were performed by microfluidic qRT-PCR, and functional and phenotypic characteristics were confirmed by measuring expression of chemokine receptors, cytotoxic molecules and cytokines using flow cytometry.

Results

M. tb-specific TSCM were not detected in QFT-negative persons. After QFT conversion frequencies of TSCM increased to measurable levels and remained detectable thereafter, suggesting that primary M. tb infection induces TSCM cells. Gene expression (GE) profiling of tetramer+ TSCM showed that these cells were distinct from bulk CD4+ naïve T cells (TN) and shared features of bulk TSCM and M. tb-specific tetramer+ TCM and TEFF cells. These TSCM were predominantly CD95+ and CXCR3+, markers typical of CD8+ TSCM. Tetramer+ TSCM expressed significantly higher protein levels of CCR5, CCR6, CXCR3, granzyme A, granzyme K, and granulysin than bulk TN and TSCM cells. M. tb-specific TSCM were also functional, producing IL-2, IFN-γ, and TNF-α upon antigen stimulation, and their frequencies correlated positively with long-term BCG-specific CD4+ T cell proliferative potential after infant vaccination.

Conclusion

Human infection with M. tb induced distinct, antigen-specific CD4+ TSCM cells endowed with effector functions, including expression of cytotoxic molecules and Th1 cytokines, and displayed chemokine receptor profiles consistent with memory Th1/17 cells. Induction of CD4+ TSCM should be considered for vaccination approaches that aim to generate long-lived memory T cells against M. tb.

NK cell recovery after haploidentical HSCT with posttransplant cyclophosphamide: dynamics and clinical implications

The use of posttransplant cyclophosphamide (PT-Cy) as graft-versus-host disease (GVHD) prophylaxis has revolutionized haploidentical hematopoietic stem cell transplantation (HSCT), allowing safe infusion of unmanipulated T cell-replete grafts. PT-Cy selectively eliminates proliferating alloreactive T cells, but whether and how it affects natural killer (NK) cells and their alloreactivity is largely unknown. Here we characterized NK cell dynamics in 17 patients who received unmanipulated haploidentical grafts, containing high numbers of mature NK cells, according to PT-Cy-based protocols in 2 independent centers. In both series, we documented robust proliferation of donor-derived NK cells immediately after HSCT. After infusion of Cy, a marked reduction of proliferating NK cells was evident, suggesting selective purging of dividing cells. Supporting this hypothesis, proliferating NK cells did not express aldehyde dehydrogenase and were killed by Cy in vitro. After ablation of mature NK cells, starting from day 15 after HSCT and favored by the high levels of interleukin-15 present in patients' sera, immature NK cells (CD62L⁺NKG2A⁺KIR^-) became highly prevalent, possibly directly stemming from infused hematopoietic stem cells. Importantly, also putatively alloreactive single KIR⁺ NK cells were eliminated by PT-Cy and were thus decreased in numbers and antileukemic potential at day 30 after HSCT. As a consequence, in an extended series of 99 haplo-HSCT with PT-Cy, we found no significant difference in progression-free survival between patients with or without predicted NK alloreactivity (42% vs 52% at 1 year, P = NS). Our data suggest that the majority of mature NK cells infused with unmanipulated grafts are lost upon PT-Cy administration, blunting NK cell alloreactivity in this transplantation setting.

T memory stem cells in health and disease

T memory stem (T_SCM) cells are a rare subset of memory lymphocytes endowed with the stem cell-like ability to self-renew and the multipotent capacity to reconstitute the entire spectrum of memory and effector T cell subsets. Cumulative evidence in mice, nonhuman primates and humans indicates that T_SCM cells are minimally differentiated cells at the apex of the hierarchical system of memory T lymphocytes. Here we describe emerging findings demonstrating that T_SCM cells, owing to their extreme longevity and robust potential for immune reconstitution, are central players in many physiological and pathological human processes. We also discuss how T_SCM cell stemness could be leveraged therapeutically to enhance the efficacy of vaccines and adoptive T cell therapies for cancer and infectious diseases or, conversely, how it could be disrupted to treat T_SCM cell driven and sustained diseases, such as autoimmunity, adult T cell leukemia and HIV-1.

Gene Therapy Approaches to Immunodeficiency

Transfer of gene-corrected autologous hematopoietic stem cells in patients with primary immunodeficiencies has emerged as a new therapeutic approach. Patients with various conditions lacking a suitable donor have been treated with retroviral vectors and a gene-addition strategy. Initial promising results were shadowed by the occurrence of malignancies in some of these patients. Current trials, developed in the last decade, use safer viral vectors to overcome the risk of genotoxicity and have led to improved clinical outcomes. This review reflects the progresses made in specific disorders, including adenosine deaminase deficiency, X-linked severe combined immunodeficiency, chronic granulomatous disease, and Wiskott-Aldrich syndrome.

NY-ESO-1 TCR single edited stem and central memory T cells to treat multiple myeloma without graft-versus-host disease

Transfer of T-cell receptors (TCRs) specific for tumor-associated antigens is a promising approach for cancer immunotherapy. We developed the TCR gene editing technology that is based on the knockout of the endogenous TCR α and β genes, followed by the introduction of tumor-specific TCR genes, and that proved safer and more effective than conventional TCR gene transfer. Although successful, complete editing requires extensive cell manipulation and 4 transduction procedures. Here we propose a novel and clinically feasible TCR "single editing" (SE) approach, based on the disruption of the endogenous TCR α chain only, followed by the transfer of genes encoding for a tumor-specific TCR. We validated SE with the clinical grade HLA-A2 restricted NY-ESO-1_157-165-specific TCR. SE allowed the rapid production of high numbers of tumor-specific T cells, with optimal TCR expression and preferential stem memory and central memory phenotype. Similarly to unedited T cells redirected by TCR gene transfer (TCR transferred [TR]), SE T cells efficiently killed NY-ESO-1^pos targets; however, although TR cells proved highly alloreactive, SE cells showed a favorable safety profile. Accordingly, when infused in NSG mice previously engrafted with myeloma, SE cells mediated tumor rejection without inducing xenogeneic graft-versus-host disease, thus resulting in significantly higher survival than that observed in mice treated with TR cells. Overall, single TCR gene editing represents a clinically feasible approach that is able to increase the safety and efficacy of cancer adoptive immunotherapy.

Chimeric Antigen Receptors: A Cell and Gene Therapy Perspective

Chimeric antigen receptors (CARs) are synthetic receptors that reprogram T lymphocytes to target chosen antigens. The targeting of CD19, a cell surface molecule expressed in the vast majority of leukemias and lymphomas, has been successfully translated in the clinic, earning CAR therapy a special distinction in the selection of "cancer immunotherapy" by Science as the breakthrough of the year in 2013. CD19 CAR therapy is predicated on advances in genetic engineering, T cell biology, tumor immunology, synthetic biology, target identification, cell manufacturing sciences, and regulatory compliance-the central tenets of CAR therapy. Here, we review two of these foundations: the genetic engineering approaches and cell types to engineer.

Tracking the Fate and Origin of Clinically Relevant Adoptively Transferred CD8+ T Cells In Vivo

Adoptively transferred tumor-specific cells can mediate tumor regression in cancers refractory to conventional therapy. Autologous polyclonal tumor-specific cytotoxic T cells (CTL) generated from peripheral blood and infused into patients with metastatic melanoma show enhanced persistence, compared to equivalent numbers of more extensively expanded monoclonal CTL, and are associated with complete remissions (CR) in select patients. We applied high-throughput T cell receptor Vβ sequencing (HTTCS) to identify individual clonotypes within CTL products, track them in vivo post-infusion and then deduce the pre-adoptive transfer (endogenous) frequencies of cells ultimately responsible for tumor regression. The summed in vivo post-transfer frequencies of the top 25 HTTCS-defined clonotypes originally detected in the infused CTL population were comparable to enumeration by binding of antigen peptide-HLA multimers, revealing quantitative HTTCS is a reliable, multimer-independent alternative. Surprisingly, the polyclonal CTL products were composed predominantly of clonotypes that were of very low frequency (VLF) in the endogenous samples, often below the limit of HTTCS detection (0.001%). In patients who achieved durable CRs, the composition of transferred CTLs was dominated (57-90%) by cells derived from a single VLF clonotype. Thus, HTTCS now reveals that tumor-specific CTL enabling long-term tumor control originate from endogenous VLF populations that exhibit proliferative/survival advantages. Along with results indicating that naïve cell populations are most likely to contain cells that exist at VLF within the repertoire, our results provide a strong rationale for favoring T cells arising from VLF populations and with early-differentiation phenotypes when selecting subset populations for adoptive transfer.

CRISPR/Cas9 β-globin gene targeting in human haematopoietic stem cells

The β-haemoglobinopathies, such as sickle cell disease and β-thalassaemia, are caused by mutations in the β-globin (HBB) gene and affect millions of people worldwide. Ex vivo gene correction in patient-derived haematopoietic stem cells followed by autologous transplantation could be used to cure β-haemoglobinopathies. Here we present a CRISPR/Cas9 gene-editing system that combines Cas9 ribonucleoproteins and adeno-associated viral vector delivery of a homologous donor to achieve homologous recombination at the HBB gene in haematopoietic stem cells. Notably, we devise an enrichment model to purify a population of haematopoietic stem and progenitor cells with more than 90% targeted integration. We also show efficient correction of the Glu6Val mutation responsible for sickle cell disease by using patient-derived stem and progenitor cells that, after differentiation into erythrocytes, express adult β-globin (HbA) messenger RNA, which confirms intact transcriptional regulation of edited HBB alleles. Collectively, these preclinical studies outline a CRISPR-based methodology for targeting haematopoietic stem cells by homologous recombination at the HBB locus to advance the development of next-generation therapies for β-haemoglobinopathies.

Interleukin-15 enhances the proliferation, stimulatory phenotype, and antitumor effector functions of human gamma delta T cells

Background

Adoptive immunotherapy is gaining momentum to fight malignancies, whereby γδ T cells have received recent attention as an alternative cell source as to natural killer cells and αβ T cells. The advent of γδ T cells is largely due to their ability to recognize and target tumor cells using both innate characteristic and T cell receptor (TCR)-mediated mechanisms, their capacity to enhance the generation of antigen-specific T cell responses, and their potential to be used in an autologous or allogeneic setting.

Methods

In this study, we explored the beneficial effect of the immunostimulatory cytokine interleukin (IL)-15 on purified γδ T cells and its use as a stimulatory signal in the ex vivo expansion of γδ T cells for adoptive transfer. The expansion protocol was validated both with immune cells of healthy individuals and acute myeloid leukemia patients.

Results

We report that the addition of IL-15 to γδ T cell cultures results in a more activated phenotype, a higher proliferative capacity, a more pronounced T helper 1 polarization, and an increased cytotoxic capacity of γδ T cells. Moreover γδ T cell expansion starting with peripheral blood mononuclear cells from healthy individuals and acute myeloid leukemia patients is boosted in the presence of IL-15, whereby the antitumor properties of the γδ T cells are strengthened as well.

Conclusions

Our results support the rationale to explore the use of IL-15 in clinical adoptive therapy protocols exploiting γδ T cells.

Improving Adoptive T Cell Therapy: The Particular Role of T Cell Costimulation, Cytokines, and Post-Transfer Vaccination

Adoptive cellular therapy (ACT) is a form of immunotherapy whereby antigen-specific T cells are isolated or engineered, expanded ex vivo, and transferred back to patients. Clinical benefit after ACT has been obtained in treatment of infection, various hematological malignancies, and some solid tumors; however, due to poor functionality and persistence of the transferred T cells, the efficacy of ACT in the treatment of most solid tumors is often marginal. Hence, much effort is undertaken to improve T cell function and persistence in ACT and significant progress is being made. Herein, we will review strategies to improve ACT success rates in the treatment of cancer and infection. We will deliberate on the most favorable phenotype for the tumor-specific T cells that are infused into patients and on how to obtain T cells bearing this phenotype by applying novel ex vivo culture methods. Moreover, we will discuss T cell function and persistence after transfer into patients and how these factors can be manipulated by means of providing costimulatory signals, cytokines, blocking antibodies to inhibitory molecules, and vaccination. Incorporation of these T cell stimulation strategies and combinations of the different treatment modalities are likely to improve clinical response rates further.

CMV-specific immune reconstitution following allogeneic stem cell transplantation

Cytomegalovirus (CMV) remains a major contributor to morbidity and mortality following allogeneic haemopoietic stem cell transplant (HSCT) despite widespread use of viraemia monitoring and pre-emptive antiviral therapy. Uncontrolled viral replication occurs primarily in the first 100 d post transplant but this high risk period can extend to many months if immune recovery is delayed. The re-establishment of a functional population of cellular effectors is essential for control of virus replication and depends on recipient and donor serostatus, the stem cell source, degree of HLA matching and post-transplant factors such as CMV antigen exposure, presence of GVHD and ongoing use of immune suppression. A number of immune monitoring assays exist but have not yet become widely accessible for routine clinical use. Vaccination, adoptive transfer of CMV specific T cells and a number of graft engineering processes are being evaluated to enhance of CMV specific immune recovery post HSCT.

Chimeric antigen receptors: driving immunology towards synthetic biology

The advent of second generation chimeric antigen receptors and the CD19 paradigm have ushered a new therapeutic modality in oncology. In contrast to earlier forms of adoptive cell therapy, which were based on the isolation and expansion of naturally occurring T cells, CAR therapy is based on the design and manufacture of engineered T cells with optimized properties. A new armamentarium, comprising not only CARs but also chimeric costimulatory receptors, chimeric cytokine receptors, inhibitory receptors and synthetic Notch receptors, expressed in naïve, central memory or stem cell-like memory T cells, is being developed for clinical use in a wide range of cancers. Immunological principles are thus finding a new purpose thanks to advances in genetic engineering, synthetic biology and cell manufacturing sciences.

Haploidentical Transplantation in Children with Acute Leukemia: The Unresolved Issues

Allogeneic hematopoietic stem cell transplantation (HSCT) remains a curative option for children with high risk and advanced acute leukemia. Yet availability of matched family donor limits its use and although matched unrelated donor or mismatched umbilical cord blood (UCB) are viable options, they fail to meet the global need. Haploidentical family donor is almost universally available and is emerging as the alternate donor of choice in adult patients. However, the same is not true in the case of children. The studies of haploidentical HSCT in children are largely limited to T cell depleted grafts with not so encouraging results in advanced leukemia. At the same time, emerging data from UCBT are challenging the existing paradigm of less stringent HLA match requirements as perceived in the past. The use of posttransplantation cyclophosphamide (PTCY) has yielded encouraging results in adults, but data in children is sorely lacking. Our experience of using PTCY based haploidentical HSCT in children shows inadequacy of this approach in younger children compared to excellent outcome in older children. In this context, we discuss the current status of haploidentical HSCT in children with acute leukemia in a global perspective and dwell on its future prospects.

Role of memory T cell subsets for adoptive immunotherapy

Adoptive transfer of primary (unmodified) or genetically engineered antigen-specific T cells has demonstrated astonishing clinical results in the treatment of infections and some malignancies. Besides the definition of optimal targets and antigen receptors, the differentiation status of transferred T cells is emerging as a crucial parameter for generating cell products with optimal efficacy and safety profiles. Long-living memory T cells subdivide into phenotypically as well as functionally different subsets (e.g. central memory, effector memory, tissue-resident memory T cells). This diversification process is crucial for effective immune protection, with probably distinct dependencies on the presence of individual subsets dependent on the disease to which the immune response is directed as well as its organ location. Adoptive T cell therapy intends to therapeutically transfer defined T cell immunity into patients. Efficacy of this approach often requires long-term maintenance of transferred cells, which depends on the presence and persistence of memory T cells. However, engraftment and survival of highly differentiated memory T cell subsets upon adoptive transfer is still difficult to achieve. Therefore, the recent observation that a distinct subset of weakly differentiated memory T cells shows all characteristics of adult tissue stem cells and can reconstitute all types of effector and memory T cell subsets, became highly relevant. We here review our current understanding of memory subset formation and T cell subset purification, and its implications for adoptive immunotherapy.