Extensive replicative capacity of human central memory T cells

Antigen specificities of HIV-infected cells: A role in infection and persistence?

Antigen-experienced memory CD4⁺ T cells are the major target of HIV infection and support both productive and latent infections, thus playing a key role in HIV dissemination and persistence, respectively. Here, we reviewed studies that have shown direct association between HIV infection and antigen specificity. During untreated infection, some HIV-specific cells host productive infection, while other pathogen-specific cells such as cytomegalovirus (CMV) and Mycobacterium tuberculosis also contribute to viral persistence on antiretroviral therapy (ART). These patterns could be explained by phenotypic features differing between these pathogen-specific cells. Mechanisms involved in these preferential infection and selection processes include HIV entry and restriction, cell exhaustion, survival, self-renewal and immune escape. For instance, MIP-1β expressing cells such as CMV-specific memory cells were shown to resist infection by HIV CCR5 coreceptor downregulation/inhibition. Conversely, HIV-infected CMV-specific cells undergo clonal expansion during ART. We have identified several research areas that need further focus such as the role of other pathogens, viral genome intactness, inducibility and phenotypic features. However, given the sheer diversity of both the CD4⁺ T cell repertoire and antigenic history of each individual, studying HIV-infected, antigen-experienced cells still imposes numerous challenges.

Trafficking and persistence of alloantigen-specific chimeric antigen receptor regulatory T cells in Cynomolgus macaque

Adoptive transfer of chimeric antigen receptor regulatory T cells (CAR Tregs) is a promising way to prevent allograft loss without the morbidity associated with current therapies. Non-human primates (NHPs) are a clinically relevant model to develop transplant regimens, but manufacturing and engraftment of NHP CAR Tregs have not been demonstrated yet. Here, we describe a culture system that massively expands CAR Tregs specific for the Bw6 alloantigen. In vitro, these Tregs suppress in an antigen-specific manner without pro-inflammatory cytokine secretion or cytotoxicity. In vivo, Bw6-specific CAR Tregs preferentially traffic to and persist in bone marrow for at least 1 month. Following transplant of allogeneic Bw6+ islets and autologous CAR Tregs into the bone marrow of diabetic recipients, CAR Tregs traffic to the site of islet transplantation and maintain a phenotype of suppressive Tregs. Our results establish a framework for the optimization of CAR Treg therapy in NHP disease models.

Targeting the epichaperome as an effective precision medicine approach in a novel PML-SYK fusion acute myeloid leukemia

The epichaperome is a new cancer target composed of hyperconnected networks of chaperome members that facilitate cell survival. Cancers with an altered chaperone configuration may be susceptible to epichaperome inhibitors. We developed a flow cytometry-based assay for evaluation and monitoring of epichaperome abundance at the single cell level, with the goal of prospectively identifying patients likely to respond to epichaperome inhibitors, to measure target engagement, and dependency during treatment. As proof of principle, we describe a patient with an unclassified myeloproliferative neoplasm harboring a novel PML-SYK fusion, who progressed to acute myeloid leukemia despite chemotherapy and allogeneic stem cell transplant. The leukemia was identified as having high epichaperome abundance. We obtained compassionate access to an investigational epichaperome inhibitor, PU-H71. After 16 doses, the patient achieved durable complete remission. These encouraging results suggest that further investigation of epichaperome inhibitors in patients with abundant baseline epichaperome levels is warranted.

A high migratory capacity of donor T-cells in response to the lymph node homing receptor CCR7 increases the incidence and severity of GvHD

The pathogenesis of GvHD involves migration of donor T-cells into the secondary lymphoid organs in the recipient, which is steered by two homing molecules, CD62L and CCR7. Therefore, we investigated whether the migratory capacity of donor T-cells is associated with GvHD. This single center prospective study included 85 donor-recipient pairs. In vitro chemotaxis assays of the lymphocytes of the apheresis product were performed in parallel to the analysis of CD62L and CCR7 by flow cytometry. The migratory index to the CCR7 ligands, CCL19 and CCL21, was higher in T-cells from donors whose recipients will develop GvHD. Similarly, the acute GvHD (aGvHD) group received higher percentage of CD4+CCR7+ T-cells, whereas chronic GvHD (cGvHD) patients were transplanted with higher percentages of CD8+CCR7+ T-cells compared with the non-GvHD group. These results were confirmed when patients were subdivided according to degrees of severity. Further, multivariate analysis confirmed that the proportions of CCR7+ CD4+ and CCR7+ CD8+ T-cells are risk factors for the development and severity of aGvHD and cGvHD, respectively. Functional experiments demonstrated that CCR7+ T-cells exhibited higher potential for activation than CCR7- T-cells did. We therefore propose that the selective depletion of CCR7-expressing T-cells may be an effective preventive therapy for GvHD.

Current status of chimeric antigen receptor therapy for haematological malignancies

The field of adoptive cell transfer includes chimeric antigen receptor (CAR) engineered T cells, constructs that emerged from basic research into principles of immunology and have transformed into clinically effective therapies for haematological malignancies. T cells engineered to express these artificial receptors hold great promise, but also carry significant risk. While permanent genetic modification of mature T cells appears safe, modulating their in vivo function is difficult, partly because the robust response can trigger other arms of the immune system. Suicide systems and toxicity management with cytokine blockade or signal transduction modulators have emerged as a new frontier in this field, a far cry from early problems getting CAR T cells to work at all. Currently, clinical trials in patients with relapsed or refractory B cell malignancies treated with CD19-specific CAR T cells have induced durable remissions in adults and children. Results from these trials indicate that more work needs to be done to understand biomarkers of efficacy, the role of T cell persistence and how to integrate this care into standard practice. Cell therapy will not be a 'one size fits all' class of medicine, and here we will discuss the development of this therapy and important questions for its future.

Chimeric Antigen Receptor- and TCR-Modified T Cells Enter Main Street and Wall Street

The field of adoptive cell transfer (ACT) is currently comprised of chimeric Ag receptor (CAR)- and TCR-engineered T cells and has emerged from principles of basic immunology to paradigm-shifting clinical immunotherapy. ACT of T cells engineered to express artificial receptors that target cells of choice is an exciting new approach for cancer, and it holds equal promise for chronic infection and autoimmunity. Using principles of synthetic biology, advances in immunology, and genetic engineering have made it possible to generate human T cells that display desired specificities and enhanced functionalities. Clinical trials in patients with advanced B cell leukemias and lymphomas treated with CD19-specific CAR T cells have induced durable remissions in adults and children. The prospects for the widespread availability of engineered T cells have changed dramatically given the recent entry of the pharmaceutical industry to this arena. In this overview, we discuss some of the challenges and opportunities that face the field of ACT.

Effect of age on the CD4⁺ T-cell impairment in HIV-infected persons without and with cART

BACKGROUND

Knowledge about HIV infection in older persons is becoming increasingly important. CD4⁺ T cells are essential for protective immunity, but little is known about the effect of age on the CD4⁺ T-cell impairment in HIV infection.

METHODS

Treatment-naive patients aged older than 50 or younger than 40 years were studied for absolute and relative frequencies of CD31⁺ naive and CD31⁻ naive CD4⁺ T cells, central memory, effector memory, and terminally differentiated CD4⁺ T cells, and compared with age-matched controls. In addition, cellular proliferation and cytokine secretion properties were determined. CD4⁺ T-cell reconstitution was analyzed in older and younger patients with <350 or ≥ 350 CD4⁺ T cells per microliter at initiation of combination antiretroviral therapy (cART).

RESULTS

CD4⁺ T cells of older but not younger HIV-infected patients showed age-inappropriate low levels of CD31⁻ naive cells, increased levels of effector memory cells, and enhanced interferonγ and interleukin-17 secretion. Impaired CD4⁺ T-cell composition persisted in patients who initiated cART at <350 CD4⁺ T cells per microliter. In patients with CD4⁺ T cells ≥ 350 per microliter, alterations were less pronounced and were reversible with cART. Compared with age-matched controls, total CD4⁺ T-cell counts did not differ between treated younger and older HIV-infected patients.

CONCLUSIONS

These data demonstrate that aging enhances the CD4⁺ T-cell impairment in HIV-infected persons mainly by a loss of CD31⁻ naive cells, accumulation of effector memory cells, and increased pro-inflammatory effector functions. Age-related changes in CD4⁺ T-cell composition can be prevented by an early initiation of cART.

Chimeric antigen receptor therapy for cancer

Improved outcomes for patients with cancer hinge on the development of new targeted therapies with acceptable short-term and long-term toxicity. Progress in basic, preclinical, and clinical arenas spanning cellular immunology, synthetic biology, and cell-processing technologies has paved the way for clinical applications of chimeric antigen receptor-based therapies. This new form of targeted immunotherapy merges the exquisite targeting specificity of monoclonal antibodies with the potent cytotoxicity and long-term persistence provided by cytotoxic T cells. Although this field is still in its infancy, clinical trials have already shown clinically significant antitumor activity in neuroblastoma, chronic lymphocytic leukemia, and B cell lymphoma, and trials targeting a variety of other adult and pediatric malignancies are under way. Ongoing work is focused on identifying optimal tumor targets and on elucidating and manipulating both cell- and host-associated factors to support expansion and persistence of the genetically engineered cells in vivo. The potential to target essentially any tumor-associated cell-surface antigen for which a monoclonal antibody can be made opens up an entirely new arena for targeted therapy of cancer.

T cell-based gene therapy of cancer

Adoptive immunotherapy using gene engineered T cells is a promising and rapidly evolving field, and the ability to engineer T cells to manifest desired phenotypes and functions has become a practical reality. In this review, we describe and summarize current thought about gene engineering of T cells. We focus on the identified requirements for the successful application of T cell based immunotherapy and discuss gene-therapy based strategies that address these requirements and have the potential to enhance the successful implementation of this promising approach to treat cancer.

Immunologic consequences of chemotherapy for acute myeloid leukemia

There are few data characterizing the immunologic consequences of chemotherapy for acute myeloid leukemia (AML) and almost nothing is known about the effects of chemotherapy in a pediatric AML cohort. We identified T-cell subsets, B-cell subsets, and used Enzyme-linked immunosorbent spot analyses to define the function of T cells and B cells in 7 pediatric patients with AML on chemotherapy. The data show that the effects of chemotherapy disproportionately target the B cell and depletion of B cells is associated with impaired responses to the inactivated influenza vaccine. Diminished T-cell numbers were also observed although the magnitude of the effect was less than what was seen for B cells. Furthermore, measures of T-cell function were largely intact. We conclude that humoral immunity is significantly affected by chemotherapy for AML.

Ex vivo interleukin-12-priming during CD8(+) T cell activation dramatically improves adoptive T cell transfer antitumor efficacy in a lymphodepleted host

BACKGROUND

Clinical application of adoptive T cell therapy has been hindered by an inability to generate adequate numbers of nontolerized, functionally active, tumor-specific T cells, which can persist in vivo. In order to address this, we evaluated the impact of interleukin (IL)-12 signaling during tumor-specific CD8(+) T cell priming in terms of persistence and antitumor efficacy using an established B16 melanoma tumor adoptive therapy model.

STUDY DESIGN

B6 mice were injected subcutaneously with B16 melanoma tumor cells. On day 12 of tumor growth, mice were preconditioned with cyclophosphamide (4mg dose, intraperitoneally), and 1 day later were treated by adoptive transfer of tumor-specific pmel-1 CD8(+) T cells primed ex vivo 3 days earlier with both IL-12 and antigen (hGP100(25-33) peptide) or antigen only. Tumors were measured biweekly, and infused donor T cells were analyzed for persistence, localization to the tumor, phenotype, and effector function.

RESULTS

Adoptive transfer of tumor-specific CD8(+) T cells primed with IL-12 was significantly more effective in reducing tumor burden in mice preconditioned with cyclophosphamide compared with transfer of T cells primed without IL-12. This enhanced antitumor response was associated with increased frequencies of infused T cells in the periphery and tumor as well as elevated expression of effector molecules including granzyme B and interferon-γ (IFNγ).

CONCLUSIONS

Our findings demonstrate that ex vivo priming of tumor-specific CD8(+) T cells with IL-12 dramatically improves their in vivo persistence and therapeutic ability on transfer to tumor-bearing mice. These findings can be directly applied as novel clinical trial strategies.

Adoptive cellular therapy

Cell-based therapies with various lymphocytes and antigen-presenting cells are promising approaches for cancer immunotherapy. The transfusion of T lymphocytes, also called adoptive cell therapy (ACT), is an effective treatment for viral infections, has induced regression of cancer in early stage clinical trials, and may be a particularly important and efficacious modality in the period following hematopoietic stem cell transplantation (HSCT). Immune reconstitution post-SCT is often slow and incomplete, which in turn leads to an increased risk of infection and may impact relapse risk in patients with malignant disease. Immunization post-HSCT is frequently unsuccessful, due to the prolonged lymphopenia, especially of CD4 T cells, seen following transplant. ACT has the potential to enhance antitumor and overall immunity, and augment vaccine efficacy in the post-transplant setting. The ability to genetically engineer lymphocyte subsets has the further potential to improve the natural immune response, correct impaired immunity, and redirect T cells to an antitumor effector response. This chapter focuses on various applications of ACT for cancer immunotherapy, and we discuss some of the latest progress and hurdles in translating these technologies to the clinic.

Engineering lymphocyte subsets: tools, trials and tribulations

Cell-based therapies with various lymphocyte subsets hold promise for the treatment of several diseases, including cancer and disease resulting from inflammation and infection. The ability to genetically engineer lymphocyte subsets has the potential to improve the natural immune response and correct impaired immunity. In this Review we focus on the lymphocyte subsets that have been modified genetically or by other means for therapeutic benefit, on the technologies used to engineer lymphocytes and on the latest progress and hurdles in translating these technologies to the clinic.

Post-transplant adoptive T-cell immunotherapy

Immune reconstitution following haematopoietic stem cell transplantation (SCT) is an often slow and incomplete process that leads to increased risk of infection and malignant disease. Immunization in SCT is frequently unsuccessful due to the prolonged lymphopenia, especially of CD4 T cells, seen following transplant. The transfusion of T cells, also called 'adoptive T-cell therapy', has the potential to enhance anti-tumour and overall immunity, and augment vaccine efficacy in the post-transplant setting. Recent advances in tissue culture, cellular immunology and tumour biology are guiding new approaches to adoptive T-cell therapy. This chapter will discuss the challenges that face the field before adoptive T-cell therapy can be translated into routine clinical practice.

Synthetic CD4+ T cell-targeted antigen-presenting cells elicit protective antitumor responses

CD4(+) helper T cells are critical for protective immune responses and yet suboptimally primed in response to tumors. Cell-based vaccination strategies are under evaluation in clinical trials but limited by the need to derive antigen-presenting cells (APC) from patients or compatible healthy donors. To overcome these limitations, we developed CD4(+) T cell-targeted synthetic microbead-based artificial APC (aAPC) and used them to activate CD4(+) T lymphocytes specific for a tumor-associated model antigen (Ag) directly from the naive repertoire. In vitro, aAPC specifically primed Ag-specific CD4(+) T cells that were activated to express high levels of CD44, produced mainly interleukin 2, and could differentiate into Th1-like or Th2-like cells in combination with polarizing cytokines. I.v. administration of aAPC led to Ag-specific CD4(+) T-cell activation and proliferation in secondary lymphoid organs, conferred partial protection against subcutaneous tumors, and prevented the establishment of lung metastasis. Taken together, our data support the use of cell-free, synthetic aAPC as a specific and versatile alternative to expand peptide-specific CD4(+) T cells in adoptive and active immunotherapy.

T lymphocyte engineering ex vivo for cancer and infectious disease

BACKGROUND

Basic research contributions towards the molecular and cellular understanding of immune mediated control of cancer and infectious diseases have created opportunities to develop new forms of T-cell-based vaccination for cancer and chronic infections like HIV. In the past two decades, there has been a dramatic increase in the number of cell therapy clinical trials around the world aimed at enhancing antitumor immunity, restoring immune function to infectious diseases and augmenting vaccine efficacy.

OBJECTIVE

To provide a review of new and emerging methods of T lymphocyte engineering, gene transfer to T cells and clinical trials.

METHODS

A review of recent clinical trials, along with a brief historical perspective, with a focus on challenges and recent advances in the field and requirements for successful T-cell therapies.

CONCLUSION

Advances in the technological approaches and methods for ex vivo manipulation have led to T lymphocytes endowed with enhanced potency and unique functions, with promise as the new generation of infused therapeutics.

Adoptive immunotherapy: good habits instilled at youth have long-term benefits

Many recent advances in basic cell biology and immunology are a harbinger of progress in adoptive cell therapy (ACT) including (1) the finding that host lymphodepletion enhances engraftment and efficacy, (2) the recognition that in vitro T cell functions may not correlate with in vivo efficacy, and (3) the development of advanced ex vivo culture methods to expand lymphocytes to therapeutically effective numbers. In this article, we focus on the development of artificial antigen presenting cells (aAPCs) in our laboratory and their applicability to augment ACT protocols. We also describe how aAPCs can be used to broaden ACT to treat patients with a wide variety of cancers, chronic infectious diseases, and autoimmune manifestations.

Principles of adoptive T cell cancer therapy

The transfusion of T cells, also called adoptive T cell therapy, is an effective treatment for viral infections and has induced regression of cancer in early-stage clinical trials. However, recent advances in cellular immunology and tumor biology are guiding new approaches to adoptive T cell therapy. For example, use of engineered T cells is being tested as a strategy to improve the functions of effector and memory T cells, and manipulation of the host to overcome immunotoxic effects in the tumor microenvironment has led to promising results in early-stage clinical trials. Challenges that face the field and must be addressed before adoptive T cell therapy can be translated into routine clinical practice are discussed.

'Normal counterparts' of nodal peripheral T-cell lymphoma

Peripheral T-cell lymphomas (PTCL) have been difficult to classify. A homogeneous principle of classification is still lacking, partly because lymph node compartments containing functionally distinct T-cell subsets have not been identified. A correlation to differentiated T-cell subsets, as CD4(+) or CD8(+) cells as well as cytotoxic populations has not revealed clinically meaningful entities. Upon antigen encounter, mature T-cells pass through distinct stages characterized by their surface molecule expression. Naïve T-cells are CD45RA(+)/CD45R0(-)/CD27(+)/CCR7(+), however, after antigen contact CD45RA expression is replaced by CD45R0. They differentiate to central memory cells, which retain CD27 and CCR7, or to effector-memory cells, which loose expression of both molecules depending on the strength of the antigen interaction. Immunohistological analysis of PTCL showed an effector or effector-memory cell phenotype (CD45RA(-)/CD45R0(+)/CD27(-)) for both angioimmunoblastic T-cell lymphoma (AILT) and anaplastic large cell lymphoma (ALCL), but different cytotoxic and activation markers expressed by these tumours. A subset of CD4(+) PTCL-not otherwise specified (PTCL-NOS) may correspond to a central memory cell phenotype (CD45RA(-)/CD45R0(+)/CD27(+)). Thus, a correlation of PTCL to stages of differentiation, rather than to the direction of differentiation, may reveal homogeneous categories. A comparison between the lymphomas and their normal counterparts may contribute to the understanding of the underlying transformation mechanisms.

Complexity of Anti-immunosenescence Strategies in Humans

Immunosenescence is characterized by three main aspects: (i) the shrinkage of the T cell repertoire and the accumulation of oligoclonal expansions (megaclones) of memory/effector cells directed toward ubiquitary infectious agents; (ii) the involution of the thymus and the exhaustion of naïve T cells; and (iii) a chronic inflammatory status called inflamm-aging. We present here possible strategies to counteract these main aspects of immunosenescence in humans with particular attention to the reduction of antigenic load by pathogens, such as CMV, and the normalization of intestinal microflora, the possible utilization of IL-7 to reverse thymic involution, the purging of megaclones, the forced expression of CD28 on T lymphocytes, the reduction of inflamm-aging and the administration of nutrients such as vitamin D. Possible drawbacks of all these strategies are discussed. Finally, the complexity of a rejuvenation approach is stressed, with particular attention to the inhibitory role played by the "old microenvironment" on the performance of progenitor cells, the best candidate to counteract the decline in regenerative potential characteristic of organs and tissues from old organisms.

Nodal peripheral T-cell lymphomas correspond to distinct mature T-cell populations

Peripheral T-cell lymphomas (PTCL) have not been successfully correlated with specific developmental stages of reactive T-cells. Mature T-cells pass through distinct stages upon antigen encounter. Naïve T-cells are CD45RA(+)/CD45R0(-)/CD27(+)/CCR7(+). After antigen contact they replace CD45RA expression with CD45R0. The mature T-cells differentiate to central memory cells, which retain CD27 and CCR7, or to effector memory cells, which lose expression of both molecules depending on the strength of the antigen interaction. In this study, we evaluated lymph node biopsies from eight PTCL-not otherwise specified (PTCL-NOS), seven angioimmunoblastic T-cell lymphomas (AILT), and 15 anaplastic large cell lymphomas (ALCL). Detection of tumour cells with antibodies that recognize specific rearranged T-cell receptor Vbeta segments allowed us to investigate the expression of various differentiation-associated molecules. Results were analysed by hierarchical cluster analysis. All AILT and ALCL showed a homogeneous effector cell phenotype (CD45RA(-)/CD45R0(+)/CD27(-)), but differed in the cytotoxic and activation markers expressed. Several (5/8) PTCL-NOS clustered together; these cases all exhibited a CD4(+) central memory cell phenotype (CD45RA(-)/CD45R0(+)/CD27(+)) and four expressed the lymph node homing receptor CCR7. In conclusion, AILT and ALCL tumour cells correspond to different subsets of effector cells, while a subset of PTCL-NOS correlates with a non-effector T-cell population.

A high proportion of donor CD4+ T cells expressing the lymph node-homing chemokine receptor CCR7 increases incidence and severity of acute graft-versus-host disease in patients undergoing allogeneic stem cell transplantation for hematological malignancy

CC-chemokine receptor 7 (CCR7), a chemokine receptor required for transmigration into lymphoid organs, is only expressed by naive and central memory T cells. T cells with a capacity of homing into lymphoid organs can initiate acute graft-versus-host disease (GVHD) in mice and respond vigorously in vitro to alloantigens in humans, but their impact on clinical outcomes is unknown. We evaluated prospectively the distribution of naive, central memory and CCR7neg memory T-cell subsets in 39 bone marrow and 23 granulocyte colony-stimulating factor-mobilized peripheral blood stem cell allografts and investigated their impact on patient outcomes. Ranges of the relative proportions of CCR7+ cells within CD4+ and CD8+ T-cell populations were broad, but did not differ between the two sources of allografts. By multivariate analysis, high percentage of donor-derived CD4+CCR7+ T cells (>73.5%) significantly correlated with incidence, earliness of onset and severity of acute GVHD, conferring the highest adjusted hazard ratio (HR=3.9; 95% confidence interval 1.4-10.8; P=0.008) without interfering in other clinical events, especially chronic GVHD and relapse. Determination of the percentage of CD4+CCR7+ T cells in the graft provides a predictive indicator of acute GVHD. Partial depletion of this subset may reduce the risk of acute GVHD while preserving immunotherapeutic effects.

Evaluating the impact of hepatitis C virus (HCV) on highly active antiretroviral therapy-mediated immune responses in HCV/HIV-coinfected women: role of HCV on expression of primed/memory T cells

OBJECTIVE

To evaluate the impact of hepatitis C virus (HCV) on the immune system before receipt of highly active antiretroviral therapy (HAART) and on immune recovery after receipt of HAART among human immunodeficiency virus (HIV)/HCV-coinfected women enrolled in the Women's Interagency HIV Study.

METHODS

The study included 294 HIV-infected women who initiated HAART and attended 2 follow-up visits. The women were grouped on the basis of positive HCV antibody and HCV RNA tests. There were 148 women who were HCV antibody negative, 34 who were HCV antibody positive but RNA negative, and 112 who were HCV antibody and RNA positive. Immune recovery was measured by flow-cytometric assessment for markers of activation and maturation on CD4+ and CD8+ T cells. Data analysis used repeated measures of variance.Results. HIV/HCV coinfection is associated with an increased number of CD4+ and CD8+ primed/memory T cells. HIV/HCV coinfection, however, did not affect any further decreases in CD4+ or CD4+ and CD8+ naive/memory T cell counts or enhanced T cell activation. HIV/HCV coinfection also did not affect HAART responses in the CD4+ and CD8+ T cell compartment.

CONCLUSIONS

HCV does not affect immune responses to HAART in HIV/HCV-coinfected individuals but is associated with an expansion of CD4+ and CD8+ memory T cell subsets. Functional impairment in the CD4+ and CD8+ T cell compartments still needs to be assessed in coinfected patients.

Distinct mechanisms control human naive and antigen-experienced CD8+ T lymphocyte proliferation

Human Ag-specific CD8(+) T lymphocytes are heterogeneous and include functionally distinct populations. In this study, we report that at least two distinct mechanisms control the expansion of circulating naive, memory, and effector CD8(+) T lymphocytes when exposed to mitogen or Ag stimulation. The first one leads to apoptosis and occurs shortly after in vitro stimulation. Susceptibility to cell death is prominent among primed T cell subsets, and it is inversely correlated with the size of the ex vivo Bcl-2(high) population within these subsets. Importantly, the Bcl-2(high) phenotype is associated to the proportion of responsive CD8(+) T cells, independently of their differentiation stage. The second one depends on the expression of newly synthesized cyclin-dependent kinase inhibitor p16(INK4a) that occurs in a significant fraction of T cells that had been actively cycling, leading to their cell cycle arrest upon stimulation. Strikingly, accumulation of p16(INK4a) protein preferentially occurs in naive as opposed to primed derived T lymphocytes and is not related to apoptosis. Significant levels of p16 are readily detectable in a small number of ex vivo CD8(+) T cells. Our observations reveal that activation-induced p16 expression represents an alternative process to apoptosis, limiting the proliferation potential of activated naive derived T lymphocytes.

Adoptive T cell therapy of solid cancers

The development of immune-based approaches for the treatment of cancer has been actively investigated for many years. One strategy that has emerged as a potentially effective strategy for the treatment of aggressive established malignancies is adoptive T cell therapy. The power of this approach has been repeatedly observed in preclinical animal models. However, moving from homogeneous animal models to the heterogeneous human clinical setting has been very difficult. It is only in recent times that we have been able to pinpoint the problems of the clinical translation of adoptive T cell therapy. Some of the major problems are sources of tumor-specific T cells, ex vivo expansion, persistence, and anti-tumor activity. This review overviews the nature of these problems and some of the emerging solutions.

Acquisition of full effector function in vitro paradoxically impairs the in vivo antitumor efficacy of adoptively transferred CD8+ T cells

T cell differentiation is a progressive process characterized by phenotypic and functional changes. By transferring tumor-specific CD8+ T cells into tumor-bearing mice at various stages of differentiation, we evaluated their efficacy for adoptive immunotherapy. We found that administration of naive and early effector T cells, in combination with active immunization and IL-2, resulted in the eradication of large, established tumors. Despite enhanced in vitro antitumor properties, more-differentiated effector T cells were less effective for in vivo tumor treatment. Several events may underlie this paradoxical phenomenon: (a) downregulation of lymphoid-homing and costimulatory molecules; (b) inability to produce IL-2 and access homeostatic cytokines; and (c) entry into a proapoptotic and replicative senescent state. While the progressive acquisition of terminal effector properties is characterized by pronounced in vitro tumor killing, in vivo T cell activation, proliferation, and survival are progressively impaired. These findings suggest that the current methodology for selecting T cells for transfer is inadequate and provide new criteria for the generation and the screening of optimal lymphocyte populations for adoptive immunotherapy.

Interleukin-7 signalling is sufficient to phenotypically and functionally prime human CD4 naive T cells

Interleukin-7 (IL-7) is produced by bone marrow and lymphoid stromal cells and is involved in the synthesis, survival and homeostasis of T cells. These attributes are the basis for current strategies to utilize IL-7 as an immune modulator for several clinical conditions to replenish depleted T-cell numbers. Because we had previously determined that IL-7 can induce potent human immunodeficiency virus replication in the otherwise non-permissive CD4(+) naive T-cell compartment, we evaluated here the impact of IL-7 on the phenotype and functional potential of naive CD4(+) T cells in an attempt to understand the mechanism of this induction. We demonstrate that IL-7 mediated the up-regulation of CD25, CD95 and human leucocyte antigen-DR, while it did not alter the expression of CD45RO, CD69, CD40, or CD154. Examination of the cytokine profile of IL-7-treated naive T cells using a Type1/Type2 Proteome Array indicated a remarkable IL-7-mediated induction of interferon-gamma production, while the other cytokines evaluated (IL-2, IL-12, tumour necrosis factor-alpha, IL-4, IL-5, IL-10 and IL-13) were not affected. Intracellular staining of IL-7-treated naive T cells for interferon-gamma verified the Proteome data. IL-7 did not induce cell cycle proliferation of naive CD4(+) T cells, as evaluated by 7-AAD/pyronin immunostaining and carboxyfluorescein diacetate succinimidyl ester dye tracking. IL-7 treatment of naive CD4(+) T cells induced their ability to prime monocytes, as was indicated by induction of CD80 and CD86 expression on monocytes cocultured with IL-7-treated naive CD4(+) T cells. Collectively, these data indicate that IL-7 signalling is sufficient to phenotypically and functionally prime human CD4(+) naive T cells independent of antigen stimulation.