Tumor immunity via homeostatic T cell proliferation: mechanistic aspects and clinical perspectives

γδ T Cells in Skin Inflammation

Gamma delta (γδ) T cells are a subset of T lymphocytes that express T cell receptor γ and 5 chains and display structural and functional heterogeneity. γδ T cells are typically of low abundance in the body and account for 1-5% of the blood lymphocytes and peripheral lymphoid tissues. As a bridge between innate and adaptive immunity, γδ T cells are uniquely poised to rapidly respond to stimulation and can regulate immune responses in peripheral tissues. The dendritic epidermal T cells in the skin epidermis can secrete growth factors to regulate skin homeostasis and re-epithelization and release inflammatory factors to mediate wound healing during skin inflammatory responses. Dermal γδ T cells can regulate the inflammatory process by producing interleukin-17 and other cytokines or chemokines. Here, we offer a review of the immune functions of γδ T cells, intending to understand their role in regulating skin barrier integrity and skin wound healing, which may be crucial for the development of novel therapeutics in skin diseases like atopic dermatitis and psoriasis.

Pre-immunization of donor lymphocytes with GITR agonistic antibody enhances antitumor immunity in autologous hematopoietic stem cell transplantation

The lymphopenic condition following autologous hematopoietic stem cell transplantation (HSCT) enhances the proliferation of T cells by engaging tumor-associated antigens, leading to the alteration of the T-cell repertoire towards antitumor immunity. However, cure by autologous HSCT alone have rarely occurred in the clinical setting. Since tumor-reactive lymphocytes preferentially proliferate during reconstitution of the immune system, we examined whether the priming of donor lymphocytes can strengthen the antitumor effect by HSCT in a CT26 murine colon cancer model. The systemic administration of an anti-glucocorticoid-induced TNF receptor (GITR) agonistic antibody (Ab) significantly increased the number of CT26-responsive T cells but not that of auto-reactive lymphocytes in donor mice. The infusion of non-primed and GITR Ab-primed donor lymphocytes suppressed the CT26 tumor growth, and only the primed lymphocytes eliminated tumors in all the treated mice. The frequency of CT26-responsive T cells was elevated in recipient mice infused with both primed and non-primed lymphocytes until 4 weeks after transplantation, while the frequency in recipients with primed lymphocytes was markedly elevated compared with that in mice harboring non-primed lymphocytes at 2 weeks. The frequencies of regulatory T cells and myeloid-derived suppressor cells were elevated in recipient mice infused with primed and non-primed lymphocytes 2 weeks after transplantation, and returned to normal levels by week 4. The combination of autologous HSCT with pre-immunization of donor lymphocytes is a promising strategy to induce strong antitumor immunity.

Absolute lymphocyte counts at end of induction correlate with distinct immune cell compartments in pediatric B cell precursor acute lymphoblastic leukemia

Several retrospective studies in children with B cell precursor (BCP) acute lymphoblastic leukemia (ALL) provided clinical evidence that higher absolute lymphocyte counts (ALC) early into treatment significantly correlated with improved relapse-free and overall survival. It still remains unknown, however, whether the predictive role of higher ALCs reflects general bone marrow recovery or a more specific attribute of immune function. To investigate this question, we implemented a prospective observational cohort study in 20 children with BCP ALL on day 29 (D29) of induction chemotherapy and immunophenotyped their lymphoid (T, B and natural killer cells) and myeloid (neutrophils, monocytes, dendritic cells) compartments. In a first evaluation of a cohort treated with Children's Oncology Group-based induction chemotherapy, the immune cell compartments were differentially depleted at D29. Neither gender, risk status, minimal residual disease, nor bone marrow recovery markers correlated with D29 ALC. In contrast, both CD3+ T cell and dendritic cell compartments, which did not correlate with age, significantly correlated with D29 ALC (p < 0.0001). In addition, subset complexity of cellular immune compartments was preserved at D29. This study reveals that D29 ALC significantly correlates with distinct immune cell compartments but not with bone marrow recovery markers, suggesting that higher D29 ALCs may contribute to leukemia control by inducing specific host immune activity.

Immune Reconstitution after Allogeneic Hematopoietic Stem Cell Transplantation: Time To T Up the Thymus

The success of allogeneic hematopoietic stem cell transplantation, a key treatment for many disorders, is intertwined with T cell immune reconstitution. The thymus plays a key role post allogeneic hematopoietic stem cell transplantation in the generation of a broad but self-tolerant T cell repertoire, but it is exquisitely sensitive to a range of insults during the transplant period, including conditioning regimens, corticosteroids, infections, and graft-versus-host disease. Although endogenous thymic repair is possible it is often suboptimal, and there is a need to develop exogenous strategies to help regenerate the thymus. Therapies currently in clinical trials in the transplant setting include keratinocyte growth factor, cytokines (IL-7 and IL-22), and hormonal modulation including sex steroid inhibition and growth hormone administration. Such regenerative strategies may ultimately enable the thymus to play as prominent a role after transplant as it once did in early childhood, allowing a more complete restoration of the T cell compartment.

Immunotherapy Targeting WT1: Designing a Protocol for WT1 Peptide-Based Cancer Vaccine

There is much current excitement about the potential of cancer immunotherapy. WT1 is high on the National Cancer Institute's list of priority antigens for immune therapy. In this chapter we describe a protocol for a clinical trial using a WT1 peptide-based cancer vaccine.

Interaction of natural killer cells with neutrophils exerts a significant antitumor immunity in hematopoietic stem cell transplantation recipients

Autologous hematopoietic stem cell transplantation (HSCT) can induce a strong antitumor immunity by homeostatic proliferation (HP) of T cells and suppression of regulatory T cells following preconditioning‐induced lymphopenia. However, the role of innate immunity including natural killer (NK) cells is still not understood. Here, first, we examined whether NK cells exert an antitumor effect after syngeneic HSCT in a murine colon cancer model. Flow cytometry showed that NK cells as well as T cells rapidly proliferated after HSCT, and the frequency of mature NK cells was increased in tumor during HP. Furthermore, NK cells undergoing HP were highly activated, which contributed to substantial tumor suppression. Then, we found that a large number of neutrophils accumulated in tumor early after syngeneic HSCT. It was recently reported that neutrophil‐derived mediators modulate NK cell effector functions, and so we examined whether the neutrophils infiltrated in tumor are associated with NK cell‐mediated antitumor effect. The depletion of neutrophils significantly impaired an activation of NK cells in tumor and increased the fraction of proliferative NK cells accompanied by a decrease in NK cell survival. The results suggested that neutrophils in tumor prevent NK cells from activation‐induced cell death during HP, thus leading to a significant antitumor effect by NK cells. This study revealed a novel aspect of antitumor immunity induced by HSCT and may contribute to the development of an effective therapeutic strategy for cancer using HSCT.

Preimmunization of donor lymphocytes enhances antitumor immunity of autologous hematopoietic stem cell transplantation

Lymphopenia-induced homeostatic proliferation (HP) of T cells following autologous hematopoietic stem cell transplantation (HSCT) skews the T-cell repertoire by engaging tumor-associated antigens (TAAs), leading to an induction of antitumor immunity. Here, as the tumor-reactive lymphocytes preferentially proliferate during the condition of HP, we examined whether the priming of a donor lymphocytes to TAAs could enhance HP-induced antitumor immunity in autologous HSCT recipients. First, to examine whether the tumor-bearing condition of donor influences the antitumor effect of HSCT, the lymphocytes isolated from CT26 tumor-bearing mice were infused into lethally irradiated mice. The growth of tumors was substantially suppressed in the mice that received HSCT from a tumor-bearing donor compared with a naïve donor, suggesting that a fraction of donor lymphocytes from tumor-bearing mice are primed in response to TAAs and remain responsive upon transplantation. We previously reported that type I interferon (IFN) maturates the dendritic cells and promotes the priming of T cells. We then investigated whether the further priming of donor cells by IFN-α can strengthen the antitumor effect of HSCT. The intratumoral IFN-α gene transfer significantly increased the number of IFN-γ-positive lymphocytes in response to CT26 cells but not the syngeneic lymphocytes in donor mice. The infusion of primed donor lymphocytes markedly suppressed the tumor growth in recipient mice, and cured 64% of the treated mice. Autologous HSCT with the infusion of primed donor lymphocytes is a promising strategy to induce an effective antitumor immunity for solid cancers.

Vascular endothelial growth factor-D-mediated blockade of regulatory T cells within tumors is induced by hematopoietic stem cell transplantation

Lymphopenia-induced homeostatic proliferation of T cells after autologous hematopoietic stem cell transplantation (HSCT) skews the T cell repertoire by engaging tumor-associated Ags, leading to an induction of antitumor immunity. However, how HSCT alters the immunosuppressive microenvironment in the tumors is unknown. In this study, we first analyzed the kinetics of regulatory T cells (Tregs) in the tumors after syngeneic HSCT. Unexpectedly, the frequency of CD4⁺ cells expressing Foxp3 was increased in the spleens, whereas the frequency was clearly decreased in the tumors after HSCT. The origin of reconstituted CD4⁺ and Foxp3⁺ cells in the tumors was mainly from the expansion of transferred splenic T cells. Then, to examine the mechanism of Treg suppression after HSCT, we isolated CD11c⁺ cells from tumors. A large amount of Treg-inhibitory cytokine IL-6 was secreted from the CD11c⁺ cells in the tumors, but not in the spleens in the recipient mice. Furthermore, to understand what factor affects the activity of CD11c⁺ cells in the tumors after HSCT, we analyzed the expression of various cytokines/chemokines with mouse cytokine Ab arrays, and noticed that VEGF-D concentration was increased in the tumors in the early period after HSCT. The CD11c⁺ cells produced IL-6 in response to VEGF-D stimulation, and an administration of VEGF receptor-3 neutralizing Ab significantly suppressed the production of IL-6 from CD11c⁺ cells accompanied with the increase of Tregs in the tumors of HSCT recipients. Autologous HSCT creates an environment that strongly supports the enhancement of antitumor immunity in reconstituted lymphopenic recipients through the suppression of Tregs.

Depletion of radio-resistant regulatory T cells enhances antitumor immunity during recovery from lymphopenia

Cytotoxic lymphodepletion therapies augment antitumor immune responses. The generation and therapeutic efficacy of antitumor effector T cells (T(E)s) are enhanced during recovery from lymphopenia. Although the effects of lymphodepletion on naive T cells (T(N)s) and T(E)s have been studied extensively, the influence of lymphodepletion on suppressor cells remains poorly understood. In this study, we demonstrate a significant increase of CD4(+)CD25(+)Foxp3(+) regulatory T cells (Tregs) in sublethally irradiated lymphopenic mice. These radio-resistant Tregs inhibited the induction of T(E)s in tumor-draining lymph-nodes (TDLNs) during recovery from lymphopenia. The transfer of T(N)s into lymphopenic tumor-bearing mice resulted in some antitumor effects; however, Treg depletion after whole-body irradiation and reconstitution strongly inhibited tumor progression. Further analyses revealed that tumor-specific T cells were primed from the transferred T(N)s, whereas the Tregs originated from irradiated recipient cells. As in irradiated lymphopenic mice, a high percentage of Tregs was observed in cyclophosphamide-treated lymphopenic mice. The inhibition of Tregs in cyclophosphamide-treated mice significantly reduced tumor growth. These results indicate that the Tregs that survive cytotoxic therapies suppress antitumor immunity during recovery from lymphopenia and suggest that approaches to deplete radio and chemo-resistant Tregs can enhance cancer immunotherapies.

Increased frequency of suppressive regulatory T cells and T cell-mediated antigen loss results in murine melanoma recurrence

Therapeutic treatment of large established tumors using immunotherapy has yielded few promising results. We investigated whether adoptive transfer of tumor-specific CD8(+) T cells, together with tumor-specific CD4(+) T cells, would mediate regression of large established B16BL6-D5 melanomas in lymphopenic Rag1(-/-) recipients devoid of regulatory T cells. The combined adoptive transfer of subtherapeutic doses of both TRP1-specific TCR transgenic Rag1(-/-) CD4(+) T cells and gp100-specific TCR transgenic Rag1(-/-) CD8(+) T cells into lymphopenic recipients, who received vaccination, led to regression of large (100-400 mm(2)) melanomas. The same treatment strategy was ineffective in lymphoreplete wild-type mice. Twenty-five percent of mice (15/59) had tumors recur (15-180 d postregression). Recurrent tumors were depigmented and had decreased expression of gp100, the epitope targeted by the CD8(+) T cells. Mice with recurrent melanoma had increased CD4(+)Foxp3(+) TRP1-specific T cells compared with mice that did not show evidence of disease. Importantly, splenocytes from mice with recurrent tumor were able to suppress the in vivo therapeutic efficacy of splenocytes from tumor-free mice. These data demonstrate that large established tumors can be treated by a combination of tumor-specific CD8(+) and CD4(+) T cells. Additionally, recurrent tumors exhibited decreased Ag expression, which was accompanied by conversion of the therapeutic tumor-specific CD4(+) T cell population to a Foxp3(+)CD4(+) regulatory T cell population.

Syngeneic hematopoietic stem cell transplantation enhances the antitumor immunity of intratumoral type I interferon gene transfer for sarcoma

Sarcoma at advanced stages remains a clinically challenging disease. Interferons (IFNs) can target cancer cells by multiple antitumor activities, including the induction of cancer cell death and enhancement of immune response. However, the development of an effective cancer immunotherapy is often difficult, because cancer generates an immunotolerant microenvironment against the host immune system. An autologous hematopoietic stem cell transplantation (HSCT) is expected to reconstitute a fresh immune system, and expand tumor-specific T cells through the process of homeostatic proliferation. Here we examined whether a combination of autologous HSCT and IFNs could induce an effective tumor-specific immune response against sarcoma. First, we found that a type I IFN gene transfer significantly suppressed the cell growth of various sarcoma cell lines, and that IFN-β gene transfer was more effective in inducing cell death than was IFN-α in sarcoma cells. Then, to examine the antitumor effect in vivo, human sarcoma cells were inoculated in immune-deficient mice, and a lipofection of an IFN-β-expressing plasmid was found to suppress the growth of subcutaneous tumors significantly. Finally, the IFN gene transfer was combined with syngeneic HSCT in murine osteosarcoma models. Intratumoral IFN-β gene transfer markedly suppressed the growth of vector-injected tumors and inhibited formation of spontaneous lung and liver metastases in syngeneic HSCT mice, and an infiltration of many immune cells was recognized in metastatic tumors of the treated mice. The treated mice showed no significant adverse events. A combination of intratumoral IFN gene transfer with autologous HSCT could be a promising therapeutic strategy for patients with sarcoma.

Immunotherapy of diffuse gliomas: biological background, current status and future developments

Despite aggressive multimodal treatment approaches, the prognosis for patients with diffuse gliomas remains disappointing. Glioma cells often extensively infiltrate in the surrounding brain parenchyma, a phenomenon that helps them to escape surgical removal, radiation exposure and chemotherapy. Moreover, conventional therapy is often associated with considerable local and systemic side effects. Therefore, the development of novel therapeutic approaches is essential to improve the outcome of these patients. Immunotherapy offers the opportunity to specifically target residual radio-and chemoresistant tumor cells without damaging healthy neighboring brain tissue. Significant progress has been made in recent years both in understanding the mechanisms of immune regulation in the central nervous system (CNS) as well as tumor-induced and host-mediated immunosuppression elicited by gliomas. In this review, after discussing the special requirements needed for the initiation and control of immune responses in the CNS, we focus on immunological phenomena observed in glioma patients, discuss different immunological approaches to attack glioma-associated target structures and touch on further strategies to improve the efficacy of immunotherapy of gliomas.

Lymphocyte proliferation in immune-mediated diseases

Defects in T cell homeostatic mechanisms can result in T cell lymphopenia, defined as decreased numbers of lymphocytes. Lymphopenia results in homeostatic proliferation in order to maintain T cell homeostasis. It has been proposed that homeostatic proliferation can expand the pool of autoreactive T cells that promote autoimmunity, and indeed recent studies have further substantiated this observation in both animal models and humans. Conversely, homeostatic proliferation can promote tumor immunity by allowing tumor-specific T cells to accumulate. In this review, we discuss how the outcome of homeostatic proliferation can function both in a deleterious manner in autoimmunity and a beneficial way in tumor immunity. We also discuss the roles of various cytokines and T regulatory cells that control homeostatic proliferation.

Memory-like CD8+ and CD4+ T cells cooperate to break peripheral tolerance under lymphopenic conditions

The onset of autoimmunity in experimental rodent models and patients frequently correlates with a lymphopenic state. In this condition, the immune system has evolved compensatory homeostatic mechanisms that induce quiescent naive T cells to proliferate and differentiate into memory-like lymphocytes even in the apparent absence of antigenic stimulation. Because memory T cells have less stringent requirements for activation than naive cells, we hypothesized that autoreactive T cells that arrive to secondary lymphoid organs in a lymphopenic environment could differentiate and bypass the mechanisms of peripheral tolerance such as those mediated by self-antigen cross-presentation. Here, we show that lymphopenia-driven proliferation and differentiation of potentially autoreactive CD8(+) T cells into memory-like cells is not sufficient to induce self-reactivity against a pancreatic antigen. Induction of an organ-specific autoimmunity required antigen-specific CD4(+) T cell help. Notably, we found that this function could be accomplished by memory-like CD4(+) T cells generated in vivo through lymphopenia-induced proliferation. These helper cells promoted the further differentiation of memory-like CD8(+) T cells into effectors in response to antigen cross-presentation, resulting in their migration to the tissue of antigen expression where autoimmunity ensued. Thus, the cooperation of self-reactive memory-like CD4(+) and CD8(+) T cells under lymphopenic conditions overcomes cross-tolerance resulting in autoimmunity.

Impaired negative regulation of homeostatically proliferating T cells

Acute lymphopenia-induced homeostatic proliferation (HP) of T cells promotes antitumor immunity, but the mechanism is unclear. We hypothesized that this is due to a lack of inhibitory signals that allows activation of T cells with low affinity for self-antigens. Tumors resist immunity in part by expressing inhibitory molecules such as PD-1 ligand 1 (PD-L1), B7-H4, and TGF-beta. In irradiated mice undergoing HP, we found that T cells displayed a severe deficit in the activation-induced expression of inhibitory molecules PD-1 and CTLA-4, and TGF-beta1-induced expression of Foxp3. HP T cells were also less suppressed by B7-H4/Ig and, unlike control T cells, failed to produce IL-10 in response to this molecule. This deficiency in regulation was reversed as normal T-cell numbers were restored. We conclude that T cells are weakly regulated by inhibitory molecules during the acute phase of HP, which could explain their increased effectiveness in cancer immunotherapy.

Adoptive transfer of T(reg) depleted autologous T cells in advanced renal cell carcinoma

PURPOSE

CD4(+)CD25(+) regulatory T (T(reg)) cells are present in increased numbers in patients with advanced cancer and CD25(+) T cell depletion potentiates tumour immunity in animal models. The aim of this study was to assess the feasibility and safety of adoptive transfer of CD25(+) depleted autologous T cells in patients with advanced renal cell carcinoma and to examine resulting changes in lymphocyte subsets.

PATIENTS AND METHODS

Six patients with advanced renal cell carcinoma underwent leukapheresis followed by conditioning chemotherapy with cyclophosphamide and fludarabine. The autologous leukapheresis product was depleted of CD25(+) cells using CliniMACS System then re-infused into the patient.

RESULTS

Efficient CD25(+) depletion from all leukapheresis products was achieved and 0.55-5.87 x 10(7)/kg CD3(+) cells were re-infused. Chemotherapy related haematological toxicity was observed, but blood counts recovered in all patients allowing discharge after a mean inpatient stay of 21 days. One patient subsequently developed a rapidly progressive neurological syndrome. A transient reduction in CD25(+) subset was noted in the peripheral blood of 5 out of 6 patients with evidence of increased T cell responses to PHA in 4 out of 6 patients. One patient showed increased specific proliferative responses to the tumour associated antigen h5T4 coinciding with the nadir of T(reg) cells.

CONCLUSIONS

Given the transient nature of the reduction in CD25(+) subset and the observed toxicity there is a need to explore further strategies to improve the safety and efficacy of this approach. Nevertheless, the results provide proof of concept in potentiation of tumour antigen T cell responses when T(reg) cell levels are depleted.

Allogeneic MHC gene transfer enhances an effective antitumor immunity in the early period of autologous hematopoietic stem cell transplantation

PURPOSE

In autologous hematopoietic stem cell transplantation (HSCT), lymphopenia-induced homeostatic proliferation of T cells is driven by the recognition of self-antigens, and there is an opportunity to skew the T-cell repertoire during the T-cell recovery by engaging tumor-associated antigens, leading to a break of tolerance against tumors. However, the homeostatic proliferation-driven antitumor responses seem to decline rapidly in association with tumor growth. We hypothesized that a tumor-specific immune response induced by an immune gene therapy could enhance and sustain homeostatic proliferation-induced antitumor immunity.

EXPERIMENTAL DESIGN

The antitumor effect of allogeneic MHC (alloMHC) gene transfer was examined at the early phase of the immune reconstitution after syngeneic HSCT.

RESULTS

Syngeneic HSCT showed significant tumor growth inhibition of syngeneic colon cancer cells within a period of 30 days; however, the tumor then resumed rapid growth and the survival of the mice was not prolonged. In contrast, when the alloMHC plasmid was intratumorally injected at the early phase after syngeneic HSCT, the established tumors were markedly regressed and the survival of recipient mice was prolonged without significant toxicities, whereas no survival advantage was recognized in recipient mice injected with a control plasmid. This tumor suppression was evident even in the other tumors that were not injected with the alloMHC plasmid. The antitumor response was characterized by the development of tumor-specific T cell- and natural killer cell-mediated cytotoxicities.

CONCLUSION

The results suggest the efficacy and safety of integrating intratumoral alloMHC gene transfer with an autologous HSCT for the treatment of solid cancers.

Lymphoid reconstruction and vaccines

Allogeneic HSCT is the most reliable, robust, and effective cell-based biotherapy currently available to pediatric and adult patients with hematologic malignancies. The central role of donor-derived lymphocytes in mediating an effective antitumor effect, preventing and controlling opportunistic infections, and causing GVHD is well documented in animal experiments and human trials. The profound lymphopenia after conditioning regimens coupled with molecular tools to distinguish host versus donor cells provides investigators a window into immune recovery after allogeneic HSCT. Serial analyses of T cell subsets linking immunophenotype with function have revealed the kinetics of donor-derived T cell recovery after allografting and provided insights into ways the immune system can be manipulated to augment the graft-versus-tumor (GVT) effect without inducing GVHD. As this review demonstrates, investigators are not limited to being passive observers of this immune reconstitution; rather, we have an opportunity to shape the allografted T cells repertoire to selectively augment immune function.

Combined IL-15/IL-15Ralpha immunotherapy maximizes IL-15 activity in vivo

IL-15 has substantial potential as an immunotherapeutic agent for augmenting immune responses. However, the activity of IL-15 is mediated by a unique mechanism in which the cytokine is transpresented by cell-bound high-affinity IL-15Ralpha to target cells expressing the IL-15Rbeta and the common gamma-chain. Thus, the efficacy of administered IL-15 alone may be limited by the availability of free IL-15Ralpha. We now show that administration of soluble IL-15/IL-15Ralpha complexes greatly enhanced IL-15 half-life and bioavailability in vivo. Treatment of mice with this complex, but not with IL-15 alone, resulted in robust proliferation of memory CD8 T cells, NK cells, and NK T cells. The activity of the complex required IL-15Rbeta, but not IL-15Ralpha, expression by the responding cells and was IL-7-independent. Interestingly, IL-15/IL-15Ralpha immunotherapy also caused naive CD8 T cell activation and development into effector cells and long-term memory T cells. Lastly, complexed IL-15, as compared with IL-15 alone, dramatically reduced tumor burden in a model of B16 melanoma. These findings hold significant importance for the use of IL-15 as a potential adjuvant/therapeutic and inducer of homeostatic proliferation, without the necessity for prior immunodepletion.