IL-2 during in vitro priming promotes subsequent engraftment and successful adoptive tumor immunotherapy by persistent memory phenotypic CD8(+) T cells

Fueling Cancer Immunotherapy With Common Gamma Chain Cytokines

Adoptive T cell transfer therapy (ACT) using tumor infiltrating lymphocytes or lymphocytes redirected with antigen receptors (CAR or TCR) has revolutionized the field of cancer immunotherapy. Although CAR T cell therapy mediates robust responses in patients with hematological malignancies, this approach has been less effective for treating patients with solid tumors. Additionally, toxicities post T cell infusion highlight the need for safer ACT protocols. Current protocols traditionally expand T lymphocytes isolated from patient tumors or from peripheral blood to large magnitudes in the presence of high dose IL-2 prior to infusion. Unfortunately, this expansion protocol differentiates T cells to a full effector or terminal phenotype in vitro, consequently reducing their long-term survival and antitumor effectiveness in vivo. Post-infusion, T cells face further obstacles limiting their persistence and function within the suppressive tumor microenvironment. Therapeutic manipulation of T cells with common γ chain cytokines, which are critical growth factors for T cells, may be the key to bypass such immunological hurdles. Herein, we discuss the primary functions of the common γ chain cytokines impacting T cell survival and memory and then elaborate on how these distinct cytokines have been used to augment T cell-based cancer immunotherapy.

Soluble γc receptor attenuates anti-tumor responses of CD8+ T cells in T cell immunotherapy

Previous studies have shown that soluble common γ-chain (sγc) modulates CD4⁺ T cell immunity with antagonistic functions in γc cytokine signaling. However, the role of sγc in functional properties of effector CD8⁺ T cells has not been fully defined. In this study, we report a new mechanism by which the anti-tumor activity of mouse CD8⁺ T cells is suppressed in sγc of their own producing. While sγc significantly inhibits cytotoxicity of CD8⁺ T cells, blocking sγc production by genetic modification leads to potentiated effector function of CD8⁺ T cells, establishing persistent CD8⁺ T cells. This is due to the modulation of IL-2 and IL-15 signaling, which is required for expansion and survival of CD8⁺ T cells as well as for optimal cytotoxic activity. More efficient management of tumor growth was achieved by an adoptive transfer of sγc-deficient CD8⁺ T cells than that of wild-type or sγc-overexpressing CD8⁺ T cells. Blocking of IL-2 and IL-15 signaling by sγc attenuates the capacity of CD8⁺ T cells to mount an optimal response to the tumor, with both quantitative and qualitative effects on antigen-specific CD8⁺ T cells. These results could have a critical implication for the generation and survival of optimal effector T cells for adoptive immunotherapy of cancer.

LFA-1 defect-induced effector/memory CD8+ T cell apoptosis is mediated via Bcl-2/Caspase pathways and associated with downregulation of CD27 and IL-15R

LFA-1 signaling is required for the generation of central memory CD8(+) T cells in priming phase. However, its role for effector and memory CD8(+) T cell survival in transition and maintenance phases is elusive. We transferred effector and memory CD8(+) T cells into C57BL/6 and CD54(-/-) mice, which were generated by cultivation of ovalbumin (OVA)-pulsed dendritic cells (DC(OVA)) with naïve CD8(+) T cells derived from transgenic OT I mice and purified from effector CD8(+) T cell-transferred C57BL/6 mice, respectively. We then assessed kinetics of T cell survival using PE-H2-K(b)/OVAI tetramer and FITC-CD8 staining by flow cytometry. We found that survival of transferred effector and memory CD8(+) T cells in CD54(-/-) mice significantly decreased (p<0.05) compared to that in C57BL/6 mice due to an increased T cell apoptosis, which is mediated via downregulation of proapoptotic Bid, anti-apoptotic Bcl-2, Bcl-X(L) and pro-Caspase-8, and up-regulation of apoptotic Bax and cleaved Caspase-3 and -7 by RNA array and Western blotting analyses. Decreased expression of CD27 and IL-15R on transferred CD8(+) T cells with less survival was found to be associated with increased T cell apoptosis, which was confirmed by silencing CD27 with siRNA transfection or using CD8(+) (IL-15R(-/-))T cells for adoptive transfer into C57BL/6 mice. These data indicate that LFA-1 signal defect-induced CD8(+) T cell apoptosis is associated with reduced CD27 costimulation and IL-15R survival signal. Therefore, our study provides important evidence on and elucidates the molecular mechanism associated with the role LFA-1 signaling plays in effector and memory CD8(+) T cell survival.

Incubation of antigen-sensitized T lymphocytes activated with bryostatin 1 + ionomycin in IL-7 + IL-15 increases yield of cells capable of inducing regression of melanoma metastases compared to culture in IL-2

Regression of established tumors can be induced by adoptive immunotherapy (AIT) with tumor draining lymph node (DLN) lymphocytes activated with bryostatin and ionomycin (B/I). We hypothesized that B/I-activated T cells cultured in IL-7 + IL-15 might proliferate and survive in culture better than cells cultured in IL-2, and that these cells would have equal or greater anti-tumor activity in vivo. Tumor antigen-sensitized DLN lymphocytes from either wild-type or T cell receptor transgenic mice were harvested, activated with B/I, and expanded in culture with either IL-2, IL-7 + IL-15 or a regimen of alternating cytokines. Cell yields, proliferation, apoptosis, phenotypes, and in vitro responses to tumor antigen were compared for cells grown in different cytokines. These T cells were also tested for anti-tumor activity against melanoma lung metastases established by prior i.v. injection of B16 melanoma cells. IL-7 + IL-15 or alternating cytokines resulted in much faster and prolonged proliferation and much less apoptosis of B/I-activated T cells than culturing the same cells in IL-2. This resulted in approximately tenfold greater yields of viable cells. Culture in IL-7 + IL-15 yielded higher proportions of CD8+ T cells and a higher proportion of cells with a central memory phenotype. Despite this, T cells grown in IL-7 + IL-15 had higher IFN-gamma release responses to tumor antigen than cells grown in IL-2. Adoptive transfer of B/I-activated T cells grown in IL-7 + IL-15 or the alternating regimen had equal or greater efficacy on a "per-cell" basis against melanoma metastases. Activation of tumor antigen-sensitized T cells with B/I and culture in IL-7 + IL-15 is a promising modification of standard regimens for production of T cells for use in adoptive immunotherapy of cancer.

Modeling the CD8+ T effector to memory transition in adoptive T-cell antitumor immunotherapy

Adoptive T-cell therapy with CD8(+) CTLs is often characterized by poor persistence of the transferred T cells and limited effector responses. Improved persistence and therapeutic efficacy have been noted when antigen-activated CD8(+) T cells express properties of memory cells. The current study was undertaken to more precisely characterize the development of memory-like CD8(+) T cells from short-term CTLs in vitro and upon transfer in vivo, including their antitumor activity. Ovalbumin (OVA)-specific OT-I CTLs acquired phenotypic and functional properties of memory cells 2 to 3 days later either by lowering the concentration of antigen to a level that does not support primary responses and providing a survival signal through transgenic Bcl-2 in vitro or simply by transferring early day 3 CTLs to antigen-free lymphoid-replete mice. In lymphoid-replete mice, established OVA-expressing E.G7 tumor was rejected by short-term CTLs that simultaneously acquired memory-like properties in secondary lymphoid tissues, where tumor antigen level remained low. Collectively, these data indicate that CTLs readily converted to memory-like cells upon lowering antigen to a concentration that selectively supports memory responses and suggest that such conversion predicts successful adoptive immunotherapy.

Non-redundant role for IL-7R signaling for the survival of CD8+ memory T cells

IL-7 and IL-15 are important cytokines for CD8 memory T cells. However, the extent that IL-7 is essential for CD8 T cell memory remains unclear because blocking IL-7 in vivo results in near complete inhibition of T cell development with the few mature T cells exhibiting functional abnormalities. To bypass this complication, CD8 memory development was examined utilizing a mouse model where transgenic IL-7Ralpha was selectively expressed in the thymus of IL-7Ralpha(-/-) mice. T cell development was corrected but the resulting peripheral T cells were essentially IL-7 non-responsive. Activation of IL-7R-defective OT-I CD8(+) T cells with OVA(257-264) and IL-2 readily yielded CTL. Upon further culture with IL-15, these CTL expressed phenotypic and functional properties of central memory-like cells. Thus, IL-7R-defective CD8(+) T cells do not exhibit intrinsic defects in effector or memory development. When IL-7R-defective OT-I CTL were adoptively transferred into normal or IL-15(-/-) recipient mice in a non-inflammatory setting, they converted into memory-like cells, but did not persist, which was even more striking in IL-15(-/-) recipients. This poor persistence was rescued after expression of transgenic Bcl-2 in IL-7R-defective OT-I T cells. Collectively, these data indicate that IL-7 is non-redundantly required for the survival of CD8 memory T cells.

CD137 stimulation delivers an antigen-independent growth signal for T lymphocytes with memory phenotype

CD137 has long been recognized as a costimulatory receptor for growth and functional maturation of recently activated T cells in the presence of T-cell receptor signal. In this report, we present the fact that, in the absence of MHC and antigen, triggering of CD137 by an agonist monoclonal antibody induces vigorous growth of both CD8(+) and CD4(+) T cells with memory phenotype, whereas it does not affect naive T cells. Moreover, T cells with memory phenotype accumulate progressively in transgenic mice overexpressing CD137 ligand. CD137-mediated proliferation of memory T cells is directly through CD137 on T cells and does not require IL-15 and IFN-gamma. Our results define a new role of CD137 signal in the growth of memory T cells.

Control of CD4 + T‐cell memory by cytokines and costimulators

During T-cell priming, cytokines and costimulatory molecules provide important signals that determine the magnitude and quality of the response. Although the functions of defined cytokines and costimulators in the primary T-cell response are well characterized, much less is known about how these factors contribute to memory T-cell development and survival. Since memory cells are thought to be long-lived progeny of the primary response, it is conceivable that the same signals shaping initial T-cell expansion and differentiation also contribute to memory generation. Here, we review evidence and show novel data on the role of the cytokines interleukin-2 (IL-2) and IL-7 and the costimulator CD28 in CD4+ memory T-cell development. We emphasize that transient IL-2 and CD28 signals during priming imprint a long-lasting survival advantage in primed T cells, thus contributing to the persistence of a memory population. The requirement for IL-2 and CD28 signals is not linked to promoting T-cell division and expansion but most likely due to their capacity to (i) promote effector cell differentiation; (ii) induce survival proteins, and, as we discuss in more detail; (iii) program expression of receptors for 'memory survival factors' such as IL-7. Studies exploring the therapeutic potential of these insights are also discussed.

Murine B16 Melanomas Expressing High Levels of the Chemokine Stromal-Derived Factor-1/CXCL12 Induce Tumor-Specific T Cell Chemorepulsion and Escape from Immune Control

The chemokine, stromal-derived factor-1/CXCL12, is expressed by normal and neoplastic tissues and is involved in tumor growth, metastasis, and modulation of tumor immunity. T cell-mediated tumor immunity depends on the migration and colocalization of CTL with tumor cells, a process regulated by chemokines and adhesion molecules. It has been demonstrated that T cells are repelled by high concentrations of the chemokine CXCL12 via a concentration-dependent and CXCR4 receptor-mediated mechanism, termed chemorepulsion or fugetaxis. We proposed that repulsion of tumor Ag-specific T cells from a tumor expressing high levels of CXCL12 allows the tumor to evade immune control. Murine B16/OVA melanoma cells (H2b) were engineered to constitutively express CXCL12. Immunization of C57BL/6 mice with B16/OVA cells lead to destruction of B16/OVA tumors expressing no or low levels of CXCL12 but not tumors expressing high levels of the chemokine. Early recruitment of adoptively transferred OVA-specific CTL into B16/OVA tumors expressing high levels of CXCL12 was significantly reduced in comparison to B16/OVA tumors, and this reduction was reversed when tumor-specific CTLs were pretreated with the specific CXCR4 antagonist, AMD3100. Memory OVA-specific CD8+ T cells demonstrated antitumor activity against B16/OVA tumors but not B16/OVA.CXCL12-high tumors. Expression of high levels of CXCL12 by B16/OVA cells significantly reduced CTL colocalization with and killing of target cells in vitro in a CXCR4-dependent manner. The repulsion of tumor Ag-specific T cells away from melanomas expressing CXCL12 confirms the chemorepellent activity of high concentrations of CXCL12 and may represent a novel mechanism by which certain tumors evade the immune system.

Adoptive immunotherapy against experimental visceral leishmaniasis with CD8+ T cells requires the presence of cognate antigen

CD8+ T cells have a protective role in experimental visceral leishmaniasis. However, the observation that inflammatory cytokines induce bystander activation of CD8+ T cells questions the need for antigen-dependent effector function. Here, we demonstrate that successful adoptive immunotherapy with CD8+ T cells is strictly dependent upon the presence of cognate antigen.

Lack of ICAM-1 on APCs during T cell priming leads to poor generation of central memory cells

ICAM-1/LFA-1 interactions are known to enhance T cell/APC interactions and to promote T cell activation and cytokine secretion. We have analyzed the consequences of ICAM-1-mediated signaling on the generation of memory T cell subsets. We report that lack of ICAM-1 on APCs, but not on T cells, leads to poor T cell activation and proliferation in vitro and in vivo, and that the defect can be compensated by Ag dose, exogenous IL-2, additional costimulation, and by increasing responder T cell density on APCs. ICAM-1-null mice do not respond to immunization with OVA peptide, but immunization with OVA or with Salmonella typhimurium leads to good T cell proliferation 7-10 days later, and clearance of a challenge infection is equivalent to that of wild-type mice. However, when followed over time, recall proliferation and antibacterial immunity decay rapidly in ICAM-1-null mice, while recall cytokine responses are unaffected. The decline in immunity is not related to poor survival of T cells activated on ICAM-1-null APCs, or to poor generation of effectors in ICAM-1-null mice. Phenotypic analysis of T cells stimulated on ICAM-1-null APCs reveals preferential generation of CD44(high) CD62L(low) effector memory cells (T(EM)) over CD44(high) CD62L(high) central memory cells (T(CM)). Further, while the proportion of naive:memory T cells is similar in unmanipulated wild-type and ICAM-1-null mice, there is an accumulation of T(EM) cells, and a high T(EM):T(CM) ratio in aging ICAM-1-null mice. Together, the data indicate that signaling through LFA-1 during T cell activation may be involved in commitment to a proliferation-competent memory pool.

IL-2 production by dendritic cells is not critical for the activation of cognate and innate effectors in draining lymph nodes

Dendritic cells (DC) are unique antigen-presenting cells capable of triggering NK cell effector functions and priming naive T cells in vivo. Microbial stimulation induces early IL-2 production by mouse DC. Previous reports demonstrated that IL-2 is enriched at the site of DC/T cell interaction and promotes allogeneic T cell proliferation. However, the direct role of DC-derived IL-2 in the differentiation of cytotoxic T lymphocytes and in NK cell triggering in vivo has not been investigated. Lipopolysaccharide (LPS) stimulation of mouse bone marrow-derived DC results in early IL-2 production unless IL-4 is introduced in DC cultures. Here we show that IL-2 produced by LPS-activated DC is dispensable for cognate T cell responses since IL-2 loss of function DC elicit OVA-specific Tc1 effector and memory lymphocytes in draining lymph nodes in a setting where ex vivo cultured DC do not transfer antigens to host DC. Moreover, adoptively transferred IL-2 loss of function DC maintain their capacity to trigger NK cell proliferation/recruitment in lymph nodes. Therefore, immediate inducible IL-2 production by DC following microbial infection might play a regulatory role at ports of entry rather than in secondary lymphoid organs.

Initial Antigen Encounter Programs CD8+T Cells Competent to Develop into Memory Cells That Are Activated in an Antigen-Free, IL-7- and IL-15-Rich Environment

Although much is known concerning the immunobiology of CD8+ T memory cells, the initial events favoring the generation of CD8+ T memory cells remain poorly defined. Using a culture system that yields memory-like CD8+ T cells, we show that 1 day after Ag encounter, Ag-activated T cells developed into memory-like T cells, but this optimally occurred 3 days after Ag encounter. Key phenotypic, functional, and molecular properties that typify central memory T cells were expressed within 48 h when the activated CD8+ T cells were cultured with IL-7 or IL-15 in the absence of Ag or following transfer into normal mice. These data support a model whereby Ag activation of naive CD8+ T cells not only programs effector cell expansion and contraction but the potential to develop into a memory cell which ensues in an Ag-free environment containing IL-7 or IL-15.

Therapeutic limitations in tumor-specific CD8+ memory T cell engraftment

BACKGROUND

Adoptive immunotherapy with cytotoxic T lymphocytes (CTL) represents an alternative approach to treating solid tumors. Ideally, this would confer long-term protection against tumor. We previously demonstrated that in vitro-generated tumor-specific CTL from the ovalbumin (OVA)-specific OT-I T cell receptor transgenic mouse persisted long after adoptive transfer as memory T cells. When recipient mice were challenged with the OVA-expressing E.G7 thymoma, tumor growth was delayed and sometimes prevented. The reasons for therapeutic failures were not clear.

METHODS

OT-I CTL were adoptively transferred to C57BL/6 mice 21-28 days prior to tumor challenge. At this time, the donor cells had the phenotypical and functional characteristics of memory CD8+ T cells. Recipients which developed tumor despite adoptive immunotherapy were analyzed to evaluate the reason(s) for therapeutic failure.

RESULTS

Dose-response studies demonstrated that the degree of tumor protection was directly proportional to the number of OT-I CTL adoptively transferred. At a low dose of OT-I CTL, therapeutic failure was attributed to insufficient numbers of OT-I T cells that persisted in vivo, rather than mechanisms that actively suppressed or anergized the OT-I T cells. In recipients of high numbers of OT-I CTL, the E.G7 tumor that developed was shown to be resistant to fresh OT-I CTL when examined ex vivo. Furthermore, these same tumor cells no longer secreted a detectable level of OVA. In this case, resistance to immunotherapy was secondary to selection of clones of E.G7 that expressed a lower level of tumor antigen.

CONCLUSIONS

Memory engraftment with tumor-specific CTL provides long-term protection against tumor. However, there are several limitations to this immunotherapeutic strategy, especially when targeting a single antigen. This study illustrates the importance of administering large numbers of effectors to engraft sufficiently efficacious immunologic memory. It also demonstrates the importance of targeting several antigens when developing vaccine strategies for cancer.

Transforming growth factor-beta induces apoptosis in antigen-specific CD4+ T cells prepared for adoptive immunotherapy

Transforming growth factor-beta (TGF-beta), found at the site of most tumors, has been recognized as one of the mechanisms involved in tumor immunological escape. To evaluate its impact on adoptive immunotherapy against cancer, we examined the susceptibility of tumor-specific T cells to TGF-beta in the setting of these T cells being prepared for adoptive transfer. Hepatitis B virus (HBV)-specific CD4(+) T cells were ex vivo generated by activating with HBV-transfected dendritic cells and selecting with antibodies to CD25 activation molecules, and then expanded with antibodies to CD3/CD28. These T cells expressed higher levels of the type II TGF-beta receptor than nai;ve T cells and exhibited enhanced apoptosis when exposed to TGF-beta. The underlying apoptotic pathway was linked to the dissipation of the mitochondrial inner membrane potential and activation of caspase-9. The absence of caspase-8 activity in TGF-beta-treated T cells suggests that the death receptor system may not be involved in this type of apoptosis. Interleukin-2 (IL-2), which is concomitantly administered with tumor-specific T cells in adoptive immunotherapy, was unable to protect HBV-specific CD4(+) T cells from the pro-apoptotic effect of TGF-beta when added simultaneously with TGF-beta. Interesting, IL-2-pretreated T cells displayed the type II TGF-beta receptor at lower levels and were more resistant to TGF-beta. Together, our findings indicate that the effectiveness of adoptive cancer immunotherapy may be impaired by tumor-derived TGF-beta and appropriate manipulation of exogenous IL-2 might overcome this hurdle.

Butyric acid derivative induces allospecific T cell anergy and prevents graft-versus-host disease

Graft-versus-host-disease (GVHD) is a common and potentially fatal complication following bone marrow transplantation. This study was initiated to test whether MEB [n-butyrate 2-(4-morpholinyl) ethyl butyrate hydrochloride], a derivative of the G1 blocker butyric acid, could specifically inactivate the alloantigen-specific T cells that mediate GVHD. MEB was shown to inhibit proliferation in a one-way mixed lymphocyte reaction (MLR) in which spleen cells from C57BL/6 mice (H-2b) were stimulated with spleen cells from DBA/2 mice (H-2d). The addition of MEB to the MLR prevented the expansion of alloantigen-stimulated CD8+ and CD4+ T cells in association with decreased IL-2 production. In addition, MEB inhibited the CTL activity of CD8+ T cells from the MLR. Most importantly, T cells from the MEB-treated MLR, unlike T cells from an untreated MLR, were unable to induce the splenomegaly and increased serum TNF-alpha levels characteristic of acute GVHD when injected into B6D2F1 mice. The splenomegaly found in the B6D2F1 mice injected with T cells from an untreated MLR encompassed the expansion and activation of CD8+ T cells, CD4+ T cells, B cells and macrophages. In contrast, the spleens of mice injected with T cells from MEB-treated MLR looked essentially identical to those of control B6D2F1 mice in terms of the numbers and activation state of the spleen cell populations. Similarly, the increase in IFN-gamma and TNF-alpha production by CD4+ and CD8+ T cells from the spleens of mice undergoing acute GVHD was not observed if the mice were injected with T cells from an MEB-treated MLR instead of an untreated MLR. The use of MEB to inactivate host-specific T cells ex vivo underlines the potential clinical importance of this compound in the prevention and treatment of unwanted immune responses such as GVHD.

Current status of adoptive immunotherapy of malignancies

Adoptive immunotherapy involves the transfer of immune effectors with antitumour activity into the tumour bearing host. Early approaches such as lymphokine activator killer (LAK) cells and tumour infiltrating lymphocytes (TILs) have yielded occasional clinical responses. More recently, attempts to stimulate and/or select antigen-specific T-cells in vitro have demonstrated that tumour-specific adoptive immunotherapy is possible. These approaches require complicated and time consuming in vitro stimulation procedures. Therefore, genetic modification of bulk T-cell populations is an attempt to create a large population of T-cells with a single specificity. In addition to work being done to develop the most potent effector, other studies are working on improving T-cell trafficking to tumours and interfering with the tumour-induced immunosuppression that can impair in vivo T-cell activity.