Adoptive immunotherapy for cancer: building on success

Abstract

Adoptive cell transfer after host preconditioning by lymphodepletion represents an important advance in cancer immunotherapy. Here, we describe how a lymphopaenic environment enables tumour-reactive T cells to destroy large burdens of metastatic tumour and how the state of differentiation of the adoptively transferred T cells can affect the outcome of treatment. We also discuss how the translation of these new findings might further improve the efficacy of adoptive cell transfer through the use of vaccines, haematopoietic-stem-cell transplantation, modified preconditioning regimens, and alternative methods for the generation and selection of the T cells to be transferred.

Conflict of interest statement

Competing interests statement

The authors declare no competing financial interests.

Figures

Figure 1. Current clinical protocols for adoptive cell therapy

Adoptive cell therapy (ACT) requires the generation of highly avid tumour-antigen-reactive T cells. Tumour-specific T cells, derived from tumour-infiltrating lymphocytes (TILs), can be efficiently isolated ex vivo from melanoma lesions using high levels of interleukin-2 (IL-2). TILs are successively selected for their ability to secrete high levels of interferon-γ (IFNγ) when cultured with autologous or allogeneic MHC-matched tumour-cell lines. Alternatively, cell-mediated lysis has been used to identify tumour-reactive T cells for transfer. Highly avid, tumour-antigen-reactive T-cell populations selected for ACT are rapidly expanded (to up to 1011 cells) using CD3-specific antibody, exogenously supplied IL-2 and irradiated allogeneic peripheral-blood mononuclear ‘feeder’ cells, and are validated for activity before transfer. Patients now receive systemic immunosuppression before the adoptive transfer of antitumour lymphocytes. Published lymphodepleting regimens consist of a non-myeloablative, but lymphodepleting, conditioning chemotherapy comprised of cyclophosphamide and fludarabine before administration of T cells. Newer, as yet unpublished, regimens also include total body irradiation. ELISA, enzyme-linked immunosorbent assay. This figure is reproduced with permission from REF. © (2005) Elsevier Science.

Figure 2. Antitumour response induced by lymphodepletion and adoptive cell therapy

Computed tomography (CT) scans of the liver in a patient with metastatic melanoma show dramatic tumour regression of liver metastases after the administration of tumour-reactive tumour-infiltrating lymphocytes (TILs) following lymphodepletion. The patient is still disease-free after 27 months.

Figure 3. Mechanisms underlying the impact of lymphodepletion on adoptively transferred T cells

A | Adoptive cell therapy (ACT) in a lymphoreplete host. In a lymphoreplete environment, antitumour responses mediated by adoptively transferred tumour-reactive CD8+ T cells might be reduced because of: a | competition for antigen at the surface of antigen-presenting cells (APCs) and inefficient lymphocyte activation in the absence of co-stimulatory molecules by immature dendritic cells (DCs); b | reduced availability of activating cytokines (including interleukin-2 (IL-2), IL-7 and IL-15) by cellular ‘sinks’ for these cytokines, which include B cells, T cells and natural killer (NK) cells; and c | the suppressive activities of regulatory T (TReg) cells, myeloid suppressor cells (MSCs) and possibly NK cells. TReg-cell suppression is mediated by direct T-cell contact and possibly by the release of inhibitory cytokines such as IL-10 and transforming growth factor-β. MSCs mediate T-cell inhibition through direct T-cell contact and the use of enzymes involved in L-arginine metabolism such as the inducible forms of arginase and nitric-oxide synthase, ARG1 and NOS2. B | Systemic chemotherapy or radiation before ACT might modify the tumour-bearing host. APCs are reduced in number by direct killing but there might be a net increase in lymphocyte activation because of reduced competition for antigen at the APC surfaces. At the same time, as a result of the liberation of Toll-like receptor (TLR) agonists after mucosal damage, DCs might be mature, increasing lymphocyte activation. Activating cytokines, such as IL-2, IL-7 and IL-15 might be increased because of the removal of cellular ‘sinks’; and TReg cells, MSCs, NK cells and their suppressive activities are decreased. These modifications might promote the full activation of adoptively transferred tumour-reactive CD8+ T cells and ultimately tumour destruction.

Figure 4. Inverse relationship of in vitro and in vivo antitumour functions of adoptively transferred naive and effector T-cell subsets

At increasing strength of stimulation, naive CD8+ T cells proliferate and progressively differentiate through early, intermediate and late effector stages. The phenotypic and functional changes that characterize this process are illustrated as no expression (–), intermediate expression (+) and high expression (hi) of the various markers. T cells progressively lose telomere length and proliferative potential, and subsequently become senescent and undergo apoptosis. The progressive acquisition of full effector functions (dashed burgundy line) is associated with a decreased ability of T cells to cause tumour regression after adoptive transfer (black line). The molecular mechanisms underlying this inverse correlation might be comprised of: decreased expression by T cells of lymph-node homing and co-stimulatory molecules, which reduce activation of T cells in vivo; the inability of terminally differentiated T cells to produce interleukin-2 (IL-2); a reduction in the amount of receptors required to receive activating signals from homeostatic cytokines; and finally, an inversion of the expression of pro- and anti-apoptotic molecules with the corresponding acquisition of replicative senescence. Adoptively transferred tumour-infiltrating lymphocytes (TILs) contain several clonotypes with a differentiation state ranging between intermediate and late effector stages, whereas tumour-reactive CD8+ T-cell clones are uniformly late effector T cells. KLRG1, killer-cell lectin-like receptor G1. This figure is reproduced with permission from REF. © (2005) Highwire Press.

Figure 5. Generation of less-differentiated, central-memory-like tumour-antigen-specific CD8+ T cells by TCR transduction

a | Retroviral transduction of peripheral-blood lymphocytes (PBLs). PBLs at different stages of differentiation, naive (grey), early (green), intermediate (beige) and late effector (burgundy) are activated in vitro with CD3-specific antibody in the presence of interleukin-2 (IL-2) to promote integration of tumour-specific T-cell receptor (TCR) retroviral constructs. This procedure results in the generation of more-differentiated TCR transductants. Pairing with endogenous receptor can reduce the number of tumour-specific TCRs. b | Lentiviral transduction of naive CD8+ T cells. Naive CD8+ T cells isolated through selective sorting can be transduced with tumour-specific TCR by using lentiviral constructs that do not require activation and consequent differentiation. Pairing with endogenous receptor can reduce the number of tumour-specific TCRs. c | Lentiviral transduction of haematopoietic stem cells (HSCs). CD34+CD38− HSCs isolated though selective sorting can be transduced with tumour-specific TCR using lentiviral constructs. HSCs can be induced to differentiate into naive CD8+ T cells in vitro through Notch-mediated signalling. Repression of recombination-activating genes by the transduced tumour-specific TCR allows for the uniform expression of tumour-specific TCRs.