Single-chain VαVß T-cell receptors function without mispairing with endogenous TCR chains.

Transduction of exogenous T-cell receptor (TCR) genes into patients' activated peripheral blood T cells is a potent strategy to generate large numbers of specific T cells for adoptive therapy of cancer and viral diseases. However, the remarkable clinical promise of this powerful approach is still being overshadowed by a serious potential consequence: mispairing of the exogenous TCR chains with endogenous TCR chains. These 'mixed' heterodimers can generate new specificities that result in graft-versus-host reactions. Engineering TCR constant regions of the exogenous chains with a cysteine promotes proper pairing and reduces the mispairing, but, as we show here, does not eliminate the formation of mixed heterodimers. By contrast, deletion of the constant regions, through use of a stabilized Vα/Vß single-chain TCR (scTv), avoided mispairing completely. By linking a high-affinity scTv to intracellular signaling domains, such as Lck and CD28, the scTv was capable of activating functional T-cell responses in the absence of either the CD3 subunits or the co-receptors, and circumvented mispairing with endogenous TCRs. Such transduced T cells can respond to the targeted antigen independent of CD3 subunits via the introduced scTv, without the transduced T cells acquiring any new undefined and potentially dangerous specificities.

In vivo migration and function of transferred HIV-1-specific cytotoxic T cells.

The persistence of HIV replication in infected individuals may reflect an inadequate host HIV-specific CD8+ cytotoxic T lymphocyte (CTL) response. The functional activity of HIV-specific CTLs and the ability of these effector cells to migrate in vivo to sites of infection was directly assessed by expanding autologous HIV-1 Gag-specific CD8+ CTL clones in vitro and adoptively transferring these CTLs to HIV-infected individuals. The transferred CTLs retained lytic function in vivo, accumulated adjacent to HIV-infected cells in lymph nodes and transiently reduced the levels of circulating productively infected CD4+ T cells. These results provide direct evidence that HIV-specific CTLs target sites of HIV replication and mediate antiviral activity, and indicate that the development of immunotherapeutic approaches to sustain a strong CTL response to HIV may be a useful adjunct to treatment of HIV infection.

Characterization of circulating T cells specific for tumor-associated antigens in melanoma patients.

We identified circulating CD8+ T-cell populations specific for the tumor-associated antigens (TAAs) MART-1 (27-35) or tyrosinase (368-376) in six of eleven patients with metastatic melanoma using peptide/HLA-A*0201 tetramers. These TAA-specific populations were of two phenotypically distinct types: one, typical for memory/effector T cells; the other, a previously undescribed phenotype expressing both naive and effector cell markers. This latter type represented more than 2% of the total CD8+ T cells in one patient, permitting detailed phenotypic and functional analysis. Although these cells have many of the hallmarks of effector T cells, they were functionally unresponsive, unable to directly lyse melanoma target cells or produce cytokines in response to mitogens. In contrast, CD8+ T cells from the same patient were able to lyse EBV-pulsed target cells and showed robust allogeneic responses. Thus, the clonally expanded TAA-specific population seems to have been selectively rendered anergic in vivo. Peptide stimulation of the TAA-specific T-cell populations in other patients failed to induce substantial upregulation of CD69 expression, indicating that these cells may also have functional defects, leading to blunted activation responses. These data demonstrate that systemic TAA-specific T-cell responses can develop de novo in cancer patients, but that antigen-specific unresponsiveness may explain why such cells are unable to control tumor growth.

T-cell mediated rejection of gene-modified HIV-specific cytotoxic T lymphocytes in HIV-infected patients.

The introduction and expression of genes in somatic cells is an innovative therapy for correcting genetic deficiency diseases and augmenting immune function. A potential obstacle to gene therapy is the elimination of such gene-modified cells by an immune response to novel protein products of the introduced genes. We are conducting an immunotherapy trial in which individuals seropositive for human immunodeficiency virus (HIV) receive CD8+ HIV-specific cytotoxic T cells modified by retroviral transduction to express a gene permitting positive and negative selection. However, five of six subjects developed cytotoxic T-lymphocyte responses specific for the novel protein and eliminated the transduced cytotoxic T cells. The rejection of genetically modified cells by these immunocompromised hosts suggests that strategies to render gene-modified cells less susceptible to host immune surveillance will be required for successful gene therapy of immunocompetent hosts.

Eradication of disseminated murine leukemia by chemoimmunotherapy with cyclophosphamide and adoptively transferred immune syngeneic Lyt-1+2- lymphocytes.

The phenotype of T cells therapeutically effective in immunotherapy of advanced Friend virus-induced (FBL) leukemia in vivo and cytotoxic to FBL in vitro was determined. Mice bearing disseminated FBL leukemia were successfully treated by a combination of cyclophosphamide and adoptive transfer of syngeneic immune lymphocytes. Therapeutic efficacy was largely dependent on the presence of Lyt-1+2- T cells in the transferred cells, whereas cells cytotoxic to FBL tumor in vitro were derived from the Lyt-1+2+ and Lyt-1-2+ subsets. Thus, the predominate cell required to eradicate tumor in adoptive chemoimmunotherapy was not cytolytic to tumor in vitro. Potentially, the Lyt-1+2- cell may operate in vivo as an amplifier cell rather than by a direct anti-tumor effect. Elimination of the Lyt-1+ population with alpha-Lyt-1 and complement prevented the generation of significant cytotoxic responses during both primary in vitro sensitization to alloantigens and in vitro sensitization of tumour-primed cells. The capacity of Lyt-1+ cell-depleted population to generate cytotoxic responses was partially reconstituted by addition, at the initiation of culture, of interluekin 2, a T cell growth factor derived from Lyt-1+2- cells, which contain the CTL and CTL precursors, were nearly as effective in vitro as unseparated immune cells. If the remaining effector cells (i.e., Lyt-1+2- T cells) function in vivo predominantly as amplifier cells, than the tumour-bearing host must be capable of making a positive contribution to the outcome of therapy.

Augmentation of the anti-tumor therapeutic efficacy of long-term cultured T lymphocytes by in vivo administration of purified interleukin 2.

Spleen cells from C57BL/6 mice immunized in vivo with a syngeneic Friend virus-induced leukemia, FBL-3, were specifically activated by culture for 7 d with FBL-3, then nonspecifically induced to proliferate in vitro for 12 d by addition of supernatants from concanavalin A-stimulated lymphocytes containing interleukin 2 (IL-2). Such long-term cultured T lymphocytes have previously been shown to specifically lyse FBL-3 and to mediate specific adoptive therapy of advanced disseminated FBL-3 when used as an adjunct to cyclophosphamide (CY) in adoptive chemoimmunotherapy. Because the cultured cells are dependent upon IL-2 for proliferation and survival in vitro, their efficacy in vivo is potentially limited by the availability of endogenous IL-2. Thus, the aim of the current study was to determine whether exogenously administered purified IL-2 could augment the in vivo efficacy of long-term cultured T lymphocytes. Purified IL-2 alone or as an adjunct to CY as ineffective in tumor therapy. However, IL-2 was extremely effective in augmenting the efficacy of IL-2-dependent long-term cultured T lymphocytes in adoptive chemoimmunotherapy. The mechanism by which IL-2 functions in vivo is presumably by promoting in vivo growth and/or survival of adoptively transferred cells. This assumption was supported by the findings that IL-2 did not enhance the modest therapeutic efficacy of irradiated long-term cultured cells that were incapable of proliferating in the host and was ineffective in augmenting the in vivo efficacy of noncultured immune cells that are not immediately dependent upon exogenous IL-2 for survival.

Therapy of disseminated murine leukemia with cyclophosphamide and immune Lyt-1+,2- T cells. Tumor eradication does not require participation of cytotoxic T cells.

The ability of noncytolytic Lyt-1+,2- T cells immune to FBL-3 leukemia to effect eradication of disseminated FBL-3 was studied. Adult thymectomized, irradiated, and T-depleted bone marrow-reconstituted (ATXBM) B6 hosts were cured of disseminated FBL-3 by treatment with 180 mg/kg cyclophosphamide (CY) and adoptively transferred Lyt-1+,2- T cells obtained from congenic B6/Thy-1.1 donors immune to FBL-3. Analysis of the T cell compartment of ATXBM hosts treated and rendered tumor-free by this therapy revealed that the only T cells present in the mice were donor-derived Lyt-1+,2- T cells. In vitro stimulation of these T cells with FBL-3 tumor cells, which express class I but no class II major histocompatibility complex antigens, induced lymphokine secretion, but did not result in the generation of cytotoxic T lymphocytes (CTL). Thus, in a setting in which mice lack Lyt-2+ T cells, and in which no CTL of either host or donor origin could be detected, immune Lyt-1+,2- T cells, in conjunction with CY, mediated eradication of a disseminated leukemia. The results suggest that delayed-type hypersensitivity responses induced by immune T cells represent a potentially useful effector mechanism for in vivo elimination of disseminated tumor cells.

An evaluation of the potential to use tumor-associated antigens as targets for antitumor T cell therapy using transgenic mice expressing a retroviral tumor antigen in normal lymphoid tissues.

A major obstacle to the development of T cell therapy for the treatment of human tumors has been the difficulty generating T cells specifically reactive with the tumor. Most of the characterized human tumor antigens have been classified as tumor associated, because of demonstrable expression at low levels in some normal cells, and thus have not been extensively studied as potential targets of a therapeutic immune response. However, the quantitative difference in expression of such antigens between the tumor and normal cells might permit the generation of antigen-specific T cells capable of selective antitumor and not autoimmune activity. To address this issue, transgenic (TG) mice were generated that expressed low levels of Friend murine leukemia virus (FMuLV) envelope protein in lymphoid cells under the control of an immunoglobulin promoter. This protein is expressed at high levels by a Friend virus-induced erythroleukemia of C57BL/6 (B6) origin, FBL, and has been shown to serve as an efficient tumor-specific rejection antigen in B6 mice. The env-TG mice were tolerant to envelope, as reflected by the failure to detect an envelope-specific response after in vivo priming and in vitro stimulation with preparations of FMuLV envelope. However, adoptively transferred envelope-specific T cells from immunized non-TG B6 mice mediated complete eradication of FBL tumor cells in TG mice, and did not induce detectable autoimmune damage to TG lymphoid tissues. The transferred immune cells were not permanently inactivated in the TG mice, since donor T cells responded to envelope after removal from the TG mice. The lack of autoimmune injury did not reflect inadequate expression of envelope by TG lymphocytes for recognition by T cells, since TG lymphocytes functioned effectively in vitro as stimulators for envelope-specific T cells. The results suggest that this and analogous strains of TG mice may prove useful for elucidating principles for the generation and therapeutic use of tumor-reactive T cells specific for tumor-associated antigens.

Antigen-driven long term-cultured T cells proliferate in vivo, distribute widely, mediate specific tumor therapy, and persist long-term as functional memory T cells.

Mice bearing disseminated syngeneic FBL-3 leukemia were treated with cyclophosphamide plus long term-cultured T cells immune to FBL-3. The cultured T cells for therapy had been induced to grow in vitro for 62 d by intermittent stimulation with irradiated FBL-3. At the time of therapy, such antigen-driven long term-cultured T cells were greatly expanded in number, proliferated in vitro in response to FBL-3, and were specifically cytotoxic. Following adoptive transfer, donor T cells persisting in the host were identified and counted using donor and host mice congenic for the T cell marker Thy-1. The results show that antigen-driven long term-cultured T cells proliferated rapidly in vivo, distributed widely in host lymphoid organs, and were effective in tumor therapy. Moreover, the already rapid in vivo growth rate of donor T cells could be augmented by administration of exogenous IL-2. When cured mice were examined 120 d after therapy, donor L3T4+ T cells and donor Lyt-2+ T cells could be found in large numbers in host ascites, spleen, and mesenteric and axillary lymph nodes. The persisting donor T cells proliferated in vitro, and became specifically cytotoxic in response to FBL-3, demonstrating that antigen-driven long term-cultured T cells can persist long term in vivo and provide immunologic memory.

FBL-reactive CD8+ cytotoxic and CD4+ helper T lymphocytes recognize distinct Friend murine leukemia virus-encoded antigens.

Immunization of C57BL/6 (B6) mice with FBL, a Friend murine leukemia virus (F-MuLV), induces both tumor-specific cytolytic CD8+ (CTL) and lymphokine-producing CD4+ Th that are effective in adoptive therapy of B6 mice bearing disseminated FBL leukemia. The current study evaluated the F-MuLV antigenic determinants expressed on FBL that are recognized by FBL-reactive CD8+ and CD4+ T cells. To identify the specificity of the FBL-reactive CD8+ CTL, Fisher rat embryo fibroblast (FRE) cells transfected with plasmids encoding F-MuLV gag or envelope (env) gene products plus the class I-restricting element Db were utilized. FBL-reactive CTL recognized FRE target cells transfected with the F-MuLV gag-encoded gene products, but failed to recognize targets expressing F-MuLV env. Attempts to generate env-specific CD8+ CTL by immunization with a recombinant vaccinia virus containing an inserted F-MuLV env gene were unsuccessful, despite the generation of a cytolytic response to vaccinia epitopes, implying that B6 mice fail to generate CD8+ CTL to env determinants. By contrast, CD4+ Th clones recognized FRE target cells transfected with env and not gag genes, and immunization with the recombinant vaccinia virus induced an env-specific CD4+ T cell response. These data show that in a Friend retrovirus-induced tumor model in which tumor rejection can be mediated by either CTL or Th, antigens derived from discrete retroviral proteins are predominantly responsible for activation of each T cell subset.

Melanocyte destruction after antigen-specific immunotherapy of melanoma: direct evidence of t cell-mediated vitiligo.

Current strategies for the immunotherapy of melanoma include augmentation of the immune response to tumor antigens represented by melanosomal proteins such as tyrosinase, gp100, and MART-1. The possibility that intentional targeting of tumor antigens representing normal proteins can result in autoimmune toxicity has been postulated but never demonstrated previously in humans. In this study, we describe a patient with metastatic melanoma who developed inflammatory lesions circumscribing pigmented areas of skin after an infusion of MART-1-specific CD8(+) T cell clones. Analysis of the infiltrating lymphocytes in skin and tumor biopsies using T cell-specific peptide-major histocompatibility complex tetramers demonstrated a localized predominance of MART-1-specific CD8(+) T cells (>28% of all CD8 T cells) that was identical to the infused clones (as confirmed by sequencing of the complementarity-determining region 3). In contrast to skin biopsies obtained from the patient before T cell infusion, postinfusion biopsies demonstrated loss of MART-1 expression, evidence of melanocyte damage, and the complete absence of melanocytes in affected regions of the skin. This study provides, for the first time, direct evidence in humans that antigen-specific immunotherapy can target not only antigen-positive tumor cells in vivo but also normal tissues expressing the shared tumor antigen.

Deficient cellular immunity--finding and fixing the defects.

The critical role of cellular immunity in resistance to infectious diseases is glaringly revealed by life-threatening infections if T cell function is disrupted by an inherited or acquired immunodeficiency. Although treatment has historically focused on infectious complications, understanding of the cellular and molecular basis of immunodeficiency and technologies useful for enhancing cellular immunity have both been rapidly evolving. A new era of molecular and cellular therapy is emerging as approaches to correct abnormal genes, the loss of T cell subpopulations, and aberrant T cell homeostasis make the transition from bench to bedside.

Restoration of viral immunity in immunodeficient humans by the adoptive transfer of T cell clones.

The adoptive transfer of antigen-specific T cells to establish immunity is an effective therapy for viral infections and tumors in animal models. The application of this approach to human disease would require the isolation and in vitro expansion of human antigen-specific T cells and evidence that such T cells persist and function in vivo after transfer. Cytomegalovirus-specific CD8+ cytotoxic T cell (CTL) clones could be isolated from bone marrow donors, propagated in vitro, and adoptively transferred to immunodeficient bone marrow transplant recipients. No toxicity developed and the clones provided persistent reconstitution of CD8+ cytomegalovirus-specific CTL responses.

The role of B cells for in vivo T cell responses to a Friend virus-induced leukemia.

B cells can function as antigen-presenting cells and accessory cells for T cell responses. This study evaluated the role of B cells in the induction of protective T cell immunity to a Friend murine leukemia virus (F-MuLV)-induced leukemia (FBL). B cell-deficient mice exhibited significantly reduced tumor-specific CD4+ helper and CD8+ cytotoxic T cell responses after priming with FBL or a recombinant vaccinia virus containing F-MuLV antigens. Moreover, these mice had diminished T cell responses to the vaccinia viral antigens. Tumor-primed T cells transferred into B cell-deficient mice effectively eradicated disseminated FBL. Thus, B cells appear necessary for efficient priming but not expression of tumor and viral T cell immunity.

Acquired cancer resistance to combination immunotherapy from transcriptional loss of class I HLA.

Understanding mechanisms of late/acquired cancer immunotherapy resistance is critical to improve outcomes; cellular immunotherapy trials offer a means to probe complex tumor-immune interfaces through defined T cell/antigen interactions. We treated two patients with metastatic Merkel cell carcinoma with autologous Merkel cell polyomavirus specific CD8+ T cells and immune-checkpoint inhibitors. In both cases, dramatic remissions were associated with dense infiltration of activated CD8+s into the regressing tumors. However, late relapses developed at 22 and 18 months, respectively. Here we report single cell RNA sequencing identified dynamic transcriptional suppression of the specific HLA genes presenting the targeted viral epitope in the resistant tumor as a consequence of intense CD8-mediated immunologic pressure; this is distinguished from genetic HLA-loss by its reversibility with drugs. Transcriptional suppression of Class I loci may underlie resistance to other immunotherapies, including checkpoint inhibitors, and have implications for the design of improved immunotherapy treatments.

Cytotoxic and proliferative T cell responses in HIV-1-infected Macaca nemestrina.

Macaca nemestrina has been described as an animal model for acute HIV-1 infection. This animal, unlike most infected humans, appears to contain HIV-1 replication. Therefore analysis of HIV-1-specific proliferative and cytotoxic T lymphocyte (CTL) responses following HIV-1 challenge of M. nemestrina may provide information into the role of such responses in both the control of acute HIV infection and protective immunity. Although CD4+ T cell responses to HIV-1 are generally difficult to detect in HIV-1-infected humans, early and persistent CD4+ T cell proliferative responses to HIV-1 antigens were detected in all HIV-1-inoculated M. nemestrina. HIV-1-specific CD8+ CTL responses were evaluated in PBMC by stimulation with autologous cells expressing HIV-1 genes, limiting dilution precursor frequency analysis, and T cell cloning. CTL reactive with gag, env, and nef were present 4-8 wk after infection, and persisted to 140 wk after infection. The presence of both CD4+ and CD8+ T cell responses before and after clearance of HIV-1 viremia is consistent with a role for these responses in the successful control of HIV-1 viral replication observed in M. nemestrina. Further studies of T cell immunity in these animals that resist disease should provide insights into the immunobiology of HIV-1 infection.

HIV-specific cytotoxic T lymphocytes traffic to lymph nodes and localize at sites of HIV replication and cell death.

We have tracked the in vivo migration and have identified in vivo correlates of cytotoxic T-lymphocyte (CTL) activity in HIV-seropositive subjects infused with autologous gene-marked CD8(+) HIV-specific CTL. The number of circulating gene-marked CTL ranged from 1.6 to 3.5% shortly after infusion to less than 0.5% 2 weeks later. Gene-marked CTL were present in the lymph node at 4.5- to 11-fold excess and colocalized within parafollicular regions of the lymph node adjacent to cells expressing HIV tat fusion transcripts, a correlate of virus replication. The CTL clones expressed the CCR5 receptor and localized among HIV-infected cells expressing the ligands MIP-1alpha and MIP-1beta, CC-chemokines produced at sites of virus replication. Aggregates of apoptotic cells and cells expressing granzyme-B localized within these same sites. In contrast, lymph node sections from untreated HIV-seropositive subjects, all with significant viral burden (> 50,000 HIV RNA copies/mL plasma), showed no CC-chemokine expression and exhibited only sporadic and randomly distributed cells expressing granzymes and/or apoptotic cells. These studies show that the infused CTL specifically migrate to sites of HIV replication and retain their antigen-specific cytolytic potential. Moreover, these studies provide a methodology that will facilitate studies of both the magnitude and functional phenotype of Ag-specific CD8(+) T cells in vivo.

CD8+ cytotoxic T cell therapy of cytomegalovirus and HIV infection.

The development of CD8+ cytotoxic T cell responses to viral pathogens is crucial for the prompt resolution of acute infections and for the control of viruses which persist in the host. Thus, cytomegalovirus often causes life threatening disease in immunosuppressed humans who fail to develop or maintain CD8+ cytotoxic T cells. Similarly, the loss of CD8+ cytotoxic T cell responses to HIV correlates with the development of AIDS. Recent investigations in the immunobiology of cytomegalovirus and HIV have resulted in the application of immunotherapeutic strategies designed to reconstitute or augment deficient CD8+ cytotoxic T cell responses to these human pathogens.

Prospects for adoptive T cell therapy.

Since the establishment of methods to isolate genes encoding cytotoxic T lymphocyte defined tumor antigens, several antigens have been identified and characterized for suitability as target antigens for immunotherapy. The development of innovative strategies to generate T cells targeting these antigens and lessons learned from clinical trials of adoptive immunotherapy of viral diseases should facilitate the design of clinical trials for specific adoptive immunotherapy of cancer.

In vivo tracking of tumor-specific T cells.

Novel immunologic assays now enable visualization of the antigen-specific response to an extent not previously possible. Assessment of not only the numeric frequency but also the functional properties of individual tumor-specific T cells in the endogenous and manipulated immune response has provided insights that will facilitate the development of immunotherapeutic strategies.