Cassian Yee

Adoptive T cell therapy using antigen-specific CD8+ T cell clones for the treatment of patients with metastatic melanoma: In vivo persistence, migration, and antitumor effect of transferred T cells

Adoptive T cell therapy, involving the ex vivo selection and expansion of antigen-specific T cell clones, provides a means of augmenting antigen-specific immunity without the in vivo constraints that can accompany vaccine-based strategies. A phase I study was performed to evaluate the safety, in vivo persistence, and efficacy of adoptively transferred CD8+ T cell clones targeting the tumor-associated antigens, MART1/MelanA and gp100 for the treatment of patients with metastatic melanoma. Four infusions of autologous T cell clones were administered, the first without IL-2 and subsequent infusions with low-dose IL-2 (at 0.25, 0.50, and 1.0 × 106 units/m2 twice daily for the second, third, and fourth infusions, respectively). Forty-three infusions of MART1/MelanA-specific or gp100-specific CD8+ T cell clones were administered to 10 patients. No serious toxicity was observed. We demonstrate that the adoptively transferred T cell clones persist in vivo in response to low-dose IL-2, preferentially localize to tumor sites and mediate an antigen-specific immune response characterized by the elimination of antigen-positive tumor cells, regression of individual metastases, and minor, mixed or stable responses in 8 of 10 patients with refractory, metastatic disease for up to 21 mo.

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.

Treatment of Metastatic Melanoma with Autologous CD4+ T Cells against NY-ESO-1

We developed an in vitro method for isolating and expanding autologous CD4+ T-cell clones with specificity for the melanoma-associated antigen NY-ESO-1. We infused these cells into a patient with refractory metastatic melanoma who had not undergone any previous conditioning or cytokine treatment. We show that the transferred CD4+ T cells mediated a durable clinical remission and led to endogenous responses against melanoma antigens other than NY-ESO-1.

Autoreactive T Cells in Healthy Individuals

The presence of autoreactive CD4+ T cells in the peripheral blood of healthy human subjects was investigated after removal of CD4+CD25+ regulatory T cells (Treg). CD4+ T cells that were directed against the type 1 diabetes-associated autoantigen glutamic acid decarboxylase 65, the melanocyte differentiation Ag tyrosinase, and the cancer/testis tumor Ag NY-ESO-1 were readily derived from PBMC of healthy individuals. These autoreactive T cells could be visualized, using Ag-specific class II tetramer reagents, in the peripheral blood of most individuals examined. Addition of CD4+CD25+ Treg back to the CD4+CD25− population suppressed the expansion of the autoreactive T cells. Autoreactive T cells were cloned based on tetramer binding, and expressed characteristic activation markers upon self-Ag stimulation. These results show that autoreactive T cells are present in most healthy individuals and that Treg likely play an important role of keeping these autoreactive T cells in check.

Transferred WT1-reactive CD8+ T cells can mediate antileukemic activity and persist in post-transplant patients

Donor-derived WT1-specific CD8+ T cells transferred after hematopoietic cell transplantation mediate antileukemic activity and can establish persistent responses without toxicity to normal tissues in high-risk leukemia patients. Targeting Leukemic Cells for Destruction After a patient is diagnosed with leukemia, the first line of treatment is generally chemotherapy. If it doesn’t work, the patient can get a bone marrow transplant, which can sometimes cure otherwise untreatable leukemia. However, for patients who have already relapsed after a transplant, or whose cancer has particularly unfavorable characteristics, few options remain. Such patients’ prognosis is generally very poor, with a high risk of relapse and death from leukemia. Immune cells derived from the donor bone marrow can help fight the cancer by attacking malignant cells inside the graft recipient. At the same time, however, they often attack the recipient’s healthy cells as well and cause graft-versus-host disease (GVHD), which can itself be lethal. Now, Chapuis and coauthors report a way to harness the power of the donors’ immune cells against some leukemias, without triggering GVHD in the bone marrow recipients. In this pilot trial, the authors enrolled 11 patients who had leukemia with poor prognostic characteristics and who had each undergone a bone marrow transplant. The patients then received T cells that were derived from their respective donors and selected for their ability to recognize Wilms tumor antigen 1 (WT1). Very small amounts of WT1 are present in some healthy cells, but its expression in malignant cells is much greater and corresponds to the aggressiveness of the cancer. In the first seven patients, the authors found that T cells that recognized WT1 could suppress the leukemia temporarily, but the new cells disappeared within 14 days, and the cancer rebounded. In the last four patients, the authors tried a modified protocol, pretreating the cells with interleukin-21 (IL-21) before infusion into the recipients. T cells pretreated with IL-21 developed characteristics of memory cells, including a greatly extended life span. At this time, all four patients who received IL-21–treated T cells are still alive, with no recurrence of their cancer up to 30 months after the T cell infusion. Notably, none of the patients who received WT1-specific T cells in this study have developed GVHD, supporting the idea that WT1 targeting is specific to the tumor cells and safe for patient use. The study by Chapuis et al. is a small pilot trial, and its results must be replicated with larger groups of patients before this protocol can become standard practice. Nevertheless, the combination of targeting WT1 in leukemia and pretreating leukemia-targeting T cells with IL-21 to extend their life span looks very promising and offers a potential safe and effective treatment for patients who have few other options. Relapse remains a leading cause of death after allogeneic hematopoietic cell transplantation (HCT) for patients with high-risk leukemias. The potentially beneficial donor T cell–mediated graft-versus-leukemia (GVL) effect is often mitigated by concurrent graft-versus-host disease (GVHD). Providing T cells that can selectively target Wilms tumor antigen 1 (WT1), a transcription factor overexpressed in leukemias that contributes to the malignant phenotype, represents an opportunity to promote antileukemic activity without inducing GVHD. HLA-A*0201–restricted WT1-specific donor-derived CD8+ cytotoxic T cell (CTL) clones were administered after HCT to 11 relapsed or high-risk leukemia patients without evidence of on-target toxicity. The last four treated patients received CTL clones generated with exposure to interleukin-21 (IL-21) to prolong in vivo CTL survival, because IL-21 can limit terminal differentiation of antigen-specific T cells generated in vitro. Transferred cells exhibited direct evidence of antileukemic activity in two patients: a transient response in one patient with advanced progressive disease and the induction of a prolonged remission in a patient with minimal residual disease (MRD). Additionally, three treated patients at high risk for relapse after HCT survive without leukemia relapse, GVHD, or additional antileukemic treatment. CTLs generated in the presence of IL-21, which were transferred in these latter three patients and the patient with MRD, all remained detectable long term and maintained or acquired in vivo phenotypic and functional characteristics associated with long-lived memory CD8+ T cells. This study supports expanding efforts to immunologically target WT1 and provides insights into the requirements necessary to establish potent persistent T cell responses.

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.

Adoptive immunotherapy: Engineering T cell responses as biologic weapons for tumor mass destruction

Adoptive T cell immunotherapy is an evolving technology with the potential of providing a means to safely and effectively target tumor cells for destruction.

Transferred melanoma-specific CD8+ T cells persist, mediate tumor regression, and acquire central memory phenotype

Adoptively transferred tumor-specific T cells offer the potential for non–cross-resistant therapy and long-term immunoprotection. Strategies to enhance in vivo persistence of transferred T cells can lead to improved antitumor efficacy. However, the extrinsic (patient conditioning) and intrinsic (effector cell) factors contributing to long-term in vivo persistence are not well-defined. As a means to enhance persistence of infused T cells in vivo and limit toxicity, 11 patients with refractory, progressive metastatic melanoma received cyclophosphamide alone as conditioning before the infusion of peripheral blood mononuclear cell-derived, antigen-specific, CD8+ cytotoxic T-lymphocyte (CTL) clones followed by low-dose or high-dose IL-2. No life-threatening toxicities occurred with low-dose IL-2. Five of 10 evaluable patients had stable disease at 8 wk, and 1 of 11 had a complete remission that continued for longer than 3 y. On-target autoimmune events with the early appearance of skin rashes were observed in patients with stable disease or complete remission at 4 wk or longer. In vivo tracking revealed that the conditioning regimen provided a favorable milieu that enabled CTL proliferation early after transfer and localization to nonvascular compartments, such as skin and lymph nodes. CTL clones, on infusion, were characterized by an effector memory phenotype, and CTL that persisted long term acquired phenotypic and/or functional qualities of central memory type CTLs in vivo. The use of a T-cell product composed of a clonal population of antigen-specific CTLs afforded the opportunity to demonstrate phenotypic and/or functional conversion to a central memory type with the potential for sustained clinical benefit.

Ultra-sensitive detection of rare T cell clones

Advances in high-throughput sequencing have enabled technologies that probe the adaptive immune system with unprecedented depth. We have developed a multiplex PCR method to sequence tens of millions of T cell receptors (TCRs) from a single sample in a few days. A method is presented to test the precision, accuracy, and sensitivity of this assay. T cell clones, each with one fixed productive TCR rearrangement, are doped into complex blood cell samples. TCRs from a total of eleven samples are sequenced, with the doped T cell clones ranging from 10% of the total sample to 0.001% (one cell in 100,000). The assay is able to detect even the rarest clones. The precision of the assay is demonstrated across five orders of magnitude. The accuracy for each clone is within an overall factor of three across the 100,000 fold dynamic range. Additionally, the assay is shown to be highly repeatable.

Simultaneous Generation of CD8+ and CD4+ Melanoma-Reactive T Cells by Retroviral-Mediated Transfer of a Single T-Cell Receptor

Adoptive immunotherapy of cancer requires the generation of large numbers of tumor antigen-reactive T cells for transfer into cancer patients. Genes encoding tumor antigen-specific T-cell receptors can be introduced into primary human T cells by retroviral mediated gene transfer as a potential method of providing any patient with a source of autologous tumor-reactive T cells. A T-cell receptor-specific for a class I MHC (HLA-A2)-restricted epitope of the melanoma antigen tyrosinase was isolated from a CD4(+) tumor-infiltrating lymphocyte (TIL 1383I) and introduced into normal human peripheral blood lymphocytes by retroviral transduction. T-cell receptor-transduced T cells secreted various cytokines when cocultured with tyrosinase peptide-loaded antigen-presenting cells as well as melanoma cells in an HLA-A2-restricted manner, and could also lyse target cells. Furthermore, T-cell clones isolated from these cultures showed both CD8(+) and CD4(+) transduced T cells could recognize HLA-A2(+) melanoma cells, giving us the possibility of engineering class I MHC-restricted effector and T helper cells against melanoma. The ability to confer class I MHC-restricted tumor cell recognition to CD4(+) T cells makes the TIL 1383I TCR an attractive candidate for T-cell receptor gene transfer-based immunotherapy.