Adoptive cell transfer
Adoptive cell transfer is the transfer of cells into a patient. The cells may have originated from the patient or from another individual. The cells are most commonly derived from the immune system with the goal of improving immune functionality and characteristics. In autologous cancer immunotherapy, T cells are extracted from the patient, genetically modified and cultured in vitro and returned to the same patient. Comparatively, allogeneic therapies involve cells isolated and expanded from a donor separate from the patient receiving the cells.
History
In the 1960s, lymphocytes were discovered to be the mediators of allograft rejection in animals. Attempts to use T cells to treat transplanted murine tumors required cultivating and manipulating T cells in culture. Syngeneic lymphocytes were transferred from rodents heavily immunized against the tumor to inhibit growth of small established tumors, becoming the first example of ACT.Description of T cell growth factor interleukin-2 in 1976 allowed T lymphocytes to be grown in vitro, often without loss of effector functions. High doses of IL-2 could inhibit tumor growth in mice. 1982, studies demonstrated that intravenous immune lymphocytes could treat bulky subcutaneous FBL3 lymphomas. Administration of IL-2 after cell transfer enhanced therapeutic potential.
In 1985 IL-2 administration produced durable tumor regressions in some patients with metastatic melanoma. Lymphocytes infiltrating the stroma of growing, transplantable tumors provided a concentrated source of tumor-infiltrating lymphocytes and could stimulate regression of established lung and liver tumors. In 1986, human TILs from resected melanomas were found to contain cells that could recognize autologous tumors. In 1988 autologous TILs were shown to reduce metastatic melanoma tumors. Tumor-derived TILs are generally mixtures of CD8+ and CD4+ T cells with few major contaminating cells.
In 1989 Zelig Eshhar published the first study in which a T cell's targeting receptor was replaced, and noted that this could be used to direct T cells to attack any kind of cell; this is the essential biotechnology underlying CAR-T therapy.
Responses were often of short duration and faded days after administration. In 2002, lymphodepletion using a nonmyeloablative chemotherapy regimen administered immediately before TIL transfer increased cancer regression, as well as the persistent oligoclonal repopulation of the host with the transferred lymphocytes. In some patients, the administered antitumor cells represented up to 80% of the CD8+ T cells months after the infusion.
Initially, melanoma was the only cancer that reproducibly yielded useful TIL cultures. In 2006 administration of normal circulating lymphocytes transduced with a retrovirus encoding a T-cell receptor that recognized the MART-1 melanoma-melanocyte antigen, mediated tumor regression. In 2010 administration of lymphocytes genetically engineered to express a chimeric antibody receptor against B cell antigen CD19 was shown to mediate regression of an advanced B cell lymphoma.
By 2010, doctors had begun experimental treatments for leukemia patients using CD19-targeted T cells with added DNA to stimulate cell division. As of 2015 trials had treated about 350 leukemia and lymphoma patients. Antigen CD19 appears only on B cells, which go awry in lymphoma and leukemia. Loss of B cells can be countered with immunoglobulin.
Startups including Juno Therapeutics exploit the combination of aggressive tumors and FDA willingness to approve potential therapies for such ailments to accelerate approvals for new therapies.
In checkpoint therapy, antibodies bind to molecules involved in T-cell regulation to remove inhibitory pathways that block T-cell responses, known as immune checkpoint therapy.
As of 2015 the technique had expanded to treat cervical cancer, lymphoma, leukemia, bile duct cancer and neuroblastoma and in 2016, lung cancer, breast cancer, sarcoma and melanoma. In 2016, CD19-specific chimeric antigen receptor -modified T cells were used to treat patients with relapsed and refractory CD19+ B cell malignancies, including B cell acute lymphoblastic leukemia harboring rearrangement of the mixed lineage leukemia gene with CD19 CAR-T cells.
In 2016, researchers developed a technique that used cancer cells' RNA to produce T cells and an immune response. They encased the RNA in a negatively charged fatty membrane. In vivo, this electrical charge guided the particles towards the patient's dendritic immune cells that specify immune system targets.
In 2017, researchers announced the first use of donor cells to defeat leukemia in two infants for whom other treatments had failed. The cells had four genetic modifications. Two were made using TALENs. One changed the cells so that they did not attack all the cells of another person. Another modification made tumor cells their target.
As of February 2024, 27 advanced cell therapy products were approved by FDA. These included hematopoietic stem cell products ; CART products ; gene therapies Zynteglo, Casgevy, Skysona, and Lyfgenia; and various other cell therapy products.
Process
In melanoma, a resected melanoma specimen is digested into a single-cell suspension or divided into multiple tumor fragments. The result is individually grown in IL-2. Lymphocytes overgrow. They destroy the tumors in the sample within 2 to 3 weeks. They then produce pure cultures of lymphocytes that can be tested for reactivity against other tumors, in coculture assays. Individual cultures are then expanded in the presence of IL-2 and excess irradiated anti-CD3 antibodies. The latter targets the epsilon subunit within the human CD3 complex of the TCR. 5–6 weeks after resecting the tumor, up to 1011 lymphocytes can be obtained.Prior to infusion, a lymphodepleting preparative regimen is undergone, typically 60 mg/kg cyclophosphamide for 2 days and 25 mg/m2 fludarabine administered for 5 days. This substantially increases infused cell persistence and the incidence and duration of clinical responses. Then cells and IL-2 at 720,000 IU/kg to tolerance are infused.
Interleukin-21 may play an important role in enhancing the efficacy of T cell based in vitro therapies.
In early trials, preparing engineered T cells cost $75,000 to manufacture cells for each patient.
Interleukin-2 is normally added to the extracted T cells to boost their effectiveness, but in high doses it can have a toxic effect. The reduced number of injected T cells is accompanied by reduced IL-2, thereby reducing side effects. In vitro tests on melanoma and kidney cancer models met expectations.
In 2016 Strep-tag II sequences were introduced into synthetic CAR or natural T-cell receptors to serve as a marker for identification, rapid purification, tailoring spacer length for optimal function and selective, antibody-coated, microbead-driven, large-scale expansion. This facilitates cGMP manufacturing of pure populations of engineered T cells and enables in vivo tracking and retrieval of transferred cells for downstream research applications.
Genetic engineering
Antitumor receptors genetically engineered into normal T cells can be used for therapy. T cells can be redirected by the integration of genes encoding either conventional alpha-beta TCRs or CARs. CARs were pioneered in the late 1980s and can be constructed by linking the variable regions of the antibody heavy and light chains to intracellular signaling chains such as CD3-zeta, potentially including costimulatory domains encoding CD28 or CD137. CARs can provide recognition of cell surface components not restricted to major histocompatibility complexes. They can be introduced into T cells with high efficiency using viral vectors.Correlations between T cell differentiation status, cellular persistence, and treatment outcomes
Improved antitumor responses have been seen in mouse and monkey models using T cells in early differentiation stages. CD8+ T cells follow a progressive pathway of differentiation from naïve T cells into stem cell memory, central memory, effector memory, and ultimately terminally differentiated effector T cell populations. CD8+ T cells paradoxically lose antitumor power as they acquire the ability to lyse target cells and to produce the cytokine interferon-γ, qualities otherwise thought to be important for antitumor efficacy. Differentiation state is inversely related to proliferation and persistence. Age is negatively correlated with clinical effectiveness. CD8+ T cells can exist in a stem cell–like state, capable of clonal proliferation. Human T memory stem cells express a gene program that enables them to proliferate extensively and differentiate into other T cell populations.CD4+ T cells can also promote tumor rejection. CD4+ T cells enhance CD8+ T cell function and can directly destroy tumor cells. Evidence suggests that T helper 17 cells can promote sustained antitumor immunity.