The ability of the immune system to protect us against infections has been used by clinical medicine since Edward Jenner's vaccination against Smallpox at the end of the 18th century. In the beginning of the 20th century it was postulated that the immune system in addition protects us against tumour formation, which now has been proven to be correct.
During the last decades, the increasing insights into the cellular and molecular mechanisms that mediate immunity both against infectious agents and malignancy have made new medical treatments possible. SentoClone® is an immunotherapy which utilizes one of the most important components of the adaptive immune system, namely the T-lymphocyte, to treat cancer.
T-lymphocytes recognize foreign substances with its T-cell receptor, which is unique for each T-cell. T-lymphocytes are produced by the bone marrow and undergo further maturation in the thymus, where those recognizing autologous proteins are negatively selected. The mature T-lymphocytes which have not displayed auto reactivity are allowed to leave the thymus and begin to recirculate between blood and peripheral lymphoid organs; lymph nodes and spleen. In these organs, the T-cells are exposed to both foreign and self proteins, which are presented as peptides, bound to HLA-molecules (transplantation antigens) on the surface of professional antigen-presenting cells, such as dendritic cells and macrophages (Figure 1). If a T-cell recognizes HLA in combination with a foreign peptide and also receives activating signals from the antigen-presenting cell, it begins to divide. The result of cell division is a clone of identical daughter cells equipped with T-cell receptors of the same specificity – directed against the foreign substance (the antigen).
During activation the T-lymphocyte also develops so-called effector functions, which it uses to combat the intruder. On the basis of the expression of cell surface molecules, two subpopulations of T-cells can be identified in blood and lymph nodes: CD4+ T-helper cells, which mainly produce cytokines and CD8+ T-cells which have direct cytotoxic functions ("T-killer cells"). Following the immune response some of the clonally expanded lymphocytes remain as long-lived memory cells. These can mount a secondary response, which is both faster and stronger than the primary immune response, in case of a re-infection. In animal models, an efficient activation of CD4+ T- helper cells has proved to be important for the development of a strong immunological memory.
Cancer is the result of genetic mutations in the DNA of a cell, which give rise to altered proteins. These proteins, in turn, produce the malignant phenotype, as characterised by unrestrained growth and ability to spread to additional sites of the body (metastasize). However, these altered proteins can be recognized as foreign by the immune system, in the same way as those derived from bacteria and viruses. It has been demonstrated in animal models that T-lymphocytes and production of the cytokine interferon-γ is necessary for efficient, immunological protection against cancer.
In solid tumours, the first presentation of tumour antigens occurs in the primary draining lymph node (the so-called "sentinel node"). Our research group has previously found tumour-reactive lymphocytes in sentinel nodes from patients with solid tumours (see references 1 and 2). Upon stimulation with autologous tumour, the cells divided and produced interferon-γ.
In the presence of an established malignancy the anti-tumour immune response is, evidently, insufficient. A possible reason for this is production of immunosuppressive substances by the tumour cells. The basic idea of SentoClone® is to remove the tumour-reactive lymphocytes from the suppressive effects of the tumour by placing them in a cell culture with addition of growth factors and re-activate them with an extract from the patient's tumour. Hereby, optimal conditions for an efficient secondary response against tumour antigens are created. This response can be used therapeutically by re-transfusing the cells to the patient. Thus, the method constitutes an example of adoptive immunotherapy.
In short, the method is performed as follows: upon tumour surgery, sentinel nodes are identified. A tracer substance, Patent blue, is injected around the tumour. The colour follows the lymphatic drainage and accumulates in the sentinel node, which turns blue. A piece of the lymph node is obtained and transported to the SentoClone® laboratory, where the lymphocytes are acquired and placed in cell culture. A piece of the primary tumour is used to prepare a tumour antigen extract. The growth factor interleukin-2 and the tumour extract are then added to the cell culture. Activation of the lymphocytes and the following clonal expansion in vitro takes approximately 4 weeks, after which the tumour-reactive lymphocytes are given back to the patient as a regular blood transfusion.
A difference between our method and other adoptive cell therapies is that we use cells from the sentinel node, which constitutes a natural reservoir for clonally expanded, tumour-reactive lymphocytes. Another difference is that most other protocols in adoptive tumour immunotherapy focus on CD8+ T lymphocytes. The results of the Sentinel node-acquired lymphocyte expansions is instead a mixed cell population with a predominance of interferon-γ-producing CD4+ T-helper cells (a so-called Th1 response), which in theory provides possibilities for development of immunological memory and protection against tumour recurrence. The treatment is individual and specific for each patient, in that the autologous tumour is used as antigen, and it does not require any preceding knowledge on tumour antigen expression of the tumour.
1) Marits P, Karlsson M, Dahl K, Lasson P, Wanders A, Thörn M and Winqvist O. (2006): Sentinel node lymphocytes: tumour reactive lymphocytes identified intraoperatively for the use in immunotherapy of colon cancer. Br J Cancer. 94, 1478-1484.
2) Marits P, Karlsson M, Sherif A, Garske U, Thörn M and Winqvist O. (2006): Detection of immune responses against urinary bladder cancer in sentinel lymph nodes. Eur Urol. 49, 59-70.