Cell therapy, an innovative way of treatment

Cell therapy, which is defined as the administration of cells that are either therapeutic effector cells to treat a disease or cells supporting other therapies, has evolved rapidly over the past decades.

It has proven to be successful in the treatment of many diseases and it is expected to hold enormous promise for future therapeutic strategies. Besides the established haematopoietic stem cell transplantation, many new and innovative cell therapies are evolving and their efficacy is currently assessed in various clinical trials.

Two strategies of immonotherapy

Immunotherapy is a highly active and promising area in the field of cell therapy that is progressing rapidly. The potential of immunotherapy is increasingly recognized in the field of oncology, but also in other disease areas as autoimmune diseases, (chronic) infections, transplantation and allergy this form of therapy is exploited.

Within immunotherapy, two strategies can be distinguished:
1. Active immunization or vaccination is broadly used to fight viral infections, but is also applied in for example cancer therapy.
2. Passive immunization includes adoptive T cell therapy, in which the T cells are harvested from a patient or donor followed by isolation of specific T cells, expansion and/or modification in the lab followed by (re-)infusion into the patient.

Evidence-based

In the past decades, substantial evidence has been collected showing that T cells indeed can help to control tumour growth.

Several trials with patients bearing solid tumours have provided evidence for (partial) antitumour immune response by adoptive transfer of tumour specific T cells [1-3]. In addition, it has been demonstrated that a specific subset of leukaemia patient,s experiencing relapse after stem cell transplantation, could be cured from their disease by transfusion of donor derived T cells (a donor lymphocyte infusion) [4,5].

T cell clones

The recent advances in T cell isolation, culture technology and the increasing knowledge of T cell responses to viruses have made it possible to produce viral antigen specific T cells clones. These are intended for clinical application in immunocompromised patients [6-9]. Indeed, adoptive transfer of virus-specific T cells lead to virus clearance in patients that had received a SCT [9].

New antigens needed

Although promising, adoptive T cell therapy is still challenging. In solid tumours the immune escape of tumour cells remains problematic, while DLI often faces unwanted severe graft-versus-host responses. Likewise, viruses have developed several strategies to evade recognition and/or killing by the T cells, which can make T cells of particular specificities less effective in clearing the viral infection.

Identification of new antigens recognized by T cells is therefore indispensable to improve current immunotherapy regimens.

Process of recognizing new antigens

Finding the right peptides for HLA-monomers is essential for identifying new T cell antigens.

The current method to identify disease specific T cells is to first calculate MHC-peptide binding with a computer based prediction algorithm. Subsequently, MHC-peptide binding of the proposed high affinity binding peptides has to be confirmed by production of the tetramer. Finally, biological relevance can be determined by staining of T cells. Clearly, this process is often laborious and time consuming what makes it inappropriate for high-throughput screening.

High throughput

A close collaboration between Sanquin and the Netherlands Cancer Institute resulted in the development of two innovative technologies that in combination provide a state-of-the-art tool for high-throughput T cell epitope discovery.

Simultaneous indentification and production

The UV-induced peptide exchange protocol enables parallel identification and production of multiple MHC-peptide complexes, substituting the prediction algorithm and the laborious tetramer production. This technique facilitates performing extensive MHC-peptide binding studies within one day and is therefore a valuable tool for high-throughput screening of multiple pathogen-, tumour-associated-, autoimmune- and disease related antigens.

Innovative flowcytometry technique

Next to UV-induced peptide exchange, combinatorial coding can be performed to quickly monitor T cell recognition of the MHC-peptide complexes. This innovative flowcytometry technique allows the simultaneous detection of 28 antigen specific T cells within a single blood sample. With this method a unique dual-colour code is assigned to each MHC/peptide complex of interest.

The researchers of Sanquin and the NCI were able to develop a high-tech flowcytometry protocol in which they can combine 8 fluorescent markers, together identifying 28 different MHC-peptide specific T cell populations.

Both techniques helped to reveal high affinity binding peptides for leukaemia cells[10], melanoma-tumour cells[11] and influenza H5N1[12]. Similarly, this principle can be applied for other tumours, various pathogens and for autoimmune disorders.

Knowledge obtained with the UV-induced peptide exchange and combinatorial coding is not only important for the development of new therapies, but valuable information is also provided for immunomonitoring of patients and application in diagnostic tools.

Currently, Sanquin, the NCI and the RIVM have joint forces to make progress in the field of viral vaccine development. For several viruses multiple peptides are screened on MHC binding capacity and immunoreactivity to define the optimal peptide composition of new vaccines and to monitor T cell responses in patients. The latter is needed to identify the efficacy of the vaccines. In addition, panels may be created for diagnostic tools to identify the phase of viral infection in a patient.

Literature

1. J Weber, et al. (2011) Immunotherapy Task Force of the NCI Investigational Drug Steering Committee. White paper on adoptive cell therapy for cancer with tumor-infiltrating lymphocytes: a report of the CTEP subcommittee on adoptive cell therapy. Clin Cancer Res. 17: 1664-1673
2. L Hershkovitz, et al. (2010) Focus on adoptive T cell transfer trials in melanoma. Clin Dev Immunol. 2010: 260267
3. K Palucka, H Ueno, J Banchereau. (2011) Recent developments in cancer vaccines. J Immunol. 186: 1325-1331
4. WA Marijt, et al. (2003) Hematopoiesis-restricted minor histocompatibility antigens HA-1- or HA-2-specific T cells can induce complete remissions of relapsed leukemia. Proc Natl Acad Sci U S A. 100: 2742-2747
5. C Roddie, KS Peggs. (2011) Donor lymphocyte infusion following allogeneic hematopoietic stem cell transplantation. Expert Opin Biol Ther. 11: 473-487
6. R Casalegno-Garduño, et al. (2010) Multimer technologies for detection and adoptive transfer of antigen-specific T cells. Cancer Immunology, Immunotherapy 59: 195-202
7. M Knabel, et al. (2002) Reversible MHC multimer staining for functional isolation of T-cell populations and effective adoptive transfer. Nature Medicine 8: 631-637
8. J Neudorfer, et al. (2007) Reversible HLA multimers (Streptamer) for the isolation of human cytotoxic T lymphocytes functionally active against tumor- and virus-derived antigens. JIM 320: 119-131
9. A Schmitt, et al. (2011) Adoptive transfer and selective reconstitution of streptamer-selected cytomegalovirus-specific CD8+ T cells leads to virus clearance in patients after allogeneic peripheral blood stem cell transplantation. Transfusion ;51:591-599
10. P Hombrink, et al. (2011) High-Throughput Identification of Potential Minor Histocompatibility Antigens by MHC Tetramer-Based Screening: Feasibility and Limitations. PLoS ONE 6: e22523
11. AH Bakker, et al. (2008) Conditional MHC class I ligands and peptide exchange technology for the human MHC gene products HLA-A1, -A3, -A11, and -B7. PNAS 105: 3825-3830
12. M Toebes, et al. (2006) Design and use of conditional MHC class I ligands.
Nature Medicine 12:246-251