The use of antigen presenting cell/tumour cell hybrids for the in vitro induction of tumour-specific T cells

Malignant tumours are the second main cause of mortality worldwide, with haematological malignancies representing 10%. Current treatment strategies, such as chemotherapy, radiotherapy, and stem cell transplantation, are mostly effective but may induce serious side effects. In addition, tumours are developing resistance against most of these conventional therapies. Immunotherapy is a promising investigational approach, especially hybrid cell vaccination, in which a professional APC is fused to a tumour cell, and the fusion product mostly combines the antigenicity of the tumour cell partner, processed and presented through the relevant APC-machinery, and associated with co-stimulatory molecules CD80, CD86, and CD40 expression, for proper induction of anti-tumour immune responses. I investigated the phenotypic and functional characteristics of a group of previously-made hybrid cell lines, generated by in vitro fusion of a human APC (HMy2; EBV B-lymphoblastoid cell line) with haematological ex vivo or immortalized tumour cells. On co-culture with allogeneic (normal donors) peripheral blood lymphocytes, hybrid cell lines induced elevated levels of T-cell proliferation compared with their relevant tumour cells, which was dependent on expression of co-stimulatory molecules CD80 and CD86, and MHC class I and class II antigens. The hybrid cell lines induced proliferation of naive, central memory, and effector memory populations of CD4+, CD8+ T-cells. Moreover, the hybrid cells expressed a range of tumour associated antigens not expressed by HMy2 cells, or by normal PBMC. Depending on that, tumour-specific cytotoxic T lymphocytes were induced in vitro by stimulation of allogeneic or autologous PBMCs for multiple rounds with selected hybrid cell lines in the presence of rhIL-2. Tumour- and antigen-specificity of the activated T cells were assessed by IFN-γ releasing ELISpot, MHC class I (HLA-A2)-restricted tumour peptide-specific pentamer staining, and 51Cr-release cytotoxicity assays. Hybrid cell vaccines generated in this way may therefore represent a novel strategy for use in immunotherapy of haematological malignancies, and possibly in other forms of cancer as well.