Immunohistochemical characterisation of immunological changes at the tumour site after chemo-immunotherapy with doxorubicin, interleukin-2 and interferon-gamma.
Chemo-immunotherapy for the treatment of cancer, whilst promising from a preclinical and clinical perspective, remains limited by a lack of clear understanding of the in vivo antitumour mechanisms of this multi modality strategy. There is now strong evidence that systemic immunological parameters do not correlate with therapeutic activity. In contrast, information on therapy related immunological change at the tumour site is scarce. Having previously demonstrated that the therapeutic activity of doxorubicin chemotherapy can be significantly augmented by the co-administration of two cytokines, interleukin-2 (IL-2) and interferon-gamma (IFN-gamma), the objective of the present study was to investigate the mechanism of action of this enhanced therapeutic activity by characterising the effect of single, double and triple agent therapy upon local tumour immune parameters. Twenty-four hours after the administration of treatment to WAG rats bearing solid tumour implants of a colonic adenocarcinoma, the extent of tumour infiltration in response to the therapy was assessed in haematoxylin and eosin stained tumour sections. Treatment with doxorubicin/IL-2/IFN-gamma or IL-2/IFN-gamma was associated with a marked augmentation of the size of the tumour infiltrate (P < 0.001), as compared to untreated tumours or to those treated with any other single or double agent combination. Phenotypic evaluation of the tumour infiltrate using immunoperoxidase stained tumour sections revealed that a considerable proportion of the infiltrating cells were T cells and macrophages, whilst B cells were not detected in significant numbers. Although this phenotypic profile was not qualitatively influenced by therapy, marked quantitative differences were observed. Most notably, tumours treated with either doxorubicin/IL-2/IFN-gamma or IL-2/IFN-gamma exhibited a significant increase in the numbers of CD25+ infiltrating cells (P < 0.001). These changes in the tumour immunological response closely paralleled the therapeutic responses described previously. Thus, the enhanced therapeutic activity of the triple agent regimen may result from a profound augmentation of the size of the tumour infiltrate, together with a similar increase in the numbers of activated infiltrating cells. This study supports the concept that the immune response within the tumour is the appropriate site for investigations into the immunological antitumour mechanisms of immunotherapy and chemo-immunotherapy.