IMMUNOHISTOCHEMICAL CHARACTERIZATION OF IMMUNOLOGICAL CHANGES AT THE TUMOR SITE AFTER CHEMO-IMMUUOTHERAPY 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 immunol ogical parameters do not correlate with therapeutic activity. In contr ast, information on therapy related immunological change at the tumour site is scarce. Having previously demonstrated that the therapeutic a ctivity of doxorubicin chemotherapy can be significantly augmented by the co-administration of two cytokines, interleukin-2 (IL-2) and inerf eron-gamma (IFN-gamma), the objective of the present study was to inve stigate the mechanism of action of this enhanced therapeutic activity by characterising the effect of single, double and triple agent therap y upon local tumour immune parameters. Twenty-four hours after the adm inistration of treatment to WAG rats bearing solid tumour implants of a colonic adenocarcinoma, the extent of tumour infiltration in respons e 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 i nfiltrate (P<0.001), as compared to untreated tumours or to those trea ted with any other single or double agent combination. Phenotypic eval uation of the tumour infiltrate using immunoperoxidase stained tumour sections revealed that a considerable proportion of the infiltrating c ells were T cells and macrophages, whilst B cells were not detected in qualitatively influenced by therapy, marked quantitative differences were observed. Most notably, tumours treated with either doxorubicin/I L-2/IFN-gamma or IL-2/IFN-gamma exhibited a significant increase in th e numbers of CD25(+) infiltrating cells (P<0.001). These changes in th e tumour immunological response closely paralleled the therapeutic res ponses described previously. Thus, the enhanced therapeutic activity o f 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 o f immunotherapy and chemo-immunotherapy.