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Because renal-cell carcinoma (RCC) is considered relatively resistant to radio- and chemotherapy, RCC patients may benefit from new treatment modalities, e.g. immunotherapy. In vitro and in vivo studies suggest that combinations of cytokines such as interferon gamma or interferon alpha (IFN-gamma, IFN-alpha) and tumor necrosis factor alpha (TNF-alpha) may act synergistically. In this study we tested whether a monoclonal antibody (MAb) G250, reactive with a RCC-associated antigen, showed anti-tumor effects in vivo in nude mice with established s.c. human RCC xenografts, and also whether this MAb could enhance the anti-tumor effect of combinations of IFNs and TNF-alpha. Treatment with combinations of IFN-alpha/TNF-alpha or IFN-gamma/TNF-alpha, or with MAb G250 alone, resulted in a significant inhibition of tumor growth. Treatment with MAb G250, in combination with IFN-gamma/TNF-alpha, did not result in an improve anti-tumor effect as compared to that of either treatment alone. In contrast, MAb G250 combined with IFN-alpha/TNF-alpha resulted in a significantly enhanced anti-tumor response. In one experiment, 3 out of 10 mice showed complete tumor regression, with no recurrence after 90 days. Large numbers of infiltrating macrophages were found surrounding viable and necrotic tumor tissue after treatment with G250 combined with IFN-alpha/TNF-alpha. These results suggest that combination therapy, consisting of IFN-alpha, TNF-alpha and MAbs, may have therapeutic value in the treatment of RCC.

A study was made of the relative effects of size and binding strength of various forms of the monoclonal antibody (MAb) G250, reacting with primary and metastatic human renal-cell carcinoma (RCC), on the localization in human RCC xenografts in nude mice. Preferential tumor localization was demonstrated after injection of 125I-labelled intact IgG, with increasing tumor/non-tumor ratios in time. Approximately 27.4% of the injected dose/gram (%ID/g) was localized in the xenograft 24 hr post-injection. A control MAb did not preferentially localize in xenografts. With F(ab')2 fragments, higher tumor/blood ratios were obtained, although a lower percentage of injected dose per gram was bound to the tumor, 24 and 48 hr post-injection. Using a bispecific MAb CD3/G250 F(ab')2 fragment, which reacts with CD3 on human T lymphocytes and binds monovalently to RCC, an enhanced accumulation in tumor tissue was also observed. The %ID/g tumor obtained with bispecific CD3/G250 F(ab')2 was comparable with %ID/g tumor found with G250 F(ab')2. The 10-fold lower binding affinity to RCC compared with intact IgG or F(ab')2 had only marginal effects on %ID/g tumor. These results show that MAb G250 preferentially localizes to RCC xenografts. Because injection of F(ab')2 fragments resulted in higher tumor/non-tumor ratios, G250 F(ab')2 may therefore be more suitable for diagnostic evaluation of RCC in patients. The tumor uptake is more dependent on size than on affinity. Furthermore, the data obtained with bispecific MAb CD3/G250 F(ab')2 support the hypothesis that this bispecific MAb may be able to target cytotoxic T lymphocytes to RCC in humans to mediate destruction of RCC.