A novel biodegradable poly(lactic acid) microsphere formulation was evaluated for in vivo cytokine immunotherapy of cancer in a human tumor xenograft/ severe combined immunodeficiency (SCID) mouse model. Co-injection of interleukin-2 (IL-2)-loaded microspheres with tumor cells into a subcutaneous site resulted in the complete suppression of tumor engraftment in 80% of animals. In contrast, bovine-serum-albumin(BSA)-loaded particles or bolus injections of poly(ethylene glycol)/IL-2 were ineffective in preventing tumor growth. The antitumor effect of IL-2 released by the microspheres was shown to be mediated by the mouse natural killer cells. This is the first evidence that the rejection of human tumor xenografts can be provoked by the sustained in vivo delivery of IL-2 from biodegradable microspheres. The use of poly(lactic acid) microspheres to deliver cytokines to the tumor environment could provide a safer and simpler alternative to gene therapy protocols in the treatment of cancer.

These results suggest that CD40 expression on lung cancer may play a role in metastatic spread, and also may serve as a prognostic marker and an indicator of advanced disease.

To determine the possible functional significance of CD40 expression on human non-small cell lung carcinomas and to assess the potential of CD40 as a therapeutic target, 18 lung tumor cell lines were established from biopsy tissues and were monitored for phenotypic changes on the cell surface and alterations in tumor cell proliferation after the ligation of CD40 with a trimeric fusion protein complex of CD40 ligand (CD40Lt). CD40 cross-linking resulted in up to a 6-fold increase in the surface expression of major histocompatibility complex (MHC) class I, Fas and intracellular adhesion molecule (ICAM)-1 in a subset of tumors expressing the highest levels of CD40. Suppression of tumor proliferation was seen after the ligation of CD40 on CD40Lt-responsive cell lines. The suppression was dose dependent, reversible and resulted from a delay of the tumor cells entering S-phase. No change in the cell phenotype or in proliferation were observed in CD40-negative tumors or in tumors expressing moderateto-low levels of CD40 after incubation with CD40Lt. CD40-negative tumors transfected with the CD40 gene expressed high levels of CD40 on their surface, but were also unresponsive to CD40Lt cross-linking of CD40. Our data establish that CD40 is required (but not sufficient) for transducing a signal that results in phenotypic changes in human lung tumors and suppression in their proliferation. We conclude that CD40 on non-small cell lung tumors may represent a potential therapeutic target, but only on a subset of the CD40؉ tumors. CD40, a molecule that has been recognized on B cells, dendritic cells and monocytes, is a member of the tumor necrosis factor (TNF)/nerve growth factor (NGF) receptor superfamily of molecules that include Fas and CD30. 1-4 CD40 is known to play a critical role in normal B-cell and dendritic cell development and function and in the survival, activation, differentiation and apoptosis of cells. 2,5 The ligand for CD40 (CD154) is transiently expressed on activated T cells. 2,5 The CD40 molecule is also expressed on other normal cells including fibroblasts and basal cells of the skin and on human neoplastic cells, that is, carcinomas of the colon, bladder, prostate, breast ovary and melanomas. 6 -11 Although the consequences and functional significance of CD40 ligation on B cells have been extensively studied, comparatively little is known about the effects of CD40 cross-linking on other cell types. CD40 engagement has been shown to inhibit the growth of primary epithelial cells in vitro and to induce differentiation, 12-14 and the ligation of CD40 on normal keratinocytes results in phenotypic changes such as enhanced secretion of interleukin-6 (IL-6) and TNF-␣ and up-regulation of intracellular adhesion molecule (ICAM)-1. 14 -16 Very little is known about the function of CD40 on neoplastic cells, and the effects of CD40 ligation on tumors has not been studied extensively.Because CD40 appears to play a significant role in the activation, proliferation and differentiation of normal cells, we have investi...

The human tumor microenvironment includes a mixture of tumor cells, inflammatory cells, fibroblasts, and endothelial cells, all of which are tethered to an extracellular matrix. It has been difficult to study the dynamic interactions of these cells in human tumors in situ for obvious ethical and logistical considerations that prohibit experimental manipulations of tumors while still in patients. Fresh tissue from human lung tumor biopsy implanted into SCID mice was shown to remain viable, and the histologic appearance of the tumor microenvironment was maintained in the tumor xenografts for at least 3 months. In this study, the authors established that the inflammatory cells within human tumor xenografts can suppress tumor growth, and that this suppression is a result, in part, of endogenously produced interleukin-12 (IL-12) because IL-12 neutralizing antibodies enhance the growth of the tumor xenografts. The tumor-inhibitory activity of the inflammatory leukocytes is also enhanced by the local and sustained release of human recombinant IL-12 into the tumor microenvironment from cytokine-loaded biodegradable microspheres. Neither the anti-IL-12 neutralizing antibody nor the delivery of exogenous IL-12 from microspheres had any effect on tumor xenografts in the absence of the inflammatory leukocytes. In conclusion, the inflammatory cells within the tumor microenvironment of human lung tumor xenografts are functional and can suppress tumor growth, and the dynamic effects of the inflammatory cells can be modulated by exogenous cytokines.

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