Retroviral-mediated transfer of genes encoding interleukin-2 and interleukin-12 into fibroblasts increases host antitumor responsiveness

The transfer of genes encoding cytokines into tumor cells has emerged as a new strategy to increase in vivo host reactivity to a variety of tumors. Be cause gene transfer into tumor cells cannot be easily applied in the clinic al setting, we have developed an experimental model of gene transfer into f ibroblasts and examined the capacity of these engineered cells to elicit an antitumor immune response. Interleukin-12 (IL-12) is a heterodimeric cytok ine with pleiotropic activities presenting strong antitumor and antimetasta tic effects in murine models. A bicistronic retroviral vector was construct ed that contained the cDNAs encoding both chains (p40 and p35) of murine IL -12 separated by an internal ribosomal entry site sequence. Syngeneic cutan eous fibroblasts obtained from newborn mice and transduced to secrete eithe r IL-12 or IL-2 were injected subcutaneously with B16F0 or B16F1 melanoma c ells. The lime of tumor occurrence and overall survival of mice were signif icantly prolonged when B16F1 cells were coinjected with cytokine-producing fibroblasts compared with B16F1 alone or B16F1 together with unmanipulated fibroblasts. Systemic effects were seen in the mice injected with either IL -2- or IL-12-secreting fibroblasts, with the highest proliferation capabili ty and interferon-gamma production observed in vitro from splenocytes from recipients of IL-2-secreting fibroblasts. Injection of IL-2-secreting fibro blasts or coinjection of IL-2- and IL-12-producing fibroblasts resulted in a significant increase of survival in the B16F0 model; in some cases, compl ete disease eradication was observed. These results suggest that cutaneous fibroblasts represent a target of choice for gene transfer and would be use ful in the treatment of minimal residual disease in humans. The transfer of genes encoding cytokines into tumor cells has emerged as a new strategy to increase in vivo host reactivity to a variety of tumors. Because gene tran sfer into tumor cells cannot be easily applied in the clinical setting, we have developed an experimental model of gene transfer into fibroblasts and examined the capacity of these engineered cells to elicit an antitumor immu ne response. Interleukin-12 (IL-12) is a heterodimeric cytokine with pleiot ropic activities presenting strong antitumor and antimetastatic effects in murine models. A bicistronic retroviral vector was constructed that contain ed the cDNAs encoding both chains (p40 and p35) of murine IL-12 separated b y an internal ribosomal entry site sequence. Syngeneic cutaneous fibroblast s obtained from newborn mice and transduced to secrete either IL-12 or IL-2 were injected subcutaneously with B16F0 or B16F1 melanoma cells. The lime of tumor occurrence and overall survival of mice were significantly prolong ed when B16F1 cells were coinjected with cytokine-producing fibroblasts com pared with B16F1 alone or B16F1 together with unmanipulated fibroblasts. Sy stemic effects were seen in the mice injected with either IL-2- or IL-12-se creting fibroblasts, with the highest proliferation capability and interfer on-gamma production observed in vitro from splenocytes from recipients of I L-2-secreting fibroblasts. Injection of IL-2-secreting fibroblasts or coinj ection of IL-2- and IL-12-producing fibroblasts resulted in a significant i ncrease of survival in the B16F0 model; in some cases, complete disease era dication was observed. These results suggest that cutaneous fibroblasts rep resent a target of choice for gene transfer and would be useful in the trea tment of minimal residual disease in humans.