may increase expression of Class-I antigens (e.g. IFN-gamma), 29 which in turn 
increases tumor immunogenicity and renders the target cell more vulnerable 
to cytotoxic attack. Alternatively, a combination of these effects may be 
produced. For example, IL-2 can recruit both cytotoxic T and NK cells 
directly and also induces release of the secondary cytokine IFN-gamma, which 
augments MHC expression on tumor cells. 46,26 Additional, non-immune, 
effector mechanisms probably also contribute, since the tumor sites may be 
infiltrated with eosinophils and macrophages. Analysis of the mechanisms 
directly involved in anti-tumor immunity may be easier in cytokine transduction 
studies than after systemic exposure to the same agents, since the non-specific 
immunologic "noise" generated by high doses of cytokines should be absent. 
3.4 Application to Human Malignancy 
Although these effects are intriguing, there is as yet no evidence that cytokine 
transduction of tumor cells will have any relevance for treating or for 
immunizing against naturally occurring human cancers. To study the possible 
relevance of the approach it is necessary to transduce the patient’s own tumor 
cells with a vector encoding both the cytokine gene and a selective marker so 
that the small proportion of cells that have been successfully modified can be 
selected and then re-injected. This selection procedure can only take place if 
it is possible to regularly grow patient tumor cells ex vivo. This currently limits 
the applicability of the cytokine gene transfer approach, and the only currently 
approved protocols use TNF or IL2 transduced melanoma, colon or renal 
cells, and TIL therapy. 47 Early reports of the first two patients receiving TNF 
modified melanoma cells suggest that a delayed type hypersensitivty (DTH)- 
like response occurs around injected modified tumor cells, which then regress 
after 10-14 days. It is not yet known how regression of the injected cells is 
mediated. It is also unknown if that particular tumor/cytokine combination is 
an ideal paradigm to explore the immunological/therapeutic potential of the 
approach. We propose to investigate the safety and efficacy of this 
methodology in a different tumor with a different cytokine. 
3.5 Neuroblastoma Gene Transfer 
In June 1991, St. Jude Children’s Research Hospital was the first center 
outside the NIH to receive RAC/FDA approval for human gene transfer. 48 ' 50 
Amongst the protocols approved was the insertion of a selectable marker gene 
(neomycin resistance) in the LNL6 vector into the marrow of children with 
advanced neuroblastoma. This marrow is reinfused as an autologous bone 
marrow transplant (ABMT). The primary aim is to determine whether 
neuroblastoma cells at relapse are marked, since >70% of the children will 
likely relapse after treatment on our frontline study. If neuroblasts are 
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