The immunological tests revealed the following two main messages: i) repeated application of gene-modified MSCs, even in combination with GCV, is immunologically safe: no significant signs of systemic inflammatory reaction (except some mild and temporary increase of IL-6), no detectable intratissue (tumor) endothelial activation, no immunogenicity of the cell product, no hints of negative immunomodulation/ -suppression; ii) the therapy induces a switch of the functional properties of monocytes to a more inflammatory phenotype (TNF/IL-10 ratio). The gene discussed is TNF; the disease is neoplasm.