Infiltration of NK cells and DCs into cell clusters formed by inoculation of the tumor cybrids into the B6 mice. (A) Identification by histochemical analysis of the mononuclear cells that infiltrated into cell clusters. P29mtB6 and P29mtNZB formed small cell clusters on day 4 after inoculation into B6 mice. P29mtB6 showed an increase in cluster size from day 4–12, but P29mtNZB showed a decrease in cluster size. H&E staining showed preferential infiltration of the mononuclear cells into cell clusters of P29mtNZB. Photographs of higher magnification of boxed areas are shown below. Immunohistochemical analyses showed preferential infiltration of CD11c⁺ DCs into cell clusters of P29mtNZB at day 4. Bars: (gray) 5 mm; (black) 20 µm. (B) Quantitative estimation of the NK cells and DCs that infiltrated into cell clusters by flow cytometric analysis using CD45⁺ lymphocytes isolated from the cell clusters. CD11c, B220, CD3, and NK1.1 are lineage-specific markers for DCs, B cells, T cells, and NK cells, respectively. The red boxes in the top and bottom panels indicate NK cells (CD3⁻ and NK1.1⁺) and DCs (CD11c⁺ and B220⁻), respectively. (C) Transcription of cytokines in cell clusters. Total RNA was prepared from cell clusters, and RT-PCR analyses were performed. Similar results were obtained in two independent experiments.