Peripheral blood tumor-infiltrating lymphocytes in a neuroblastoma model

To detect tumor-infiltrating lymphocytes (TILs) in the peripheral blood (PB) of a preclinical neuroblastoma model.

Two types of preclinical models - immunodeficient mice and immunocompetent mice - were generated by injecting a cell suspension of neuroblastoma cell line NB36769 with MYCN gene (TH-MYCN+) overexpression. Spleen, tumor, and peripheral blood were studied using flow cytometry to detect PD-1+ T-cells. TCR-β immunosequencing was performed in matched samples (tumor and peripheral blood).

Most PB T-cells of immunodeficient mice were CD4 (control: 83.1%; tumor: 86.1%), with a small proportion of PD-1+ T-cells (control: 0.4%; tumor: 0.3%). However, the percentage of PD-1+ T-cells in the spleen was higher (control: 6.5%; tumor: 6.2%), and it was expressed in the CD4+ subset only. Regarding the TCR repertoire of immunocompetent mice, the proportion of the 10 most frequent sequences was significantly higher in tumors (11.09% ± 2.83%) than in the peripheral blood (1.59% ± 0.59%) (p=0.024). These findings are suggestive of clonotype enrichment within the tumor. 9 out of the 10 most frequent tumor clones were identified in the matched peripheral blood sample in 2 mice, and 6 out of 10 in one mouse. In addition, TILs with shared sequences from different animals were found.

Our results in terms of immunophenotype and clonality suggest the presence of PB T-cells which could include TILs in a preclinical neuroblastoma model.