Notably, the transcriptomes of tumor lesions in chickens infected with recombinant MDV (rMDV) with L-Meq and those infected with rMDV encoding Meq without the insertion were similar; however, chickens infected with rMDV harboring L-Meq exhibited higher proportions of CD4+ T cells and regulatory T cells, which are targets for transformation by MDV, in the early post-infection phase, suggesting accelerated tumorigenesis. Here, CD4 is linked to neoplasm.