Fig. 4. Orthotopic Cdk5-deficient tumors exhibit increased PD-L1 staining, CD4⁺ tumor–infiltrating lymphocytes (TILs), and accumulating infiltrates of CD11b⁺ populations.

(A) Tumors extracted 14 days postinoculation from MM1 WT, shCdk5, or shNS mice stained for PD-L1 expression. Dashed line represents margin between tumor (T) and stroma. Black arrows point to increased PD-L1⁺ and IBA-1⁺ cells in the tumor stroma. Scale bars, 400 μm. (B and C) Fluorescence-activated cell sorting (FACS) analysis of MM1 WT (black circle) and MM1 crCdk5 (orange square) tumor infiltrate by percentage of cell type. (D) Ratio of total CD8⁺:CD4⁺ cell infiltrate. (E) FACS analysis of the percentage of PD-1⁺ or PD-L1⁺ cells in the CD4⁺ or CD8⁺ populations. (F) FACS analysis of the percentage of myeloid cells in tumor infiltrate based on differential CD45 staining (left) or Ly6C staining among CD11b⁺CD45⁺ cells (right). (G) Percent of total CD11b⁺ population (left) and subpopulations (right) present in tumor infiltrate that express PD-L1. (H) MFI of PD-L1 expression among CD11b⁺ total population (left) and subpopulations (right). (B), (C), (D), (E), (F), and (G) were graphed as means ± SD. (H) was graphed as individual MFI with mean indicated. n = 9 per group. Each data point represents pooled samples from three mice. *P < 0.05; **P < 0.01. Significance was determined using the Student's t test.