Failure of B7.1-modified tumor to evoke full activation of CD8+ tumor-infiltrating lymphocytes in the central nervous system: prevention of parental tumor growth in the subcutaneous environment.
OBJECTIVE
It is well known that the central nervous system (CNS) is an immunologically privileged site. To characterize CD8+ tumor-infiltrating lymphocytes (TILs) recovered from the CNS, the authors compared these cells with TILs recovered from subcutaneous tissue by using a B7.1 gene-modified tumor implantation model.


METHODS
The authors established a B7.1 gene-modified EL4 murine lymphoma cell line (EL4-B7.1) and implanted the cells into the CNS to observe the duration of tumor-free survival. Although EL4-B7.1 cells were completely rejected in a subcutaneous implantation model, 40% of animals died after the CNS implantation (all animals in which the parent tumor was implanted died within 16 days). Therefore, the authors isolated TILs from each implantation site and analyzed the expressions of activation antigens CD25 and CD69 by performing the anti-CD8 magnetic beads separation method and flow cytometric analysis. After implantation of the parent tumor, there was no difference in the number of TILs from each site (CD25 1.7-3.2%, CD69 21.9-34.3%). After implantation of the B7.1-modified tumor, the CD25-expressing TIL population from the subcutaneous site was 4.68 times higher than that from the CNS site (17.8% compared with 3.8%). Based on these findings, the authors used a mitomycin C-treated EL4-B7.1 subcutaneous vaccination with various protocols. Vaccination before tumor challenge was sufficient to prevent the development of the tumor. For animals with established tumor, the vaccination protocol was able to prolong host survival (p = 0.0053).


CONCLUSIONS
The data clearly demonstrate that the CNS environment fails to activate CD8+ TILs fully. These are the first data indicating in detail a difference between CD8+ TILs from the CNS and those from other sites based on a B7.1-modified tumor model.
Department of Neurosurgery, Gifu University School of Medicine, Japan.
Hiromichi
H
Ando
Masanao
M
Saio
Noriyuki
N
Tamakawa
Naoyuki
N
Ohe
Takashi
T
Nakayama
Hai
H
Yu
Yasuhiko
Y
Kaku
Toru
T
Iwama
Jun
J
Shinoda
Noboru
N
Sakai
Tsuyoshi
T
Takami
D000818:Animals; D018122:B7-1 Antigen / Q000235:genetics / Q000276:immunology*; D001932:Brain Neoplasms / Q000235:genetics / Q000276:immunology*; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D002490:Central Nervous System / Q000276:immunology*; D004195:Disease Models, Animal; D005260:Female; D008213:Lymphocyte Activation / Q000235:genetics / Q000276:immunology*; D016246:Lymphocytes, Tumor-Infiltrating / Q000276:immunology*; D016399:Lymphoma, T-Cell / Q000235:genetics / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D012867:Skin / Q000276:immunology*; D014162:Transfection; D014407:Tumor Cells, Cultured
D018122:B7-1 Antigen