Yonago Acta medica 2015;58:39–44

Original Article

Upregulation of Immune Checkpoint Molecules, PD-1 and LAG-3, on CD4+
and CD8+ T Cells after Gastric Cancer Surgery
Seigo Takaya, Hiroaki Saito and Masahide Ikeguchi
Division of Surgical Oncology, Department of Surgery, School of Medicine, Tottori University Faculty of Medicine, Yonago 683-8504,
Japan

ABSTRACT

because it involves the complete surgical removal of any
residual cancer cells in the tumor bed. However, a substantial number of patients experience recurrence evenafter R0 resection because of the occurrence of micrometastasis. Therefore, Japanese gastric cancer treatment
guidelines recommend adjuvant chemotherapy with
TS-1 for stage II/III gastric cancer patients to control
micrometastasis and prevent recurrence.2 This recommendation is based on the results of the Adjuvant Chemotherapy Trial of TS-1 for Gastric Cancer study, whichshowed a survival benefit with adjuvant chemotherapy
after D2 gastrectomy compared with surgery alone forstage II/III gastric cancer patients.3
The immune response is also thought to control
micrometastasis. Yokohama et al. demonstrated in amouse model of human gastric cancer micrometastasis
that spontaneous regression of isolated tumor cells in
the regional lymph nodes occurred following removal of
the primary tumor and that this appeared to be primarily through natural killer (NK) cell mediated antitumor
activity.4 However, surgical stress generally induces
suppression of cell-mediated immunity that is harmful
to patients with cancer because it may diminish theirability to prevent postoperative infections and tumor recurrence.5–7 T cells are a critical component of cellularimmunity that are involved in the recruitment and activation of effector cells and amplification of the specificimmune response to pathogens and cancer cells. T cell
dysfunctions are characterized by diminished cytokine
production, impaired killing and hypoproliferation.
Wichmann et al. demonstrated a significant decreasein cell numbers of lymphocyte subpopulations, such as
helper T (Th) lymphocytes, cytotoxic T lymphocytes andNK cells.5 Brune et al. reported that interferon-gamma,
tumor necrosis factor-alpha and interleukin-2 production
by T cells decreases significantly after conventional cholecystectomy.6 Decker et al. showed that surgical stressinduces a shift in the Th1/Th2 balance toward Th2, suggesting that cell-mediated immunity is downregulated
and antibody-mediated immunity is upregulated after
surgery.7 However, the detailed mechanisms responsible
for T cell dysfunction after surgery remain unclear.
Recently, several intrinsic factors, including lymphocyte-activation gene 3 (LAG-3) and programmed

Background

Surgery has been reported to suppress
cell-mediated immunity; however, the detailed mechanisms responsible for this remain unclear. This study
determined the expression of lymphocyte activation
gene 3 (LAG-3) and programmed cell death 1 (PD-1) inlymphocytes following surgery for gastric cancer.
Methods LAG-3 and PD-1 expression on both CD4+
and CD8+ T cells obtained pre- and post-operatively
from gastric cancer patients were evaluated by multicolor flow cytometry.
Results The total lymphocyte count decreased rapidly
from preoperative levels, reaching a minimum on postoperative day 1 and remaining significantly decreased ondays 3 and 7. PD-1+CD4+ T cells significantly increased,reaching a maximum on postoperative day 1 and remaining significantly elevated on day 3. PD-1+CD8+ T
cells significantly increased and reached a maximum on
day 7 before returning to the preoperative level on day
30. There were no statistically significant differences in
the frequency of LAG-3+CD4+ or LAG-3+CD8+ T cells
after surgery. There were significant positive correlations
between PD-1 and LAG-3 expression on both CD4+ andCD8+ T cells.
Conclusion PD-1 and LAG-3 expression on both
CD4+ and CD8+ T cells was up-regulated and might berelated to impaired cell-mediated immunity after surgery for gastric cancer.
Key words

gastric cancer; lymphocyte activation gene
3; programmed cell death 1; T-cell

Gastric cancer is one of the most common malignancies
and ranks second among all cancer deaths worldwide.1
Radical (R0) resection offers the best chance for a cure
Corresponding author: Hiroaki Saito, MD
sai10@med.tottori-u.ac.jp
Received 2014 December 22
Accepted 2015 January 5
Abbreviations: CTLA-4, cytotoxic T-lymphocyte-associated antigen 4; CRP, C-reactive protein; FACS, fluorescence-activated cellsorting; FITC, fluorescein isothiocyanate; IgG, immunoglobulin G;
LAG-3, lymphocyte activation gene 3; NK, natural killer; PD-1,
programmed death 1; PD-L, PD-1-ligand; R0, radical; Th, helper T;
TIL, tumor-infiltrating lymphocyte

39

S. Takaya et al.

tumors, such as melanomas and lymphomas.24 Importantly, LAG-3 is closely correlated with the dysfunctionof T cells in patients with chronic viral infection 22 andcancer.23
Given the association between PD-1 and LAG-3 expression on CD4+ and CD8+ T cells and T cell dysfunction in HIV, HCV and cancer patients, it is likely thatthese might be related to suppression of cell-mediatedimmunity after surgery. The purpose of the current
study was therefore to examine the expression of PD-1
and LAG-3 on lymphocytes to determine the role ofthese molecules in the immune suppression that occurs
after surgery for gastric cancer.

cell death 1 (PD-1), have been recognized as negative
regulatory proteins that block the expansion and suppress the effector function of antigen-specific CD8+ T
cells.8–10 PD-1 (CD279) was identified as a gene that was
upregulated in a T cell hybridoma undergoing apoptotic
cell death.11 PD-1 is inducibly expressed on CD4+ T
cells, CD8+ T cells, natural killer-like T cells, B cells
and monocytes upon activation.11, 12 Recent studies haveshown that PD-1 is highly expressed by CD8+ T cells
during chronic lymphocytic choriomeningitis virus infection and that the PD-1–PD-1 ligand (PD-L) pathway
plays a major role in regulating T cell exhaustion during
infection.13 Furthermore, several new studies suggest arole for the PD-1–PD-L pathway in the exhaustion of virus-specific CD8+ T cells during HIV infection. Several
reports have shown that PD-1 expression is elevated on
HIV-specific CD8+ T cells and that blocking the PD-1–
PD-L pathway leads to increased T cell proliferationand effector cytokine production.14–16 Previous work
has shown that PD-L1 is upregulated in HIV infection.17
Collectively, these observations suggest that the PD-1–
PD-L pathway may indeed be operating during chronic
HIV infection.
LAG-3, a CD4+ homolog that binds to major histocompatibility complex class II,18 is expressed on activated T cells, NK cells, B cells and dendritic cells, plays
an important but incompletely understood role in thefunction of these lymphocyte subsets.19–21 Recent studies have documented a role for LAG-3 in CD8+ T cell
exhaustion during chronic viral infection22 and LAG3 negatively regulated the tumor-infiltrating NY-ESO1-specific CD8+ T cells in human ovarian cancer.23 Demeure et al. reported that increased expression of LAG3 was found on tumor-infiltrating lymphocytes (TILs)
isolated from human renal cell carcinomas and other

MATERIALS AND METHODSPatients

This study enrolled 33 patients treated at Tottori University Hospital who had a pathological diagnosis of gastricadenocarcinoma. None of the patients received radiotherapy, chemotherapy or other medical interventions
before surgery. The clinicopathological characteristics ofthese patients, according to the Japanese Classificationof Gastric Carcinoma25 are shown in Table 1.
The study protocol was approved by the Institutional
Review Board at Tottori University Hospital. Informed
consent for drawing of blood samples was obtained fromall individuals.
Assessments

Leukocyte and lymphocyte counts, C-reactive protein(CRP) levels and PD-1 and LAG-3 expression on CD4+
and CD8+ T cells were determined before surgery andon postoperative days 1, 3, 7 and 30.
Preparation of peripheral blood mononuclear cells

After informed consent was obtained, approximately
40 mL of peripheral blood was drawn from the patients
before surgery and on postoperative days 1, 3, 7 and 30.
Blood samples were prepared by centrifugation over a
Ficoll-Paque (Pharmacia, Uppsala, Sweden) density gradient.

Table 1. Clinicopathological characteristics of the patients included in the current study
Age, mean (SD) [range], yr
GenderHistopathology*
Depth of invasion†
Lymph node metastasis
Stage

66.7 (11.8) [55–79]
Male		26
Female		 7
Differentiated		15
Undifferentiated		
18
T1 (early)		
19
T2/T3/T4 (advanced)
14
Absent		
22
Present		 11Stage I/II		
25
Stage III/IV		
8

Flow cytometry analysis

Fluorescence-activated cell sorting (FACS) analysis was
performed using a FACS Calibur (Becton Dickinson,
Franklin Lakes, NJ). The following antibodies were used
to determine cell phenotype: anti-CD4-FITC (RPA-T4),
anti-CD8-FITC (HIT8a), anti-PD-1-PE (EH12.1) (BD
Pharmingen, Franklin Lakes, NJ), anti-LAG-3-PE (R&D
Systems, Minneapolis, MN) and anti-CD3-PE-Cy5(UCHT1) (BD Pharmingen, Franklin Lakes, NJ). Furthermore, the following antibodies were used for negative control: FITC mouse immunoglobulin G1 (IgG1),* Differentiated, papillary or tubular adenocarcinoma; undifferentiated, poorly differentiated or mucinous adenocarcinoma, or
signet-ring cell carcinoma.
† T1, tumor has invaded lamina propria or submucosa; T2, tumor
has invaded the muscularis propria or the subserosa; T3, penetrating the serosa; T4, invading adjacent organs.

40Immunosuppression after gastric surgery

Fig. 1. Changes in total leukocyte count (a), serum concentration of C-reactive protein (CRP) (b) and total lymphocyte count (c) after surgery. POD, postoperative day; Pre-op, preoperation.

PE mouse IgG1, PE-Cy5 mouse IgG1 (clone MOPC-21;
BD Pharmingen, Franklin Lakes, NJ) and goat IgG PEconjugated antibody (R&D Systems).

creased, it was still significantly elevated on day 3 (Fig.
1a). A significant increase in CRP levels was also observed on postoperative days 1, 3 and 7, compared withpreoperative values (Fig. 1b). In contrast, a rapid and significant decrease in the total lymphocyte count was observed on day 1 after surgery (Fig. 1c). The lymphocyte
count reached a minimum on day 1 and then increased,
but was still significantly lower than before surgery ondays 3 and 7.

Statistical analysis

Statistical differences between two groups were determined by paired t-test. The accepted level of significancewas P < 0.05. The GraphPad Prism software (GraphPad
Software, La Jolla, CA) was used for all statistical analyses.

PD-1 and LAG-3 expression on CD4+ and CD8+ T
cells

RESULTS
The total leukocyte count increased postoperatively
and reached a maximum on day 1. Although it then de-

The frequency of PD-1+CD4+ T cells significantly increased postoperatively and reached a maximum on day
1. It then decreased, but remained significantly elevatedon day 3 (Fig. 2). The frequency of LAG-3+CD4+ T cells

Fig. 2. (a) The reaction of isotypic control to CD4+ T cells after
surgery by FACS. (b) Representative results for PD-1 on CD4+
T cells in peripheral blood obtained from gastric cancer patients
after surgery by FACS. (c) Changes in PD-1 expression on CD4+
T cells after surgery. POD, postoperative day; Pre-op, preoperation.

Fig. 3. (a) The reaction of isotypic control to CD4+ T cells after
surgery by FACS. (b) Representative results for LAG-3 on CD4+
T cells in peripheral blood obtained from gastric cancer patients
after surgery by FACS. (c) Changes in LAG-3 expression on CD4+
T cells after surgery. POD, postoperative day; Pre-op, preoperation.

Absolute leukocyte and lymphocyte counts and
CRP levels

41

S. Takaya et al.

Fig. 4. (a) The reaction of isotypic control to CD8+ T cells after
surgery by FACS. (b) Representative results for PD-1 on CD8+
T cells in peripheral blood obtained from gastric cancer patients
after surgery by FACS. (c) Changes in PD-1 expression on CD8+
T cells after surgery. POD, postoperative day; Pre-op, preoperation.

Fig. 5. (a) The reaction of isotypic control to CD8+ T cells after
surgery by FACS. (b) Representative results for LAG-3 on CD8+
T cells in peripheral blood obtained from gastric cancer patients
after surgery by FACS. (c) Changes in LAG-3 expression on CD8+
T cells after surgery. POD, postoperative day; Pre-op, preoperation.

also increased and was slightly higher than the preoperative level on day 3 (Fig. 3; P = 0.098). The frequency of
PD-1+CD8+ T cells significantly increased and reached amaximum on day 7 after surgery before returning to thepreoperative level on day 30 (Fig. 4). The frequency of
LAG-3+CD8+ T cells was slightly higher on day 7 thanthe preoperative level (Fig. 5; P = 0.077).
Because increases in both PD-1 and LAG-3 expression on CD4+ T cells were observed on day 3, the correlation between PD-1 and LAG-3 expression on CD4+
T cells on day 3 was determined; a significant positive
correlation was found (Fig. 6a; r = 0.39, P = 0.024). Increases in PD-1 and LAG-3 expression on CD8+ T cells
were observed on day 7 and a significant positive correlation was found on day 7 (Fig. 6b; r = 0.37, P = 0.033).

DISCUSSION
During the perioperative and postoperative periods, acomplex biological response takes place in response
to surgical stress. This response is intended to restore
homeostasis as one aspect of host defenses against surgical stress and is thus a very important response for thehost. However, surgical stress induces suppression ofcell-mediated immunity that is harmful to patients withcancer who have undergone surgery because it may diminish their ability to prevent postoperative infections.
Importantly, surgical stress-induced suppression of cellmediated immunity may also place a patient at higher
risk for tumor recurrence. T cells are a critical component of cellular immunity and in the current study theabsolute number of lymphocytes significantly decreased

Fig. 6. Correlation between PD-1 and LAG-3 expression on CD4+ (a) and CD8+ T cells (b).

42Immunosuppression after gastric surgery

after surgery in gastric cancer patients. There was evidence of impaired cell-mediated immunity after operation, consistent with a previous report by Wichmann etal.5
Regulatory pathways that limit the immune responseof T cells are becoming increasingly well characterized.
For instance, cosignaling molecules are cell-surface
glycoproteins that can direct, modulate and fine-tune
T cell receptor signals. On the basis of their functional
outcome, cosignaling molecules can be divided into costimulators and coinhibitors, which promote or suppress
T cell activation, respectively. Through expression at theappropriate time and location, cosignaling molecules
positively and negatively control the priming, growth,differentiation and functional maturation of a T cell response.26 PD-1 and LAG-3 are coinhibitors. In the current study, we determined the PD-1 and LAG-3 expression on both CD4+ and CD8+ T cells to demonstrate thedetailed mechanisms responsible for the impaired cell
immunity observed after surgery in gastric cancer patients. The expression of both PD-1 and LAG-3 was upregulated on CD4+ and CD8+ T cells after surgery. We
have previously reported that PD-1 expression on CD4+
and CD8+ T cells was increased compared with normal
controls in gastric cancer patients.27 Furthermore, PD1-positive CD4+ and CD8+ T cells produced significantly
less interferon-gamma than PD-1-negative CD4+ andCD8+ T cells, indicating that upregulation of PD-1 on
both CD4+ and CD8+ T cells may be, in part, responsible
for the immune evasion observed in gastric cancer patients.27 The current results indicate that surgical stressinduces further suppression of cell-mediated immunity
in the postoperative period. Although increases in LAG3 expression observed in the current study were less thanthose for PD-1, LAG-3 expression tended to be higher
than preoperative levels during the postoperative period.
Turnis et al. demonstrated the coexpression of LAG-3
and PD-1 by TILs.28, 29 This coexpression is enriched inlymphocytes infiltrating certain human cancers and correlates with impaired CD8+ effector function. Woo et al.
demonstrated that LAG-3 and PD-1 synergistically regulate T cell function to promote tumoral immune escapein mice.30 Furthermore, Okazaki et al. showed that PD-1
and LAG-3 act synergistically to prevent autoimmunity
in mice.31 These data show that synergistic action ofboth LAG-3 and PD-1 plays an extremely important role
in regulating T cell function in various situations. In
fact, there were significant positive correlations between
PD-1 and LAG-3 expression in both CD4+ and CD8+ T
cells in the current study.
Recently, regulatory pathways that limit the immune response to cancer have attracted considerable

attention as an important target for immunotherapy.
Cytotoxic T lymphocyte-associated antigen 4 (CTLA-4)
is one of the representative molecules that downregulates T cell activation pathways.32 Ipilimumab, a fully
human monoclonal antibody that blocks CTLA-4, hasrecently been shown to promote antitumor immunity
and improve overall survival in patients with previously
treated metastatic melanoma.33 Furthermore, it has been
demonstrated that treatment with the anti-PD-1 antibody
pembrolizumab (lambrolizumab) resulted in a high rateof sustained tumor regression, with mainly grade 1 or
2 adverse events, in patients with advanced melanoma,
including those who had disease progression during
previous treatment with ipilimumab.34 These results
clearly indicate that immunotherapy targeting immune
checkpoint molecules is effective for cancer therapy.
The suppression of cell-medicated immunity induced
by gastric cancer surgery puts patients at high risk ofrecurrence. However, adjuvant chemotherapy cannot begiven immediately after surgery to prevent recurrence
because it is likely that early initiation of chemotherapy
increases the risk of complications. In contrast, immunotherapy targeting immune checkpoint molecules
might be well suited to this situation. Because PD-1 andLAG-3 expression on both CD4+ and CD8+ T cells is
upregulated after gastric cancer surgery, immunotherapy
targeting PD-1 and LAG-3 may be effective in the treatment of gastric cancer. However, the correlation between
overexpression of PD-1 and LAG-3 on lymphocytes anddysfunction of cell-mediated immunity in postoperative
situation has not been determined in the current study.
Further investigations are urgently required to show thepossibility of treatment targeting PD-1 and LAG-3 forthe treatment of gastric cancer patients after surgery.
In conclusion, PD-1 and LAG-3 expression on both
CD4+ and CD8+ T cells was upregulated and might berelated to impaired cell-mediated immunity after surgery for gastric cancer.
The authors declare no conflict of interest.
REFERENCES
1 Jemal A, Bray F, Center MM, Ferlay J, Ward E, Forman D.
Global cancer statistics. CA Canaer J Clin. 2011;61:69-90.
PMID: 21296855.
2 Japanese Gastric Cancer Association. [Japanese gastric cancer
treatment guidelines 2014 (ver. 4)]. Tokyo: Kanehara-shuppan;
2014. Japanese.
3 Sakuramoto S, Sasako M, Yamaguchi T, Kinoshita T, Fujii
M, Nashimoto A, et al. Adjuvant chemotherapy for gastriccancer with S-1, an oral fluoropyrimidine. N Engl J Med.
2007;357:1810-20. PMID: 17978289.
4 Yokoyama H, Nakanishi H, Kodera Y, Ikehara Y, Ohashi
N, Ito Y, et al. Biological significance of isolated tumor cells
and micrometastasis in lymph nodes evaluated using a green

43

S. Takaya et al.
1994;39:213-7. PMID: 7506235.
20 Kisielow M, Kisielow J, Capoferri-Sollami G, Karjalainen
K. Expression of lymphocyte activation gene 3 (LAG-3) on B
cells is induced by T cells. Eur J Immunol. 2005;35:2081-8.
PMID: 15971272.
21 Workman CJ, Wang Y, El Kasmi KC, Pardoll DM, Murray PJ,
Drake CG, et al. LAG-3 regulates plasmacytoid dendritic cellhomeostasis. J Immunol. 2009;182:1885-91. PMID: 19201841.
22 Blackburn SD, Shin H, Haining WN, Zou T, Workman CJ,
Polley A, et al. Coregulation of CD8+ T cell exhaustion bymultiple inhibitory receptors during chronic viral infection.
Nat Immunol. 2009;10:29-37. PMID: 19043418.
23 Matsuzaki J, Gnjatic S, Mhawech-Fauceglia P, Beck A, Miller
A, Tsuji T, et al. Tumor-infiltrating NY-ESO-1-specific CD8+
T cells are negatively regulated by LAG-3 and PD-1 in humanovarian cancer. Proc Natl Acad Sci U S A. 2010;107:7875-80.
PMID: 20385810.
24 Demeure CE, Wolfers J, Martin-Garcia N, Gaulard P, Triebel F.
T Lymphocytes infiltrating various tumour types express the
MHC class II ligand lymphocyte activation gene-3 (LAG-3):
role of LAG-3/MHC class II interactions in cell-cell contacts.
Eur J Cancer. 2001;37:1709-18. PMID: 11527700.
25 Japanese Gastric Cancer Association. Japanese classificationof gastric carcinoma: 3rd English edition. Gastric Cancer
2011;14:101-12. DOI: 10.1007/s10120-011-0041-5.
26 Chen L. Co-inhibitory molecules of the B7-CD28 family inthe control of T-cell immunity. Nat Rev Immunol. 2004;4:33647. PMID: 15122199.
27 Saito H, Kuroda H, Matsunaga T, Osaki T, Ikeguchi M.
Increased PD-1 expression on CD4+ and CD8+ T cells is
involved in immune evasion in gastric cancer. J Surg Oncol.
2013;107:517-22. PMID: 23129549.
28 Grosso JF, Goldberg MV, Getnet D, Bruno TC, Yen HR, Pyle
KJ, et al. Functionally distinct LAG-3 and PD-1 subsets on
activated and chronically stimulated CD8 T cells. J Immunol.
2009;182:6659-69. PMID: 19454660.
29 Baitsch L, Legat A, Barba L, Fuertes Marraco SA, Rivals JP,
Baumgaertner P, et al. Extended co-expression of inhibitory
receptors by human CD8 T-cells depending on differentiation,
antigen-specificity and anatomical localization. PloS One.
2012;7:e30852. PMID: 22347406.
30 Woo SR, Turnis ME, Goldberg MV, Bankoti J, Selby M,
Nirschl CJ, et al. Immune inhibitory molecules LAG-3 andPD-1 synergistically regulate T-cell function to promote tumoral immune escape. Cancer Res. 2012;72:917-27. PMID:
22186141.
31 Okazaki T, Okazaki IM, Wang J, Sugiura D, Nakaki F, Yoshida T, et al. PD-1 and LAG-3 inhibitory co-receptors act
synergistically to prevent autoimmunity in mice. J Exp Med.
2011;208:395-407. PMID: 21300912.
32 Melero I, Hervas-Stubbs S, Glennie M, Pardoll DM, Chen L.
Immunostimulatory monoclonal antibodies for cancer therapy.
Nat Rev Cancer. 2007;7:95-106. PMID: 17251916.
33 Hodi FS, O’Day SJ, McDermott DF, Weber RW, Sosman JA,
Haanen JB, et al. Improved survival with ipilimumab in patients with metastatic melanoma. N Engl J Med. 2010;363:71123. PMID: 20525992.
34 Hamid O, Robert C, Daud A, Hodi FS, Hwu WJ, Kefford R,
et al. Safety and tumor responses with lambrolizumab (antiPD-1) in melanoma. N Engl J Med. 2013;369:134-44. PMID:
23724846.

fluorescent protein-tagged human gastric cancer cell line. Clin
Cancer Res. 2006;12:361-8. PMID: 16428473.
5 Wichmann MW, Huttl TP, Winter H, Spelsberg F, Angele
MK, Heiss MM, et al. Immunological effects of laparoscopic
vs open colorectal surgery: a prospective clinical study. Arch
Surg. 2005;140:692-7. PMID: 16027336.
6 Brune IB, Wilke W, Hensler T, Holzmann B, Siewert JR.
Downregulation of T helper type 1 immune response and altered pro-inflammatory and anti-inflammatory T cell cytokine
balance following conventional but not laparoscopic surgery.
Am J Surg. 1999;177:55-60. PMID: 10037309.
7 Decker D, Schondorf M, Bidlingmaier F, Hirner A, vonRuecker AA. Surgical stress induces a shift in the type-1/
type-2 T-helper cell balance, suggesting down-regulation ofcell-mediated and up-regulation of antibody-mediated immunity commensurate to the trauma. Surgery. 1996;119:316-25.
PMID: 8619187.
8 Workman CJ, Vignali DA. Negative regulation of T cell homeostasis by lymphocyte activation gene-3 (CD223). J Immunol. 2005;174:688-95. PMID: 15634887.
9 Rodig N, Ryan T, Allen JA, Pang H, Grabie N, Chernova T,
et al. Endothelial expression of PD-L1 and PD-L2 down-regulates CD8+ T cell activation and cytolysis. Eur J Immunol.
2003;33:3117-26. PMID: 14579280.
10 Gajewski TF, Fallarino F, Fields PE, Rivas F, Alegre ML.
Absence of CTLA-4 lowers the activation threshold of primed
CD8+ TCR-transgenic T cells: lack of correlation with Src
homology domain 2-containing protein tyrosine phosphatase.
J Immunol. 2001;166:3900-7. PMID: 11238634.
11 Okazaki T, Honjo T. The PD-1-PD-L pathway in immunological tolerance. Trends Immunol. 2006;27:195-201. PMID:
16500147.
12 Greenwald RJ, Freeman GJ, Sharpe AH. The B7 family revisited. Annu Rev Immunol. 2005;23:515-48. PMID: 15771580.
13 Barber DL, Wherry EJ, Masopust D, Zhu B, Allison JP,
Sharpe AH, et al. Restoring function in exhausted CD8 T cells
during chronic viral infection. Nature. 2006;439:682-7. PMID:
16382236.
14. Petrovas C, Casazza JP, Brenchley JM, Price DA, Gostick E,
Adams WC, et al. PD-1 is a regulator of virus-specific CD8+
T cell survival in HIV infection. J Exp Med. 2006;203:228192. PMID: 16954372.
15 Day CL, Kaufmann DE, Kiepiela P, Brown JA, Moodley
ES, Reddy S, et al. PD-1 expression on HIV-specific T cells
is associated with T-cell exhaustion and disease progression.
Nature. 2006;443:350-4. PMID: 16921384.
16 Trautmann L, Janbazian L, Chomont N, Said EA, Gimmig
S, Bessette B, et al. Upregulation of PD-1 expression on HIVspecific CD8+ T cells leads to reversible immune dysfunction.
Nat Med. 2006;12:1198-202. PMID: 16917489.
17 Trabattoni D, Saresella M, Biasin M, Boasso A, Piacentini
L, Ferrante P, et al. B7-H1 is up-regulated in HIV infection
and is a novel surrogate marker of disease progression. Blood.
2003;101:2514-20. PMID: 12468426.
18 Triebel F, Jitsukawa S, Baixeras E, Roman-Roman S, Genevee
C, Viegas-Pequignot E, et al. LAG-3, a novel lymphocyte activation gene closely related to CD4. J Exp Med. 1990;171:1393405. PMID: 1692078.
19 Huard B, Gaulard P, Faure F, Hercend T, Triebel F. Cellular expression and tissue distribution of the human LAG3-encoded protein, an MHC class II ligand. Immunogenetics.

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