|
|
||||||||
Cutting Edge |


,¶
*
Transplantation Unit, Surgical Services, Massachusetts General Hospital, Boston, MA 02114;
Laboratory of Immunogenetics and Transplantation, Renal Division, Department of Medicine, Brigham and Womens Hospital, Boston, MA 02115;
Division of Rheumatology, Department of Medicine, University of Pennsylvania, Philadelphia, PA 19104; and
Department of Cancer Biology, Harvard School of Public Health; and
¶ Department of Medicine, Harvard Medical School, Boston, MA 02115
| Abstract |
|---|
|
|
|---|
| Introduction |
|---|
|
|
|---|
The study of graft rejection in the absence of a direct pathway for CD4+ T cell stimulation was made possible by the generation of class II-deficient mice. These mice can be used as donors, which leaves only the indirect pathway available for the activation of recipient CD4+ T cells. More recently, the insertion of a class II transgene that is expressed only on thymic epithelium into the class II-deficient mice has generated animals with normal numbers of CD4+ T cells but no class II molecules on their APCs. These mice can be used as recipients to study rejection when only the direct pathway is available for CD4+ T cell activation. Using these genetically modified mouse strains, we tested the effectiveness of costimulatory blockade for prolonging allograft survival when only one or the other pathway was available.
| Materials and Methods |
|---|
|
|
|---|
Normal mice were obtained from The Jackson Laboratory (Bar Harbor, ME). Mice lacking MHC Ags (II-) and mice expressing MHC class II Ags only on their thymic epithelium (II-, 4+) were bred in our laboratories.
The generation and phenotype of mice lacking MHC class II Ags have been previously described (7). For these experiments, mice from the thirteenth generation backcross of (B6 x 129)F1 to B6 mice were used.
Mice expressing MHC class II Ags only on their thymic epithelium were
generated by breeding class II-deficient mice with a B6-transgenic
strain, 36.5 (the gift of Dr. D. Lo, The Scripps Research Institute, La
Jolla, CA), which expresses the E
transgene only on thymic
epithelium (8). These mice are class II deficient on all
cells other than thymic epithelium. They have normal numbers of
peripheral CD4+ cells, which proliferate in an
allogeneic MLR in vitro (9).
Skin grafting
Trunk skin grafts were placed on the lateral thoracic area (10). Rejection was recorded when there was >90% destruction of the tissue.
Heterotopic heart transplantation
Vascularized heart grafts were transplanted using microsurgical techniques essentially as described by Corry et al. (11).
Reagents, Abs, and in vivo T cell depletion
Cyclosporin A (CsA)3 (Sandimmune; Novartis Pharmaceuticals, East Hanover, NJ), 35 mg/kg/day, was administered subcutaneously in olive oil started on the day of transplantation for 14 days. MR1, a hamster mAb specific for murine CD154 (Bioexpress Cell Culture Services, West Lebanon, NH), and a control purified hamster Ig (ICN Pharmaceuticals, Aurora, OH), were administered i.p. (250 µg) at the time of transplantation (12). The fusion protein murine CTLA4Ig (a kind gift of Dr. R. Peach from Bristol-Myers Squibb, Princeton, NJ) and a control Ig, murine mAb L6 (Oncogene, Seattle, WA), were administered i.p. (250 µg) 2 days after transplantation (13). Anti-CD4 (GK1.5; rat anti-mouse CD4) and anti-CD8 (2.43; rat anti-mouse CD8) ascites were prepared from hybridomas obtained from the American Type Culture Collection (Manassas, VA). CD4+ T cells and CD8+ T cells were depleted using the GK1.5 and 2.43, respectively. All treated mice received 0.1 ml i.p. of unpurified ascites (roughly equivalent to 100 µg of purified Ab) on -6, -3, and -1 days before and twice a week after transplantation until graft rejection (14, 15).
Statistics
Kaplan-Meier survival graphs were constructed, and the log-rank comparisons of the groups were used to calculate p values. Differences were considered to be significant at p < 0.05.
| Results |
|---|
|
|
|---|
A series of murine cardiac allografts were transplanted into MHC-mismatched recipients using anti-CD40L Ab (MR1), CTLA4-Ig, or both reagents together for immunosuppression. Mice from normal strains were used as donors and recipients and, in addition, mice from genetically altered strains lacking either donor or recipient MHC class II molecules were used to eliminate either the direct or indirect pathway for CD4+ T cell activation. In addition, some recipients were treated with anti-CD8 Ab so that any rejection observed would clearly depend on the CD4+ T cell response.
As shown in Fig. 1
, elimination of the
indirect pathway made it more difficult to achieve prolonged graft
survival using any of the costimulatory blocking combinations. Not only
was graft survival shorter in the absence of the indirect pathway than
in the absence of the direct pathway, but graft survival was also
shorter in the absence of the indirect pathway than when both pathways
were available. Thus, contrary to our initial expectation that
eliminating one or the other pathway of alloreactivity might make it
easier to prolong survival, eliminating the indirect pathway actually
made it harder.
|
To determine whether the results obtained in Fig. 1
would also be
obtained for a different type of transplant, skin grafts were performed
using combined costimulatory blockade in the same strain combinations.
All of the recipients were treated with anti-CD8 Ab to ensure that
rejection depended on CD4+ T cells. As shown in
Fig. 2
, survival was again shortest in
recipients that lacked an indirect pathway, and it was significantly
shorter than in the recipients that could generate both a direct and an
indirect response.
|
Although the previous experiments included treatment with anti-CD8 Ab, they did not eliminate the possibility of an unusual humoral mechanism of rejection in the recipients lacking MHC class II Ags. Therefore, alloantibody production was measured in the various types of recipients of cardiac allografts. No alloantibody response was detected in mice lacking the indirect pathway, whether or not costimulatory-blocking agents were administered (data not shown). High levels of donor alloantibody were detected in normal mice after cardiac allograft rejection, and these levels were diminished after treatment with CTLA-4Ig and eliminated by treatment with anti-CD40L. Thus there was no evidence for an unusual humoral mechanism to explain the rejection by recipients lacking MHC class II molecules after treatment with costimulatory-blocking agents.
The recipients lacking MHC class II molecules are not inherently more resistant to immunosuppression
Takeda et al. (16) and Kirberg et al.
(17) have shown that CD4+ cells do
not survive for long periods of time in vivo in the absence of self
class II molecules. Thus it is likely that CD4+
cells in the II-4+ mice
turn over rapidly and represent recent thymic emigrants. Therefore, it
was possible that the CD4+ cells in these mice
are inherently more resistant to immunosuppression than the cells in
normal animals. To address this possibility, skin grafts were performed
in the same strain combinations, but the immunosuppression was changed
to suboptimal doses of CsA coupled with anti-CD8 Ab treatment. As
shown in Fig. 3
, the trend in the
susceptibility to this immunosuppressive protocol was the opposite of
that shown with costimulatory blockade. Mice lacking an indirect
pathway showed more prolonged graft survival than mice with both
pathways, and it was easier to suppress mice lacking an indirect
response than mice lacking a direct response. Thus there is no
generalized resistance to immunosuppressive therapy on the part of
CD4+ cells in the
II-4+ mice.
|
Another possibility for the findings shown above is that CD4+ cells from II-4+ recipients are selectively resistant to costimulatory blocking agents compared with cells from normal mice. MLRs were therefore performed with both types of CD4+ cells, and inhibition was attempted with anti-CD40L Ab and/or CTLA4-Ig. In these strain combinations, both types of T cell responses were equally susceptible in vitro to inhibition by CTLA4-Ig while neither was susceptible to inhibition by anti-CD40L Ab (data not shown). Thus there did not appear to be a selective resistance by CD4+ cells from II-4+ mice to costimulatory blockade.
An additional experiment was performed in vivo to determine whether
CD4+ cells from normal animals would be
susceptible to costimulatory blockade if they were transferred into
recipients that lacked MHC class II molecules. Three types of hosts
were used for these adoptive transfer experiments: normal mice,
II-4+ mice, and ordinary
class II knockout mice. In each case, the hosts were depleted of
CD4+ and CD8+ cells by Ab
treatment and then were given CD8-depleted T cells from normal mice and
treatment with costimulatory blockade. As shown in Fig. 4
, cardiac allografts survived
indefinitely with costimulatory blockade on normal mice that received
the adoptive transfer of normal T cells, but they were rejected by both
types of recipients that lacked their own class II molecules. These
results indicate that it is not the nature of the
CD4+ T cells in
II-4+ mice that make them
resistant to costimulatory blockade, but rather the absence of the
recipient class II molecules (and thus the capacity to mount an
indirect response) that allows graft rejection. Therefore, it appears
that costimulatory blockade requires the induction of an active
alloimmune indirect response in the recipient to achieve prolonged
graft survival.
|
| Discussion |
|---|
|
|
|---|
One possible explanation for the results was that some unusual feature of the II-4+ mice (the recipients lacking the indirect pathway) made them capable of rejecting heart grafts by alternative mechanisms that are resistant to costimulatory blockade. We examined this possibility by looking for B cell or CD8-dependent mechanisms to account for the rejection by these recipients. However, our experiments indicate that the resistance to costimulation does involve the CD4+ cells in these animals. We also considered the possibility that the CD4+ cells in these mice are different from those in normal animals in some way that makes them resistant to immunosuppressive treatment. However we found that even normal CD4+ cells transferred into recipients lacking MHC class II molecules are resistant to costimulatory blockade. When performing this experiment we were concerned that the CD4+ cells that were adoptively transferred into the class II-negative recipients might not survive for long enough in this environment. However, the outcome was that rejection did occur after this transfer, and thus adequate survival was not the problem. Therefore, we concluded that the correct interpretation of our findings is that to achieve prolonged allograft survival using costimulatory blockade, CD4+ T cells must be able to respond actively through the indirect pathway. It is possible that a select population of regulatory CD4+ T cells fails to survive in the class II-deficient mice. This explanation for our findings is consistent with our interpretation that the indirect pathway is required to achieve prolonged survival using costimulatory blockade.
Although we did not anticipate the outcome of these experiments, our findings are consistent with those obtained by several other laboratories that have been studying transplantation tolerance. For example, earlier studies showing that prolonged allograft survival can be achieved after intrathymic injection of donor MHC peptides had already suggested that manipulations of the indirect pathway can alter the course of rejection when both the direct and indirect responses are available (18, 19). In addition, several laboratories have shown that active regulatory T cells are induced by various tolerance-inducing strategies, including the use of costimulatory blockade and of nondepleting T cell Abs (20, 21, 22, 23, 24, 25, 26, 27, 28, 29). Thus it is not necessarily surprising that eliminating one of the pathways of T cell alloreactivity should turn out to eliminate the capacity to generate the active T cell regulation that allows graft survival to occur.
The important contribution of our experiments to the work that has been done by others is that our experiments address the issue of the specificity of the regulatory T cell population. Other groups have provided information about the phenotype of these cells, characterizing them as CD4+CD25+, at least in some cases. However, there is very limited information available about what determinants are recognized by these regulatory cells. Waldmann and colleagues (30) have reported that regulatory T cells can be specific for determinants presented by the indirect pathway. In contrast, the finding of linked suppression, which has often been associated with regulatory T cells, has suggested to others that the critical suppressor determinant (the one recognized by the regulatory T cell population) was likely to be one on donor APCs. This is because coexpression of the intact donor Ag and the linked determinant on a donor APC would be the simplest explanation for the linkage phenomenon. The results of our experiments agree with those of Waldmanns because they suggest that at least a component of the regulatory T cell response must involve recognition of peptides of donor Ags presented by recipient MHC molecules. They go further than the previous results because our findings suggest that regulation through the indirect pathway is not only possible, but it is required.
A limitation of our studies is that they suggest conclusions based on what does not occur in the class II-deficient mice. Therefore, it will be essential to perform experiments in normal mice treated with costimulatory blockade to confirm that a population of regulatory T cells specific for indirect determinants is induced by this treatment. Our preliminary studies in normal animals support this conclusion (data not shown).
A perplexing aspect of these and earlier findings is that regulatory T cells that are specific for determinants of the indirect pathway apparently have the capacity to affect the function of T cells that are specific for determinants of the direct response. Because these determinants are presented by two different sets of APCs (those of the recipient in the first case and those of the donor in the second), it is not clear what accounts for the linkage that is associated with regulatory T cell tolerance. This linkage does exist, because transplantation tolerance induced by costimulatory blockade does show specificity. However, the simple idea that linkage is achieved by coexpression of determinants on a single APC is not sufficient to explain our findings.
| Acknowledgments |
|---|
| Footnotes |
|---|
2 Address correspondence and reprint requests to Dr. Hugh Auchincloss, Jr., Massachusetts General Hospital, WAC478, 15 Parkman Street, Boston, MA 02114-3117. E-mail address: auchincloss{at}helix.mgh.harvard.edu ![]()
3 Abbreviations used in this paper: CsA, cyclosporin A. ![]()
Received for publication July 2, 2001. Accepted for publication September 17, 2001.
| References |
|---|
|
|
|---|
5+ T cells by transgenic I-E restricted to thymic medullary epithelium. J. Immunol. 151:3954.[Abstract]
This article has been cited by other articles:
![]() |
W. F. N. Chan, H. Razavy, and C. C. Anderson Differential Susceptibility of Allogeneic Targets to Indirect CD4 Immunity Generates Split Tolerance J. Immunol., October 1, 2008; 181(7): 4603 - 4612. [Abstract] [Full Text] [PDF] |
||||
![]() |
T. Fehr, F. Haspot, J. Mollov, M. Chittenden, T. Hogan, and M. Sykes Alloreactive CD8 T Cell Tolerance Requires Recipient B Cells, Dendritic Cells, and MHC Class II J. Immunol., July 1, 2008; 181(1): 165 - 173. [Abstract] [Full Text] [PDF] |
||||
![]() |
C. J. Callaghan, F. J. Rouhani, M. C. Negus, A. J. Curry, E. M. Bolton, J. A. Bradley, and G. J. Pettigrew Abrogation of Antibody-Mediated Allograft Rejection by Regulatory CD4 T Cells with Indirect Allospecificity J. Immunol., February 15, 2007; 178(4): 2221 - 2228. [Abstract] [Full Text] [PDF] |
||||
![]() |
D. Golshayan, S. Jiang, J. Tsang, M. I. Garin, C. Mottet, and R. I. Lechler In vitro-expanded donor alloantigen-specific CD4+CD25+ regulatory T cells promote experimental transplantation tolerance Blood, January 15, 2007; 109(2): 827 - 835. [Abstract] [Full Text] [PDF] |
||||
![]() |
H. Noorchashm, A. J. Reed, S. Y. Rostami, R. Mozaffari, G. Zekavat, B. Koeberlein, A. J. Caton, and A. Naji B Cell-Mediated Antigen Presentation Is Required for the Pathogenesis of Acute Cardiac Allograft Rejection J. Immunol., December 1, 2006; 177(11): 7715 - 7722. [Abstract] [Full Text] [PDF] |
||||
![]() |
D. Tokita, M. Shishida, H. Ohdan, T. Onoe, H. Hara, Y. Tanaka, K. Ishiyama, H. Mitsuta, K. Ide, K. Arihiro, et al. Liver Sinusoidal Endothelial Cells That Endocytose Allogeneic Cells Suppress T Cells with Indirect Allospecificity J. Immunol., September 15, 2006; 177(6): 3615 - 3624. [Abstract] [Full Text] [PDF] |
||||
![]() |
C. K. Asiedu, K. J. Goodwin, G. Balgansuren, S. M. Jenkins, S. Le Bas-Bernardet, U. Jargal, D. M. Neville Jr, and J. M. Thomas Elevated T Regulatory Cells in Long-Term Stable Transplant Tolerance in Rhesus Macaques Induced by Anti-CD3 Immunotoxin and Deoxyspergualin J. Immunol., December 15, 2005; 175(12): 8060 - 8068. [Abstract] [Full Text] [PDF] |
||||
![]() |
A. S. Krupnick, A. E. Gelman, W. Barchet, S. Richardson, F. H. Kreisel, L. A. Turka, M. Colonna, G. A. Patterson, and D. Kreisel Cutting Edge: Murine Vascular Endothelium Activates and Induces the Generation of Allogeneic CD4+25+Foxp3+ Regulatory T Cells J. Immunol., November 15, 2005; 175(10): 6265 - 6270. [Abstract] [Full Text] [PDF] |
||||
![]() |
D. Watson, G. Y. Zhang, M. Sartor, and S. I. Alexander "Pruning" of Alloreactive CD4+ T Cells Using 5- (and 6-)Carboxyfluorescein Diacetate Succinimidyl Ester Prolongs Skin Allograft Survival J. Immunol., December 1, 2004; 173(11): 6574 - 6582. [Abstract] [Full Text] [PDF] |
||||
![]() |
K. Kishimoto, X. Yuan, H. Auchincloss Jr., A. H. Sharpe, D. A. Mandelbrot, and M. H. Sayegh Mechanism of Action of Donor-Specific Transfusion in Inducing Tolerance: Role of Donor MHC Molecules, Donor Co-stimulatory Molecules, and Indirect Antigen Presentation J. Am. Soc. Nephrol., September 1, 2004; 15(9): 2423 - 2428. [Abstract] [Full Text] [PDF] |
||||
![]() |
J. R. Torrealba, M. Katayama, J. H. Fechner Jr., E. Jankowska-Gan, S. Kusaka, Q. Xu, J. M. Schultz, T. D. Oberley, H. Hu, M. M. Hamawy, et al. Metastable Tolerance to Rhesus Monkey Renal Transplants Is Correlated with Allograft TGF-{beta}1+CD4+ T Regulatory Cell Infiltrates J. Immunol., May 1, 2004; 172(9): 5753 - 5764. [Abstract] [Full Text] [PDF] |
||||
![]() |
V. Mirenda, I. Berton, J. Read, T. Cook, J. Smith, A. Dorling, and R. I. Lechler Modified Dendritic Cells Coexpressing Self and Allogeneic Major Histocompatability Complex Molecules: An Efficient Way to Induce Indirect Pathway Regulation J. Am. Soc. Nephrol., April 1, 2004; 15(4): 987 - 997. [Abstract] [Full Text] [PDF] |
||||
![]() |
A. van Maurik, B. F. de St. Groth, K. J. Wood, and N. D. Jones Dependency of Direct Pathway CD4+ T Cells on CD40-CD154 Costimulation Is Determined by Nature and Microenvironment of Primary Contact with Alloantigen J. Immunol., February 15, 2004; 172(4): 2163 - 2170. [Abstract] [Full Text] [PDF] |
||||
![]() |
Y. Chen, Y. Demir, A. Valujskikh, and P. S. Heeger The Male Minor Transplantation Antigen Preferentially Activates Recipient CD4+ T Cells through the Indirect Presentation Pathway In Vivo J. Immunol., December 15, 2003; 171(12): 6510 - 6518. [Abstract] [Full Text] [PDF] |
||||
![]() |
L. Makhlouf, A. Yamada, T. Ito, R. Abdi, M. J. I. Ansari, C. Q. Khuong, H. J. Winn, H. Auchincloss Jr., and M. H. Sayegh Allorecognition and Effector Pathways of Islet Allograft Rejection in Normal versus Nonobese Diabetic Mice J. Am. Soc. Nephrol., August 1, 2003; 14(8): 2168 - 2175. [Abstract] [Full Text] [PDF] |
||||
![]() |
W.-P. Min, D. Zhou, T. E. Ichim, G. H. Strejan, X. Xia, J. Yang, X. Huang, B. Garcia, D. White, P. Dutartre, et al. Inhibitory Feedback Loop Between Tolerogenic Dendritic Cells and Regulatory T Cells in Transplant Tolerance J. Immunol., February 1, 2003; 170(3): 1304 - 1312. [Abstract] [Full Text] [PDF] |
||||
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |