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Chimerism in transplantation and in spontaneously occurring autoimmune disease
Chimerism in Transplantation and in Spontaneously Occurring Autoimmune Disease J.L. Nelson
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HIS PAPER explores implications of observations in transplantation chimerism for spontaneously occurring autoimmune diseases.1 Chronic graft-vs-host disease (cGVHD) is a common complication of allogeneic stem cell transplantation and has noted clinical similarities with some spontaneously occurring autoimmune diseases. The most striking similarities are with scleroderma (SSc) and primary biliary cirrhosis with other cGVHD manifestations resembling systemic lupus, Sjo ¨gren’s syndrome, and myositis.2 Most patients with cGVHD have antinuclear antibodies as do the majority of patients with the above autoimmune diseases. GENERATION OF THE HYPOTHESIS: IS SOME AUTOIMMUNE DISEASE AUTOALLOIMMUNE OR ALLOAUTOIMMUNE?
Three key observations led me to hypothesize that microchimerism is involved in the pathogenesis of some autoimmune diseases, and to propose an initial focus on SSc.3 The first of these is the seminal observation by Bianchi et al4 that fetal progenitor cells (CD341CD381) persist in the peripheral blood of normal women for decades after pregnancy. Second, autoimmune diseases affect more women than men and the peak incidence of SSc in women occurs following childbearing years.2 Third, as described above, cGVHD has numerous clinical similarities to autoimmune diseases, particularly SSc. Although there are differences, both exhibit progressive induration of the skin, often involve gut and lungs, and can be accompanied by Sjo ¨gren’s syndrome and sometimes myositis. Autoantibodies to topoisomerase I are highly specific for patients with diffuse SSc and also have been described in some cGVHD patients.2 Persistent fetal microchimerism does not apply to men or women who have never been pregnant, however, alternative sources of microchimerism include engraftment from a twin, blood transfusion, or from the mother.2 COROLLARY HYPOTHESIS: HLA COMPATIBILITY OF A CHILD INCREASES RISK OF SUBSEQUENT SSc IN THE MOTHER
In other studies of transplantation chimerism, GVHD has been described in immunocompetent individuals who receive blood transfusions from family members who are HLA compatible due to homozygosity.2 In the corollary 0041-1345/99/$–see front matter PII S0041-1345(98)01775-8
hypothesis,3 HLA compatibility of a child is examined from the mother’s perspective and includes both an HLA-identical child and an HLA-homozygous child, although the latter is of particular interest. STUDIES INVESTIGATING MICROCHIMERISM IN PATIENTS WITH SSc
Bianchi et al4 found that most healthy women had persistent fetal microchimerism.4 We, therefore, conducted a blinded study of women with SSc and healthy controls using a quantitative assay to study microchimerism.6 Women with at least one son were selected because of the technical ease with which male DNA can be detected in a female host. Some women had also given birth to daughters or had early pregnancy losses. A radioactive quantitative direct polymerase chain reaction (PCR) assay was used that amplifies a Y chromosome-specific sequence and results are expressed as the number of male cell DNA equivalents in a 16-mL sample of whole blood. Nested PCR was not used in any of our studies, contrary to an erroneous statement in an accompanying editorial. In this first report of microchimerism in an autoimmune disease, male DNA was found both more frequently and was quantitatively greater in women with SSc than in healthy women. Among healthy women, the range of male cell equivalents was 0 to 2, mean 0.38. In contrast, women with SSc had a range of 0 to 61 male cell equivalents, mean 11.1, P 5 .0007. Several women with SSc had levels of male DNA that were higher than that found in most women who are currently pregnant with a male fetus, although the patients had given birth to their sons decades previously. This observation was extended in another study that examined microchimerism in the skin of patients with SSc.7 DNA extracted from skin biopsy specimens was tested using a nested PCR assay for a Y chromosome-specific sequence, and positive results were found for some women with SSc but not in control women (P , .001). Two patients with SSc From the Department of Immunogenetics, Fred Hutchinson Cancer Research Center, Seattle, Washington. Supported by NIH grants AI 38583 and AI 41721. Address reprint requests to J. Lee Nelson, Immunogenetics D2-100, Fred Hutchinson Cancer Research Center, 1100 Fairview Ave N, Seattle, WA 98109-1024. © 1999 by Elsevier Science Inc. 655 Avenue of the Americas, New York, NY 10010
798
Transplantation Proceedings, 31, 798–799 (1999)
AUTOIMMUNE DISEASE
with positive results did not have sons, but one had a prior pregnancy termination in addition to daughters, and for another the pregnancy history was unknown. The pregnancy history of most controls was not known, however some were known to have sons. Male cells were seen in skin from SSc patients using fluorescence in situ hybridization and not in controls although the pregnancy history for controls studied using in situ hybridization was not provided. Studies of peripheral blood, although not quantitative, confirmed the observation that microchimerism is more frequently found in women with SSc than controls.7,8 We also conducted HLA studies for 136 individuals from 21 SSc families and 130 individuals from 32 control families.6 The hypothesis proposes that having given birth to at least one HLA-compatible child increases risk of SSc (not that the number of children or multiparity is the risk factor). Therefore, a study design requirement was that all living children be willing to participate. Noninclusion of any child could result in the misclassification of a patient or a control. Women with SSc were almost 9 times more likely to have given birth to a child prior to disease onset that was compatible for the basic DR families DRB1*01 through DRB1*14 DRB1, and 19 times more likely if the child was compatible due to DRB1 homozygosity. No association was observed for HLA class I antigens. HOW MICROCHIMERISM MIGHT CONTRIBUTE TO SSc: INSIGHTS AFFORDED BY TRANSPLANTATION CHIMERISM
Models of cGVHD have shown the importance of a population of donor T cells that are not deleted and not tolerized to the host.9 However, caution is indicated in direct analogy of SSc with cGVHD because there are clinical and pathologic differences between the two disorders and because there are quantitative differences of chimerism. The ratio of nonhost to host cells can be estimated from our studies6 at most as less than 1 to a million white blood cells, or if lymphocytes, 1 to 500,000 contrasting to patients with cGVHD in whom donor cells replace circulating host cells. Although it is possible that large numbers of chimeric cells are sequestered in disease-affected tissues, studies of skin specimens suggest that levels of microchimerism are also not marked in skin.7,8 Microchimerism with donor cells is found in recipients of organ transplants who are able to withdraw immunosuppressive medications without rejection and it has been
799
proposed that donor microchimerism facilitates graft acceptance.10 Pregnancy requires tolerance of a fetal allograft and this concept offers an appealing explanation for microchimerism during pregnancy, and could also be relevant to the pregnancy-induced remission of another autoimmune disease, rheumatoid arthritis.11 However, it is enigmatic why fetal microchimerism should persist for decades after pregnancy or cause disease. A small number of persistent nonhost cells could have a disproportionate effect if the role was primarily that of dysregulating host cells, allowing damage by autoreactive host cells, and/or a shift in cytokine milieu with ensuing damage. The effect could be mediated by nonhost peptides, nonhost cells, or both. A model that is consistent with few nonhost cells is that of indirect antigen presentation; this model has been described in chronic allograft rejection which also has pathologic similarities to SSc.12,13 Interaction between host and nonhost cells might be hypothesized if a small number of CD81 fetal cells co-opted help from CD41 host cells, possibly facilitated by HLA-DRB1 compatibility. Nonresponsiveness in maternal cells could also be induced by fetal “veto” cells, an antigenpresenting cell that inactivates a T cell with which it interacts.14 The above possibilities are not mutually exclusive and it is perhaps likely that more than one mechanism is involved.2 REFERENCES 1. Rose NR, Bona C: Immunol Today 14:426, 1993 2. Nelson JL: Curr Opin Rheumatol (in press) 3. Nelson JL: Arthritis Rheum 39:191, 1996 4. Bianchi DW, Zickwolf GK, Weil GJ, et al: Proc Natl Acad Sci USA 93:705, 1996 5. Bell SA, Faust H, Mittermuller J, et al: Br J Dermatol 134:848, 1996 6. Nelson JL, Furst DE, Maloney S, et al: Lancet 351:559, 1998 7. Artlett CM, Smith JB, Jimenez, SA: N Engl J Med 338:1186, 1998 8. Nelson JL: N Engl J Med 338:1224, 1998 9. Hakim FT, Mackall CL: In Ferrara JL, Deeg HJ, Burakof St. (eds): Graft-vs-Host Disease, 2nd Ed. New York: Marcel Dekker; 1997, p 274 10. Starzl TE, Demetris AJ, Murase N, et al: Immunol Today 17:577, 1996 11. Nelson JL, Hughes KA, Smith AG, et al: N Engl J Med 329:466, 1993 12. Pandley JP, LeRoy EC: Arthritis Rheum 41:10, 1998 13. Sayegh MH, Carpenter CB: Int Rev Immunol 13:221, 1996 14. Miller RG: Immunol Today 7:112, 1986
T
HIS PAPER explores implications of observations in transplantation chimerism for spontaneously occurring autoimmune diseases.1 Chronic graft-vs-host disease (cGVHD) is a common complication of allogeneic stem cell transplantation and has noted clinical similarities with some spontaneously occurring autoimmune diseases. The most striking similarities are with scleroderma (SSc) and primary biliary cirrhosis with other cGVHD manifestations resembling systemic lupus, Sjo ¨gren’s syndrome, and myositis.2 Most patients with cGVHD have antinuclear antibodies as do the majority of patients with the above autoimmune diseases. GENERATION OF THE HYPOTHESIS: IS SOME AUTOIMMUNE DISEASE AUTOALLOIMMUNE OR ALLOAUTOIMMUNE?
Three key observations led me to hypothesize that microchimerism is involved in the pathogenesis of some autoimmune diseases, and to propose an initial focus on SSc.3 The first of these is the seminal observation by Bianchi et al4 that fetal progenitor cells (CD341CD381) persist in the peripheral blood of normal women for decades after pregnancy. Second, autoimmune diseases affect more women than men and the peak incidence of SSc in women occurs following childbearing years.2 Third, as described above, cGVHD has numerous clinical similarities to autoimmune diseases, particularly SSc. Although there are differences, both exhibit progressive induration of the skin, often involve gut and lungs, and can be accompanied by Sjo ¨gren’s syndrome and sometimes myositis. Autoantibodies to topoisomerase I are highly specific for patients with diffuse SSc and also have been described in some cGVHD patients.2 Persistent fetal microchimerism does not apply to men or women who have never been pregnant, however, alternative sources of microchimerism include engraftment from a twin, blood transfusion, or from the mother.2 COROLLARY HYPOTHESIS: HLA COMPATIBILITY OF A CHILD INCREASES RISK OF SUBSEQUENT SSc IN THE MOTHER
In other studies of transplantation chimerism, GVHD has been described in immunocompetent individuals who receive blood transfusions from family members who are HLA compatible due to homozygosity.2 In the corollary 0041-1345/99/$–see front matter PII S0041-1345(98)01775-8
hypothesis,3 HLA compatibility of a child is examined from the mother’s perspective and includes both an HLA-identical child and an HLA-homozygous child, although the latter is of particular interest. STUDIES INVESTIGATING MICROCHIMERISM IN PATIENTS WITH SSc
Bianchi et al4 found that most healthy women had persistent fetal microchimerism.4 We, therefore, conducted a blinded study of women with SSc and healthy controls using a quantitative assay to study microchimerism.6 Women with at least one son were selected because of the technical ease with which male DNA can be detected in a female host. Some women had also given birth to daughters or had early pregnancy losses. A radioactive quantitative direct polymerase chain reaction (PCR) assay was used that amplifies a Y chromosome-specific sequence and results are expressed as the number of male cell DNA equivalents in a 16-mL sample of whole blood. Nested PCR was not used in any of our studies, contrary to an erroneous statement in an accompanying editorial. In this first report of microchimerism in an autoimmune disease, male DNA was found both more frequently and was quantitatively greater in women with SSc than in healthy women. Among healthy women, the range of male cell equivalents was 0 to 2, mean 0.38. In contrast, women with SSc had a range of 0 to 61 male cell equivalents, mean 11.1, P 5 .0007. Several women with SSc had levels of male DNA that were higher than that found in most women who are currently pregnant with a male fetus, although the patients had given birth to their sons decades previously. This observation was extended in another study that examined microchimerism in the skin of patients with SSc.7 DNA extracted from skin biopsy specimens was tested using a nested PCR assay for a Y chromosome-specific sequence, and positive results were found for some women with SSc but not in control women (P , .001). Two patients with SSc From the Department of Immunogenetics, Fred Hutchinson Cancer Research Center, Seattle, Washington. Supported by NIH grants AI 38583 and AI 41721. Address reprint requests to J. Lee Nelson, Immunogenetics D2-100, Fred Hutchinson Cancer Research Center, 1100 Fairview Ave N, Seattle, WA 98109-1024. © 1999 by Elsevier Science Inc. 655 Avenue of the Americas, New York, NY 10010
798
Transplantation Proceedings, 31, 798–799 (1999)
AUTOIMMUNE DISEASE
with positive results did not have sons, but one had a prior pregnancy termination in addition to daughters, and for another the pregnancy history was unknown. The pregnancy history of most controls was not known, however some were known to have sons. Male cells were seen in skin from SSc patients using fluorescence in situ hybridization and not in controls although the pregnancy history for controls studied using in situ hybridization was not provided. Studies of peripheral blood, although not quantitative, confirmed the observation that microchimerism is more frequently found in women with SSc than controls.7,8 We also conducted HLA studies for 136 individuals from 21 SSc families and 130 individuals from 32 control families.6 The hypothesis proposes that having given birth to at least one HLA-compatible child increases risk of SSc (not that the number of children or multiparity is the risk factor). Therefore, a study design requirement was that all living children be willing to participate. Noninclusion of any child could result in the misclassification of a patient or a control. Women with SSc were almost 9 times more likely to have given birth to a child prior to disease onset that was compatible for the basic DR families DRB1*01 through DRB1*14 DRB1, and 19 times more likely if the child was compatible due to DRB1 homozygosity. No association was observed for HLA class I antigens. HOW MICROCHIMERISM MIGHT CONTRIBUTE TO SSc: INSIGHTS AFFORDED BY TRANSPLANTATION CHIMERISM
Models of cGVHD have shown the importance of a population of donor T cells that are not deleted and not tolerized to the host.9 However, caution is indicated in direct analogy of SSc with cGVHD because there are clinical and pathologic differences between the two disorders and because there are quantitative differences of chimerism. The ratio of nonhost to host cells can be estimated from our studies6 at most as less than 1 to a million white blood cells, or if lymphocytes, 1 to 500,000 contrasting to patients with cGVHD in whom donor cells replace circulating host cells. Although it is possible that large numbers of chimeric cells are sequestered in disease-affected tissues, studies of skin specimens suggest that levels of microchimerism are also not marked in skin.7,8 Microchimerism with donor cells is found in recipients of organ transplants who are able to withdraw immunosuppressive medications without rejection and it has been
799
proposed that donor microchimerism facilitates graft acceptance.10 Pregnancy requires tolerance of a fetal allograft and this concept offers an appealing explanation for microchimerism during pregnancy, and could also be relevant to the pregnancy-induced remission of another autoimmune disease, rheumatoid arthritis.11 However, it is enigmatic why fetal microchimerism should persist for decades after pregnancy or cause disease. A small number of persistent nonhost cells could have a disproportionate effect if the role was primarily that of dysregulating host cells, allowing damage by autoreactive host cells, and/or a shift in cytokine milieu with ensuing damage. The effect could be mediated by nonhost peptides, nonhost cells, or both. A model that is consistent with few nonhost cells is that of indirect antigen presentation; this model has been described in chronic allograft rejection which also has pathologic similarities to SSc.12,13 Interaction between host and nonhost cells might be hypothesized if a small number of CD81 fetal cells co-opted help from CD41 host cells, possibly facilitated by HLA-DRB1 compatibility. Nonresponsiveness in maternal cells could also be induced by fetal “veto” cells, an antigenpresenting cell that inactivates a T cell with which it interacts.14 The above possibilities are not mutually exclusive and it is perhaps likely that more than one mechanism is involved.2 REFERENCES 1. Rose NR, Bona C: Immunol Today 14:426, 1993 2. Nelson JL: Curr Opin Rheumatol (in press) 3. Nelson JL: Arthritis Rheum 39:191, 1996 4. Bianchi DW, Zickwolf GK, Weil GJ, et al: Proc Natl Acad Sci USA 93:705, 1996 5. Bell SA, Faust H, Mittermuller J, et al: Br J Dermatol 134:848, 1996 6. Nelson JL, Furst DE, Maloney S, et al: Lancet 351:559, 1998 7. Artlett CM, Smith JB, Jimenez, SA: N Engl J Med 338:1186, 1998 8. Nelson JL: N Engl J Med 338:1224, 1998 9. Hakim FT, Mackall CL: In Ferrara JL, Deeg HJ, Burakof St. (eds): Graft-vs-Host Disease, 2nd Ed. New York: Marcel Dekker; 1997, p 274 10. Starzl TE, Demetris AJ, Murase N, et al: Immunol Today 17:577, 1996 11. Nelson JL, Hughes KA, Smith AG, et al: N Engl J Med 329:466, 1993 12. Pandley JP, LeRoy EC: Arthritis Rheum 41:10, 1998 13. Sayegh MH, Carpenter CB: Int Rev Immunol 13:221, 1996 14. Miller RG: Immunol Today 7:112, 1986