BritishJournaf ofHaemafofogy, 1976,34, 521.
Annotation BONE MARROW TRANSPLANTATION There are now about roo people alive whose haemopoietic function has been dependent for I year or longer on a bone-marrow graft. W e can be certain that virtually all would, but for their graft, have succumbed to bone marrow aplasia, acute leukaemia or combined immunity deficiency. It is an appropriate moment to examine the current bone marrow transplant prospectus.
Histoco mpa t i bilty Foremost among the requisites for successful transplantation is a detailed understanding of tissue compatibility, in particular the major histocompatibility complex (MHC). Genetic analysis has shown a broadly similar constitution for all species studied-mouse, rat, dog, monkey and man-in the form of a number of closely linked genes; two of these in man code for antigens which are serologically determined (SD) and have become well known as the HLA loci A and B; others code for determinants which either induce a response by foreign lymphocytes (LD or D locus) or are immune-associated (IA), i.e. effector rather than inducer (see Histocompatibility Testing, 1975). It is the D locus which is receiving most attention and a number of methods have been devised for its analysis. For example, in the primed lymphocyte test (PLT) (Sheehyet al, 1976), responder lymphocytes are stimulated first by an inoculation of priming foreign lymphocytes; the reaction reaches its peak in 5-6 d and then falls to zero; subsequent addition of a second inoculum of stimulator cells produces a very rapid ‘second-set’ response measurable at 24 h if the two populations ofstimulator cells share one or more LD antigens. Alternatively lymphocytes from D homozygotes (painstakingly gleaned from the progeny of consanguineous marriages) can be enlisted to form a panel of typing cells; failure of such honiozygous cells to stimulate responder cells indicates one haplotype of the responder. With proper controls it may be possible to use cultured cell-lines derived from a typing panel thus providing an almost unlimited supply of reference cells. Thirdly and perhaps of the greatest practical use, the D antigens, although initially detected through mixed lymphocyte culture (MLC), can also induce, and be detected on B-lymphocytes by, serum antibodies, which thus provide an alternative system of analysis (Van Rood et al, 1975). Van Rood et al (1976) have shown serologically that the number of D alleles in man is not impossibly large since 60% of a sample population could be fully typed by as few as five sera. Despite some discrepancies between the methods and the probable subdivision of the D system into at least two parts, there is thus a reasonable hope that unrelated donors could be found for most recipients who would give in an MLC test the same degree of identity as an identical sib. The occasional success of MLC-compatible, SD (A or B)-different grafts in severe combined immunity deficiency (SCID) encourages the belief that the A and B differences are relatively unimportant and could be ignored (Koch et a/, 1973 ; Dupont et a/, 1976; Niethammer et al, 1976). Correspondence: Dr H. E. M. Kay, Department of Haematology, Royal Marsden Hospital, Fulham Road, London, S.W.3. 521
522
Annotation
Other Histocornputibility Systems The importance of the ABO blood group system is not yet entirely determined: there does not appear to be any difficulty in grafting group 0 marrow into group A recipients and no graft-versus-host (GvH) reaction results. The reverse is more difficult since there may be rejection of group A by group 0 recipients, perhaps on account of high titre immune anti-A, but some successes have nevertheless been recorded (Thomas et al, 1975). On the other hand, the high frequency (70%) of GvH reactions in MLC-compatible sib grafts, and the fact that graft rejection of MLC-matched sib marrow occurs if there has been presensitization, indicate that other unidentified histocompatibility systems are important. Some ingenious tests have been devised to detect the antigens concerned using target cell lysis rather than effector cell stimulation as the end point. Such cell-mediated lympholysis (CML) may be dependent or independent of the presence of antibody, and can be revealed by such means as the prior use ofphytohaemagglutinin or the addition of third party cells (Histocompatibility Testing, 1975;Jeannet & Speck, 1976; Parkman et al, 1976). Preliminary evidence suggests that this histocompatibility system is remote from the MHC and it could, of course, be multiple: its resolution will depend upon analyses similar to those used for the MHC. Meanwhile where more than one MLC-matched sib exists, efforts should be made to determine which is the most compatible by the various CML tests; where there is no choice weshall need to discover what probability of graft rejection or what severity of GvH reaction is to be expected from particular measurements of CMGincompatibility. Obviously this additional knowledge will enhance the chances of trouble-free grafting when all tests indicate compatibility, but conversely the more stringent criteria of compatibility will reduce the opportunities to graft. That is, of course, regrettable but nobody who has had to care for patients with severe GvH reactions will wish to ignore the relevant tests. Instead, we must hope that mcans are found either to reduce the component in the graft responsible for GvH reactions, presumed to be post-thymic T-cells, or, better still, to engender mutual specific tolerance between graft and host (Binz & Wigzell, 1976). As yet it is uncertain how tolerance is achieved in chimeras, whether through clonal deletion on the lines of classical theory, or by the activity of suppressor T-cells (Gcngozian & Urso, 1976);blocking antibodies seem to be of minor importance at most (see Brent et a[, 1976). One way or another there is a good chance that graft tolerance of host could be ensured but the converse may be less easy. Leaving aside ‘genetic resistance’, a phenomenon which may be restricted to certain strains of mice (Trentin, 1976), rejection of a matched graft is almost always due to presensitization as by blood transfusion. In dogs even a single transfusion given I d before whole-body irradiation is fatally preseiisitizing (Storb et a!, 1970). Regimens using procarbazine and ATG can to some extent overcome presensitization in dogs but have been much less effective in man (Storb et al, 1974); thus it is as vital as ever to avoid unnecessary transfusions and never, ever, to use family members as donors in these circumstances, except a spouse or offspring who would not induce immunity to sib-antigens any more often than would an unrelated donor. Graft-uersus-Host Reactions Lack of tolerance by grafted lymphocytes towards the host cells leads to GvH reactions, a phenomenon first described 20 years ago (Barnes et al, 1956). All the accumulated evidence
Annotation
523
since then has confirmed the notion that the severity of GvH reactions is a product of three factors-the antigenic disparity, the presence of infection and the quantity of prior cytotoxic therapy (radiation or drugs) to the host. The first of these alone is seldom enough to cause a reaction and the absence of the latter factors in early-diagnosed and grafted SCID largely accounts for the infrequency and mildness of the reactions in these cases. In aplasia and leukaemia, on the other hand, the diverse and multitudinous flora including many endogenous viruses, and the need to give immunosuppressive and anti-leukaemic agents, provide all the circumstances for GvH reactions. Experimentally controlled infection of grafted, germ-free mice gives some idea of which organisms might be most noxious in this context, e.g. Salmonellae are pathogenic, but Lactobacillus carei, serratia, bacteroides, clostridia and the Bittner, leukaemia and LCM viruses are not (Pollard et al, 1976). Extrapolation to man emphasizes the need for strict microbiological control of exogenous organisms; whatever may be the merits ofprotective isolation and decontamination procedures in other circumstances, there is general agreement on the need for a high standard of asepsis and for some reduction of bacterial flora in bone marrow transplants. Of course, it is virtually impossible to suppress viruses such as herpes and cytomegalovirus(CMV) and these agents, moreover, in addition to their possible enhancement of GvH can also precipitate severe, sometimes fatal, illness in the immunosuppressed patient either early or late after grafting. This is because recovery of immune competence after an allogeneic graft is slow and incomplete; even a year later, despite the return of lymphocyte and immunoglobulin levels to the normal range (or above), the immune response to specific antigens remains very much depressed and there persists a liability to severe zoster or hepatitis (Thomas et al, 1975). The components of the immune system after a graft may be of donor alone or of mixed origin-donor T-cells and recipient B-cells; the precise outcome depends on the nature and intensity of the preconditioning regimen. Thus, paradoxically, those with SCID who require no preconditioning to accept an allograft can expect to gain the best immune function.
Severe Combined Immunity Deficiency The first babies grafted for this condition are now 6 or 7 years old and enjoy good health. Mostly they are split chimeras with a donor lymphoid system but with native red cells, granulocytes and platelets. Where a compatible sib exists the transplant is usually a simple affair since no pre-transplant immunosuppression is required, a limited number of cells (5 x Io6/kg) is enough, and GvH reactions, if they occur, are mild (Van Bekkum, 1972). Of course only a minority of babies have a sib, or rarely another relative, who is compatible, so for the majority the search for unrelated donors must continue. Meanwhile the favourable factors of low cell requirement and relative microbiological cleanliness can sometimes enable unmatched fetal liver cells to supply a lymphoid graft. In some instances this has caused GvH reactions but in one or two recent cases a donor liver of less than 14 weeks gestation has apparently yielded a tolerant graft (Keightley et al, 1975; Buckley et al, 1976). The situation in other syndromes of immunity deficiency is more complex since a partial degree of natural immunity must be depressed to allow the graft to be accepted. The existence of one long-standing graft in a boy with the Wiskott-Aldrich syndrome is a hopeful portent (Bach et al, 1968).
524
Annotation
Bone Marrow Aphia The potential for grafting in bone marrow aplasia can be gauged from the record of totally compatible grafts, i.e. using an identical twin as donor. Thomas quotes five successful grafts in this situation and believes that in only one instance has a graft failed to take, given adequate numbers of cells and enough time for proliferation. This evidence makes it unlikely that it is the environment of the haemopoietic cell which is to blame for aplasia and that most often therc is a sheer lack of competent haemopoietic stem-cells. The problems, then, are those of compatibility. Even a histocompatible sib graft needs immunosuppressivc preconditioning and the standard method has employcd high dose cyclophosphamidefrom the fifth to the second day before the graft. As originally devised by Santos (1967) in mice the cyclophosphamide is preceded by a sensitizing transfusion of donor cells (Thomas et al, 1975). Hypothetically these cells trigger the competent recipient lymphocytes into a state of proliferation which renders them selectively susceptible to the cyclophosphamide. The method certainly works in mice, dogs and man but carries hazards attributable to the size of the dose of cyclophosphamide. Cardiotoxicity and damage to the urinary epithelium are immediate and specific effects, and thc former may be rapidly fatal. Later cffects on immunity and on the respiratory and gastrointestinal system may also be severe but are difficult to disentangle from other causesdisease, prior infection and GvH reaction. A possible alternative, therefore, is the use of antithymocyte serum, which is less immediately toxic, but which, by virtue of its anti-stem cell activity, is inhibitory to the grafted cells, and the yield of successful engraftment is lower (Speck et al, 1976). The second advantage claimed for ATG is the avoidance of GvH reactions, but at present, perhaps because of limited supplies of reliable ATG, the cyclophosphamide method is still most often used. A good comparative study is necded. The pattern of results of the cyclophosphaniide-assisted transplants is now becoming clear (Thomas et a!, 1975). In minimally transfused unsensitized recipients the vast majority should gain a functional graft but, despite prophylactic methotrexate, the majority will encounter GvH reactions of greater or lesser severity and, among the former, many will die despitc the therapeutic use of ATG. If these casualties are added to infective deaths occurring during and soon after establishment of the graft a survival rate of about 50% is found. This figure is dependent on many factors of which the age of patient and recipient is critical; most successful transplants are younger than 20 and few do well over the age of 30. Other dcterniinant factors are the condition of the recipient and the experience and selective practice of the transplant team; variation in these factors invalidates any generalization about success rate. Meanwhile for the majority of potential recipients who lack a compatible sib donor thcre is some hope through the use of adjuvant semicompatible temporary transplants. The proponents of this scheme are Speck and Jcannet (Speck et ul, 1976) who have claimed that liaemopoietic recovery is facilitated in bone-marrow aplasia if HLA-haplotype-similar bone marrow is given in conjunction with ATG. In these circumstances there is a temporary proliferation of the graftcd cells but permanent recovery is dependent on the restoration of the patient’s own bone-marrow cells to normal activity. The mechanism is unknown. An attempt to evaluate this approach by a controlled trial using grafe plus ATG, ATG alone, and supportive treatment alone is in progress. A lot will depend upon the existence of a potent ATG with minimal anti-stem cell activity.
Annotation
525
Leu kaemia In treating leukaemia by substitution for the patients haemopoietic cells of a normal graft, all the problems of grafting are at their maximum and there is the additional major problem of discovering a reliable regime to eradicate the leukaemic clone. In Seattle a combination of cyclophosphamide and whole body irradiation has been tried with some success (Thomas et al, 1975). Failure is due to early infective mortality, graft rejection, GvH reaction, late infective deaths and recurrence of leukaemia in host or graft cells leaving 27% (20 out of 73) in remission at 3 months. That may appear a low return for heroic clinical endeavours but these efforts have been achieved in patients for whom standard treatment has already failed and who have already withstood large doses of cytotoxic agents. Treatment at an earlier stage should yieId a higher survival in remission rate and, furthermore, in the case of acute myeloid leukaemia (AML) the longest remissions represent some of the very few cases where eradication of the leukaemia appears to have been achieved. If it is the case that both acute and chronic myeloid leukaemia can only be treated successfully by replacement with foreign bone marrow-perhaps because there are usually no normal haemopoietic cells in the patients marrow at the time of diagnosis?-then efforts at bone marrow grafting are to be encouraged. A more elaborate schedule aimed at eradication of the leukaemic cells using a powerful sequence of cytosine arabinoside, thioguanine, daunorubicin, cyclophosphamide and whole-body irradiation is giving some encouraging early results (Cline ct al, 1975) and it may soon be reasonable to try this as a first treatment in AML where there is a good donor, i.e. a young fully-compatible sib-best of all an identical twin. Meanwhile experiments have been done to show whether an immune reaction of the graft can operate usefully against any residual leukaemic cells : a small effect is claimed but it is doubtful whether this could be of significant value (Rortin et al, 1976). Future Progress Bone-marrow transplantation may be the conclusive treatment of a wide range of blood disorders, especially perhaps thalassaemia and the haenioglobinopathies, diseases which until now have seldom been treated in this way. Twenty years ago these vast possibilities seemed to be just round the corner and are perhaps only slightly closer today; but if progress in the understanding and the creation of tissue tolerance could advance one more step the chances would be within reach and would certainly traiisform the practice of haematology. Dcpartmrnt of Haewiatology, Roya 1 Marsdorz Hospital, London,S. w . ~
H. E. M. KAY
REFERENCES BACH,F.H., ALBERTINI, R.J., ANDERSON, J.L., Joo, P. & BORTIN, M.M. (1968) Bone marrow transplantation in a patient with the Wiskott-Aldrich syndrome. Lancet, ii, 1364. BARNES, D.W.H.,ILBERY, P.L.T.&LouTIT,J.F. (1956) Avoidance of secondary disease in radiation chimera. Nature, 177, 452.
BEKKUM, D.W. (1972) Use and abuse of hacmopoietic cell grafts in irnmune deficiency diseases. Transplantation Reviews, 9, 3 . BINZ,H. & WIGZELL, H . (1976) Successful induction of specific tolerance to transplantation antigens using auto-immunisationagainst the recipient's own natural antibodies. Nature, 262, 294. VAN
526
Annotation
BORTIN,M.M., TRUITT,R.L., RIMM, A.A., SALTZATEIN,E.C. & ROSE,W.C. (1976) Graft-versusleukaemia for AKR spontaneous leukaemialymphoma. Proceedings ofPierre L‘Esperance Memorial Symposium (in press). BRENT, L., BROOKS,C.G., MEDAWAR,P.B. & SIMPSON,E. (1976) Transplantation tolerance. British Medical Bulletin, 32, 101. BUCKLEY, R.H., WHISNANT, J.K., SCHIFF, R.I., GILBERTSON, R.B., HUANG,A.T. & PLATT,M.S. (1976) Correction of severe combined immunodeficiency by fetal liver cells. New EnglandJournal OJ’ Medicine, May 13, p 1076. CLINE,M.J., GALE,R.P., STIEHM,E.R., OPELZ,G., YOUNG,L.S., FEIG,S.A. & FAHEY,J.L. (1975) Bone marrow transplantation in man. Annals .f Iiiteriial Medicine, 83, 691. DUPONT,B., HANSEN,J.A. & YUNIS,J.E. (1976) Advances in Immunology, 23 (in press). GENGOZIAN, N. & URSO,P. (1976) Functional activity of T and B lymphocytes in radiation chimeras. Proceedings of Pierre L‘Esperance Memorial Sympasirrna (in press). HISTOCOMPATIBILITY TESTING (1975) Report of the W International Histocotiipatibility Workshop and Confretice. Munksgaard, Copenhagen. JEANNET, M. & SPECK,B. (1976) Evaluation de neuveaux tests d’histocompatibilits pour la transplantation de moelle osseuse. Schweirerische Gesampte Hematologie (in press). KEIGHTLEY, R.G., LAWTON, A.R., COOPER,M.D. & YUNIS,E. J. (1975) Successful fetal liver transplantation in a child with severe combined inimunodeficiency. Lancet, ii, 850. KOCH, C., HENRIKSEN, K., JUHL, F., WIIK, A. & FABER, V. (1973) Bone marrow transplantation from an HL-A non-identical, but mixed-lymphocyteculture identical, donor. Lancet, i, I 146. NIETHAMMER, D., GOLMAN, S.F. & HAAS,R.J. (1976) Transplantation Proceedings (in press). PARKMAN, R., ROSEN,F.S., RAPPEPORT, J., CAMITI‘A, B., LEVEY, R.L. & NATHAN, D.G. (1976) Detection of genetically determined histocompatibility antigen differences between HL-A identical and MLC nonreactive siblings. Transplantarion, 21, I 10.
POLLARD, M., CHANG,C.F. & KUNWAR, K. (1976) The role of microflora in development of graft vs. host disease (GVHD). Proceedings of Pierre L’Esperance Memorial Symposium (in press). VAN ROOD, J.J., VAN LEEUWEN, A., PARLEVLIET, J., TERMIJELEN, A. & KEUNING, J.J. (1975) In: Histocompatibility Testing, p 629. Munksgaard Copenhagen. VAN ROOD,J.J., VAN LEEUWEN, A,, TERMIJTKLEN, A. & KEUNING, J.J. (1976) Major and niinor histocompatibility system in man and their importance in bone marrow transplantation. Proceedings o/ Pierre L’Esperance Memorial Symposium (in press). SANTOS, G.W. (1967) Induction of specific tolerance to soluble and particulate antigens in man and tissue allografts in mice with cyclophosphaniide. Experimental Hematology, 14,32. SHEEHY,M.J., SONDEL,P.M., BACH,F.H., SOPORI, M.L. & BACH,M.L. (1976) In: Histocontpatibility Testing, p 569. Munksgaard, Copenhagen. SPECK,B., BUCKNER, C.D., CORNU,P. & JEANNET, M. (1976) Rationale for the use ofALC as sole immunosuppressant in allogeneic bone marrow transplantation in aplastic aneniia. Transplantation Proceedirigs (in press). STORE,R., EPSTEIN, R.B., RUDOLPH R.H. & THOMAS, E.D. (1970) The effects of prior transfusion on marrow grafts between histocompatible canine siblings.Journal of Immunology, 10s.627. STORB,R., FLOERSHEIM, G.L., WEIDEN,P.L., KOLB, H.-J., LERNER,K.G., SCHROEDER,M.-L. & THOMAS, E.D. (1974) Effect of prior blood transfusion on marrow grafts: abrogation of sensitization by procarbazine and antithymocyte serum. JoMrnal of Imnitmology, 112. 1508. THOMAS, E. D., STORB,R., CLIFE,R.A., FEFER,A., JOHNSON,F.L., NBIMAN,P.A., LERNER,K.G., GLUCKSBERG, H. & BUCKNER, C.D. (197s) Bonemarrow transplantation. New England Jowrnal of Medicine, April 17, p 832, and April 24, p 895. TRENTIN, J.J. (1976) Xenogeneic and genetic resistance to bone marrow transplantation. Proceedings of Pierre L‘Espernnce Memorial Sympositriw (in press).
Annotation BONE MARROW TRANSPLANTATION There are now about roo people alive whose haemopoietic function has been dependent for I year or longer on a bone-marrow graft. W e can be certain that virtually all would, but for their graft, have succumbed to bone marrow aplasia, acute leukaemia or combined immunity deficiency. It is an appropriate moment to examine the current bone marrow transplant prospectus.
Histoco mpa t i bilty Foremost among the requisites for successful transplantation is a detailed understanding of tissue compatibility, in particular the major histocompatibility complex (MHC). Genetic analysis has shown a broadly similar constitution for all species studied-mouse, rat, dog, monkey and man-in the form of a number of closely linked genes; two of these in man code for antigens which are serologically determined (SD) and have become well known as the HLA loci A and B; others code for determinants which either induce a response by foreign lymphocytes (LD or D locus) or are immune-associated (IA), i.e. effector rather than inducer (see Histocompatibility Testing, 1975). It is the D locus which is receiving most attention and a number of methods have been devised for its analysis. For example, in the primed lymphocyte test (PLT) (Sheehyet al, 1976), responder lymphocytes are stimulated first by an inoculation of priming foreign lymphocytes; the reaction reaches its peak in 5-6 d and then falls to zero; subsequent addition of a second inoculum of stimulator cells produces a very rapid ‘second-set’ response measurable at 24 h if the two populations ofstimulator cells share one or more LD antigens. Alternatively lymphocytes from D homozygotes (painstakingly gleaned from the progeny of consanguineous marriages) can be enlisted to form a panel of typing cells; failure of such honiozygous cells to stimulate responder cells indicates one haplotype of the responder. With proper controls it may be possible to use cultured cell-lines derived from a typing panel thus providing an almost unlimited supply of reference cells. Thirdly and perhaps of the greatest practical use, the D antigens, although initially detected through mixed lymphocyte culture (MLC), can also induce, and be detected on B-lymphocytes by, serum antibodies, which thus provide an alternative system of analysis (Van Rood et al, 1975). Van Rood et al (1976) have shown serologically that the number of D alleles in man is not impossibly large since 60% of a sample population could be fully typed by as few as five sera. Despite some discrepancies between the methods and the probable subdivision of the D system into at least two parts, there is thus a reasonable hope that unrelated donors could be found for most recipients who would give in an MLC test the same degree of identity as an identical sib. The occasional success of MLC-compatible, SD (A or B)-different grafts in severe combined immunity deficiency (SCID) encourages the belief that the A and B differences are relatively unimportant and could be ignored (Koch et a/, 1973 ; Dupont et a/, 1976; Niethammer et al, 1976). Correspondence: Dr H. E. M. Kay, Department of Haematology, Royal Marsden Hospital, Fulham Road, London, S.W.3. 521
522
Annotation
Other Histocornputibility Systems The importance of the ABO blood group system is not yet entirely determined: there does not appear to be any difficulty in grafting group 0 marrow into group A recipients and no graft-versus-host (GvH) reaction results. The reverse is more difficult since there may be rejection of group A by group 0 recipients, perhaps on account of high titre immune anti-A, but some successes have nevertheless been recorded (Thomas et al, 1975). On the other hand, the high frequency (70%) of GvH reactions in MLC-compatible sib grafts, and the fact that graft rejection of MLC-matched sib marrow occurs if there has been presensitization, indicate that other unidentified histocompatibility systems are important. Some ingenious tests have been devised to detect the antigens concerned using target cell lysis rather than effector cell stimulation as the end point. Such cell-mediated lympholysis (CML) may be dependent or independent of the presence of antibody, and can be revealed by such means as the prior use ofphytohaemagglutinin or the addition of third party cells (Histocompatibility Testing, 1975;Jeannet & Speck, 1976; Parkman et al, 1976). Preliminary evidence suggests that this histocompatibility system is remote from the MHC and it could, of course, be multiple: its resolution will depend upon analyses similar to those used for the MHC. Meanwhile where more than one MLC-matched sib exists, efforts should be made to determine which is the most compatible by the various CML tests; where there is no choice weshall need to discover what probability of graft rejection or what severity of GvH reaction is to be expected from particular measurements of CMGincompatibility. Obviously this additional knowledge will enhance the chances of trouble-free grafting when all tests indicate compatibility, but conversely the more stringent criteria of compatibility will reduce the opportunities to graft. That is, of course, regrettable but nobody who has had to care for patients with severe GvH reactions will wish to ignore the relevant tests. Instead, we must hope that mcans are found either to reduce the component in the graft responsible for GvH reactions, presumed to be post-thymic T-cells, or, better still, to engender mutual specific tolerance between graft and host (Binz & Wigzell, 1976). As yet it is uncertain how tolerance is achieved in chimeras, whether through clonal deletion on the lines of classical theory, or by the activity of suppressor T-cells (Gcngozian & Urso, 1976);blocking antibodies seem to be of minor importance at most (see Brent et a[, 1976). One way or another there is a good chance that graft tolerance of host could be ensured but the converse may be less easy. Leaving aside ‘genetic resistance’, a phenomenon which may be restricted to certain strains of mice (Trentin, 1976), rejection of a matched graft is almost always due to presensitization as by blood transfusion. In dogs even a single transfusion given I d before whole-body irradiation is fatally preseiisitizing (Storb et a!, 1970). Regimens using procarbazine and ATG can to some extent overcome presensitization in dogs but have been much less effective in man (Storb et al, 1974); thus it is as vital as ever to avoid unnecessary transfusions and never, ever, to use family members as donors in these circumstances, except a spouse or offspring who would not induce immunity to sib-antigens any more often than would an unrelated donor. Graft-uersus-Host Reactions Lack of tolerance by grafted lymphocytes towards the host cells leads to GvH reactions, a phenomenon first described 20 years ago (Barnes et al, 1956). All the accumulated evidence
Annotation
523
since then has confirmed the notion that the severity of GvH reactions is a product of three factors-the antigenic disparity, the presence of infection and the quantity of prior cytotoxic therapy (radiation or drugs) to the host. The first of these alone is seldom enough to cause a reaction and the absence of the latter factors in early-diagnosed and grafted SCID largely accounts for the infrequency and mildness of the reactions in these cases. In aplasia and leukaemia, on the other hand, the diverse and multitudinous flora including many endogenous viruses, and the need to give immunosuppressive and anti-leukaemic agents, provide all the circumstances for GvH reactions. Experimentally controlled infection of grafted, germ-free mice gives some idea of which organisms might be most noxious in this context, e.g. Salmonellae are pathogenic, but Lactobacillus carei, serratia, bacteroides, clostridia and the Bittner, leukaemia and LCM viruses are not (Pollard et al, 1976). Extrapolation to man emphasizes the need for strict microbiological control of exogenous organisms; whatever may be the merits ofprotective isolation and decontamination procedures in other circumstances, there is general agreement on the need for a high standard of asepsis and for some reduction of bacterial flora in bone marrow transplants. Of course, it is virtually impossible to suppress viruses such as herpes and cytomegalovirus(CMV) and these agents, moreover, in addition to their possible enhancement of GvH can also precipitate severe, sometimes fatal, illness in the immunosuppressed patient either early or late after grafting. This is because recovery of immune competence after an allogeneic graft is slow and incomplete; even a year later, despite the return of lymphocyte and immunoglobulin levels to the normal range (or above), the immune response to specific antigens remains very much depressed and there persists a liability to severe zoster or hepatitis (Thomas et al, 1975). The components of the immune system after a graft may be of donor alone or of mixed origin-donor T-cells and recipient B-cells; the precise outcome depends on the nature and intensity of the preconditioning regimen. Thus, paradoxically, those with SCID who require no preconditioning to accept an allograft can expect to gain the best immune function.
Severe Combined Immunity Deficiency The first babies grafted for this condition are now 6 or 7 years old and enjoy good health. Mostly they are split chimeras with a donor lymphoid system but with native red cells, granulocytes and platelets. Where a compatible sib exists the transplant is usually a simple affair since no pre-transplant immunosuppression is required, a limited number of cells (5 x Io6/kg) is enough, and GvH reactions, if they occur, are mild (Van Bekkum, 1972). Of course only a minority of babies have a sib, or rarely another relative, who is compatible, so for the majority the search for unrelated donors must continue. Meanwhile the favourable factors of low cell requirement and relative microbiological cleanliness can sometimes enable unmatched fetal liver cells to supply a lymphoid graft. In some instances this has caused GvH reactions but in one or two recent cases a donor liver of less than 14 weeks gestation has apparently yielded a tolerant graft (Keightley et al, 1975; Buckley et al, 1976). The situation in other syndromes of immunity deficiency is more complex since a partial degree of natural immunity must be depressed to allow the graft to be accepted. The existence of one long-standing graft in a boy with the Wiskott-Aldrich syndrome is a hopeful portent (Bach et al, 1968).
524
Annotation
Bone Marrow Aphia The potential for grafting in bone marrow aplasia can be gauged from the record of totally compatible grafts, i.e. using an identical twin as donor. Thomas quotes five successful grafts in this situation and believes that in only one instance has a graft failed to take, given adequate numbers of cells and enough time for proliferation. This evidence makes it unlikely that it is the environment of the haemopoietic cell which is to blame for aplasia and that most often therc is a sheer lack of competent haemopoietic stem-cells. The problems, then, are those of compatibility. Even a histocompatible sib graft needs immunosuppressivc preconditioning and the standard method has employcd high dose cyclophosphamidefrom the fifth to the second day before the graft. As originally devised by Santos (1967) in mice the cyclophosphamide is preceded by a sensitizing transfusion of donor cells (Thomas et al, 1975). Hypothetically these cells trigger the competent recipient lymphocytes into a state of proliferation which renders them selectively susceptible to the cyclophosphamide. The method certainly works in mice, dogs and man but carries hazards attributable to the size of the dose of cyclophosphamide. Cardiotoxicity and damage to the urinary epithelium are immediate and specific effects, and thc former may be rapidly fatal. Later cffects on immunity and on the respiratory and gastrointestinal system may also be severe but are difficult to disentangle from other causesdisease, prior infection and GvH reaction. A possible alternative, therefore, is the use of antithymocyte serum, which is less immediately toxic, but which, by virtue of its anti-stem cell activity, is inhibitory to the grafted cells, and the yield of successful engraftment is lower (Speck et al, 1976). The second advantage claimed for ATG is the avoidance of GvH reactions, but at present, perhaps because of limited supplies of reliable ATG, the cyclophosphamide method is still most often used. A good comparative study is necded. The pattern of results of the cyclophosphaniide-assisted transplants is now becoming clear (Thomas et a!, 1975). In minimally transfused unsensitized recipients the vast majority should gain a functional graft but, despite prophylactic methotrexate, the majority will encounter GvH reactions of greater or lesser severity and, among the former, many will die despitc the therapeutic use of ATG. If these casualties are added to infective deaths occurring during and soon after establishment of the graft a survival rate of about 50% is found. This figure is dependent on many factors of which the age of patient and recipient is critical; most successful transplants are younger than 20 and few do well over the age of 30. Other dcterniinant factors are the condition of the recipient and the experience and selective practice of the transplant team; variation in these factors invalidates any generalization about success rate. Meanwhile for the majority of potential recipients who lack a compatible sib donor thcre is some hope through the use of adjuvant semicompatible temporary transplants. The proponents of this scheme are Speck and Jcannet (Speck et ul, 1976) who have claimed that liaemopoietic recovery is facilitated in bone-marrow aplasia if HLA-haplotype-similar bone marrow is given in conjunction with ATG. In these circumstances there is a temporary proliferation of the graftcd cells but permanent recovery is dependent on the restoration of the patient’s own bone-marrow cells to normal activity. The mechanism is unknown. An attempt to evaluate this approach by a controlled trial using grafe plus ATG, ATG alone, and supportive treatment alone is in progress. A lot will depend upon the existence of a potent ATG with minimal anti-stem cell activity.
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525
Leu kaemia In treating leukaemia by substitution for the patients haemopoietic cells of a normal graft, all the problems of grafting are at their maximum and there is the additional major problem of discovering a reliable regime to eradicate the leukaemic clone. In Seattle a combination of cyclophosphamide and whole body irradiation has been tried with some success (Thomas et al, 1975). Failure is due to early infective mortality, graft rejection, GvH reaction, late infective deaths and recurrence of leukaemia in host or graft cells leaving 27% (20 out of 73) in remission at 3 months. That may appear a low return for heroic clinical endeavours but these efforts have been achieved in patients for whom standard treatment has already failed and who have already withstood large doses of cytotoxic agents. Treatment at an earlier stage should yieId a higher survival in remission rate and, furthermore, in the case of acute myeloid leukaemia (AML) the longest remissions represent some of the very few cases where eradication of the leukaemia appears to have been achieved. If it is the case that both acute and chronic myeloid leukaemia can only be treated successfully by replacement with foreign bone marrow-perhaps because there are usually no normal haemopoietic cells in the patients marrow at the time of diagnosis?-then efforts at bone marrow grafting are to be encouraged. A more elaborate schedule aimed at eradication of the leukaemic cells using a powerful sequence of cytosine arabinoside, thioguanine, daunorubicin, cyclophosphamide and whole-body irradiation is giving some encouraging early results (Cline ct al, 1975) and it may soon be reasonable to try this as a first treatment in AML where there is a good donor, i.e. a young fully-compatible sib-best of all an identical twin. Meanwhile experiments have been done to show whether an immune reaction of the graft can operate usefully against any residual leukaemic cells : a small effect is claimed but it is doubtful whether this could be of significant value (Rortin et al, 1976). Future Progress Bone-marrow transplantation may be the conclusive treatment of a wide range of blood disorders, especially perhaps thalassaemia and the haenioglobinopathies, diseases which until now have seldom been treated in this way. Twenty years ago these vast possibilities seemed to be just round the corner and are perhaps only slightly closer today; but if progress in the understanding and the creation of tissue tolerance could advance one more step the chances would be within reach and would certainly traiisform the practice of haematology. Dcpartmrnt of Haewiatology, Roya 1 Marsdorz Hospital, London,S. w . ~
H. E. M. KAY
REFERENCES BACH,F.H., ALBERTINI, R.J., ANDERSON, J.L., Joo, P. & BORTIN, M.M. (1968) Bone marrow transplantation in a patient with the Wiskott-Aldrich syndrome. Lancet, ii, 1364. BARNES, D.W.H.,ILBERY, P.L.T.&LouTIT,J.F. (1956) Avoidance of secondary disease in radiation chimera. Nature, 177, 452.
BEKKUM, D.W. (1972) Use and abuse of hacmopoietic cell grafts in irnmune deficiency diseases. Transplantation Reviews, 9, 3 . BINZ,H. & WIGZELL, H . (1976) Successful induction of specific tolerance to transplantation antigens using auto-immunisationagainst the recipient's own natural antibodies. Nature, 262, 294. VAN
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BORTIN,M.M., TRUITT,R.L., RIMM, A.A., SALTZATEIN,E.C. & ROSE,W.C. (1976) Graft-versusleukaemia for AKR spontaneous leukaemialymphoma. Proceedings ofPierre L‘Esperance Memorial Symposium (in press). BRENT, L., BROOKS,C.G., MEDAWAR,P.B. & SIMPSON,E. (1976) Transplantation tolerance. British Medical Bulletin, 32, 101. BUCKLEY, R.H., WHISNANT, J.K., SCHIFF, R.I., GILBERTSON, R.B., HUANG,A.T. & PLATT,M.S. (1976) Correction of severe combined immunodeficiency by fetal liver cells. New EnglandJournal OJ’ Medicine, May 13, p 1076. CLINE,M.J., GALE,R.P., STIEHM,E.R., OPELZ,G., YOUNG,L.S., FEIG,S.A. & FAHEY,J.L. (1975) Bone marrow transplantation in man. Annals .f Iiiteriial Medicine, 83, 691. DUPONT,B., HANSEN,J.A. & YUNIS,J.E. (1976) Advances in Immunology, 23 (in press). GENGOZIAN, N. & URSO,P. (1976) Functional activity of T and B lymphocytes in radiation chimeras. Proceedings of Pierre L‘Esperance Memorial Sympasirrna (in press). HISTOCOMPATIBILITY TESTING (1975) Report of the W International Histocotiipatibility Workshop and Confretice. Munksgaard, Copenhagen. JEANNET, M. & SPECK,B. (1976) Evaluation de neuveaux tests d’histocompatibilits pour la transplantation de moelle osseuse. Schweirerische Gesampte Hematologie (in press). KEIGHTLEY, R.G., LAWTON, A.R., COOPER,M.D. & YUNIS,E. J. (1975) Successful fetal liver transplantation in a child with severe combined inimunodeficiency. Lancet, ii, 850. KOCH, C., HENRIKSEN, K., JUHL, F., WIIK, A. & FABER, V. (1973) Bone marrow transplantation from an HL-A non-identical, but mixed-lymphocyteculture identical, donor. Lancet, i, I 146. NIETHAMMER, D., GOLMAN, S.F. & HAAS,R.J. (1976) Transplantation Proceedings (in press). PARKMAN, R., ROSEN,F.S., RAPPEPORT, J., CAMITI‘A, B., LEVEY, R.L. & NATHAN, D.G. (1976) Detection of genetically determined histocompatibility antigen differences between HL-A identical and MLC nonreactive siblings. Transplantarion, 21, I 10.
POLLARD, M., CHANG,C.F. & KUNWAR, K. (1976) The role of microflora in development of graft vs. host disease (GVHD). Proceedings of Pierre L’Esperance Memorial Symposium (in press). VAN ROOD, J.J., VAN LEEUWEN, A., PARLEVLIET, J., TERMIJELEN, A. & KEUNING, J.J. (1975) In: Histocompatibility Testing, p 629. Munksgaard Copenhagen. VAN ROOD,J.J., VAN LEEUWEN, A,, TERMIJTKLEN, A. & KEUNING, J.J. (1976) Major and niinor histocompatibility system in man and their importance in bone marrow transplantation. Proceedings o/ Pierre L’Esperance Memorial Symposium (in press). SANTOS, G.W. (1967) Induction of specific tolerance to soluble and particulate antigens in man and tissue allografts in mice with cyclophosphaniide. Experimental Hematology, 14,32. SHEEHY,M.J., SONDEL,P.M., BACH,F.H., SOPORI, M.L. & BACH,M.L. (1976) In: Histocontpatibility Testing, p 569. Munksgaard, Copenhagen. SPECK,B., BUCKNER, C.D., CORNU,P. & JEANNET, M. (1976) Rationale for the use ofALC as sole immunosuppressant in allogeneic bone marrow transplantation in aplastic aneniia. Transplantation Proceedirigs (in press). STORE,R., EPSTEIN, R.B., RUDOLPH R.H. & THOMAS, E.D. (1970) The effects of prior transfusion on marrow grafts between histocompatible canine siblings.Journal of Immunology, 10s.627. STORB,R., FLOERSHEIM, G.L., WEIDEN,P.L., KOLB, H.-J., LERNER,K.G., SCHROEDER,M.-L. & THOMAS, E.D. (1974) Effect of prior blood transfusion on marrow grafts: abrogation of sensitization by procarbazine and antithymocyte serum. JoMrnal of Imnitmology, 112. 1508. THOMAS, E. D., STORB,R., CLIFE,R.A., FEFER,A., JOHNSON,F.L., NBIMAN,P.A., LERNER,K.G., GLUCKSBERG, H. & BUCKNER, C.D. (197s) Bonemarrow transplantation. New England Jowrnal of Medicine, April 17, p 832, and April 24, p 895. TRENTIN, J.J. (1976) Xenogeneic and genetic resistance to bone marrow transplantation. Proceedings of Pierre L‘Espernnce Memorial Sympositriw (in press).
