Serum Levels of IL-7 in Bone Marrow Transplant Recipients: Relationship to Clinical Characteristics and Lymphocyte Count

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Bone Marrow Transplantation, (1999) 23, 783–788  1999 Stockton Press All rights reserved 0268–3369/99 $12.00 http://www.stockton-press.co.uk/bmt Serum levels of IL-7 in bone marrow transplant recipients: relationship to clinical characteristics and lymphocyte count

E Bolotin, G Annett, R Parkman and K Weinberg

Divisions of Research Immunology and Bone Marrow Transplantation and Hematology/Oncology, Department of Pediatrics, Childrens Hospital Los Angeles, University of Southern California School of Medicine, Los Angeles, CA, USA

Summary: interactions with the microenvironment of the bone marrow and lymphopoietic organs. The ability of the stromal cells IL-7 is produced by stromal cells and is the major lym- to support lymphopoiesis after BMT is adversely affected pho- and thymopoietic cytokine. IL-7 induces prolifer- by age, graft-versus-host disease (GVHD), irradiation, ation and differentiation of immature thymocytes, and immunosuppressive therapy and infections. However, the protects thymocytes from apoptosis by induction of bcl- recipients of allogeneic BMT who do not have GVHD and 2 expression. The regulation of IL-7 production is recipients of autologous BMT are also immune poorly characterized, although down-regulation by deficient.10–16 transforming growth factor-␤ (TGF-␤) has been There is growing evidence that production of T lympho- described. We measured the serum levels of IL-7 before cytes is dependent upon interleukin-7 (IL-7). IL-7 is a cyto- and after bone marrow transplant (BMT) in 32 children kine produced by bone marrow and thymic stroma. IL-7 undergoing BMT for genetic diseases (severe combined was originally identified by its ability to induce prolifer- immune deficiency (SCID) and thalassemia), aplastic ation of B cell progenitors in vitro and in vivo and was anemia, and acute lymphoblastic and non-lymphoblas- subsequently shown to stimulate T lymphopoiesis.17–26 tic leukemia (ALL and ANLL). Prior to BMT, the high- Recently, we have shown that administration of IL-7 sig- est IL-7 levels were observed in patients with SCID and nificantly enhances immune recovery in mice after T cell- ALL, ie those patients with genetic or acquired lympho- depleted BMT.27 Therefore, production of IL-7 may be one penia. Patients with thalassemia and ANLL had normal of the mechanisms regulating de novo production of T lym- levels of IL-7. Over the 8 weeks following BMT, the IL- phocytes after BMT. 7 levels of patients with SCID and ALL fell as the absol- In the present study we analyzed serum IL-7 levels by ute lymphocyte count (ALC) increased. No detectable ELISA in patients before and after BMT in relation to the change in IL-7 levels was observed in the patients with patients’ clinical characteristics and absolute lymphocyte thalassemia and ANLL. Levels of IL-7 were highest in count (ALC). We found that lymphopenic patients and the young infants with SCID compared to the age- patients less than 1 years old had higher levels of serum matched controls. Together, the data demonstrate that IL-7. Understanding of the mechanisms of endogenous IL- serum levels of IL-7 in lymphopenic patients are 7 response to lymphopenia may add to understanding of inversely related to patient age and the absolute lym- the mechanism of immune reconstitution after BMT and phocyte count (ALC). The inverse relationship to ALC chemotherapy. suggests that there is either direct regulation of stromal production or more likely, binding of secreted IL-7 to lymphocytes expressing IL-7 receptors. Materials and methods Keywords: interleukin-7; immune reconstitution; immune deficiency; bone marrow transplantation Patients

Normal controls: Sixty-eight samples from controls were Immune deficiency after bone marrow transplantation tested for serum IL-7 levels. All serum samples were (BMT) contributes significantly to morbidity and mortality obtained from blood remaining after routine immunologic from a variety of infections, particularly fungal and viral, testing. Blood samples were obtained from infants undergo- which are normally controlled by functional T and B lym- ing open heart surgery for correction of congenital heart 1–3 phocytes. Lymphopenia is a common finding in patients disease (n ϭ 13), healthy siblings of patients undergoing 4–9 after BMT and its etiology is multifactorial. The growth BMT, or from BMT donors (n ϭ 55). Seventeen controls and differentiation of lymphocytes involve the complex less than 1 years old, 21 children older than 1 year, and thirty adults (Ͼ21 years of age) were included in the study. None of the patients with congenital heart disease had Correspondence: Dr E Bolotin, Divisions of Hematology/Oncology, and Research Immunology and Bone Marrow Transplantation, Childrens Hos- DiGeorge syndrome clinically and by fluorescence in situ pital Los Angeles, 4650 Sunset Boulevard, Los Angeles, CA 90027, USA hybridization for deletion of the DiGeorge syndrome criti- Received 10 August 1998; accepted 16 November 1998 cal region on chromosome 22q11. IL-7 levels in BMT patients E Bolotin et al 784 BMT recipients: All BMT recipients were patients treated (R&D Systems, Minneapolis, MN, USA), according to the on the BMT unit at Childrens Hospital Los Angeles from manufacturer’s instructions. A standard curve was prepared 1992 to 1994. Thirty-two BMT patients were included in for each plate, plotting OD vs different concentrations of the study. Five pre-BMT diagnoses were selected for study recombinant human IL-7. All standards and samples were because they included children of various ages, had either tested in duplicate. normal lymphocyte counts or had congenital or acquired lymphopenias, and had either received or not received Statistical analyses chemotherapy pre-BMT. The diagnostic groups were severe combined immune deficiency (SCID), acute lympho- Mean values and standard deviation were calculated using blastic leukemia (ALL), acute non-lymphoblastic leukemia routine methods. The probability of the differences was (ANLL), ␤-thalassemia major (THAL) and aplastic anemia determined with Student’s t-test, when two groups were (AA). The diagnosis of SCID was based on history and analyzed, and with the use of ANOVA and Student–New- physical examination, lymphocyte count, immunopheno- man–Keuls multiple-range tests to define the unique subsets type, and lack of proliferative responses to mitogens and within the study, when multiple groups were analyzed. All antigens. The patients with ALL had received multi-agent analyses were carried out at the alpha ϭ 0.05 level of sig- chemotherapy and were in either first or second remission. nificance. Correlation statistics were based on the calcu- ANLL patients were transplanted in first remission after lation of the Pearson correlation coefficient. four courses of chemotherapy with dexamethasone, cyto- sine arabinoside, 6-thioguanine, etoposide and adriamycin (DCTER).28 The THAL and AA patients had received sup- Results portive care with transfusions. One patient with AA had received 10 doses of anti-thymocyte globulin (ATG) before Patient characteristics his matched unrelated donor (MUD) BMT. The patient characteristics are shown in Table 1. There BMT preparation, source, and post-BMT care: All patients were seven patients with SCID, 12 with ALL, six with except five received pre-BMT conditioning with busulfan ANLL, three with thalassemia, and four with AA. There (1 mg/kg p.o. every 6 h for 16 doses total) followed by were no statistically significant differences between patients cyclophosphamide (50 mg/kg i.v. daily for four doses). One with regard to age, sex and race (not shown), except for patient with SCID received four doses of anti-thymocyte the SCID patients who were younger than the rest of the globulin (ATG) before his histocompatible BMT, and did patients and were predominantly boys. The mean age of Ϯ not receive marrow ablative therapy. The preparative regi- the patients with SCID was 0.53 0.32 years, compared Ϯ men for the four patients with AA consisted of total lymph- to the mean of 7.0 2.8 years for the rest of the patients. oid irradiation (TLI), cyclophosphamide 50 mg/kg i.v. daily The high proportion of boys in the SCID group was due for two doses, and ATG. to the presence of four patients with X-linked SCID. The GVHD prophylaxis was administered to all patients, type of donor cells used was related to the diagnosis: hap- except those who received autologous marrow. Recipients loidentical, T cell-depleted BMT was only used for the of allogeneic marrow, who were less than 10 years of age SCID patients, autologous BMT only for the ALL and received methotrexate (MTX) 10 mg/m2 on days 1, 3, 6 ANLL patients, and MUD BMT only for the ALL and and 11 after BMT, while those greater than 10 years of age AA patients. received MTX plus cyclosporin A (CsA). Recipients of T cell-depleted marrow were treated with methylprednisolone Normal control 2 mg/kg/day from days 5–18 and ATG every other day for 5–7 days from days 5–18. Recipients of matched unrelated Normal absolute lymphocyte count (ALC): The ALC in the ϫ 3 donor (MUD) marrow received MTX, CSA, and ATG. control group ranged from 1176 to 3986 10 /ml. Higher The research protocols for BMT and investigation of ALC were observed in children less than 1 year old, com- Ϯ ϫ 3 immune function in BMT, normal donors, and cardiac sur- pared to older children and adults (2696 698 10 /ml; Ϯ ϫ 3 Ϯ ϫ 3 gery patients were approved by the Committee on Clinical 2143 1012 10 /ml, 1610 837 10 /ml, Investigations (Institutional Review Board) of the Childrens respectively). Hospital Los Angeles. Normal IL-7 levels: The serum IL-7 levels were low in all Ϯ ϭ Blood samples normal adults (2.82 1.3 pg/ml, n 30) and children over 1 year of age (4.32 Ϯ 3.9 pg/ml, n ϭ 21). However, we Blood samples from BMT recipients were drawn at the time observed significantly higher IL-7 levels in infants (Ͻ1 of admission to the BMT unit and weekly thereafter. After year old) compared to the rest of the normal controls (7.9 centrifugation, the serum samples were frozen in duplicate Ϯ 4.8 pg/ml, P Ͻ 0.05 (Figure 1). There was no statistically Ϫ ° aliquots at 70 C in order to batch specimens for measure- significant correlation between the ALC and serum levels ment. of IL-7 in the control group. Enzyme-linked immunoabsorbent assay ( ELISA ) for detection of IL-7 BMT patients The IL-7 concentration in the serum samples was analyzed Absolute lymphocyte count (ALC): The pre-BMT ALC using a commercially available high sensitivity ELISA-kit varied from 20 to 2786 ϫ 103/ml. Higher ALC were found IL-7 levels in BMT patients E Bolotin et al 785 Table 1 Preclinical characteristics and bone marrow source in BMT patients

Diagnosis Sex Age (years) Marrow source (F/M) mean ± s.d. Allo Auto Mud Haplo

SCID 2/5 0.53 ± 0.32 1 6 (n ϭ 7) ALL 6/6 6.5 ± 3.5 5 4 3 (n ϭ 12) ANLL 2/4 7.25 ± 2.9 4 2 (n ϭ 6) AA 2/2 6.0 ± 3.0 3 1 (n ϭ 4) THAL 1/2 10.25 ± 3.5 3 (n ϭ 3) Total 13/19 4.6 ± 3.98 16 6 4 6

18 60 IL-7 600 16 ALC 14 50 500 12 10 n = 17 40 400

8 /ml 3 pg/ml n = 21 6 30 300 10 4 n = 30 × 2 IL-7 pg/ml 0 20 200 ALC Infants, <1 y.o. Children, >1 y.o. Adults 10 100 Figure 1 Serum IL-7 levels in normal controls. An increase in serum Ͻ levels of IL-7 is noted in children 1 year old or less (P 0.05). All values 0 0 are mean Ϯ s.d. Pre-BMT Day 9-16 Post-BMT (6-8 weeks) in ANLL, AA and THAL patients than SCID and ALL Figure 3 Serum level of IL-7 and ALC in SCID patients. The highest patients. Patients with SCID had the lowest ALC (Figure level of serum IL-7 was observed at the time of the ALC nadir. All values 2). The ALC of the patients with ALL was intermediate are mean Ϯ s.e. between those with SCID and those with ANLL, AA, and thalassemia. Lymphopenia was seen in all patients after BMT. The (Table 2, Figure 2). The highest levels were found in SCID lowest ALC was observed between day 9 and 16. The ALC and ALL patients (33 Ϯ 5.2 pg/ml, and 16.5 Ϯ 4.1 pg/ml, began to increase by the third week post-BMT, but the respectively). IL-7 levels in SCID patients were signiﬁ- patients remained lymphopenic throughout the period of the cantly higher than in age-matched controls. Lower levels study (8 weeks after BMT). of IL-7 were found pre-transplant in the ANLL (2.8 Ϯ 1.2 pg/ml ), AA (3.12 Ϯ 2.8 pg/ml), and THAL (8.0 Ϯ 1.8 pg/ml) patients. The pre-transplant level of IL-7 in the IL-7 levels BMT patients was inversely related to the pre-transplant Pre-transplant IL-7 levels: The pre-transplant levels of IL- ALC (r ϭϪ0.38, P Ͻ 0.05). 7 in the BMT patients was related to the the diagnosis Post-transplant IL-7 levels: The levels of IL-7 were meas-

35 ALC 5000 ured weekly over the ﬁrst 8 weeks after BMT (Table 2). 4500 30 IL-7 The levels of IL-7 throughout the post-BMT period corre- 4000 lated with the pre-transplant levels (r ϭ 0.882, P Ͻ 0.05). 25 3500 /ml

3 When analyzed separately, serum IL-7 levels in patients 20 3000

2500 10 with SCID and ALL were signiﬁcantly correlated with the 15 2000 × ALC (Figures 3 and 4). In the SCID and ALL groups, the 1500 IL-7 pg/ml 10

ALC highest level of serum IL-7 was found at the time of mini- 1000 5 mal ALC; with the recovery of the ALC, the IL-7 level 500 ϭϪ ϭϪ 0 0 decreased (r 0.432 for ALL, and r 0.39 for SCID, SCID ALL ANLL AA THAL P Ͻ 0.05) (Figures 3 and 4). In the ANLL, AA and THAL Figure 2 Pretransplant IL-7 levels and ALC in BMT patients. An inverse patients, no correlation between post-BMT serum IL-7 lev- correlation between IL-7 levels and ALC is noted prior to BMT. The ALC els and ALC was observed. In these patients, the serum IL- in normal controls ranged from 1176 to 3986 ϫ 103/ml. 7 levels were signiﬁcantly lower than predicted for the IL-7 levels in BMT patients E Bolotin et al 786 Table 2 Serum levels of IL-7 pre- and post-transplantation

Diagnosis Serum Il-7 levels (pg/ml)

Post-BMT (weeks) Pre- BMT 1 2 3 4 5 6–8

SCID 33.0 Ϯ 5.2 45.6 Ϯ 3.8 39.8 Ϯ 6.8 39.9 Ϯ 7.9 24.8 Ϯ 2.5 33.8 Ϯ 4.2 17.4 Ϯ 3.4 (n ϭ 7) ALL 16.5 Ϯ 4.1 16.4 Ϯ 2.3 18.2 Ϯ 1.7 14.5 Ϯ 3.1 12.6 Ϯ 3.7 3.2 Ϯ 1.4 11.6 Ϯ 2.6 (n ϭ 12) ANLL 2.8 Ϯ 12 8.0 Ϯ 1.3 3.6 Ϯ 1.1 3.7 Ϯ 1.2 2.5 Ϯ 0.9 2.5 Ϯ 1.0 ND (n ϭ 6) AA 3.1 Ϯ 2.8 4.1 Ϯ 2.4 3.6 Ϯ 3.0 7.3 Ϯ 3.2 4.1 Ϯ 2.0 6.3 Ϯ 2.3 4.0 Ϯ 2.0 (n ϭ 4) THAL 8.0 Ϯ 1.8 4.4 Ϯ 1.1 4.5 Ϯ 1.3 8.3 Ϯ 2.3 6.1 Ϯ 1.5 6.1 Ϯ 1.3 5.9 Ϯ 1.9 (n ϭ 3)

Values of IL-7 are expressed as mean Ϯ s.d. SCID ϭ severe combined immunodeﬁciency; ALL ϭ acute lymphocytic leukemia; ANLL ϭ acute non-lymphocytic leukemia; AA ϭ aplastic anemia; THAL ϭ thalassemia.

25 IL-7 800 lysis or non-speciﬁc uptake. IL-7 is made by stroma from ALC 700 fetal liver, thymus, and bone marrow. The IL-7 producing 20 cell in the mouse thymus is an MHC class II-bearing epi- 600 thelial cell.29 The IL-7 promoter sequence has a structure

500 /ml 15 3 typical of housekeeping genes (no TATAA or CAAT

400 10 boxes, large number of CpG dinucleotides), and it is not × 10 300 known whether IL-7 gene expression by stromal cells is IL-7 pg/ml ALC up-regulated by any external stimuli.30 Recent data indicate 200 5 that IL-7 production is negatively regulated by TGF-␤.31 100 Studies of mice with GVHD have suggested that IL-7 pro- 0 0 duction may also be down-regulated by IL-1 and interferon- Pre-BMT Day 9-16 Post-BMT ␥ (IFN-␥).32 (6-8 weeks) IL-7 consumption by IL-7R-bearing cells is probably Figure 4 Serum IL-7 levels and ALC in patients with ALL. All values rapid and extensive. In a previous study of IL-7 adminis- are mean Ϯ s.e. tration in a murine model of BMT, IL-7 levels were unde- tectable within 30 min of i.v. administration of recombinant human IL-7 (E Bolotin, unpublished observations). IL-7R degree of lymphopenia. In all BMT patients IL-7 levels did not correlate with the incidence of GVHD and type of BMT are expressed by nearly all circulating lymphocytes as well conditioning regimen (chemotherapy and/or TLI). as many progenitors. The number of such IL-7R-bearing cells is likely to be decreased in lymphopenic patients, in whom the absolute number of lymphocytes is depressed. In Discussion the present study, the patients with SCID were most lymphopenic and thus most likely to have abnormal clearance The present study examined the relationship of serum IL- of IL-7. In addition, the patients with X-SCID in the present ␥ 7 levels to lymphocyte recovery in the early period after study have a specific defect in the c subunit of the IL-7R, clinical BMT. Our results indicate that in younger and lym- making it unlikely that there was any physiologic clearance 33 phopenic patients (SCID and ALL), IL-7 levels were elev- of IL-7 by receptor-binding in these patients, although ated above normal levels and were inversely related to the slow clearance by low affinity IL-7R could not be ruled ALC both pre- and post-BMT. An increase in serum IL-7 out. The patients with ALL were also lymphopenic, which levels was also observed in these patients in the first 3 was probably due to exposure to particularly lymphotoxic weeks after BMT, which was followed by a decline in the drugs, eg glucocorticoids, vincristine, and purine nucleo- IL-7 levels. In non-lymphopenic patients, (ANLL, AA and sides, used in treatment of ALL. Interestingly, the patients THAL), the pre-transplant levels of IL-7 were comparable with ANLL were much less lymphopenic than the ALL to those seen in normal controls. However, in these latter patients, suggesting that the marrow-suppressive therapy groups, there was no correlation between IL-7 levels and used in ANLL treatment has less effect on mature lympho- ALC post-BMT. cytes. Steady-state levels of IL-7 are most likely determined by Although direct upregulation of IL-7 production in the equilibrium between IL-7 production and either con- response to lymphopenia is an attractive hypothesis, we sumption of IL-7 by IL-7R-bearing cells and any proteo- think that it is more likely that the increased IL-7 levels IL-7 levels in BMT patients E Bolotin et al 787 observed in lymphopenic patients, was due to altered tution following bone marrow transplantation: comparison of consumption. recipients of T-cell depleted marrow with recipients of con- Previous studies have shown an inverse correlation ventional marrow grafts. Blood 1989; 73: 1340–1350. between serum levels of G-CSF and absolute neutrophil 3 Atkinson K. Reconstruction of the haemopoietic and immune count;34,35 serum erythropoietin level and red blood cell systems after marrow transplantation. Bone Marrow Trans- plant 1990; 5: 209–226. count;36–38 FLT 3 and blood cell number;39 and thrombopo- 40–42 4 Mackall CL, Fleisher TA, Brown MR et al. Age, thymopo- ietin and megakaryocyte number and platelet count. iesis, and CD4ϩ T-lymphocyte regeneration after intensive These inverse relationships between the levels of cytokines chemotherapy. New Engl J Med 1995; 332: 143–149. and the progeny that develop in response to the cytokines 5 Weinberg K, Annett G, Kashyap A et al. The effect of thymic have been thought to represent consumption of ligand by function on immunocompetence following bone marrow trans- receptor-bearing progenitors or mature cells. By analogy, plantation. Biol Blood Marrow Transplant 1995; 1: 18–23. we propose that binding to IL-7R is a homeostatic mech- 6 Seddik M, Seemayer TA, Lapp WS. T cell functional defect anism, which regulates circulating IL-7 levels. associated with thymic epithelial cell injury induced by a An additional determinant of IL-7 levels may be age. We graft-versus-host reaction. Transplantation 1980; 29: 61–66. found that among the normal controls, the highest IL-7 lev- 7 Desbarats J, Lapp WS. Thymic selection and thymic major els were found in the infants less than 1 year of age. Fur- histocompatibility complex class II expression are abnormal in mice undergoing graft-versus-host reactions. J Exp Med thermore, the highest levels among the patients was in the 1993; 178: 805–814. SCID group, who were the youngest patients in the study. 8 Schalke BC, Mertens HG, Kirchner T et al. Long-term treat- Since there were no infants in the other diagnostic groups, ment with azathioprine abolishes thymic lymphoid follicular it is not possible to state unequivocally that the high IL-7 hyperplasia in myasthenia gravis (letter). Lancet 1987; 2: 682. levels in the SCID group were due only to their lympho- 9 Friedrich W, O’Reilly RJ, Koziner B et al. T-lymphocyte penia. Previous studies have demonstrated age-dependent reconstitution in recipients of bone marrow transplants with declines in thymopoietic capacity in chemotherapy and and without GVHD: imbalances of T-cell subpopulations hav- BMT recipients, beginning in adolescence.4,5 It is possible ing unique regulatory and cognitive functions. Blood 1982; that the high IL-7 levels in infants and lower levels in chil- 59: 696–701. dren and adults in the present study represent one facet of 10 Bengtsson M, Totterman TH, Smedmyr B et al. Regeneration the age-dependent decline in thymic function. Consistent of functional and activated NK and T sub-subset cells in the with this hypothesis are studies of marrow stroma from marrow and blood after autologous bone marrow transplan- aged mice, which have shown decreased secretion of IL-7 tation: a prospective phenotypic study with 2/3-color FACS 43 analysis. Leukemia 1989; 3: 68–75. with age. 11 Mackall CL, Granger L, Sheard MA et al. T-cell regeneration In summary, our data indicate that IL-7 levels are after bone marrow transplantation: differential CD45 isoform increased in infants and lymphopenic patients, and the lev- expression on thymic-derived versus thymic-independent pro- els rise in response to further lymphopenia in the post-BMT geny. Blood 1993; 82: 2585–2594. period. This is most consistent with IL-7 production being 12 Miller RA, Daley J, Ghalie R, Kaizer H. Clonal analysis of age-dependent, while consumption of IL-7 is related to the T-cell deficiencies in autotransplant recipients. Blood 1991; number of IL-7R-bearing cells. The latter can be affected 77: 1845–1850. by pre-transplant conditions (SCID) or treatment (ALL). 13 Weinberg K, Hershfield MS, Bastian J et al. T lymphocyte The regulation of IL-7 levels by IL-7R binding may be ontogeny in adenosine deaminase-deficient severe combined a general mechanism for lymphocyte homeostasis. Further immune deficiency after treatment with polyethylene glycol- analysis of the relationship between IL-7 levels and long- modified adenosine deaminase. J Clin Invest 1993; 92: 596– term reconstitution will be necessary to determine the role 602. of IL-7 in the immune reconstitution after BMT. 14 Welte K, Ciobanu N, Moore MA et al. Defective interleukin 2 production in patients after bone marrow transplantation and in vitro restoration of defective T lymphocyte proliferation by highly purified interleukin 2. Blood 1994; 64: 380–385. Acknowledgements 15 Roux E, Helg C, Dumont-Girard F et al. Analysis of T-cell repopulation after allogeneic bone marrow transplantation: The technical assistance of K Wilson, D DeClerk, E Smogorzew- significant differences between recipients of T-cell depleted ska, J Brooks and F Burroto is gratefully acknowledged. The sup- and unmanipulated grafts. Blood 1996; 87: 3984–3992. port of physicians and nursing staff of the BMT unit is appreci- 16 Kruger G, Welte K, Ciobanu N et al. Interleukin-2 correction ated. This work was supported by grants from the Concern 2 of defective in vitro T-cell mitogenesis in patients with com- Foundation and the National Institutes of Health 3 M01 RR00043 mon varied immunodeficiency. J Clin Immunol 1984; 4: (EB); and the TJ Martell Foundation and the National Institutes 295–303. of Health 1R01 HL54729 (KW). Dr Bolotin is a recipient of an 17 Morrissey PJ, Goodwin RG, Nordan RP et al. Recombinant NIH Clinical Associate Physician grant in the General Clinical interleukin 7, pre-B cell growth factor, has costimulatory Research Center at the University of Southern California. activity on purified mature T cells. J Exp Med 1989; 169: 707–716. 18 Wiles MV, Ruiz P, Imhof BA. Interleukin-7 expression during References mouse thymus development. Eur J Immunol 1992; 22: 1037–1042. 1 Lum LG. The kinetics of immune reconstitution after human 19 Welch PA, Namen AE, Goodwin RG et al. Human IL-7: a marrow transplantation. Blood 1987; 69: 369–380. novel T cell growth factor. J Immunol 1989; 143: 3562–3567. 2 Keever CA, Small TN, Flomenberg N et al. Immune reconsti- 20 Murray R, Suda T, Wrighton N et al. IL-7 is a growth and IL-7 levels in BMT patients E Bolotin et al 788 maintenance factor for mature and immature thymocyte sub- of IL-1 treatment on the reconstitution of the hemopoietic and sets. Int Immunol 1989; 1: 526–531. immune systems after sublethal radiation. J Immunol 1988; 21 Uckun FM, Tuel-Ahlgren L, Obuz V et al. Interleukin 7 recep- 140: 4204–4210. tor engagement stimulates tyrosine phosphorylation, inositol 33 Noguchi M, Nakamura Y, Russell SM et al. Interleukin-2 phospholipid turnover, proliferation, and selective differen- receptor gamma chain: a functional component of the interleu- tiation to the CD4 lineage by human fetal thymocytes. Proc kin-7 receptor. Science 1993; 262: 1877–1880. Natl Acad Sci USA 1991; 88: 6323–6327. 34 Mempel K, Pietsch T, Menzel T et al. Increased serum levels 22 Fabbi M, Groh V, Strominger JL. IL-7 induces proliferation of granulocyte colony-stimulating factor in patients with sev- of CD3Ϫ/low CD4Ϫ CD8Ϫ human thymocyte precursors by ere congenital neutropenia. Blood 1991; 77: 1919–1922. an IL-2 independent pathway. Int Immunol, 1992; 4: 1–5. 35 Cairo MS, Suen Y, Sender L et al. Circulating granulocyte 23 Sudo T, Nishikawa S, Ohno N et al. Expression and function colony-stimulating factor (G-CSF) levels after allogeneic and of the interleukin 7 receptor in murine lymphocytes. Proc Natl autologous bone marrow transplantation: endogenous G-CSF Acad Sci USA 1993; 90: 9125–9129. production correlates with myeloid engraftment. Blood 1992; 24 Muegge K, Vila MP, Durum SK. Interleukin-7: a cofactor for 79: 1869–1873. V(D)J rearrangement of the T cell receptor beta gene. Science 36 Bray GL, Taylor B, O’Donnell R. Comparison of the erythro- 1993; 261: 93–95. poietin response in children with aplastic anemia, transient 25 Peschon JJ, Morrissey PJ, Grabstein KH et al. Early lympho- erythroblastopenia, and iron deficiency. J Pediatr 1992; 120: cyte expansion is severely impaired in interleukin 7 receptor- 528–532. deficient mice. J Exp Med 1994; 180: 1955–1960. 37 Ascensao JL, Bilgrami S, Zanjani ED. Erythropoietin. Biology 26 Grabstein KH, Waldschmidt TJ, Finkelman FD et al. Inhi- and clinical applications. Am J Pediatr Hematol Oncol 1991; bition of murine B and T lymphopoiesis in vivo by an anti- 13: 376–387. interleukin 7 monoclonal antibody. J Exp Med 1993; 178: 38 Ireland RM, Atkinson K, Concannon A et al. Serum erythropoietin changes in autologous and allogeneic bone marrow 257–264. transplant patients. Br J Haematol 1990; 76: 128–134. 27 Bolotin E, Smogorzewska M, Smith S et al. Enhancement of 39 Lyman SD, Seaberg M, Hanna R et al. Plasma/serum levels of thymopoiesis after bone marrow transplant by in vivo interleu- flt3 ligand are low in normal individuals and highly elevated in kin-7. Blood 1996; 88: 1887–1894. patients with Fanconi anemia and acquired aplastic anemia. 28 Woods WG, Kobrinsky N, Buckley JD et al. Timed-sequential Blood 1995; 86: 4091–4096. induction therapy improves postremission outcome in acute 40 Bartley TD, Bogenberger J, Hunt P et al. Identification and myeloid leukemia: a report from the Children’s Cancer Group. cloning of a megakaryocyte growth and development factor Blood 1996; 87: 4979–4989. that is a ligand for the cytokine receptor Mpl. Cell 1994; 77: 29 Oosterwegel MA, Haks MC, Jeffry U et al. Induction of TCR 1117–1124. gene rearrangements in uncommitted stem cells by a subset 41 de Sauvage FJ, Hass PE, Spencer SD et al. Stimulation of of IL-7 producing, MHC class-II-expressing thymic stromal megakaryocytopoiesis and thrombopoiesis by the c-Mpl cells. Immunity 1997; 6: 351–360. ligand. Nature 1994; 369: 533–538. 30 Lupton SD, Gimpel S, Jerzy R et al. Characterization of the 42 Ballmaier M, Schulze H, Strauss G et al. Thrombopoietin in human and murine IL-7 genes. J Immunol 1990; 144: 3592– patients with congenital thrombocytopenia and absent radii: 3601. elevated serum levels, normal receptor expression, but defec- 31 Tang J, Nuccie BL, Ritterman I et al. TGF-beta down-regu- tive reactivity to thrombopoietin. Blood 1997; 90: 612–619. lates stromal IL-7 secretion and inhibits proliferation of human 43 Stephan RP, Reilly CR, Witte PL. Impaired ability of bone B cell precursors. J Immunol 1997; 159: 117–125. marrow stromal cells to support B-lymphopoiesis with age. 32 Morrissey P, Charrier K, Bressler L, Alpert A. The influence Blood 1998; 91: 75–88.