Introduction

The positive outcome of allogeneic stem cell transplantation in many hematological malignancies is mainly due to graft-versus-leukemia (GVL) effects mediated by donor T lymphocytes and natural killer (NK) cells present in the graft.¹ Barnes et al.² noticed that recipients of allogeneic grafts, although less likely to relapse, died of graft-versus-host disease (GVHD).³ GVHD represents the major obstacle even following transplantation of MHC compatible donors. GVHD is much more aggressive and usually fatal following transplantation of MHC mismatched stem cell allografts, yet the intensity of GVL effects is directly related to the severity of GVHD.^{4, 5}

Post-grafting immunosuppression or pre-grafting T-cell depletion are mandatory for control or prevention of GVHD, but both modalities impair GVL effects and result in increased susceptibility to infectious complications. Thus, innovative strategies that effectively separate the beneficial GVL effects from the toxicity of GVHD while improving immunological reconstitution post-grafting are necessary for improving the cure rate and enhancing survival after stem cell transplantation.

Interleukin-7 (IL-7) is produced by stromal cells in the thymus and bone marrow.⁶ Administration of IL-7 has several stimulatory effects on T-cell development, including increased thymopoiesis in mice, both in vitro and in vivo^{7, 8} and T cell-dependent function in humans.⁹ IL-7 was shown to increase the number of peripheral CD4⁺ and CD8⁺ antigens in non-activated T cells,¹⁰ and enhance the anti-viral or anti-tumor activity of cytotoxic T cells that were clonally expanded in vitro for adoptive T-cell therapy.^{11, 12} Pre-clinical experiments in murine BMT models documented that administration of IL-7 after transplantation enhanced the reconstitution of T cells in syngeneic or allogeneic BMT recipients through increased thymopoiesis.¹³ IL-7 increased homeostatic proliferation of transferred and de novo generated mature T cells, and decreased apoptosis of peripheral T cells.^{8, 13, 14, 15} Since donor T cells play a most important role in induction of GVL effects following allogeneic BMT, we focused on the role of IL-7 in facilitation of GVL effects by naive and sensitized C57BL/6 MHC mismatched spleen cells in mice treated in vivo with IL-7 following inoculation of murine B-cell leukemia (BCL₁).

Materials and methods

Mice

C57BL/6 (H-2^b)(B6), (BALB/c C57BL/6) F₁(H-2^d/b) (F₁) mice aged 2–4 months were purchased from Harlan at the Hebrew University—Hadassah Medical School's Animal Facility, Jerusalem, Israel. All the animals were kept under standard conditions in top filtered cages and given acidified water (pH 2.7) and food ad libitum. Cages, sawdust and water bottles were autoclaved once a week.

All animal procedures were approved by the Institutional Committee for Animal Experimentation.

Murine BCL₁

BCL₁, a B-cell leukemia/lymphoma of BALB/c origin described by Slavin and Strober,¹⁶ was maintained in vivo by serial passage in BALB/c recipients. B-cell leukemia/lymphoma was characterized by extreme splenomegaly (50 normal size by weight or cell number), extreme peripheral blood lymphocytosis (up to 500 000/mm³) and death of all the recipients.

Human recombinant IL-7 and IL-2

IL-7 was purchased from Peprotech (Princeton, NJ, USA) as lyophilized powder soluble in water. The IL-7 was reconstituted in PBS to a concentration of 100 g/ml.

Human recombinant IL-2

IL-2 was purchased from Chiron BV (Amsterdam, The Netherlands) as 1 mg proleukin (18 10⁶ international units). The IL-2 as initially diluted with water for injection, and subsequently rediluted with dextrose 5%.

Conditioning for transplantation

Non-myeloablative conditioning consisted of a total dose of 250 mg/kg cyclophosphamide (Cy) injected intraperitoneally (i.p.) 24 h before transplantation.

Preparation of cells for transplantation

Spleen cells from B6 donors were suspended in RPMI 1640 supplemented with 10% fetal bovine serum, washed twice and resuspended in the same medium and injected intravenously (i.v.).

Adoptive transfer experiments

Untreated BALB/c mice received 10⁵ spleen cells (i.v.) obtained from each experimental group, to determine whether or not clonogenic BCL₁ cells were present in the spleen of treated donors. Recipients were observed daily for survival. Splenomegaly and peripheral blood counts were monitored weekly to check for signs of leukemia and to confirm that leukemia was indeed the cause of death.

Administration of IL-7 and IL-2 in vivo

All F₁ recipient mice were conditioned with Cy and transfused with 15 10⁶ naive or in vitro sensitized B6 spleen cells 24 h later. On day +1 post transplantation, treatment was initiated with IL-7, IL-2, IL-7 + IL-2, or saline (control group). IL-7 was administered at a dose of 100 ng 2/day i.p. for 10 days starting on day +1 post transplantation to one group twice daily, while a second group received two cycles of IL-7, 10 days apart (10 days daily IL-7; 10 days interval; 10 additional days IL-7). IL-2 was injected i.p. with 1000 IU 2/day for 10 days in one group, while a second group received two cycles 10 days apart. The group that received combined IL-7+IL-2 was injected i.p. for 10 days with the same doses of IL-7 and IL-2 as specified above.

Flow cytometric analysis for detection of chimerism

Blood samples collected in heparin (50 l) were incubated on ice for 30 min with mouse anti-mouse MHC class I H-2K^b R-Phycoerythrin (Serotec, Oxford Biotechnology, Oxford, UK), and conjugated mouse anti-mouse H-2K^d monoclonal antibody (Pharmingen, San Diego, CA, USA). All normal F₁ and BALB/c cells stained positive for H-2K^d, and all normal F₁ and B6 cells stained positive for H-2K^b. The percentage of circulating B6 cells in F₁ recipients was determined by calculating the number of cells negative for H-2K^d using the following formula: 100% cells staining positive for H-2K^b-% tested cells staining positive for H-2K^d.

Phenotype analysis by flow cytometry

Cell phenotype was determined by direct immunofluorescence using a fluorescence-activated cell sorter (FACStarplus, Becton Dickinson Immunofluoremetry Systems, Mountain View, CA, USA). Cells were analyzed after 2 day culture of C57BL/6 spleen cells with irradiated BCL₁ in the presence and in the absence of IL-7 (10 ng/ml). Cells (10⁶) were stained with PE-conjugated anti-NK cells, and PE-conjugated anti-CD8 mAb (Pharmingen). Experiments were repeated twice.

In vitro proliferative responses to mitogens

Two mice from each group were sacrificed on days 10, 15, 20, 30 and 45 post transplantation 2 10⁵. Spleen and 10⁶ thymus were cultured with concanavalin A (ConA; Miles-Yeda, Rehovot, Israel) 5 g/ml, and phytohemagglutinin (PHA; Difco Laboratories, Detroit, MI, USA) 2 g/ml. Samples were pulsed with 2 Ci of [³H]-thymidine (Nuclear Research Center, Negev, Israel) for 16–18 h. Cultures were harvested by a multiple cell harvester, and [³H]-thymidine incorporation was measured using a Beckman scintillation counter. Assays were performed in triplicate.

Experimental design

Sensitization of donor T lymphocytes

To augment the GVL effect by donor lymphocytes against BCL₁, allogeneic spleen cells obtained from B6 mice were cultured against irradiated BCL₁ (3000 cGy) in vitro for 2 days. Cells were cultured under conditions shown above. For testing GVL effects and GVHD across major histocompatibility barriers, F₁ mice were inoculated with 10⁴ BCL₁ cells and mice were followed for signs of leukemia and survival.

Enhancement of anti-leukemia effects induced by naive spleen cells

Spleen cells (15 10⁶) obtained from B6 donor mice and 10⁴ BCL₁ cells were transplanted i.v. into F₁ mice 24 h after conditioning with Cy. The mice were then divided into four groups:

Group A: F₁ control group that received saline injections; group B: mice treated with one cycle of IL-7 i.p. at a concentration of 100 ng/mouse twice daily for 10 days, starting 1 day following B6 infusion; group C: mice treated with two cycles of IL-7, 10 days apart, starting 1 day following B6 infusion; group D: F₁ controls receiving BCL₁ cells only.

Enhancement of anti-leukemia effects by IL-7 using sensitized lymphocytes

A total of 10 10⁶ spleen cells/ml obtained from B6 mice were cultured for 2 days with irradiated BCL₁ cells in a mixed lymphocyte-tumor culture system. Of these cells, 2/3 were responder cells and 1/3 stimulator cells. Twenty ng/ml IL-7, or saline, were added to the culture medium. After sensitization, the cells were collected with a cell scraper and centrifuged. A total of 10 10⁶ mononuclear cells from each experimental group, cultured with IL-7 or saline, were injected together with 10⁴ fresh BCL₁ cells into the lateral vein of the F₁ mice conditioned with Cy 250 mg/kg.

Experimental mice were divided into five groups: group A—F₁ mice that received one cycle of IL-7 (100 ng 2/day i.p.) in vivo for 10 days, starting 1 day post transplantation; group B—F₁ mice that received two cycles of IL-7 treatment, 10 days apart, starting 1 day post transplantation; group C—F₁ mice that received fresh BCL₁ leukemia cells treated with one cycle of IL-7; group D—F₁ mice that received fresh BCL₁ cells only, and served as positive controls; group E—a control group that received saline in vivo.

Statistics

The Kaplan–Meier test was used to evaluate survival data. The Student's t-test was used to assess the differences in cell numbers and proliferative response.

Results

Chimerism

Following infusion of spleen cells, chimerism was detected at 3 and 6 weeks following transplantation. Circulating and spleen cells of all recipients were 80 and 90% of donor origin in 3 and 6 weeks, respectively, as confirmed by FACS analysis. Recipients transplanted with C57BL/6 spleen cells and treated by IL-7 in vivo had mild signs of GVHD like weight loss and runt disease.

Enhancement of anti-leukemia effects induced by C57BL/6 spleen cells and in vivo administration of IL-7

Leukemia eradication and disease-free survival were investigated after Cy conditioning followed by treatment with B6 spleen cells activated in vivo with IL-7. F₁ mice were conditioned with Cy i.p. and 24 h later were injected i.v. with 15 10⁶ B6 spleen cells as immunotherapy treatment and 10⁴ fresh BCL₁ cells, to mimic a stage of minimal residual disease. They were then treated with two daily doses of saline injections (group A), 100 ng IL-7 i.p. for 10 days (group B) or with two similar cycles 10 days apart (group C). As shown in Figure 1 (one experiment of two with similar results), 66.6% of the mice in group C survived 60 days post transplantation, in comparison to 50% in group B. In contrast, only 16.6% of the control groups treated with saline (group A) survived until day 60. The cause of death of mice in groups A, B and C was GVHD. All the control mice (positive control) that received BCL₁ only (group D) died of leukemia within 21 days.

Figure 1.

Effect of IL-7 on GVL phenomenon. (BALB/c C57BL/6)F₁ were conditioned with cyclophosphamide (250 mg/kg i.p.) and 1 day later transplanted with 15 10⁶ C57BL/6 spleen cells mixed with 10⁴ BCL₁ cells, and treated in vivo with one or two cycles of IL-7 (100 ng 2/day i.p. for 10 days). BCL₁=B-cell leukemia; GVL=graft-versus-leukemia; IL-7=interleukin-7; i.p.=intraperitoneally.

Full figure and legend (26K)

A comparison of group C (treated with two cycles of IL-7) and group A (treated with saline only) by the log-rank test showed a statistically significant value of P=0.0432.

Facilitation of anti-leukemia effects induced by alloreactive lymphocytes sensitized in vitro against leukemia in the presence of IL-7

Spleen cells of B6 donors were sensitized against irradiated BCL₁ in the presence and in the absence of IL-7, and injected at a dose of 10 10⁶ cells into Cy-conditioned F₁ mice that had been treated with one or two cycles of IL-7, as described previously. As shown in Figure 2, treatment with lymphocytes sensitized in vitro with IL-7 followed by in vivo treatment with two cycles of IL-7 resulted in 71% leukemia-free survival (group B) as compared to 36% after one cycle of in vivo IL-7 treatment (group A). Only 21% of mice that received B6 spleen cells sensitized against BCL₁ cells in the presence of IL-7 but treated with saline in vivo (group E) survived more than 80 days. Most of the mice died of GVHD (group F), whereas adding IL-7 in vitro or in vivo reduced or postponed the GVHD mortality. The positive controls that received BCL₁ cells only, and mice that received BCL₁ cells followed by one cycle of IL-7 in vivo, died of leukemia (groups D and C, respectively), that is, IL-7 had no direct effect on the development of leukemia. Mice that received spleen cells sensitized against BCL₁ without IL-7 in vitro and with no additional treatment with IL-7 in vivo developed severe GVHD and died within 40 days (Figure 2, group F). Adding IL-7 in vitro to sensitized B6 spleen cells mildly improved the survival of mice, but to a lesser extent as compared with in vivo administration of IL-7.

Figure 2.

Effect of IL-7 on GVL phenomenon in mice transplanted with BCL₁-sensitized allogeneic spleen cells. (BALB/c C57BL/6)F₁ mice were conditioned with cyclophosphamide (250 mg/kg i.p.) and 1 day later transplanted with 10 10⁶ BCL₁-sensitized C57BL/6 spleen cells in the presence of IL-7 in vitro. The mice received another IL-7 treatment in vivo (100 ng/kg i.p. for 10 days, one cycle or two cycles) beginning 1 day post transplantation. BCL₁=B-cell leukemia; GVL=graft-versus-leukemia; IL-7=interleukin-7; i.p.=intraperitoneally.

Full figure and legend (42K)

Log-rank test showed a statistically significant value of P<0.0001 in the group treated with one cycle of IL-7 (group A) compared to the BCL₁+IL-7 control group (group C).

Assessment of minimal residual disease by adoptive transfer experiment

BALB/C mice were used to identify residual leukemic cells in the F₁-transplanted and -treated mice. None of the adoptive recipient BALB/c mice that were inoculated with 10⁵ spleen cells from Cy-conditioned F₁ mice inoculated with BCL₁ and transplanted with B6 spleen cells, and subsequently treated with one or two cycles of IL-7 as well as the group that received allogeneic spleen cells from non-IL-7-treated F₁ mice, developed leukemia (Figure 3).

Figure 3.

Effect of IL-7 on residual BCL₁ cells. (BALB/c C57BL/6)F₁ were conditioned with cyclophosphamide (250 mg/kg i.p.) and 1 day later transplanted with 10 10⁶ C57BL/6 spleen cells and then treated in vivo with one of two cycles of IL-7 (100 ng 2/day i.p. for 10 days). 10⁵ spleen cells from each group were adoptively transferred to naive BALB/c mice. The results represent the development of leukemia in the adoptive recipient mice. BCL₁=B-cell leukemia; IL-7=interleukin-7; i.p.=intraperitoneally.

Full figure and legend (25K)

All adoptive recipient BALB/c mice that received cells from F₁ mice injected with BCL₁ cells only or BCL₁ and IL-7 in vivo developed leukemia within 28 days (Figure 3).

Log-rank statistics showed a statistically significant value of P<0.01 in the group treated with two cycles of IL-7 compared to the group treated with one cycle.

An evaluation of mortality from leukemia among the recipient mice, based on the results of adoptive transfer experiment, showed that only 29% mice treated with two cycles of IL-7 in vivo died, while mortality among the mice treated with one cycle of IL-7 in vivo was 64% and mortality in the group that did not receive IL-7 treatment in vivo was 79% (Figure 4).

Figure 4.

Summary of mortality from leukemia. (C57BL/6 BALB/c)F₁ mice transplanted with BCL₁-sensitized C57BL/6 allogeneic spleen cells in the presence of IL-7 (for 2 days) and treatment with IL-7 in vivo. BCL₁=B-cell leukemia; IL-7=interleukin-7.

Full figure and legend (14K)

Splenic and thymic lymphoid organ cellularity and proliferative capacity of lymphocytes, comparison of the effect of IL-7 and IL-2

F₁ mice received Cy (250 mg/kg) and were transplanted with 15 10⁶ B6 spleen cells. One group received IL-7 100 ng 2/day for 10 days in vivo, a second group received IL-2 1000 cetus units 2/day for 10 days, another group received (IL-2+IL-7) and control group received saline. The number of spleen and thymic cells were counted on days +10, +15, +20, +30 and +45 post transplantation, and the proliferative capacity of lymphocytes in response to ConA and PHA was monitored.

Significant differences were achieved on days +10, +20, +30 and +45 (P<0.05), and showed splenic and thymic cell cellularity measured in the IL-7-treated group (Figures 5a and b). IL-2 and IL-7 and combination of both resulted in significant elevation (P<0.05) of the thymic cellularity. IL-7 alone enhanced the proliferative responses of spleen cells from treated mice in response to PHA (P<0.05 on days 10 and 15) significantly more than IL-2, and there seemed to be no advantage in using a combination of IL-7 and IL-2 (Figure 6a). Similarly, IL-7 alone enhanced the proliferative responses of thymic cells in response to PHA (P<0.05 on days 20, 30 and 45 post transplant) more than IL-2 (Figure 6b).

Figure 5.

Effects of rIL-2 and rIL-7 on splenic (a) and thymic (b) cell mass. (BALB C57BL/6)F₁ mice were injected with cyclophosphamide 250 mg/kg and received 15 10⁶ B6 spleen cells with fresh BCL₁ leukemia. The mice were treated with rIL-2, rIL-7, and the combination of both for 10 days. Spleen and thymic (two each on the indicating days post BMT) were disrupted, and single cell suspensions were made. The number of mononuclear cells ( 10⁶) per organ is depicted. The effect of the cytokines on the splenic cells was significant on day 10 (P<0.05), and on the thymic cells on day 15 post transplantation. BCL₁=B-cell leukemia; rIL=recombinant interleukin.

Full figure and legend (98K)

Figure 6.

Functional analysis of splenic (a) and thymic (b) T cells. A total of 2 10⁶ splenic cells/well and 10⁶ thymic cells/well (saline, rIL-2, rIL-7, and combination of IL-2+IL-7) from the four treatment groups were incubated with PHA (2 g/ml) at the indicating days post BMT. [³H]T dR incorporation by the splenic and thymic cells of the saline-treated mice at each indicated day was used to determine the effect of rIL-2 and rIL-7. The difference in proliferative response of the splenic and thymic cells to the two cytokines was assessed by the Student's t-test, and was found significant on day 15 (P<0.03) for the spleen and P<0.05 for the thymus on day 20. Each value represents the ratio of [³H]T dR incorporation by the experimental versus control (saline) cells. The percentages represent the results of one of three similar experiments. IL-7=interleukin-7; PHA=phytohemagglutinin; rIL=recombinant interleukin.

Full figure and legend (95K)

The effect of IL-7 in vitro on cell populations

C57BL/6 spleen cells were cultured in the presence of irradiated BCL₁ cells with or without additional IL-7, for 2 days. The cells were collected and were examined by fluorescent antibodies: anti-CD8 and anti-NK cells. The results show that IL-7 augmented CD8⁺ cells from 16.3 to 23.6% (145%) compared to the control. There is no beneficial effect on the NK cells (Table 1).

Table 1 - The influence of IL-7 in cultures of C57BL/6 spleen against irradiated BCL₁ on the different cell populations.

Full table

Discussion

Allogeneic SCT is the treatment of choice for an increasing number of malignant and non-malignant disorders. The success rate of the SCT procedure depends to a great extent on the reconstitution of the functions of the immune system after conditioning and infusion of donor cells. Engraftment depends on adequate suppression of the host, while the incidence and severity of GVHD depend on the degree and intensity of alloreactive donor T cells infused against host alloantigens. Newly developing lymphocytes from donor stem cells are likely to become tolerant, but it seems important to facilitate the immune maturation and functionality of newly developing donor lymphocytes. Alloreactivity of donor lymphocytes is important for induction of GVL effects, since the major benefit of the SCT procedure depends on successful induction of GVL effects. Unfortunately, the successful induction of GVL effects is frequently accompanied by intractable acute and chronic GVHD. In this regard, stimulation of anti-tumor effector mechanism induced by T cells may also increase the incidence and severity of GVHD. Thus, the net effect of the SCT procedure depends on the engraftment of donor cells and induction of maximal GVL effects on the one hand, and minimization and/or control of GVHD on the other. In patients with an MHC compatible donor, GVL effects are mediated primarily by T lymphocytes. However, the large majority of patients in need of SCT have no matched sibling or matched unrelated donor available, and for these patients, transplantation of haploidentically mismatched allografts may represent the next best alternative. In such cases, T-cell depletion at the time of transplantation is mandatory to prevent GVHD, but no post-grafting immunosuppression is required due to tolerance induction by newly emerging donor T lymphocytes maturing in the host.^{17, 18} Whereas T cells cause GVHD in most cases, NK cells that may also be facilitated by IL-7 do not cause GVHD, only anti-leukemia effects. However, control of other post transplantation complications, especially viral, fungal and bacterial infections, depends to a great extent on the reconstitution of the patient's immune system, and in patients receiving post-graft immunosuppression for the prevention or control of GVHD, the period of immunosuppression is further prolonged. At present, no effective method for the facilitation of reconstitution of the patient's immune system post transplantation is available. Previous investigations by our group^{13, 19, 20} and other groups^{14, 15} suggest that IL-7 may be a most effective agent for facilitation of reconstitution of the number and function of T-cell subsets and B lymphocytes in vivo. Based on pre-clinical animal data, the use of IL-7 to facilitate immunological reconstitution post-grafting seems a most attractive future modality that has yet to be tested in man. Our results showed that IL-7 significantly augmented CD8⁺ cells in vitro. We have previously showed²¹ that CD8⁺ cells are responsible for eradication of BCL₁ cells. These results can indicate and explain the mechanism of IL-7 activity on the immune response by maturation and differentiation of cells toward cytotoxic CD8⁺ T cells against leukemic cells.

The present experiments indicate that IL-7, an agent with known capacity to facilitate immunological reconstitution in vitro and in vivo, can be used in pre-clinical animal models to enhance the number and function of lymphocytes in the thymus and the spleen, as well as to enhance GVL effects induced by MHC incompatible lymphocytes against lethal murine leukemia. In vivo administration of IL-7 was shown to induce immunological reconstitution, while a short pre-treatment of donor lymphocytes with IL-7 in vitro before inoculation further enhanced the GVL effects. Investigation on the role of IL-7 on different cell subsets in the spleen indicated similar proportions of NK, CD45RA and mild increase of CD8⁺ cells in IL-7-treated mice (data not shown).

Studies such as ours may provide the scientific basis for preliminary clinical trials using IL-7 for immunological reconstitution in vivo or in vitro following culturing of donor-derived cells before transplantation. Facilitation of immunological reconstitution in clinical practice and potent action of GVL effects, especially in patients with no clinically overt GVHD, or following transplantation of T-cell depleted stem cells, when newly developing donor T cells have to mature in the thymus of the host is likely to improve the outcome of SCT. It remains to be seen whether IL-7, in addition to beneficial facilitation of immunological reconstitution and GVL effects post-grafting, as well as engraftment by activation of donor T cells, may also result in aggravation of GVHD. This could be the case if grafts containing significant proportions of mature donor T cells are transplanted. However, transplantation of T-cell depleted stem cells, which is mandatory in recipients of haploidentically mismatched allografts, but optional in recipients of allografts from MHC compatible donors, is unlikely to result in GVHD, because alloreactive donor lymphocytes maturing in the thymus of the host are likely to become tolerant due to apoptosis of potentially self-reactive T cells. On the other hand, in addition to the risk of GVHD, stimulation of B cells by IL-7 may theoretically increase the risk of post transplant lymphoproliferative disorders, especially in recipients of T-cell depleted allografts.

In conclusion, based on the ability of IL-7 to facilitate immunological reconstitution following transplantation, using IL-7 for improving the outcome of allogeneic stem cell transplantation for malignant and non-malignant disorders seems highly warranted.

References

1. Truitt R, Johnson B, McCabe C, Weiler M. Graft-versus-leukemia. In: Ferrara J, Deeg H, Bukaroff S (eds). Graft-vs-Host Disease, 2nd edn. Marcel Dekker Inc.: New York, 1997, pp 385–424.
2. Barnes DHW, Loutit JF. Treatment of murine leukaemia with x-rays and homologous bone marrow. II. Br J Haematol 1957; 3: 241–252. | PubMed | ISI | ChemPort |
3. Mathé G, Amiel JL, Schwarzenberg L, Cattan A, Schneider M, Devries MJ et al. Successful allogeneic bone marrow transplantation in man: chimerism, induced specific tolerance and possible antileukemic effects. Blood 1965; 25: 179. | PubMed |
4. Weiden PL, Sullivan KM, Flournoy N, Storb R, Thomas ED. Anti-leukemic effect of chronic graft-versus-host-disease: contribution to improved survival after allogeneic marrow transplantation. N Engl J Med 1981; 304: 1529–1531. | PubMed | ISI | ChemPort |
5. Horowitz MM, Gale RP, Sondel PM, Goldman JM, Kersey J, Kolb HJ et al. Graft-versus-leukemia reactions after bone marrow transplantation. Blood 1990; 75: 555–562. | PubMed | ISI | ChemPort |
6. Fry TJ, Mackall CL. Interleukin-7: from bench to clinic. Blood 2002; 99: 3892–3904. | Article | PubMed | ISI | ChemPort |
7. Sempowski GD, Gooding ME, Liao HX, Le PT, Haynes BF. T cell receptor excision circle assessment of thymopoiesis in aging mice. Mol Immunol 2002; 38: 841–848. | Article | PubMed | ChemPort |
8. Bolotin E, Smogorzewska M, Smith S, Widmer M, Weinberg K. Enhancement of thymopoiesis after bone marrow transplant by in vivo interleukin-7. Blood 1996; 88: 1887–1894. | PubMed | ISI | ChemPort |
9. Okamoto Y, Douek DC, McFarland RD, Koup RA. Effects of exogenous interleukin-7 on human thymus function. Blood 2002; 99: 2851–2858. | Article | PubMed | ISI | ChemPort |
10. Geiselhart LA, Humphries CA, Gregorio TA, Mou S, Subleski J, Komschlies KL. IL-7 administration alters the CD4:CD8 ratio, increases T cell numbers, and increases T cell function in the absence of activation. J Immunol 2001; 166: 3019–3027. | PubMed | ISI | ChemPort |
11. Lynch DH, Miller RE. Interleukin 7 promotes long-term in vitro growth of antitumor cytotoxic T lymphocytes with immunotherapeutic efficacy in vivo. J Exp Med 1994; 179: 31–42. | Article | PubMed | ISI | ChemPort |
12. Wiryana P, Bui T, Faltynek CR, Ho RJ. Augmentation of cell-mediated immunotherapy against herpes simplex virus by interleukins: comparison of in vivo effects of IL-2 and IL-7 on adoptively transferred T cells. Vaccine 1997; 15: 561–563. | Article | PubMed | ISI | ChemPort |
13. Abdul-Hai A, Or R, Slavin S, Friedman G, Weiss L, Matsa D et al. Stimulation of immune reconstitution by interleukin-7 after syngeneic bone marrow transplantation in mice. Exp Hematol 1996; 24: 1416–1422. | PubMed | ChemPort |
14. Alpdogan O, Schmaltz C, Muriglan SJ, Kappel BJ, Perales MA, Rotolo JA et al. Administration of interleukin-7 after allogeneic bone marrow improves immune reconstitution without aggravating graft-versus-host disease. Blood 2001; 98: 2256–2265. | Article | PubMed | ISI | ChemPort |
15. Mackall CL, Fry TJ, Bare C, Morgan P, Galbraith A, Gress RE. IL-7 increases both thymic-dependent and thymic-independent T-cell regeneration after bone marrow transplantation. Blood 2001; 97: 1491–1497. | Article | PubMed | ISI | ChemPort |
16. Slavin S, Strober S. Spontaneous murine B-cell leukaemia. Nature 1978; 272: 624–626. | Article | PubMed | ISI | ChemPort |
17. Aversa F, Tabilio A, Velardi A, Cunningham I, Terenzi A, Falzetti F et al. Treatment of high-risk acute leukemia with T-cell-depleted stem cells from related donors with one fully mismatched HLA haplotype. N Engl J Med 1998; 339: 1186–1193. | Article | PubMed | ISI | ChemPort |
18. Aversa F, Velardi A, Tabilio A, Reisner Y, Martelli MF. Haploidentical stem cell transplantation in leukemia. Blood Rev 2001; 15: 111–119. | Article | PubMed | ISI | ChemPort |
19. Or R, Abdul-Hai A, Ben-Yehuda A. Reviewing the potential utility of interleukin-7 as a promoter of thymopoiesis and immune recovery. Cytokines Cell Mol Ther 1998; 4: 287–294; Review. | PubMed | ISI | ChemPort |
20. Abdul-Hai A, Weiss L, Slavin S, Or R. Improved survival following induction of GVHD following lipopolysaccharide immunization. Exp Hematol 2006; 34: 549–553. | Article | PubMed | ISI | ChemPort |
21. Weiss L, Reich S, Slavin S. Allogeneic cell therapy in murine B-cell leukemia (BCL1): 2. The role of non-activated and rIL-2-activated CD4⁺ and CD8⁺ T cells in immunotherapy for leukemia. Cytokines Cell Mol Ther 1999; 5: 153–158. | PubMed | ISI | ChemPort |

Acknowledgements

We thank the Danny Cunniff Leukemia Research Laboratory for its continuous support of our ongoing basic and clinical research.