Recombinant human growth hormone promotes human lymphocyte engraftment in immunodeficient mice and results in an increased incidence of human Epstein Barr virus-induced B-cell lymphoma

Use of Hu-PBL Mice to Study Pathogenesis of Human-Restricted Viruses

Different humanized mouse models have been developed to study human diseases such as autoimmune illnesses, cancer and viral infections. These models are based on the use of immunodeficient mouse strains that are transplanted with human tissues or human immune cells. Among the latter, mice transplanted with hematopoietic stem cells have been widely used to study human infectious diseases. However, mouse models built upon the transplantation of donor-specific mature immune cells are still under development, especially in the field of viral infections. These models can retain the unique immune memory of the donor, making them suitable for the study of correlates of protection upon natural infection or vaccination. Here, we will review some of these models and how they have been applied to virology research. Moreover, the future applications and the potential of these models to design therapies against human viral infections are discussed.

Mortality and cancer incidence among patients treated with recombinant growth hormone during childhood in Israel

CONTEXT

The inconclusive evidence regarding long-term safety of recombinant human growth hormone (rhGH) therapy underlines the need for long-term large-scale cohorts.

OBJECTIVE

To assess long-term mortality and cancer incidence among patients treated with rhGH during childhood in Israel.

DESIGN

A population-based cohort study.

SETTING

Data were retrieved from a national register established in 1988. Mortality data from the national population register were available through 31 December 2014. Data on cancer incidence from the national cancer registry were available through 31 December 2012.

PARTICIPANTS

All patients ≤19 years approved for rhGH treatment during 1988-2009 were included. Patients were assigned to three risk categories, according to the underlying condition leading to growth disorder.

MAIN OUTCOME MEASURES

All-cause mortality and cancer incidence rates were calculated, based on person-years at risk. Standardized mortality ratios (SMRs) and standardized incidence ratios (SIRs) were calculated, using the Israeli general population as a reference.

RESULTS

Included were 1687 patients assigned to the low-risk category and 440 patients assigned to the intermediate-risk category. In the low-risk category, all-cause mortality and cancer incidence were not significantly different than expected (SMR 0·81, 95% CI 0·22-2·08 and SIR 0·76, 95% CI 0·09-2·73). In the intermediate-risk category, all-cause mortality and cancer incidence were significantly higher than expected (SMR 4·05, 95% CI 1·62-8·34 and SIR 4·52, 95% CI 1·22-11·57).

CONCLUSIONS

No increased risk of mortality or cancer incidence was found in low-risk patients treated with rhGH during childhood. Patients with prior risk factors were at higher risk of both mortality and cancer.

GH, but not GHRH, plays a role in the development of experimental autoimmune encephalomyelitis

GH has been suggested to influence the function of the immune system in several species. Experimental autoimmune encephalomyelitis (EAE) (an animal model for multiple sclerosis) has been reported not to occur in GH-deficient (GHD) mice. The aim of this study was to elucidate the effects of GH and GHRH replacement on development of EAE in a mouse model of isolated GHD due to removal of the GHRH gene [GHRH knockout (GHRHKO)]. We studied two groups of adult female mice: 12 GH-sufficient animals (control) and 36 GHRHKO animals. All mice were immunized with myelin oligodendrocyte glycoprotein peptide, a peptide known to induce EAE. GHRHKO mice were left untreated or were treated for 4 wk with daily sc injections of recombinant GH or of a GHRH super agonist JI-38 (JI38-GHD). Evaluation of EAE symptoms was carried out daily, and T-proliferative assay and histopathological analysis of the spinal cord were performed. GHRHKO mice were less prone to develop EAE when compared with control mice. GH (but not JI-38) restored the original susceptibility of mice to the disease, despite lack of complete serum IGF-I normalization. GH treatment was also associated with a markedly increase in spleen size and T-cell proliferation specific to myelin oligodendrocyte glycoprotein peptide. GH (but not GHRH) plays an important role in the development of EAE.

Growth hormone supplementation increased latency to tumourigenesis in Atm-deficient mice

Growth hormone (GH) is important for cell growth and differentiation, has multiple effects on lymphoid tissue and may promote blast cell proliferation and cancer development. We studied the effect of GH on longevity and tumour formation in Atm-deficient mice, an established model of the human cancer prone syndrome ataxia telangiectasia (AT). AT is a devastating recessive disorder that is characterized by progressive cerebellar ataxia, immunodeficiency, chromosomal instability and cancer susceptibility. Since AT patients also show endocrinological abnormalities the question has been raised as to whether GH therapy could be beneficial and/or increase the cancer risk in AT. We found that treatment with GH significantly increased longevity of Atm-deficient mice. In addition, GH ameliorated locomotoric behaviour and improved T-cell immunity. Thus, our data demonstrated that GH treatment is not necessarily accompanied by increased cancer development in diseases with chromosomal instability and cancer susceptibility and might be beneficial for AT patients.

Mouse models with human immunity and their application in biomedical research

Biomedical research in human beings is largely restricted to in vitro studies that lack complexity of a living organism. To overcome this limitation, humanized mouse models are developed based on immunodeficient characteristics of severe combined immunodeficiency (SCID) or recombination activating gene (Rag)(null) mice, which can accept xenografts. Peripheral constitution of human immunity in SCID or Rag(null) mice has been achieved by transplantation of mature human immune cells, foetal human thymus, bone marrow, liver tissues, lymph nodes or a combination of these, although efficiency needs to be improved. These mouse models with constituted human immunity (defined as humanized mice in the present text) have been widely used to investigate the basic principles of human immunobiology as well as complex pathomechanisms and potential therapies of human diseases. Here, elements of an ideal humanized mouse model are highlighted including genetic and non-genetic modification of recipient mice, transplantation strategies and proposals to improve engraftments. The applications of the humanized mice to study the development and response of human immune cells, human autoimmune diseases, virus infections, transplantation biology and tumour biology are reviewed as well.

Thymic hyperplasia in a child treated with growth hormone

OBJECTIVE

To report a case of thymic hyperplasia diagnosed three months after initiation of recombinant human growth hormone (GH) for the treatment of GH deficiency.

DESIGN

Retrospective chart review was conducted to evaluate the temporal relationship between treatment with GH and thymic enlargement in a 7-year-old girl who had a history of embryonal rhabdomyosarcoma of the nasopharynx diagnosed at the age of 3 years.

RESULTS

The diagnosis of GH deficiency was made based on clinical and auxological criteria, an insufficient response to clonidine-arginine stimulation testing (peak GH level of 4.8 microg/L) and low insulin-like growth factor 1 (IGF-1) level (30 ng/mL, -2.7 SD). The patient was started on GH at a dose of 0.3mg/kg/week. At the initiation of treatment with GH, the baseline growth velocity was 0.8 cm/year (-6.0 SD) and height was 112.5 cm (-1.7 SD). After three months of treatment with GH, her height increased by 4.2 cm (from -1.7 to -1.2 SD), and the IGF-1 level from -2.7 SD to -1.1 SD. A chest CT performed at that time for recurrence surveillance showed 89% increase in thymic volume relative to previous scan before treatment with growth hormone. A thoracoscopic biopsy of the thymus was performed and revealed hyperplasia with normal thymic architecture without evidence of malignancy.

CONCLUSIONS

The timing of the development of thymic hyperplasia, along with data from in vitro and in vivo animal studies showing that GH and IGF-1 can directly stimulate growth of the thymus, suggests that GH contributed to the development of thymic hyperplasia in this patient.

Human interleukin-15 improves engraftment of human T cells in NOD-SCID mice

Human nonobese diabetic-severe combined immune deficiency (NOD-SCID) mouse chimeras have been widely used as an in vivo model to assess human immune function. However, only a small fraction of transferred human T lymphocytes can be detected in human peripheral blood lymphocyte (huPBL)-NOD-SCID chimeras. To improve the reconstitution of human T lymphocytes in NOD-SCID mice, the use of recombinant human interleukin-15 (rhIL-15) as a stimulator of human lymphocytes was explored. Administration of rhIL-15 after transplantation of huPBLs into NOD-SCID mice increased reconstitution of human T lymphocytes in a dose-dependent manner, with an optimal dosage of 1 microg/mouse. The number of human T lymphocytes (HLA-ABC+ CD3+) in the lymphoid organs or tissue of rhIL-15-treated huPBL-NOD-SCID mice increased 11- to 80-fold, and phytohemagglutinin-induced T-lymphocyte proliferation and cytokine production were significantly enhanced. Additionally, although mature human cells have not been thought to enter the murine thymus, human T lymphocytes were detected in the huPBL-NOD-SCID thymus after rhIL-15 treatment. Thus, rhIL-15 can be used to optimize long-term peripheral T-cell engraftment in these human-mouse chimeras and may also be useful in clinical treatment of T-cell deficiencies.

Hodgkin lymphoma in temporal association with growth hormone replacement

The association between growth hormone (GH) replacement and malignancy has long been debated. We report a case of Hodgkin lymphoma that developed in temporal association with the initiation of GH replacement in a 57-year-old woman with panhypopituitarism secondary to a non-secretory pituitary macroadenoma. Treatment of her pituitary tumor included transphenoidal surgery, external beam radiation, Bromocriptine and Cabergaline therapy. In addition to replacement steroid, thyroid and sex hormones, she insisted on GH replacement. Approximately 2 years after GH initiation, the diagnosis of Hodgkin lymphoma was made. Although the exact contribution of GH to the development of Hodgkin disease in our patient is unclear and a causal effect cannot be concluded, the temporal association is suggestive, and warrants reporting as part of ongoing surveillance for potential complications of GH replacement.

Insights into thymic aging and regeneration

The deterioration of the immune system with progressive aging is believed to contribute to morbidity and mortality in elderly humans due to the increased incidence of infection, autoimmunity, and cancer. Dysregulation of T-cell function is thought to play a critical part in these processes. One of the consequences of an aging immune system is the process termed thymic involution, where the thymus undergoes a progressive reduction in size due to profound changes in its anatomy associated with loss of thymic epithelial cells and a decrease in thymopoiesis. This decline in the output of newly developed T cells results in diminished numbers of circulating naive T cells and impaired cell-mediated immunity. A number of theories have been forwarded to explain this 'thymic menopause' including the possible loss of thymic progenitors or epithelial cells, a diminished capacity to rearrange T-cell receptor genes and alterations in the production of growth factors and hormones. Although to date no interventions fully restore thymic function in the aging host, systemic administration of various cytokines and hormones or bone marrow transplantation have resulted in increased thymic activity and T-cell output with age. In this review, we shall examine the current literature on thymic involution and discuss several interventional strategies currently being explored to restore thymic function in elderly subjects.

Growth hormone accelerates immune recovery following allogeneic T-cell-depleted bone marrow transplantation in mice

OBJECTIVE

To test in a murine model whether recombinant human growth hormone can promote immune recovery after allogeneic T-cell-depleted bone marrow transplantation.

MATERIALS AND METHODS

Lethally irradiated (8.5 Gy) BALB/c mice (H2(d)) were transplanted with 5 x 10(6) T cell-depleted bone marrow cells from C57BL/6 mice (H2(b)). Recipient mice were injected intraperitoneally with recombinant human growth hormone (20 microg/dose/day) or saline for the first 4 weeks after transplantation. These animals were followed for phenotypic and functional immune recovery.

RESULTS

Administration of human recombinant growth hormone improved the CD4(+) T-cell counts in peripheral blood on day +14 (44+/-14 vs 33+/-7/microL blood, p<0.05) and day +21 (281+/-109 vs 187+/-76/microL blood, p<0.01) compared with the saline control. These differences were no longer significant by day +28 despite continued growth hormone administration. Similar effects were also observed on CD8(+) T cells and B220(+) B cells. The improvements in peripheral T-cell counts were at least partially as a result of enhanced thymopoiesis because there was an increase in total thymocytes after treatment with growth hormone. T-cell-depleted bone marrow recipients treated with growth hormone rejected the third-party grafts faster than those treated with saline control (median survival time: 20 days vs 26 days, p<0.05).

CONCLUSIONS

These data demonstrated that recombinant human growth hormone can accelerate phenotypic and functional immune reconstitution following allogeneic T-cell-depleted bone marrow transplantation in mice.

Immunologic and hematopoietic effects of recombinant human prolactin after syngeneic bone marrow transplantation in mice

The period of immune deficiency following bone marrow transplantation (BMT) results in a susceptibility to opportunistic infections and remains a growing obstacle in improving the efficacy of BMT. Neuroendocrine hormones have been shown to affect numerous immunologic and hematologic responses after in vivo administration. We investigated whether neuroendocrine hormones, notably prolactin (PRL), could be administered after BMT and result in improved immunologic recovery. Mice were given lethal total body irradiation followed with a congeneic or a syngeneic BMT. Some groups then received recombinant human PRL (rhPRL) daily for 3 weeks. Effects on immune reconstitution and function were then monitored. The results show that PRL could increase thymic cellularity and donor T-cell reconstitution after congeneic BMT. Increases in B cells and myeloid progenitors were also observed. Mitogenic responses by both T and B cells were observed after PRL treatment. These results suggest that PRL may be of use to promote immune and myeloid reconstitution after BMT.

Age-associated loss of bone marrow hematopoietic cells is reversed by GH and accompanies thymic reconstitution

Deterioration of the thymus gland during aging is accompanied by a reduction in plasma GH. Here we report gross and microscopic results from 24-month-old Wistar-Furth rats treated with rat GH derived from syngeneic GH3 cells or with recombinant human GH. Histological evaluation of aged rats treated with either rat or human GH displayed clear morphologic evidence of thymic regeneration, reconstitution of hematopoietic cells in the bone marrow, and multiorgan extramedullary hematopoiesis. Quantitative evaluation of formalin-fixed, hematoxylin and eosin-stained sections of bone marrow from aged rats revealed at least a 50% reduction in the number hematopoietic bone marrow cells, compared with that of young 3-month-old rats. This age-associated decline in bone marrow leukocytes, as well as the increase in bone marrow adipocytes, was significantly reversed by in vivo treatment with GH. Restoration of bone marrow cellularity was caused primarily by erythrocytic and granulocytic cells, but all cell lineages were represented and their proportions were similar to those in aged control rats. On a per-cell basis, GH treatment in vivo significantly increased the number of in vitro myeloid colony forming units in both bone marrow and spleen. Morphological evidence of enhanced extramedullary hematopoiesis was observed in the spleen, liver, and adrenal glands from animals treated with GH. These results confirm that GH prevents thymic aging. Furthermore, these data significantly extend earlier findings by establishing that GH dramatically promotes reconstitution of another primary hematopoietic tissue by reversing the accumulation of bone marrow adipocytes and by restoring the number of bone marrow myeloid cells of both the erythrocytic and granulocytic lineages.

Growth hormone interacts with the Marek's disease virus SORF2 protein and is associated with disease resistance in chicken

Marek's disease (MD) is a lymphoproliferative disease of chickens induced by a herpesvirus, the MD virus (MDV). Because MD is a significant economic problem to the poultry industry, there is great interest in enhancing genetic resistance, which is controlled by multiple genes. The influence of the MHC has been clearly demonstrated, and several relevant quantitative trait loci have been mapped; however, no single gene influencing MD resistance has been identified. Transcription of SORF2 is perturbed in the MDV recombinant clone RM1 due to a solo insertion of the reticuloendotheliosis virus long terminal repeat, which may explain the loss of oncogenicity for this strain. Hypothesizing that SORF2-interacting host proteins are involved in MD resistance, we screened a chicken splenic cDNA library by the yeast two-hybrid assay using SORF2 as bait. The chicken growth hormone (GH) structural peptide was identified, and the specific interaction was verified by coimmunoprecipitation. Immunohistochemical staining and indirect immunofluorescence assay indicated that GH and SORF2 can be coexpressed in MDV-infected cells both in vitro and in vivo. Furthermore, polymorphism in the GH gene (GH1) is associated with the number of tissues with tumors in commercial White Leghorn chickens with the MHC B*2/B*15 genotype. We conclude that GH1 may well be a MD resistance gene.

Primary central nervous system lymphoma in childhood presenting as progressive panhypopituitarism

We report a 15-year-old boy who had isolated central diabetes insipidus initially diagnosed at age 11 years. A brain magnetic resonance imaging (MRI) was normal at the time. At age 12 years, growth hormone (GH) testing was performed because of a decline in linear growth rate and demonstrated GH deficiency. After a repeat normal brain MRI, GH therapy was begun. Three years later, hormonal testing revealed prepubertal gonadotropins and low testosterone levels, free thyroxine index, and morning cortisol levels. Repeat brain MRI demonstrated a 9-mm enhancing lesion in the region of the pituitary stalk. The pathologic diagnosis was that of a high-grade malignant B-cell lymphoma, suggestive of Burkitt Lymphoma. Growth hormone therapy has not been associated with an increased incidence of lymphoma. This report underscores the need for vigilance in follow-up brain imaging and hormonal evaluation in children with diabetes insipidus, especially those with evolving anterior hormone deficiencies.

Acute leukaemia in acromegaly patients

Acromegaly patients are known to have an increased risk of malignancies, especially colonic adenocarcinoma. This may be as a result of the growth-stimulating effect of growth hormone (GH). The clustering of leukaemia in children treated with GH has also caused concern. There have been a few reports of leukaemia in acromegaly patients. We report two patients with acute lymphoblastic leukaemia and one patient with acute myeloid leukaemia among 106 acromegaly patients treated over a 15-year period. Two of the cases received radiotherapy as part of their treatment. Adjusted for age and follow-up years, the incidence of leukaemia in this cohort is significantly higher than the general population. The incidence is also higher than would be expected as a result of radiotherapy alone, suggesting that GH may play a synergistic role.

The roles of prolactin, growth hormone, insulin-like growth factor-I, and thyroid hormones in lymphocyte development and function: insights from genetic models of hormone and hormone receptor deficiency

An extensive literature suggesting that PRL, GH, IGF-I, and thyroid hormones play an important role in immunity has evolved. Because the use of one or more of these hormones as immunostimulants in humans is being considered, it is of critical importance to resolve their precise role in immunity. This review addresses new experimental evidence from analysis of lymphocyte development and function in mice with genetic defects in expression of these hormones or their receptors that calls into question the presumed role played by some of these hormones and reveals unexpected effects of others. These recent findings from the mutant mouse models are integrated and placed in context of the wider literature on endocrine-immune system interactions. The hypothesis that will be developed is that, with the exception of a role for thyroid hormones in B cell development, PRL, GH, and IGF-I are not obligate immunoregulators. Instead, they apparently act as anabolic and stress-modulating hormones in most cells, including those of the immune system.

Growth hormone in immune reconstitution

Immune cell death or dysfunction is induced by HIV infection and results in an immunocompromised state. Newer treatments are able to control viral replication to prevent massive cytoreduction. Attention must now focus on therapies that will rapidly reconstitute the immune system to provide defense against future HIV attacks as well as opportunistic infections. In addition to increasing the rate of differentiation of myeloid and lymphoid precursors from marrow stem cells, ideal therapies should improve thymic function as well. Growth hormone (GH), a member of the hematopoietic cytokine superfamily and its receptors, is expressed in multiple sites within the immune system. GH has been shown to have a stimulatory effect on the function of thymic cells, as well as other immune cell types. In this paper, we consider the use of GH to reconstitute the immune system following cytoreduction due to HIV infection.

Human and Nonhuman Primate Lymphocytes Engrafted into SCID Mice Reside in Unique Mesenteric Lymphoid Structures

The present study compares the location and phenotype of B lineage lymphocytes in tissues from SCID mice engrafted with PBMC of human, chimpanzee, and pig-tailed macaque origin. In mice repopulated with both human and nonhuman primate lymphocytes, plasma cells were found in the peritoneal cavity in vascularized structures located in the mesentery near the pancreas, intestines, and spleen. The predominant isotype of the plasma cells was IgG; IgM and IgA cells were also present. κ and λ light chains were expressed by 62% and 38% of the Ig-containing cells, respectively. J chain expression occurred in most cells irrespective of the Ig isotype. In the SCID mice engrafted with human lymphocytes, a few IgM-containing cells were found in the spleen; plasma cells were not found in other tissues, including the intestine. The aggregation of plasma cells did not appear to be a result of infection with EBV. T cells were rarely found in the lymphoid aggregates but were recovered from the spleen and peritoneal lavage. Human Ig levels in the serum of engrafted mice reflected the isotype distribution of the cells with IgG &gt; IgM ≥ IgA.

Recombinant human growth hormone promotes hematopoietic reconstitution after syngeneic bone marrow transplantation in mice

Recombinant human growth hormone (rhGH) was administered to mice after syngeneic bone marrow transplantation (BMT) to determine its effect on hematopoietic reconstitution. BALB/c mice were given 10 microg intraperitoneal injections of rhGH every other day for a total of 10 injections following syngeneic BMT. Mice that received rhGH exhibited significant increases in total hematopoietic progenitor cell content (colony-forming unit-culture) in both bone marrow and spleen. Erythroid cell progenitor content (burst-forming unit-erythroid) was also significantly increased after rhGH treatment. Analysis of peripheral blood indicated that administration of rhGH resulted in significant increases in the rate of white blood cell and platelet recovery. Granulocyte marker 8C5+ cells were also increased in the bone marrow and spleens of treated mice. Red blood cell, hematocrit, and hemoglobin levels were increased at all time points after rhGH treatment. No significant pathologic effects or weight gain were observed in mice receiving repeated injections of 10 microg rhGH. Thus, rhGH administration after syngeneic BMT promoted multilineage hematopoietic reconstitution and may be of clinical use for accelerating hematopoiesis after autologous BMT.

Pilot study of the immunologic effects of recombinant human growth hormone and recombinant insulin-like growth factor in HIV-infected patients

OBJECTIVE

To study the immunologic effects of recombinant human growth hormone (rhGH), recombinant human insulin-like growth factor type 1 (rhIGF-1), or the combination, in patients with moderately advanced HIV infection.

DESIGN

Randomized but not blinded trial.

SETTING

Government medical research center.

PATIENTS

Twenty-four HIV-infected patients with CD4 cell counts of 100-400 x 10(6)/l who were receiving nucleoside antiretroviral therapy.

INTERVENTIONS

Either rhGH, rhIGF-1, or the combination was administered subcutaneously for 12 weeks.

MAIN OUTCOME MEASURES

Immunologic parameters, including T-cell subsets and assays of in vitro interleukin (IL)-2 production in response to antigens and mitogens, and safety profile.

RESULTS

Plasma IGF-1 levels were low or low-normal prior to treatment and increased with all three therapies. There were no significant changes in CD4 cell counts, RA/RO CD4 cell subsets, natural killer cell function, immunoglobulin levels, or in vitro IL-2 production in response to mitogen or alloantigens. However, there was an upward trend (and for p18IIIB a statistically significant increase) in the in vitro IL-2 production in response to each of five HIV envelope peptides. Potential toxic effects included fatigue, arthralgia, edema, myalgia, and headache. Patients also were noted to have weight gain averaging 4 kg early in the course of treatment.

CONCLUSIONS

These results suggest that treatment with rhGH/rhIGF-1 was reasonably well tolerated and that modest improvement in HIV-specific immune function was attained. Further studies will help clarify the therapeutic potential of rhGH/rhIGF-1 as an immunostimulator in the setting of HIV infection.

Insulin growth factor-I inhibits apoptosis in hematopoietic progenitor cells. Implications in thymic aging

A decline in plasma concentrations of both growth hormone and IGF-I occurs during aging of humans and rodents, and this is accompanied by involution of the thymus gland. Exogenous growth hormone induces the synthesis of IGF-I, which acts on bone marrow-derived hematopoietic progenitors of the myeloid and lymphoid lineages to promote their replication and survival. The increase in survival of these cells is caused by the ability of IGF-I to inhibit their apoptotic death. In contrast to the multipotential colony-stimulating-factor IL-3, inhibition of apoptosis by IGF-I requires the activation of the critical intracellular effector PI 3-kinase. These data establish that hematopoietic progenitors can use more than one intracellular signaling pathway in order to maintain their survival. The data also extend the original hypothesis that IGF-I shares with the colony-stimulating factors the properties of promoting DNA synthesis and inhibiting programmed cell death. Collectively, these data establish that hematopoietic progenitor cells are important targets for IGF-I, and this is likely to be important in understanding thymic aging.

Effects of growth hormone and insulin-like growth factor I on T- and B-lymphocytes and immune function

The concept of a neuro-endocrine-immune axis was proposed more than 50 years ago. Growth hormone (GH), a central component of this axis has many functions at both a molecular and cellular level, including thymocyte proliferation, stimulation of the cytotoxic activity of natural killer cells and induction of lymphocyte proliferation. Binding of GH to its receptors on lymphocytes stimulates the production of insulin-like growth factor I (IGF-I), which mediates the effects of GH on cell proliferation. Other effects of GH on the immune system appear to be direct, such as priming monocytes for enhanced production of hydrogen peroxide in response to phorbol esters, and stimulating neutrophils to secrete superoxide anions associated with enhanced phagocytic activity. Many of the effects of GH are shared by IGF-I. Despite these observations, and the fact that GH is produced and secreted in immunological tissues such as the thymus and spleen, immune deficiency is not characteristic of GH deficiency in humans. The question remains as to whether GH and IGF-I could be used as immunotherapy. Currently, both agents have been used in adults to diminish wasting due to acquired immunodeficiency syndrome, and GH has been shown to stimulate CD8+ cell counts. However, they had little impact on CD4+ cell counts, which may be due to IGF-I and GH resistance in these individuals. The use of GH and IGF-I as immunotherapies merits further study.

Effects of CD40 stimulation in the prevention of human EBV-lymphomagenesis

CD40 is a molecule present on B lineage cells, both normal and neoplastic. Signalling through CD40 has been demonstrated to promote B cell growth and differentiation in vitro. In contrast to its effects on normal B cells, we have found that CD40 stimulation can inhibit the growth of various aggressive histology human B cell lymphomas both in vitro and in vivo. Moreover, using a human/mouse chimera model in which human EBV-induced B cell lymphomas can spontaneously arise, we have found that CD40 stimulation an prevent the occurrence of this human lymphoma in mice. However, normal human B cell engraftment and function was not adversely affected in these mice by CD40 stimulation. This indicates that CD40 stimulation is selective in its effects on aggressive histology B cell lymphomas. Thus, CD40 stimulation either by antibody or a recombinant soluble ligand, may be of potential clinical use, not only in the treatment of EBV-induced B cell lymphomas, but also in their prevention.

Analysis of the colonization of unirradiated and irradiated SCID mice by human lymphoma and non-malignant lymphoid cells

We have evaluated the severe combined immunodeficient (SCID) mouse as an in-vivo model for the study of non-Hodgkin's lymphomas (NHL). Characterization of the immune system of the animals in our SCID mouse colony was carried out to assess the numbers of lymphoid cells present, to determine natural killer (NK) cell activity as a function of age and to examine the histology of the lymphoid organs. In this study four human NHL established cell lines (Daudi, Namalwa, U937, MC116), lymphoma cells from four fresh NHL biopsies and normal peripheral blood mononuclear cells (PBMC) and bone marrow cells were investigated, after intraperitoneal injection into the mice. The presence of the human NHL cells in the peritoneum and spleen was assessed by FACS analysis. The colonization potential was investigated in a range of tissues by polymerase chain reaction (PCR) amplification of human repetitive sequences. These studies revealed clear differences in the abilities of the NHL cell types to colonize the SCID mice. Namalwa, Daudi and U937 cells demonstrated the highest efficiency of colonization and readily formed tumours, whereas MC116, the NHL biopsy cell populations and the non-malignant lymphoid cells showed little ability to survive and colonize other tissues in the SCID mice. Whole body irradiation of the SCID mice appeared to improve the survival of human PBMC, NHL biopsy cells and MC116 cells in the peritoneum, but had little effect on their colonization potential. The significance of these studies is discussed.

Immunoregulatory properties of growth hormone and prolactin

Reciprocal communication between the neuroendocrine and immune systems is critical to the establishment of host homeostatic and defence mechanisms. The production and utilisation of common ligands and their receptors by cells of the immune and neuroendocrine systems constitutes a biochemical information circuit between and within the immune and neuroendocrine systems. Although the structures of the various signalling components appear to be similar in both systems, the regulation of their synthesis may be different. Growth hormone and prolactin have similar and marked influences on the function/activity of each of the major immune cell types, both in vitro and in vivo. The underlying molecular mechanisms are just beginning to be unravelled, and it is anticipated that further work in this rapidly developing field will establish abnormal pituitary and/or lymphocyte growth hormone and prolactin synthesis and function as a contributory factor to a number of pathologic situations, including leukaemia and autoimmunity.

Effects of growth hormone and prolactin immune development and function

Growth hormone and prolactin are neuroendocrine hormones that exert numerous effects on immune system function and development. Several fundamental questions are addressed in this review. Do neuroendocrine hormones affect specific immune cell types? What is the physiological significance of these effects? Can these effects be exploited clinically? While it is clear that there are indeed significant interactions between the neuroendocrine and immune systems, there are relatively few examples with demonstrated physiological significance. Present studies indicate that growth hormone and prolactin may exert markedly different effects on immune cell types depending on their stage in differentiation. Recent emphasis has also been focussed on the use of these hormones or their antagonists clinically in the treatment of AIDS, cancer, and autoimmune disease states due to their pleiotropic effects and low toxicity after systemic administration. However, we do not yet have a clear picture of how the influence of neuroendocrine hormones may be used to favorably alter pathophysiologic processes affecting immune function and development.

Growth hormone promotes human T cell adhesion and migration to both human and murine matrix proteins in vitro and directly promotes xenogeneic engraftment

Recombinant human growth hormone (rhGH) promotes human T cell engraftment in mice with severe combined immunodeficiency, suggesting that rhGH may have effects on T cell adhesion and migration in vivo. The ability of rhGH to directly affect the adhesion capacity of human T cells to a variety of human or murine adhesion molecules and extracellular matrix proteins was examined. rhGH induced significant human T cell adherence to both human and murine substrates via either beta 1 or beta 2 integrin molecules. rhGH was capable of inducing significant migration of resting and activated human T cells and their subsets. Most of the migratory response to rhGH was chemokinetic rather than chemotactic. In vivo engraftment studies in severe combined immunodeficiency mice receiving human T cells revealed that treatment with rhGH resulted in improved thymic engraftment, whereas treatment with non-human-reactive ovine GH demonstrated no significant effects. These data demonstrate that rhGH directly augments human T cell trafficking to peripheral murine lymphoid tissues. rhGH appears to be capable of directly altering the adhesive and migratory capacity of human T cells to molecules of either murine or human origin. Therefore, GH may, under either isogeneic or xenogeneic conditions, play a role in normal lymphocyte recirculation.