Randomized prospective study evaluating tenofovir disoproxil fumarate prophylaxis against hepatitis B virus reactivation in anti-HBc-positive patients with rituximab-based regimens to treat hematologic malignancies: The Preblin study

BACKGROUND

Hepatitis B virus (HBV) reactivation in patients with resolved HBV infection (HBsAg negative, antiHBc positive) is uncommon, but potentially fatal. The role of HBV prophylaxis in this setting is uncertain. The aim of this study was to compare the efficacy of tenofovir disoproxil fumarate (TDF) prophylaxis versus close monitoring in antiHBc-positive, HBsAg-negative patients under treatment with rituximab (RTX)-based regimens for hematologic malignancy.

METHODS

PREBLIN is a phase IV, randomized, prospective, open-label, multicenter, parallel-group trial conducted in 17 hospitals throughout Spain. Anti-HBc-positive, HBsAg-negative patients with undetectable HBV DNA were randomized to receive TDF 300 mg once daily (Group I) or observation (Group II). The primary endpoint was the percentage of patients showing HBV reactivation during 18 months following initiation of RTX treatment. Patients with detectable HBV DNA (Group III) received the same dose of TDF and were analyzed together with Group I to investigate TDF safety.

RESULTS

Sixty-one patients were enrolled in the study, 33 in the TDF treatment group and 28 in the observation group. By ITT analysis, HBV reactivation was 0% (0/33) in the study group and 10.7% (3/28) in the observation group (p = 0.091). None of the patients in either group showed significant differences in liver function parameters between baseline and the last follow-up sample. TDF was generally well tolerated and there were no severe treatment-related adverse events.

CONCLUSION

In patients with hematological malignancy and resolved hepatitis B infection receiving RTX-based regimens, HBV reactivation did not occur in patients given TDF prophylaxis.

T-cell depleted allogeneic hematopoietic cell transplants as a platform for adoptive therapy with leukemia selective or virus-specific T-cells

Allogeneic hematopoietic cell transplants adequately depleted of T-cells can reduce or prevent acute and chronic GVHD in both HLA-matched and haplotype-disparate hosts, without post-transplant prophylaxis with immunosuppressive drugs. Recent trials indicate that high doses of CD34+ progenitors from G-CSF mobilized peripheral blood leukocytes isolated and T-cell depleted by immunoadsorption to paramagnetic beads, when administered after myeloablative conditioning with TBI and chemotherapy or chemotherapy alone can secure consistent engraftment and abrogate GVHD in patients with acute leukemia without incurring an increased risk of a recurrent leukemia. Early clinical trials also indicate that high doses of in vitro generated leukemia-reactive donor T-cells can be adoptively transferred and can induce remissions of leukemia relapse without GVHD. Similarly, virus-specific T-cells generated from the transplant donor or an HLA partially matched third party, have induced remissions of Rituxan-refractory EBV lymphomas and can clear CMV disease or viremia persisting despite antiviral therapy in a high proportion of cases. Analyses of treatment responses and failures illustrate both the advantages and limitations of donor or banked, third party-derived T-cells, but underscore the potential of adoptive T-cell therapy in the absence of ongoing immunosuppression.

Ludwik Gross, Sarah Stewart, and the 1950s discoveries of Gross murine leukemia virus and polyoma virus

The Polish-American scientist Ludwik Gross made two important discoveries in the early 1950s. He showed that two viruses - murine leukemia virus and parotid tumor virus - could cause cancer when they were injected into susceptible animals. At first, Gross's discoveries were greeted with skepticism: it seemed implausible that viruses could cause a disease as complex as cancer. Inspired by Gross's initial experiments, similar results were obtained by Sarah Stewart and Bernice Eddy who later renamed the parotid tumor virus SE polyoma virus after finding it could cause many different types of tumors in mice, hamsters, and rats. Eventually the "SE" was dropped and virologists adopted the name "polyoma virus." After Gross's work was published, additional viruses capable of causing solid tumors or blood-borne tumors in mice were described by Arnold Graffi, Charlotte Friend, John Moloney and others. By 1961, sufficient data had been accumulated for Gross to confidently publish an extensive monograph--Oncogenic Viruses--the first history of tumor virology, which became a standard reference work and marked the emergence of tumor virology as a distinct, legitimate field of study.

Managing the future: the Special Virus Leukemia Program and the acceleration of biomedical research

After the end of the Second World War, cancer virus research experienced a remarkable revival, culminating in the creation in 1964 of the United States National Cancer Institute's Special Virus Leukemia Program (SVLP), an ambitious program of directed biomedical research to accelerate the development of a leukemia vaccine. Studies of cancer viruses soon became the second most highly funded area of research at the Institute, and by far the most generously funded area of biological research. Remarkably, this vast infrastructure for cancer vaccine production came into being before a human leukemia virus was shown to exist. The origins of the SVLP were rooted in as much as shifts in American society as laboratory science. The revival of cancer virus studies was a function of the success advocates and administrators achieved in associating cancer viruses with campaigns against childhood diseases such as polio and leukemia. To address the urgency borne of this new association, the SVLP's architects sought to lessen the power of peer review in favor of centralized Cold War management methods, fashioning viruses as "administrative objects" in order to accelerate the tempo of biomedical research and discovery.

Report on influenza A and B viruses: their coinfection in a Saudi leukemia patient

PURPOSE

Influenza A and B viruses are the leading cause of respiratory infections in children worldwide, particularly in developing countries. There is a lack of data on coinfection of influenza A and B viruses circulating in Saudi Arabia. In this study, we aimed to identify the circulation of influenza viruses that contribute to respiratory tract infections in Saudi children.

METHODS

We collected 80 nasopharyngeal aspirates (NPAs) from hospitalized children with acute respiratory illness (ARI) at Riyadh during the period extended from October 2010 till April 2011. Samples were tested for the common respiratory viruses including influenza viruses by RT-PCR.

RESULTS

Overall, 6 samples were found positive for influenza A and/or B viruses. Among these positive clinical samples, only one collected sample from a female one-year-old immunocompromised child with leukemia showed a coinfection with influenza A and B viruses. In present study coinfection was confirmed by inoculation of the clinical specimen in specific pathogenfree embryonating chicken eggs and identification of the virus isolates by hemagglutination and one-step RT-PCR.

CONCLUSION

This study opens the scene for studying the role of influenza virus's coinfection in disease severity and virus evolution. Further studies are required to better understand the clinical importance of viral coinfection.

Multiplex real-time PCR for prompt diagnosis of an outbreak of human parainfluenza 3 virus in children with acute leukemia

Introduction

Human parainfluenza virus type 3 (HPIV-3) causes significant morbimortality in immunocompromised patients. Outbreaks of severe pneumonitis have been previously described in this setting.

Materials and methods

Retrospective observational study in children diagnosed with acute leukemia and a documented HPIV-3 infection in the context of a nosocomial outbreak occurred in a single center.

Result

During summer 2012, an HPIV-3 infection was detected in six hospitalized children with acute leukemia. All the patients had respiratory symptoms and one of them suffered from parotitis.

Conclusion

Early diagnoses using multiplex real-time polymerase chain reaction (PCR) let us control this outbreak. A phylogenetic analysis confirmed person-to-person transmission of a single HPIV-3 variant.

Aggressive mature natural killer cell neoplasms: from epidemiology to diagnosis

Mature natural killer (NK) cell neoplasms are classified by the World Health Organization into NK/T cell lymphoma, nasal type (NKTCL), aggressive NK-cell leukemia (ANKCL) and chronic lymphoproliferative disorders of NK-cells, the latter being considered provisionally. NKTCL and ANKCL are rare diseases, with higher prevalence in Asia, Central and South America. Most NKTCL present extranodal, as a destructive tumor affecting the nose and upper aerodigestive tract (nasal NKTCL) or any organ or tissue (extranasal NKTCL) whereas ANKCL manifests as a systemic disease with multiorgan involvement and naturally evolutes to death in a few weeks. The histopathological hallmark of these aggressive NK-cell tumors is a polymorphic neoplastic infiltrate with angiocentricity, angiodestruction and tissue necrosis. The tumor cells have cytoplasmatic azurophilic granules and usually show a CD45(+bright), CD2(+), sCD3(-), cytCD3epsilon(+), CD56(+bright), CD16(−/+), cytotoxic granules molecules(+) phenotype. T-cell receptor genes are in germ-line configuration. Epstein-Barr virus (EBV) -encoded membrane proteins and early region EBV RNA are usually detected on lymphoma cells, with a pattern suggestive of a latent viral infection type II. Complex chromosomal abnormalities are frequent and loss of chromosomes 6q, 11q, 13q, and 17p are recurrent aberrations. The rarity of the NK-cell tumors limits our ability to standardize the procedures for the diagnosis and clinical management and efforts should be made to encourage multi-institutional registries.

Time-varying coefficient proportional hazards model with missing covariates

Missing covariates often arise in biomedical studies with survival outcomes. Existing approaches for missing covariates generally assume proportional hazards. The proportionality assumption may not hold in practice, as illustrated by data from a mouse leukemia study with covariate effects changing over time. To tackle this restriction, we study the missing data problem under the varying-coefficient proportional hazards model. On the basis of the local partial likelihood approach, we develop inverse selection probability weighted estimators. We consider reweighting and augmentation techniques for possible improvement of efficiency and robustness. The proposed estimators are assessed via simulation studies and illustrated by application to the mouse leukemia data.

Expansion of highly differentiated CD8+ T-cells or NK-cells in patients treated with dasatinib is associated with cytomegalovirus reactivation

The tyrosine kinase inhibitor dasatinib exerts immunosuppressive effects on T-cells and NK-cells in vitro. However, in some dasatinib-treated leukemia patients, clonal lymphocytosis with large granular lymphocyte (LGL) morphology develops, and this is associated with enhanced therapeutic responses. To elucidate the mechanistic basis for this paradoxical observation, we conducted detailed phenotypic and functional analyses of T-cell and NK-cell populations from 25 dasatinib-treated leukemia patients. All tested patients with LGL expansions (15/16) were cytomegalovirus (CMV) immunoglobulin (IgG) seropositive with high frequencies of CMV-specific CD8(+) T-cells; 5/16 LGL patients also experienced symptomatic CMV reactivation during dasatinib therapy. Expanded T-cell and NK-cell populations exhibited late differentiated (CD27(-)CD57(+)) phenotypes; this was associated with a predisposition to apoptosis within the T-cell compartment and impaired NK-cell cytotoxicity. Only 3/9 non-LGL patients were CMV IgG seropositive. Dasatinib inhibited in vitro lymphocyte functions, similarly in LGL patients and controls. Notably, distinct CD8(high) and CD8(low) T-cell subsets were observed in LGL patients; this phenotypic dichotomy was also apparent in CMV-specific CD8(+) T-cell populations, and exhibited features consistent with antigen-driven activation. In addition, plasma levels of IP-10, IL-6, monokine induced by interferon-γ and interleukin-2R were significantly increased in LGL patients. These data provide evidence that dasatinib-associated LGL expansion is linked to CMV reactivation and suggest a potential mechanism for this phenomenon.

Efficient in vivo delivery of plasmids and oligonucleotides using hemagglutinating virus of Japan envelope (HVJ-E) vector in immunological disease models

This unit describes a method for in vivo delivery of oligonucleotides or plasmids using the hemagglutinating virus of Japan envelope (HVJ-E), an inactivated Sendai virus particle, as a delivery system. Viral transfection methods generally show a higher transfection efficiency than nonviral methods for the delivery of genes to cells. However, in using these methods one must bear in mind that the introduction of a virus particle into a host carries a risk for leukemia induction and for creation of disturbances in immune function due to cytotoxicity.

[Long-term results of HBV and HCV infection in patients with blood system diseases]

AIM

To specify trends in clinical and laboratory manifestations of virus hepatitis B and C (HBV and HCV) in patients with blood diseases from the moment of the first positive specific tests for HBV and HCV markers; to assess effects of HBV and HCV infection on efficacy of treatment of blood disease treatment, i.e. lifespan of patients with hematological diseases.

MATERIAL AND METHODS

The study enrolled 257 patients: 205 with acute leukemia - AL, 40 with lymphoproliferative diseases, 4 - with CML and 8 - others; 8 healthy bone marrow donors. The patients were admitted to Russian Hematological Research Center in 2004-2006 Follow-up median was 253 days. A total of 7800 biological samples were studied, among them about 4000 tests for HBV DNA and HCV RNA.

RESULTS

Positive tests for specific markers of HBV and HCV were absent only in 78 (29.4%) patients. Positive markers of coinfection were detected in 57 (32.8%) of 174 patients with HBV infection and in 81.4% of 70 patients with HCV infection. Probability of detection of HCV markers after positive tests for HBV markers and vice versa is about 3 times higher than probability of their isolated detection. Among patients infected with HBVsymptoms of hepatitis B are likely to appear in 56% patients to day 500 of follow-up from the date of the first positive specific test. Median of the interval between the first positive test for HBV markers and probable clinical signs of hepatitis was 30 days. Among patients with HCV infection, 85% develop hepatitis to follow-up day 300 since the date of the first specific positive test. Almost 100% patients infected with two viruses develop hepatitis to follow-up day 600. Median of the interval between the first positive test for HBV and HCV markers and probable hepatitis picture was 47 days. Overall 3-year survival of AL patients was 40%, of patients with lymphoproliferative diseases - 58%. Overall 7-month survival was 75% in AA patients. HBV infection in patients with blood disease is associated with high risk of death, especially in AA and AL. Association between HCV infection and survival is not proved.

CONCLUSION

A high rate of clinical realization of viral hepatitis B and C, especially in coinfection, calls for virological and clinical monitoring of patients with any positive test for HBV and HCV markers.

Antileukemia and antitumor effects of the graft-versus-host disease: a new immunovirological approach

In leukemic mice, the native host's explicit and well-defined immune reactions to the leukemia virus (a strong exogenous antigen) and to leukemia cells (pretending in their native hosts to be protected "self" elements) are extinguished and replaced in GvHD (graft-versus-host disease) by those of the immunocompetent donor cells. In many cases, the GvHD-inducer donors display genetically encoded resistance to the leukemia virus. In human patients only antileukemia and anti-tumor cell immune reactions are mobilized; thus, patients are deprived of immune reactions to a strong exogenous antigen (the elusive human leukemia-sarcoma retroviruses). The innate and adaptive immune systems of mice have to sustain the immunosuppressive effects of leukemia-inducing retroviruses. Human patients due to the lack of leukemiainducing retroviral pathogens (if they exist, they have not as yet been discovered), escape such immunological downgrading. After studying leukemogenic retroviruses in murine and feline (and other mammalian) hosts, it is very difficult to dismiss retroviral etiology for human leukemias and sarcomas. Since no characterized and thus recognized leukemogenic-sarcomagenic retroviral agents are being isolated from the vast majority of human leukemias-sarcomas, the treatment for these conditions in mice and in human patients vastly differ. It is immunological and biological modalities (alpha interferons; vaccines; adoptive lymphocyte therapy) that dominate the treatment of murine leukemias, whereas combination chemotherapy remains the main remission-inducing agent in human leukemias-lymphomas and sarcomas (as humanized monoclonal antibodies and immunotoxins move in). Yet, in this apparently different backgrounds in Mus and Homo, GvHD, as a treatment modality, appears to work well in both hosts, by replacing the hosts' anti-leukemia and anti-tumor immune faculties with those of the donor. The clinical application of GvHD in the treatment of human leukemias-lymphomas and malignant solid tumors remains a force worthy of pursuit, refinement and strengthening. Graft engineering and modifications of the inner immunological environment of the recipient host by the activation or administration of tumor memory T cells, selected Treg cells and natural killer (NKT) cell classes and cytokines, and the improved pharmacotherapy of GvHD without reducing its antitumor efficacy, will raise the value of GvHD to the higher ranks of the effective antitumor immunotherapeutical measures. Clinical interventions of HCT/HSCT (hematopoietic cell/stem cell transplants) are now applicable to an extended spectrum of malignant diseases in human patients, being available to elderly patients, who receive non-myeloablative conditioning, are re-enforced by post-transplant donor lymphocyte (NK cell and immune T cell) infusions and post-transplant vaccinations, and the donor cells may derive from engineered grafts, or from cord blood with reduced GvHD, but increased GvL/GvT-inducing capabilities (graft-versus leukemia/tumor). Post-transplant T cell transfusions are possible only if selected leukemia antigen-specific T cell clones are available. In verbatim quotation: "Ultimately, advances in separation of GvT from GvHD will further enhance the potential of allogeneic HCT as a curative treatment for hematological malignancies" (Rezvani, A.R. and Storb, R.F., Journal of Autoimmunity 30:172-179, 2008 (see in the text)). It may be added: for cure, a combination of the GvL/T effects with new targeted therapeutic modalities, as elaborated on in this article, will be necessary.

Escalated regimen of hepatitis B vaccine in childhood hematological malignancies while on chemotherapy

This prospective study was conducted to find the effective vaccination schedule against hepatitis B virus (HBV) infection for children with hematological malignancies. Sixty patients ages 2-15 years old with hematological malignancies on chemotherapy, negative for hepatitis B surface antigen (HBsAg) and never vaccinated for HBV before, were vaccinated with 40 microg of vaccine at 0, 1 and 2 months. Antibody titers were measured 6 weeks after administration of last dose. Out of the 60 children enrolled, 5 died during the course of treatment and 4 dropped out before completion, leaving 51 for final analysis. More than 70% exhibited protective levels of antibodies (> 10 mIU/ml) against hepatitis B virus. There were no significant effects of age or sex on the antibody response, although antibodies were higher among girls (90.9%) than boys (65%). Patients with non-Hodgkin's lymphoma were found to exhibit a better antibody response than leukemic children (p = 0.024). Children with hematological cancers should be vaccinated with an escalated regimen of the vaccine.

Hematopoietic stem cells and retroviral infection

Retroviral induced malignancies serve as ideal models to help us better understand the molecular mechanisms associated with the initiation and progression of leukemogenesis. Numerous retroviruses including AEV, FLV, M-MuLV and HTLV-1 have the ability to infect hematopoietic stem and progenitor cells, resulting in the deregulation of normal hematopoiesis and the development of leukemia/lymphoma. Research over the last few decades has elucidated similarities between retroviral-induced leukemogenesis, initiated by deregulation of innate hematopoietic stem cell traits, and the cancer stem cell hypothesis. Ongoing research in some of these models may provide a better understanding of the processes of normal hematopoiesis and cancer stem cells. Research on retroviral induced leukemias and lymphomas may identify the molecular events which trigger the initial cellular transformation and subsequent maintenance of hematologic malignancies, including the generation of cancer stem cells. This review focuses on the role of retroviral infection in hematopoietic stem cells and the initiation, maintenance and progression of hematological malignancies.

Earlier onset of delta-retrovirus-induced leukemia after splenectomy

Infection by δ-retroviruses such as human T-lymphotropic virus type 1 (HTLV-1) and bovine leukemia virus (BLV) is mostly asymptomatic. Indeed, only a minority (<5%) of δ-retrovirus infected hosts will develop either lymphoproliferative or neurodegenerative diseases after long latency periods. In fact, the host immune response is believed to tightly control viral replication but this assumption has not been definitely proven in vivo. Here, we provide direct experimental evidence demonstrating that integrity of the spleen is required to control pathogenesis. In the BLV model, we show that asplenia decreases efficiency of the immune response and induces an imbalance in cell dynamics resulting in accelerated onset of leukemia. These observations enlighten a potential threat in splenectomized HTLV-1 carriers and justify a regular preventive evaluation.

High Prevalence of SV40 Infection in Patients with Nodal Non-Hodgkin's Lymphoma But Not Acute Leukemia Independent of Contaminated Polio Vaccines in Taiwan

Recent studies have linked simian virus 40 (SV40) to non-Hodgkin's lymphoma (NHL), especially in countries in which people were exposed to contaminated polio vaccines prior to 1963. In Taiwan, nearly all children were not exposed to contaminated polio vaccine during this period; the relationship between SV40 infection and hematological malignancies is unclear and deserves to be studied. Using PCR amplification of SV40 large T antigen DNA, confirmed by Southern blot hybridization and sequence analysis, 91 frozen lymph nodes from NHL patients were examined. Thirteen (14.3 percent) showed positive for SV40. All other test samples, including diagnostic bone marrow from patients with acute leukemia, peripheral blood from 10 relatives of SV40 positive-patients and 91 age-matched normal volunteers, and 5 reactive hyperplastic lymphoid tissues, showed negative. These results may reflect that human-to-human transmission of SV40 is independent of contaminated polio vaccines; and SV40 is possibly associated with the development of NHL in Taiwan (p = 0.0001). Prospective studies are needed to determine the prevalence of SV40 infections in our and other human populations and to explore the means of transmission of the virus.

Human herpesvirus-6 DNAemia in immunosuppressed adult patients with leukemia at risk for mold infection

Little is known about human herpesvirus-6 (HHV-6) in leukemia patients. We prospectively followed 37 leukemia patients at risk for mold infection. HHV-6 DNA was detected from whole blood specimens in 11 patients (30%). History of granulocyte transfusions (p=0.05) and prior relapse of leukemia (p=0.07) were the only independent predictors of HHV-6 DNAemia.

The investigation of parvovirus B19 infection in patients with haematological disorders by using PCR and ELISA techniques

Parvovirus B19 has a marked tropism for erythroid progenitor cells. This may lead to chronic anemia in predisposed individuals. The purpose of the study was to investigate the frequency of parvovirus B19 infections in patients with diagnosis of haematological disorders. In order to determine the diagnostic use of different markers of parvovirus B19 infection, serum specimens obtained from 79 patients with haematological disorders were tested for specific antibodies and viral DNA through the use of ELISA and PCR techniques. Evidence of parvovirus B19 infection was found in 23/79 (29.1%) patients by demonstrating viral DNA and/or specific IgM antibody. B19 infection was established in 3 of 11 patients with chronic myeloid leukemia, in 3 of 11 acute myeloid leukemia, in 2 of 11 patients with multiple myeloma, in 3 of 8 patients with Hodgkin's lymphoma, in 5 of 10 patients with non-Hodgkin's lymphoma, in 1 of 6 patients with myelodysplastic syndrome, in 4 of 11 patients with chronic lymphocytic leukemia, and in 2 of 11 patients with acute lymphocytic leukemia. In 4 of 23 positive patients, only parvovirus B19 DNA could be detected, while 7 patients were tested positive for both parvovirus B19 DNA and specific IgM. Nine patients were tested positive for both B19 DNA and specific IgG. In the remaining 3 positive patients only specific IgM could be detected. Due to the discrepancies between DNA and IgM results, the diagnostic procedures should include a search for specific DNA by PCR methods if specific IgM has been found to be negative.

Preclinical assessment of FHIT gene replacement therapy in human leukemia using a chimeric adenovirus, Ad5/F35

PURPOSE

Expression of the FHIT protein is lost or reduced in most solid tumors and a significant fraction of hematopoietic malignancies. Adenovirus 5 (Ad5) virus or adeno-associated viral vectors have been used to study the tumor suppressor function of FHIT in solid tumors, but these tools have not been effective in leukemias. We have generated a chimeric FHIT-containing adenovirus composed of Ad5 and the group B adenovirus called F35 with which we have been able to efficiently infect hematopoietic cells.

EXPERIMENTAL DESIGN

Infection efficiency of Ad5/F35-FHIT and Ad5/F35-GFP viruses was tested in leukemia cell lines that lacked FHIT expression, and biological effects of successful infection were assessed. An acute myelogenous leukemia, a chronic myelogenous leukemia, and four acute lymphoblastic leukemia human cell lines were examined as well as two EBV-transformed B lymphoblastoid cell lines that expressed endogenous FHIT.

RESULTS

Two of four acute lymphoblastic leukemia cell lines, Jurkat and MV4;11, which were efficiently infected with Ad5/F35-FHIT, underwent growth suppression and massive induction of apoptosis without apparent activation of caspase-8 or caspase-2 and late activation of caspase-3. Treatment of infected cells with caspase-9 and caspase-3 inhibitors partially blocked FHIT-induced apoptosis. The two remaining infected acute lymphoblastic leukemia cell lines, Molt-3 and RS4;11, were apparently unaffected. Restoration of FHIT expression in the chronic myelogenous leukemia K562 cell line and the acute myelogenous leukemia KG1a cell line also induced apoptosis but at later time points than seen in the acute lymphoblastic leukemia Jurkat and MV4;11 cell lines. I.v. injection of Ad5/F35-FHIT-infected Jurkat cells resulted in abrogation of tumorigenicity in the NOD/SCID xenogeneic engraftment model.

CONCLUSION

FHIT restoration in some FHIT-deficient leukemia cells induces both antiproliferative and proapoptotic effects involving the intrinsic caspase apoptotic pathway.

Leukaemogenic mechanism of human T-cell leukaemia virus type I

Adult T-cell leukaemia (ATL) is a neoplastic disease derived from CD4(+) T-lymphocytes and etiologically associated with human T-cell leukaemia virus type I (HTLV-I). In addition to structural genes, HTLV-I encodes regulatory and accessory genes in the pX region. Among them, Tax is thought to play a central role in leukaemogenesis through its potent transforming activity. However, since Tax is a major target of the host immune system, its expression is often lost in ATL cells, indicating Tax is dispensable in the last phase of leukaemogenesis. The HTLV-I bZIP factor (HBZ), encoded on the HTLV-I minus strand, was recently shown to be expressed in all ATL cells, and to support growth of human T-cell lines. These findings suggest that HBZ is critical to ATL onset. In addition to viral factors and genetic and epigenetic changes in cellular genes, the host immune status and genetic background also function in leukaemogenesis.

Cooperation of NF-kappaB2/p100 activation and the PDZ domain binding motif signal in human T-cell leukemia virus type 1 (HTLV-1) Tax1 but not HTLV-2 Tax2 is crucial for interleukin-2-independent growth transformation of a T-cell line

Human T-cell leukemia virus type 1 (HTLV-1) but not HTLV-2 is associated with adult T-cell leukemia, and the distinct pathogenicity of these two closely related viruses is thought to stem from the distinct biological functions of the respective transforming proteins, HTLV-1 Tax1 and HTLV-2 Tax2. In this study, we demonstrate that Tax1 but not Tax2 interacts with NF-kappaB2/p100 and activates it by inducing the cleavage of p100 into the active transcription factor p52. Using RNA interference methods, we further show that NF-kappaB2/p100 is required for the transformation induced by Tax1, as determined by the ability to convert a T-cell line (CTLL-2) from interleukin-2 (IL-2)-dependent to -independent growth. While Tax2 shows a reduced transforming activity relative to Tax1, Tax2 fused with a PDZ domain binding motif (PBM) present only in Tax1 shows transforming activity equivalent to that of Tax1 in CTLL-2 cells expressing an inducer of p52 processing. These results reveal that the activation of NF-kappaB2/p100 plays a crucial role in the Tax1-mediated transformation of T cells and that NF-kappaB2/p100 activation and PBM function are both responsible for the augmented transforming activity of Tax1 relative to Tax2, thus suggesting that these Tax1-specific functions play crucial roles in HTLV-1 leukemogenesis.

Characteristics and outcome of respiratory syncytial virus infection in patients with leukemia

BACKGROUND AND OBJECTIVES

Little is known about respiratory syncytial virus (RSV) infection in patients with leukemia. The aim of this study was to determine the characteristics, and the outcome of RSV infection with or without therapy with aerosolized ribavirin in leukemia patients.

DESIGN AND METHODS

We reviewed the records of 52 leukemia patients with RSV infection seen at our institution between October 2000 and March 2005.

RESULTS

The median age of the patients was 47 years (range, 1-83 years). Most patients were male (65%) and had acute leukemia (65%); 46% had received salvage chemotherapy and 62% corticosteroids before RSV infection. Compared to the 25 patients with upper respiratory tract infection (URI), the 27 patients with pneumonia had a higher median APACHE II score at the time of the first assessment at the hospital for respiratory symptoms (11 vs 16), and a higher rate of corticosteroid treatment in the month preceding the infection (48% vs 74%) (all p < or =0.05). Twenty-four (46%) patients received aerosolized ribavirin. Patients who presented with URI and were treated with ribavirin were less likely than non-treated patients to develop pneumonia (68% vs 96%, p<0.01) and possibly die of pneumonia (6% vs 36%, p=0.1). Multiple logistic regression analysis identified high APACHE II score and lack of ribavirin treatment as independent predictors of progression to pneumonia (p=0.01). Five patients (10%) died within 30 days of RSV infection; all had pneumonia.

INTERPRETATION AND CONCLUSIONS

RSV infection is associated with significant morbidity and mortality in leukemia patients; treatment with aerosolized ribavirin at the stage of URI may prevent pneumonia in some subsets of patients.

NK-cell lymphomas and leukemias: a spectrum of tumors with variable manifestations and immunophenotype

Natural killer (NK) cells are lymphocytes that have some phenotypic and functional similarities to cytotoxic T cells but do not express the T-cell receptor complex. NK-cell malignancies may be localized or disseminated at initial examination, and most behave aggressively. The variable presentation of NK-cell lymphomas and leukemias suggests that they represent a spectrum of disease, with Epstein-Barr virus (EBV) implicated in the pathogenesis of most cases. Using cases presented in Session 10 of the 2005 Society for Hematopathology/European Association for Haematopathology Workshop on T-cell and NK-cell malignancies, we discuss outstanding issues in the classification and diagnosis of NK-cell malignancies. These difficulties are related to unusual sites of manifestation, atypical immunophenotypic features, and EBV+ T-cell tumors that resemble classical extranodal NK/T-cell lymphoma, nasal-type (EN-NK/T-NT). Although some of these cases can be grouped into ENNK/T-NT, classification of tumors that have atypical or discordant features will remain controversial, particularly when EBV is absent.

Epstein-Barr virus early-antigen antibodies before allogeneic haematopoietic stem cell transplantation as a marker of risk of post-transplant lymphoproliferative disorders

The occurrence of post-transplant lymphoproliferative disorders (PTLDs) after allogeneic haematopoietic stem cell transplantation (allo-HSCT) represents a clinical problem. Pretransplant Epstein-Barr virus serological status and viral load was determined in 21 recipients and 28 control transplanted patients, with (+) and without (-) PTLD, respectively. Early-antigen immunoglobulin G (EA-IgG) was detected in 12/21 PTLD+ patients, but only 2/28 PTLD patients (P = 0.00023, Odds ratio = 17.42). High viral load was detected in peripheral blood mononuclear cells at PTLD diagnosis, independently of deleted LMP1. Detection of EA-IgG in allo-HSCT recipients pretransplantation might be considered as risk factor for PTLD development.

Parvovirus B19 infection in children with a variety of hematological disorders

This study was carried out to detect Parvovirus B19 (PB19) DNA together with its antibodies in the sera of children with a range of hematological disorders to clarify the contribution of this infection to changes observed in hematological picture in those populations. This study included 85 pediatric patients with different hematological disorders. Twenty healthy subjects with matched age and sex were included as controls. Patients were classified into four groups; group I included 25 patients with hemolytic anemia in aplastic crisis, group II included 20 patients with hemolytic anemia without aplastic crisis, group III included 20 acute leukemia patients under chemotherapy, group IV included 20 patients with recently diagnosed acute leukemia. Virological study for PB19 included determination of specific IgG & IgM together with viral DNA by polymerase chain reaction (PCR). In all groups of patients with positive markers for PB19, there were statistically significant differences in the mean Hb concentration and RBC count (P < 0.001 for each), presence of neutropenia (P = 0.003) and lymphocytosis (P < 0.001) compared to controls. There was statistically significant difference in the prevalence of PB19 IgM, IgG and PCR among studied groups compared to control group. In group I and group II IgG had the highest positive rate (56 and 35%, respectively). In group III IgG also had a high positive rate (45%). However, in group IV IgM had the highest positive rate (50%) followed by PCR (45%) then IgG (40%). In conclusion, PB19 infection is detected in high rates among children with hematological disorders. PB19 must be suspected and screened for when there is anemia in those patients associated with neutropenia and lymphocytosis. In patients with acute leukaemia under chemotherapy who have unexpected anemia, neutropenia and lymphocytosis Parvovirus infection should be considered before a change of chemotherapy protocol. Screening of blood for PB19 may be helpful in understanding the epidemiology of infection with this virus. The direct detection of DNA by PCR in sera needs to be coupled with serology for a more reliable diagnosis of PB19 infections in these children.

Vaccination and the risk of childhood acute leukaemia: the ESCALE study (SFCE)

BACKGROUND

In 2002, a poster alerted the French health authorities to the possibility that the risk of childhood leukaemia might be increased by hepatitis B vaccination. Elucidating the role of vaccination in the aetiology of childhood acute leukaemia (AL) was therefore included in the objectives of an ongoing national study.

METHODS

The ESCALE study was a French national population-based case-control study conducted in France in 2003 and 2004 in order to investigate the role of infectious, environmental and genetic factors in four childhood neoplastic diseases (leukaemia, lymphoma, neuroblastoma and brain tumour). The controls were randomly selected from the French population and age and gender frequency matched with the cases. A total of 776 cases of AL (91% of the eligible cases) and 1681 controls (71% of the eligible controls) were included. In a specific standardized telephone interview, which was the same for both the cases and controls, each mother was asked to read out her child's complete vaccination record.

RESULTS

No association between vaccination and the risk of childhood AL: acute lymphoblastic leukaemia or acute myeloblastic leukaemia was observed. No relationship between the risk of leukaemia and the type of vaccine, number of doses of each vaccine, total number of injections, total number of vaccine doses or number of early vaccinations was evidenced. No confounding factor was observed.

CONCLUSION

The study did not show any evidence of a role of vaccination in the aetiology of childhood leukaemia.

Trends in childhood cancer incidence: review of environmental linkages

Cancer in children is rare and accounts for about 1% of all malignancies. In the developed world, however, it is the commonest cause of disease-related deaths in childhood, carrying with it a great economic and emotional cost. Cancers are assumed to be multivariate, multifactorial diseases that occur when a complex and prolonged process involving genetic and environmental factors interact in a multistage sequence. This article explores the available evidence for this process, primarily from the environmental linkages perspective but including some evidence of the genetic factors.

Construction of doxycyline-dependent mini-HIV-1 variants for the development of a virotherapy against leukemias

T-cell acute lymphoblastic leukemia (T-ALL) is a high-risk type of blood-cell cancer. We describe the improvement of a candidate therapeutic virus for virotherapy of leukemic cells. Virotherapy is based on the exclusive replication of a virus in leukemic cells, leading to the selective removal of these malignant cells. To improve the safety of such a virus, we constructed an HIV-1 variant that replicates exclusively in the presence of the nontoxic effector doxycycline (dox). This was achieved by replacement of the viral TAR-Tat system for transcriptional activation by the Escherichia coli-derived Tet system for inducible gene expression. This HIV-rtTA virus replicates in a strictly dox-dependent manner. In this virus, additional deletions and/or inactivating mutations were introduced in the genes for accessory proteins. These proteins are essential for virus replication in untransformed cells, but dispensable in leukemic T cells. These minimized HIV-rtTA variants contain up to 7 deletions/inactivating mutations (TAR, Tat, vif, vpR, vpU, nef and U3) and replicate efficiently in the leukemic SupT1 T cell line, but do not replicate in normal peripheral blood mononuclear cells. These virus variants are also able to efficiently remove leukemic cells from a mixed culture with untransformed cells. The therapeutic viruses use CD4 and CXCR4 for cell entry and could potentially be used against CXCR4 expressing malignancies such as T-lymphoblastic leukemia/lymphoma, NK leukemia and some myeloid leukemias.

Varicella-Zoster Virus Encephalitis in a Patient Undergoing Unrelated Cord Blood Transplantation for Myelodysplastic Syndrome-Overt Leukemia

Varicella-zoster virus (VZV) infection of the central nervous system (CNS) is rare after hematopoietic stem cell transplantation (SCT). Here, we describe the first patient who developed VZV encephalitis after cord blood transplantation (CBT). A 35-year-old man with myelodysplastic syndrome-overt leukemia underwent CBT. On day +23, a neutrophil count consistently greater than 0.5 x 10(9)/L was achieved. On day +42, 1 mg/kg per day of prednisolone therapy was initiated for grade III acute graft-versus-host disease (GVHD). Then, the dose of prednisolone was slowly reduced. For exacerbation of chronic GVHD, the dose of prednisolone was again increased to 1 mg/kg per day on day +231. On day +265, localized cutaneous zoster in the left thoracic region occurred, but soon resolved after acyclovir therapy. On day +309, he suddenly developed diplopia. Subsequently, right facial palsy and hearing impairment occurred. No skin rash was observed. Magnetic resonance imaging (MRI) scans revealed multifocal abnormal high-signal intensity in the CNS. A high level of VZV DNA was detected in a cerebrospinal fluid specimen. He was diagnosed with VZV encephalitis. Acyclovir was given intravenously for 40 days. Four months after the onset, the neurologic symptoms had incompletely resolved. MRI scans showed substantial resolution but with mild residual lesions. The present report indicates that VZV should be considered as a possible causative agent in patients who develop multifocal neurologic symptoms of the CNS after SCT.

[Frequency and characteristics of hepatitis B infection in children with malignant diseases]

INTRODUCTION

Hepatitis B, a complication of blood transfusion or other means of transmission, occurs with variable frequency in children with malignant diseases.

OBJECTIVE

The objective of this study was to determine the frequency of hepatitis B virus infection in children with malignant diseases, to investigate the clinical course of the illness, and to analyse the influence of hepatitis on cytotoxic treatment.

METHOD

The study included children diagnosed and treated for malignant diseases at the University Children's Hospital in Belgrade from 1997 to 2003. HBs Ag was analysed in all patients who had elevated transaminases of twice normal value, in children who had icterus, and in one group of patients treated routinely after 2001 before, during, and after therapy. RESULTS A total of 137 male and 107 female children who had malignancies were treated. From 113 children who were evaluated for the presence of HBs Ag at the beginning of treatment, 2 (1.7%) were HBsAg+. In this group of patients HBsAg was tested in 58 (51%) children during and after chemotherapy, and HBsAg was discovered in 17 (29%) of them. Of 123 children, in whom HBsAg was not tested at the beginning of their illness, 36 (55%) out of 66 (51%) tested patients were HBsAg+. No statistical difference between those two groups of patients was ascertained (chi2 = 3.27, p > 0.05). In summary, the presence of HBsAg was discovered in 53 patients, 22% out of 244 patients and 43% of tested patients. Nine patients had the icteric form of illness, with one case proving fatal due to fulminating hepatitis.

CONCLUSION

Taking into consideration the uncertain long-term prognoses of these patients, follow-up and treatment is essential.

Fragile sites are preferential targets for integrations of MLV vectors in gene therapy

Following gene therapy of SCID-X1 using murine leukemia virus (MLV) derived vector, two patients developed leukemia owing to an activating vector integration near the LMO2 gene. We found that these integrations reside within FRA11E, a common fragile site known to correlate with chromosomal breakpoints in tumors. Further analysis showed that fragile sites attract a nonrandom number of MLV integrations, shedding light on its integration mechanism and risk-to-benefit ratio in gene therapy.

Reduced cell turnover in lymphocytic monkeys infected by human T-lymphotropic virus type 1

Understanding cell dynamics in animal models have implications for therapeutic strategies elaborated against leukemia in human. Quantification of the cell turnover in closely related primate systems is particularly important for rare and aggressive forms of human cancers, such as adult T-cell leukemia. For this purpose, we have measured the death and proliferation rates of the CD4+ T lymphocyte population in squirrel monkeys (Saimiri sciureus) infected by human T-lymphotropic virus type 1 (HTLV-1). The kinetics of in vivo bromodeoxyuridine labeling revealed no modulation of the cell turnover in HTLV-1-infected monkeys with normal CD4 cell counts. In contrast, a substantial decrease in the proliferation rate of the CD4+ T population was observed in lymphocytic monkeys (e.g. characterized by excessive proportions of CD4+ T lymphocytes and by the presence of abnormal flower-like cells). Unexpectedly, onset of HTLV-associated leukemia thus occurs in the absence of increased CD4+ T-cell proliferation. This dynamics significantly differs from the generalized activation of the T-cell turnover induced by other primate lymphotropic viruses like HIV and SIV.

Splenic large B-cell lymphoma in patients with hepatitis C virus infection

Hepatitis virus infection, especially type C (hepatitis C virus [HCV]), has been suggested to be one of the important pathogenetic factors for low- and high-grade B-cell lymphoma, including splenic marginal zone lymphoma (SMZL), in southern Europe. Here, we analyzed the incidences of HCV and hepatitis B virus (HBV) infections, and the clinicopathologic features in 29 cases of splenic diffuse large B-cell lymphoma (DLBCL), 10 SMZL, 3 splenic mantle cell lymphoma, 1 hairy cell leukemia, 13 B-chronic lymphocytic leukemia, and 12 hepatosplenic T-cell and natural killer cell lymphoma. Fifteen (51.7%) splenic DLBCL cases were HCV antibody-positive, and another 6 (20.7%) had the HBsAg. The incidence of each was significantly (P < .01) higher than those of HCV (9.3%) and HBV (1.9%) infections in 54 node-based DLBCL cases. Four examined HCV-positive DLBCL cases showed no type II cryoglobulinemia. HCV RNA was detected in fresh tumor tissues from 6 of 7 examined DLBCL cases, and HBV DNA was present in another 2, as evaluated by real-time polymerase chain reaction. Immunohistologically, tumor cells in 5 of 7 examined DLBCL cases showed intracytoplasmic reactions for HCV NS3 and E2 proteins and the viral receptor CD81. Of 6 cases, 2 showed an intranuclear reaction for the HBV surface protein. By Southern blot analysis, no rearrangement of the Bcl2 gene was detected in the tumor tissue of 7 HCV-positive DLBCL cases. For the other types of malignant lymphoma, 1 case each of SMZL (10%) and hepatosplenic T-cell and natural killer cell lymphoma (8.3%) showed HCV infection. In conclusion, persistent human hepatitis virus infections, especially HCV, may play an important role in the tumorigenesis of splenic DLBCL in Japan.

AIDS Related Viruses, their Association with Leukemia, and Raf Signaling

Leukemia is characterized by the production of an excessive number of abnormal white blood cells. Over time, this expanding population of poorly/non- functional white blood cells overwhelms the normal function of the body's blood and immune systems. DNA translocations have been found common to leukemia, including Raf mutations. While the cause of leukemia is not known, several risk factors have been identified. In this review, we present an update on the role of AIDS related viruses as an etiology for leukemia. Human immunodeficiency virus-1 and -2 (HIV-1; -2) are the cause for the development of acquired immune deficiency syndrome (AIDS). Epstein-Barr virus (EBV), human cytomegalovirus (HCMV), Human papillomavirus (HPV), and Kaposi's sarcoma-associated herpesvirus (KSHV) are specifically implicated in AIDS associated malignancies. However, there are other viruses that are associated to a lesser extent with the AIDS condition and they are Human T-cell leukemia virus-1 (HTLV-1), hepatitis B virus (HBV), hepatitis C virus (HCV), and human herpesvirus-6 (HHV-6). Of these viruses, HTLV-1 has been etiologically associated with leukemia. Recent evidence suggests that EBV, HBV, HCV, and KSHV may also play a role in the development of some types of leukemia. Raf signaling has been shown to aid in the infection and pathogenesis of many of these viruses, making Raf pathway components good potential targets for the treatment of leukemia induced by AIDS related viruses.

Investigation of the bovine leukemia virus proviral DNA in human leukemias and lung cancers in Korea

The bovine leukemia virus (BLV) is the causative agent of enzootic bovine leucosis. This study investigated the presence of the BLV in leukemia (179 acute lymphoblastic leukemia, 292 acute myeloid leukemia and 46 chronic myelogenous leukemia cases) and 162 lung cancer patients (139 adenocarcinoma, 23 squamous cell carcinoma) to determine if the BLV is a causative organism of leukemia and lung cancer in Koreans. A BLV infection was confirmed in human cells by PCR using a BLV-8 primer combination. All 517 cases of human leukemia and 162 lung cancer were negative for a PCR of the BLV proviral DNA. In conclusion, although meat has been imported from BLV endemic areas, the BLV infection does not appear to be the cause of human leukemia or lung cancer in Koreans. These results can be used as a control for further studies on the BLV in Koreans.

Human T cell leukemia virus type 1: the role of Tax in leukemogenesis

Human T cell leukemia virus type 1 (HTLV-1) is a complex human retrovirus which is the causative agent of adult T cell leukemia (ATL). ATL occurs in about 4% of carriers and develops after a long latent period. Although the precise mechanism of HTLV-1 oncogenesis remains unclear, the pathogenesis has been linked to the pleiotropic activity of the viral transcriptional activator protein Tax. Tax has been shown to regulate viral and cellular gene expression and to functionally interfere with proteins involved in cell-cycle progression and DNA repair. This review will focus on the role of Tax in p53 inhibition.

Influence of membrane fluidity on human immunodeficiency virus type 1 entry

For penetration of human immunodeficiency virus type 1 (HIV-1), formation of fusion-pores might be required for accumulating critical numbers of fusion-activated gp41, followed by multiple-site binding of gp120 with receptors, with the help of fluidization of the plasma membrane and viral envelope. Correlation between HIV-1 infectivity and fluidity was observed by treatment of fluidity-modulators, indicating that infectivity was dependent on fluidity. A 5% decrease in fluidity suppressed the HIV-1 infectivity by 56%. Contrarily, a 5% increase in fluidity augmented the infectivity by 2.4-fold. An increased temperature of 40 degrees C or treatment of 0.2% xylocaine after viral adsorption at room temperature enhanced the infectivity by 2.6- and 1.5-fold, respectively. These were inhibited by anti-CXCR4 peptide, implying that multiple-site binding was accelerated at 40 degrees C or by xylocaine. Thus, fluidity of both the plasma membrane and viral envelope was required to form the fusion-pore and to complete the entry of HIV-1.

Fate of premalignant clones during the asymptomatic phase preceding lymphoid malignancy

Almost all cancers are preceded by a prolonged period of clinical latency during which a combination of cellular events helps move carcinogen-exposed cells towards a malignant phenotype. Hitherto, investigating the fate of premalignant cells in vivo remained strongly hampered by the fact that these cells are usually indistinguishable from their normal counterparts. Here, for the first time, we have designed a strategy able to reconstitute the replicative history of the bona fide premalignant clone in an animal model, the sheep experimentally infected with the lymphotropic bovine leukemia virus. We have shown that premalignant clones are early and clearly distinguished from other virus-exposed cells on the basis of their degree of clonal expansion and genetic instability. Detectable as early as 0.5 month after the beginning of virus exposure, premalignant cells displayed a two-step pattern of extensive clonal expansion together with a mutation load approximately 6 times higher than that of other virus-exposed cells that remained untransformed during the life span of investigated animals. There was no fixation of somatic mutations over time, suggesting that they regularly lead to cellular death, partly contributing to maintain a normal lymphocyte count during the prolonged premalignant stage. This equilibrium was finally broken after a period of 18.5 to 60 months of clinical latency, when a dramatic decrease in the genetic instability of premalignant cells coincided with a rapid increase in lymphocyte count and lymphoma onset.

Prevalence of anti human herpes virus-6 IgG and its receptor in acute leukemia (membrane cofactor protein: MCP, CD46)

BACKGROUND

CD46 is a membrane cofactor protein, which acts as a cofactor for factor I proteolytic cleavage of C3, so it protects the cells expressing it on their surface from autologous complement attack. It has been recently described as a receptor for HHV-6. Also, it has been shown to be highly expressed on malignant cells as compared to normal cells, thus playing a major role by which these cells, either cells of haematological malignancy or cells of other body cancers, can protect themselves against complement attack so they can survive and metastasize.

PATIENTS AND METHODS

This study has been done to detect the seroprevalence of HHV-6 among 47 Egyptian adult cases of acute leukemia using the anti-HHV-6 IgG ELISA serological technique. CD46 receptor expression and immunophenotyping technique were performed using FCM. Twenty nine of the cases were ANLL, while 18 were ALL cases. Sixteen age- and sex-matched control cases were also studied for both anti-HHV-6 IgG and CD46 receptor expression.

RESULTS

HHV-6 IgG antibodies were encountered in 29 (100%), 14 (77.8%) and 12 (75%) of the ANLL, ALL and the control group, cases, respectively. CD46 expression was encountered in 21 (72.4%) of the ANLL cases and in 10 (55.6%) of the ALL cases. Concordance between HHV- 6 seropositivity and CD46 expression was encountered in 31 cases (29 positive and 2 negative). Disconcordance was encountered in 16 cases with 14 showing HHV-6 IgG seropositivity with no CD46 expression and 2 showing the reverse.

CONCLUSION

The lack of significant correlation between CD46 expression and seropositivity would exclude CD46 expression as a cause of contracting HHV-6 infection in leukemic patients.

Viruses and lymphoma/leukaemia

Viruses of the retrovirus and herpesvirus families are aetiological agents of human leukaemias and lymphomas. The human T-cell leukaemia virus type 1 causes adult T-cell leukaemia and the Epstein-Barr virus is associated with Burkitt's lymphoma, lymphomas in immunosuppressed people, and Hodgkin lymphoma. The discovery of human herpesvirus type 8 has led to the identification of a rare and unusual group of virus-associated lymphoproliferative diseases. Individuals infected with the human immunodeficiency virus are at greatly increased risk of developing lymphoma but here the mechanism of lymphomagenesis is indirect. Recent data suggest that hepatitis C virus infection is also associated with an increased incidence of lymphoma, whereas data relating to SV40 remain controversial.

Virus target cell conditioning model to explain some epidemiologic characteristics of childhood leukemias and lymphomas

Frequent infections in early childhood, whole-day care and a socially unprivileged environment have been reported as protective factors for childhood leukemias and lymphomas. Conversely, a protected social environment, higher level of education and growing up in families with a low number of children are considered as risk factors. Additional risk factors involve agricultural occupation of the parents and exposure to several other occupational factors. These data led to a number of hypotheses that attempted to explain the epidemiologic observations; however, a number of questions are still open. Here we propose a new concept that could explain most of the epidemiologic characteristics. This concept is based on the assumption that persistent infections with TT virus-like agents increase the risk for specific chromosomal translocations. This risk should correlate with the viral load. Interferon induction by intermittent infections should reduce the viral load and thus decrease the risk for chromosomal modifications. Some virologic observations in support of this model are presented.