Parvovirus B19 capsid protein VP2 inhibits hematopoiesis in vitro and in vivo: implications for therapeutic use

Clinical impact & pathogenic mechanisms of human parvovirus B19: A multiorgan disease inflictor incognito

Human parvovirus B19 (B19V) causes myriads of clinical diseases; however, owing to lack of awareness and undetermined clinical impact, it has failed to become a virus pathogen of global concern. Cryptically, B19V causes significant morbidity and mortality. Half of the world population and 60 per cent of Indians are known to be serologically naive and are at risk of acquiring B19V infections. Cumulatively, our data showed 21.3 per cent B19V-infected patients with juvenile chronic arthropathy, recurrent abortions, multi-transfused thalassaemia and leukaemia. In addition, B19V-infected cases that ended fatally included patients with pure red cell aplasia, fulminant hepatitis and haemophagocytic syndrome. Novel clinical associations of B19V observed were amegakaryocytic thrombocytopaenia, myositis and non-occlusive ischaemic gangrene of bowel. B19V possesses multiple receptors which are distributed widely in human tissues. Vascular endothelial cell infection by B19V causes endothelialitis and vasculitic injuries besides antibody-dependent enhancement which empowered B19V to cause multiorgan diseases. Owing to lack of suitable animal model for B19V, true causal role remains to be determined, but numerous reports on B19V infections substantiate a causal role in multiorgan diseases. Hence, B19V infections need to be recognized, investigated and treated besides making efforts on vaccine developments.

Molecular Study of Parvovirus B19 Infection in Children with Acute Myeloid Leukemia

Background:

Parvovirus B19 is a common viral infection in children. Nearby evidences are present about its association with acute leukemia, especially acute lymphoblast leukemia. Nevertheless, scanty reports have discussed any role in acute myeloid leukemia (AML).

Purpose:

To evaluate the frequency of virological markers of B19 infection including its DNA along with specific immunoglobulins G (IgG) and M (IgM) among children with newly diagnosed AML. Besides, describing the clinical importance of Parvovirus B19 infection in those patients.

Patients and methods:

A case-control retrospective study was conducted on 48 children recently diagnosed with AML before and during chemotherapy induction and 60 healthy control. Specific serum IgM and IgG levels were determined by enzyme linked immunosorbant assay (ELISA) and DNA detection by polymerase chain reaction (PCR).

Results:

Parvovirus DNA was detected in 20 patients with AML. IgM was found in sera of four patients and one case had positive DNA and IgG (5%). Patients with recent parvovirus B19 infection had a significantly reduced hemoglobin levels, RBCs counts, platelet counts, neutrophil counts and absolute lymphocytosis (p=0.01, p=0.0001, p=0.01, p=0.02, p=0.0003, respectively). There were no clinical findings with statistically significant association to recent infection. Half of the patients with AML had positive PCR and/or IgM for parvovirus B19. Among children with AML under chemotherapy, there were reduced hemoglobin levels (P=0.03), reduced platelet counts (P=0.0001) and absolute neutropenia (mean±SD, 1.200 ±1.00) in those with parvovirus B19 infection. More than half of patients with parvovirus B19 (72.2%) had positive PCR and/or IgM and 36.4% of them had positive IgG.

Conclusion:

This study highlights that parvovirus B19 is common in children with AML either at diagnosis or under chemotherapy. There are no clinical manifestations that can be used as markers for its presence, but hematological laboratory findings can provide evidence for infection in the presence of anemia and neutropenia. Detection of parvovirus B19 by combined molecular and serological markers is required in such patients for accurate diagnosis.

Fetal gene therapy: opportunities and risks

Advances in human prenatal medicine and molecular genetics have allowed the diagnosis of many genetic diseases early in gestation. In-utero transplantation of allogeneic hematopoietic stem cells (HSC) has been successfully used as a therapy in different animal models and recently also in human fetuses. Unfortunately, clinical success of this novel treatment is limited by the lack of donor cell engraftment in non-immunocompromised hosts and is thus restricted to diseases where the fetus is affected by severe immunodeficiency. Gene therapy using genetically modified autologous HSC circumvents allogeneic HLA barriers and constitutes one of the most promising new approaches to correct genetic deficits in the fetus. Recent developments of strategies to overcome failure of efficient transduction of quiescent hematopoietic cells include the use of new vector constructs and transduction protocols. These improvements open new perspectives for gene therapy in general and for prenatal gene transfer in particular. The fetus may be especially susceptible for successful gene therapy due to the immunologic naiveté of the immature hematopoietic system during gestation, precluding an immune reaction towards the transgene. Ethical issues, in particular those regarding treatment safety, must be taken into account before clinical trials with fetal gene therapy in human pregnancies can be initiated.

Perinatal stem-cell and gene therapy for hemoglobinopathies

Most genetic diseases of the lymphohematopoietic system, including hemoglobinopathies, can now be diagnosed early in gestation. However, as yet, prenatal treatment is not available. Postnatal therapy by hematopoietic stem cell (HSC) transplantation from bone marrow, mobilized peripheral blood, or umbilical cord blood is possible for several of these diseases, in particular for the hemoglobinopathies, but is often limited by a lack of histocompatible donors, severe treatment-associated morbidity, and preexisting organ damage that developed before birth. In-utero transplantation of allogeneic HSC has been performed successfully in various animal models and recently in humans. However, the clinical success of this novel treatment is limited to diseases in which the fetus is affected by severe immunodeficiency. The lack of donor cell engraftment in nonimmunocompromised hosts is thought to be due to immunologic barriers, as well as to competitive fetal marrow population by host HSCs. Among the possible strategies to circumvent allogeneic HLA barriers, the use of gene therapy by genetically corrected autologous HSCs in the fetus is one of the most promising approaches. The recent development of strategies to overcome failure of efficient transduction of quiescent hematopoietic cells using new vector constructs and transduction protocols opens new perspectives for gene therapy in general, as well as for prenatal gene transfer in particular. The fetus might be especially susceptible for successful gene therapy approaches because of the developing, expanding hematopoietic system during gestation and the immunologic naiveté early in gestation, precluding immune reaction towards the transgene by inducing tolerance. Ethical issues, in particular regarding treatment safety, must be addressed more closely before clinical trials with fetal gene therapy in human pregnancies can be initiated.

Molecular mechanism underlying B19 virus inactivation and comparison to other parvoviruses

BACKGROUND

B19 virus (B19V) is a human pathogen frequently present in blood specimens. Transmission of the virus occurs mainly via the respiratory route, but it has also been shown to occur through the administration of contaminated plasma-derived products. Parvoviridae are highly resistant to physicochemical treatments; however, B19V is more vulnerable than the rest of parvoviruses. The molecular mechanism governing the inactivation of B19V and the reason for its higher vulnerability remain unknown.

STUDY DESIGN AND METHODS

After inactivation of B19V by wet heat and low pH, the integrity of the viral capsid was examined by immunoprecipitation with two monoclonal antibodies directed to the N-terminal of VP1 and to a conformational epitope in VP2. The accessibility of the viral DNA was quantitatively analyzed by a hybridization-extension assay and by nuclease treatment.

RESULTS

The integrity of the viral particles was maintained during the inactivation procedure; however, the capsids became totally depleted of viral DNA. The DNA-depleted capsids, although not infectious, were able to attach to target cells. Comparison studies with other members of the Parvoviridae family revealed a remarkable instability of B19V DNA in its encapsidated state.

CONCLUSION

Inactivation of B19V by heat or low pH is not mediated by capsid disintegration but by the conversion of the infectious virions into DNA-depleted capsids. The high instability of the viral DNA in its encapsidated state is an exclusive feature of B19V, which explains its lower resistance to inactivation treatments.