Bidirectional signal transduction is a newly elucidated mechanism in intercellular communication. The bidirectional signal transduction mediated by the Eph-ephrin is an important representative in this field. The Eph family receptor tyrosine kinases and their membrane-bound ligands, the ephrins, play pivotal roles in the development of nervous system, angiogenesis, etc. The signal transduction into cells by Eph receptors is the forward signal, whereas the signal transduction by ephrins is the reverse signal. Based on their molecular structures, the ephrins can be divided into two subclasses, i.e. ephrinA and ephrinB. The ephrinBs are transmembrane proteins, which can activate FAK, JNK and Wnt signal transduction pathways through phosphotyrosine-dependent signaling and PDZ-binding motif-dependent signaling. The ephrinAs are glycosylphosphotidylinositol (GPI) anchored proteins, which can also mediate reverse signal transduction.

Cell death as the partner of cell proliferation is one of the basic mechanism in cell biology. Recently, it became obscure since more and more patterns of cell death were reported. However, the classification of cell death, which was recommended by the Nomenclature Committee on Cell Death (NCCD) in 2009, clarified the criteria. The theme of the recommendation and recent data from the literature were discussed in this review. The significance of studies on cell death was discussed.

After near a century of research,the diverse and complicated relationship between viruses and tumors has been elucidated gradually.Last century it was demonstrated that some retroviruses and some herpes viruses could induce lymphoma and leukemia in some animals.However,it is more complicated in human.During the last two decades it has been confirmed that several types of hepatitis viruses could cause hepatocellular carcinoma and the relationship between human papillomaviruses and cervix carcinoma has been established.These viral vaccines became useful tools to prevent prevalence of these carcinomas.Because of the successful inoculation of live attenuated viral vaccines all around the world in recent 15 years,oncolytic virotherapy is revived,and provides a novel strategy for treatment of refractory tumors.

As novel organisms,tumors undergo microevolution in limited time and space in vivo.Due to genetic mutations and epigenetic mechanisms,tumor cell clones undergo linear or branching evolution.In most clinic patients,tumors develop through branching evolution pathways,causing tumor heterogeneity and affecting tumor progression.Microevolution is the biological basis for the refractoriness and recurrence of tumors and has been paid attention in research and clinic recently.In this paper,acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS) are used as examples to demonstrate tumor microevolution and the concept of linear and branching evolution.Questions and perspective in the field of tumor microevolution research are also discussed.

Human herpesviruses (HHV) are widespread all over the world,and persist in human in latent infection.When reactivated,HHV plays an important role in the pathogenesis and development of tumor and other diseases.Much attention has been paid on EB virus which can cause different tumors and other diseases.Studies within this half century have elucidated the mechanism of oncogenesis of γ-HHV.Recently it was reported that other HHV may have oncomodulation functions.

The disturbance of life rhythm exerts negative influence on modem life.The relationship between the disruption of circadian rhythms and tumor growth has attracted much attention.It has been studied in breast cancer and prostate cancer,and chronotherapeutics has been used for treatment of some cancers in clinic.Researchers have begun to investigate the association of circadian rhythms with leukemia/lymphoma outside China.The literatures were reviewed and the launch of research on this field was appealed.

Viral etiology of tumor has been studied for a century.Seven human tumor viruses were identified over the past half century.The complexity and regularity of the pathogenic mechanisms of human tumor viruses have been elucidated preliminarily.Human genome sequencing indicated that 8 ％ of human genes were composed of human endogenous retroviruses (HERVs).Owing to the findings that adult T-cell leukemia virus (HTLV) can cause human adult T-cell leukemia and animal exogenous and HERVs can induce tumors and malignant diseases,the relationship between HERVs and human tumors has attracted much attention receutly.Here this article discusses the association of the expression of HERVs with leukemia and solid tumors progression,which may be an important aspect of tumor virology.

Dormant follicular lymphoma, prostate carcinoma and breast carcinoma are frequently detected by autopsy of non-tumor patients. Dormancy of malignant cells in hematopoietic malignancies is associated with genesis, development and treatment of these diseases. Dormancy is the universally applied strategy by living organism during survival competition. As the in vivo neoplasm, tumor cells keep this property. Recently, much attention has been paid to the mechanisms of tumor dormancy. These studies not only have theoretical significance, provide new ways for the prevention and treatment of tumors, but also help the understanding of over-diagnosis, over-treatment and provide clues for precise medicine. This paper reviewed cellular mechanism of tumor cell dormancy,immunological and vascular regulation of dormant tumors. The clinical significance,application of these mechanisms and direction of further study, which will provide new clues for the treatment of hematopoietic malignancies, were also discussed.

Human herpesvirus 6 (HHV-6) is recognized as a ubiquitous dsDNA virus in human with widespread cell tropism in vivo, which could induce lifelong latent infection and be reactivated in some immunocompromised individuals leading to serious diseases. With the increasing application of hematopoietic stem cell transplantation (HSCT), it is obvious that HHV-6 reactivation has a close relationship with several complications including encephalitis after transplantation. On the other hand, among about 1 % infected people, HHV-6 and subtelomeric region of cell chromosomes in the state of endogenous persistent infection play a part in activated virus infection. As the detection methods make a great progress in HHV-6 detection, clinical data reveals the relationship between HHV-6 reactivation and lots of chronic diseases, especially lymphoma, leukemia as well as some chronic hematopoietic and immunological diseases.

Allee effect is a phenomenon in ecology characterized by a correlation between population size or density and the mean individual fitness of population or species.It is consistent with density dependent phenomenon in biomedical field.Recently,Allee effect has been studied by theoretical biologist in detail for oncology biological research.Leukemia cells,which reside in organic microenvironment,show an obvious Allee effect.The authors compared Allee effect with density dependent growth of leukemia cells based on their work experience and literature data.No principle distinction was found between these two terms.In this paper,Allee effect in leukemia cell culture and leukemia,especially in minimal residual disease,will be discussed in the view of ecology.The association between Allee effect and leukemogenesis and relapse dynamics will also be explored in the future research.