Citrobacter rodentium Induces Tissue-Resident Memory CD4+ T Cells.

Tissue-resident memory T cells (TRM cells) are a novel population of tissue-restricted antigen-specific T cells. TRM cells are induced by pathogens and promote host defense against secondary infections. Although TRM cells cannot be detected in circulation, they are the major memory CD4+ and CD8+ T-cell population in tissues in mice and humans. Murine models of CD8+ TRM cells have shown that CD8+ TRM cells maintain tissue residency via CD69 and though tumor growth factor ß-dependent induction of CD103. In contrast to CD8+ TRM cells, there are few models of CD4+ TRM cells. Thus, much less is known about the factors regulating the induction, maintenance, and host defense functions of CD4+ TRM cells. Citrobacter rodentium is known to induce IL-17+ and IL-22+ CD4+ T cells (Th17 and Th22 cells, respectively). Moreover, data from IL-22 reporter mice show that most IL-22+ cells in the colon 3 months after C. rodentium infection are CD4+ T cells. This collectively suggests that C. rodentium may induce CD4+ TRM cells. Here, we demonstrate that C. rodentium induces a population of IL-17A+ CD4+ T cells that are tissue restricted and antigen specific, thus meeting the criteria of CD4+ TRM cells. These cells expand and are a major source of IL-22 during secondary C. rodentium infection, even before the T-cell phase of the host response in primary infection. Finally, using FTY 720, which depletes circulating naive and effector T cells but not tissue-restricted T cells, we show that these CD4+ TRM cells can promote host defense.

Characterization of in vitro biotransformation of the new oral anticoagulants, the factor VIIa inhibitors AS1927819-00 and AS1932804-00.

We recently developed a prodrug (AS1932804-00, CMP) of the novel FVIIa inhibitor AS1924269-00, which possesses a carbamate amidine backbone. In addition, we developed another type of prodrug (AS1927819-00, OXP) with an oxime amidine backbone. In this study, we investigated the efficiency of conversion of these novel FVIIa prodrugs to their active forms by evaluating the production of the active form in vitro by using microsomes, mitochondria, and cryopreserved hepatocytes, and compared it with the in vivo conversion mechanisms of the prodrugs (oxime amidine vs. carbamate amidine). We observed that OXP and CMP showed improved oral absorption, and the efficiency of conversion of CMP to the active form was higher than that of OXP. The in vivo rate of conversion of OXP to its active form was low in rats, and compared to liver microsomes and mitochondria, cryopreserved hepatocytes supplemented with serum and coenzymes were an appropriate metabolic test tool. On the other hand, the efficiency of conversion of CMP to its active from could be appropriately evaluated using small intestinal microsomes. The development of a prodrug can be optimized when information about the stability of carboxylic acid esters in the presence of serum esterases, membrane permeability of intermediate forms, and differential tissue specificity to metabolic activities for carbamate and oxime backbones of amidine can be obtained.

Pharmacokinetics of the amidine prodrug of a novel oral anticoagulant factor VIIa inhibitor (AS1924269-00) in rats.

AS1924269-00 is a promising orally applicable anticoagulant that inhibits FVIIa but has very low oral absorption. Therefore, in this study, we aimed to develop a prodrug of AS1924269-00, which possesses a carbamate-added amidine functional group, with high membrane permeability. We investigated the pharmacokinetics of the carbamate-type prodrug of AS1924269-00 in rats. The Caco-2 cell monolayer was used as an in vitro model and in parallel an artificial membrane permeability assay (PAMPA) was performed to examine the transport mechanisms of the prodrug. The bioavailability of the active form was determined to be only 0.3% in rats, but the oral absorption of the prodrug was markedly improved, and its bioavailability was 36%. Our in vivo result was consistent with the finding that compared to AS1924269-00, the prodrug showed favorable permeability in Caco-2 cells and PAMPA. We introduced carbamate into the amidine functional group of the FVIIa inhibitor, which possesses the amidine backbone, and converted it to a prodrug using carboxylic acid ethyl ester. This novel prodrug had favorable absorption and membrane permeability in vivo and in vitro. Thus, we suggest a clinical application of the carbamate-added amidine prodrug of the FVIIa inhibitor.

Intracellular bacteria recognition contributes to maximal interleukin (IL)-12 production by IL-10-deficient macrophages.

Interleukin (IL)-12 is a key factor that induces T helper cell type 1-mediated immunity and inflammatory diseases. In some colitis models, such as IL-10 knock-out (KO) mice, IL-12 triggers intestinal inflammation. An abundant amount of IL-12 is produced by intestinal macrophages in response to stimulation by commensal bacteria in IL-10 KO mice. Intact bacteria are more potent inducers of macrophage IL-12 production than cell surface components in this model. This suggested that cell surface receptor signalling and intracellular pathogen recognition mechanisms are important for the induction of IL-12. We addressed the importance of intracellular recognition mechanisms and demonstrated that signal transducers and activator of transcription 1 (STAT1) signalling activated bacterial phagocytosis and was involved in the induction of abnormal IL-12 production. In IL-10 KO mouse bone marrow-derived (BM) macrophages, Escherichia coli stimulation induced increased IL-12p70 production compared to lipopolysaccharide combined with interferon (IFN)-γ treatment. Significant repression of IL-12 production was achieved by inhibition of phagocytosis with cytochalasin D, and inhibition of de novo protein synthesis with cycloheximide. Induction of IFN regulatory factors-1 and -8, downstream molecules of STAT1 and the key transcription factors for IK-12 transcription, following E. coli stimulation, were mediated by phagocytosis. Interestingly, STAT1 was activated after stimulation with E. coli in IL-10 KO BM macrophages, although IFN-γ could not be detected. These data suggest that molecules other than IFN-γ are involved in hyper-production mechanisms of IL-12 induced by E. coli stimulation. In conclusion, enteric bacteria stimulate excessive IL-12p70 production in IL-10 KO BM macrophages via phagocytosis-dependent signalling.

The Bacterial Connection between the Oral Cavity and the Gut Diseases.

More than 100 trillion symbiotic microorganisms constitutively colonize throughout the human body, including the oral cavity, the skin, and the gastrointestinal tract. The oral cavity harbors one of the most diverse and abundant microbial communities within the human body, second to the community that resides in the gastrointestinal tract, and is composed of >770 bacterial species. Advances in sequencing technologies help define the precise microbial landscape in our bodies. Environmental and functional differences render the composition of resident microbiota largely distinct between the mouth and the gut and lead to the development of unique microbial ecosystems in the 2 mucosal sites. However, it is apparent that there may be a microbial connection between these 2 mucosal sites in the context of disease pathogenesis. Accumulating evidence indicates that resident oral bacteria can translocate to the gastrointestinal tract through hematogenous and enteral routes. The dissemination of oral microbes to the gut may exacerbate various gastrointestinal diseases, including irritable bowel syndrome, inflammatory bowel disease, and colorectal cancer. However, the precise role that oral microbes play in the extraoral organs, including the gut, remains elusive. Here, we review the recent findings on the dissemination of oral bacteria to the gastrointestinal tract and their possible contribution to the pathogenesis of gastrointestinal diseases. Although little is known about the mechanisms of ectopic colonization of the gut by oral bacteria, we also discuss the potential factors that allow the oral bacteria to colonize the gut.

Rad51 accumulation at sites of DNA damage and in postreplicative chromatin.

Rad51, a eukaryotic RecA homologue, plays a central role in homologous recombinational repair of DNA double-strand breaks (DSBs) in yeast and is conserved from yeast to human. Rad51 shows punctuate nuclear localization in human cells, called Rad51 foci, typically during the S phase (Tashiro, S., N. Kotomura, A. Shinohara, K. Tanaka, K. Ueda, and N. Kamada. 1996. Oncogene. 12:2165-2170). However, the topological relationships that exist in human S phase nuclei between Rad51 foci and damaged chromatin have not been studied thus far. Here, we report on ultraviolet microirradiation experiments of small nuclear areas and on whole cell ultraviolet C (UVC) irradiation experiments performed with a human fibroblast cell line. Before UV irradiation, nuclear DNA was sensitized by the incorporation of halogenated thymidine analogues. These experiments demonstrate the redistribution of Rad51 to the selectively damaged, labeled chromatin. Rad51 recruitment takes place from Rad51 foci scattered throughout the nucleus of nonirradiated cells in S phase. We also demonstrate the preferential association of Rad51 foci with postreplicative chromatin in contrast to replicating chromatin using a double labeling procedure with halogenated thymidine analogues. This finding supports a role of Rad51 in recombinational repair processes of DNA damage present in postreplicative chromatin.

IL23 differentially regulates the Th1/Th17 balance in ulcerative colitis and Crohn's disease.

BACKGROUND: A novel T helper (Th) cell lineage, Th17, that exclusively produces the proinflammatory cytokine interleukin 17 (IL17) has been reported to play important roles in various inflammatory diseases. IL23 is also focused upon for its potential to promote Th17. Here, the roles of the IL23/IL17 axis in inflammatory bowel diseases such as ulcerative colitis (UC) and Crohn's disease (CD) were investigated. METHODS: Mucosal samples were obtained from surgically resected specimens (controls, n = 12; UC, n = 17; CD, n = 22). IL17 production by isolated peripheral blood (PB) and lamina propria (LP) CD4(+) cells was examined. Quantitative PCR amplification was performed to determine the mRNA expression levels of IL17, interferon gamma (IFNgamma), IL23 receptor (IL23R) and retinoic acid-related orphan receptor gamma (RORC) in LP CD4(+) cells, and IL12 family members, such as IL12p40, IL12p35 and IL23p19, in whole mucosal specimens. The effects of exogenous IL23 on IL17 production by LP CD4(+) cells were also examined. RESULTS: IL17 production was higher in LP CD4(+) cells than in PB. Significant IL17 mRNA upregulation in LP CD4(+) cells was found in UC, while IFNgamma was increased in CD. IL23R and RORC were upregulated in LP CD4(+) cells isolated from both UC and CD. IL17 production was significantly increased by IL23 in LP CD4(+) cells from UC but not CD. Upregulated IL23p19 mRNA expression was correlated with IL17 in UC and IFNgamma in CD. CONCLUSIONS: IL23 may play important roles in controlling the differential Th1/Th17 balance in both UC and CD, although Th17 cells may exist in both diseases.

A specific gene-microbe interaction drives the development of Crohn's disease-like colitis in mice.

Bacterial dysbiosis is associated with Crohn's disease (CD), a chronic intestinal inflammatory disorder thought to result from an abnormal immune response against intestinal bacteria in genetically susceptible individuals. However, it is unclear whether dysbiosis is a cause or consequence of intestinal inflammation and whether overall dysbiosis or specific bacteria trigger the disease. Here, we show that the combined deficiency of NOD2 and phagocyte NADPH oxidase, two CD susceptibility genes, triggers early-onset spontaneous TH1-type intestinal inflammation in mice with the pathological hallmarks of CD. Disease was induced by Mucispirillum schaedleri, a Gram-negative mucus-dwelling anaerobe. NOD2 and CYBB deficiencies led to marked accumulation of Mucispirillum, which was associated with impaired neutrophil recruitment and killing of the bacterium by luminal neutrophils. Maternal immunoglobulins against Mucispirillum protected mutant mice from disease during breastfeeding. Our results indicate that a specific intestinal microbe triggers CD-like disease in the presence of impaired clearance of the bacterium by innate immunity.

Unique Raman Spectroscopic Fingerprints of B-Cell Non-Hodgkin Lymphoma: Implications for Diagnosis, Prognosis and New Therapies.

OBJECTIVE: Raman spectroscopy is a non-invasive laser-based technique that identifies molecular chemical composition of tissues and cells. The objective of the work was to demonstrate that unique Raman spectroscopic fingerprints of B-cell non-Hodgkin lymphoma cells could be distinguished from normal B-cells. METHODS: Normal B-cells and B-cell non-Hodgkin lymphoma cells were mounted on aluminum slides and analyzed by Raman spectroscopy using Asymmetric Least Squares and Principal Component Analysis. RESULTS: Clustering by Principal Component Analysis differentiated normal B-cells from B-cell non-Hodgkin lymphoma cells as well as between the different B-cell non-Hodgkin lymphoma cell types. CONCLUSIONS: Raman spectroscopy technology provided a different paradigm in analyzing tumor cells which could be used for diagnosis as well as contribute new information on unique characteristics of cancer cells to understand pathogenesis and potential novel treatments.

Double minute chromosomes in acute myeloblastic leukemia.

Two patients with acute myeloblastic leukemia (AML) with double minute chromosomes (dmins) are described. One patient had dmins in approximately one-third of bone marrow cells examined at diagnosis; no other karyotypic changes were observed. The dmins disappeared when the patient achieved a complete remission. The second patient developed acute leukemia as a second cancer, having previously received radiotherapy and chemotherapy for a breast carcinoma. At the time of diagnosis of AML, the patient exhibited dmins in 12% of bone marrow cells; other complex karyotypic changes were observed. Data on the clinical and cytogenetic features of these cases are compared with those of other reported cases of acute leukemia with dmins. The possible biologic and clinical significance of dmins in acute leukemia is discussed.

Establishment and characterization of human signet ring cell gastric carcinoma cell lines with amplification of the c-myc oncogene.

Two unique human signet ring cell gastric carcinoma cell lines (designated HSC-39 and HSC-40A) were established in vitro from the ascites of a 54-year-old male patient. Both cell lines were biologically quite similar, grew in vitro in suspension with a population doubling time of 28-30 h, and had cytological features of mucinous epithelial tumor cells. They formed colonies in soft agar, with a cloning efficiency of 0.8-1.0%. Ultrastructurally, numerous granules were observed in the cytoplasm, suggesting secretory activity. The frequent presence of desmosome and the tight junction at the cell boundary certifies the epithelial origin of the lines. Immunocytochemistry and radioimmunoassay showed production of tumor marker antigens (carcinoembryonic antigen, CA 19-9, and sialyl-Lex-i) and gastrin in both lines. These lines were transplantable in athymic BALB/c nude mice. The histopathology of each line growing in athymic BALB/c nude mice was similar to that of the original tumor. The karyotype of the cells was highly aberrant with structural and numerical changes. The presence of numerous double minute chromosomes and loss of the 13 chromosome and Y-chromosome characterize these lines. In addition, the amplified c-myc oncogene (16-32-fold) was found in both cell lines and original ascitic tumor cells. Overexpression of the c-myc mRNA was noted. These cell lines may be a useful tool, providing both in vivo and in vitro systems for further studies of the biology and therapy of human signet ring cell (or Borrmann's type IV carcinoma) gastric carcinoma.

Chromosome abnormalities in adult T-cell leukemia/lymphoma: a karyotype review committee report.

Karyotypes of 107 cases with adult T-cell leukemia/lymphoma (58 male, 49 female; 81 acute or lymphoma type, 26 chronic or smoldering type) were reviewed by a panel of cytogeneticists and were correlated with the subtypes of the disease. Clonal chromosome abnormalities were found in 103 (96%) cases, of which four had hypotetraploidy. Of 184 numerical abnormalities in the remaining 99 cases with near- or pseudodiploidy, trisomies for chromosomes 3 (21% of cases), 7 (10%), and 21 (9%), monosomy for X chromosome (38%) in the female, and loss of a Y chromosome (17%) in the male were more frequent than expected (P less than 0.01). Of 373 structural abnormalities in all the 103 aneuploid cases, translocations involving 14q32 (28%) or 14q11 (14%) and deletion of 6q (23%) were most frequent, followed by deletion of 10p (9%), 3q (8%), 5q, 9q, and 13q (7% each), and 1p and 7p (6% each). The proportion of cases with aneuploid clones (with greater than or less than 46 chromosomes), the average numbers per case of both numerical and structural abnormalities, and marker chromosomes were larger in the aggressive acute or lymphoma type than in the nonaggressive chronic or smoldering type (P less than 0.01). The combination of rearrangement in 14q32 and monosomy X (seven cases) or deletion of 10p (six cases), and that of trisomy 3 and deletion in 6q21 (six cases), occurred only in the acute or lymphoma type and may be associated with the aggressiveness in adult T-cell leukemia/lymphoma.

Alterations of the double-strand break repair gene MRE11 in cancer.

MRE11 plays a role in DNA double-strand break repair. Hypomorphic mutations of MRE11 have been demonstrated in ataxia-telangiectasia (AT)-like disorder. ATM mutations play a causal role in AT and have been demonstrated in lymphoid malignancies in patients without AT histories. By analogy with the relationship of ATM to lymphoid malignancies, it is probable that alterations of MRE11 are associated with tumor formation. We performed a mutation analysis of MRE11 in 159 unselected primary tumors. Three missense mutations at conserved positions were found in breast and lymphoid tumors. Additionally, an aberrant transcript without genomic mutation was found in a breast tumor. These findings suggest an occasional role for MRE11 alterations in the development of primary tumors.

Antitumor cytotoxicity mediated by ligand-activated human V alpha24 NKT cells.

Human V alpha24 NKT cells bearing an invariant V alpha24J alphaQ antigen receptor, the counterpart of the murine V alpha14 NKT cells, are activated by the specific ligand, alpha-galactosylceramide (alpha-GalCer) in a CD1d-dependent manner. Here, we demonstrate that the alpha-GalCer-activated V alpha24 NKT cells exert a potent perforin-dependent cytotoxic activity against a wide variety of human tumor cell lines. In addition, we demonstrate that V alpha24 NKT cells and dendritic cells (DCs) from melanoma patients are functionally normal, even in the tumor-bearing status. The potential use of alpha-GalCer-activated V alpha24 NKT cells and/or DCs from patients for cancer immunotherapy is discussed.

S phase specific formation of the human Rad51 protein nuclear foci in lymphocytes.

The Rad51 protein, which is a homologue of the bacterial RecA protein, is involved in mitotic and meiotic recombination and in repair of double-strand breaks of DNA in yeast. The Rad51 homologue is conserved from yeast to human. In this study, the Rad51 protein was shown to be induced in peripheral blood lymphocytes (PBLs) 36 h after phytohemagglutinin (PHA) stimulation. Immunofluorescence study revealed that the distribution of the Rad51 protein in the nucleus was not uniform and focus-like staining was observed. Formation of the Rad51 foci was induced at 36 h after treatment of the cells with PHA. Twenty five percent of the cells had the foci at this time and the number of cells with foci declined thereafter. Cell cycle study using laser microscope by double staining method suggested that the appearance of the Rad51 nuclear foci was S phase specific. Furthermore, double staining study for the Rad51 protein and incorporated BrdU confirmed S phase specific appearance of the Rad51 nuclear foci. Formation of the Rad51 nuclear foci in PHA-stimulated lymphocytes might be involved in DNA recombination or DNA repair in S phase. The roles of RAD51 foci in S-phase will be discussed.

Identification of illegitimate recombination hot spot of the retinoic acid receptor alpha gene involved in 15;17 chromosomal translocation of acute promyelocytic leukemia.

Acute promyelocytic leukemia (APL) has been characterized by 15;17 chromosomal translocation, which involves the retinoic acid receptor alpha (RARA) gene on chromosome 17 and the PML gene on chromosome 15. The breakpoints have been mapped to three cluster regions in the PML gene, and to RARA gene intron 2. We have examined the distribution of breakpoints within RARA gene intron 2. An extremely restricted region (ERR) of 50 bp within RARA gene intron 2 was identified as the cluster region of breakpoints by polymerase chain reaction and sequence analysis of DNA from APL patients. To study experimentally the mechanism involved in the translocation, ERR was tested in NIH3T3 cells by in vitro transfection-recombination assay, in which target sequences were placed either downstream of the SV40 promoter or upstream of the neo gene. Cells were conferred resistance to G418 only when the promoter was fused to the neo gene by recombination of two target sequences during transfection. The molecular junctions were analysed in five clones, and all of them were shown to be confined within a 20 bp region in a 148 bp DNA fragment containing ERR. This suggests that ERR might be the illegitimate recombination hot spot in mammalian cells.

MLLT3 gene on 9p22 involved in t(9;11) leukemia encodes a serine/proline rich protein homologous to MLLT1 on 19p13.

Recently, the MLL gene at 11q23 was found to be involved in a subset of leukemias with an 11q23 abnormality. In the present study, we isolated chimeric cDNAs between the MLL and a gene designated MLLT3 at 9p22 from a cDNA library of an IMS-M1 cell line with a t(9;11)(p22;q23) translocation, a representative karyotypic abnormality seen in acute monocytic leukemia. We also isolated a normal MLLT3 cDNA and found an open reading frame encoding at least 318 amino acids with high serine/proline content (24.8%). The chimeric mRNAs were demonstrated to be fused to MLL in frame, as found in t(11;19) and t(4;11) leukemias. The predicted MLLT3 protein demonstrated a significant homology to that of the MLLT1 gene at 19p13 involved in t(11;19) leukemia. The highest homology, up to 74.1%, was found in 86 amino acids of the C-terminus, suggesting that this region is of particular importance for leukemogenesis in t(9;11) leukemia. Northern blot analysis with the MLLT3 cDNA probe against normal tissues revealed multiple transcripts in lymphoid organs. A survey of hematopoietic cell lines demonstrated relatively stronger signals in cells belonging to megakaryocytic and erythroid lineages. As previously found in t(11;19) leukemia, heterogeneous MLL-MLLT3 chimeric mRNAs could be detected by the reverse transcriptase-polymerase chain reaction (RT-PCR) in t(9;11) leukemia samples.

Cytogenetic 2; 18 and 18; 22 translocation in chronic lymphocytic leukemia with juxtaposition of bcl-2 and immunoglobulin light chain genes.

The majority of follicular lymphoma cells carry the typical chromosome translocation 14;18, which juxtaposes the bcl-2 gene to the immunoglobulin heavy-chain (IgH) gene. Variant translocations of the bcl-2 gene to the Ig lambda or Ig kappa gene have been found by molecular biological techniques in a significant fraction (approximately 10%) of chronic lymphocytic leukemia (CLL). However, there have been no reports describing the presence of cytogenetic 18;22 and 2;18 translocations in CLL, in spite of extensive karyotypic studies. We present here two cases of CLL, one with cytogenetically detected t(2;18)(p11;q21) and the other with the t(18;22)(q21;q11). The molecular analysis revealed that these translocations juxtaposed the bcl-2 and immunoglobulin light-chain (IgL) genes. The t(18;22) broke the 5' flanking region of the bcl-2 gene and juxtaposed to the immunoglobulin lambda light-chain (Ig lambda) gene in a head-to-head configuration, as in the cases previously described. In the case of the t(2;18), the bcl-2 gene and immunoglobulin kappa light-chain (Ig kappa) gene were juxtaposed in a head-to-tail configuration, which is opposite to that expected from the orientation of the genes on chromosomes. The breakpoint was located within the 5' untranslated region of the bcl-2 gene. The results presented here indicate that the bcl-2/immunoglobulin light-chain (IgL) gene juxtaposition seen in a fraction of CLL is the result of cytogenetically detectable reciprocal chromosome translocations 2;18 and 18;22.

Mutations in the RAD54 recombination gene in primary cancers.

Association of a recombinational repair protein RAD51 with tumor suppressors BRCA1 and BRCA2 suggests that defects in homologous recombination are responsible for tumor formation. Also recent findings that a protein associated with the MRE11/RAD50 repair complex is mutated in Nijmegen breakage syndrome characterized by increased cancer incidence and ionizing radiation sensitivity strongly support this idea. However, the direct roles of BRCA proteins and the protein responsible for NBS in recombinational repair are not clear though they are associated with the recombinational repair complexes. Since RAD51 forms a complex with other members of the RAD52 epistasis group and with BRCA proteins, it is reasonable to ask if alterations of members of the RAD52 epistasis group lead to tumor development. Here we describe missense mutations at functional regions of RAD54 and the absence of the wild-type RAD54 expression resulting from aberrant splicing in primary cancers. Since RAD54 is a recombinational protein associated with RAD51, this is the first genetic evidence that cancer arises from a defect in repair processes involving homologous recombination.

Mutations of a novel human RAD54 homologue, RAD54B, in primary cancer.

Association of breast tumor susceptibility gene products BRCA1 and BRCA2 with the RAD51 recombination protein suggested that cancer could arise through defects in recombination. The identification of NBS1, responsible for Nijmegen breakage syndrome, from the MRE11/RAD50 recombination protein complex also supports this hypothesis. However, our mutation analysis revealed that known members of the RAD52 epistasis group are rarely mutated in human primary cancer. Here we describe the isolation of a novel member of the SNF2 superfamily, characterized with sequence motifs similar to those in DNA and RNA helicases. The gene, designated RAD54B, is significantly homologous to the RAD54 recombination gene. The expression of RAD54B was high in testis and spleen, which are active in meiotic and mitotic recombination. These findings suggest that RAD54B may play an active role in recombination processes in concert with other members of the RAD52 epistasis group. RAD54B maps to human chromosome 8q21.3-q22 in a region associated with cancer-related chromosomal abnormalities. Homozygous mutations at highly conserved positions of RAD54B were observed in human primary lymphoma and colon cancer. These findings suggest that some cancers arise through alterations of the RAD54B function.