Positive intergroup contact modulates fusiform gyrus activity to black and white faces

In this study, we investigated the effect of intergroup contact on processing of own- and other-race faces using functional Magnetic Resonance Imaging (fMRI). Previous studies have shown a neural own-race effect with greater BOLD response to own race compared to other race faces. In our study, white participants completed a social-categorization task and an individuation task while viewing the faces of both black and white strangers after having answered questions about their previous experiences with black people. We found that positive contact modulated BOLD activity in the right fusiform gyrus (rFG) and left inferior occipital gyrus (lIOC), regions associated with face processing. Within these regions, higher positive contact was associated with higher activity when processing black, compared to white faces during the social categorisation task. We also found that in both regions a greater amount of individuating experience with black people was associated with greater activation for black vs. white faces in the individuation task. Quantity of contact, implicit racial bias and negatively valenced contact showed no effects. Our findings suggest that positive contact and individuating experience directly modulate processing of out-group faces in the visual cortex, and illustrate that contact quality rather than mere familiarity is an important factor in reducing the own race face effect.

Abstract PR05: IRF8 regulates GM-CSF expression in T cells and tumor cells to mediate myeloid-derived suppressor cell differentiation

Myeloid cells are a heterogenous and abundant population of haematopoietic cells that are virtually present in all mammalian tissues, where they monitor local microenvironment to maintain homeostasis. All myeloid cells originate from the pluripotent hematopoietic stem cells that undergo progressive restriction in their lineage potential to give rise to mature granulocytes and macrophages. Lineage restriction and differentiation are regulated by timely activation of specific set of lineage-specific transcription factors in concert with down-regulation of other set(s) of transcription factors that are important for alternative cell lineage potential. Altered expression of these lineage-specific transcription factors often leads to deregulation of myelopoiesis and resultant hematopoietic disorders. Therefore, lineage-specific transcription factors are essential for myeloid cell lineage differentiation and maturation. Mice with a null mutation of irf8, the gene that encodes IFN regulatory factor 8 (IRF8), exhibit massive accumulation of CD11b+Gr1+ immature myeloid cells (IMCs). Therefore, IRF8 is a myeloid cell lineage-specific transcription factor that plays an essential function in the regulation of myelopoiesis. Particularly, IRF8 may determine differentiation, lineage commitment, and immune function of monocytes versus granulocytes under physiological conditions.

A hallmark of cancer-bearing mice is the accumulation of CD11b+Gr1+ myeloid-derived suppressor cells (MDSCs). Interestingly, IRF8 is silenced in MDSCs from tumor-bearing mice. Therefore, IRF8 is apparently a key transcription factor that mediates MDSC differentiation. However, the molecular mechanism underlying IRF8 regulation of MDSCs is largely unknown. Because MDSCs is induced by inflammation, we therefore hypothesized that IRF8 may repress the expression of proinflammatory factors to mediate differentiation of MDSCs/IMCs under physiological and pathological conditions. To test this hypothesis, we made use of conventional IRF8 KO mice, mice with IRF8 deficiency only in myeloid cells, mice with IRF8 deficiency only in T cells, and tumor-bearing mouse models. Here we report an intriguing finding that although IRF8 conventional mice exhibit deregulated myeloid cell differentiation and resultant accumulation of CD11b+Gr1+ IMCs, surprisingly, mice with IRF8 deficiency only in myeloid cells exhibit normal myeloid cell lineage differentiation. Instead, mice with IRF8 deficiency only in T cells exhibited deregulated myeloid cell differentiation and IMC accumulation. We further demonstrated that IRF8-deficient T cells exhibit elevated GM-CSF expression and secretion. Treatment of mice with GM-CSF increased IMC accumulation, and adoptive transfer of IRF8-deficient T cells, but not GM-CSF-deficient T cells, increased IMC accumulation in the recipient chimera mice. Moreover, overexpression of IRF8 decreased GM-CSF expression in T cells. These data thus determine that IRF8 functions in T cells to repress GM-CSF expression to suppress IMCs. However, in tumor-bearing mice, IRF8 is silenced in MDSCs but not in T cells, suggesting a different mechanism of MDSC regulation by IRF8. We observed that silencing IRF8 using IRF8-specific siRNA dramatically increase GM-CSF expression in tumor cells. Therefore, IRF8 represses GM-CSF expression in tumor cells to mediate MDSC differentiation. In summary, we determine that IRF8 regulates GM-CSF expression in T cells and tumor cells, respectively, to mediate myelopoiesis under physiological and pathological conditions.

This abstract is also presented as Poster A84.

Citation Format: Amy Paschall, Ruihua Zhang, Kankana Bardhan, Chen-Feng Qi, Liang Peng, Geming Lu, Jianjun Yang, Miriam Merad, Mary Zimmerman, Tracy McGaha, Gang Zhou, Andrew Mellor, Scott I. Abrams, Herbert Morse, Keiko Ozato, Huabao Xiong, Kebin Liu. IRF8 regulates GM-CSF expression in T cells and tumor cells to mediate myeloid-derived suppressor cell differentiation. [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy: A New Chapter; December 1-4, 2014; Orlando, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2015;3(10 Suppl):Abstract nr PR05.

Abstract A84: IRF8 regulates GM-CSF expression in T cells and tumor cells to mediate myeloid-derived suppressor cell differentiation

This abstract is being presented as a short talk in the scientific program. A full abstract is printed in the Proffered Abstracts section (PR05) of the Conference Proceedings.

Citation Format: Amy Paschall, Ruihua Zhang, Kankana Bardhan, Chen-Feng Qi, Liang Peng, Geming Lu, Jianjun Yang, Miriam Merad, Mary Zimmerman, Tracy McGaha, Gang Zhou, Andrew Mellor, Scott I. Abrams, Herbert Morse, Keiko Ozato, Huabao Xiong, Kebin Liu. IRF8 regulates GM-CSF expression in T cells and tumor cells to mediate myeloid-derived suppressor cell differentiation. [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy: A New Chapter; December 1-4, 2014; Orlando, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2015;3(10 Suppl):Abstract nr A84.

Specific deletion of TRAF3 in myeloid cells leads to spontaneous inflammation and tumor development in mice (INC6P.304)

TRAF3, a cytoplasmic adaptor protein, is used in signaling by the TNFR superfamily and pattern recognition receptors. A number of these receptors are constitutively or inducibly expressed by myeloid cells, the crucial players in innate immunity and inflammation. To investigate the in vivo functions of TRAF3 in myeloid cells, we generated myeloid cell-specific TRAF3-/- (M-TRAF3-/-; TRAF3flox/floxLysM+/Cre) mice. We previously showed that young adult M-TRAF3-/- mice have normal frequencies and numbers of lymphocyte and myeloid cell populations in lymphoid organs, suggesting that TRAF3 ablation did not affect the maturation or homeostasis of myeloid cells. Here we report that 15- to 22-month-old M-TRAF3-/- mice spontaneously developed chronic inflammation or tumors, often affecting multiple organs. Diseased M-TRAF3-/- mice exhibited drastically altered lymphocyte and myeloid cell populations in lymphoid organs. Furthermore, we found that M‑TRAF3‑/- mice with spontaneous inflammation or tumor development contained strikingly elevated serum levels of a variety of chemokines and cytokines, including G-CSF, CCL1, IL-17, IP-10, MCP-1, MCP-5, CXCL9, TIMP-1, and TREM-1. This suggests that dysregulation of myeloid cells actively contributes to the pathogenesis of spontaneous inflammation and tumor development observed in aging M‑TRAF3‑/- mice. Taken together, our findings indicate that TRAF3 expressed in myeloid cells inhibits spontaneous inflammation and tumor development in mice.

Interleukin 6 (IL6) is an important upstream contributor towards the progression of SLE-like disease in BXSB.Yaa mice (BA11P.134)

Systemic lupus erythematosus (SLE) is a multigenic autoimmune disorder that results in the production of autoantibodies (autoAbs) and deposition of immune complexes leading to tissue inflammation and organ damage. Typical disease characteristics include glomerulonephritis, splenomegaly and monocytosis. To understand disease mechanism, we studied spontaneous autoimmune BXSB.Yaa strain in which male mice develops SLE-like features with intricacy paralleling human SLE. It was shown that an extended pseudo-autosomal region on Y chromosome carrying a duplication of Tlr7 gene is responsible for the disease. TLR7 binds with ssRNA that consequently leads to production of inflammatory cytokines. We previously reported that IL21, produced by CD4 T follicular helper cells (TFH), plays a critical role in the disease of BXSB.Yaa mice. Since TFH cells require IL6 for their differentiation and maintenance from naïve T cells and dysregulated IL6 production has pathological consequences in SLE patients, we sought to determine if IL6 plays important upstream role in disease progression. We found that increased serum levels of IL6 in BXSB.Yaa mice correlated with the production of autoAbs, Ig secretion and hyperactive B cells. Moreover, abrogating IL6 signaling not only improved survival of BXSB.Yaa mice but they also had reduced numbers of TFH and lesser B cell activation. Thus, we conclude that IL6 signaling is an important determinant in the progression of SLE-like disease in BXSB.Yaa mice.

IRF8 expressed in T cells regulates GM-CSF expression to control myeloid derived suppressor cell differentiation (TUM6P.955)

During hematopoiesis, hematopoietic stem cells differentiate into granulocytes and macrophages via a distinct differentiation program that is controlled by myeloid lineage-specific transcription factors. Mice with a null mutation of IFN Regulatory Factor 8 (IRF8) accumulate CD11b+Gr1+ myeloid cells that phenotypically and functionally resemble tumor-induced myeloid-derived suppressor cells (MDSCs), indicating an essential role of IRF8 in myeloid cell lineage differentiation. However, whether IRF8 functions intrinsically or extrinsically in regulation of myeloid cell differentiation is not fully understood. Here we report an intriguing finding that mice with IRF8 deficiency only in myeloid cells exhibit no abnormal myeloid cell lineage differentiation. Instead, mice with IRF8 deficiency only in T cells exhibited MDSC accumulation. We further demonstrated that IRF8-deficient T cells exhibit elevated GM-CSF expression and secretion. Treatment of mice with GM-CSF increased MDSC accumulation, and adoptive transfer of IRF8- deficient T cells, but not GM-CSF-deficient T cells, increased MDSC accumulation in the recipient mice. Overexpression of IRF8 decreased GM-CSF in T cells. Our data determine that in addition to its intrinsic role as an apoptosis regulator in myeloid cells, IRF8 also acts extrinsically to repress GM-CSF expression in T cells to control myeloid cell lineage differentiation, revealing a novel mechanism of adaptive immune cell regulation of myelopoiesis in vivo.

An IL21 reporter mouse reveals a novel population of TFH precursors in young mice. (LYM8P.630)

T follicular helper cells (TFH) are a specific subset of activated CD4+ T cells that localize to germinal centers (GC) and secrete Interleukin 21 (IL21). IL21 is vital for driving the proliferation of antigen-stimulated B cells within GC and their differentiation into memory B cells and antibody-secreting plasma cells. TFH and IL21 are crucial for normal humoral immunity, but their dysregulation has been implicated in immunodeficiencies and autoimmune diseases. However, the processes that result in the normal development of TFH and their expression of IL21 are still poorly understood. Here we use a novel IL21-venus fluorescent protein (VFP) reporter mouse to investigate the signals and pathways involved in the early differentiation of TFH and expression of IL21. Using this approach, we have identified a naturally occurring population of IL21-expressing CD44hi CD4+ T cells that are detected in the thymus and periphery of naïve C57BL/6J mice by 2 wks of age. RNAseq profiling and adoptive transfer experiments showed that these IL21-expressing cells are the earliest identified precursor (termed nascent TFH, nTFH) to the fully mature TFH state. nTFH display a highly diverse TCR repertoire, but restricting their TCR to a high affinity foreign antigen does not prevent their development. From this, we propose that nTFH arise by tonic self-antigenic stimulation and are primed for efficient differentiation to mature TFH in response to foreign or autoimmune antigen challenges.

A novel population of interleukin 21-producing pre-follicular T helper cells develop spontaneously in young naïve mice (LYM3P.743)

Interleukin 21 is a cytokine vital for driving the proliferation of antigen-stimulated B cells within the germinal center and their subsequent differentiation into antibody-secreting plasmablasts and plasma cells. IL21 is predominately produced by a subset of activated CD4+ T cells known as T follicular helper cells. These cells develop at the T cell-B cell border and express ICOS, PD1, CD44, CXCR5 and BCL6. While this cell type has been identified, the processes that ultimately result in TFH differentiation are poorly understood. Here we use a novel IL21-venus fluorescent protein reporter mouse to investigate the signals and pathways involved in the earliest stages of development of TFH cells and production of IL21. We identify and characterize a naturally occurring population of ICOShi CD44hi CD4+ T cells that produce IL21 and are present within 4 weeks of age in naïve healthy C57BL/6J mice. These T cells show characteristics of TFH cells, including the upregulation of Bcl6 and Sostdc1, but lack surface staining for CXCR5 and PD1 and, surprisingly, develop in the absence of B cells. Therefore, these spontaneously arising cells actively producing IL21 appear to identify the earliest precursor to the mature TFH state.

ENPP1-positive B cells and activation in human peripheral blood (LYM6P.772)

ENPP1 (ectonucleotide pyrophosphatase/phosphodiesterase 1), also known as PC1 (plasma cell alloantigen 1), is a homodimeric type II transmembrane glycoprotein that mediates nucleotide recycling by breaking down ATP to AMP. Previous studies of mouse B lineage cells showed that levels of PC1 expression could distinguish two distinct subsets of peritoneal B -1a cells. In addition, PC1 expression increases progressively on germinal center B cells and splenic plasma cells with highest levels on bone marrow plasma cells. To determine if PC1 might also help define human B1-like cells, we have used a mouse mAb to human PC1 to characterize its expression on human cells. The frequency of PC1-positive cells from cord blood (mean 6%, n=10) was higher than that from adult peripheral blood (1.34%, n=15). These PC1-positive cells are mostly derived from CD27- naïve B cells expressing CD38, IgM and IgD, and were detected in plasmablast/plasma cells in peripheral blood. In contrast to B-1a cells in mice, human PC1-positive cells did not secrete natural Abs or produce IL10. Expression of PC1 was greatly increased on purified peripheral blood B cells stimulated with anti-CD40, IL4 and IL21. These activated PC1-positive cells expressed low levels of CD5, HLA-DR, surface IgM, and high levels of B cell activation markers and CD138. Our results indicated that PC1-positive B cell populations in humans are different from either CD20+CD27+CD43+ B1 cells in human, or CD5+ B-1a cells in mice.

p85a recruitment by the CD300f phosphatidylserine receptor mediates apoptotic cell clearance required for autoimmunity suppression (BA4P.222)

The rapid and efficient removal of apoptotic cells (AC) prevents the release of the potentially toxic or immunogenic components from dying cells, thereby reducing inflammatory and autoimmune responses. Phagocytosis is the major means of clearing AC, which is dependent on the interaction between “eat-me” signals on AC and receptors on phagocytes. The externalized phosphatidylserine (PS) on AC is the best-known “eat-me” signal. We demonstrate that mouse CD300f (CLM-1) recognizes outer membrane-exposed PS and regulates AC phagocytosis. CD300f accumulates in phagocytic cups at AC contact sites. Phosphorylation within CD300f cytoplasmic tail tyrosine-based motifs initiates signals that positively or negatively regulate AC phagocytosis. Y276 phosphorylation is necessary for enhanced CD300f-mediated phagocytosis through the recruitment of the p85a regulatory subunit of phosphatidylinositol-3-kinase (PI3K). CD300f-PI3K association leads to activation of downstream Rac/Cdc42 GTPase and mediates changes of F-actin that drive AC engulfment. Importantly, primary macrophages from CD300f-deficient mice have impaired phagocytosis of ACs. The biological consequence of CD300f deficiency is predisposition to autoimmune disease development, as FcgRIIB-deficient mice develop a systemic lupus erythematosus-like disease at a markedly accelerated rate if CD300f is absent. This is the first report identifying the mechanism and role of CD300f in AC phagocytosis and maintenance of immune homeostasis.

ATM-deficiency in the absence of T cells promotes the development of B cell lymphomas with dependence on NF-kB (TUM7P.927)

The protein product of the ataxia-telangiectasia mutated gene, ATM, is a kinase that plays a central role in maintaining genomic integrity and protecting cells from oncogenic transformation. Mutations of the human ATM gene cause ataxia-telangiectasia, an autosomal recessive disorder that is associated with increased incidence of malignancies, especially lymphoid tumors. ATM-deficient mice have been useful tools to study thymic lymphomas, which occur at high frequency in these mice, but the early onset of these tumors has prevented analysis of other types of malignancies. In this study we generated ATM- and CD3ε-deficient mice that lacked T cells. These mice do not develop thymic lymphomas, but routinely develop early onset B cell lymphomas that express surface markers characteristic of mature activated B cells. These B cell lymphomas resemble human diffuse large B cell (DLBC) lymphomas and possess complex karyotypes with genetic amplifications, deletions and unbalanced translocations. Interestingly all lymphomas (10/10) contain an amplification of a 5Mb region on chromosome 18 containing MALT1. These lymphomas also express NF-kB and are dependent on MALT1 and NF-kB signaling for in vitro survival. As such they represent a mouse model for NF-kB- dependent human DLBC lymphomas of the ABC- subtype.

Intricate interplay of cytokines determine the progression of SLE-like disease in BXSB.Yaa mice (BA12P.104)

Systemic lupus erythematosus (SLE) is a complex multi-organ disease that affects mostly females. It is caused by several environmental, genetic and stochastic factors. BXSB.Yaa is a recombinant inbred strain of mice with major manifestations that parallel those of human SLE, thereby making it a model system to investigate genetic and non-genetic determinants of disease initiation and progression. The Yaa mutation in male results due to translocation of a 4Mb chromosomal region, including Tlr7 gene, from X to the Y chromosome, making them susceptible to disease. The disease pathogenesis involves an intricate interplay of key cytokines such as IL-21, IL-6, Type I interferon (IFN) and IL-10. Enhanced expression of IL-21 by CD4-T (Tfh) cells expands autoreactive B cells that differentiate into plasmablasts and secrete autoantibodies. IL21 also promotes the development of CD8-T cells and NK cells which retard early disease development. Gene expression profiles of cells from young IL-21R deficient BXSB.Yaa mice revealed an “IFN signature” similar to human SLE females. Purified plasmacytoid dendritic cells (pDCs) from male mice produced higher levels of Type-I IFN than females. Type I IFN further stimulates IL6 producing B cells that drives differentiation of CD4 Tfh cells. IL6 also contributes to accelerated mortality in BXSB.Yaa mice. Moreover, BXSB.Yaa mice express IL10 and ablation of IL10 in these mice results in accelerated mortality.

Abstract 3852: Bcl-xL and IL-6 act independently and synergistically to accelerate plasmacytopoiesis and plasma cell tumor formation in Balb/c mice

Accelerated development of spontaneous plasma cell tumors (PCT) occurs in mucosal-associated lymphoid tissues of mice bearing both IL-6 and BCL-XL transgenes (double transgenic (dTg)). 91% of dTG mice developed PCTs at a mean age of 89 days. In contrast, 53% of the IL-6 Tg mice developed PCTs at a mean age of 301 days and 12% BCL-XL Tg mice developed PCTs with a mean age of 433 days. The PCTs formed primarily in Peyer's Patches, medullary cords of the mesenteric lymph node and/or the lamina propria of small intestinal villi where they were preceded by massive plasma cell hyperplasia. To investigate the molecular basis of the cooperation between IL-6 and BCL-xL transgenes to accelerate PCT development we performed detailed analysis of cell lines developed from dTG mice and and spontaneous or pristane-induced tumors of Bcl-xL TG mice. All the tumors carry Ig/Myc-deregulating chromosomal translocations, which are thought to be the initiating event of PCT development. Therefore we focused on finding possible differences in secondary alterations. Although the subsets were poorly distinguished by microarray-based gene expression profiling, there were significant differences in the expression of p21, p19ARF, p53, HUWE1 and pRb as determined by western blotting and qPCR. DTG tumors were characterized by alterations in pathways governing expression of pRb that included increased expression of INK4A and down regulation of pRb itself as well as down regulation of p19ARF. Most notably we discovered discordance between protein and mRNA levels for pRb and p19Arf. Efforts to understand the molecular basis for these distinctions and their contributions to the biology of these PCT subsets are in progress.

Citation Format: Tomomi Sakai, Alexander L. Kovalchuk, Herbert Morse. Bcl-xL and IL-6 act independently and synergistically to accelerate plasmacytopoiesis and plasma cell tumor formation in Balb/c mice. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3852. doi:10.1158/1538-7445.AM2013-3852

The IgM Fc receptor, FCMR, promotes B cell development and modulates antigen-driven immune responses (176.9)

FCMR is a Fc receptor specific for pentameric IgM expressed at high levels by B cells. Although circulating IgM has profound effects on responses to pathogens, autoimmunity and B cell homeostasis, the biologic consequences of its binding to FCMR are poorly understood. We interrogated FCMR contributions to B cell function by studying mice lacking FCMR. FCMR transcripts are expressed at highest levels by follicular (FO) B cells and at much lower levels by developing B cells and other mature B cell subsets. FCMR-deficient mice have reduced numbers of developing B cells, splenic FO and peritoneal B-2 cells, but increased levels of peritoneal B-1a cells and autoantibodies. Following immunization, germinal center B cell and plasma cell numbers are increased. FCMR-deficient B cells are resistant to apoptosis induced by BCR ligation. Our studies demonstrate that FCMR functions are critical for B cell homeostasis, the prevention of autoreactive B cells and responsiveness to antigenic challenge.

Identification of novel subsets of CD5+ B-1a cells reveals layered populations with distinct innate-like functions (67.2)

B-1a cells are found to contribute significantly to circulating natural antibodies and mucosal immunity as well as to immunoregulation. These various functional attributes of B-1a are often presented as reflecting the repertoire of all B-1a cells, while understanding how these functions are fulfilled at the clonal level is rather limited. Here we show that B-1a cells can be subdivided into two distinct stable subsets based on differing expression of the plasma cell alloantigen 1 (PC1), also known as ectonucleotide pyrophosphatase phosphodiesterase 1 (ENPP1), an enzyme involved primarily in hydrolysis of ATP at the cell surface. One subset that we term PC1lo, expresses ENPP1 at low levels, whereas the second subset, designated PC1hi, expresses ENPP1 at high levels. These subsets are distinguishable by gene expression profiles, VH gene usage and time of development. Adoptively transferred PC1lo cells secret significantly more circulating natural IgM and intestinal IgA than PC1hi cells. In contrast, PC1hi cells produce more IL-10 than PC-1lo cells when stimulated with LPS and PMA. Furthermore, PC1lo cells generate antigen-specific IgM responses to pneumococcal polysaccharide antigens whereas PC1hi cells do not. We conclude that the classic B-1a functions segregate quite cleanly between these two subsets and the identification of PC1lo and PC1hi cells extends the concept of a layered immune system.

Specific deletion of TRAF3 in B lymphocytes leads to B lymphoma development in mice (138.6)

TRAF3 is a cytoplasmic adaptor protein utilized by the tumor necrosis factor receptor superfamily and Toll-like receptors for signaling. To explore the in vivo functions of TRAF3 in B cells, we recently generated B cell-specific TRAF3-deficient (B-TRAF3-/-) mice, and reported that TRAF3 is a critical regulator of peripheral B cell survival. In this study, we examined the hypothesis that the prolonged survival of TRAF3-/- B cells may predispose them to transformation. We found that approximately 50% of B-TRAF3-/- mice spontaneously developed B lymphomas by the age of 18 months. Our histopathological and immunophenotyping data revealed that B1 lymphomas, marginal zone B lymphomas, and immunoblastic B lymphomas developed in different individual B-TRAF3-/- mice. TRAF3-/- B lymphoma cells were malignant, as demonstrated by the identification of clonal B lymphoma cells in multiple organs in diseased mice, including spleen, ascites, bone marrow, cervical and mesenteric lymph nodes, and occasionally, kidney and lung. Corroborating our findings, recent evidence demonstrates that deletions and mutations of the TRAF3 gene frequently occur in human patients with B-cell lymphomas and multiple myeloma. Thus, our results, together with the evidence from human patients, indicate that TRAF3 is a tumor suppressor gene in B lymphocytes. Our findings suggest that TRAF3 downstream signaling components may serve as important therapeutic targets for the treatment of B lymphomas.

CD8+ T suppressor cells protect from Lupus-like autoimmunity (143.31)

Systemic lupus erythematosus (SLE) inflicts damage via autoantibody complexes that result in multiorgan damage and renal failure. The BXSB.Yaa mouse is a well-established model of SLE. We show that genetic disruption of multiple components of the MHC I axis greatly accelerates autoimmune disease in this model. Mice lacking both CD8 and IL15 succumb to SLE-like disease earliest (mean age 14 wks), implying a protective role for CD8 T cells and potentially natural killer cells dependent on IL15. BXSB.Yaa mice develop an expanded population of CD8 T cells with increased expression of both CD122 and IL15Rα, which we propose is due to increased expression of IL15R on these cells. Neither Foxp3 nor CD25 are elevated, and IL10 deficient BXSB.Yaa mice fail to show accelerated disease. However, lytic function appears significant as BXSB.Yaa mice deficient in perforin show decreased survival. TCR analysis failed to suggest a biased CD8 T cell repertoire, suggesting that the cellular targets of suppression are not antigenically discrete. Overall, the results suggest the existence of potent MHC I-dependent suppressor cell population(s) that normally protect BXSB.Yaa mice from an even more aggressive form of SLE-like disease. Moreover, the results support a model in which suppression is unlikely to be mediated by cytokine regulation but instead by lytic mechanisms. Harnessing this inherent regulatory cell population could provide a novel strategy to treat SLE and related syndromes.

ENPP1 is a novel cell surface marker of germinal center and memory B cells and is highly expressed in plasma cells (36.3)

The ectonucleotide pyrophosphatase phosphodiesterase 1 (ENPP1), also known as plasma cell (PC) alloantigen 1 (PC-1), is expressed on PCs and many non-lymphoid tissues. ENPP1 hydrolyzes NTP to generate NMP and pyrophosphate (PPi). PPi is an important factor for controlling mineralization of the bone. In addition, ENPP1 directly associates with the insulin receptor and regulates insulin receptor signaling. Abnormal expression of ENPP1 has been associated with diabetes and insulin resistance. Although ENPP1 was first identified in PCs, its expression and function in B lineage cells remains poorly understood. Here we describe a previously unknown expression pattern of ENPP1 in murine late stage B cells. By using an anti-ENPP1 mAb and flow cytometry, we found that the expression levels of ENPP1 in early and mature naïve B cells were relatively low. However, germinal center (GC) B cells, PCs and memory B cells expressed 2-4-fold more ENPP1 than resting B cells. Moreover, gene expression profiling studies of primary lymphomas in NFS.V+ congenic mice revealed high expression levels of ENPP1 in plasmacytomas, immunoblastic lymphomas, and centroblastic-follicular lymphoma types, corresponding with their PC and GC origins. These studies demonstrate that ENPP1 can be a useful marker for identification of stages in GC and post-GC cell differentiation and of lymphomas with a GC or PC origin. The function of ENPP1 in B cells is currently under investigation.

Anaplastic plasmacytomas associated with NFATc2 deficiency in aged B6 mice (100.4)

NFATc2 is an intrinsic negative regulator of lymphocyte proliferation that promotes T cell anergy, cell cycle arrest, and possibly differentiation to the Fox-P3+ T regulatory phenotype. NFATc2 knockout (KO) mice show systemic peripheral expansion of lymphocytes with reduced thresholds for T cell activation. Unlike NFATc2 KO in mixed (H2b X H2bc) or H2d backgrounds, homozygous NFATc2 B6 KO mice did not develop splenomegaly, but instead developed systemic lymphadenopathy that was most pronounced in mesenteric and submandibular lymph nodes. The mice retained a reduced threshold of activation for both B- and T-cells. When compared to wild type and heterozygous littermates, mice had greater frequency of mixed lymphocytic infiltrates in kidney, liver, and salivary glands. Six of 11 NFATc2 KO mice that were allowed to reach 16 to 20 months of age developed anaplastic plasmacytomas in the mesenteric lymph nodes, a phenotype that was not seen in 17 age matched WT or heterozygous KO littermates. This suggests NFATc2 deficiency facilitates development of plasma cell tumors in the H2b background. We propose this may be driven by chronic antigenic stimulation and is due to poorly restrained intrinsic negative regulation and not due to extrinsic immunologic defects. These mice represent a valuable resource to explore mechanisms that account for progression from inflammation to malignancy. SLH and JFM contributed equally to this work.

Characterizing the pathophysiology of Systemic Lupus Erythematosis disease progression in the BXSB Yaa CD8-/-, IL15 -/- mouse model (99.16)

Systemic Lupus Erythematosis (SLE) is a common autoimmune disease affecting mainly women and people of non Caucasian descent. This disease varies in severity and presentation but death due to renal failure is the most common outcome. The BXSB Yaa mouse has been a widely accepted model for the study of SLE. In an attempt to further illuminate the pathogenesis of this disease, CD8 and interleukin 15 were genetically removed from this model. The resulting congenic mouse develops an SLE like disease at an accelerated rate, succumbing to disease in half the time of the BXSB Yaa (3 months versus 6 months of age). Immunoglobulin levels are high at an early age in these mice. A loss of architecture and overwhelming plasmablast cell populations are seen histologically in the spleen and lymph nodes. These plasmablast cells were also found in the gastric mucosa, lung parenchyma, and renal tissues. Through immunoflorescence (IFA) and flow cytometry of splenic tissue, a number of these cells appear to be B220 negative and CD138 positive. There also appears to be an association with CD5, CD49b, and CD43. IFA has also revealed a loss of normal orientation between B220 labeled and CD4 labeled cells in the spleen and lymph nodes of these mice as well as many CD138 positive cells throughout these tissues. Further characterization of these cells is being pursued as well as age related studies in these mice to further define the pathogenesis of SLE.

Conditional Expression of the CTCF-Paralogous Transcriptional Factor BORIS in Normal Cells Results in Demethylation and Derepression of MAGE-A1 and Reactivation of Other Cancer-Testis Genes

Brother of the Regulator of Imprinted Sites (BORIS) is a mammalian CTCF paralog with the same central 11Zn fingers (11ZF) that mediate specific interactions with varying approximately 50-bp target sites. Regulated in vivo occupancy of such sites may yield structurally and functionally distinct CTCF/DNA complexes involved in various aspects of gene regulation, including epigenetic control of gene imprinting and X chromosome inactivation. The latter functions are mediated by meCpG-sensitive 11ZF binding. Because CTCF is normally present in all somatic cells, whereas BORIS is active only in CTCF- and 5-methylcytosine-deficient adult male germ cells, switching DNA occupancy from CTCF to BORIS was suggested to regulate site specificity and timing of epigenetic reprogramming. In addition to 11ZF-binding paternal imprinting control regions, cancer-testis gene promoters also undergo remethylation during CTCF/BORIS switching in germ cells. Only promoters of cancer testis genes are normally silenced in all somatic cells but activated during spermatogenesis when demethylated in BORIS-positive germ cells and are found aberrantly derepressed in various tumors. We show here that BORIS is also expressed in multiple cancers and is thus itself a cancer-testis gene and that conditional expression of BORIS in normal fibroblasts activates cancer-testis genes selectively. We tested if replacement of CTCF by BORIS on regulatory DNA occurs in vivo on activation of a prototype cancer-testis gene, MAGE-A1. Transition from a hypermethylated/silenced to a hypomethylated/activated status induced in normal cells by 5-aza-2'-deoxycytidine (5-azadC) was mimicked by conditional input of BORIS and is associated with complete switching from CTCF to BORIS occupancy at a single 11ZF target. This site manifested a novel type of CTCF/BORIS 11ZF binding insensitive to CpG methylation. Whereas 5-azadC induction of BORIS takes only few hours, derepression of MAGE-A1 occurred 1 to 2 days later, suggesting that BORIS mediates cancer-testis gene activation by 5-azadC. Indeed, infection of normal fibroblasts with anti-BORIS short hairpin RNA retroviruses before treatment with 5-azadC blocked reactivation of MAGE-A1. We suggest that BORIS is likely tethering epigenetic machinery to a novel class of CTCF/BORIS 11ZF target sequences that mediate induction of cancer-testis genes.

A Bsr BI polymorphism in exon 1C of the human interleukin-1 receptor type I (IL-1RI) gene

We have identified a single nucleotide polymorphism in the 5' region of the human interleukin-1 receptor type I (IL-1RI) gene, a C-->A transversion at position 52 in exon 1C (GenBank accession number AF172151) which creates a Bsr BI restriction endonuclease site. Allele frequencies in a Caucasian population were 0.72 (C allele) and 0.28 (A allele).

Identification of novel single nucleotide polymorphisms in intron 1B and exon 1C of the human interleukin-1 receptor type I (IL-1RI) gene

We have identified two novel single nucleotide polymorphisms in the 5' region of the human IL-1RI gene: (1) A-->G at position 52 in intron 1B (GenBank accession number AF146426), which creates an Mspl restriction endonuclease site. Allele frequencies in a Caucasian population were 0.1 (A allele) and 0.9 (G allele). (2) A-->T at position 140 in exon 1C (GenBank accession number AF146427). Allele frequencies in a Caucasian population were 0.27 (A allele) and 0.73 (T allele).

Caffeine enhanced measurement of mutagenesis by low levels of gamma-irradiation in human lymphocytes

The well-known action of caffeine in synergizing mutagenesis (including chromosome aberrations) of agents like ionizing radiation by inhibition of cellular repair processes has been incorporated into a rapid procedure for detection of mutagenicity with high sensitivity. Effects of 5-10 rads of gamma-irradiation, which approximate the human lifetime dose accumulation from background radiation, can be detected in a two-day procedure using an immortalized human WBC culture. Chromosomally visible lesions are scored on cells incubated for 2 h after irradiation in the presence and absence of 1.0 mg/ml of caffeine. An eightfold amplification of scorable lesions is achieved over the action of radiation alone. This approach provides a closer approximation to absolute mutagenicity unmitigated by repair processes, which can vary in different situations. It is proposed that mutagenesis testing of this kind, using caffeine or other repair-inhibitory agents, be employed to identify mutagens in their effective concentrations to which human populations may be exposed; to detect agents such as caffeine that may synergize mutagenic actions and pose epidemiologic threats; and to discover effective anti-mutagens. Information derived from the use of such procedures may help prevent cancer and newly acquired genetic disease.

Development of a somatic cell hybrid mapping panel and molecular probes for human chromosome 3

A somatic cell hybrid mapping panel and molecular probes have been developed for human chromosome 3. This panel defines 11 regions for the short and long arms of the chromosome. Four hundred thirty-two probes have been mapped using these hybrids. One hundred thirty-one of these probes were derived from EcoRI and HindIII flow-sorted libraries. The remaining 301 probes were isolated from NotI boundary and random (partial MboI) libraries constructed from a hybrid that provided a relative enrichment in 3p DNA sequences. For some regions of the chromosome, significant differences in the distribution of probes were noted. This was observed for both the unique sequence flow-sorted and NotI probes. These differences are in agreement with previous suggestions that Giemsa light bands are GC-rich, and therefore gene-rich (especially housekeeping genes), and that the Giemsa dark bands may contain DNA that is more highly condensed. The isolation of probes from different types of libraries, or by different screening strategies, appears to reduce deficiencies that might arise from the use of probes derived with a more limited approach. These hybrids and probes should facilitate the construction of physical and genetic linkage maps to identify various disease loci involving chromosome 3.

Heterogeneity of acute "undifferentiated" leukemia of childhood: ultrastructural, immunophenotypic, and karyotypic analyses

The present study was undertaken in an attempt to reclassify the 19 cases of childhood acute undifferentiated leukemia (AUL) diagnosed at our institution during the past 12 years. Based on ultrastructural and immunophenotypic data, seven of the cases were reclassified as lymphoid, nine as myeloid, and three remain unclassifiable. Clinical features, clonal karyotypes, and responses to treatment were also examined. Abnormal clonal karyotypes were found in 16 of 17 cases, including eight cases with translocations, three with monosomy 7 or 7q, and one with numerous complex structural rearrangements. Fourteen patients had greater than 10% French-American-British L2 blasts in bone marrow. Although nine of 15 patients who initially received induction therapy for acute lymphoblastic leukemia (ALL) achieved remission, only one patient is a long-term survivor. Only one of 10 patients who received therapy for acute nonlymphoblastic leukemia during the course of their disease remains a long-term survivor. These data suggest that the majority of cases of AUL can be reclassified as either myeloid or lymphoid leukemias, that AUL is associated with a high frequency of chromosomal abnormalities, and that AUL carries a very poor prognosis.

A panel of irradiation-reduced hybrids selectively retaining human chromosome 11p13: their structure and use to purify the WAGR gene complex

The irradiation-fusion technique offers a means to isolate intact subchromosomal fragments of one mammalian species in the genetic background of another. Irradiation-reduced somatic cell hybrids can be used to construct detailed genetic and physical maps of individual chromosome bands and to systematically clone genes responsible for hereditary diseases on the basis of their chromosomal position. To assess this strategy, we constructed a panel of hybrids that selectively retain the portion of human chromosome band 11p13 that includes genes responsible for Wilms tumor, aniridia, genitourinary anomalies, and mental retardation (constituting the WAGR syndrome). A hamster-human hybrid containing the short arm of chromosome 11 as its only human DNA (J1-11) was gamma-irradiated and fused to a Chinese hamster cell line (CHO-K1). We selected secondary hybrid clones that express MIC1 but not MER2, cell-surface antigens encoded by bands 11p13 and 11p15, respectively. These clones were characterized cytogenetically by in situ hybridization with human repetitive DNA and were tested for their retention of 56 DNA, isozyme, and antigen markers whose order on chromosome 11p is known. These cell lines appear to carry single, coherent segments of 11p spanning MIC1, which range in size from 3000 kb to more than 50,000 kb and which are generally stable in the absence of selection. In addition to the selected region of 11p13, two cell lines carry extra fragments of the human centromere and two harbor small, unstable segments of 11p15. As a first step to determine the size and molecular organization of the WAGR gene complex, we analyzed a subset of reduced hybrids by pulsed-field gel electrophoresis. A small group of NotI restriction fragments comprising the WAGR complex was detected in Southern blots with a cloned Alu repetitive probe. One of the cell lines (GH3A) was found to carry a stable approximately 3000-kb segment of 11p13 as its only human DNA. The segment encompasses MIC1, a recurrent translocation breakpoint in acute T-cell leukemia (TCL2), and most or all of the WAGR gene complex, but does not include the close flanking markers D11S16 and delta J. This hybrid forms an ideal source of molecular clones for the developmentally fascinating genes underlying the WAGR syndrome.

Pigmented spleens in C57BL mice

Approximately 15% of our highly inbred C57BL/6 mice show a spleen with a pigmented cranial part. Microscopically, abundant aggregates of pigment granules are observed primarily scattered between cells of the red pulp. They give a positive reaction with Perls' Prussian blue and stain heavily with silver-methenamine. Most of the granules are stored in macrophages. In some cases a number of granules are surrounded by a membrane. This abnormality may be designated haemosiderosis. In the present study we demonstrate that it is not related to the consumption of iron within the range normally found in laboratory animal diets. This suggests a genetic origin, although confirmation would require further research. If so, comparison with human idiopathic haemochromatosis is tempting. However, contrary to the human condition, organs other than the spleen are not affected, with exception of the liver. This organ contains minor deposits of pigment granules. Nor do affected animals appear to show any ill effects. Nevertheless, it seems worthwhile to investigate whether this phenomenon in C57BL mice could serve as a model for the human disease provided that a practical criterium becomes available for detection in the intact animal.

Long-term survival of children with acute non-lymphoblastic leukemia

Results of a pilot protocol employing chemoimmunotherapy for treatment of 23 children with acute non-lymphoblastic leukemia consecutively diagnosed between 1975 and 1979 are reported. Twenty-two children achieved remission, ten of whom are surviving 6.5-9.5 years after completion of primary systemic therapy (median 7.8 years). Treatment consisted of intermittent courses of Daunomycin, Cytosine Arabinoside, 6-Thioguanine, VP-16, with or without Decadron, Connaught BCG applied between courses of chemotherapy for the first 8 months of treatment, and cranial irradiation/intrathecal Cytosine Arabinoside in early first remission. Five patients with leukemic cells in spinal fluid at diagnosis had myelomonoblastic or monoblastic subtypes and a median diagnostic white blood cell count (WBC) of 149,000/mm3 compared with a median WBC of 12,000/mm3 for the other 18 patients (P = .007).

Comparison of mackerel-oil and lard-fat enriched diets on plasma lipids, cardiac membrane phospholipids, cardiovascular performance, and morphology in young pigs

Purified mackerel-oil extract or lard fat (9.1% wt/wt) was added to a basal diet of young pigs for 8 wk. Effects on plasma lipids, glucose and insulin, cardiac membrane phospholipids, cardiovascular performance, and morphology were studied. A time-dependent reduction of plasma triglyceride (62%), total cholesterol (41%), and HDL cholesterol (47%) was found in the mackerel-oil-fed pigs. The postprandial glucose and insulin response may indicate a mackerel-oil-induced resistance of insulin receptors. Although the polyunsaturated fatty acid composition of cardiac sarcolemma widely differed between the two groups, all determined indices of heart function were equal. It is concluded that consumption of a fish-oil diet with a low content of monoenes and supplemented with antioxidants reduces plasma lipid levels without producing pathological side effects.

Chromosomal assignment of the human erythropoietin gene and its DNA polymorphism

Erythropoietin (EPO), a glycoprotein hormone, is the major physiological regulator of erythrocyte production in mammals. A cDNA clone containing the entire human EPO-coding region was used for Southern blot analysis of a series of human-Chinese hamster somatic cell hybrids containing different combinations of human chromosomes. Synteny analysis revealed 100% concordance between the EPO gene and human chromosome 7. Further localization to the region q11-q22 was accomplished by in situ hybridization of 3H-labeled human EPO cDNA to metaphase chromosomes prepared from both human lymphocytes and the cell hybrid 879-2a that contained human chromosomes 5, 7, 9, 12, and 21. In addition, restriction fragment length polymorphisms were detected at a frequency of approximately 20% in a Chinese population using restriction enzymes either HindIII or HinfI. These polymorphisms were inherited in a Mendelian fashion. Thus, the EPO marker is reasonably polymorphic and should be useful in linkage analysis with other genetic markers on chromosome 7, including the locus for cystic fibrosis.

The E7-associated cell-surface antigen: a marker for the 11p13 chromosomal deletion associated with aniridia-Wilms tumor

Unbalanced interstitial deletions of the p13 region of human chromosome 11 have been associated with congenital hypoplasia or aplasia of the iris, mental retardation, ambiguous genitalia, and predisposition to Wilms tumor of the kidney. Utilizing somatic cell hybrids containing either the normal or abnormal chromosome 11 from a child with Wilms tumor and aniridia, we previously mapped the E7 cell-surface antigen to the 11p1300-to-11p15.1 region. To localize even further the site of this antigen on chromosome arm 11p, we have produced somatic cell hybrids from the fibroblasts of a second child with Wilms tumor and aniridia and a different deletion of 11p [46,XY, del (11)(pter----p14.1::p11.2----qter)]. Furthermore, the normal and deleted chromosome 11 could also be distinguished on the basis of a restriction fragment length polymorphism for the beta-globin gene. Hybrid cells containing the deleted chromosome were not killed in the presence of complement and the E7 monoclonal antibody (which recognizes E7 cell surface antigen), while hybrid cells containing the patient's normal chromosome 11 were killed. Thus, expression of the E7-associated cell-surface antigen can be mapped to the 11p13 region, and it appears to be a potential marker of the chromosome abnormality associated with aniridia-Wilms tumor.

Assignment of the gene for human sphingolipid activator protein-2 (SAP-2) to chromosome 10

Sphingolipid activator protein-2 (SAP-2) has been found to stimulate the enzymatic hydrolysis of glucosylceramide, galactosylceramide, and sphingomyelin. When human skin fibroblast extracts were subjected to sodium dodecylsulfate-polyacrylamide gel electrophoresis followed by electroblotting and immunochemical staining using monospecific antibodies against SAP-2, two or three major bands with estimated mol. wts. of 9,000-10,000 were found. These antibodies did not crossreact with purified SAP-1, another activating protein, or with extracts of CHO-K1 cells. A series of 22 human/Chinese hamster ovary cell hybrids containing different human chromosomes were examined by this method. All eight hybrid clones containing human chromosome 10 were found to have crossreacting protein in this region. Other chromosomes could be excluded by this method. From these results, we conclude that the gene coding for human SAP-2 is located on chromosome 10.

Chromosome 3q (22-ter) encodes the human transferrin receptor

The human transferrin receptor is an integral membrane glycoprotein of 180,000 molecular weight (mol. wt.) formed from two subunits of 90,000 mol. wt. A clone panel of Chinese hamster-human somatic cell hybrids was screened using a single cell plating cytotoxicity assay and rabbit antiserum raised to purified human transferrin receptor. Chromosome 3 displayed the highest rate of concordance with the presence of human transferrin receptor, as assayed by cytotoxicity. Antitransferrin receptor serum-resistant segregants of chromosome 3 positive, receptor-positive hybrids were selected, using antiserum and complement. The segregants consistently lost chromosome 3. 125I human transferrin binding studies confirmed synteny between the functional human transferrin receptor and chromosome 3. Examination of hybrids with either translocated or deleted chromosome 3's allows regional mapping to 3q(22-ter).

Structural gene coding for multifunctional protein carrying orotate phosphoribosyltransferase and OMP decarboxylase activity is located on long arm of human chromosome 3

In humans, deficiency in the last two enzymes of UMP biosynthesis, orotate phosphoribosyltransferase (OPRT) and OMP decarboxylase results in the inborn error of metabolism hereditary orotic aciduria, type 1. In this manuscript, we present immunologic, molecular, biochemical, and genetic evidence that the gene coding for this set of enzymatic activities is located on the long arm of human chromosome 3. The evidence presented here is consistent with both these activities being carried on the same multifunctional protein in mammalian cells. These studies allow further genetic analysis of human chromosome 3, confirming that human markers ACY-1, previously assigned to 3p21, and beta-gal, previously assigned by others to the region 3(p21-q21), must be in the region 3 (cen-p21) and confirming the regional assignment of a human DNA segment, D3S1, to 3q12. The significance of these studies to genetic analysis of genes on human chromosome 3, some of which appear to play a role in some forms of malignancy, is discussed.

Acute nonlymphoblastic leukemia in childhood

Cytogenetic studies have been done on a group of childhood patients over a period of 3 1/2 years in which time Giemsa trypsin banding was applied to all specimens. Fifteen of the 107 patients (14%) were diagnosed as having acute nonlymphoblastic leukemia (ANLL). Twelve of the 15 had chromosomal abnormalities. The most common was an involvement of the No. 7 chromosome which occurred in five patients. Three patients had trisomy 19. No correlation could be found between the disease subgroup and the karyotypic aberration in patients with anomalies involving a common chromosome.

Cytogenetic studies of chronic myelocytic leukemia in children and adolescents

In a 3 1/2 year cytogenetic study of 107 leukemia patients diagnosed in childhood and adloescence, 8 presented with chronic myelogenous leukemia (CML). Seven of the 8 had chromosomal abnormalities. Six had the Ph1 chromosome; 5 had the usual 9;22 translocation. Two patients had involvement with chromosome 15; one had a 9;15 translocation in Ph1 positive cells during remission while a second had a 1;15 translocation during blastic crisis. The 2 patients who did not have a Ph1 chromosome survived 13 and 30 months, respectively, considerably less time than the 4+ year survival in most of those with Ph1 positive CML.

Chromosome 1 abnormalities in relapse and terminal stages in childhood leukemia

Seven of 114 children with leukemia were shown to have abnormalities of chromosome 1. These included trisomy of parts of chromosome 1 as well as translocations of chromosome 1 to other chromosomes. The abnormalities were found during a relapse or terminal stage, after which the patient was refractory to therapy in all cases.

Cytogenetic studies in an acute leukemia patient following cerebellar astrocytoma

Acute, monomyelogenous leukemia (AMML) was diagnosed in a patient with a derived 13;14 translocation and prior treatment for a cerebellar astrocytoma. A bone marrow aspirate at the time of diagnosis of leukemia showed abnormalities of chromosome 11, 12 and 16 in addition to the constitutional aberration. The patient's mother carried the same 13;14 translocation, as did 2 siblings, a maternal uncle, and four of his six children. The father had a reciprocal translocation between numbers 1 and 19 which was incidental to the present study.

Remission of relapsed leukaemia during a graft-versus-host reaction. A "graft-versus-leukaemia reaction" in man?

Acute lymphoblastic leukaemic in two boys relapsed after engraftment of marrow from siblings identical at HLA A, B, and D loci but went into remission during subsequent graft-versus-host reactions without specific anti-leukaemia therapy. Later leukaemic relapse was primarily in extramedullary sites, with little or no involvement of bone-marrow, liver, or spleen. Cytogenetic studies in both cases showed that the relapsed leukaemic blasts were those of the recipients while marrow cells and blood lymphocytes detected during marrow remission originated from the female donors. Blood lymphocytes from one of the recepients kiled. 51Cr-labelled autologous lymphoblast. The prolonged bone-marrow remission in the face of active and even massive extramedullary leukaemia suggests a graft-versus-leukaemia reaction in these two patients.