Altered lymphopoiesis and immunodeficiency in miR-142 null mice.

MicroRNAs (miRNAs) are a class of powerful posttranscriptional regulators implicated in the control of diverse biological processes, including regulation of hematopoiesis and the immune response. To define the biological functions of miR-142, which is preferentially and abundantly expressed in immune cells, we created a mouse line with a targeted deletion of this gene. Our analysis of miR-142(-/-) mice revealed a critical role for this miRNA in the development and homeostasis of lymphocytes. Marginal zone B cells expand in the knockout spleen, whereas the number of T and B1 B cells in the periphery is reduced. Abnormal development of hematopoietic lineages in miR-142(-/-) animals is accompanied by a profound immunodeficiency, manifested by hypoimmunoglobulinemia and failure to mount a productive immune response to soluble antigens and virus. miR-142(-/-) B cells express elevated levels of B-cell-activating factor (BAFF) receptor (BAFF-R) and as a result proliferate more robustly in response to BAFF stimulation. Lowering the BAFF-R gene dose in miR-142(-/-) mice rescues the B-cell expansion defect, suggesting that BAFF-R is a bona fide miR-142 target through which it controls B-cell homeostasis. Collectively, our results uncover miR-142 as an essential regulator of lymphopoiesis, and suggest that lesions in this miRNA gene may lead to primary immunodeficiency.

Consequences of the recurrent MYD88(L265P) somatic mutation for B cell tolerance.

MYD88(L265P) has recently been discovered as an extraordinarily frequent somatic mutation in benign monoclonal IgM gammopathy, Waldenström's macroglobulinemia, and diffuse large B cell lymphoma. In this study, we analyze the consequences for antigen-activated primary B cells of acquiring MYD88(L265P). The mutation induced rapid B cell division in the absence of exogenous TLR ligands and was inhibited by Unc93b1(3d) mutation and chloroquine or TLR9 deficiency, indicating continued dependence on upstream TLR9 activation. Proliferation and NF-κB activation induced by MYD88(L265P) were nevertheless rapidly countered by the induction of TNFAIP3, an NF-κB inhibitor frequently inactivated in MYD88(L265P)-bearing lymphomas, and extinguished by Bim-dependent apoptosis. MYD88(L265P) caused self-reactive B cells to accumulate in vivo only when apoptosis was opposed by Bcl2 overexpression. These results reveal checkpoints that fortify TLR responses against aberrant B cell proliferation in response to ubiquitous TLR and BCR self-ligands and suggest that tolerance failure requires the accumulation of multiple somatic mutations.

Somatic KRAS mutations associated with a human nonmalignant syndrome of autoimmunity and abnormal leukocyte homeostasis.

Somatic gain-of-function mutations in members of the RAS subfamily of small guanosine triphosphatases are found in > 30% of all human cancers. We recently described a syndrome of chronic nonmalignant lymphadenopathy, splenomegaly, and autoimmunity associated with a mutation in NRAS affecting hematopoietic cells, and initially we classified the disease as a variant of the autoimmune lymphoproliferative syndrome. Here, we demonstrate that somatic mutations in the related KRAS gene can also be associated with a nonmalignant syndrome of autoimmunity and breakdown of leukocyte homeostasis. The activating KRAS mutation impaired cytokine withdrawal-induced T-cell apoptosis through the suppression of the proapoptotic protein BCL-2 interacting mediator of cell death and facilitated proliferation through p27(kip1) down-regulation. These defects could be corrected in vitro by mitogen-activated protein kinase/extracellular signal-regulated kinase kinase 1 or phosphatidyl inositol-3 kinase inhibition. We suggest the use of the term RAS-associated autoimmune leukoproliferative disease to differentiate this disorder from autoimmune lymphoproliferative syndrome.

Detection of immunoglobulin heavy chain genes rearrangements in B-cell leukemias, lymphomas, multiple myelomas, monoclonal and polyclonal gammopathies.

Polymerase chain reaction (PCR) based assays were found to be a realistic alternative to Southern blot hybridization for the assessment of clonal immunoglobulin heavy chain gene rearrangements. However, a comparison of the different PCR based studies reveals considerable variation in experimental design and marked differences in the reported results. This study compared different single- and double-step PCR assays relying on various FR3, FR2, FR1 and JH based primers for the detection of B cell clonality in acute lymphoblastic leukemias (ALL), non-Hodgkin's-lymphoma (NHL), multiple myeloma (MM), monoclonal gammopathies of unknown significance (MGUS) and three polyclonal gammopathies (PG). The highest monoclonality rate was observed using seminested CDR-III region amplification. This method achieved a monoclonal product in 6 of 13 pro-B ALL 21 of 29 c-ALL, 7 of 8 pre-B-ALL, 18 of 21 B-ALL, 14 of 17 B-NHL (intermediate or high grade) with bone marrow involvement, 0 of 9 B-NHL without bone marrow involvement, 9 of 9 low grade B-NHL (immunocytoma and including chronic lymphocytic leucemia), 13 of 19 MM, 2 of 9 MGUS, and 0 of 3 PG. Additional monoclonality was detected with nested CDR I PCR in 1 pro-B-ALL, 1 c-ALL, and 2 MM. CDR III IgH PCR has been confirmed as an efficient method for determining clonality in B-cell neoplasias. Some additional monoclonal products can be seen with CDR I-based PCR. Detection of monoclonality depends on the maturation grade of the neoplastic B-cell population.

Role of cytokines in the pathogenesis of monoclonal gammopathies.

OBJECTIVE: To review data that postulate a role for cytokines and oncogenes in the pathogenesis of monoclonal gammopathies. DESIGN: Published studies that provide evidence of the clinical progression of normal B cells to monoclonal gammopathy of undetermined significance (MGUS) to active myeloma are discussed. RESULTS: On the basis of mouse plasmacytoma models, increased expression of c-myc in B lymphocytes may be the initial oncogenic event that leads to MGUS in humans. Over time, this monoclonal subpopulation may acquire additional genetic abnormalities, such as aberrant interleukin (IL) 1 beta expression. Because IL 1 beta has potent osteoclast activating factor activity, increased production of IL 1 beta by monoclonal plasma cells may be the genetic event responsible for the progression of MGUS to myeloma. The in vivo plasma cell labeling index (proliferative rate) is the most powerful prognostic factor in patients with myeloma. The proliferative compartment observed in myeloma may parallel normal B-cell development because cytoplasmic immunoglobulin-positive cells with the ability to proliferate exist normally. With continued progression of disease, the ratio of proliferating monoclonal plasmablasts to nonproliferating monoclonal plasma cells may increase under the influence of cytokines such as IL 6. CONCLUSION: A more complete understanding of the basic biologic features of myeloma should lead to innovative therapies in the future.

Angiocentric immunoproliferative lesions: a molecular analysis of eight cases.

Angiocentric immunoproliferative lesions (AILs) are believed to represent a unique type of extranodal malignant lymphoma on the basis of clinicopathologic and immunophenotypic evidence. However, molecular studies to assess clonality have been performed on a small number of cases. In this study we assessed the clonality of eight AILs using restriction fragment analysis, the Southern blot technique, and probes to assess the configuration of the T-cell receptor beta, gamma, and delta chain genes and the immunoglobulin heavy and K light chain genes. In addition, the presence of the Epstein-Barr (EB) viral genome was assessed by using both Southern blot analysis (seven cases) and polymerase chain reaction amplification (five cases). Our results demonstrate that gene rearrangements are rare in AILs. A clonal gene rearrangement was identified in only one case, a grade III AIL with a rearrangement of the T-cell receptor delta chain gene. In two additional AILs (both grade III), the EB viral genome was detected as a single band by Southern blot analysis with a probe derived from the terminal repeat region of the virus, suggesting that a single episomal configuration of the EB viral genome was present in each case, as would occur in a clonal population of infected cells. In the remaining cases there was no evidence of clonality, although EB sequences were detected in one of four cases using the polymerase chain reaction. The rarity or absence of gene rearrangements in AILs is difficult to explain if AILs are malignant, presumably monoclonal lymphomas. However, their frequent association with the EB virus may suggest an analogy between AILs and lymphoproliferative disorders that occur in immunosuppressed patients. These findings further emphasize the unique clinicopathologic aspects of AILs and may also be useful diagnostically in the differential diagnosis of lymphoproliferative disorders.

Detection of Epstein-Barr virus genomes in archival tissues by polymerase chain reaction.

We used oligonucleotide primers designed from DNA sequences unique to the long internal direct repeated region of Epstein-Barr virus (EBV) to enzymatically amplify this segment of the EBV genome in formalin-fixed, paraffin-embedded tissues. The products amplified from EBV templates were detected by hybridization with a labeled probe specific for this highly conserved, reiterated region. Epstein-Barr virus-related sequences were detected in the spleen of a patient with infectious mononucleosis, in lung and lymph node specimens from a patient with pulmonary manifestations of infectious mononucleosis, in various tissues from seven immunosuppressed organ transplant recipients with immunoproliferative disorders, and in small biopsy specimens from a patient with nasopharyngeal carcinoma. No viral sequences were detected in 20 histologically normal spleens or 10 lymph nodes. Polymerase chain reaction technology provides an effective means for documenting EBV infection in archival tissues. This approach should facilitate the diagnosis of posttransplant lymphoproliferative disorders and difficult cases of infectious mononucleosis and nasopharyngeal carcinoma.

The biologic significance of human natural autoimmune responses: relationship to the germline, early immune and malignant B cell variable gene repertoire.

The potential for autoreactivity that has been well documented in normal individuals implies that natural autoimmune responses must serve some physiologic function. To investigate the genetic mechanisms involved in the emergence of such responses, we have determined the sequences of heavy (VH) and light (VL) chain variable region genes for several human monoclonal autoantibodies and compared these with corresponding sequences reported for other antibodies and autoantibodies. Our data reveal that natural autoantibodies can be encoded by nonmutated germline VH and VL genes which are essentially identical to V genes expressed in early B cell ontogeny as well as in some B-lineage tumors. Taken together with other structural data on human autoantibodies, these findings suggest that natural autoimmune responses originate early in ontogeny and that such antibodies may play a regulatory role in development of the normal immune repertoire and possibly in suppressing pathogenic autoimmune or malignant responses.