Cytidine Deaminase Deficiency Research Articles

Activation-induced cytidine deaminase deficiency causes organ-specific autoimmune disease.

Activation-induced cytidine deaminase (AID) expressed by germinal center B cells is a central regulator of somatic hypermutation (SHM) and class switch recombination (CSR). Humans with AID mutations develop not only the autosomal recessive form of hyper-IgM syndrome (HIGM2) associated with B cell hyperplasia, but also autoimmune disorders by unknown mechanisms. We report here that AID−/− mice spontaneously develop tertiary lymphoid organs (TLOs) in non-lymphoid tissues including the stomach at around 6 months of age. At a later stage, AID−/− mice develop a severe gastritis characterized by loss of gastric glands and epithelial hyperplasia. The disease development was not attenuated even under germ-free (GF) conditions. Gastric autoantigen -specific serum IgM was elevated in AID−/− mice, and the serum levels correlated with the gastritis pathological score. Adoptive transfer experiments suggest that autoimmune CD4+ T cells mediate gastritis development as terminal effector cells. These results suggest that abnormal B-cell expansion due to AID deficiency can drive B-cell autoimmunity, and in turn promote TLO formation, which ultimately leads to the propagation of organ-specific autoimmune effector CD4+ T cells. Thus, AID plays an important role in the containment of autoimmune diseases by negative regulation of autoreactive B cells.

Anticipating gemcitabine-related severe/lethal toxicities: A feasibility study

14652 Background: Gemcitabine is an antimetabolite drug extensively used for treating solid tumors in adults. Gemcitabine pharmacokinetics is altered by Cytidine Deaminase (CDA) gene polymorphism, resulting in impaired detoxification, systemic overexposure and potentially severe toxicities in deficient patients. To ensure a better safety in the handling of gemcitabine, we have developed a simple and rapid phenotypic test to determine the CDA status in patients with cancer. The aim of this work was to evaluate the feasibility and relevance of screening CDA status in patients undergoing gemcitabine-based therapy. Methods: CDA status was evaluated by measuring spectrophotometrically the residual CDA activity in serum. This retrospective study was performed in 100 adult patients (56M/44F, 64± 16 years) with either lung, pancreatic or vesical cancers. Early toxicities were monitored following standard NCI grading. Results: Four patients (2M/2F, mean age 68± 9 years, mean gemcitabine dose: 1200± 240 mg/m2) displayed early severe toxicities (e.g., > grade 3), including one toxic-death. Mean recorded CDA activities in non-toxic patients were 3.5± 2 U/mg protein. Conversely, mean CDA activities in patients with severe/lethal toxicities upon gemcitabine intake were as low as 0.8± 0.14 U/mg (i.e., -77% vs non-toxic patients), thus suggesting that CDA deficiency could be at the origin of the side-effects reported. Conclusions: In this study, 4% of the patients administred with gemcitabine displayed severe or lethal (1%) toxicities. All of them showed marked impairment in CDA function, as measured with the phenotypic test we used. These preliminary data strongly suggests, therefore, that our simple test could be of interest in a routine setting to detect CDA-deficient patients at risk with gemcitabine, a major drug extensively used in clinical oncology. No significant financial relationships to disclose.

Hyper IgM Syndrome Due To AID Deficiency In Two Patients From The Dominican Republic

Hyper IgM (HIGM) syndrome is a primary immunodeficiency characterized by a defect in immunoglobulin switch recombination that produces normal or high concentrations of IgM with low or absent IgG, IgA and IgE. The inheritance of this defect can be X-linked or recessive. Activation-Induced Cytidine Deaminase deficiency (AID) is an autosomal recessive form of HIGM, that has been described in patients from Europe, Africa, Asia and North America.

Case studies in immunology: A clinical companion, 5th Ed. by Raif Geha and the late Fred Rosen

Raif Geha and the late Fred Rosen, Garland Science, New York and London, 2008, 344 pp., ISBN 0-8153-4145-8/9-780815-341451, $49.95. E. J. Wood*, * Centre for Bioscience, The Higher Education Academy, University of Leeds, Leeds LS2 9JT, United Kingdom. This case studies volume is aimed mostly at the more advance medical students but would also be of interest to those taking immunology courses. It contains 47 case studies of a variety of immunological diseases both common and rare, and, the authors say, is updated and has some new cases compared with the previous editions. Each case gives initially some background, then presents the case (based on real patients—the names are changed to protect the innocent), and then a description is given followed by 4–6 questions for students to self-test their understanding. Answers are given at the back of the book. Many cases have pictures of the patients plus histology and other clinical information. Most cases are accompanied by excellent diagrams. This is not simple immunology (perhaps immunology is never simple anyway), but the cases are complicated and required a great deal of insight and knowledge. To give just one example: “Deficiency of the C8 component of complement,” the introduction gives details of the lytic part of the complement cascade with diagrams and electron micrographs, and the following description, after the case has been presented, tells us about the frequency of complement component deficiencies in various ethnic populations along with the known molecular biology of the mutations for C8 deficiency. One of the questions at the end is, “Hemolytic complement levels were determined by measuring the CH50. What is that and how is the test performed?” This is not stated in the text and indicates the level of sophistication and background knowledge expected. There is a lot of biochemistry in the book, but of course the emphasis is mainly clinical/immunological. Some examples of cases presented are as follows: interleukin-1 receptor-associated kinase deficiency; activation-induced cytidine deaminase deficiency; multiple myeloma; mixed essential cryoglobulinemia; lepromatous leprosy; AIDS; contact sensitivity to poison ivy; hemolyic disease of the newborn; graft-versus-host disease. The book will be useful to medical students toward the end of their clinical training and to those on a clinical immunology track, but those teaching immunology courses will also find that the content will provide useful, real, examples to illustrate their lectures (or use in problem-based sessions).

Toxic death case in a patient undergoing gemcitabine-based chemotherapy in relation with cytidine deaminase downregulation

Gemcitabine is an antimetabolite drug used in the treatment of various solid tumours, including lung, pancreatic or gynaecological cancers. Innovative combinational strategies (e.g. gemcitabine+capecitabine or gemcitabine+oxaliplatin) make gemcitabine an extensively prescribed drug now. Gemcitabine is characterized by a narrow therapeutic index, and its liver elimination depends upon a key enzymatic step, driven by cytidine deaminase (CDA). CDA is prone to gene polymorphism, including the 208A>G mutation, which can result in marked enzymatic deficiency with subsequent impact on drug exposure levels and related toxicities. We have developed a simple and inexpensive method to determine phenotypically CDA status in cancer patients, as an attempt to detect those at risk upon gemcitabine intake. Conjointly to genotypic investigations, this method was used to phenotype, in a retrospective setting, a female patient displaying extremely severe, and eventually lethal, toxicities after administration of a standard gemcitabine/carboplatin protocol. Phenotypic investigation showed a marked CDA deficiency (-75%) in this patient when compared with a reference, nontoxic population. Genetic studies undertaken next to screen mutations, possibly at the origin of this deficiency, showed heterozygosity for the 79A>C single-point mutation, whereas surprisingly the canonical CDA 208A>G polymorphism was not found. Taken together, this case report demonstrates, for the first time, that CDA downregulation can lead to toxic-death in patients exposed to gemcitabine. Besides, we showed here that our cost-effective and simple phenotypic approach should enable, in the future, the detection of deficient patients at risk upon gemcitabine administration.

Characterization of immunoglobulin mutations in humans with activation-induced cytidine deaminase deficiency

Somatic hypermutation (SHM) is initiated in germinal center (GC) B cells expressing high levels of activation-induced cytidine deaminase (AID), which targets WRC (W = A/T, R = A/G) motifs generating a uracil:guanidine mismatch. During SHM, 73% of the mutations are attributed to AID and error-prone polymerase eta (POLη). To characterize the nature of other mutations, 316 genomic nonproductive V(D)J rearrangements amplified and sequenced from three AID-/- patients were analyzed. The mutation frequency was 20-fold less than normals (0.09% versus 2%) but ~5 × 104-fold more than non-B cells. Reduced RGY (6% versus 27%) and WRC (6% versus 15%) motif mutations and decreased replacements in complementarity determining regions were attributed to the lack of AID. Reduced WA motif mutations (12% versus 23%) suggested POLη activity was decreased. Prominent G>C and A>T biases suggested that mutation and repair mechanisms occurred preferentially on one DNA strand. A high percentage of the mutations were G substitutions on the sense strand (43% versus 29% in normals), reflecting C mutational targeting on the opposite strand. These were primarily G to A transitions, suggesting that UNG activity was reduced even though UNG is upregulated in normal GC B cells and large GCs occur in AID-/- patients. The mutation pattern suggests that AID-independent C substitutions contribute a small proportion of SHM but lack the targeting provided by AID. Finally, a low level of SHM clearly can develop in the absence of AID; however, this mechanism is inefficient at altering the binding capacity of immunoglobulin heavy chain genes.

Clinical, immunologic and genetic analysis of 29 patients with autosomal recessive hyper-IgM syndrome due to Activation-Induced Cytidine Deaminase deficiency

Mutations of the Activation-Induced Cytidine Deaminase ( AID) gene have been found in patients with autosomal recessive hyper-IgM (HIGM) syndrome type 2. We retrospectively analyzed clinical, immunologic and genetic characteristics of 29 patients from 22 families with AID deficiency. Patients' median age at diagnosis and at last evaluation was 4.9 years (range: 0 to 53) and 14.2 years (range: 2.7 to 63), respectively. Most patients had suffered from recurrent and severe infections, however, intravenous immunoglobulin (IVIG) replacement therapy resulted in a dramatic decrease in the number of infections. Lymphoid hyperplasia developed in 22 patients and persisted in 7 at last follow-up. It is striking to note that six patients developed autoimmune or inflammatory disorders including diabetes mellitus, polyarthritis, autoimmune hepatitis, hemolytic anemia, immune thrombocytopenia, Crohn's disease and chronic uveitis. Fifteen distinct AID mutations were found but there was no significant genotype–phenotype correlation. In conclusion, AID-deficient patients are prone to infections and lymphoid hyperplasia, which may be prevented by early-onset IVIG replacement, but also to autoimmune and inflammatory disorders.

Hyper-immunoglobulin-M syndromes caused by an intrinsic B cell defect.

Elucidation of the molecular basis of hyper-immunoglobulin-M syndromes has provided considerable insight into the molecular events involved in antibody maturation, including immunoglobulin class switch recombination and the generation of somatic hypermutation. The identification of activation-induced cytidine deaminase deficiency (hyper-immunoglobulin-M syndrome 2) has revealed the key role played by this inducible B cell-specific molecule in both class switch recombination and somatic hypermutation. Data from Escherichia coli and in-vitro assays have strongly suggested that activation-induced cytidine deaminase acts as a DNA-editing enzyme in these processes. The recent description of a new hyper-immunoglobulin-M syndrome caused by mutations in the gene encoding the uracil-N glycosylase provided further evidence that activation-induced cytidine deaminase acts on deoxycytidine in the switch and variable regions. Indeed, uracil-N glycosylase is required to remove the uracil residues integrated into DNA following deoxycytidine deamination by activation-induced cytidine deaminase. Another hyper-immunoglobulin-M condition has recently been described (hyper-immunoglobulin-M syndrome 4). Its molecular basis is unknown, but it appears to be a homogeneous entity characterized by an intrinsic B cell defective class switch recombination but normal generation of somatic hypermutation. It is probably caused by a class switch recombination-specific DNA repair defect because class switch recombination-induced DNA breaks in S regions are normally detected in patients with this condition. The heterogeneity in hyper-immunoglobulin-M syndromes will continue to shed light on the molecular mechanisms of class switch recombination and somatic hypermutation. The description of hyper-immunoglobulin-M syndromes may therefore lead to improvements in the care of these patients.

The block in immunoglobulin class switch recombination caused by activation-induced cytidine deaminase deficiency occurs prior to the generation of DNA double strand breaks in switch mu region.

Affinity maturation of the Ab repertoire in germinal centers leads to the selection of high affinity Abs with selected heavy chain constant regions. Ab maturation involves two modifications of the Ig genes, i.e., somatic hypermutation and class switch recombination. The mechanisms of these two processes are not fully understood. As shown by the somatic hypermutation and class switch recombination-deficient phenotype of activation-induced cytidine deaminase (AID)-deficient patients (hyperIgM type 2 syndrome) and mice, both processes require the AID molecule. Somatic DNA modifications require DNA breaks, which, at least for class switch recombination, lead to dsDNA breaks. By using a ligation-mediated PCR, it was found that class switch recombination-induced dsDNA breaks in S mu switch regions were less frequent in AID-deficient B cells than in AID-proficient B cells, thus indicating that AID acts upstream of DNA break induction.

CYTIDINE DEAMINASE DEFICIENCY AND IMMUNODEFICIENCY MORE THAN A COINCIDENCE ?: 155

A 9 month-old boy, the fourth and the only surviving child of consanguineous parents of tunisian origin, was investigated for severe immunodeficiency associated with autoimmune anemia and thrombocytopenia. Increased serum immunoglobulin levels contrasted with an absence of antibody response after sensitization and blood T lymphocytes increased in number were incapable of proliferating normally in the presence of mitogens, antigens or of OKT3 antibody. Defective secretion of IL2 and of IFNrby patient's leukocytes was observed whatever the inducer used. Proliferative response as well as IFNr secretion were restored by incubation in the presence of exogenous IL2. Enzyme study disclosed a profound deficiency in cytidine deaminase (CDA) in the patient's lymphocytes (10-21-23 pmol.min−1.10−6 cells, normal value 130 ± 30, n = 39). Low values were found in the father (20-21) and the mother (18-55). Cytidine (100 μM) did reverse the inhibitory effect of pyrazofurin on parents' lymphocytes PHA-induced proliferation but not that of patient's lymphocytes. During a 6-months survey lymphocyte CDA activity of the patient, his father and mother rose to 63, 140 and 130 pmol.min−1.10−6 cells, respectively. The fact that CDA deficiency has been transitory in the parents rules out an hereditary enzymatic defect. Nevertheless, our results suggest that CDA activity should be systematically determined in immunodeficient patients.