Expression of human adenosine deaminase after fusion of adenosine deaminase-deficient cells with mouse fibroblasts

Adenosine deaminase augments SARS-CoV-2 specific cellular and humoral responses in aged mouse models of immunization and challenge

Despite numerous clinically available vaccines and therapeutics, aged patients remain at increased risk for COVID-19 morbidity. Furthermore, various patient populations, including the aged can have suboptimal responses to SARS-CoV-2 vaccine antigens. Here, we characterized vaccine-induced responses to SARS-CoV-2 synthetic DNA vaccine antigens in aged mice. Aged mice exhibited altered cellular responses, including decreased IFNγ secretion and increased TNFα and IL-4 secretion suggestive of TH2-skewed responses. Aged mice exhibited decreased total binding and neutralizing antibodies in their serum but significantly increased TH2-type antigen-specific IgG1 antibody compared to their young counterparts. Strategies to enhance vaccine-induced immune responses are important, especially in aged patient populations. We observed that co-immunization with plasmid-encoded adenosine deaminase (pADA)enhanced immune responses in young animals. Ageing is associated with decreases in ADA function and expression. Here, we report that co-immunization with pADA enhanced IFNγ secretion while decreasing TNFα and IL-4 secretion. pADA expanded the breadth and affinity SARS-CoV-2 spike-specific antibodies while supporting TH1-type humoral responses in aged mice. scRNAseq analysis of aged lymph nodes revealed that pADA co-immunization supported a TH1 gene profile and decreased FoxP3 gene expression. Upon challenge, pADA co-immunization decreased viral loads in aged mice. These data support the use of mice as a model for age-associated decreased vaccine immunogenicity and infection-mediated morbidity and mortality in the context of SARS-CoV-2 vaccines and provide support for the use of adenosine deaminase as a molecular adjuvant in immune-challenged populations.

Adenosine Deaminase (ADA)-Deficient Severe Combined Immune Deficiency (SCID): Molecular Pathogenesis and Clinical Manifestations

Deficiency of adenosine deaminase (ADA, EC3.5.4.4), a housekeeping enzyme of purine metabolism encoded by the Ada gene, is a cause of human severe combined immune deficiency (SCID). Numerous deleterious mutations occurring in the ADA gene have been found in patients with profound lymphopenia (T^- B^- NK^-), thus underscoring the importance of functional purine metabolism for the development of the immune defense. While untreated ADA SCID is a fatal disorder, there are multiple life-saving therapeutic modalities to restore ADA activity and reconstitute protective immunity, including enzyme replacement therapy (ERT), allogeneic hematopoietic stem cell transplantation (HSCT) and gene therapy (GT) with autologous gene-corrected hematopoietic stem cells (HSC). We review the pathogenic mechanisms and clinical manifestations of ADA SCID.

Efficiency and limitations of the hn-cDNA library approach for the isolation of human transcribed genes from hybrid cells

The use of splice donor site consensus sequences as primers in cDNA synthesis (to make a cDNA library from heterogeneous RNA or unprocessed transcript--an hn-cDNA library) and the screening of such an hn-cDNA library with human repeat DNA probe in order to isolate human genes from somatic cell hybrids have been demonstrated. Here, we optimize and evaluate the efficiency and limitations of the approach. Computer analysis of genomic sequences of 22 randomly selected human genes indicated that hexamers CTTACC, CTCACC, and CCTACC were most efficient at beginning first-strand cDNA synthesis at donor splice sites of hnRNA and suggested that the procedure is efficient for priming cDNA synthesis of at least one exon from most every gene. Primer extension experiments established conditions in which the primers would initiate synthesis of cDNA starting from a perfectly matched position on the RNA template at more than 60-fold higher yield than any other product. By isolation of a clone containing exon III of the human DNA repair gene ERCC1, we indicate that the approach is capable of cloning exons from weakly expressed genes. Sequencing of clones revealed a structure of hn-cDNA clones consistent with the expectations of the cloning strategy and indicated the potential of the clones in detecting polymorphisms. Finally, we demonstrate that the expression of these hn-cDNA sequences in cells can be detected efficiently at the hnRNA level by reverse transcriptase-polymerase chain reaction (RT/PCR).

Identification and characterization of transcriptional arrest sites in exon 1 of the human adenosine deaminase gene

Analysis of human adenosine deaminase (ADA) gene transcription in four different cell lines indicated that a high density of RNA polymerase II complexes is present at the 5' end of the gene and that the extent of transcription elongation beyond the promoter-proximal region governs gene expression. To determine the sequence requirements for a potential transcription arrest site in the promoter-proximal region, genomic clones containing the ADA promoter, exon 1, and various lengths of intron 1 were injected into Xenopus laevis oocyte germinal vesicles. Transcription analysis indicated that nascent ADA transcripts were highly represented at the promoter-proximal region of the injected templates, suggesting that transcription arrest occurred in the oocyte transcription system. Analysis of the transcription products indicated that ADA transcription initiated at the authentic start site and that the most prominent, short ADA transcripts were 105 nucleotides in length. The 3' end of these transcripts mapped within exon 1, 10 nucleotides downstream of the translation initiation codon. Deletion analysis demonstrated that sequences within exon 1 were sufficient to specify the synthesis of the 105-nucleotide transcripts. Taken together, these data suggest that a transcription arrest mechanism operates in the promoter-proximal region of the human ADA gene and that regulation of elongation beyond this point plays a major role in regulating ADA gene expression.

Identification and characterization of transcriptional arrest sites in exon 1 of the human adenosine deaminase gene

Analysis of human adenosine deaminase (ADA) gene transcription in four different cell lines indicated that a high density of RNA polymerase II complexes is present at the 5' end of the gene and that the extent of transcription elongation beyond the promoter-proximal region governs gene expression. To determine the sequence requirements for a potential transcription arrest site in the promoter-proximal region, genomic clones containing the ADA promoter, exon 1, and various lengths of intron 1 were injected into Xenopus laevis oocyte germinal vesicles. Transcription analysis indicated that nascent ADA transcripts were highly represented at the promoter-proximal region of the injected templates, suggesting that transcription arrest occurred in the oocyte transcription system. Analysis of the transcription products indicated that ADA transcription initiated at the authentic start site and that the most prominent, short ADA transcripts were 105 nucleotides in length. The 3' end of these transcripts mapped within exon 1, 10 nucleotides downstream of the translation initiation codon. Deletion analysis demonstrated that sequences within exon 1 were sufficient to specify the synthesis of the 105-nucleotide transcripts. Taken together, these data suggest that a transcription arrest mechanism operates in the promoter-proximal region of the human ADA gene and that regulation of elongation beyond this point plays a major role in regulating ADA gene expression.

Hypomethylation and ADA gene expression in mouse CAK cells

The adenosine deaminase (ADA) locus appears to be under complex transcriptional control since levels of ADA enzyme activity vary greatly between different tissues and stages of development. Evidence that a trans-acting factor may be involved with the regulation of this locus came from previous experiments where fusion of ADA-negative human JEG cells and mouse ADA-positive cells led to the trans-activation of human ADA in a hybrid nucleus. Here, we demonstrate that the near euploid mouse embryo fibroblast cell line, CAK, also lacks detectable ADA enzyme activity due to altered gene regulation. We further demonstrate that ADA in CAK cells is not amenable to activation by somatic cell fusion. Following treatment with 5-azacytidine and Xyl-A selection (for ADA), however, CAK clones were obtained that stably express the ADA gene. Molecular analysis of the parental CAK cells and the ADA-positive derivative clones demonstrated that both 5' and 3' regions of the ADA gene had become hypomethylated in the ADA+ clones. We conclude that methylation is another element involved with the transcriptional control of the ADA gene and that ADA might serve as a useful model for studying the interaction of cis- and trans-acting regulational elements.

Molecular aspects of erythroenzymopathies associated with hereditary hemolytic anemia

Since the discovery of glucose 6-phosphate dehydrogenase (G6PD) and of pyruvate kinase deficiencies, erythroenzymopathies associated with hereditary hemolytic anemia have been extensively investigated. Kinetic and electrophoretic studies have shown that most, if not all, erythroenzymopathies are caused by the production of a mutant enzyme. Except for a few enzymes that are abundant in blood and tissues, it is difficult to obtain enough sample to study the functional and structural abnormalities of mutant enzymes associated with genetic disorders in man. The primary structures of only two normal red cell enzymes which can cause hereditary hemolytic anemia, phosphoglycerate kinase (PGK) and adenylate kinase, have been determined. Single amino acid substitutions of PGK variants have been found, and the identification of the exact molecular abnormalities of such variants has helped us to understand the accompanying functional abnormality. Gene cloning makes possible the identification of the DNA sequence that codes for enzyme proteins. Recently, human complementary DNA (cDNA) for aldolase, PGK, G6PD, and adenosine deaminase (ADA) have been isolated, and the nucleotide sequences for PGK and ADA determined. In the near future, human cDNA sequencing should permit identification of the gene alteration that gives rise to the mutant enzymes.

An approach to a selection system for adenosine-deaminase-positive (ADA+) cells and detection of rat ADA+ "revertants"

We have substituted deoxyadenosine or adenosine for hypoxanthine in the standard HAT selection system in an attempt to select for ADA-normal (ADA+) cells. ADA- human lymphoid line cells could not utilize deoxyadenosine as an alternative to hypoxanthine as a purine source (DAT) and failed to grow but were only somewhat inhibited in growth when adenosine was substituted for hypoxanthine (AAT). In contrast, ADA+ cells utilized adenosine or deoxyadenosine as efficiently as hypoxanthine as a purine source. Growth in DAT, but not in HAT, of an artificial mixture of one ADA+ human lymphoid cells in 1,000 ADA- cells resulted in enrichment of ADA+ cells to 25-86% of total cells. When we grew a rat ADA- cell line in two variations of the DAT system, we detected at least three electrophoretically different ADA+ patterns, one of which corresponded to normal rat ADA. These could represent "revertants."

Genetic heterogeneity in partial adenosine deaminase deficiency

Inherited deficiency of the enzyme adenosine deaminase (ADA) results in a syndrome of severe combined immunodeficiency (SCID). Children with ADA- -SCID lack ADA in all cells and tissues. In contrast, a "partial" deficiency of ADA has been described in six immunologically normal children from four different "families." These children lack ADA in their erythrocytes but retain variable amounts of activity in their lymphoid cells. We have examined ADA activity in lymphoid line cells from four of these children, who are unrelated, for evidence of genetic heterogeneity. One child, who is Caucasian, has an enzyme with increased electrophoretic mobility, a diminished isoelectric point (pI 4.8 vs. Nl = 4.9) and very low activity (2.3 vs. Nl = 82.9 +/- 12.9 nmol/mg protein per min); as a second child has an enzyme with normal electrophoretic mobility but increased isoelectric point (pI = 5.0), markedly diminished heat stability at 56 degrees C (t1/2 = 4.2' vs. Nl = 40') and low activity (12.1); a third has an enzyme with only diminished heat stability (t1/2 = 6.5'), no detectable abnormality in charge and almost normal activity (41.9); while the fourth exhibits only diminished ADA activity (25.0) with no striking qualitative abnormalities. Thus, we have found evidence for three different mutations at the structural locus for ADA in three of these individuals, (a) an acidic, low activity heat stable mutation (b) a basic, somewhat higher activity, heat labile mutation, and (c) a relatively normal activity heat labile mutation. In the fourth, there is as yet no compelling evidence for a mutation at the structural locus for ADA and a mutation at a regulatory locus cannot be excluded.

Adenosine deaminase messenger RNAs in lymphoblast cell lines derived from leukemic patients and patients with hereditary adenosine deaminase deficiency

Hereditary deficiency of adenosine deaminase (ADA) usually causes profound lymphopenia with severe combined immunodeficiency disease. Cells from patients with ADA deficiency contain less than normal, and sometimes undetectable, amounts of ADA catalytic activity and ADA protein. The molecular defects responsible for hereditary ADA deficiency are poorly understood. ADA messenger RNAs and their translation products have been characterized in seven human lymphoblast cell lines derived as follows: GM-130, GM-131, and GM-2184 from normal adults; GM-3043 from a partially ADA deficient, immunocompetent !Kung tribesman; GM-2606 from an ADA deficient, immunodeficient child; CCRF-CEM and HPB-ALL from leukemic children. ADA messenger (m)RNA was present in all lines and was polyadenylated. The ADA synthesized by in vitro translation of mRNA from each line reacted with antisera to normal human ADA and was of normal molecular size. There was no evidence that posttranslational processing of ADA occurred in normal, leukemic, or mutant lymphoblast lines. Relative levels of specific translatable mRNA paralleled levels of ADA protein in extracts of the three normal and two leukemic lines. However, unexpectedly high levels of ADA specific, translatable mRNA were found in the mutant GM-2606 and GM-3043 lines, amounting to three to four times those of the three normal lines. Differences in the amounts of ADA mRNA and rates of ADA synthesis appear to be of primary importance in maintaining the differences in ADA levels among lymphoblast lines with structurally normal ADA. ADA deficiency in at least two mutant cell lines is not caused by deficient levels of translatable mRNA, and unless there is some translational control of this mRNA, the characteristic cellular ADA deficiency is most likely secondary to synthesis and rapid degradation of a defective ADA protein.

The transfer of 5'-methylthioadenosine from B82 cells through the medium to CHW-1102 cells

The Chinese hamster cell line. CHW-1102, which is deficient in hypoxanthine guanine phosphoribosyl transferase (HGPRT+), incorporated a [3H]purine metabolite(s) from medium in which B82 cells, but not V79, A9 and BHK cells, had been grown for 24 h with [3H]hypoxanthine. A thin-layer chromatographic comparison of the medium revealed a large radioactive peak that was unique to the B82 medium and co-chromatographed with methylthioadenosine (MTA), but not with most other common purine bases and nucleosides. The addition of either MTA, adenine, or adenosine to B82 medium reduced the amount of radioactive material incorporated by CHW-1102 cells. Methylglyoxal bis(guanylhydrazone) inhibited the production of the [3H]metabolite(s) that were incorporated from B82 medium by CHW-1102 cells. Little MTA phosphorylase activity was detected in the mouse L cell lines, L929, B82, and A9, but activity was present in CHW-1102 cells. These results suggest that one of the metabolites in B82 medium is [3H]MTA, and this is taken up and cleaved by CHW-1102 cells to yield [3H]adenine, which is incorporated into nucleic acids. This accounts for the majority of contact-independent metabolite transfer (CIMT). In cocultures some interactions between B82 and CHW-1102 cells were positive for contact-dependent metabolite transfer (CDMT) or metabolic cooperation.

Basic defect in the expression of adenosine deaminase in ADA- SCID disease investigated through the cells of an obligate heterozygote

The nature of the defect of a female baby who died of severe combined immunodeficiency (SCID) disease associated with adenosine deaminase deficiency (ADA-) was investigated. Since tissue or tissue culture material was not available for subsequent studies, the expression of ADA in her cells was investigated in the somatic cell hybrid clones derived from a fusion between the lymphocytes from one of her two obligate heterozygote parents and thymidine kinase deficient Chinese hamster (a3) fibroblasts. The results of analyses of the human chromosomes and biochemical markers in 12 independent clones and 27 subclones indicated that the ADA deficiency in the patient is determined probably by a mutation in the structural gene for ADA in chromosome 20 leading either to the production of catalytically defective molecules or to the cessation of the production of ADA. Incidentally, the involvement of chromosome 2, which carries a gene for adenosine deaminase complexing protein (ADCP), in the causation of ADA deficiency was excluded. The in vitro approach through the cells from an obligate heterozygote described in this paper may have a general application in pursuing studies on other cases of inborn errors of metabolism whenever the material from the affected individuals (i.e., the homozygotes) is not available or not suitable for direct investigations.

Somatic cell genetics of adenosine deaminase expression and severe combined immunodeficiency disease in humans

The somatic cell hybrid method has been used to study the number and different types of human genes involved in the expression of adenosine deaminase (ADA; adenosine aminohydrolase, EC 3.5.4.4) in normal cells and cells from a patient with ADA-deficient severe combined immunodeficiency disease (SCID). Genetic and biochemical characterization of ADA in SCID and the ADA tissue-specific isozymes in normal human cells indicates that additional genes, besides the ADA structural gene on chromosome 20, are involved in ADA expression. Human chromosome 6 encodes a gene, ADCP-1, whose presence is necessary for the expression of an ADA-complexing protein in human-mouse somatic cell hybrids [Koch, G. & Shows, T. B. (1978) Proc. Natl. Acad. Sci. USA 75, 3876-3880]. We report the identification of a second gene, ADCP-2, on human chromosome 2, that is also involved in the expression of the ADA-complexing protein. The data indicate that these two ADCP genes must be present in the same cell for that cell to express the complexing protein. Human-mouse somatic cell hybrids, in which the human parental cells were fibroblastss from an individual with ADA-deficient SCID, also required human chromosomes 2 and 6 to express the ADA-complexing protein, indicating that neither ADCP-1 nor ADCP-2 is involved in the ADA deficiency in SCID. The SCID-mouse hybrid cells expressed no human ADA even when human chromosome 20 had been retained. The deficiency of human ADA in these hybrids maps to human chromosome 20, and therefore is not due to the repression or inhibiton of ADA or its product by unlinked genes or gene products. We propose that the expression of the polymeric ADA tissue isozymes in human cells requires at least three genes: ADA on chromosome 20, ADCP-1 on chromosome 6, and ADCP-2 on chromosome 2. A genetic scheme is presented and the different genes involved in ADA expression and their possible functions are discussed.

Simultaneous decrease in deamination of 5'-adenylic acid and 5'-deoxy-5'-S-isobutylthioadenosine in chick-embryo fibroblasts infected by Rous sarcoma virus

The rate of deamination of 5'-deoxy-5'-S-isobutylthioadenosine [(iBuS5'Ado] in chick embryo fibroblasts was substantially reduced after their infection and morphological transformation by Rous sarcoma virus. Concomitant with the reduction in rate of (iBuS)5'Ado deamination there was a decrease in adenosine deaminase and 5'-adenylic acid deaminase activities. The drop of these activities was related to infection and not to the expression of the src gene. (iBuS)5'Ado was deaminated by at least three enzymes or isoenzymes whose apparent molecular weights have been estimated to be 295000, 121000 and 37000 respectively. Two of these enzymes have been characterized as 5'-adenylic acid deaminase and the heavy form of adenosine deaminase, respectively.

Supermelanotic hybrids derived from mouse melanomas and normal mouse cells

Hybrids formed between HPRT- Cloudman mouse melanoma and normal cells were isolated. The parental origin of the hybrids was verified by isoenzyme and karyotype analyses. These hybrid cells differed in two major characteristics from hybrids of melanoma and established fibroblastic cells. (1) They grew as tumors when injected into mice, and (2) they expressed differentiated melanocytic functions. At least one of the differentiated functions was overexpressed. The specific activity of tyrosinase was 3-20 times higher in the hybrid cells than in the parental mouse melanoma. The overexpression of tyrosinase in these hybrid cells has been stable for more than a year, has been transmitted to subclones of the original hybrid cell lines, and has been expressed in tumors that grew after injections of hybrid cells into animals.

Necessity for two human chromosomes for human chorionic gonadotropin production in human-mouse hybrids

Through a series of human-mouse hybrids we have identified that two human chromosomes, 10 and 18, must be present for production of the pregnancy protein hormone human chorionic gonadotropin (hCG). Human choriocarcinoma cells producing hCG were hybridized to mouse cells. From 49 independent clones three hybrid clones continued to produce whole hCG. Chromosomal analysis was done on the 3 producer clones and 5 nonproducer clones. The additional 41 nonproducer clones were genetically characterized by isozymes. Only when chromosomes 10 and 18 were present in a clone would the whole hCG molecule be produced. Clones with only 10 or only 18 did not produce hormone. Nine subclones of a producer clone confirmed this observation. Three subclones retaining both 10 and 18 continued to produce hCG. This study demonstrated the need to use cellular chromosome data and population enzyme data to identify two chromosomes necessary for hCG production in heterogeneous human-mouse hybrids.

Some recent progress in the analysis of malignancy by cell fusion

Malignancy, as measured by the ability of cells to grow progressively in vivo, is intimately linked to the presence of a structural abnormality in the polysaccharide moiety of one particular membrane glycoprotein. This abnormality is present in a wide range of different tumours; it co-segregates with malignancy in all crosses between malignant and non-malignant cells that have so far been tested; and it remains linked to malignancy in a stringent new test in which non-malignant variants are selected from tumour cell populations by the use of a lectin. Current work indicates that the abnormal membrane glycoprotein is, in all probability, one of the glucose transport proteins.

Indirect estimates of mutation rates in tribal Amerindians

Three different formulations have been used to estimate the average rate/locus/generation with which mutation results in electrophoretically detectable variants of 28 proteins in 12 tribal Amerindian populations. All methods are indirect--i.e., they assume a reasonable approximation to equilibrium between mutation and loss of mutants from the population--and are based on the further assumption that the biochemical traits under consideration are essentially neutral in their phenotypic effects. Despite the fact that the methods draw on somewhat different aspects of the available data, there is satisfactory agreement between them, the average of the three estimates being 1.6 X 10(-5)/locus/generation. This average does not encompass mutation that does not result in a change in electrophoretic mobility or that results in loss of enzyme activity. It is noteworthy that this estimate is in satisfactory agreement with a recent estimate by Neel and Thompson [Neel, J. V. & Thompson, E. A. (1978) Proc. Natl. Acad. Sci. USA 75, 1904--1908] of the mutation pressure necessary to maintain the number of "private" genetic polymorphisms being encountered in Amerindian tribes, if selection is not a factor.

Mutation and disease in man

Efforts to evaluate the burden of genetic disease maintained by mutation pressure are reviewed. Various individuals and committees have suggested that approximately 1800 per 100,000 liveborn infants will ultimately exhibit clearly defined disease due to chromosomal or point mutation. Direct estimates of human chromosomal and point mutation now permit the identification of about 370 per 100,000 liveborn infants with defect due to mutation in the preceding generation. Recent technical advances permit the study of mutation to shift to the protein level. In Amerindians, mutations resulting in electrophoretic variants of a series of proteins of the blood serum and erythrocyte occur at at rate of 1.6 x 10(-5)/locus/generation. While it is debatable what proportion of electrophoretic variants result in impaired health as heterozgotes or homozgotes in man, we are increasingly aware of disease due to an absence of enzyme or receptor protein due to homozygosity for "null" alleles. A conservative calculation of the possible impact of these "null" mutations on health proceeds as follows: if the rate of mutation to electrophoretic variants in man is only 1.0 x 10(-5)/locus/generation, and if in man the ratio of nulls to electrophoretic variants is only 2:1 rather than 5:1 of Drosophila, then null mutants with respect to protein should be 2.0 x 10(-5)/locus/generation. There are perhaps 5,000 proteins in man whose absence can lead to disease. It is clear we are just beginning to recognize a class of mutations whose impact on health in toto may exceed the commonly visualized gross phenotypic abnormalities. However, many of the conceptuses homozygous for these null mutations may be eliminated in utero and not come to clinical attention.

Electrophoretic shift mutants in Chinese hamster ovary cells: evidence for genetic diploidy

Electrophoretic shift mutants induced in Chinese hamster ovary (CHO) cells indicate that these cells not extensively functionally hemizygotic. Therefore, effective haploidy is unsatisfactory as a general theory to explain the frequency of recessive mutants in this cell line. CHO cells were screened for electrophoretic shift variants of enzymes coded by approximately 40 genetic loci. Clones isolated after exposure to ultraviolet radiation were examined by starch gel and Cellogel electrophoresis. Shift variants were recovered for enzymes representing 11 different loci. Variant clones were subcloned to demonstrate the heritability of the variations Mutants at nine loci produced multiple-banded patterns consistent with the patterns expected of genes at loci represented twice (diploid). Chromosome localization of these diploid loci in other mammalian species where they have been mapped, suggests that they represent a random sample of CHO genes. Chromosome analysis of mutant subclones indicated that the variation did not take place in tetraploid cells. The data indicate that the quasi-diploid CHO cells appear only as functionally hemizygous as would be expected of a slightly hypodiploid cell line derived from an organism in which the haploid number is 11.