Enzyme replacement therapy for adenosine deaminase deficiency and severe combined immunodeficiency

ATP depletion as a consequence of adenosine deaminase inhibition in man

Hereditary deficiency of the enzyme adenosie deaminase (adenosine aminohydrolase, EC 3.5.4.4) results in an immunodeficiency syndrome characterized by a marked reduction in circulating lymphocytes. We have administered 2'-deoxycoformycin, a potent inhibitor of adenosine deaminase, to a patient with a lymphoproliferative malignancy. The clinical consequences of pharmacologic inhibition of adenosine deaminase activity included an abrupt decrease in the lymphocyte count, abnormalities of renal and hepatic function, and hemolytic anemia. The plasma concentrations of adenosine and deoxyadenosine rose to peak values of 13 microM and 5 microM, respectively, and erythrocyte dATP levels increased to 110 pmol/10(6) cells over 9 days. There was a corresponding decrease in erythrocyte ATP levels from 128 to < 6 pmol/10(6) cells. A similar profound reductin in ATP occurred in the erythrocytes of a second patient. The rapid and unexpected depletion of ATP associated with dATP accumulation may account, at least in part, for the toxicity associated with 2'-deoxycoformycin administration. The inverse relationship of ATP and dATP raises major questions about the control of energy metabolism in erythrocytes.

Heterogeneity of b lymphocyte differentiation in severe combined immunodeficiency disease

Pokeweed mitogen-induced B lymphocyte differentiation in vitro into antibody secreting plaque-forming cells (PFC) was investigated in nine patients with severe combined immunodeficiency having variable proportions of circulating B lymphocytes. When cultured by themselves, the peripheral blood mononuclear cells did not respond to stimulation with pokeweed mitogen in any patient. In the presence of irradiated allogeneic T cells as helpers, however, PFC responses were elicited in lymphocyte cultures from peripheral blood and/or bone marrow in some patients. In one of these patients, results of allogeneic co-culture experiments were suggestive of genetically restricted suppressor cells. In a single patient with deficiency of the enzyme adenosine deaminase, PFC were generated in bone marrow lymphocyte cultures only when they were supplemented with exogenous adenosine deaminase and allogeneic helper cells. A parallel study of T lymphocyte differentiation in vitro performed in fractionated bone marrow cells was suggestive of arrested differentiation at different steps along the differentiation pathway. In two patients with evidence of functional B cell precursors, deficiencies of helper T cell function could be attributed to differentiation defects at the level of the stem cells in one and the thymus in the other. The findings reported here further substantiate the heterogeneity of the severe combined immunodeficiency disease syndromes.

Severe combined immunodeficiency and adenosine deaminase deficiency: failure of enzyme replacement therapy

A first-born baby boy presented at age 3 months with persistent diarrhoea, failure to thrive, and recurrent bacterial and fungal infections. Severe combined immunodeficiency was demonstrated. A deficiency of adenosine deaminase (ADA) activity was suggested by the presence of extensive skeletal abnormalities, and the ADA activity in erythrocyte and leucocyte lysates was < 0.005 nmol/h per mg protein. Culture of ADA-negative peripheral blood mononuclear cells, together with purified calf ADA, did not alter the absent phytohaemagglutinin response. Treatment with immunoglobulin, pentamidine, and co-trimoxazole was started and a programme of ADA enzyme replacement, with infusions of plasma and frozen irradiated erythrocytes, was begun at age 4 months and achieved blood ADA levels in excess of 30 nmol/h per mg haemoglobin. Although resolution of the interstitial pneumonitis and skeletal abnormalities was observed, there was no evidence of immunological reconstitution. The patient died at age 17 months after a parainfluenza pneumonitis. Features of importance in predicting lack of benefit from enzyme replacement by erythrocyte infusion in ADA-negative severe combined immunodeficiency appear to be early clinical presentation with associated severe skeletal abnormalities, a very low level of residual ADA activity in peripheral blood mononuclear cells, and lack of effect of exogenous ADA on the absent in vitro mitogen response of ADA-negative blood mononuclear cells.

Lymphocyte subpopulations in patients with various immunodeficiencies

We have studied patients with various immunodeficiencies for the occurrence of blood lymphocytes bearing six different surface markers: the affinity to sheep erythrocytes (Es) to identify T cells, the presence of surface-bound immunoglobulins (sIg) to distinguish B cells, the affinity to mouse erythrocytes (Em) as a second B cell marker, and the receptors for the Fc part of IgM (IgM-FcR), the Fc part of IgG (IgG-FcR) and for complement (CR). IgG-FcR bearing lymphocytes were present in normal proportions and the same was found for CR-positive lymphocytes. None of the patients with congenital agammaglobulinaemia had sIg-bearing or Em-binding B lymphocytes. Four patients with ataxia teleangiectasia had low B cells and 3 out of 4 also had low proportions of IgM-FcR-bearing (T) cells. A child with partial DiGeorge syndrome did not have a grossly abnormal marker pattern although there appeared to be a shift in the T/B cell ratio in favour of the B cells. In a patient with selective cellular immunodeficiency associated with a purine nucleoside phosphorylase deficiency, who was followed during reconstitution therapy with plasma and red cells, a positive change in the marker pattern was seen. Similar observations were made in a child with combined immunodeficiency during treatment. The findings are being discussed in the light of the current knowledge of the functions and ontogeny of lymphocyte subsets.

Plasma deoxyadenosine, adenosine, and erythrocyte deoxyATP are elevated at birth in an adenosine deaminase-deficient child

We have determined concentrations of adenosine, deoxyadenosine, and deoxyATP (dATP) in cord blood from an infant prenatally diagnosed as ADA deficient. Plasma deoxyadenosine and adenosine were already elevated in cord blood (0.7 and 0.5 microM vs. normal of less than 0.07 microM). Elevation of plasma deoxyadenosine has not previously been documented in these children. Erythrocyte dATP content was also elevated at birth (215 nmol/ml packed erythrocytes vs. normal of 2.9). These elevated concentrations of adenosine, deoxyadenosine, and dATP are similar to those we observed in another older adenosine deaminase-deficient patient and may explain the impaired immune function and lymphopenia seen at birth.

Erythrocyte metabolism in purine nucleoside phosphorylase deficiency after enzyme replacement therapy by infusion of erythrocytes

Purine nucleoside phosphorylase deficiency is associated with a severely defective T-cell immunity. A patient with purine nucleoside phosphorylase deficiency was treated with transfusions of irradiated erythrocytes and plasma. This resulted in a remarkable correction of the metabolic disturbances in the patient. The urinary excretion of inosine, deoxyinosine, guanosine, and deoxyguanosine decreased, whereas uric acid excretion as well as serum uric acid concentration increased. It could be shown that the enzyme activity of the circulating erythrocytes correlated inversely with the urinary excretion of nucleosides and directly with the excretion of uric acid. As a consequence of the therapy, several glycolytic intermediates of the erythrocytes were increased, especially 2,3-diphosphoglycerate. The high 2,3-diphosphoglycerate level caused a shift to the right of the oxygen dissociation curve (P50 = 32.9 mm Hg). The immunological status of the patient showed definite improvement after the enzyme replacement therapy.

Screening tests for cell-mediated immunodeficiency diseases

As our knowledge of immunology has become more sophisticated we have had to alter our ideas of the etiology of many immune deficiency diseases. Indeed, current concepts now prevalent have led to reclassification of a number of disease entities. In order to keep our diagnostic efforts abreast of the information being generated by the extensive immunology research programs now in progress, the clinical laboratory has been required to offer a new array of sophisticated tests on a relatively routine basis. This article is intended to serve as a brief review of immunobiology and immunodeficiency diseases with an indepth coverage of specialized tests generally available at the large centers. With an understanding of the principles, procedures, and pitfalls of the tests carried out the laboratory scientist is in a better position to assist the clinician in reaching the correct diagnosis. The detailed review is concerned with methods available to separate, classify, and subclassify lymphocytes and thereby allow a categorization of immune deficiency diseases. Toward that end there is a discussion of surface markers, rosetting, mitogenic and antigenic responsiveness as well as lymphokine production. With a view to present day research tests that might eventually find their way into the armamentarium of the clinical laboratory in the future, there is brief discussion of the methods presently used to classify T-cells as helper, suppressor, or effector cells, assays of some of the lymphokines, and measurement of antibody synthesis in cell culture.

Family study on the kindred of an adenosine deaminase deficient child with severe combined immunodeficiency

A study was performed on the family of a child with severe combined immunodeficiency and deficiency of the purine salvage pathway enzyme, adenosine deaminase (ADA). Sixteen relatives over three generations were studied. Erythrocyte ADA levels clearly indicated the heterozygous status of five members. A sixth member, whose erythrocyte ADA level of 48 nmol/hr/ml Hb was within two standard deviations (32) of the mean (76) was shown by ADA determination on platelets to be clearly heterozygous. Similarly, consideration of ADA data of either serum, platelets or lymphocytes only, would have failed to identify all heterozygotes. The survey shows that the identification of phenotype by the indirect means of enzyme level determination is enhanced by the simultaneous study of several tissues.

Adenosine-adenosine deaminase modulation of histamine release from human basophils in vitro

Since extracellular adenosine is a physiologically important regulator of adenylate cyclase and cell function in various mammalian tissues, we have examined the effect of adenosine on histamine release from human basophils. Adenosine inhibited IgE-mediated histamine release by its ability to increase leukocyte cyclic AMP levels; the same concentrations of adenosine which inhibited histamine release increased the cyclic AMP level of mixed leukocytes. Inhibition of histamine release was also observed with an adenosine deaminase (ADA) inhibitor [erythro-9-(2-hydroxy-3-nonyl)-adenine: EHNA] in the presence of autologous serum. We suggest that the adenosine-ADA system normally modulates histamine release and that this contributes to the severe combined immune deficiency (SCID) associated with a lack of ADA.

In vivo and in vitro effects of thymosin and adenosine deaminase on adenosine-deaminase-deficient lymphocytes

Two siblings with adenosine deaminase deficiency were studied before and during "enzyme replacement" therapy (partial exchange transfusions with normal red cells containing the missing enzyme). The younger sib showed improvement of immunologic function during red-cell therapy alone, whereas in the older sib this improvement occurred only when the transfusions were supplemented by thymosin injections. Their clinical courses correlated with in vitro findings: lymphocytes from the younger sib differentiated to T-cell-rosette-forming cells upon addition of adenosine deaminase alone; lymphocytes from the older sibling required supplemental thymosin to form these cells. Thymic factors appear to influence the response to transfusion therapy in some patients deficient in adenosine deaminase, and supplementation of red-cell transfusion with thymic factors may be required.

S-adenosylhomocysteine hydrolase is an adenosine-binding protein: a target for adenosine toxicity

When adenosine deaminase activity is inhibited, low concentrations of adenosine are toxic to human lymphoblast mutants that are unable to convert adenosine to intracellular nucleotides. In order to identify the mediator of this cytotoxicity, we searched for a cytoplasmic protein capable of binding adenosine with high affinity. Such a protein was identified in extracts of human lymphoblasts and placenta as the enzyme S-adenosylhomocysteine hydrolase.

Limited effect of erythrocyte and plasma infusions in adenosine deaminase deficiency

A 10-month-old child with a profound deficiency of adenosine deaminase and severe combined immunodeficiency was treated for a period of 17 months with red cell and plasma transfusions containing normal amounts of the deficient enzyme. Following each transfusion, the plasma adenosine, red cell and lymphocyte ATP, urinary adenine, and urinary deoxyadenosine decreased transiently. During this period, the absolute blood lymphocyte count rose and a limited increased in the response of the lymphocytes to PHA-P was observed. Delayed hypersensitivity skin tests remained negative during the transfusion periods. A quantitative elevation of serum immunoglobulins occurred, but specific antibody formation was not elicited. In contrast to a previous report of successful therapy of ADA deficiency with red cell and plasma infusions, this patient responded poorly to enzyme replacement therapy. The difference may be related to a more profound enzyme deficiency in our patient.

Abnormal platelet aggregation in severe combined immunodeficiency disease with adenosine deaminase deficiency

The platelets from a boy with adenosine deaminase deficiency-severe combined immunodeficiency disease (ADA-SCID) showed markedly subnormal aggregation in response to collagen and ADP. In contrast with normal platelets, ATP, AMP and adenosine had little effect in inhibiting ADP-induced aggregation of ADA-SCID platelets. These observations suggest that altered adenosine metabolism exists in ADA-SCID platelets.

A new form of nucleoside phosphorylase deficiency in two brothers with defective T-cell function

Two brothers, age 9 and 11, respectively, have marked deficiency of nucleoside phosphorylase associated with defective T-cell function and normal B-cell function. Unlike the previously described five patients with this syndrome, each of these children has sufficient NP catalytic activity in their red blood cells (below 1% of the normal level) to be visualized after electrophoresis and staining for the enzyme. Their healthy sibling has normal NP activity and a normal isozyme pattern. The nonconsanguineous parents have about half-normal NP activity, but their electrophoretic patterns differ from each other's and from those of their affected children. These findings are consistent with genetic heterogeneity at the NP structural gene locus, resulting in compound heterozygosity for two different abnormal alleles.

Adenine and adenosine are toxic to human lymphoblast mutants defective in purine salvage enzymes

Mutants deficient in adenosine kinase or adenine phosphoribosyltransferase activities were selected from the WI-L2 line of human lymphoblasts. The adenosine kinase-deficient mutant was still as sensitive as its parent to growth inhibition caused by adenosine deaminase was inhibited. Similarly, the adenine phosphoribosyltransferase mutant remained sensitive to growth inhibition caused by adenine. Thus, the toxicity of adenine and adenosine to human lymphoblasts is not mediated by nucleotides to which they may be converted.

Circulating thymic-hormone activity in congenital immunodeficiency

Circulating thymic-hormone activity was assayed by measuring Thy 1-2 antigen induction on null lymphocytes from athymic mice incubated with human plasma or serum. Plasma from 19 normal children aged under 10 had inductive activity equivalent to 10-6-16-2 ng thymopoitin/ml. Plasma from 15 infants were severe combined immuno-deficiency, 2 of whom had appreciable immunoglobulin synthesis, and from 2 infants with DiGeorge syndrome had little or no inductive activity. Successful reconstitution with thymus or bone-marrow grafts and with red-cell infusions (if adenosine-deaminase deficiency is present) was followed by a rise in circulating thymic-hormone activity.

Adenosine as a natural prostaglandin antagonist in vascular smooth muscle

Adenosine has actions on smooth muscle similar to those of prostaglandin (PG) antagonists. Like some PG antagonists it is a phosphodiesterase inhibitor and seems to interfere with calcium effects. It has agonist/antagonist interactions with theophylline, a PG antagonist. In rat mesenteric vascular smooth muscle adenosine blocked responses to noradrenaline which depend on release of intracellular calcium but not those to potassium ions which depend on calcium entry from extracellular fluid. Partial inhibition of endogenous PG synthesis by indomethacin enhanced the adenosine effect. In preparations in which vascular reactivity had been abolished by indomethacin and then partly restored by 1 or 5 ng/ml PG2, adenosine also inhibited responses to noradrenaline: the curve for the 5 ng/ml PG2 concentration was to the right of and parallel to the 1 ng/ml curve consistent with a competitive interaction between adenosine and PG2. Similar interactions between adenosine and PG2 were shown in human lymphocytes in which activation also depends on calcium release. These findings suggest how calcium-dependent metabolic responses may be controlled and indicate further reasons for caution in the interpretation of cyclic AMP experiments.