Lymphocyte dysfunction caused by deficiencies in purine metabolism

Purine Nucleoside Phosphorylase Deficiency in Two Unrelated Patients with Autoimmune Hemolytic Anemia and Eosinophilia: Two Novel Mutations

Two Iranian patients with purine nucleoside phosphorylase (PNP) deficiency are described in terms of their clinical and molecular evaluations. PNP deficiency is a rare form of combined immunodeficiency with a profound cellular defect. Patients with PNP deficiency suffer from variable recurrent infections, hypouricemia, and neurological manifestations. Furthermore, patient 1 developed mild cortical atrophy, and patient 2 presented developmental delay, general muscular hypotonia, and food allergy. The two unrelated patients with developed autoimmune hemolytic anemia and T cells lymphopenia and eosinophilia were referred to Immunology, Asthma and Allergy Research Institute (IAARI) in 2019. After taking blood and DNA extraction, genetic analysis of patient 1 was performed by PCR and direct sequencing and whole exome sequencing was applied for patient 2 and the result was confirmed by direct sequencing in the patient and his parents. The genetic result showed two novel variants in exon 3 (c.246_285+9del) and exon 5 (c.569G>T) PNP (NM_000270.4) in the patients, respectively. These variants are considered likely pathogenic based on the American College of Medical Genetics and Genomics (ACMG) guideline. PNP deficiency has a poor prognosis; therefore, early diagnosis would be vital to receive hematopoietic stem cell transplantation (HSCT) as a prominent and successful treatment.

Neurologic Status of Patients with Purine Nucleoside Phosphorylase Deficiency Before and After Hematopoetic Stem Cell Transplantation

BACKGROUND

Purine nucleoside phosphorylase (PNP) deficiency is a rare autosomal recessive combined immunodeficiency. The phenotype is profound T cell deficiency with variable B and NK cell functions and results in recurrent and persistent infections that typically begin in the first year of life. Neurologic findings occur in approximately two-thirds of patients. The mechanism of neurologic abnormalities is unclear. Hematopoietic stem cell transplantation (HSCT) is the only curative treatment for PNP deficiency.

METHODS

We report here six patients from five unrelated families with PNP deficiency treated in two centers in Turkey. We evaluated the neurological status of patients and compared to post-transplantation period if available. Then, we performed PubMed, Google Scholar, and Researchgate searches using the terms "PNP" and "hematopoietic stem cell transplantation" to find all reported cases of PNP transplantation and compared to our cohort.

RESULTS

Six patients were treated in two centers in Turkey. One patient died from post-transplant complications. The other four patients underwent successful HSCT with good immune reconstitution after transplantation (follow-up 21-48 months) and good neurological outcomes. The other patient with a new mutation is still waiting for a matching HLA donor.

DISCUSSION

In PNP deficiency, clinical manifestations are variable, and this disease should be considered in the presence of many different clinical findings. Despite the comorbidities that occurred before transplantation, HSCT currently appears to be the only treatment option for this disease. HSCT not only cures immunologic disorders, but probably also improves or at least stabilizes the neurologic status of patients.

Metabolomics Analysis of the Effect of GAT-2 Deficiency on Th1 Cells in Mice

The classic neurotransmitter γ-aminobutyric acid (GABA) has been shown to shape the activation and function of immune cells. There are four high-affinity GABA transporters (GATs, including GAT-1, GAT-2, GAT-3, and GAT-4) responsible for the transmembrane transport of GABA in mice. To explore the effect of GAT-2 on type 1 helper T (Th1) cells, naïve CD4⁺ T cells were isolated from splenocytes of GAT-2 knockout (KO) and wild-type (WT) mice and cultured for Th1 cell differentiation, and then, metabolomics analysis of Th1 cells was performed via gas chromatography coupled to time-of-flight mass spectrometry added with multivariate analyses. Based on the variable importance projection value > 1 and P < 0.05, a total of nine differentially expressed metabolites (DEMs) were identified between WT and KO. Then, DEMs were mapped to the KEGG database, and five metabolic pathways were significantly enriched, including the cysteine and methionine metabolism, the riboflavin metabolism, the purine metabolism, the glycerolipid metabolism, and the glycerophospholipid metabolism. Collectively, our metabolomics analysis revealed that deficiency of GAT-2 influenced the metabolomics profile of Th1 cells, which will provide insights into T cell response to GAT-2 deficiency in mice. Data are available via MetaboLights with identifier MTBLS3358.

The Broad Clinical Spectrum and Transplant Results of PNP Deficiency

PURPOSE

Purine nucleoside phosphorylase (PNP) is a known yet rare cause of combined immunodeficiency with a heterogeneous clinical presentation. We aim to add to the expanding clinical spectrum of disease, and to summarize the available data on bone marrow transplant for this condition.

METHODS

Data was collected from patient files retrospectively. A review of the literature of hematopoietic stem cell transplantation (HSCT) for PNP deficiency was conducted.

RESULTS

Four patients were treated in two centers in Israel. One patient died of EBV-related lymphoma with CNS involvement prior to transplant. The other three patients underwent successful HSCT with good immune reconstitution post-transplant (follow-up 8-108 months) and excellent neurological outcomes.

CONCLUSION

PNP is a variable immunodeficiency and should be considered in various clinical contexts, with or without neurological manifestations. HSCT offers a good treatment option, with excellent clinical outcomes, when preformed in a timely manner.

Aging. Polymorphism, compartmentalization and environmental impact

The proportion of elderly in our population is steadily increasing and so is the need to provide sophisticated health care. We must intensify research which provides results, leading to the design of preventive medicine, before the increased proportion of aged causes a crisis in our health care and social systems. The potential impact of such research represents the best and most cost-effective means of preparing for the future, and providing directions for a better quality of life with reduced chronic and debilitating illness for the elderly. Indeed, prevention appears to be the only approach able to lower the enormous economic burden of the cost of geriatric medicine [1,2]. There are many precedents in medical research for preventive measures being much more cost-effective than therapeutic means: one of them is immunization against poliomyelitis as an alternative to development of improved models of iron lungs.

Biochemical consequences of 2'-deoxycoformycin treatment in a patient with T-cell lymphoma. Some unusual findings

The nucleotide content of the various blood cells and the urinary excretion of purine and pyrimidine metabolites were studied in a patient with a T-cell lymphoma (early T-cell phenotype) before and during treatment with deoxycoformycin (dCF; given intravenously [iv] during 3 days, biweekly). During and after the administration of dCF, high amounts of dATP were found in the lymphoid cells and the erythrocytes (maximally, 480 pmol/10(6) lymphocytes and 5.5 nmol/10(6) erythrocytes), but not in the polymorphonuclear leukocytes. The amount of dATP in the erythrocytes, however, was significantly lower than described in the literature. During each administration of dCF, the number of blast cells in the peripheral blood rose initially, followed by a rapid decrease. After three courses, a hematologic remission was achieved and maintained for 6 weeks; then an autologous bone-marrow transplantation was performed. During the first dCF course a large amount of deoxyadenosine was found in the urine. During the second course, this excretion was much lower, but still higher than in healthy individuals. In the patient described, dCF showed a highly specific toxicity for the immature T-lymphoblast; hardly any changes were seen in the numbers of the other hematopoietic cells, both in the blood and in the bone marrow.

Isoprinosine restores in vitro T lymphocyte functions of cyclophosphamide immunosuppressed mice

The effect and the mechanism of action of isoprinosine has been investigated in several models of in vitro activation of lymphocytes. Isoprinosine added to spleen cell cultures enhanced lymphocyte proliferation induced by concanavalin A or allogeneic stimulation as well as the generation of allospecific cytotoxic T cells. The effect of isoprinosine on T lymphocyte proliferation in vitro was specially marked when mice were treated with cyclophosphamide (75-200 mg/kg) 16-24 h before the onset of cultures. No effect was observed on B cell proliferation to LPS. Addition of inosine or adenosine also enhanced proliferation of cells from both normal and cyclophosphamide treated mice. Isoprinosine and inosine and, more markedly, adenosine, augmented interleukin-2 activity in concanavalin A supernatants of spleen cells from the same animals.

Purine nucleoside phosphorylase (PNP) deficiency leading to accumulation of lymphocytes in S-phase

Freshly isolated mononuclear cells of a patient with purine nucleoside phosphorylase (PNP) deficiency contained 7-11% cells in S-phase. During treatment with deoxycytidine and tetrahydrouridine these cells disappeared from peripheral circulation, indicating that the in vivo accumulation of S-phase cells is caused by a shortage in deoxycytidine triphosphate. In vitro it was not possible to cause a blockade in S-phase by culturing normal or PNP-deficient lymphocytes in the presence of deoxyguanosine.

Differential influence of 2'-deoxyguanosine on the induction and expression of suppressor T lymphocytes in vivo

Subcutaneous (sc) immunization of mice with allogeneic spleen cells can induce delayed-type hypersensitivity (DTH) to histocompatibility antigens. Intravenous immunization with irradiated allogeneic spleen cells, on the other hand, induces suppressor T (Ts) lymphocytes. These Ts cells are capable of suppressing the host-versus-graft (HvG) DTH reactivity which normally arises after sc immunization. Moreover they can suppress the development of antihost DTH effector T cells during graft-versus-host (GvH) reactions. These models for HvG and GvH DTH reactivity were used to study the influence of 2'-deoxyguanosine (dGuo) on the induction, further development, and expression of Ts cells in vivo. It was found that administration of dGuo inhibits the proliferation-dependent induction and further development of Ts cells, but not the suppression mediated by already activated Ts cells.

Effects of pentostatin (2'deoxycoformycin), an inhibitor of adenosine deaminase, on type II collagen-induced arthritis in rats

Pentostatin (2'-deoxycoformycin), a potent inhibitor of adenosine deaminase, was administered therapeutically to rats with type II collagen-induced arthritis and the effects on hindpaw swelling, serum haptoglobin concentration, and anticollagen antibody titer determined. Daily intraperitoneal administration of pentostatin at 10.0 or 1.0 mg/kg/day for three weeks produced significant enhancement of hind-paw swelling and elevation of serum haptoglobin. Continuous subcutaneous infusion of pentostatin at 1.0 or 0.1 mg/kg/day had the same effects. None of the dosing regimens had any effect on anticollagen antibody titer.

Distribution of enzymes of purine metabolism in lymphocytes of horse, Equus caballus

A microassay requiring as few as 2 X 10(5) cells per assay was developed for systematic analysis of 9 purine enzymes in lymphocytes from equine peripheral blood, spleen, lymph node, thymus and bone marrow. The activities of adenosine deaminase (ADA), purine nucleoside phosphorylase (PNP), adenosine kinase (AK), deoxyadenosine kinase (dAK), deoxycytidine kinase (dCK), 5'-nucleotidase (5'-N), AMP deaminase, hypoxanthine-guanine phosphoribosyl transferase (HGPRT or HPRT), and adenine phosphoribosyl transferase (APRT) were measured by this microassay in lymphocytes from peripheral blood from four different breeds of horses (Arabian, Quarter Horse, Thoroughbred and Shetland Pony). There were no significant differences in the enzyme activities among the various breeds. Peripheral blood lymphocytes (PBL) from foals exhibited enzyme activities similar to those observed for adult animals. All lymphoid tissue contained similar levels of activity for each kinase (AK, dAK and dCK). Spleen had the highest activity for ADA, PNP, 5'-N, and HGPRT. The lowest activity for ADA, APRT, PNP and AMP deaminase was found in thymus. Enzymatic activities that varied the most among the tissue were 5'-N, ADA, APRT, HGPRT and AMP deaminase.

Lymphocyte maturation in the human thymus. Relevance of purine nucleotide metabolism for intrathymic T cell function

The combination of centrifugal elutriation as an efficient and reproducible method to separate thymocytes by size, micromethods to assess purine interconversion enzymes, and assessment of purine (deoxy)nucleoside inhibition of mitogen responses enabled us to study purine metabolism at the intrathymic level. Out of six fractions, four (nos. 3-6), containing medium- and large-sized lymphocytes, showed a proliferative response after stimulation with phytohaemagglutinin (PHA). In fractions 1-6 the number of cells with an immature immunological phenotype gradually decreased, and cells with the phenotype of mature cells gradually increased. The enzyme activity ratio of adenosine deaminase to purine nucleoside phosphorylase gradually decreased from 21 in fraction 1 to 7 in the last fraction (blood T-cell value, 0.7). We conclude that this enzyme activity ratio is a useful marker for intrathymic T-cell maturation stages. In PHA-responsive cell fractions (3-6), the sensitivity to inhibition of the PHA response by (deoxy)adenosine and deoxyguanosine was inversely related to the enzyme activity ratio of ecto-5'-nucleotidase to deoxycytidine kinase. These findings are compatible with the hypothesis that intracellular concentrations of phosphorylated (deoxy)nucleosides are related to this inhibition. We conclude that the differences in purine metabolism among the various (mitogen-responsive) human thymocyte fractions are related to lymphoid cell function. Since the number of cells contributing to the enzyme activities and the number of cells contributing to the proliferative response (about 15% of unseparated cells) differ considerably, it is not possible to evaluate enzyme activities in unseparated thymocytes in terms of relationships between purine metabolism and lymphocyte function.

Dietary fat alters the fatty acid composition of lymphocyte membranes and the rate at which suppressor capacity is lost

SJL/J mice were fed from conception two nutritionally adequate semi-purified diets that differed only in polyunsaturated to saturated fatty acid content. The effect of diet fat on the fatty acid composition of membranes from spleen and thymus cells was determined. Diet fat was found to significantly alter the fatty acid composition of lymphocyte membrane phosphatidylcholine and phosphatidylethanolamine. Diet also altered the degree of resistance against tolerance-induction.

Aging and the immune system

Information is presented on changes in the aging immune system. An analysis of separate streams of cellular aging in the inbred mouse is presented. It is demonstrated that there is extensive polymorphism in the aging of different types of executive and regulatory cell lines.

Regulation of thymocyte proliferation by endogenous adenosine and adenosine deaminase

Spontaneous proliferation of thymocytes after 20-25 h of culture was significantly increased by the presence of adenosine deaminase (ADA) or theophylline. The effect of ADA was counteracted by the ADA inhibitor EHNA. When given alone, EHNA inhibited proliferation. This effect was not blocked by inhibition of adenosine uptake with dipyridamol. These results suggest that proliferation in culture is regulated by a balance between endogenous adenosine and ADA, controlling the influence of adenosine on the intracellular cyclic AMP level via an adenosine receptor on the surface of thymocytes. According to the hypothesis, ADA would stimulate proliferation by decreasing extracellular adenosine levels and theophylline by blocking adenosine receptors on thymocytes. EHNA would inhibit proliferation by increasing extracellular adenosine levels. In accordance with this interpretation, the adenosine analogue phenylisopropyl adenosine (PIA) inhibited proliferation and the effect could be inhibited by theophylline. The postulated effect of endogenous adenosine could not be mimicked by a single administration of exogenous adenosine. Whereas most doses of adenosine were without effect, a high dose of adenosine (0.1 mM) in combination with EHNA unexpectedly stimulated proliferation. Since the effect was blocked by dipyridamol, an intracellular site of action for adenosine is suggested in this case.