Role of natural killer cells in the modulation of primary antibody production by purine nucleosides and their analogs

Search for adenosine A2A spare receptors on peripheral human lymphocytes

Some ligand–receptor couples involve spare receptors, which are apparent when a maximal response is achieved with only a small fraction of the receptor population occupied. This situation favours cross-reactions with low-affinity ligands, which may be detrimental for cell signaling. In the case of the adenosine A_2A receptors (A_2AR), which have an immunosuppressive effect on lymphocytes through cAMP production, the presence of spare A_2AR remains to be established. We examined the situation using patients over-expressing lymphocyte A_2AR and an agonist-like mAb to A_2AR. We found that maximal mAb binding and functional response varied among the patients whereas the dissociation constant and half-maximal effective concentration had similar mean values (0.19 and 0.18 μM, respectively). Lymphocyte A_2AR expression was correlated to plasma adenosine level and A_2AR occupation but not to A_2AR response. These results are consistent with a lack of a reserve of functional A_2AR on human lymphocytes as a general rule and suggest that the amount and functional state of the expressed A_2AR determine the maximal level of the lymphocyte response to adenosine.

Intracellular disposition of fludarabine triphosphate in human natural killer cells

PURPOSE

Fludarabine is a key component of several reduced-intensity conditioning regimens for hematopoietic cell transplantation (HCT). Shortly after reduced-intensity conditioning, the percent of donor natural killer (NK) cells has been associated with progression-free survival. Insufficient suppression of the recipient's NK cells by fludarabine may lead to lower donor chimerism; however, the effect of fludarabine upon NK cells is poorly understood. Thus, in purified human NK cells we evaluated the uptake and activation of fludarabine to its active metabolite, fludarabine triphosphate (F-ara-ATP), and assessed the degree of interindividual variability in F-ara-ATP accumulation.

METHODS

Intracellular F-ara-ATP was measured in purified NK cells isolated from healthy volunteers (n = 6) after ex vivo exposure to fludarabine. Gene expression levels of the relevant transporters and enzymes involved in fludarabine uptake and activation were also measured in these cells.

RESULTS

F-ara-ATP accumulation (mean +/- SD) was 6.00 +/- 3.67 pmol/1 x 10(6) cells/4 h, comparable to average levels previously observed in CD4(+) and CD8(+) T-lymphocytes. We observed considerable variability in F-ara-ATP accumulation and mRNA expression of transporters and enzymes relevant to F-ara-ATP accumulation in NK cells from different healthy volunteers.

CONCLUSIONS

Human NK cells have the ability to form F-ara-ATP intracellularly and large interindividual variability was observed in healthy volunteers. Further studies are needed to evaluate whether F-ara-ATP accumulation in NK cells are associated with apoptosis and clinical outcomes.

Adenosine receptors and inflammation

Extracellular adenosine is produced in a coordinated manner from cells following cellular challenge or tissue injury. Once produced, it serves as an autocrine- and paracrine-signaling molecule through its interactions with seven-membrane-spanning G-protein-coupled adenosine receptors. These signaling pathways have widespread physiological and pathophysiological functions. Immune cells express adenosine receptors and respond to adenosine or adenosine agonists in diverse manners. Extensive in vitro and in vivo studies have identified potent anti-inflammatory functions for all of the adenosine receptors on many different inflammatory cells and in various inflammatory disease processes. In addition, specific proinflammatory functions have also been ascribed to adenosine receptor activation. The potent effects of adenosine signaling on the regulation of inflammation suggest that targeting specific adenosine receptor activation or inactivation using selective agonists and antagonists could have important therapeutic implications in numerous diseases. This review is designed to summarize the current status of adenosine receptor signaling in various inflammatory cells and in models of inflammation, with an emphasis on the advancement of adenosine-based therapeutics to treat inflammatory disorders.

Rituximab in Combination With Fludarabine Chemotherapy in Low-Grade or Follicular Lymphoma

Purpose

To evaluate the safety and efficacy of fludarabine plus rituximab in treatment-naïve or relapsed patients with low-grade and/or follicular non-Hodgkin's lymphoma.

Patients and Methods

This was an open-label, single-arm, single-center phase II study enrolling 40 patients. During the first week of the study, patients received two infusions of rituximab 375 mg/m2 administered 4 days apart. Seventy-two hours after the second infusion of rituximab, patients received the first of six cycles of fludarabine chemotherapy (25 mg/m2/d for 5 days on a 28-day cycle). Single infusions of rituximab were administered 72 hours before the second, fourth, and sixth cycles of fludarabine, and two infusions of rituximab were given 4 weeks after the last cycle of fludarabine. Treatment duration was 26 weeks.

Results

An overall response rate of 90% (80% complete response rate) was achieved in the intent-to-treat population. Similar response rates were seen in treatment-naïve and previously treated patients. The median duration of response has not been reached at 40+ months. The median follow-up time in this study is 44 months (range, 15 to 66 months). In patients positive for the 14;18 translocation in blood and/or marrow at enrollment, molecular remission was achieved in 88% of cases, with patients remaining negative for up to 4 years to date. Hematologic toxicity was manageable, and except for a 15% incidence of herpes simplex/zoster infections, infectious complications were rare. Nonhematologic toxicities were minimal.

Conclusion

Rituximab plus fludarabine was well tolerated and associated with an excellent complete response rate, including molecular remissions, in patients with low-grade or follicular lymphoma.

Adenosine acts through a novel extracellular receptor to inhibit granule exocytosis by natural killer cells

Adenosine concentrations in solid tumors are elevated as a result of altered metabolism by hypoxic cancer cells within the tumor microenvironment. In this study we show that adenosine inhibits mouse natural killer (NK) cell function by interfering with the process of granule exocytosis. Adenosine, at concentrations ranging from 5-25 microM, had a marked inhibitory effect on granule exocytosis by mouse spleen cells stimulated with phorbol myristate acetate and ionomycin. Selective depletion of spleen cell subsets by antibody and complement treatments established that granule exocytosis was mediated by NK cells. Blocking the cellular uptake of adenosine with NBTI or dilazep failed to prevent the inhibitory effect of adenosine, indicating the involvement of a cell-surface receptor. However, adenosine-induced inhibition of granule exocytosis was not blocked by the nonselective A1 and A2 receptor antagonists theophylline and 8-phenyltheophylline, the A1 receptor antagonist DPCPX, or the A2 receptor antagonist DMPX. In addition, the A3 receptor agonists APNEA and NECA failed to affect granule exocytosis. Taken together, these data provide evidence that adenosine inhibits NK cell granule exocytosis by interacting with a novel extracellular receptor. A similar inhibitory effect of tumor-elaborated adenosine on the function of NK cells and other cytotoxic lymphocytes may contribute to tumor survival in the face of host cell-mediated immune defenses.

Multicentre prospective randomised trial of fludarabine versus cyclophosphamide, doxorubicin, and prednisone (CAP) for treatment of advanced-stage chronic lymphocytic leukaemia. The French Cooperative Group on CLL

BACKGROUND

Fludarabine seems to be a promising treatment for patients with advanced chronic lymphocytic leukaemia (CLL). We compared fludarabine therapy with the combination of cyclophosphamide, doxorubicin, and prednisone (CAP) for treatment of CLL in a randomised, multicentre prospective trial.

METHODS

Patients older than 18 years of age were entered into the study if they presented with previously untreated B-cell lineage CLL (B-CLL) of Binet stages B or C or relapsed B-CLL pretreated with chorambucil or similar non-anthracycline-containing regimens. Patients were randomly assigned to either fludarabine (25 mg/m2 per day on days 1-5) or CAP (cyclophosphamide 750 mg/m2 per day and doxorubicin 50 mg/m2 per day on day 1, and prednisone 40 mg/m2 per day on days 1-5), both given for six courses.

FINDINGS

Of 196 evaluable patients, 100 were previously untreated whereas 96 patients had received prior therapy. Remission rates were significantly higher after fludarabine than CAP, with overall response rates of 60% and 44%, respectively (p = 0.023). A higher response rate to fludarabine was observed in both untreated (71% vs 60%, p = 0.26) and pretreated (48% vs 27%, p = 0.036) cases, although the difference was statistically significant only in pretreated cases. In the latter group, remission duration and survival did not differ between treatment groups with a median remission duration of 324 days after fludarabine and 179 days after CAP (p = 0.22) and median survival times of 728 days and 731 days, respectively. In untreated cases, on the other hand, fludarabine induced significantly longer remissions than CAP with the median not yet reached after fludarabine and a median of 208 days after CAP (p < 0.001). This effect also translated into a tendency towards longer overall survival after fludarabine (p = 0.087). Treatment-associated side-effects consisted in both regimens of predominantly myelosuppression and in particular granulocytopenia. CAP-treated patients had a higher frequency and severity of nausea and vomiting (25% vs 5%, p < 0.001) and alopecia (65% vs 2%, p < 0.001).

INTERPRETATION

Fludarabine provided an effective and well-tolerated therapy for patients with advanced CLL, which compared favourably with CAP as one of the most effective standard regimens. In second-line therapy, fludarabine induced a significantly higher rate of complete and partial remissions, while in first-line therapy a significant prolongation of remission was obtained, which may translate into an improvement of overall survival.

Natural killer cell activity in chronic lymphocytic leukemia patients treated with fludarabine

Fludarabine, the 5'-monophosphate of 9-beta-D-arabinofuranosyl-2- fluoroadenine (FaraAMP), is effective in the treatment of chronic lymphocytic leukemia (CLL) and has been demonstrated to increase natural killer (NK) cell lytic activity (NKa) in humans and mice. To determine the effect of FaraAMP on NK cells in CLL, we analyzed NKa toward K562 targets after in vitro incubation with FaraAMP and after in vivo exposure to fludarabine. Pretreatment analysis of peripheral blood from 12 CLL patients (9 untreated) revealed: median number of NK cells 500/microliter (range 290-1160); median NKa lytic unit30/10(6) cells (range 5-80). These results were similar to those from healthy adult donors. After exposure to 3, 30 or 300 microM FaraAMP, the median maximum stimulation index (NKa FaraAMP/NKa) was 1.2 (range 0.9-1.5), within the range observed in normal adults. FaraA also stimulated NKa in vitro toward autologous CLL cells in two of five patients as measured by a dye-exclusion assay. In three patients following three or more treatment courses of fludarabine (30 mg/m2 per day for 5 days) the NK cell number and NKa were maintained near pretreatment values. Phenotypic analysis of the peripheral mononuclear cells in 34 consecutive CLL patients revealed a marked reduction in CD5/CD20 and CD4 cell numbers after three courses of fludarabine with less effect on CD8 and CD56 cells. These results indicate that fludarabine spares NK cells and may stimulate NKa in some CLL patients.

Hirschsprung's disease: clinical and experimental observations

Hirschsprung's disease (HD) is a relatively common cause of intestinal obstruction in the newborn. It is characterized by an absence of ganglion cells in the distal bowel beginning at the internal sphincter and extending proximally for varying distances. The etiology of HD-associated enterocolitis remains a complex issue. This study has provided further support for a possible infectious etiology of enterocolitis complicating HD.

Mucosal immune defence mechanisms in enterocolitis complicating Hirschsprung's disease

Enterocolitis remains an important cause of morbidity and mortality in Hirschsprung's disease. The aetiology of enterocolitis is uncertain-ischaemic and bacterial causes and recently, rotavirus infections, have been suggested. Bowel tissue from 12 patients with Hirschsprung's disease who underwent Swenson's operation (five of whom had clinical evidence of enterocolitis) and colon from six controls subjects were examined to investigate possible immunopathological mechanisms associated with the disease. IgA, IgM, and J chain (but not IgG) containing plasma cells were significantly increased in the lamina propria along the entire length of resected bowel in enterocolitis patients, compared with non-enterocolitis patients and controls (p less than 0.01). Luminal secretory component staining of the anganglionic segment of colon from enterocolitis patients was considerably reduced. Lamina propria CD68 positive monocyte/macrophages and CD45RO positive leukocytes were increased in enterocolitis patients compared with non-enterocolitis patients (p less than 0.01). CD57 positive natural killer (NK) cells showed a unique distribution pattern compared with other cell types. Patients with enterocolitis showed a significant increase in CD57 positive NK cells in the lamina propria of ganglionic bowel only (p less than 0.05). NK cell values in ganglionic bowel of non-enterocolitis patients and in aganglionic bowel in all patients were similar to controls. The diversity of altered local immune response seen in this study may reflect a multifactorial microbial aetiology in enterocolitis associated with Hirschsprung's disease.