Immune responses to adenovirus and adeno-associated virus in humans

Vectors based on human adenovirus (Ad) and adeno-associated virus (AAV) are being evaluated for human gene therapy. The response of the host to the vector, in terms of antigen-specific immunity, will play a substantial role in clinical outcome. We have surveyed cohorts of normal subjects and cystic fibrosis patients for pre-existing immunity to these viruses, caused by naturally acquired infections. A number of humoral and cellular assays to adenovirus serotype 5 (Ad5) and adeno-associated virus serotype 2 (AAV2) were performed from serum and peripheral blood mononuclear cells. Virtually all subjects had Ig to Ad5 although only 55% of these antibodies neutralized virus (NAB). Approximately two of three patients demonstrated CD4+ T cells that proliferated to Ad antigens of which most were of the TH1 subset, based on cytokine secretion. A substantially different pattern of immune responses was observed to AAV2. Although virtually all patients had Ig to AAV2, most of these antibodies were not neutralizing (32% NAB) and only 5% of patients had peripheral blood lymphocytes that proliferated in response to AAV2 antigens. These studies demonstrate marked heterogeneity in pre-existing immunity to Ad5 and AAV2 in human populations. The impact of these findings on outcome following gene therapy will require further study.

Ultradian oscillations of leptin secretion in humans

We have recently demonstrated the nocturnal increase in leptin secretion in humans. In the present study we have examined the pulsatile pattern of leptin secretion using two different experimental protocols. The first protocol utilized blood samples withdrawn at 30 minute intervals immediately after meals, at 1 hour intervals between meals, and at 2 hour intervals during the night from 4 lean, 11 obese, and 5 obese NIDDM subjects. Analysis of circulating leptin levels by ULTRA algorithmic program and using matched intra-assay coefficient of variations demonstrated 1 to 7 ultradian oscillations with a mean of 3.25 +/- 0.36 (SEM) pulses per 24 hour period (period: 10.0 +/- 1.5 hours; mean relative amplitude: 0.52 +/- 0.06, n = 20). Significant positive correlations were observed for changes in absolute amplitude with body mass index (p < 0.025) and fasting leptin levels (< 0.0001). In the second series of experiments utilizing 15 minute blood sampling from 10 overnight fasted obese subjects (BMI 35.9 +/- 2.0 kg/m2), ultradian oscillations for leptin were more frequent, i.e., 2 to 7 oscillations (4.20 +/- 0.59), over a 12 hour duration (period: 3.44 +/- 0.49; mean relative amplitude: 0.28 +/- 0.03). The number of oscillations over a 12 hour period correlated significantly with BMI (p < 0.001), fasting leptin levels (p < 0.01), and absolute amplitude (p < 0.005) in a 15 minute sampling protocol. In summary, similar to other hormones, ultradian oscillations of leptin are observed in humans, although the physiological significance in relation to obesity or feeding behavior is not yet understood.

Nocturnal rise of leptin in lean, obese, and non-insulin-dependent diabetes mellitus subjects

We studied 24-h profiles of circulating leptin levels using a sensitive and specific RIA in lean controls and obese subjects with or without non-insulin-dependent diabetes mellitus (NIDDM) during normal routine activity. Serum leptin levels were significantly higher in obese (41.7 +/- 9.0 ng/ml; n = 11) and obese NIDDM (30.8 +/- 6.7; n = 9) subjects compared with those in lean controls (12.0 +/- 4.4, n = 6). In all the three groups, serum leptin levels were highest between midnight and early morning hours and lowest around noon to midafternoon. The nocturnal rise in leptin levels was significant when data were analyzed by ANOVA (lean: F = 3.17, P < 0.0001, n = 4; obese: F = 2.02, P < 0.005, n = 11; and obese NIDDM: F = 4.9, P < 0.0001, n = 5). The average circadian amplitude between acrophase and nadir was 75.6% in lean, 51.7%, in obese and 60.7% in obese NIDDM groups, respectively. No significant correlations (P > 0.05) were observed between circulating levels of leptin and either insulin or glucose levels in any of the 20 subjects studied for 24-h profiles. The nocturnal rise in leptin observed in the present study resembles those reported for prolactin, thyroid-stimulating hormone, and free fatty acids. We speculate that the nocturnal rise in leptin could have an effect in suppressing appetite during the night while sleeping.