Development of a sensitive, quantitative assay with broad subtype specificity for detection of total HIV-1 nucleic acids in plasma and PBMC

An LTR-based quantitative PCR (qPCR) assay was modified and optimized for the quantification of total HIV-1 nucleic acids in plasma and PBMC. TaqMan qPCR primers and probes were designed against the NCBI/LANL HIV-1 compendium database by analyzing sequences used in assays for sensitive cross-clade detection of HIV-1 as reported in the literature and elucidating regions of improved cross-subtype specificity. Inosine and mixed nucleotide bases were included at polymorphic sites. Real-time RT-qPCR and qPCR were performed on plasma viral RNA and cellular lysates. A step-up amplification approach to allow binding of primers across polymorphic regions showed improved sensitivity compared to universal cycling. Unlike a lead competing laboratory-developed assay, all major HIV-1 subtypes, and a wide range of recombinants from a 127-member diversity panel were detected and accurately quantified in spiked plasmas. Semi-nested PCR increased detection sensitivity even further. The assay was able to detect down to 88 copies/mL of HIV-1 in plasma with 95% efficiency or the equivalent of a single infected cell. The PCR assay will be valuable in studies that monitor very low viral levels including residual or break through HIV-1 in patients receiving antiretroviral therapy, in HIV-1 cure, and in other research studies.

Human labour is associated with altered regulatory T cell function and maternal immune activation

During human pregnancy, regulatory T cell (T_reg ) function is enhanced and immune activation is repressed allowing the growth and development of the feto-placental unit. Here, we have investigated whether human labour is associated with a reversal of the pregnancy-induced changes in the maternal immune system. We tested the hypothesis that human labour is associated with a decline in T_reg function, specifically their ability to modulate Toll-like receptor (TLR)-induced immune responses. We studied the changes in cell number, activation status and functional behaviour of peripheral blood, myometrial (myoMC) and cord blood mononuclear cells (CBMC) with the onset of labour. We found that T_reg function declines and that T_reg cellular targets change with labour onset. The changes in T_reg function were associated with increased activation of myoMC, assessed by their expression of major histocompatibility complex (MHC) class II molecules and CBMC inflammatory cells. The innate immune system showed increased activation, as shown by altered monocyte and neutrophil cell phenotypes, possibly to be ready to respond to microbial invasion after birth or to contribute to tissue remodelling. Our results highlight changes in the function of the adaptive and innate immune systems that may have important roles in the onset of human labour.

Myometrial cytokines and their role in the onset of labour

Human labour is an inflammatory event, physiologically driven by an interaction between hormonal and mechanical factors and pathologically associated with infection, bleeding and excessive uterine stretch. The initiation and communicators of inflammation is still not completely understood; however, a key role for cytokines has been implicated. We summarise the current understanding of the nature and role of cytokines, chemokines and hormones and their involvement in signalling within the myometrium particularly during labour.

Low-dose growth hormone for 40 weeks induces HIV-1-specific T cell responses in patients on effective combination anti-retroviral therapy

Recombinant human growth hormone (rhGH) administered to combination anti-retroviral therapy (cART)-treated human immunodeficiency virus-1 (HIV-1)-infected individuals has been found to reverse thymic involution, increase total and naive CD4 T cell counts and reduce the expression of activation and apoptosis markers. To date, such studies have used high, pharmacological doses of rhGH. In this substudy, samples from treated HIV-1(+) subjects, randomized to receive either a physiological dose (0·7 mg) of rhGH (n = 21) or placebo (n = 15) daily for 40 weeks, were assessed. Peptide-based enzyme-linked immunospot (ELISPOT) assays were used to enumerate HIV-1-specific interferon (IFN)-γ-producing T cells at baseline and week 40. Individuals who received rhGH demonstrated increased responses to HIV-1 Gag overlapping 20mer and Gag 9mer peptide pools at week 40 compared to baseline, whereas subjects who received placebo showed no functional changes. Subjects with the most robust responses in the ELISPOT assays had improved thymic function following rhGH administration, as determined using CD4(+) T cell receptor rearrangement excision circle (TREC ) and thymic density data from the original study. T cells from these robust responders were characterized further phenotypically, and showed decreased expression of activation and apoptosis markers at week 40 compared to baseline. Furthermore, CD4 and CD8 T cell populations were found to be shifted towards an effector and central memory phenotype, respectively. Here we report that administration of low-dose rhGH over 40 weeks with effective cART resulted in greater improvement of T lymphocyte function than observed with cART alone, and provide further evidence that such an approach could also reduce levels of immune activation.

Dysregulated immunophenotypic attributes of plasmacytoid but not myeloid dendritic cells in HIV-1 infected individuals in the absence of highly active anti-retroviral therapy

Dendritic cells (DC) in HIV-1-infected individuals are decreased and their dysfunction has been implicated in HIV-1 immunopathogenesis. The mechanism of their dysfunction remains unclear, thus we analysed the expression of membrane molecules associated with immune regulation and DC activation in myeloid (mDC) and plasmacytoid DC (pDC) in therapy-naive and highly active anti-retroviral therapy (HAART)-treated HIV-1(+) patients. DC from healthy controls, untreated HIV-1(+) and HAART-treated patients were assessed by flow cytometry for expression of: anergy and apoptosis inducing molecules [programmed death (PD)-1 and its ligands PD-L1 and PD-L2], inhibitory and regulatory T cell-inducing molecules [immunoglobulin-like transcript (ILT)-3 and ILT-4], interferon (IFN)-α inhibitory receptor (ILT-7) and co-stimulatory molecules (CD80, CD83, and CD86). pDC from untreated HIV-1(+) patients expressed significantly lower levels of ILT-7 compared to healthy controls, while HAART-treated patients showed normal expression. pDC were also found to express moderately higher levels of PD-L1 and ILT-3 and lower levels of PD-L2 receptors in untreated patients compared to controls and HAART-treated patients. No significant changes were observed in mDC. There were no associations between the percentages and levels of expression of these molecules by pDC and viral load or CD4 T cell count. In conclusion, pDC but not mDC from HIV-1(+) patients with active viraemia display higher levels of apoptosis and T regulatory-inducing molecules and may be predisposed to chronically produce IFN-α through down-regulation of ILT-7. HAART restored normal expression levels of these receptors.

HIV-1 clade A infection and viral control: an immunological perspective on a case of underquantification

Although a vast majority of HIV-1-positive patients in the UK are infected with clade B virus, a large number of newly diagnosed cases of heterosexually transmitted HIV-1 are acquired abroad, in countries where non-B clade HIV-1 predominates. Since the development of the viral load assay in 1988, assessment of HIV-1 plasma viraemia has become an integral part of HIV clinical care; however, the contemporary viral load assay was developed and optimized for clade B HIV-1. Here we report the underquantification of viraemia in an individual infected with clade A virus, and the consequent initial classification of the patient as an HIV controller (HIC). Immunological investigations of interferon (IFN)-γ and lymphoproliferative responses to HIV-1 clade B antigens and peptides, in parallel with mitogenic stimulation, were performed. Subsequent comparison with responses observed within clade B-infected HIC led to viral sequencing, confirmation of infecting clade and recommendation of antiretroviral therapy initiation. We emphasize the growing need for awareness of possible limitations of the commonly used viral load assays, which cannot be relied upon unreservedly in a clinical setting. Furthermore, this case highlights the increasing need for more detailed investigation into both viral genetics and fitness when defining patients as HIC.

Single-nucleotide polymorphism-defined class I and class III major histocompatibility complex genetic subregions contribute to natural long-term nonprogression in HIV infection

We performed a genome-wide association study comparing a cohort of 144 human immunodeficiency virus (HIV type 1-infected, untreated white long-term nonprogressors (LTNPs) with a cohort of 605 HIV-1-infected white seroconverters. Forty-seven single-nucleotide polymorphisms (SNPs), located from class I to class III major histocompatibility complex (MHC) subregions, show statistical association (false discovery rate, <0.05) with the LTNP condition, among which 5 reached genome-wide significance after Bonferonni correction. The MHC LTNP-associated SNPs are ordered in ≥4 linkage disequilibrium blocks; interestingly, an MHC class III linkage disequilibrium block (defined by the rs9368699 SNP) seems specific to the LTNP phenotype.

Altered phenotype of regulatory T cells associated with lack of human immunodeficiency virus (HIV)-1-specific suppressive function

Mechanisms by which CD4+ regulatory T cells (T(regs)) mediate suppression of virus-specific responses remain poorly defined. Adenosine, mediated via CD39 and CD73, has been shown to play a role in the action of murine T(regs) . In this study we investigate the phenotype of T(regs) in the context of human immunodeficiency virus (HIV)-1 infection, and the function of these cells in response to HIV-1-Gag and cytomegalovirus (CMV) peptides. Phenotypic data demonstrate a decrease in forkhead box transcription factor 3 (FoxP3+) T(reg) numbers in the peripheral blood of HIV-1+ individuals compared to healthy controls, which is most pronounced in those with high HIV-1 RNA plasma load. Due to aberrant expression of CD27 and CD127 during HIV-1 disease, these markers are unreliable for T(reg) identification. The CD3+ CD4+ CD25(hi) CD45RO+ phenotype correlated well with FoxP3 expression in both the HIV-1+ and seronegative control cohorts. We observed expression of CD39 but not CD73 on T(regs) from HIV-1+ and healthy control cohorts. We demonstrate, through T(reg) depletion, the suppressive potential of T(regs) over anti-CMV responses in the context of HIV-1 infection; however, no recovery of the HIV-1-specific T cell response was observed indicating a preferential loss of HIV-1-specific T(reg) function. We propose that before immunotherapeutic manipulation of T(regs) is considered, the immunoregulatory profile and distribution kinetics of this population in chronic HIV-1 infection must be elucidated fully.

Programmed death (PD)-1 molecule and its ligand PD-L1 distribution among memory CD4 and CD8 T cell subsets in human immunodeficiency virus-1-infected individuals

Human immunodeficiency virus (HIV)-1 causes T cell anergy and affects T cell maturation. Various mechanisms are responsible for impaired anti-HIV-1-specific responses: programmed death (PD)-1 molecule and its ligand PD-L1 are negative regulators of T cell activity and their expression is increased during HIV-1 infection. This study examines correlations between T cell maturation, expression of PD-1 and PD-L1, and the effects of their blockade. Peripheral blood mononuclear cells (PBMC) from 24 HIV-1(+) and 17 uninfected individuals were phenotyped for PD-1 and PD-L1 expression on CD4(+) and CD8(+) T cell subsets. The effect of PD-1 and PD-L1 blockade on proliferation and interferon (IFN)-gamma production was tested on eight HIV-1(+) patients. Naive (CCR7(+)CD45RA(+)) CD8(+) T cells were reduced in HIV-1 aviraemic (P = 0.0065) and viraemic patients (P = 0.0130); CD8 T effector memory subsets [CCR7(-)CD45RA(-)(T(EM))] were increased in HIV-1(+) aviraemic (P = 0.0122) and viraemic (P = 0.0023) individuals versus controls. PD-1 expression was increased in CD4 naive (P = 0.0496), central memory [CCR7(+)CD45RA(-) (T(CM)); P = 0.0116], T(EM) (P = 0.0037) and CD8 naive T cells (P = 0.0133) of aviraemic HIV-1(+) versus controls. PD-L1 was increased in CD4 T(EMRA) (CCR7(-)CD45RA(+), P = 0.0119), CD8 T(EM) (P = 0.0494) and CD8 T(EMRA) (P = 0.0282) of aviraemic HIV-1(+)versus controls. PD-1 blockade increased HIV-1-specific proliferative responses in one of eight patients, whereas PD-L1 blockade restored responses in four of eight patients, but did not increase IFN-gamma-production. Alteration of T cell subsets, accompanied by increased PD-1 and PD-L1 expression in HIV-1 infection contributes to anergy and impaired anti-HIV-1-specific responses which are not rescued when PD-1 is blocked, in contrast to when PD-L1 is blocked, due possibly to an ability to bind to receptors other than PD-1.

Restoration of anti-tetanus toxoid responses in patients initiating highly active antiretroviral therapy with or without a boost immunization: an INITIO substudy

INITIO is an open-labelled randomized trial evaluating first-line therapeutic strategies for human immunodeficiency virus-1 (HIV-1) infection. In an immunology substudy a tetanus toxoid booster (TTB) immunization was planned for 24 weeks after initiation of highly active antiretroviral therapy (HAART). All patients had received tetanus toxoid immunization in childhood. Generation of proliferative responses to tetanus toxoid was compared in two groups of patients, those receiving a protease inhibitor (PI)-sparing regimen (n = 21) and those receiving a PI-containing (n = 54) regimen. Fifty-two participants received a TTB immunization [PI-sparing (n = 15), PI-containing (n = 37)] and 23 participants did not [PI-sparing (n = 6) or PI-containing (n = 17)]. Cellular responses to tetanus antigen were monitored by lymphoproliferation at time of immunization and every 24 weeks to week 156. Proportions with a positive response (defined as stimulation index > or = 3 and Delta counts per minute > or = 3000) were compared at weeks 96 and 156. All analyses were intent-to-treat. Fifty-two participants had a TTB immunization at median 25 weeks; 23 patients did not. At weeks 96 and 156 there was no evidence of a difference in tetanus-specific responses, between those with or without TTB immunization (P = 0.2, P = 0.4). There was no difference in the proportion with response between those with PI-sparing or PI-containing regimens at both time-points (P = 0.8, P = 0.7). The proliferative response to tetanus toxoid was unaffected by initial HAART regimen. Anti-tetanus responses appear to reconstitute eventually in most patients over 156 weeks when treated successfully with HAART, irrespective of whether or not a TTB immunization has been administered.

Immune modulation and reconstitution of HIV-1-specific responses: novel approaches and strategies

Efficacious protection for future generations from HIV-1 infection through the development of prophylactic vaccines is the best hope for the millions of individuals living with the threat of HIV-1 infection. Advances in the development of non-curative chemotherapy for those already infected have changed the course of the epidemic for those with access to the drugs. However in the ten years since the advent of highly active anti-retroviral therapy, the expectancy of curative chemotherapy has been quashed, and the constant need for a next generation of drugs is evident. As our understanding of HIV-1 pathogenesis increases, it is becoming apparent that novel approaches and strategies will be required to halt the global progression of HIV-1. Immune-based therapies are being considered in the context of effective antiretroviral therapy. Such immune-based therapy must allow the induction or regeneration of HIV-1-specific T-cell responses with the potential to control viremia and purge viral reservoirs. Studies of therapy substitution, treatment interruption, therapeutic vaccines and/or cytokines and/or hormones have been carried out and are briefly summarised in this review.

Immunological and virological consequences of patient-directed antiretroviral therapy interruption during chronic HIV-1 infection

Increasing numbers of patients are choosing to interrupt highly active antiretroviral therapy (HAART). We describe the effect of patient-directed treatment interruption (PDTI) on plasma viral loads (pVL), proviral DNA (pDNA), lymphocyte subsets and immune responses in 24 chronically HIV-1 infected individuals. Patients were divided into group A with pVL > 50 copies/ml and group B with pVL < 50 copies/ml, prior to the PDTI. pVL rose significantly in group B during the first month off HAART and was associated with a significant decrease in CD4 T-cell count. At baseline there was a significant difference in HIV-1 pDNA levels between groups A and B, however, levels significantly increased in group B, but not in group A during PDTI becoming equivalent after 1 month PDTI. We have previously shown no increase in pDNA over the time of substitution in patients switching HAART regimens despite a small rebound in pVL. These observations indicate that to protect low pDNA levels PDTI should be discouraged and that changing regimen at the first sign of failure should be advised where possible. Only transient, no longer than 4 week, HIV-1-specific responses were observed during PDTI in 5/24 patients, 2 from group A and 3 from group B. The low numbers of responders and the transient nature of the anti-HIV-1 immune responses do not favour the auto-vaccination hypothesis.

Mycobacterial immune reconstitution inflammatory syndrome in HIV-1 infection after antiretroviral therapy is associated with deregulated specific T-cell responses: beneficial effect of IL-2 and GM-CSF immunotherapy

BACKGROUND

With the advent of antiretroviral therapy (ART) cases of immune reconstitution inflammatory syndrome (IRIS) have increasingly been reported. IRIS usually occurs in individuals with a rapidly rising CD4 T-cell count or percentage upon initiation of ART, who develop a deregulated immune response to infection with or without reactivation of opportunistic organisms. Here, we evaluated rises in absolute CD4 T-cells, and specific CD4 T-cell responses in 4 HIV-1+ individuals presenting with mycobacterial associated IRIS who received in conjunction with ART, IL-2 plus GM-CSF immunotherapy.

METHODS

We assessed CD4 T-cell counts, HIV-1 RNA loads, phenotype for naïve and activation markers, and in vitro proliferative responses. Results were compared with those observed in 11 matched, successfully treated asymptomatic clinical progressors (CP) with no evidence of opportunistic infections, and uninfected controls.

RESULTS

Median CD4 T-cell counts in IRIS patients rose from 22 cells/microl before initiation of ART, to 70 cells/microl after 8 months of therapy (median 6.5 fold increase). This coincided with IRIS diagnosis, lower levels of naïve CD4 T-cells, increased expression of immune activation markers, and weak CD4 T-cell responses. In contrast, CP had a median CD4 T-cell counts of 76 cells/microl at baseline, which rose to 249 cells/microl 6 months post ART, when strong T-cell responses were seen in > 80% of patients. Higher levels of expression of immune activation markers were seen in IRIS patients compared to CP and UC (IRIS > CP > UC). Immunotherapy with IL-2 and GM-CSF paralleled clinical recovery.

CONCLUSION

These data suggest that mycobacterial IRIS is associated with inadequate immune reconstitution rather than vigorous specific T-cell responses, and concomitant administration of IL-2 and GM-CSF immunotherapy with effective ART may correct/augment T-cell immunity in such setting resulting in clinical benefit.

Evidence of thymic reconstitution after highly active antiretroviral therapy in HIV-1 infection

OBJECTIVES

We aimed to provide evidence of thymic reconstitution after highly active antiretroviral therapy (HAART) in HIV-1 infected patients and to correlate this with the restoration of peripheral naïve T cells.

METHODS

Positron emission tomography (PET) enables definitive evidence of thymic activity, indicating functional potential. In this case study, a single patient who initiated HAART demonstrated reconstitution of the naïve T-cell pool and underwent thymic PET scans at baseline and 2 and 6 months following initiation of therapy. Two patients who failed to demonstrate such reconstitution acted as controls. These patients (mean age 27 years) had chronic HIV infection with low CD4 T-cell counts (mean 82, range 9-160 cells/microL blood). Increased function of the thymus visualized by PET was correlated with phenotypic changes in CD4 and CD8 T cells in the periphery measured by flow cytometry, and with numbers of recent thymic emigrants measured by quantification of the numbers of T-cell receptor excision circles (TRECs) in peripheral cells.

RESULTS

In one patient, clear correlations could be drawn between visible activity within the thymus, as measured by increased [F18]fluorodeoxyglucose (FDG) uptake, and regeneration of naïve CD4 (CD45RA/CD62L) T cells, increased numbers of CD4 T cells, controlled viraemia and increased numbers of recent thymic emigrants. A second patient displayed no increase in peripheral CD4 count and no increase in thymic activity. The third patient elected to stop therapy following the 2-month time point.

CONCLUSIONS

The use of PET suggests that thymic activity may increase after HAART, indicating that the thymus has the potential to be functional even in HIV-1 infected persons with low CD4 T-cell counts.

A pilot study of the safety and efficacy of thymosin alpha 1 in augmenting immune reconstitution in HIV-infected patients with low CD4 counts taking highly active antiretroviral therapy

To study the safety and efficacy of thymosin alpha1 in stimulating immune reconstitution in combination with highly active antiretroviral therapy (HAART), a phase II randomized, controlled open-label trial of subcutaneous thymosin alpha1 was undertaken for 12 weeks. Twenty clinically stable patients with viral loads <400 copies/ml and CD4 counts less than 200 cells/microl were randomized to receive 3.2 mg thymosin alpha 1 subcutaneous injections twice weekly or no injections for 12 weeks. CD4 and CD8 counts, CD45 RO+ and RA+ subsets and signal joint T cell receptor excision circles (sjTREC) in peripheral blood mononuclear cells (PBMCs) were measured every 2 weeks. Thirteen patients received thymosin alpha 1 and seven were controls. Thymosin alpha 1 was well tolerated and there were no serious adverse events. There was no significant difference between the thymosin alpha1 and control groups in CD4, CD8 and CD45 lymphocyte subset changes at week 12; however, PBMC sjTREC levels increased significantly in the thymosin alpha 1-treated patients compared to controls at week 12. In conclusion, the increase in PBMC sjTREC levels in patients taking thymosin alpha1 may represent enhanced immune reconstitution; however, the clinical benefits and long-term consequences remain to be determined.

Treatment of primary HIV-1 infection with nonnucleoside reverse transcriptase inhibitor-based therapy is effective and well tolerated

OBJECTIVES

Highly active antiretroviral therapy (HAART) has been advocated for the management of primary HIV-1 infection. We investigated the use of a nonnucleoside reverse transcriptase inhibitor (NNRTI)-based regimen in this setting.

METHODS

Twenty-one antiretroviral-naïve individuals with early HIV-1 disease were treated with a combination of efavirenz and Combivir (GlaxoSmithKline, Uxbridge, Middlesex, UK). They were evaluated for immune and lymphocyte function by standard immunological assays.

RESULTS

The median time to an undetectable HIV-1 viral load was 12 weeks (range 4-36 weeks). CD4 and CD16/56 counts increased during treatment and CD8 counts decreased minimally. The main side-effects observed were transient sleep disturbances (five patients). In addition, we observed a decrease in lymphocyte activation as assessed by CD38 surface expression.

CONCLUSIONS

This study demonstrates that primary HIV-1 infection can be treated with NNRTI-based HAART.

Increased serum transforming growth factor-beta1 in human colorectal cancer correlates with reduced circulating dendritic cells and increased colonic Langerhans cell infiltration

Cancer-related cytokines may interfere with the differentiation and migration of dendritic cells (DCs) and with the associated up-regulation of co-stimulatory molecules in vitro. We determined whether cytokines affected the distribution and activation of DCs in patients with colorectal cancer by measuring the levels of serum cytokines [transforming growth factor (TGF)-beta1 and vascular endothelial growth factor (VEGF)], DC numbers and phenotype from peripheral blood and mesenteric lymph nodes draining the cancer, and the infiltration of DCs into colorectal cancer. A significant increase in the serum level of TGF-beta1 correlated with a significant reduction in the level of circulating DCs in cancer patients that was associated with an increased infiltration of Langerhans cells into colorectal mucosa. The prevalence but not intensity of co-stimulatory molecule expression in circulating and mesenteric lymph node DCs was reduced in patients with colorectal cancer compared to patients with inflammatory bowel conditions. There was no correlation between co-stimulatory molecule expression and serum TGF-beta1. Thus the circulating DC depletion in colorectal cancer could be explained by a TGF-beta1-related DC redistribution from the circulation into the colorectal cancer and adjacent mucosa where DC levels were increased. There was an impairment of DC activation within colorectal cancer that was not related to serum level of cytokines.

Loss of the CD56hiCD16- NK cell subset and NK cell interferon-gamma production during antiretroviral therapy for HIV-1: partial recovery by human growth hormone

Previous studies have shown that human natural killer (NK) cells are lost from the periphery and are functionally suppressed during HIV-1 infection, and that the administration of highly active antiretroviral therapy (HAART) results in a recovery of NK cell numbers in HIV-1-infected individuals. However, despite this recovery, interleukin (IL)-2 + IL-12-driven interferon (IFN)-gamma production by NK cells has been shown to remain suppressed after HAART. Here we show that the innate immune factor IL-15 in combination with IL-12 is also unable to recover NK cell IFN-gamma production in HAART-treated individuals. Furthermore, we also demonstrate an imbalance in the distribution of CD56loCD16hi and CD56hiCD16- NK subsets after successful HAART, CD56hiCD16- cells being reduced substantially in HIV-1 patients on HAART. Treatment of patients with combined human growth hormone and antiretroviral therapy resulted in further enhancement in the absolute numbers and the proportion of NK cells in some individuals in the absence of parallel effects on CD4+ T cells. Furthermore, in these individuals HAART with growth hormone resulted in an enhancement of cytokine-driven NK cell activation and IFN-gamma production compared to the HAART-only baseline.

Reconstitution of CD4+ T cell responses in HIV-1 infected individuals initiating highly active antiretroviral therapy (HAART) is associated with renewed interleukin-2 production and responsiveness

Reconstitution of functional CD4(+) T cell responsiveness to in vitro stimuli is associated with continuous highly active antiretroviral therapy (HAART). Thirty-six antiretroviral naive patients received HAART over 16 weeks. Antigen-specific, mitogen and interleukin (IL)-2 induced lymphocyte proliferative responses and specific IL-2 and IL-4 production were assessed at each time-point, together with quantification of HIV-1 RNA load and lymphocyte populations. Reconstitution of recall responses was limited largely to persistent antigens such as Herpes simplex virus and Candida, rather than to HIV-1 or neo-antigens. Recall antigens, mitogens and IL-2-induced renewed responses were associated with in-vitro production of IL-2, but not IL-4. Differential responsiveness to low versus high concentration IL-2 stimulus increases in a stepwise manner, suggesting normalization of IL-2 receptor expression and improved functionality. These increases in in-vitro proliferative responses thus probably reflect short lived effector clones, driven by ongoing antigenic stimulus associated with persisting long-term organisms. In this context non-responsiveness to HIV-1 antigens suggests ongoing HIV-1 specific clonal T cell anergy.

Restoration of human immunodeficiency virus-1-specific responses in patients changing from protease to non-nucleoside reverse transcriptase inhibitor-based antiretroviral therapy

The effect of altering antiretroviral therapy (ART) on responses to viral, recall and human immunodeficiency virus (HIV)-1-specific recombinant antigens and interleukin-2 (IL-2) in HIV-1-infected patients was assessed. A longitudinal cohort study in eight HIV-1 infected individuals following a clinically indicated therapy change (seven for drug intolerance and one for virological failure) from protease inhibitor (PI) to non-nucleoside reverse transcriptase inhibitor (NNRTI)-based antiretroviral regimens was performed. CD4 T-cell counts, viral loads, lymphoproliferative responses, cytokine production and latent proviral deoxyribonucleic acid (DNA) were measured at baseline and at weeks 12 and 24 after therapy substitution. Following therapy-switch there was a 33% proportional increase in mitogen response (95% confidence interval (CI), 3-33%) and a 31% increase (95% CI, 15-48%) in viral and recall-antigen responses. Six patients developed proliferative responses to low concentration IL-2 stimulation. All patients demonstrated an increase in median HIV-1-specific responses, as three had detectable virus at baseline (two being viral rebound); this may reflect an autovaccination effect. Proviral DNA changes largely reflected plasma HIV-1 ribonucleic acid (RNA). In conclusion, NNRTI substitution for a PI may favour immune reconstitution with an improvement in HIV-1-specific responses, which may reflect differential effects on antigen processing and presentation, an autovaccination effect or alternatively a potential suppressive effect of the PI.

Impact of NNRTI compared to PI-based highly active antiretroviral therapy on CCR5 receptor expression, beta-chemokines and IL-16 secretion in HIV-1 infection

Interleukin-16 (IL-16) and the beta-chemokines (RANTES, monocyte chemotactic protein-1 (MCP-1), macrophage inhibitory protein (MIP)-1alpha and (MIP)-1beta) are soluble in vitro suppressors of macrophage tropic HIV-1 strains. The reduction of HIV-1 RNA plasma levels in late-stage patients receiving protease inhibitors has been associated with increased concentrations of MIP-1alpha, MIP-1beta, RANTES and IL-16 and a decrease in levels of MCP-1. We determined plasma levels of MCP-1, MIP-1alpha, MIP-1beta, RANTES and IL-16 during the first 16 weeks of highly active antiretroviral therapy (HAART) in chronic HIV-1-infected patients. Patients were administered one of two therapeutic regimens based on either a protease inhibitor (PI) or a non-nucleoside reverse transcriptase inhibitor (NNRTI). No differences were seen in the levels of RANTES and IL-16 over the first 16 weeks of HAART in either treatment group. MCP-1 decreased significantly in the PI-treated group over the first 16 weeks of HAART (P = 0.0003). A significant increase was observed in the levels of MIP-1alpha and MIP-1beta in the NNRTI cohort (P = 0.0010 and P = 0.0012, respectively). A significant decrease in levels of MIP-1alpha and MIP-1beta (P = 0.0015 and P = 0.0299, respectively) was observed over the 16 weeks in the PI cohort. A significant difference was seen when the levels of MIP-1alpha and MIP-1beta were compared between the NNRTI and the PI cohorts at week 16 (P = 0.04 and P = 0.05, respectively). Evaluation of CCR5 expression ex vivo revealed no difference between the two treatment groups. Patients were genotyped for CCR5 Delta32 and the incidence of heterozygosity was lower than in the HIV-1 seronegative controls (3% compared to 19%).

Thymic activity in late-stage HIV-1 infected individuals receiving highly active antiretroviral therapy: potential effect of steroid therapy

OBJECTIVE

Our objective was to monitor the effect of steroid therapy on the thymic output and function of late-stage HIV-1-infected patients undergoing highly active antiretroviral therapy (HAART).

DESIGN

The indirect measurement of T cells that have recently emigrated from the thymus as a means of quantifying thymic output, and therefore thymic function, was achieved through use of the polymerase chain reaction-based signal joint T cell receptor rearrangement excision circles (sjTREC) assay. Proliferative capacity and interleukin (IL)-2 and IL-4 production by T cells after antigenic, mitogenic and IL-2 stimulation were also analysed.

METHOD

Measurements were made of sjTREC levels in peripheral blood mononuclear cell DNA samples from five HIV-1 infected patients (one on steroid therapy prior to and at the time of sample extraction) receiving HAART. IL-2 and IL-4 production and proliferative capacity were also measured in three patients, including the patient receiving steroids.

RESULT

The sjTREC assay gave an extremely weak result for the patient on steroids but, under the same assay conditions, provided clear, positive readings for the four patients not on steroids. Comparison of the patients' cytokine profiles revealed that IL-2 production was generally low or absent in all three patients tested but that IL-4 production was significantly higher in the patient given steroids. Functional potential as revealed by proliferation assays showed very low or absent cellular proliferation.

CONCLUSION

The thymic contribution to the restoration of T lymphocyte numbers, particularly during the treatment of HIV-1 infection, may become compromised if thymic inhibitory factors such as steroids are used. Furthermore, the use of steroids may also favour the development of a T helper 2 response, which could prove particularly undesirable during HIV-1 infection.

Immune responses and reconstitution in HIV-1 infected individuals: impact of anti-retroviral therapy, cytokines and therapeutic vaccination

Most patients with chronic HIV-1 infection lack functional CD4(+) and CD8(+) HIV-1-specific T cells with proliferative and cytolytic capacity, respectively. This is despite being able to produce intracellular cytokines in response to viral antigens. Protease inhibitor (PI)-based highly active anti-retroviral therapy (HAART) is unable to completely eradicate virus and fails to enable total restoration of immunity including induction of anti-HIV-1 responses. We have taken novel approaches towards the treatment of chronic HIV-1 disease with the aim of instigating long-term non-progressor status and depletion of virus reservoirs. HIV-1-specific CD4(+) and CD8(+) T cell responses were measured following the administration of cytokines, during therapeutic vaccination, and following treatment interruption (TI) or drug therapy change. Administration of cytokines, with or without therapeutic vaccination, in HAART treated patients, improved both CD4(+) and CD8(+) HIV-1-specific T cell responses even in late-stage disease. Virus-specific T cell responses were also seen during TI or when transient viraemia was apparent, and following therapy change from a PI- to a non-nucleoside-based HAART regimen. Reconstitution of HIV-1-specific immune responses was found to be transient and reversal to the previous anergic state was rapid. Viral reservoirs in the latently infected resting CD4(+) T cells, on follicular dendritic cells of germinal centers or even in infected thymic epithelium may be involved in clonal suppression and anergy. These may present major obstacles to the maintenance of HIV-1-specific responses and the eventual eradication of HIV-1.

Candidate vaccines for immunotherapy in HIV

In this short article we review the immunopathology of HIV infection and delineate the kinds of immune responses seen in acute infection and in long-term nonprogression that are understood to be necessary if the host is to maintain long-term control of the virus. In this context we discuss the potential promise of therapeutic vaccination in HIV infection.

A point mutation in CD45 may be associated with an increased risk of HIV-1 infection

The CD45 antigen is essential for normal antigen receptor-mediated signalling in lymphocytes, and different patterns of splicing of CD45 are associated with distinct functions in lymphocytes. Here we show that abnormal CD45 splicing caused by a C77G transversion in exon A of the gene encoding CD45 (PTPRC) is associated with increased susceptibility to HIV-1 infection.

Development of immunotherapeutic strategies for HIV-1

In the majority of untreated patients, HIV-1 infection presents as a progressive disease of the immune system. Recent studies indicate that immune responses can be induced in HIV-1 infected individuals, leading to some immune control of virus replication. Such immune responses are also observed in small numbers of untreated HIV-1 infected long-term non-progressor (LTNP) patients, as well as in other viral infections (including those with human herpes viruses). Emerging novel technologies, animal studies and detailed immunological studies have proven invaluable in defining the immune responses that are associated with a favourable clinical outcome. Central effector and regulatory cells are HIV-1-specific CD8+ cytotoxic T-lymphocytes (CTL) and CD4+ helper T-lymphocytes respectively. Fully functional antigen-presenting cells (APC) are also essential in all stages of HIV-1 infection and possibly some (but not all) antibody responses contribute to beneficial immunity. The availability of combination anti-retroviral drug therapy, which successfully controls viraemia, has enabled a beneficial outcome in many HIV-1 infected individuals. Since no chronically HIV-1 infected patient has been shown to eradicate virus, novel approaches utilising therapeutic immunisation and various cytokines to manipulate immune responses and to induce and steer immunity towards a desired phenotype are required. There is a clear rationale for immunotherapeutic intervention in chronic progressive HIV-1 infection, which forms the foundation for novel approaches aimed at inducing and maintaining immune control. Here we review the immunopathogenesis of HIV-1 infection and discuss the promises of therapeutic immunisation and immunotherapy in general and their potential in the treatment of chronic HIV-1 disease.

Both age and gender affect thymic output: more recent thymic migrants in females than males as they age

The thymus undergoes age-associated involution, with studies showing thymic size decreasing from birth at a rate of approximately 3% per year until middle age, and at a rate of 1% per year thereafter. The aim of this study was to determine the effect of thymic atrophy on T-lymphocyte production by the thymus, and to clarify the ongoing uncertainty regarding gender differences in thymic function. We quantified recent thymic emigrants (RTEs) in blood through the measurement of signal joint T-cell receptor rearrangement excision circles (sjTRECs), and showed that the decline in the number of RTEs in the blood with increasing age is gender-linked. Peripheral blood from females contained significantly higher levels of sjTRECs per CD3+ T cell than blood from males (P = 0.002), despite there being no significant gender difference in the absolute number of CD3+ T cells in the populations analysed (P > 0.10). Our findings suggest better thymic function in females compared with males, providing females with a higher number of recent thymic emigrants for longer periods of life. Such a finding provides a plausible explanation for the immunological gender differences observed in previous studies and possibly, for the general longer life expectancy in females compared with males.

Detection and quantification of HIV-1 specific CD4 helper and CD8 cytotoxic cells: their role in HIV-1-infected individuals and vaccine recipients

There is a strong link between virus specific CD8 T-cell function and the efficiency of regulatory CD4 helper T cells. Controlling viraemia in HIV-1-infected individuals requires the maintenance of strong CD4 and CD8 T-cell responses. These responses should be elicited by prophylactic vaccination and by postexposure immunotherapy. This review will examine the methods that are available for the detection and quantification of HIV-1 specific CD4 and CD8 T-cell responses. We will also discuss the methods that should be used to identify these responses in HIV-1-infected individuals, seropositive recipients of immunotherapy and seronegative vaccinees. Finally, we will give examples of how responses observed in vitro relate to those known to occur in vivo.

The exon A (C77G) mutation is a common cause of abnormal CD45 splicing in humans

The leukocyte common (CD45) Ag is essential for normal T lymphocyte function and alternative splicing at the N terminus of the gene is associated with changes in T cell maturation and differentiation. Recently, a statistically significant association was reported in a large series of human thymus samples between phenotypically abnormal CD45 splicing and the presence of the CC chemokine receptor 5 deletion 32 (CCR5del32) allele, which confers resistance to HIV infection in homozygotes. We show here that abnormal splicing in these thymus samples is associated with the presence of the only established cause of CD45 abnormal splicing, a C77G transversion in exon A. In addition we have examined 227 DNA samples from peripheral blood of healthy donors and find no association between the exon A (C77G) and CCR5del32 mutations. Among 135 PBMC samples, tested by flow cytometric analysis, all those exhibiting abnormal splicing of CD45 also showed the exon A C77G transversion. We conclude that the exon A (C77G) mutation is a common cause of abnormal CD45 splicing and that further disease association studies of this mutation are warranted.

Loss of CD4+ T cell proliferative ability but not loss of human immunodeficiency virus type 1 specificity equates with progression to disease

In this study, we compared human immunodeficiency virus (HIV) type 1-specific proliferative responses with HIV-1-induced intracellular cytokine production in a cohort of clinically nonprogressing patients and individuals with progressive HIV-1 infection. We found strong HIV-1-specific proliferative responses in the clinical nonprogressor cohort that correlated with significant numbers of circulating HIV-1-specific CD4(+) T cells. In contrast, HIV-1-specific proliferative responses were absent in most individuals with progressive HIV-1 infection, even though interferon-gamma-producing HIV-1-specific CD4(+) T cells were detectable by flow cytometry. The implication of these data is that the important dysfunction seen in most HIV-positive patients from very early in disease may be an inability of HIV-1-specific CD4(+) memory T cells to proliferate in response to HIV antigens rather than an absolute loss of circulating virus-specific CD4(+) T cells.

Vaccines for the control of HIV/AIDS

This review discusses the feasibility of an HIV vaccine and describes the history, efficacy and potential to succeed of old and new vaccine concepts.

Assessment of type 1 and type 2 cytokines in HIV type 1-infected individuals: impact of highly active antiretroviral therapy

Although the effect of highly active antiretroviral therapy (HAART) on HIV-1 replication has been established, the mechanisms involved in restoration of immune responses and reconstitution remain unknown. This study provides evidence of changes in expression of type 1 and type 2 cytokine-specific mRNA occurring during HIV-1 infection, before and after initiation of HAART. Unstimulated PBMCs from nine HIV-1-infected individuals obtained at different time intervals before and after the initiation of HAART were assessed for specific IFN-gamma, IL-2, IL-4, and IL-10 mRNA expression, using RT-PCR. Correlation with CD4+ T cell counts and viral load was also carried out. Before initiation of HAART, in all patients, little expression of specific IFN-gamma and IL-2 (type 1 cytokine) mRNA was noted. In contrast, expression of specific IL-4 and/or IL-10 (type 2) mRNA was readily detectable in the majority of patients. After initiation of HAART there was a continuous increase in IFN-gamma and IL-2 mRNA expression, although the latter occurred in lower amounts. This paralleled a dramatic reduction in viral load and increase in CD4+ T cell counts. Type 2 cytokine-specific mRNA expression fell to undetectable levels and in some cases reappeared later in the course of HAART. Predominant expression of type 2 cytokine mRNA, before initiation of HAART, concurs with previous findings of a dominant antiproliferative, type 2 cytokine profile during HIV-1 infection. Reversion of the cytokine profile, after HAART, to a strong type 1 profile suggests that in addition to suppressing virus replication directly the immune system may be given a chance to recover.

Induction of HIV-1-specific T cell responses by administration of cytokines in late-stage patients receiving highly active anti-retroviral therapy

Highly active anti-retroviral therapy (HAART) is associated with reduction in the morbidity and mortality of patients with advanced HIV-1 disease. The ability of such treatment to improve immune responses against HIV-1 and opportunistic pathogens is variable and limited. Addition of cytokine immunotherapy to this treatment may improve immune responses. IL-2 with or without granulocyte-macrophage colony-stimulating factor (GM-CSF) was administered to HIV-1+ individuals receiving HAART with undetectable viral loads, and CD4 counts < 100 cells/microl. In one patient presenting with Mycobacterium avium complex (MAC) infection, we evaluated the effect of cytokine immunotherapy on lymphocyte phenotype; plasma viral load; proliferative responses to mitogens, recall and HIV-1 antigens; cytokine production and message in response to non-specific and specific stimuli; and natural killer (NK) cell activity. Proliferation assays were performed in two similar patients. Before cytokine immunotherapy the predominant CD8+ population was mainly CD28-. No proliferation or IL-2 production was seen in response to mitogens, recall or HIV-1 antigens; and no HIV-1 peptide-specific interferon-gamma (IFN-gamma)-secreting cells were present. Low levels of IL-4 were detected in response to antigens to which patients had been exposed, associated with up-regulated expression of costimulatory molecules influenced by IL-4. Following IL-2 administration, loss of IL-4 was associated with increased NK cell activity and HIV-1 peptide-specific and non-specific IFN-gamma-producing cells. Proliferative responses associated with IL-2 production and responsiveness were only seen after subsequent concomitant administration of GM-CSF with IL-2. These changes mirrored clinical improvement. An imbalance of lymphocyte subsets may account for immune unresponsiveness when receiving HAART. Restoration of responses following immunotherapy suggests a shift towards a lymphocyte profile with anti-pathogen activity.

Therapeutic vaccines in HIV.1 infection

In this review we address questions which must be considered if better attempts are to be made to treat all persons presently infected with human immunodeficiency virus (HIV). There are thirty million people in the world presently living with HIV, only 10% of whom are likely to be able to access currently available drug therapy. Even when available, such therapy causes considerable inconvenience and undesirable clinical side effects, and fails to eradicate virus from a small reservoir of latently infected cells. Thus, we must ask what forms of alternative therapy might be used. One strategy that may be considered is to reduce virus levels as low as possible using highly active antiretroviral therapy (HAART), followed by modulation of host immunity with immunotherapy in order to effect an appropriate and efficient response mimicking that found in long-term asymptomatic patients, with the aim of indefinitely maintaining the asymptomatic period following discontinuation of chemotherapy, or even of eradicating the virus from the latent reservoirs. In 1987, long before the advent of highly active antiretroviral therapy, J. Salk proposed the use of a 'suitable potent non-infectious (HIV) immunogen' to delay or prevent the development of AIDS in infected individuals (1). The objective of administering such an agent was to 'enhance and prolong the presence of (immunologically) protective factors'. The stated aim at that time was 'to destroy virus and viral antigen producing cells by the induction of the immune system's cytotoxic mechanisms known to rid the host of virus and virus producing cells'. Twelve years later, and after a quarter of a century living with HIV, and with the advent of HAART, is it time to use our knowledge of the host's own immune system to fight this seemingly intractable invader?

Lack of T cell proliferation without induction of nonresponsiveness after antigen presentation by endothelial cells

BACKGROUND

After priming or reactivation in lymph nodes, T cells recirculate to sites of inflammation, and enter tissues by migrating across activated endothelium. Given that activated endothelial and tissue parenchymal cells express both class I and class II MHC molecules, it is probable that transmigrating T cells encounter cognate antigen on endothelial cells, and on tissue parenchymal cells once they have entered the tissue.

METHODS

In this study the consequences of antigen presentation by endothelial and epithelial cells to human CD4+ T cell clones were analyzed and compared by a two-step culture system.

RESULTS

T cell clones that required B7-mediated costimulation to be activated were found not to be able to proliferate to antigen presented by either endothelial or epithelial cells, unless trans-costimulation was provided by the addition of B7-transfected cells in the cultures. Furthermore, antigen presentation by epithelial cells induced nonresponsiveness in the T cell clones. In contrast, after cognate recognition on endothelial cells, the ability of the T cell clones to proliferate to a subsequent rechallenge with antigen presented on a specialized APC was unaffected.

CONCLUSIONS

These data suggest that endothelial cells have unique properties as antigen-presenting cells, in that they do not influence the subsequent reactivity of cognate T cells.

The gp200-MR6 molecule which is functionally associated with the IL-4 receptor modulates B cell phenotype and is a novel member of the human macrophage mannose receptor family

The human gp200-MR6 molecule has previously been shown to have either an antagonistic or agonistic effect on IL-4 function, demonstrated by inhibition of IL-4-induced proliferation of T cells or mimicking of IL-4-induced maturation of epithelium, respectively. We now show that gp200-MR6 ligation can also mimic IL-4 and have an anti-proliferative pro-maturational influence within the immune system, causing up-regulation of co-stimulatory molecules on B lymphocytes. Biochemical analysis and cDNA cloning reveal that gp200-MR6 belongs to the human macrophage mannose receptor family of multidomain molecules. It comprises 1722 amino acids in toto (mature protein, 1695 amino acids; signal sequence, 27 amino acids) organized into 12 external domains (an N-terminal cysteine-rich domain, a fibronectin type II domain and 10 C-type carbohydrate recognition domains), a transmembrane region and a small cytoplasmic C terminus (31 amino acids) containing a single tyrosine residue (Y1679), but no obvious kinase domain. Strong amino acid sequence identity (77%) suggests that gp200-MR6 is the human homologue of the murine DEC-205, indicating that this molecule has much wider functional activity than its classical endocytic role. We also show that the gp200-MR6 molecule is closely associated with tyrosine kinase activity; the link between gp200-MR6 and the IL-4 receptor may therefore be via intracellular signaling pathways, with multifunctionality residing in its extracellular multidomain structure.

The gp200-MR6 molecule which is functionally associated with the IL-4 receptor modulates B cell phenotype and is a novel member of the human macrophage mannose receptor family

The human gp200-MR6 molecule has previously been shown to have either an antagonistic or agonistic effect on IL-4 function, demonstrated by inhibition of IL-4-induced proliferation of T cells or mimicking of IL-4-induced maturation of epithelium, respectively. We now show that gp200-MR6 ligation can also mimic IL-4 and have an anti-proliferative pro-maturational influence within the immune system, causing up-regulation of co-stimulatory molecules on B lymphocytes. Biochemical analysis and cDNA cloning reveal that gp200-MR6 belongs to the human macrophage mannose receptor family of multidomain molecules. It comprises 1722 amino acids in toto (mature protein, 1695 amino acids; signal sequence, 27 amino acids) organized into 12 external domains (an N-terminal cysteine-rich domain, a fibronectin type II domain and 10 C-type carbohydrate recognition domains), a transmembrane region and a small cytoplasmic C terminus (31 amino acids) containing a single tyrosine residue (Y1679), but no obvious kinase domain. Strong amino acid sequence identity (77%) suggests that gp200-MR6 is the human homologue of the murine DEC-205, indicating that this molecule has much wider functional activity than its classical endocytic role. We also show that the gp200-MR6 molecule is closely associated with tyrosine kinase activity; the link between gp200-MR6 and the IL-4 receptor may therefore be via intracellular signaling pathways, with multifunctionality residing in its extracellular multidomain structure.

Association between interleukin-4-producing T lymphocyte frequencies and reduced risk of graft-versus-host disease

BACKGROUND

We have previously developed and used limiting dilution analysis to measure frequencies of alloreactive cytotoxic T cell precursors (CTLp) and interleukin (IL)-2-producing T helper cells (IL-2/HTLp) to assess the risk of graft-versus-host disease in bone marrow transplantation (BMT). However, no test has been available to measure precursor frequencies of the important IL-4-secreting subset.

METHODS

We have now established a limiting dilution analysis to measure the frequency of IL-4-producing T helper cells (IL-4/HTLp) using the IL-4-responsive indicator cell line CT.h4S and have applied this assay to measure alloreactive IL-4/HTLp frequencies in BMT donor-recipient pairs. These frequencies were then analyzed in the context of clinical data to assess the relationship between the number of donor anti-recipient IL-4-secreting T cells and disease outcome.

RESULTS

Frequencies of IL-4/HTLp have been studied in HLA-identical siblings, HLA-"matched" unrelated, and HLA-mismatched combinations and found to range from approximately 1/500,000 in HLA-identical sibling pairs to -1/2,000 in HLA-DR-mismatched pairs. These frequencies were independent of those for IL-2/HTLp and showed a negative correlation with those for CTLp. Clinical follow-up of 30 patients showed that high IL-4/HTLp frequencies are associated with a reduced risk of severe graft-versus-host disease. High IL-4/HTLp frequencies may also indicate an increased risk of leukemia relapse.

CONCLUSIONS

Our data suggest that measurement of IL-4/HTLp frequencies provides information distinct from that obtained with CTLp and IL-2/HTLp. This new assay provides a valuable additional method for optimizing donor selection in unrelated BMT.

Laser energy reaching the posterior pole during transscleral cyclophotocoagulation

OBJECTIVE

To measure scattered laser energy reaching the posterior pole during transscleral cyclophotocoagulation.

METHODS

Transscleral cyclophotocoagulation was performed on 4 cadaver eyes with Nd:YAG noncontact, Nd:YAG contact, and diode contact lasers. Energy was measured with a photodiode through a 7-mm trephined hole in the posterior pole. Average percentage power, average power, and average energy transmission were calculated. American Conference of Governmental Industrial Hygienists (ACGIH) guidelines were used to calculate allowable energy exposures for each laser.

RESULTS

All 3 lasers transmitted 3% to 5% of the power to the posterior pole. The average energy transmission was 240 to 260 mJ for all lasers. The contact lasers had an average power transmission of 120 mW. The noncontact Nd:YAG laser, with shorter pulse duration, had an average power transmission of 13,000 mW, significantly greater than that of the other lasers. The ACGIH guidelines for allowable energy exposures were 93 mJ for the noncontact Nd:YAG laser, 1300 mJ for the contact Nd:YAG laser, and 440 mJ for the contact diode laser.

CONCLUSIONS

Three percent to 5% of laser power delivered during cyclophotocoagulation reaches the posterior pole. Exposure energies may approach or exceed ACGIH guidelines. The clinical significance of these findings remains to be shown.